Showing 1–43 of 43 results for author: Knights, P

Erbium-implanted tellurite waveguides with low-temperature post-implantation activation and signal enhancement

Authors: Yuxuan Gao, Batoul Hashemi, Bruno L. Segat Frare, Niloofar Majidian Taleghani, Pooya Torab Ahmadi, Henry C. Frankis, Ponnambalam Ravi Selvaganapathy, Jonathan D. B. Bradley, Peter Mascher, Andrew P. Knights

Abstract: In this paper, we demonstrate erbium ion implantation and signal enhancement in tellurium oxide hybrid waveguides. Silicon nitride strips with a width of 2 $μ$m and a height of 100 nm were clad with a 110-nm-thick tellurium oxide layer to form hybrid waveguides, followed by erbium ion implantation at an energy of 200 keV and a dose of $1\times10^{15} ions/cm^{2}$, with a projected peak implantatio… ▽ More In this paper, we demonstrate erbium ion implantation and signal enhancement in tellurium oxide hybrid waveguides. Silicon nitride strips with a width of 2 $μ$m and a height of 100 nm were clad with a 110-nm-thick tellurium oxide layer to form hybrid waveguides, followed by erbium ion implantation at an energy of 200 keV and a dose of $1\times10^{15} ions/cm^{2}$, with a projected peak implantation depth of approximately 50 nm into the tellurium oxide layer. After low-temperature annealing at 150 °C for 30 minutes, the propagation loss decreased from 1.7 to 0.9 dB/cm, while the erbium lifetime increased from 40 $μ$m to over 800 $μ$m. We measure a small-signal enhancement of 9 dB in an 11-cm-long waveguide at a wavelength of 1550 nm. These results demonstrate progress towards a low-temperature post-ion implantation process for incorporating erbium and other rare earth ions into tellurium oxide films for integrated photonic applications. △ Less

Submitted 17 August, 2026; originally announced August 2026.

Spontaneous Nanopatterning and Strain Relaxation in SiGe Layers Grown by Oxidative Solid Phase Epitaxy

Authors: Sophie E. Bierer, Trevor R. Smith, Arezoo Mafi, Sunzhuoran Wang, Chengqian Liao, Vatsalkumar Patel, Andrew P. Knights, Ryan B. Lewis

Abstract: The wafer-scale monolithic integration of III-V materials on Si would lead to revolutionary optoelectronic hardware for data, computing and other applications. However, heteroepitaxy of III-Vs on Si requires overcoming the large lattice and thermal mismatches between the materials and reducing threading dislocations densities. In this work, we explore the oxidative solid phase epitaxy (SPE) of Ge+… ▽ More The wafer-scale monolithic integration of III-V materials on Si would lead to revolutionary optoelectronic hardware for data, computing and other applications. However, heteroepitaxy of III-Vs on Si requires overcoming the large lattice and thermal mismatches between the materials and reducing threading dislocations densities. In this work, we explore the oxidative solid phase epitaxy (SPE) of Ge+ implanted Si(111) to form ultra-thin strain-relieving SiGe metamorphic buffer layers for heteroepitaxy on Si. The SPE process is shown to result in a nanopatterning of the Ge concentration variation across the sample surface, visible by scanning and transmission electron microscopy (SEM and TEM). The concentration patterning is the result of a hexagonal network of Shockley partial dislocations at the SiGe/Si interface. Analyzing the pattern spacing observed by SEM is demonstrated as an easy, non-destructive method for obtaining the local strain state of SiGe layers. This work is important for engineering ultra-thin SiGe metamorphic buffer layers for III-V optoelectronics heteroepitaxy on the silicon platform. △ Less

Submitted 16 July, 2026; originally announced July 2026.

Comments: Main text: 17 pages, 5 figures. Supporting information: 11 pages, 6 figures

Hydrofluoric acid-free titanium etching for rare-event searches

Authors: P. Knights, I. Manthos, K. Nikolopoulos, G. Rogers, D. Spathara, P. Walters

Abstract: Rare-event search experiments require construction materials with high radiopurity to minimise background contributions. Thanks to its high mechanical strength, low density, machinability, and commercial availability in relatively radiopure forms, titanium is a suitable material for structural elements in rare-event searches. In such applications, a chemical etching stage is typically performed to… ▽ More Rare-event search experiments require construction materials with high radiopurity to minimise background contributions. Thanks to its high mechanical strength, low density, machinability, and commercial availability in relatively radiopure forms, titanium is a suitable material for structural elements in rare-event searches. In such applications, a chemical etching stage is typically performed to remove surface contamination or to prepare the surface for further treatment. However, due to its chemical resistance, the etching of titanium conventionally requires hydrofluoric acid, posing serious health and safety concerns that are further exacerbated in deep underground laboratory settings. An alternative approach is proposed, which uses sulphuric acid. Grade 1 titanium samples were etched in 20\% and 40\% sulphuric acid solutions at 20$^\circ$C and 40$^\circ$C for up to 24\,h. The effects of etching were quantified through mass change measurements, surface roughness analysis, and scanning electron microscopy. Sulphuric acid effectively etches titanium, with up to $3.5\,\pm\,0.3$ mg/cm$^2$ of titanium removed for an unagitated solution of 40\% sulphuric acid at $40^\circ$C for 24\,h. Furthermore, sulphuric acid is shown to be effective at etching at lower concentration and temperature. The formation of a passivation layer during the etching may enable control of the total mass removed. △ Less

Submitted 23 June, 2026; originally announced June 2026.

Comments: 11 pages, 8 figures

Silicon photonic paper-clip spiral delay lines with ultra-low delay loss of 0.5 dB/ns

Authors: Batoul Hashemi, Manuel Arturo Méndez-Rosales, Parimal Edke, Mohammad Rezaul Islam, Ranjan Das, Andrew P. Knights, Jonathan D. B. Bradley

Abstract: In this work, we demonstrate compact paper-clip spiral silicon photonic waveguides with ultra-low delay loss. We characterize the optical loss and group delay of single-mode and multi-mode silicon waveguides across the telecom O-, S-, C-, and L-bands. For spiral devices with 2.0-μm-wide waveguides, we measure propagation losses of 0.11 and 0.06 dB/cm at 1310 and 1550 nm, representing 10- and 20-ti… ▽ More In this work, we demonstrate compact paper-clip spiral silicon photonic waveguides with ultra-low delay loss. We characterize the optical loss and group delay of single-mode and multi-mode silicon waveguides across the telecom O-, S-, C-, and L-bands. For spiral devices with 2.0-μm-wide waveguides, we measure propagation losses of 0.11 and 0.06 dB/cm at 1310 and 1550 nm, representing 10- and 20-times improvements, respectively, compared to the singlemode waveguides. Additionally, we observe a group delay of 1163 ps for a 9.5 cm-long waveguide with a compact device footprint of (0.30 {\times} 3.00) mm2, yielding a delay loss of 0.5 dB/ns. These results are highly promising for large-scale silicon photonic integration, delay lines, and on-chip programmable systems. △ Less

Submitted 15 December, 2025; originally announced December 2025.

Overlap-aware segmentation for topological reconstruction of obscured objects

Authors: J. Schueler, H. M. Araújo, S. N. Balashov, J. E. Borg, C. Brew, F. M. Brunbauer, C. Cazzaniga, A. Cottle, D. Edgeman, C. D. Frost, F. Garcia, D. Hunt, M. Kastriotou, P. Knights, H. Kraus, A. Lindote, M. Lisowska, D. Loomba, E. Lopez Asamar, P. A. Majewski, T. Marley, C. McCabe, L. Millins, R. Nandakumar, T. Neep , et al. (8 additional authors not shown)

Abstract: The separation of overlapping objects presents a significant challenge in scientific imaging. While deep learning segmentation-regression algorithms can predict pixel-wise intensities, they typically treat all regions equally rather than prioritizing overlap regions where attribution is most ambiguous. Recent advances in instance segmentation show that weighting regions of pixel overlap in trainin… ▽ More The separation of overlapping objects presents a significant challenge in scientific imaging. While deep learning segmentation-regression algorithms can predict pixel-wise intensities, they typically treat all regions equally rather than prioritizing overlap regions where attribution is most ambiguous. Recent advances in instance segmentation show that weighting regions of pixel overlap in training can improve segmentation boundary predictions in regions of overlap, but this idea has not yet been extended to segmentation regression. We address this with Overlap-Aware Segmentation of ImageS (OASIS): a new segmentation-regression framework with a weighted loss function designed to prioritize regions of object-overlap during training, enabling extraction of pixel intensities and topological features from heavily obscured objects. We demonstrate OASIS in the context of the MIGDAL experiment, which aims to directly image the Migdal effect--a rare process where electron emission is induced by nuclear scattering--in a low-pressure optical time projection chamber. This setting poses an extreme test case, as the target for reconstruction is a faint electron recoil track which is often heavily-buried within the order(s)-of-magnitude brighter nuclear recoil track. Compared to unweighted segmentation regression, we demonstrate OASIS's novel overlap region-targeted loss function weight to be the single most important training weight for improving intensity and topological reconstructions of the low-energy electron tracks that tend to be most dominated by pixel overlap. Averaging over eight training campaigns, we further show the addition of overlap-targeted weights to improve median intensity reconstruction errors from -41.1% to -13.3% for these low-energy electrons. These performance gains demonstrate OASIS as a generalizable methodology for recovering obscured signals in overlap-dominated regions. △ Less

Submitted 15 May, 2026; v1 submitted 7 October, 2025; originally announced October 2025.

