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Contribution of exclusive diffractive processes to the measured azimuthal asymmetries in SIDIS
Authors:
J. Agarwala,
M. G. Alexeev,
G. D. Alexeev,
A. Amoroso,
V. Andrieux,
N. V. Anfimov,
V. Anosov,
A. Antoshkin,
K. Augsten,
W. Augustyniak,
C. D. R. Azevedo,
B. Badelek,
F. Balestra,
M. Ball,
J. Barth,
R. Beck,
Y. Bedfer,
J. Berenguer Antequera,
J. Bernhard,
M. Bodlak,
P. Bordalo,
F. Bradamante,
A. Bressan,
M. Buechele,
V. E. Burtsev
, et al. (182 additional authors not shown)
Abstract:
Hadron leptoproduction in Semi-Inclusive measurements of Deep-Inelastic Scattering (SIDIS) on unpolarised nucleons allows one to get information on the intrinsic transverse momentum of quarks in a nucleon and on the Boer-Mulders function through the measurement of azimuthal modulations in the cross section. These modulations were recently measured by the HERMES experiment at DESY on proton and deu…
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Hadron leptoproduction in Semi-Inclusive measurements of Deep-Inelastic Scattering (SIDIS) on unpolarised nucleons allows one to get information on the intrinsic transverse momentum of quarks in a nucleon and on the Boer-Mulders function through the measurement of azimuthal modulations in the cross section. These modulations were recently measured by the HERMES experiment at DESY on proton and deuteron targets, and by the COMPASS experiment using the CERN SPS muon beam and a $^6$LiD target. In both cases, the amplitudes of the $\cosφ_h$ and $\cos 2φ_h$ modulations show strong kinematic dependences for both positive and negative hadrons. It has been known since some time that the measured final-state hadrons in those SIDIS experiments receive a contribution from exclusive diffractive production of vector mesons, particularly important at large values of $z$, the fraction of the virtual photon energy carried by the hadron. In previous measurements of azimuthal asymmetries this contribution was not taken into account, because it was not known that it could distort the azimuthal modulations. Presently, a method to evaluate the contribution of the exclusive reactions to the azimuthal asymmetries measured by COMPASS has been developed. The subtraction of this contribution results in a better understanding of the kinematic effects, and the remaining non-zero $\cos 2φ_h$ modulation gives indication for a non-zero Boer-Mulders effect.
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Submitted 21 December, 2019;
originally announced December 2019.
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Measurement of $P_T$-weighted Sivers asymmetries in leptoproduction of hadrons
Authors:
M. G. Alexeev,
G. D. Alexeev,
A. Amoroso,
V. Andrieux,
N. V. Anfimov,
V. Anosov,
A. Antoshkin,
K. Augsten,
W. Augustyniak,
C. D. R. Azevedo,
B. Badelek,
F. Balestra,
M. Ball,
V. Barone,
J. Barth,
R. Beck,
Y. Bedfer,
J. Bernhard,
K. Bicker,
E. R. Bielert,
M. Bodlak,
P. Bordalo,
F. Bradamante,
A. Bressan,
M. Buechele
, et al. (188 additional authors not shown)
Abstract:
The transverse spin asymmetries measured in semi-inclusive leptoproduction of hadrons, when weighted with the hadron transverse momentum $P_T$, allow for the extraction of important transverse-momentum-dependent distribution functions. In particular, the weighted Sivers asymmetries provide direct information on the Sivers function, which is a leading-twist distribution that arises from a correlati…
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The transverse spin asymmetries measured in semi-inclusive leptoproduction of hadrons, when weighted with the hadron transverse momentum $P_T$, allow for the extraction of important transverse-momentum-dependent distribution functions. In particular, the weighted Sivers asymmetries provide direct information on the Sivers function, which is a leading-twist distribution that arises from a correlation between the transverse momentum of an unpolarised quark in a transversely polarised nucleon and the spin of the nucleon. Using the high-statistics data collected by the COMPASS Collaboration in 2010 with a transversely polarised proton target, we have evaluated two types of $P_T$-weighted Sivers asymmetries, which are both proportional to the product of the firsttransverse moment of the Sivers function and of the fragmentation function. The results are compared to the standard unweighted Sivers asymmetries and used to extract the first transverse moments of the Sivers distributions for $u$ and $d$ quarks.
