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Generalized Optical Theorem for Structured Neutron Beams and Consequences for Forward-Transmission Null Tests of Time-Reversal Invariance
Authors:
Sepehr Samiei
Abstract:
The simple form of the optical theorem of scattering theory, $σ_{\rm tot}^{\rm pw} = (4π/k)\,\Im f(0)$, is valid for an incident plane wave or for a wave packet whose Fourier components possess azimuthal symmetry about the incident wave vector $\vec{k}$. Previous work has shown that this expression can break down for structured beams of light which possess orbital angular momentum (OAM), despite t…
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The simple form of the optical theorem of scattering theory, $σ_{\rm tot}^{\rm pw} = (4π/k)\,\Im f(0)$, is valid for an incident plane wave or for a wave packet whose Fourier components possess azimuthal symmetry about the incident wave vector $\vec{k}$. Previous work has shown that this expression can break down for structured beams of light which possess orbital angular momentum (OAM), despite the fact that there is clearly no violation of unitarity, and the relevant modifications have been worked out for the case of massless photons. We present a form of the optical theorem involving neutron OAM states for the case of the scattering of massive nonrelativistic particles. We apply this form to Ryndin's theorem on the application of time reversal symmetry to forward scattering, indicate how the statement of the null condition for T violation in forward scattering is modified, and show that this effect is negligible compared with other sources of systematic error in neutron optics transmission experiments.
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Submitted 30 April, 2026;
originally announced April 2026.
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Development of a Modular Current-Mode NaI(Tl) Detector Array for Parity Odd (n,γ) Cross Section Measurements
Authors:
J. T. Mills,
J. G. Otero Munoz,
K. Dickerson,
I. Britt,
A. Couture,
J. Doskow,
J. Fry,
I. Ide,
M. Kitaguchi,
R. Kobayashi,
M. Luxnat,
A. Moseley,
R. Nakabe,
I. Novikov,
K. Oikawa,
T. Oku,
T. Okudaira,
A. Quintinar-Peña,
A. Richburg,
S. Samiei,
D. Schaper,
H. M. Shimizu,
D. Slone,
W. M. Snow,
S. Takada
, et al. (4 additional authors not shown)
Abstract:
The Neutron Optics Parity and Time-Reversal Violation Experiment (NOPTREX) Collaboration has developed a modular array of 24 NaI(Tl) detectors to measure parity and time-reversal symmetry violation in neutron-nucleus interactions. These detectors feature custom electronics that allow for operation in pulse or current mode. This paper describes the design, construction, characterization, and testin…
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The Neutron Optics Parity and Time-Reversal Violation Experiment (NOPTREX) Collaboration has developed a modular array of 24 NaI(Tl) detectors to measure parity and time-reversal symmetry violation in neutron-nucleus interactions. These detectors feature custom electronics that allow for operation in pulse or current mode. This paper describes the design, construction, characterization, and testing of the detectors in this array. We demonstrate the ability of the array to detect parity-odd asymmetries in neutron resonances by observing the known 0.7 eV parity-violating resonance in 139La in measurements at LANSCE.
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Submitted 7 April, 2026;
originally announced April 2026.
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Development and Application of an eV Neutron Polarization for Parity Violation Studies at CSNS Back-n Beamline
Authors:
Xu Qin,
Tianhao Wang,
Xuanbo Chen,
Changdong Deng,
Yongce Gong,
Zenghang Huang,
Wei Jiang,
Zhengquan Liu,
Guangyuan Luan,
Haotian Luo,
Qiuyue Luo,
Yongjia Lv,
You Lv,
Nikolaos Vassilopoulos,
Xichao Ruan,
William Michael Snow,
Kang Sun,
Sepehr Samiei,
Jian Tang,
Shilin Wang,
Hongyi Wu,
Xiaomin Xiong,
Xinyu Yuan,
Junpei Zhang,
Mofan Zhang
, et al. (4 additional authors not shown)
Abstract:
The dynamic enhancement of symmetry-breaking effects in neutron-nucleus resonances provides a sensitive testing ground for Time-Reversal Invariance Violation (TRIV). Exploiting this mechanism, the Neutron Optics Parity and Time Reversal Experiment (NOPTREX) seeks to elucidate the origin of the universe's baryon asymmetry. Critical to this effort is the precise measurement of Parity Violation (PV)…
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The dynamic enhancement of symmetry-breaking effects in neutron-nucleus resonances provides a sensitive testing ground for Time-Reversal Invariance Violation (TRIV). Exploiting this mechanism, the Neutron Optics Parity and Time Reversal Experiment (NOPTREX) seeks to elucidate the origin of the universe's baryon asymmetry. Critical to this effort is the precise measurement of Parity Violation (PV) asymmetries, which is essential to calibrate the nuclear parameters required for future TRIV experiments. To facilitate these studies, we developed an eV polarized neutron at the Back-n white neutron beamline of the China Spallation Neutron Source (CSNS). Neutron polarization is generated by an in-situ Spin-Exchange Optical Pumping (SEOP) $^3$He filter. Spin manipulation is performed by an adiabatic spin flipper, while spin polarization is preserved over the flight path by a vacuum transport system equipped with a solenoidal guide field. Experiments successfully measured an asymmetry of approximately $7.8 \pm 2.4$ (stat.) $\pm 0.3$ (sys.) % at the 0.747 eV p-wave resonance of $^{139}$La. These results are in agreement with previous results on this resonance and validate the system's capability for PV measurements.
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Submitted 19 February, 2026;
originally announced February 2026.