Design of high-strength, radiopure, electroformed copper-based alloys for rare-event searches: Impact of layer configuration on heat treatments

Authors: D. Spathara, P. Knights, K. Nikolopoulos

Abstract: State-of-the-art and next-generation rare-event search experiments rely on detector materials with stringent requirements on radiopurity and mechanical performance. Additive-free electroformed copper offers exceptional radiopurity, but is limited in mechanical strength, motivating the exploration of application-specific copper-based alloys. Early investigations, based on direct experimentation, ex… ▽ More State-of-the-art and next-generation rare-event search experiments rely on detector materials with stringent requirements on radiopurity and mechanical performance. Additive-free electroformed copper offers exceptional radiopurity, but is limited in mechanical strength, motivating the exploration of application-specific copper-based alloys. Early investigations, based on direct experimentation, explored the synthesis of CuCr alloys through electrodeposition and thermal processing. Subsequently, modeling tools based on the thermodynamic and kinetic properties of the alloy compositions were employed, which led to specific proposals for improved thermal processing. Moreover, the systematic application of computational thermodynamics to materials design further motivated the investigation of CuCrTi alloys, in addition to CuCr alloys. This materials design approach has shaped a trajectory towards designing high-performance, radiopure copper-based alloys, minimizing lengthy and costly trial-and-error. In this work, we explore the impact of initial layer configuration on the effectiveness of heat treatments, paving the way toward manufacturable, radiopure, multicomponent alloys for future low-background experiments. △ Less

Submitted 9 September, 2025; originally announced September 2025.

Titanium for rare-event searches: Hydrofluoric acid-free etching

Authors: P. Knights, K. Nikolopoulos, G. Rogers, D. Spathara, P. Walters

Abstract: Rare-event search experiments require construction materials with high radiopurity to minimise background contributions. Thanks to its high mechanical strength, low density, machinability, and commercial availability in relatively radio-pure forms, titanium is a suitable material for structural elements in rare event searches. To remove surface deposits on materials used, a chemical etching stage… ▽ More Rare-event search experiments require construction materials with high radiopurity to minimise background contributions. Thanks to its high mechanical strength, low density, machinability, and commercial availability in relatively radio-pure forms, titanium is a suitable material for structural elements in rare event searches. To remove surface deposits on materials used, a chemical etching stage is usually performed. However, the chemical resistance of titanium means that, conventionally, such etching is done with hydrofluoric acid. Hydrofluoric acid presents serious health risks to users, and such hazards are compounded in the case of construction in deep underground laboratories. An alternative chemical etching using sulphuric acid is presented. This is demonstrated to etch titanium, removing 3.7 $μ$m of material from the surface over the course of 20 hours. Scanning electron microscopy with back-scattered electron spectroscopy was used to study the surface and contamination of the titanium, demonstrating the removal of surface contaminants after etching. The proposed method is a potential alternative to those currently employed. △ Less

Submitted 28 August, 2025; originally announced August 2025.

Comments: 7 pages, 4 figures

Materials Design for the Synthesis of High Strength Radiopure Copper Alloys for Rare Event Detection

Authors: Dimitra Spathara, Patrick Knights, Konstantinos Nikolopoulos

Abstract: Additive-free electroformed copper has emerged as the material of choice in exceptionally radiopure detectors for rare-event searches, based on its radiopurity, physical properties, and affordability. However, copper is ductile and of limited mechanical strength posing challenges for its use in future experiments. Electroformed copper-based alloys have been identified as a promising solution. Howe… ▽ More Additive-free electroformed copper has emerged as the material of choice in exceptionally radiopure detectors for rare-event searches, based on its radiopurity, physical properties, and affordability. However, copper is ductile and of limited mechanical strength posing challenges for its use in future experiments. Electroformed copper-based alloys have been identified as a promising solution. However, their synthesis needs refining by exploring a complex parameter space of compositions and strengthening mechanisms. Here we show how a materials design approach may address current challenges and optimize alloy synthesis and processing. Alloy properties are predicted following thermal processing, using computational thermodynamics. The findings suggest a methodology to design high-performance, radiopure copper-based alloys suitable for next-generation rare-event experiments, while minimizing lengthy and expensive trial-and-error approaches. The impact on future experiments is exemplified through case-studies of the DarkSPHERE and XLZD experiments. △ Less

Submitted 8 October, 2025; v1 submitted 1 July, 2025; originally announced July 2025.

Comments: 11 pages, 5 figures, 1 table

Searches for light Dark Matter with Spherical Proportional Counters

Authors: Patrick Knights, Konstantinos Nikolopoulos

Abstract: Elucidating the nature of dark matter is a key priority that would involve discovering new fundamental physics and is essential for understanding the structure and evolution of the universe. Despite the decades-long ever-more-sensitive searches, the particle content of dark matter remains elusive. Direct searches for dark matter candidates, to-date, focused mainly on candidates in the 10 GeV to 1… ▽ More Elucidating the nature of dark matter is a key priority that would involve discovering new fundamental physics and is essential for understanding the structure and evolution of the universe. Despite the decades-long ever-more-sensitive searches, the particle content of dark matter remains elusive. Direct searches for dark matter candidates, to-date, focused mainly on candidates in the 10 GeV to 1 TeV, however, more recently lighter candidates with sub-GeV mass have been brought to the spotlight. This is an experimentally challenging mass region, which remains largely uncharted. The spherical proportional counter is a new type of gaseous detector which exhibits several features that make it ideally suited for the exploration of this mass range. In this article the invention and development of the spherical proportional counter are presented, its applications in the search for particle dark matter and beyond are reviewed, and possible future directions are discussed. △ Less

Submitted 17 February, 2025; originally announced February 2025.

Comments: 24 pages, 33 figures, review aticle

Journal ref: JAIS 2025 (2025) 548

The ionization yield in a methane-filled spherical proportional counter

Authors: M. M. Arora, L. Balogh, C. Beaufort, A. Brossard, M. Chapellier, J. Clarke, E. C. Corcoran, J. -M. Coquillat, A. Dastgheibi-Fard, Y. Deng, D. Durnford, C. Garrah, G. Gerbier, I. Giomataris, G. Giroux, P. Gorel, M. Gros, P. Gros, O. Guillaudin, E. W. Hoppe, I. Katsioulas, F. Kelly, P. Knights, P. Lautridou, A. Makowski , et al. (18 additional authors not shown)

Abstract: Spherical proportional counters (SPCs) are gaseous particle detectors sensitive to single ionization electrons in their target media, with large detector volumes and low background rates. The $\mbox{NEWS-G}$ collaboration employs this technology to search for low-mass dark matter, having previously performed searches with detectors at the Laboratoire Souterrain de Modane (LSM), including a recent… ▽ More Spherical proportional counters (SPCs) are gaseous particle detectors sensitive to single ionization electrons in their target media, with large detector volumes and low background rates. The $\mbox{NEWS-G}$ collaboration employs this technology to search for low-mass dark matter, having previously performed searches with detectors at the Laboratoire Souterrain de Modane (LSM), including a recent campaign with a 135 cm diameter SPC filled with methane. While in situ calibrations of the detector response were carried out at the LSM, measurements of the mean ionization yield and fluctuations of methane gas in SPCs were performed using a 30 cm diameter detector. The results of multiple measurements taken at different operating voltages are presented. A UV laser system was used to measure the mean gas gain of the SPC, along with $\mathrm{^{37}Ar}$ and aluminum-fluorescence calibration sources. These measurements will inform the energy response model of future operating detectors. △ Less

Submitted 11 April, 2025; v1 submitted 21 October, 2024; originally announced October 2024.

Comments: 11 pages, 8 figures

Journal ref: Ionization yield in a methane-filled spherical proportional counter, Phys. Rev. D 111, 072007 (2025)

Ultra-thin strain-relieving Si$_{1-x}$Ge$_x$ layers enabling III-V epitaxy on Si

Authors: Trevor R. Smith, Spencer McDermott, Vatsalkumar Patel, Ross Anthony, Manu Hedge, Andrew P. Knights, Ryan B. Lewis

Abstract: The explosion of artificial intelligence, possible end of Moore's law, dawn of quantum computing and continued exponential growth of data communications traffic have brought new urgency to the need for laser integration on the diversified Si platform. While diode lasers on III-V platforms have long powered internet data communications and other optoelectronic technologies, direct integration with… ▽ More The explosion of artificial intelligence, possible end of Moore's law, dawn of quantum computing and continued exponential growth of data communications traffic have brought new urgency to the need for laser integration on the diversified Si platform. While diode lasers on III-V platforms have long powered internet data communications and other optoelectronic technologies, direct integration with Si remains problematic. A paradigm-shifting solution requires exploring new and unconventional materials and integration approaches. In this work, we show that a sub-10-nm ultra-thin Si$_{1-x}$Ge$_x$ buffer layer fabricated by an oxidative solid-phase epitaxy process can facilitate extraordinarily efficient strain relaxation. The Si$_{1-x}$Ge$_x$ layer is formed by ion implanting Ge into Si(111) and selectively oxidizing Si atoms in the resulting ion-damaged layer, precipitating a fully strain-relaxed Ge-rich layer between the Si substrate and surface oxide. The efficient strain relaxation results from the high oxidation temperature, producing a periodic network of dislocations at the substrate interface, coinciding with modulations of the Ge content in the Si$_{1-x}$Ge$_x$ layer and indicating the presence of defect-mediated diffusion of Si through the layer. The epitaxial growth of high-quality GaAs is demonstrated on this ultra-thin Si$_{1-x}$Ge$_x$ layer, demonstrating a promising new pathway for integrating III-V lasers directly on the Si platform. △ Less

Submitted 6 August, 2024; originally announced August 2024.