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Submitted 9 September, 2018;
originally announced September 2018.
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Light isovector resonances in $π^- p \to π^-π^-π^+ p$ at 190 GeV/${\it c}$
Authors:
M. Aghasyan,
M. G. Alexeev,
G. D. Alexeev,
A. Amoroso,
V. Andrieux,
N. V. Anfimov,
V. Anosov,
A. Antoshkin,
K. Augsten,
W. Augustyniak,
A. Austregesilo,
C. D. R. Azevedo,
B. Badelek,
F. Balestra,
M. Ball,
J. Barth,
R. Beck,
Y. Bedfer,
J. Bernhard,
K. Bicker,
E. R. Bielert,
R. Birsa,
M. Bodlak,
P. Bordalo,
F. Bradamante
, et al. (200 additional authors not shown)
Abstract:
We have performed the most comprehensive resonance-model fit of $π^-π^-π^+$ states using the results of our previously published partial-wave analysis (PWA) of a large data set of diffractive-dissociation events from the reaction $π^- + p \to π^-π^-π^+ + p_\text{recoil}$ with a 190 GeV/$c$ pion beam. The PWA results, which were obtained in 100 bins of three-pion mass, $0.5 < m_{3π} < 2.5$ GeV/…
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We have performed the most comprehensive resonance-model fit of $π^-π^-π^+$ states using the results of our previously published partial-wave analysis (PWA) of a large data set of diffractive-dissociation events from the reaction $π^- + p \to π^-π^-π^+ + p_\text{recoil}$ with a 190 GeV/$c$ pion beam. The PWA results, which were obtained in 100 bins of three-pion mass, $0.5 < m_{3π} < 2.5$ GeV/$c^2$, and simultaneously in 11 bins of the reduced four-momentum transfer squared, $0.1 < t' < 1.0$ $($GeV$/c)^2$, are subjected to a resonance-model fit using Breit-Wigner amplitudes to simultaneously describe a subset of 14 selected waves using 11 isovector light-meson states with $J^{PC} = 0^{-+}$, $1^{++}$, $2^{++}$, $2^{-+}$, $4^{++}$, and spin-exotic $1^{-+}$ quantum numbers. The model contains the well-known resonances $π(1800)$, $a_1(1260)$, $a_2(1320)$, $π_2(1670)$, $π_2(1880)$, and $a_4(2040)$. In addition, it includes the disputed $π_1(1600)$, the excited states $a_1(1640)$, $a_2(1700)$, and $π_2(2005)$, as well as the resonancelike $a_1(1420)$. We measure the resonance parameters mass and width of these objects by combining the information from the PWA results obtained in the 11 $t'$ bins. We extract the relative branching fractions of the $ρ(770) π$ and $f_2(1270) π$ decays of $a_2(1320)$ and $a_4(2040)$, where the former one is measured for the first time. In a novel approach, we extract the $t'$ dependence of the intensity of the resonances and of their phases. The $t'$ dependence of the intensities of most resonances differs distinctly from the $t'$ dependence of the nonresonant components. For the first time, we determine the $t'$ dependence of the phases of the production amplitudes and confirm that the production mechanism of the Pomeron exchange is common to all resonances.
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Submitted 26 October, 2018; v1 submitted 16 February, 2018;
originally announced February 2018.