Comments: 16 pages, 5 figures

Search for Light Dark Matter with NEWS-G at the Laboratoire Souterrain de Modane Using a Methane Target

Authors: M. M. Arora, L. Balogh, C. Beaufort, A. Brossard, M. Chapellier, J. Clarke, E. C. Corcoran, J. -M. Coquillat, A. Dastgheibi-Fard, Y. Deng, D. Durnford, C. Garrah, G. Gerbier, I. Giomataris, G. Giroux, P. Gorel, M. Gros, P. Gros, O. Guillaudin, E. W. Hoppe, I. Katsioulas, F. Kelly, P. Knights, P. Lautridou, A. Makowski , et al. (18 additional authors not shown)

Abstract: The NEWS-G direct detection experiment uses spherical proportional counters to search for light dark matter candidates. New results from a 10 day physics run with a $135\,\mathrm{cm}$ in diameter spherical proportional counter at the Laboratoire Souterrain de Modane are reported. The target consists of $114\,\mathrm{g}$ of methane, providing sensitivity to dark matter spin-dependent coupling to pr… ▽ More The NEWS-G direct detection experiment uses spherical proportional counters to search for light dark matter candidates. New results from a 10 day physics run with a $135\,\mathrm{cm}$ in diameter spherical proportional counter at the Laboratoire Souterrain de Modane are reported. The target consists of $114\,\mathrm{g}$ of methane, providing sensitivity to dark matter spin-dependent coupling to protons. New constraints are presented in the mass range $0.17$ to $1.2\,\mathrm{GeV/c^2}$, with a 90% confidence level cross-section upper limit of $30.9\,\mathrm{pb}$ for a mass of $0.76\,\mathrm{GeV/c^2}$. △ Less

Submitted 12 April, 2025; v1 submitted 17 July, 2024; originally announced July 2024.

Comments: 9 pages, 5 figures

Journal ref: Phys. Rev. Lett. 134, 141002 (2025)

Transforming a rare event search into a not-so-rare event search in real-time with deep learning-based object detection

Authors: J. Schueler, H. M. Araújo, S. N. Balashov, J. E. Borg, C. Brew, F. M. Brunbauer, C. Cazzaniga, A. Cottle, C. D. Frost, F. Garcia, D. Hunt, A. C. Kaboth, M. Kastriotou, I. Katsioulas, A. Khazov, P. Knights, H. Kraus, V. A. Kudryavtsev, S. Lilley, A. Lindote, M. Lisowska, D. Loomba, M. I. Lopes, E. Lopez Asamar, P. Luna Dapica , et al. (18 additional authors not shown)

Abstract: Deep learning-based object detection algorithms enable the simultaneous classification and localization of any number of objects in image data. Many of these algorithms are capable of operating in real-time on high resolution images, attributing to their widespread usage across many fields. We present an end-to-end object detection pipeline designed for real-time rare event searches for the Migdal… ▽ More Deep learning-based object detection algorithms enable the simultaneous classification and localization of any number of objects in image data. Many of these algorithms are capable of operating in real-time on high resolution images, attributing to their widespread usage across many fields. We present an end-to-end object detection pipeline designed for real-time rare event searches for the Migdal effect, using high-resolution image data from a state-of-the-art scientific CMOS camera in the MIGDAL experiment. The Migdal effect in nuclear scattering, crucial for sub-GeV dark matter searches, has yet to be experimentally confirmed, making its detection a primary goal of the MIGDAL experiment. Our pipeline employs the YOLOv8 object detection algorithm and is trained on real data to enhance the detection efficiency of nuclear and electronic recoils, particularly those exhibiting overlapping tracks that are indicative of the Migdal effect. When deployed online on the MIGDAL readout PC, we demonstrate our pipeline to process and perform the rare event search on 2D image data faster than the peak 120 frame per second acquisition rate of the CMOS camera. Applying these same steps offline, we demonstrate that we can reduce a sample of 20 million camera frames to around 1000 frames while maintaining nearly all signal that YOLOv8 is able to detect, thereby transforming a rare search into a much more manageable search. Our studies highlight the potential of pipelines similar to ours significantly improving the detection capabilities of experiments requiring rapid and precise object identification in high-throughput data environments. △ Less

Submitted 9 April, 2025; v1 submitted 11 June, 2024; originally announced June 2024.

Journal ref: Phys. Rev. D 111, 072004 (2025)

Measurement of scintillation from proportional electron multiplication in liquid xenon using a needle

Authors: P. Knights, H. Sekiya, I. Katsioulas, K. Nikolopoulos, K. Kanzawa, I. Giomataris

Abstract: Charge amplification in liquids could provide single-phase xenon time projection chambers with background discrimination and fiducialisation capabilities similar to those found in dual-phase detectors. Although efforts to achieve the high electric field required for charge amplification and proportional scintillation in liquid xenon have been previously reported, their application to large-scale d… ▽ More Charge amplification in liquids could provide single-phase xenon time projection chambers with background discrimination and fiducialisation capabilities similar to those found in dual-phase detectors. Although efforts to achieve the high electric field required for charge amplification and proportional scintillation in liquid xenon have been previously reported, their application to large-scale detectors remains elusive. This work presents a new approach to this challenge, where - instead of the thin wire approach of previous studies - a needle-like high-voltage electrode is employed to demonstrate proportional charge amplification and secondary scintillation production in liquid xenon. This is an important milestone towards the development of an electrode structure that could be utilised in a large-scale, single-phase time projection chamber with dual read-out. △ Less

Submitted 4 January, 2024; originally announced January 2024.

Comments: 10 pages, 11 figures

First operation of an ACHINOS-equipped Spherical Proportional Counter with individual anode read-out

Authors: D. Herd, I. Katsioulas, P. Knights, I. Manthos, J. Matthews, L. Millins, T. Neep, K. Nikolopoulos, G. Rogers

Abstract: The multi-anode sensor ACHINOS revolutionised the capabilities of the spherical proportional counter by enabling large-size, high-pressure, operation and TPC-like reconstruction capabilities through individual anode read-out. First measurements with an individually read out ACHINOS are performed, which enables improved calibration and response homogenisation. Experimental results demonstrating the… ▽ More The multi-anode sensor ACHINOS revolutionised the capabilities of the spherical proportional counter by enabling large-size, high-pressure, operation and TPC-like reconstruction capabilities through individual anode read-out. First measurements with an individually read out ACHINOS are performed, which enables improved calibration and response homogenisation. Experimental results demonstrating the improvement in energy resolution brought by the individual anode calibration are presented. These are complemented by detailed simulation studies on the effect of sensor design and manufacturing imperfections, and how they may be corrected both in hardware and analysis. △ Less

Submitted 18 January, 2024; v1 submitted 26 September, 2023; originally announced September 2023.

Comments: 16 pages, 14 figures

Performance of a spherical high pressure gas TPC for neutrino magnetic moment measurement

Authors: R. Bouet, J. Busto, V. Cecchini, C. Cerna, P. Charpentier, A. Dastgheibi-Fard, F. Druillole, C. Jollet, P. Hellmuth, I. Katsioulas, P. Knights, I. Giomataris, M. Gros, P. Lautridou, A. Meregaglia, X. F. Navick, T. Neep, K. Nikolopoulos, F. Perrot, F. Piquemal, M. Roche, B. Thomas, R. Ward

Abstract: The measurement of neutrino magnetic moment larger than $10^{-19}μ_B$ would be a clear signature of physics beyond the standard model other than the existence of massive Dirac neutrinos. The use of a spherical proportional counter detector filled with gas at 40 bar located near a nuclear reactor would be a simple way to perform such a measurement exploiting the developments made on such a technolo… ▽ More The measurement of neutrino magnetic moment larger than $10^{-19}μ_B$ would be a clear signature of physics beyond the standard model other than the existence of massive Dirac neutrinos. The use of a spherical proportional counter detector filled with gas at 40 bar located near a nuclear reactor would be a simple way to perform such a measurement exploiting the developments made on such a technology for the search of dark matter and neutrinoless double beta decay. Different targets can be used just by replacing the gas: xenon, CF$_4$ and argon were compared and the sensitivity in one year of data taking could reach the level of $4.3 \times 10^{-12} μ_B$, $6.5 \times 10^{-12} μ_B$, and $8.5 \times 10^{-12} μ_B$, respectively. △ Less

Submitted 15 March, 2023; originally announced March 2023.

Comments: 16 pages 5 figures

Journal ref: 2023_JINST_18_P03031

Exploring light dark matter with the DarkSPHERE spherical proportional counter electroformed underground at the Boulby Underground Laboratory

Authors: L. Balogh, C. Beaufort, M. Chapellier, E. C. Corcoran, J. -M. Coquillat, A. Dastgheibi-Fard, Y. Deng, D. Durnford, C. Garrah, G. Gerbier, I. Giomataris, G. Giroux, P. Gorel, M. Gros, P. Gros, O. Guillaudin, E. W. Hoppe, I. Katsioulas, F. Kelly, P. Knights, P. Lautridou, I. Manthos, R. D. Martin, J. Matthews, J. -F. Muraz , et al. (15 additional authors not shown)

Abstract: We present the conceptual design and the physics potential of DarkSPHERE, a proposed 3 m in diameter spherical proportional counter electroformed underground at the Boulby Underground Laboratory. This effort builds on the R&D performed and experience acquired by the NEWS-G Collaboration. DarkSPHERE is primarily designed to search for nuclear recoils from light dark matter in the 0.05--10 GeV mass… ▽ More We present the conceptual design and the physics potential of DarkSPHERE, a proposed 3 m in diameter spherical proportional counter electroformed underground at the Boulby Underground Laboratory. This effort builds on the R&D performed and experience acquired by the NEWS-G Collaboration. DarkSPHERE is primarily designed to search for nuclear recoils from light dark matter in the 0.05--10 GeV mass range. Electroforming the spherical shell and the implementation of a shield based on pure water ensures a background level below 0.01 dru. These, combined with the proposed helium-isobutane gas mixture, will provide sensitivity to the spin-independent nucleon cross-section of $2\times 10^{-41} (2\times 10^{-43})$ cm$^2$ for a dark matter mass of $0.1 (1)$ GeV. The use of a hydrogen-rich gas mixture with a natural abundance of $^{13}$C provides sensitivity to spin-dependent nucleon cross-sections more than two orders of magnitude below existing constraints for dark matter lighter than 1 GeV. The characteristics of the detector also make it suitable for searches of other dark matter signatures, including scattering of MeV-scale dark matter with electrons, and super-heavy dark matter with masses around the Planck scale that leave extended ionisation tracks in the detector. △ Less

Submitted 14 December, 2023; v1 submitted 12 January, 2023; originally announced January 2023.

Comments: 19 pages, 14 figures

ACHINOS: A Multi-Anode Read-Out for Position Reconstruction and Tracking with Spherical Proportional Counters

Authors: I. Katsioulas, P. Knights, I. Manthos, J. Matthews, T. Neep, K. Nikolopoulos, R. Ward

Abstract: The spherical proportional counter is a versatile gaseous detector with physics applications ranging from rare event searches to fast neutron spectroscopy. In its simplest form, the detector operates with a single channel read-out, and uses pulse-shape information to reconstruct the interaction radius, which is used for background discrimination and target volume definition. Recent developments in… ▽ More The spherical proportional counter is a versatile gaseous detector with physics applications ranging from rare event searches to fast neutron spectroscopy. In its simplest form, the detector operates with a single channel read-out, and uses pulse-shape information to reconstruct the interaction radius, which is used for background discrimination and target volume definition. Recent developments in the read-out instrumentation have enabled the use of a multi-anode read-out structure, ACHINOS. The multiple anodes provide information about the interaction position which, coupled with the radial information, can be used to reconstruct an ionisation track. This ability has implications for several applications of the detector, for example, background discrimination in rare event searches. △ Less

Submitted 21 November, 2022; originally announced November 2022.

Comments: 4 pages, 3 figures

Journal ref: JINST 17 (2022) 08, C08025

Purification Efficiency and Radon Emanation of Gas Purifiers used with Pure and Binary Gas Mixtures for Gaseous Dark Matter Detectors

Authors: K., Altenmüller, J. F. Castel, S. Cebrián, T. Dafní, D. Díez-Ibáñez, J. Galán, J. Galindo, J. A. García, I. G. Irastorza, I. Katsioulas, P. Knights, G. Luzón, I. Manthos, C. Margalejo, J. Matthews, K. Mavrokoridis, H. Mirallas, T. Neep, K. Nikolopoulos, L. Obis, A. Ortiz de Solórzano, O. Pérez, B. Philippou, R. Ward

Abstract: Rare event searches require extreme radiopurity in all detector components. This includes the active medium, which in the case of gaseous detectors, is the operating gas. The gases used typically include noble gas mixtures with molecular quenchers. Purification of these gases is required to achieve the desired detector performance, however, purifiers are known to emanate 222 Rn, which is a potenti… ▽ More Rare event searches require extreme radiopurity in all detector components. This includes the active medium, which in the case of gaseous detectors, is the operating gas. The gases used typically include noble gas mixtures with molecular quenchers. Purification of these gases is required to achieve the desired detector performance, however, purifiers are known to emanate 222 Rn, which is a potential source of background. Several purifiers are studied for their O 2 and H 2 O purification efficiency and Rn emanation rates, aiming to identify the lowest-Rn options. Furthermore, the absorption of quenchers by the purifiers is assessed when used in a recirculating closed-loop gas system. △ Less

Submitted 18 November, 2022; originally announced November 2022.

Comments: 3 pages, 4 figures. Contribution to 2021 IEEE Nuclear Science Symposium and Medical Imaging Conference (NSS/MIC)

Journal ref: 2021 IEEE Nuclear Science Symposium and Medical Imaging Conference (NSS/MIC), 2021, pp. 1-3

Fast Neutron Spectroscopy with a High-pressure Nitrogen-filled Large Volume Spherical Proportional Counter

Authors: I. Giomataris, I. Katsioulas, P. Knights, I. Manthos, J. Matthews, T. Neep, K. Nikolopoulos, T. Papaevangelou, B. Phoenix, R. Ward

Abstract: We present a fast neutron spectroscopy system based on a nitrogen-filled, large volume gaseous detector, the Spherical Proportional Counter. The system has been successfully operated up to gas pressure of 1.5 bar. Neutron energy is estimated through measurement of the 14N(n,a)11B and 14N(n,p)14C reaction products. These reactions have comparable cross sections and Q-values with the 3He(n,p)3H reac… ▽ More We present a fast neutron spectroscopy system based on a nitrogen-filled, large volume gaseous detector, the Spherical Proportional Counter. The system has been successfully operated up to gas pressure of 1.5 bar. Neutron energy is estimated through measurement of the 14N(n,a)11B and 14N(n,p)14C reaction products. These reactions have comparable cross sections and Q-values with the 3He(n,p)3H reaction making nitrogen a good alternative to 3He use for fast neutron detection. Two detectors were built at the University of Birmingham and are currently used for the measurement of fast and thermal neutrons in the University of Birmingham and the Boulby underground laboratory, respectively. △ Less

Submitted 7 November, 2022; originally announced November 2022.

Comments: 3 pages, 6 Figures

Journal ref: 2021 IEEE Nuclear Science Symposium and Medical Imaging Conference (NSS/MIC), 2021, pp. 1-3

Subwavelength grating metamaterial waveguides and ring resonators on a silicon nitride platform

Authors: Cameron M. Naraine, Jocelyn N. Westwood-Bachman, Cameron Horvath, Mirwais Aktary, Andrew P. Knights, Jens H. Schmid, Pavel Cheben, Jonathan D. B. Bradley

Abstract: We propose and demonstrate subwavelength grating (SWG) metamaterial waveguides and ring resonators on a silicon nitride platform for the first time. The SWG waveguide is engineered such that a large overlap of 53% of the Bloch mode with the top cladding material is achieved, demonstrating excellent potential for applications in evanescent field sensing and light amplification. The devices, which h… ▽ More We propose and demonstrate subwavelength grating (SWG) metamaterial waveguides and ring resonators on a silicon nitride platform for the first time. The SWG waveguide is engineered such that a large overlap of 53% of the Bloch mode with the top cladding material is achieved, demonstrating excellent potential for applications in evanescent field sensing and light amplification. The devices, which have critical dimensions greater than 100 nm, are fabricated using a commercial rapid turn-around silicon nitride prototyping foundry process using electron beam lithography. Experimental characterization of the fabricated device reveals excellent ring resonator internal quality factor (2.11x10^5) and low propagation loss (~1.5 dB/cm) in the C-band, a significant improvement of both parameters compared to silicon based SWG ring resonators. These results demonstrate the promising prospects of SWG metamaterial structures for silicon nitride based photonic integrated circuits. △ Less

Submitted 19 September, 2022; originally announced September 2022.

Comments: 12 pages, 7 figures, submitted to Laser & Photonics Reviews for publication

Neutron spectroscopy: The case of the spherical proportional counter

Authors: I. Giomataris, I. Katsioulas, P. Knights, I. Manthos, T. Neep, K. Nikolopoulos, T. Papaevangelou, R. Ward

Abstract: Neutron spectroscopy is an invaluable tool for many scientific and industrial applications, including underground Dark Matter searches. Neutron-induced backgrounds produced by cosmic ray muons and the cavern radioactivity can mimic the expected Dark Matter signal. However, existing neutron detection methods have several drawbacks and limitations, thus measurements remain elusive. A promising new a… ▽ More Neutron spectroscopy is an invaluable tool for many scientific and industrial applications, including underground Dark Matter searches. Neutron-induced backgrounds produced by cosmic ray muons and the cavern radioactivity can mimic the expected Dark Matter signal. However, existing neutron detection methods have several drawbacks and limitations, thus measurements remain elusive. A promising new approach to neutron spectroscopy is the use of a nitrogen-filled spherical proportional counter that exploits the $^{14}$N(n,$α$)$^{11}$B and $^{14}$N(n, p)$^{14}$C reactions. This is a safe, inexpensive, effective and reliable technique. In this work, the latest instrumentation developments are incorporated in a compact detector operated at the University of Birmingham (UoB) with high gain at gas pressure up to 1.8\,bar. We demonstrate spectroscopic measurements of thermalised and fast neutrons respectively from an $^{241}$Am-$^9$Be source and from the MC40 cyclotron facility at UoB. Additionally, the detector response to neutrons is simulated using a framework developed at UoB and compared with the experimental results. △ Less

Submitted 22 July, 2022; originally announced July 2022.