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K$^{-}$ over K$^{+}$ multiplicity ratio for kaons produced in DIS with a large fraction of the virtual-photon energy
Authors:
R. Akhunzyanov,
M. G. Alexeev,
G. D. Alexeev,
A. Amoroso,
V. Andrieux,
N. V. Anfimov,
V. Anosov,
A. Antoshkin,
K. Augsten,
W. Augustyniak,
C. D. R. Azevedo,
B. Badelek,
F. Balestra,
M. Ball,
J. Barth,
R. Beck,
Y. Bedfer,
J. Bernhard,
K. Bicker,
E. R. Bielert,
M. Bodlak,
P. Bordalo,
F. Bradamante,
A. Bressan,
M. Buechele
, et al. (186 additional authors not shown)
Abstract:
The K$^{-}$ over K$^{+}$ multiplicity ratio is measured in deep-inelastic scattering, for the first time for kaons carrying a large fraction $z$ of the virtual-photon energy. The data were obtained by the COMPASS collaboration using a 160 GeV muon beam and an isoscalar $^6$LiD target. The regime of deep-inelastic scattering is ensured by requiring $Q^2>1$ (GeV/$c)^2$ for the photon virtuality and…
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The K$^{-}$ over K$^{+}$ multiplicity ratio is measured in deep-inelastic scattering, for the first time for kaons carrying a large fraction $z$ of the virtual-photon energy. The data were obtained by the COMPASS collaboration using a 160 GeV muon beam and an isoscalar $^6$LiD target. The regime of deep-inelastic scattering is ensured by requiring $Q^2>1$ (GeV/$c)^2$ for the photon virtuality and $W>5$ GeV/$c^2$ for the invariant mass of the produced hadronic system. Kaons are identified in the momentum range from 12 GeV/$c$ to 40 GeV/$c$, thereby restricting the range in Bjorken-$x$ to $0.01<x<0.40$. The $z$-dependence of the multiplicity ratio is studied for $z>0.75$. For very large values of $z$, $i.e.$ $z>0.8$, we observe the kaon multiplicity ratio to fall below the lower limits expected from calculations based on leading and next-to-leading order perturbative quantum chromodynamics. Also, the kaon multiplicity ratio shows a strong dependence on the missing mass of the single-kaon production process. This suggests that within the perturbative quantum chromodynamics formalism an additional correction may be required, which takes into account the phase space available for hadronisation.
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Submitted 6 October, 2018; v1 submitted 2 February, 2018;
originally announced February 2018.
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New analysis of $ηπ$ tensor resonances measured at the COMPASS experiment
Authors:
A. Jackura,
C. Fernandez-Ramirez,
M. Mikhasenko,
A. Pilloni,
V. Mathieu,
J. Nys,
V. Pauk,
A. P. Szczepaniak,
G. Fox,
M. Aghasyan,
R. Akhunzyanov,
M. G. Alexeev,
G. D. Alexeev,
A. Amoroso,
V. Andrieux,
N. V. Anfimov,
V. Anosov,
A. Antoshkin,
K. Augsten,
W. Augustyniak,
A. Austregesilo,
C. D. R. Azevedo,
B. Badelek,
F. Balestra,
M. Ball
, et al. (212 additional authors not shown)
Abstract:
We present a new amplitude analysis of the $ηπ$ $D$-wave in $π^- p\to ηπ^- p$ measured by COMPASS. Employing an analytical model based on the principles of the relativistic $S$-matrix, we find two resonances that can be identified with the $a_2(1320)$ and the excited $a_2^\prime(1700)$, and perform a comprehensive analysis of their pole positions. For the mass and width of the $a_2$ we find…
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We present a new amplitude analysis of the $ηπ$ $D$-wave in $π^- p\to ηπ^- p$ measured by COMPASS. Employing an analytical model based on the principles of the relativistic $S$-matrix, we find two resonances that can be identified with the $a_2(1320)$ and the excited $a_2^\prime(1700)$, and perform a comprehensive analysis of their pole positions. For the mass and width of the $a_2$ we find $M=(1307 \pm 1 \pm 6)$~MeV and $Γ=(112 \pm 1 \pm 8)$~MeV, and for the excited state $a_2^\prime$ we obtain $M=(1720 \pm 10 \pm 60)$~MeV and $Γ=(280\pm 10 \pm 70)$~MeV, respectively.