Comments: 4 pages, 6 figures, 15th Pisa Meeting on Advanced Detectors

Neutron spectroscopy with a high-pressure nitrogen-filled spherical proportional counter

Authors: I. Giomataris, S. Green, I. Katsioulas, P. Knights, I. Manthos, T. Neep, K. Nikolopoulos, T. Papaevangelou, B. Phoenix, J. Sanders, R. Ward

Abstract: The spherical proportional counter is a large volume gaseous detector which finds application in several fields, including direct Dark Matter searches. When the detector is filled with nitrogen it becomes an effective neutron spectrometer thanks to the $^{14}$N(n,$\mathrmα$)$^{11}$B and $^{14}$N(n,p)$^{14}$C reactions. Nitrogen, however, is a challenging operating gas for proportional counters and… ▽ More The spherical proportional counter is a large volume gaseous detector which finds application in several fields, including direct Dark Matter searches. When the detector is filled with nitrogen it becomes an effective neutron spectrometer thanks to the $^{14}$N(n,$\mathrmα$)$^{11}$B and $^{14}$N(n,p)$^{14}$C reactions. Nitrogen, however, is a challenging operating gas for proportional counters and requires a high electric field strength to gas pressure ratio. Benefiting from the latest advances in spherical proportional counter instrumentation and simulation techniques, we report first neutron measurements at operating pressures of up to 1.8 bar. This achievement enhances the prospects of the spherical proportional counter to act as a neutron spectrometer appropriate for challenging environments, including underground laboratories, and industrial and medical settings. △ Less

Submitted 13 February, 2023; v1 submitted 9 June, 2022; originally announced June 2022.

Comments: 15 pages, 24 figures

Journal ref: Nuclear Inst. and Methods in Physics Research, A 1049 (2023) 168124

The NEWS-G detector at SNOLAB

Authors: L. Balogh, C. Beaufort, A. Brossard, J. F. Caron, M. Chapellier, J. M. Coquillat, E. C. Corcoran, S. Crawford, A. Dastgheibi-Fard, Y. Deng, K. Dering, D. Durnford, C. Garrah, G. Gerbier, I. Giomataris, G. Giroux, P. Gorel, M. Gros, P. Gros, O. Guillaudin, E. W. Hoppe, I. Katsioulas, F. Kelly, P. Knights, L. Kwon , et al. (16 additional authors not shown)

Abstract: The New Experiments With Spheres-Gas (NEWS-G) collaboration intends to achieve $\mathrm{sub-GeV/c^{2}}$ Weakly Interacting Massive Particles (WIMPs) detection using Spherical Proportional Counters (SPCs). SPCs are gaseous detectors relying on ionization with a single ionization electron energy threshold. The latest generation of SPC for direct dark matter searches has been installed at SNOLAB in C… ▽ More The New Experiments With Spheres-Gas (NEWS-G) collaboration intends to achieve $\mathrm{sub-GeV/c^{2}}$ Weakly Interacting Massive Particles (WIMPs) detection using Spherical Proportional Counters (SPCs). SPCs are gaseous detectors relying on ionization with a single ionization electron energy threshold. The latest generation of SPC for direct dark matter searches has been installed at SNOLAB in Canada in 2021. This article details the different processes involved in the fabrication of the NEWS-G experiment. Also outlined in this paper are the mitigation strategies, measurements of radioactivity of the different components, and estimations of induced background event rates that were used to quantify and address detector backgrounds. △ Less

Submitted 4 January, 2023; v1 submitted 30 May, 2022; originally announced May 2022.

Comments: 18 pages, 9 figures, 5 tables, to be published

Coherent elastic neutrino-nucleus scattering: Terrestrial and astrophysical applications

Authors: M. Abdullah, H. Abele, D. Akimov, G. Angloher, D. Aristizabal-Sierra, C. Augier, A. B. Balantekin, L. Balogh, P. S. Barbeau, L. Baudis, A. L. Baxter, C. Beaufort, G. Beaulieu, V. Belov, A. Bento, L. Berge, I. A. Bernardi, J. Billard, A. Bolozdynya, A. Bonhomme, G. Bres, J-. L. Bret, A. Broniatowski, A. Brossard, C. Buck , et al. (250 additional authors not shown)

Abstract: Coherent elastic neutrino-nucleus scattering (CE$ν$NS) is a process in which neutrinos scatter on a nucleus which acts as a single particle. Though the total cross section is large by neutrino standards, CE$ν$NS has long proven difficult to detect, since the deposited energy into the nucleus is $\sim$ keV. In 2017, the COHERENT collaboration announced the detection of CE$ν$NS using a stopped-pion… ▽ More Coherent elastic neutrino-nucleus scattering (CE$ν$NS) is a process in which neutrinos scatter on a nucleus which acts as a single particle. Though the total cross section is large by neutrino standards, CE$ν$NS has long proven difficult to detect, since the deposited energy into the nucleus is $\sim$ keV. In 2017, the COHERENT collaboration announced the detection of CE$ν$NS using a stopped-pion source with CsI detectors, followed up the detection of CE$ν$NS using an Ar target. The detection of CE$ν$NS has spawned a flurry of activities in high-energy physics, inspiring new constraints on beyond the Standard Model (BSM) physics, and new experimental methods. The CE$ν$NS process has important implications for not only high-energy physics, but also astrophysics, nuclear physics, and beyond. This whitepaper discusses the scientific importance of CE$ν$NS, highlighting how present experiments such as COHERENT are informing theory, and also how future experiments will provide a wealth of information across the aforementioned fields of physics. △ Less

Submitted 14 March, 2022; originally announced March 2022.

Comments: contribution to Snowmasss 2021. Contact authors: P. S. Barbeau, R. Strauss, L. E. Strigari

EXCESS workshop: Descriptions of rising low-energy spectra

Authors: P. Adari, A. Aguilar-Arevalo, D. Amidei, G. Angloher, E. Armengaud, C. Augier, L. Balogh, S. Banik, D. Baxter, C. Beaufort, G. Beaulieu, V. Belov, Y. Ben Gal, G. Benato, A. Benoît, A. Bento, L. Bergé, A. Bertolini, R. Bhattacharyya, J. Billard, I. M. Bloch, A. Botti, R. Breier, G. Bres, J-. L. Bret , et al. (281 additional authors not shown)

Abstract: Many low-threshold experiments observe sharply rising event rates of yet unknown origins below a few hundred eV, and larger than expected from known backgrounds. Due to the significant impact of this excess on the dark matter or neutrino sensitivity of these experiments, a collective effort has been started to share the knowledge about the individual observations. For this, the EXCESS Workshop was… ▽ More Many low-threshold experiments observe sharply rising event rates of yet unknown origins below a few hundred eV, and larger than expected from known backgrounds. Due to the significant impact of this excess on the dark matter or neutrino sensitivity of these experiments, a collective effort has been started to share the knowledge about the individual observations. For this, the EXCESS Workshop was initiated. In its first iteration in June 2021, ten rare event search collaborations contributed to this initiative via talks and discussions. The contributing collaborations were CONNIE, CRESST, DAMIC, EDELWEISS, MINER, NEWS-G, NUCLEUS, RICOCHET, SENSEI and SuperCDMS. They presented data about their observed energy spectra and known backgrounds together with details about the respective measurements. In this paper, we summarize the presented information and give a comprehensive overview of the similarities and differences between the distinct measurements. The provided data is furthermore publicly available on the workshop's data repository together with a plotting tool for visualization. △ Less

Submitted 4 March, 2022; v1 submitted 10 February, 2022; originally announced February 2022.

Comments: 44 pages, 20 figures; Editors: A. Fuss, M. Kaznacheeva, F. Reindl, F. Wagner; updated copyright statements and funding information

Journal ref: SciPost Phys. Proc. 9, 001 (2022)

Simultaneous scintillation light and charge readout of a pure argon filled Spherical Proportional Counter

Authors: R. Bouet, J. Busto, V. Cecchini, C. Cerna, A. Dastgheibi-Fard, F. Druillole, C. Jollet, P. Hellmuth, I. Katsioulas, P. Knights, I. Giomataris, M. Gros, P. Lautridou, A. Meregaglia, X. F. Navick, T. Neep, K. Nikolopoulos, F. Perrot, F. Piquemal, M. Roche, B. Thomas, R. Ward, M. Zampaolo

Abstract: The possible use of a Spherical Proportional Counter for the search of neutrinoless double beta decay is investigated in the R2D2 R&D project. Dual charge and scintillation light readout may improve the detector performance. Tests were carried out with pure argon at 1.1 bar using a 6x6 mm2 silicon photomultiplier. Scintillation light was used for the first time to trigger in a spherical proportion… ▽ More The possible use of a Spherical Proportional Counter for the search of neutrinoless double beta decay is investigated in the R2D2 R&D project. Dual charge and scintillation light readout may improve the detector performance. Tests were carried out with pure argon at 1.1 bar using a 6x6 mm2 silicon photomultiplier. Scintillation light was used for the first time to trigger in a spherical proportional counter. The measured drift time is in excellent agreement with the expectations from simulations. Furthermore the light signal emitted during the avalanche development exhibits features that could be exploited for event characterisation. △ Less

Submitted 29 January, 2022; originally announced January 2022.

Comments: 17 pages,14 figures

Measurements of the ionization efficiency of protons in methane

Authors: NEWS-G Collaboration, :, L. Balogh, C. Beaufort, A. Brossard, J. -F. Caron, M. Chapellier, J. -M. Coquillat, E. C. Corcoran, S. Crawford, A. Dastgheibi-Fard, Y. Deng, K. Dering, D. Durnford, C. Garrah, G. Gerbier, I. Giomataris, G. Giroux, P. Gorel, M. Gros, P. Gros, O. Guillaudin, E. W. Hoppe, I. Katsioulas, F. Kelly , et al. (19 additional authors not shown)

Abstract: The amount of energy released by a nuclear recoil ionizing the atoms of the active volume of detection appears "quenched" compared to an electron of the same kinetic energy. This different behavior in ionization between electrons and nuclei is described by the Ionization Quenching Factor (IQF) and it plays a crucial role in direct dark matter searches. For low kinetic energies (below… ▽ More The amount of energy released by a nuclear recoil ionizing the atoms of the active volume of detection appears "quenched" compared to an electron of the same kinetic energy. This different behavior in ionization between electrons and nuclei is described by the Ionization Quenching Factor (IQF) and it plays a crucial role in direct dark matter searches. For low kinetic energies (below $50~\mathrm{keV}$), IQF measurements deviate significantly from common models used for theoretical predictions and simulations. We report measurements of the IQF for proton, an appropriate target for searches of Dark Matter candidates with a mass of approximately 1 GeV, with kinetic energies in between $2~\mathrm{keV}$ and $13~\mathrm{keV}$ in $100~\mathrm{mbar}$ of methane. We used the Comimac facility in order to produce the motion of nuclei and electrons of controlled kinetic energy in the active volume, and a NEWS-G SPC to measure the deposited energy. The Comimac electrons are used as reference to calibrate the detector with 7 energy points. A detailed study of systematic effects led to the final results well fitted by $\mathrm{IQF}~(E_K)= E_K^α~/~(β+ E_K^α)$ with $α=0.70\pm0.08$ and $β= 1.32\pm0.17$. In agreement with some previous works in other gas mixtures, we measured less ionization energy than predicted from SRIM simulations, the difference reaching $33\%$ at $2~\mathrm{keV}$ △ Less

Submitted 25 June, 2022; v1 submitted 24 January, 2022; originally announced January 2022.

Comments: 12 pages, 9 figures

Solar Kaluza-Klein axion search with NEWS-G

Authors: NEWS-G collaboration, :, Q. Arnaud, L. Balogh, C. Beaufort, A. Brossard, J. -F. Caron, M. Chapellier, J. -M. Coquillat, E. C. Corcoran, S. Crawford, A. Dastgheibi-Fard, Y. Deng, K. Dering, D. Durnford, C. Garrah, G. Gerbier, I. Giomataris, G. Giroux, P. Gorel, M. Gros, P. Gros, O. Guillaudin, E. W. Hoppe, I. Katsioulas , et al. (18 additional authors not shown)

Abstract: Kaluza-Klein (KK) axions appear in theories with extra dimensions as higher mass, significantly shorter lifetime, excitations of the Peccei-Quinn axion. When produced in the Sun, they would remain gravitationally trapped in the solar system, and their decay to a pair of photons could provide an explanation of the solar corona heating problem. A low-density detector would discriminate such a signal… ▽ More Kaluza-Klein (KK) axions appear in theories with extra dimensions as higher mass, significantly shorter lifetime, excitations of the Peccei-Quinn axion. When produced in the Sun, they would remain gravitationally trapped in the solar system, and their decay to a pair of photons could provide an explanation of the solar corona heating problem. A low-density detector would discriminate such a signal from the background, by identifying the separation of the interaction point of the two photons. The NEWS-G collaboration uses large volume Spherical Proportional Counters, gas-filled metallic spheres with a spherical anode in their centre. After observation of a single axionlike event in a 42 day long run with the SEDINE detector, a $90\%$ C.L. upper limit of $g_{aγγ}<8.99\cdot10^{-13}\,GeV^{-1}$ is set on the axion-photon coupling for a KK axion density on Earth of $n_{a}=4.07\cdot10^{13}\,m^{-3}$ and two extra dimensions of size $R = 1\,eV^{-1}$. △ Less

Submitted 9 January, 2022; v1 submitted 8 September, 2021; originally announced September 2021.

Comments: 19 pages, 11 figures. Updated with additional details requested during review for publication in PRD and mild relaxation of final constraint

Journal ref: Phys. Rev. D 105, 012002 (2022)

Quenching factor measurements of neon nuclei in neon gas

Authors: L. Balogh, C. Beaufort, A. Brossard, J. -F. Caron, M. Chapellier, J. -M. Coquillat, E. C. Corcoran, S. Crawford, A. Dastgheibi Fard, Y. Deng, K. Dering, D. Durnford, C. Garrah, G. Gerbier, I. Giomataris, G. Giroux, P. Gorel, M. Gros, P. Gros, O. Guillaudin, E. W. Hoppe, I. Katsioulas, F. Kelly, P. Knights, L. Kwon , et al. (25 additional authors not shown)

Abstract: The NEWS-G collaboration uses Spherical Proportional Counters (SPCs) to search for weakly interacting massive particles (WIMPs). In this paper, we report the first measurements of the nuclear quenching factor in neon gas at \SI{2}{bar} using an SPC deployed in a neutron beam at the TUNL facility. The energy-dependence of the nuclear quenching factor is modelled using a simple power law: $α$E… ▽ More The NEWS-G collaboration uses Spherical Proportional Counters (SPCs) to search for weakly interacting massive particles (WIMPs). In this paper, we report the first measurements of the nuclear quenching factor in neon gas at \SI{2}{bar} using an SPC deployed in a neutron beam at the TUNL facility. The energy-dependence of the nuclear quenching factor is modelled using a simple power law: $α$E$_{nr}^β$; we determine its parameters by simultaneously fitting the data collected with the detector over a range of energies. We measured the following parameters in Ne:CH$_{4}$ at \SI{2}{bar}: $α$ = 0.2801 $\pm$ 0.0050 (fit) $\pm$ 0.0045 (sys) and $β$ = 0.0867 $\pm$ 0.020 (fit) $\pm$ 0.006(sys). Our measurements do not agree with expected values from SRIM or Lindhard theory. We demonstrated the feasibility of performing quenching factor measurements at sub-keV energies in gases using SPCs and a neutron beam. △ Less

Submitted 3 December, 2021; v1 submitted 2 September, 2021; originally announced September 2021.

Journal ref: Phys. Rev. D. Vol. 105, No. 5, 052004 (2022)

Neutron spectroscopy with N$_2$-filled high-pressure large-volume spherical proportional counters

Authors: I. Giomataris, S. Green, I. Katsioulas, P. Knights, I. Manthos, J. Matthews, T. Neep, K. Nikolopoulos, T. Papaevangelou, B. Phoenix, J. Sanders, R. Ward

Abstract: Precise in-situ measurements of the neutron flux in underground laboratories is crucial for direct dark matter searches, as neutron induced backgrounds can mimic the typical dark matter signal. The development of a novel neutron spectroscopy technique using Spherical Proportional Counters is investigated. The detector is operated with nitrogen and is sensitive to both fast and thermal neutrons thr… ▽ More Precise in-situ measurements of the neutron flux in underground laboratories is crucial for direct dark matter searches, as neutron induced backgrounds can mimic the typical dark matter signal. The development of a novel neutron spectroscopy technique using Spherical Proportional Counters is investigated. The detector is operated with nitrogen and is sensitive to both fast and thermal neutrons through the $^{14}$N(n, $α$)$^{11}$B and $^{14}$N(n, p)$^{14}$C reactions. This method holds potential to be a safe, inexpensive, effective, and reliable alternative to $^3$He-based detectors. Measurements of fast and thermal neutrons from an Am-Be source with a Spherical Proportional Counter operated at pressures up to 2 bar at Birmingham are discussed. △ Less

Submitted 6 July, 2021; originally announced July 2021.

Comments: 4 pages, 5 figures, International Conference on Technology and Instrumentation in Particle Physics (TIPP2021)

Ionisation quenching factors from W-values in pure gases for rare event searches

Authors: Ioannis Katsioulas, Patrick Knights, Konstantinos Nikolopoulos

Abstract: The effect of ionisation quenching for ions is critical for experiments relying on the measurement of low energy recoils, such as direct Dark Matter searches. We present ionisation quenching factor estimates over a range of energies for protons, $α$-particles, and heavier ions in H$_{2}$, CH$_{4}$, N$_{2}$, Ar, CO$_{2}$, and C$_{3}$H$_{8}$ gases, estimated from the respective reference W-value mea… ▽ More The effect of ionisation quenching for ions is critical for experiments relying on the measurement of low energy recoils, such as direct Dark Matter searches. We present ionisation quenching factor estimates over a range of energies for protons, $α$-particles, and heavier ions in H$_{2}$, CH$_{4}$, N$_{2}$, Ar, CO$_{2}$, and C$_{3}$H$_{8}$ gases, estimated from the respective reference W-value measurements. The resulting ionisation quenching factors are compared with predictions from SRIM. △ Less

Submitted 11 May, 2022; v1 submitted 4 May, 2021; originally announced May 2021.