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Submitted 10 July, 2017;
originally announced July 2017.
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First measurement of transverse-spin-dependent azimuthal asymmetries in the Drell-Yan process
Authors:
Aghasyan,
R. Akhunzyanov,
M. G. Alexeev,
G. D. Alexeev,
A. Amoroso,
V. Andrieux,
N. V. Anfimov,
V. Anosov,
A. Antoshkin,
K. Augsten,
W. Augustyniak,
A. Austregesilo,
C. D. R. Azevedo,
B. Badelek,
F. Balestra,
M. Ball,
J. Barth,
R. Beck,
Y. Bedfer,
J. Bernhard,
K. Bicker,
E. R. Bielert,
R. Birsa,
M. Bodlak,
P. Bordalo
, et al. (195 additional authors not shown)
Abstract:
The first measurement of transverse-spin-dependent azimuthal asymmetries in the pion-induced Drell-Yan (DY) process is reported. We use the CERN SPS 190 GeV/$c$, $π^{-}$ beam and a transversely polarized ammonia target. Three azimuthal asymmetries giving access to different transverse-momentum-dependent (TMD) parton distribution functions (PDFs) are extracted using dimuon events with invariant mas…
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The first measurement of transverse-spin-dependent azimuthal asymmetries in the pion-induced Drell-Yan (DY) process is reported. We use the CERN SPS 190 GeV/$c$, $π^{-}$ beam and a transversely polarized ammonia target. Three azimuthal asymmetries giving access to different transverse-momentum-dependent (TMD) parton distribution functions (PDFs) are extracted using dimuon events with invariant mass between 4.3 GeV/$c^2$ and 8.5 GeV/$c^2$. The observed sign of the Sivers asymmetry is found to be consistent with the fundamental prediction of Quantum Chromodynamics (QCD) that the Sivers TMD PDFs extracted from DY have a sign opposite to the one extracted from semi-inclusive deep-inelastic scattering (SIDIS) data. We present two other asymmetries originating from the pion Boer-Mulders TMD PDFs convoluted with either the nucleon transversity or pretzelosity TMD PDFs. These DY results are obtained at a hard scale comparable to that of a recent COMPASS SIDIS measurement and hence allow unique tests of fundamental QCD universality predictions.
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Submitted 3 April, 2017;
originally announced April 2017.
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First measurement of the Sivers asymmetry for gluons from SIDIS data
Authors:
C. Adolph,
M. Aghasyan,
R. Akhunzyanov,
M. G. Alexeev,
G. D. Alexeev,
A. Amoroso,
V. Andrieux,
N. V. Anfimov,
V. Anosov,
A. Antoshkin,
K. Augsten,
W. Augustyniak,
A. Austregesilo,
C. D. R. Azevedo,
B. Badelek,
F. Balestra,
M. Ball,
J. Barth,
R. Beck,
Y. Bedfer,
J. Bernhard,
K. Bicker,
E. R. Bielert,
R. Birsa,
M. Bodlak
, et al. (202 additional authors not shown)
Abstract:
The Sivers function describes the correlation between the transverse spin of a nucleon and the transverse motion of its partons. It was extracted from measurements of the azimuthal asymmetry of hadrons produced in semi-inclusive deep inelastic scattering of leptons off transversely polarised nucleon targets, and it turned out to be non-zero for quarks. In this letter the evaluation of the Sivers a…
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The Sivers function describes the correlation between the transverse spin of a nucleon and the transverse motion of its partons. It was extracted from measurements of the azimuthal asymmetry of hadrons produced in semi-inclusive deep inelastic scattering of leptons off transversely polarised nucleon targets, and it turned out to be non-zero for quarks. In this letter the evaluation of the Sivers asymmetry for gluons in the same process is presented. The analysis method is based on a Monte Carlo simulation that includes three hard processes: photon-gluon fusion, QCD Compton scattering and leading-order virtual-photon absorption process. The Sivers asymmetries of the three processes are simultaneously extracted using the LEPTO event generator and a neural network approach. The method is applied to samples of events containing at least two hadrons with large transverse momentum from the COMPASS data taken with a 160 GeV/$c$ muon beam scattered off transversely polarised deuterons and protons. With a significance of more than two standard deviations a negative value is obtained for the gluon Sivers asymmetry. The result of a similar analysis for a Collins-like asymmetry for gluons is consistent with zero.