Comments: This work was performed in the context of the NEWS-G experiment. This project has received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement no 841261 (DarkSphere)

Journal ref: Astropart.Phys. 141 (2022) 102707

A thulium-silicon hybrid microdisk laser

Authors: Khadijeh Miarabbas Kiani, Henry C. Frankis, Cameron M. Naraine, Dawson B. Bonneville, Andrew P. Knights, Jonathan D. B. Bradley

Abstract: Silicon photonics technology enables compact, low-power and cost-effective optical microsystems on a chip by leveraging the materials and advanced fabrication methods developed over decades for integrated silicon electronics. Silicon foundries now provide many standard building blocks required for high-performance optical circuits, including passive components such as optical waveguides, filters a… ▽ More Silicon photonics technology enables compact, low-power and cost-effective optical microsystems on a chip by leveraging the materials and advanced fabrication methods developed over decades for integrated silicon electronics. Silicon foundries now provide many standard building blocks required for high-performance optical circuits, including passive components such as optical waveguides, filters and (de-)multiplexors and active optoelectronic components such as high-speed modulators, switches and photodetectors. However, because silicon is a poor light emitting material, on-chip light sources are still a significant challenge for foundry offerings. Current light-source integration methods are viewed as complex, requiring incompatible and/or expensive materials and processing steps. Here we report on an ultra-compact silicon photonic laser consisting of a thulium-silicon hybrid microdisk resonator. The microdisk design is straightforward and compatible with the fabrication steps and device dimensions available in all silicon photonics foundries, whereas the gain medium is added in a backend (final step), room temperature sputter deposition. This approach allows for low-cost and high-volume wafer-scale manufacturing and co-integration of light sources with silicon passive and active devices with no adjustment to standard process flows. The hybrid laser is pumped at standard telecom wavelengths around 1.6 μm and emits around 1.9 μm, which is within an emerging spectral region of significant interest for communications, nonlinear and quantum optics, and sensing on silicon. △ Less

Submitted 21 April, 2021; originally announced April 2021.

Comments: 16 pages, 4 figures

Copper electroplating for background suppression in the NEWS-G experiment

Authors: NEWS-G Collaboration, :, L. Balogh, C. Beaufort, A. Brossard, R. Bunker, J. -F. Caron, M. Chapellier, J. -M. Coquillat, E. C. Corcoran, S. Crawford, A. Dastgheibi Fard, Y. Deng, K. Dering, D. Durnford, G. Gerbier, I. Giomataris, G. Giroux, P. Gorel, M. Gros, P. Gros, O. Guillaudin, E. W. Hoppe, I. Katsioulas, F. Kelly , et al. (26 additional authors not shown)

Abstract: New Experiments with Spheres-Gas (NEWS-G) is a dark matter direct detection experiment that will operate at SNOLAB (Canada). Similar to other rare-event searches, the materials used in the detector construction are subject to stringent radiopurity requirements. The detector features a 140-cm diameter proportional counter comprising two hemispheres made from commercially sourced 99.99% pure copper.… ▽ More New Experiments with Spheres-Gas (NEWS-G) is a dark matter direct detection experiment that will operate at SNOLAB (Canada). Similar to other rare-event searches, the materials used in the detector construction are subject to stringent radiopurity requirements. The detector features a 140-cm diameter proportional counter comprising two hemispheres made from commercially sourced 99.99% pure copper. Such copper is widely used in rare-event searches because it is readily available, there are no long-lived Cu radioisotopes, and levels of non-Cu radiocontaminants are generally low. However, measurements performed with a dedicated 210Po alpha counting method using an XIA detector confirmed a problematic concentration of 210Pb in bulk of the copper. To shield the proportional counter's active volume, a low-background electroforming method was adapted to the hemispherical shape to grow a 500-$μ$m thick layer of ultra-radiopure copper to the detector's inner surface. In this paper the process is described, which was prototyped at Pacific Northwest National Laboratory (PNNL), USA, and then conducted at full scale in the Laboratoire Souterrain de Modane in France. The radiopurity of the electroplated copper was assessed through Inductively Coupled Plasma Mass Spectrometry (ICP-MS). Measurements of samples from the first (second) hemisphere give 68% confidence upper limits of <0.58 $μ$Bq/kg (<0.24 $μ$Bq/kg) and <0.26 $μ$Bq/kg (<0.11 $μ$Bq/kg) on the 232Th and 238U contamination levels, respectively. These results are comparable to previously reported measurements of electroformed copper produced for other rare-event searches, which were also found to have low concentration of 210Pb consistent with the background goals of the NEWS-G experiment. △ Less

Submitted 13 December, 2020; v1 submitted 7 August, 2020; originally announced August 2020.

Comments: 11 pages, 11 figures, 3 tables

Journal ref: Nucl.Instrum.Meth.A 988 (2021) 164844

R2D2 spherical TPC: first energy resolution results

Authors: R. Bouet, J. Busto, V. Cecchini, C. Cerna, A. Dastgheibi-Fard, F. Druillole, C. Jollet, P. Hellmuth, I. Katsioulas, P. Knights, I. Giomataris, M. Gros, P. Lautridou, A. Meregaglia, X. F. Navick, T. Neep, K. Nikolopoulos, F. Perrot, F. Piquemal, M. Roche, B. Thomas, R. Ward, M. Zampaolo

Abstract: Spherical time projection chambers (TPC), also known as spherical proportional counters, are employed in the search for rare phenomena, such as light Dark Matter candidates. The spherical TPC exhibits a number of essential features, making it a promising candidate for the search of neutrinoless double beta decay ($β\beta0ν$). A tonne-scale spherical TPC experiment could cover a region of parameter… ▽ More Spherical time projection chambers (TPC), also known as spherical proportional counters, are employed in the search for rare phenomena, such as light Dark Matter candidates. The spherical TPC exhibits a number of essential features, making it a promising candidate for the search of neutrinoless double beta decay ($β\beta0ν$). A tonne-scale spherical TPC experiment could cover a region of parameter space relevant for the inverted mass hierarchy with a few years of data taking. In this direction, the major R\&D goal of the R2D2 effort is the demonstration of the required energy resolution. First results from an argon-filled prototype detector are reported, demonstrating an energy resolution of 1.1\% FWHM for 5.3~MeV $α$ tracks in the 0.2 to 1.1~bar pressure range. This is a major milestone in terms of energy resolution, paving the way for further studies with xenon gas, and the possible use of this technology for $β\beta0ν$ searches. △ Less

Submitted 11 January, 2021; v1 submitted 6 July, 2020; originally announced July 2020.

A resistive ACHINOS multi-anode structure with DLC coating for spherical proportional counters

Authors: I. Giomataris, M. Gros, I. Katsioulas, P. Knights, J. -P. Mols, T. Neep, K. Nikolopoulos, G. Savvidis, I. Savvidis, L. Shang, R. Ward, Y. Zhou

Abstract: The spherical proportional counter is a gaseous detector used in a variety of applications, including direct dark matter and neutrino-less double beta decay searches. The ACHINOS multianode structure is a read-out technology that overcomes the limitations of single-anode read-out structures for large-size detectors and operation under high pressure. A resistive ACHINOS is presented, where the 3D p… ▽ More The spherical proportional counter is a gaseous detector used in a variety of applications, including direct dark matter and neutrino-less double beta decay searches. The ACHINOS multianode structure is a read-out technology that overcomes the limitations of single-anode read-out structures for large-size detectors and operation under high pressure. A resistive ACHINOS is presented, where the 3D printed central component is coated in a Diamond-Like Carbon (DLC) layer. The production and testing of the structure, in terms of stability and resolution, is described. Further applications in fundamental physics and industry are also discussed. △ Less

Submitted 26 October, 2020; v1 submitted 2 March, 2020; originally announced March 2020.

Comments: 8 pages, 8 figures

Journal ref: JINST 15 (2020) 11, P11023

Development of a Simulation Framework for Spherical Proportional Counters

Authors: I. Katsioulas, P. Knights, J. Matthews, T. Neep, K. Nikolopoulos, R. Owen, R. Ward

Abstract: The spherical proportional counter is a novel gaseous detector with numerous applications, including direct dark matter searches and neutron spectroscopy. The strengths of the Geant4 and Garfield++ toolkits are combined to create a simulation framework for spherical proportional counters. The interface is implemented by introducing Garfield++ classes within a Geant4 application. Simulated muon, el… ▽ More The spherical proportional counter is a novel gaseous detector with numerous applications, including direct dark matter searches and neutron spectroscopy. The strengths of the Geant4 and Garfield++ toolkits are combined to create a simulation framework for spherical proportional counters. The interface is implemented by introducing Garfield++ classes within a Geant4 application. Simulated muon, electron, and photon signals are presented, and the effects of gas mixture composition and anode support structure on detector response are discussed. △ Less

Submitted 8 June, 2020; v1 submitted 7 February, 2020; originally announced February 2020.

Comments: 11 pages, 11 figures, proceedings of 15th Topical Seminar on Innovative Particle and Radiation Detectors (IPRD19) 14-17 October 2019 Siena, Italy

Journal ref: JINST 15 (2020) C06013

Experimental Determination of Proton Hardness Factors at Several Irradiation Facilities

Authors: P. Allport, F. Bogelspacher, K. Bruce, R. Canavan, A. Dierlamm, L. Gonella, P. Knights, I. Mateu, M. Moll, K. Nikolopoulos, B. Phoenix, T. Price, L. Ram, F. Ravotti, C. Simpson-Allsop, C. Wood

Abstract: The scheduled High Luminosity upgrade of the CERN Large Hadron Collider presents new challenges in terms of radiation hardness. As a consequence, campaigns to qualify the radiation hardness of detector sensors and components are undertaken worldwide. The effects of irradiation with beams of different particle species and energy, aiming to assess displacement damage in semiconductor devices, are co… ▽ More The scheduled High Luminosity upgrade of the CERN Large Hadron Collider presents new challenges in terms of radiation hardness. As a consequence, campaigns to qualify the radiation hardness of detector sensors and components are undertaken worldwide. The effects of irradiation with beams of different particle species and energy, aiming to assess displacement damage in semiconductor devices, are communicated in terms of the equivalent 1 MeV neutron fluence, using the hardness factor for the conversion. In this work, the hardness factors for protons at three different kinetic energies have been measured by analysing the I-V and C-V characteristics of reverse biased diodes, pre- and post-irradiation. The sensors were irradiated at the MC40 Cyclotron of the University of Birmingham, the cyclotron at the Karlsruhe Institute of Technology, and the IRRAD proton facility at CERN, with the respective measured proton hardness factors being: 2.1 +/- 0.5 for 24 MeV, 2.2 +/- 0.4 for 23 MeV, and 0.62 +/- 0.04 for 23 GeV. The hardness factors currently used in these three facilities are in agreement with the presented measurements. △ Less

Submitted 12 November, 2019; v1 submitted 8 August, 2019; originally announced August 2019.

Comments: 13 pages, 12 figures

Journal ref: JINST 14 (2019) P12004

Precision laser-based measurements of the single electron response of SPCs for the NEWS-G light dark matter search experiment

Authors: NEWS-G Collaboration, :, Q. Arnaud, J. -P. Bard, A. Brossard, M. Chapellier, M. Clark, S. Crawford, E. C. Corcoran, A. Dastgheibi-Fard, K. Dering, P. Di Stefano, D. Durnford, G. Gerbier, I. Giomataris, G. Giroux, P. Gorel, M. Gros, P. Gros, O. Guillaudin, E. W. Hoppe, A. Kamaha, I. Katsioulas, D. G. Kelly, P. Knights , et al. (15 additional authors not shown)

Abstract: Spherical Proportional Counters (SPCs) are a novel gaseous detector technology employed by the NEWS-G low-mass dark matter search experiment for their high sensitivity to single electrons from ionization. In this paper, we report on the first characterization of the single electron response of SPCs with unprecedented precision, using a UV-laser calibration system. The experimental approach and ana… ▽ More Spherical Proportional Counters (SPCs) are a novel gaseous detector technology employed by the NEWS-G low-mass dark matter search experiment for their high sensitivity to single electrons from ionization. In this paper, we report on the first characterization of the single electron response of SPCs with unprecedented precision, using a UV-laser calibration system. The experimental approach and analysis methodology are presented along with various direct applications for the upcoming next phase of the experiment at SNOLAB. These include the continuous monitoring of the detector response and electron drift properties during dark matter search runs, as well as the experimental measurement of the trigger threshold efficiency. We measure a mean ionization energy of $\mathrm{W}=27.6\pm0.2~\mathrm{eV}$ in $\mathrm{Ne + CH_4}$ $(2\%)$ for 2.8 keV X-rays, and demonstrate the feasibility of performing similar precision measurements at sub-keV energies for future gas mixtures to be used for dark matter searches at SNOLAB. △ Less

Submitted 24 February, 2019; originally announced February 2019.

Comments: 12 pages, 8 figures, submitted to Phys. Rev. D

Journal ref: Phys. Rev. D 99, 102003 (2019)

A sparkless resistive glass correction electrode for the spherical proportional counter

Authors: I. Katsioulas, I. Giomataris, P. Knights, M. Gros, X. F. Navick, K. Nikolopoulos, I. Savvidis

Abstract: A new anode support structure for the spherical proportional counter is presented that incorporates a resistive correction electrode made of glass. This electrode improves the electric field homogeneity versus angle while suppressing the probability and intensity of sparks compared to non-resistive alternatives. The configuration of the correction electrode was optimised with simulations. Such sup… ▽ More A new anode support structure for the spherical proportional counter is presented that incorporates a resistive correction electrode made of glass. This electrode improves the electric field homogeneity versus angle while suppressing the probability and intensity of sparks compared to non-resistive alternatives. The configuration of the correction electrode was optimised with simulations. Such support structures have been constructed and measurements have demonstrated homogeneous response of the detector and operational stability. A measurement of the resistivity of the glass used is also presented. △ Less

Submitted 17 October, 2018; v1 submitted 10 September, 2018; originally announced September 2018.

Comments: This work was performed within the NEWS-G collaboration and has received funding from the French National Research Agency (ANR-15-CE31-0008)

An undergraduate laboratory study of the polarisation of annihilation photons using Compton scattering

Authors: Patrick Knights, Finlay Ryburn, Garry Tungate, Konstantinos Nikolopoulos

Abstract: An experiment for the advanced undergraduate laboratory which allows students to study the effect of photon polarisation in Compton scattering and to explore q\ uantum entanglement is described. The quantum entangled photons are produced through electron-positron annihilation in the $S$-state, and their polarisations a\ re analysed using the Compton scattering cross-section dependence on the photo… ▽ More An experiment for the advanced undergraduate laboratory which allows students to study the effect of photon polarisation in Compton scattering and to explore q\ uantum entanglement is described. The quantum entangled photons are produced through electron-positron annihilation in the $S$-state, and their polarisations a\ re analysed using the Compton scattering cross-section dependence on the photon polarisation. The equipment necessary for this experiment is available at a typ\ ical undergraduate physics laboratory. Finite geometry effects are discussed and investigated with the use of a Geant4-based simulation. △ Less

Submitted 22 March, 2018; v1 submitted 23 January, 2018; originally announced January 2018.

Comments: 11 pages, 12 figures, 1 table

Journal ref: Eur.J.Phys. 39 (2018) no. 4, 045202

Studying the effect of Polarisation in Compton scattering in the undergraduate laboratory

Authors: P. Knights, F. Ryburn, G. Tungate, K. Nikolopoulos

Abstract: An experiment for the advanced undergraduate laboratory allowing students to directly observe the effect of photon polarisation on Compton scattering is described. An initially unpolarised beam of photons is polarised via Compton scattering and analysed through a subsequent scattering. The experiment is designed to use equipment typically available at an undergraduate physics laboratory. The exper… ▽ More An experiment for the advanced undergraduate laboratory allowing students to directly observe the effect of photon polarisation on Compton scattering is described. An initially unpolarised beam of photons is polarised via Compton scattering and analysed through a subsequent scattering. The experiment is designed to use equipment typically available at an undergraduate physics laboratory. The experimental results are compared with a Geant4 simulation and geometry effects are discussed. △ Less

Submitted 23 January, 2018; v1 submitted 17 November, 2017; originally announced November 2017.

Comments: 10 pages, 7 figures, 1 table

Journal ref: Eur. J. Phys. 39, 025203 (2018)

Electrical conduction of silicon oxide containing silicon quantum dots

Authors: X. D. Pi, O. H. Y. Zalloum, A. P. Knights, P. Mascher, P. J. Simpson

Abstract: Current-voltage measurements have been made at room temperature on a Si-rich silicon oxide film deposited via Electron-Cyclotron Resonance Plasma Enhanced Chemical Vapor Deposition (ECR-PECVD) and annealed at 750 - 1000$ ^\circ$C. The thickness of oxide between Si quantum dots embedded in the film increases with the increase of annealing temperature. This leads to the decrease of current density… ▽ More Current-voltage measurements have been made at room temperature on a Si-rich silicon oxide film deposited via Electron-Cyclotron Resonance Plasma Enhanced Chemical Vapor Deposition (ECR-PECVD) and annealed at 750 - 1000$ ^\circ$C. The thickness of oxide between Si quantum dots embedded in the film increases with the increase of annealing temperature. This leads to the decrease of current density as the annealing temperature is increased. Assuming the Fowler-Nordheim tunneling mechanism in large electric fields, we obtain an effective barrier height $φ_{eff}$ of $\sim$ 0.7 $\pm$ 0.1 eV for an electron tunnelling through an oxide layer between Si quantum dots. The Frenkel-Poole effect can also be used to adequately explain the electrical conduction of the film under the influence of large electric fields. We suggest that at room temperature Si quantum dots can be regarded as traps that capture and emit electrons by means of tunneling. △ Less

Submitted 2 April, 2006; originally announced April 2006.

Comments: 14 pages, 5 figures, submitted to J. Phys. Conden. Matt