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Submitted 10 January, 2017;
originally announced January 2017.
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Sivers asymmetry extracted in SIDIS at the hard scale of the Drell-Yan process at COMPASS
Authors:
C. Adolph,
M. Aghasyan,
R. Akhunzyanov,
M. G. Alexeev,
G. D. Alexeev,
A. Amoroso,
V. Andrieux,
N. V. Anfimov,
V. Anosov,
K. Augsten,
W. Augustyniak,
A. Austregesilo,
C. D. R. Azevedo,
B. Badelek,
F. Balestra,
M. Ball,
J. Barth,
R. Beck,
Y. Bedfer,
J. Bernhard,
K. Bicker,
E. R. Bielert,
R. Birsa,
M. Bodlak,
P. Bordalo
, et al. (202 additional authors not shown)
Abstract:
Proton transverse-spin azimuthal asymmetries are extracted from the COMPASS 2010 semi-inclusive hadron measurements in deep inelastic muon-nucleon scattering in those four regions of the photon virtuality $Q^2$, which correspond to the four regions of the di-muon mass $\sqrt{Q^2}$ used in the ongoing analysis of the COMPASS Drell-Yan measurements. This allows for a future direct comparison of the…
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Proton transverse-spin azimuthal asymmetries are extracted from the COMPASS 2010 semi-inclusive hadron measurements in deep inelastic muon-nucleon scattering in those four regions of the photon virtuality $Q^2$, which correspond to the four regions of the di-muon mass $\sqrt{Q^2}$ used in the ongoing analysis of the COMPASS Drell-Yan measurements. This allows for a future direct comparison of the nucleon transverse-momentum-dependent parton distribution functions extracted from these two alternative measurements. Various two-dimensional kinematic dependences are presented for the azimuthal asymmetries induced by the Sivers transverse-momentum-dependent parton distribution function. The integrated Sivers asymmetries are found to be positive with an accuracy that appears to be sufficient to test the sign change of the Sivers function predicted by Quantum Chromodynamics.
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Submitted 17 July, 2017; v1 submitted 23 September, 2016;
originally announced September 2016.
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Azimuthal asymmetries of charged hadrons produced in high-energy muon scattering off longitudinally polarised deuterons
Authors:
C. Adolph,
M. Aghasyan,
R. Akhunzyanov,
M. G. Alexeev,
G. D. Alexeev,
A. Amoroso,
V. Andrieux,
N. V. Anfimov,
V. Anosov,
K. Augsten,
W. Augustyniak,
A. Austregesilo,
C. D. R. Azevedo,
B. Badelek,
F. Balestra,
M. Ball,
J. Barth,
R. Beck,
Y. Bedfer,
J. Bernhard,
K. Bicker,
E. R. Bielert,
R. Birsa,
M. Bodlak,
P. Bordalo
, et al. (200 additional authors not shown)
Abstract:
Single hadron azimuthal asymmetries of positive and negative hadrons produced in muon semi-inclusive deep inelastic scattering off longitudinally polarised deuterons are determined using the 2006 COMPASS data and also combined all deuteron COMPASS data. For each hadron charge, the dependence of the azimuthal asymmetry on the hadron azimuthal angle $φ$ is obtained by means of a five-parameter fitti…
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Single hadron azimuthal asymmetries of positive and negative hadrons produced in muon semi-inclusive deep inelastic scattering off longitudinally polarised deuterons are determined using the 2006 COMPASS data and also combined all deuteron COMPASS data. For each hadron charge, the dependence of the azimuthal asymmetry on the hadron azimuthal angle $φ$ is obtained by means of a five-parameter fitting function that besides a $φ$-independent term includes four modulations predicted by theory: $\sinφ$, $\sin 2 φ$, $\sin 3φ$ and $\cosφ$. The amplitudes of the five terms have been extracted, first, for the hadrons in the whole available kinematic region. In further fits, performed for hadrons from a restricted kinematic region, the $φ$-dependence is determined as a function of one of three variables (Bjorken-$x$, fractional energy of virtual photon taken by the outgoing hadron and hadron transverse momentum), while disregarding the others. Except the $φ$-independent term, all the modulation amplitudes are very small, and no clear kinematic dependence could be observed within experimental uncertainties.
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Submitted 5 December, 2018; v1 submitted 20 September, 2016;
originally announced September 2016.
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Leading-order determination of the gluon polarisation from semi-inclusive deep inelastic scattering data
Authors:
C. Adolph,
M. Aghasyan,
R. Akhunzyanov,
M. G. Alexeev,
G. D. Alexeev,
A. Amoroso,
V. Andrieux,
N. V. Anfimov,
V. Anosov,
W. Augustyniak,
A. Austregesilo,
C. D. R. Azevedo,
B. Badelek,
F. Balestra,
J. Barth,
R. Beck,
Y. Bedfer,
J. Bernhard,
K. Bicker,
E. R. Bielert,
R. Birsa,
J. Bisplinghoff,
M. Bodlak,
M. Boer,
P. Bordalo
, et al. (196 additional authors not shown)
Abstract:
Using a novel analysis technique, the gluon polarisation in the nucleon is re-evaluated using the longitudinal double-spin asymmetry measured in the cross section of semi-inclusive single-hadron muoproduction with photon virtuality $Q^2>1~({\rm GeV}/c)^2$. The data were obtained by the COMPASS experiment at CERN using a 160 GeV/$c$ polarised muon beam impinging on a polarised $^6$LiD target. By an…
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Using a novel analysis technique, the gluon polarisation in the nucleon is re-evaluated using the longitudinal double-spin asymmetry measured in the cross section of semi-inclusive single-hadron muoproduction with photon virtuality $Q^2>1~({\rm GeV}/c)^2$. The data were obtained by the COMPASS experiment at CERN using a 160 GeV/$c$ polarised muon beam impinging on a polarised $^6$LiD target. By analysing the full range in hadron transverse momentum $p_{\rm T}$, the different $p_{\rm T}$-dependences of the underlying processes are separated using a neural-network approach. In the absence of pQCD calculations at next-to-leading order in the selected kinematic domain, the gluon polarisation $Δg/g$ is evaluated at leading order in pQCD at a hard scale of $μ^2= \langle Q^2 \rangle = 3 ({\rm GeV}/c)^2$. It is determined in three intervals of the nucleon momentum fraction carried by gluons, $x_{\rm g}$, covering the range $0.04 \!<\! x_{ \rm g}\! <\! 0.28$~ and does not exhibit a significant dependence on $x_{\rm g}$. The average over the three intervals, $\langle Δg/g \rangle = 0.113 \pm 0.038_{\rm (stat.)}\pm 0.036_{\rm (syst.)}$ at $\langle x_{\rm g} \rangle \approx 0.10$, suggests that the gluon polarisation is positive in the measured $x_{\rm g}$ range.
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Submitted 22 February, 2017; v1 submitted 16 December, 2015;
originally announced December 2015.
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Longitudinal double spin asymmetries in single hadron quasi-real photoproduction at high $p_T$
Authors:
COMPASS Collaboration,
C. Adolph,
R. Akhunzyanov,
M. G. Alexeev,
G. D. Alexeev,
A. Amoroso,
V. Andrieux,
V. Anosov,
W. Augustyniak,
A. Austregesilo,
C. D. R. Azevedo,
B. Badełek,
F. Balestra,
J. Barth,
R. Beck,
Y. Bedfer,
J. Bernhard,
K. Bicker,
E. R. Bielert,
R. Birsa,
J. Bisplinghoff,
M. Bodlak,
M. Boer,
P. Bordalo,
F. Bradamante
, et al. (186 additional authors not shown)
Abstract:
We measured the longitudinal double spin asymmetries $A_{LL}$ for single hadron muo-production off protons and deuterons at photon virtuality $Q^2$ < 1(GeV/$\it c$)$^2$ for transverse hadron momenta $p_T$ in the range 0.7 GeV/$\it c$ to 4 GeV/$\it c$ . They were determined using COMPASS data taken with a polarised muon beam of 160 GeV/$\it c$ or 200 GeV/$\it c$ impinging on polarised…
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We measured the longitudinal double spin asymmetries $A_{LL}$ for single hadron muo-production off protons and deuterons at photon virtuality $Q^2$ < 1(GeV/$\it c$)$^2$ for transverse hadron momenta $p_T$ in the range 0.7 GeV/$\it c$ to 4 GeV/$\it c$ . They were determined using COMPASS data taken with a polarised muon beam of 160 GeV/$\it c$ or 200 GeV/$\it c$ impinging on polarised $\mathrm{{}^6LiD}$ or $\mathrm{NH_3}$ targets. The experimental asymmetries are compared to next-to-leading order pQCD calculations, and are sensitive to the gluon polarisation $ΔG$ inside the nucleon in the range of the nucleon momentum fraction carried by gluons $0.05 < x_g < 0.2$.
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Submitted 14 December, 2015; v1 submitted 11 September, 2015;
originally announced September 2015.
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Resonance Production and $ππ$ S-wave in $π^- + p \rightarrow π^- π^- π^+ + p_{recoil}$ at 190 GeV/c
Authors:
C. Adolph,
R. Akhunzyanov,
M. G. Alexeev,
G. D. Alexeev,
A. Amoroso,
V. Andrieux,
V. Anosov,
W. Augustyniak,
A. Austregesilo,
C. D. R. Azevedo,
B. Badełek,
F. Balestra,
J. Barth,
R. Beck,
Y. Bedfer,
J. Bernhard,
K. Bicker,
E. R. Bielert,
R. Birsa,
J. Bisplinghoff,
M. Bodlak,
M. Boer,
P. Bordalo,
F. Bradamante,
C. Braun
, et al. (185 additional authors not shown)
Abstract:
The COMPASS collaboration has collected the currently largest data set on diffractively produced $π^-π^-π^+$ final states using a negative pion beam of 190 GeV/c momentum impinging on a stationary proton target. This data set allows for a systematic partial-wave analysis in 100 bins of three-pion mass, $0.5 < m_{3π} < 2.5$ GeV/c$^2$ , and in 11 bins of the reduced four-momentum transfer squared,…
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The COMPASS collaboration has collected the currently largest data set on diffractively produced $π^-π^-π^+$ final states using a negative pion beam of 190 GeV/c momentum impinging on a stationary proton target. This data set allows for a systematic partial-wave analysis in 100 bins of three-pion mass, $0.5 < m_{3π} < 2.5$ GeV/c$^2$ , and in 11 bins of the reduced four-momentum transfer squared, $0.1 < t < 1.0$ (GeV/c)$^2$ . This two-dimensional analysis offers sensitivity to genuine one-step resonance production, i.e. the production of a state followed by its decay, as well as to more complex dynamical effects in nonresonant $3π$ production. In this paper, we present detailed studies on selected $3π$ partial waves with $J^{PC} = 0^{-+}$, $1^{++}$, $2^{-+}$, $2^{++}$, and $4^{++}$. In these waves, we observe the well-known ground-state mesons as well as a new narrow axial-vector meson $a_1(1420)$ decaying into $f_0(980) π$. In addition, we present the results of a novel method to extract the amplitude of the $π^-π^+$ subsystem with $I^{G}J^{PC} = 0^+ 0^{++}$ in various partial waves from the $π^-π^-π^+$ data. Evidence is found for correlation of the $f_0(980)$ and $f_0(1500)$ appearing as intermediate $π^- π^+$ isobars in the decay of the known $π(1800)$ and $π_2(1880)$.
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Submitted 23 February, 2017; v1 submitted 3 September, 2015;
originally announced September 2015.
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Interplay among transversity induced asymmetries in hadron leptoproduction
Authors:
Compass Collaboration,
C. Adolph,
R. Akhunzyanov,
M. G. Alexeev,
G. D. Alexeev,
A. Amoroso,
V. Andrieux,
V. Anosov,
W. Augustyniak,
A. Austregesilo,
C. D. R. Azevedo,
B. Badelek,
F. Balestra,
J. Barth,
R. Beck,
Y. Bedfer,
J. Bernhard,
K. Bicker,
E. R. Bielert,
R. Birsa,
J. Bisplinghoff,
M. Bodlak,
M. Boer,
P. Bordalo,
F. Bradamante
, et al. (185 additional authors not shown)
Abstract:
In the fragmentation of a transversely polarized quark several left-right asymmetries are possible for the hadrons in the jet. When only one unpolarized hadron is selected, it exhibits an azimuthal modulation known as Collins effect. When a pair of oppositely charged hadrons is observed, three asymmetries can be considered, a di-hadron asymmetry and two single hadron asymmetries. In lepton deep in…
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In the fragmentation of a transversely polarized quark several left-right asymmetries are possible for the hadrons in the jet. When only one unpolarized hadron is selected, it exhibits an azimuthal modulation known as Collins effect. When a pair of oppositely charged hadrons is observed, three asymmetries can be considered, a di-hadron asymmetry and two single hadron asymmetries. In lepton deep inelastic scattering on transversely polarized nucleons all these asymmetries are coupled with the transversity distribution. From the high statistics COMPASS data on oppositely charged hadron-pair production we have investigated for the first time the dependence of these three asymmetries on the difference of the azimuthal angles of the two hadrons. The similarity of transversity induced single and di-hadron asymmetries is discussed. A new analysis of the data allows to establish quantitative relationships among them, providing for the first time strong experimental indication that the underlying fragmentation mechanisms are all driven by a common physical process.
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Submitted 26 October, 2015; v1 submitted 27 July, 2015;
originally announced July 2015.
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The Spin Structure Function $g_1^{\rm p}$ of the Proton and a Test of the Bjorken Sum Rule
Authors:
C. Adolph,
R. Akhunzyanov,
M. G. Alexeev,
G. D. Alexeev,
A. Amoroso,
V. Andrieux,
V. Anosov,
A. Austregesilo,
C. Azevedo,
B. Badelek,
F. Balestra,
J. Barth,
G. Baum,
G. R. Beck,
Y. Bedfer,
J. Bernhard,
K. Bicker,
E. R. Bielert,
R. Birsa,
J. Bisplinghoff,
M. Bodlak,
M. Boer,
P. Bordalo,
F. Bradamante,
C. Braun
, et al. (182 additional authors not shown)
Abstract:
New results for the double spin asymmetry $A_1^{\rm p}$ and the proton longitudinal spin structure function $g_1^{\rm p}$ are presented. They were obtained by the COMPASS collaboration using polarised 200 GeV muons scattered off a longitudinally polarised NH$_3$ target. The data were collected in 2011 and complement those recorded in 2007 at 160\,GeV, in particular at lower values of $x$. They imp…
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New results for the double spin asymmetry $A_1^{\rm p}$ and the proton longitudinal spin structure function $g_1^{\rm p}$ are presented. They were obtained by the COMPASS collaboration using polarised 200 GeV muons scattered off a longitudinally polarised NH$_3$ target. The data were collected in 2011 and complement those recorded in 2007 at 160\,GeV, in particular at lower values of $x$. They improve the statistical precision of $g_1^{\rm p}(x)$ by about a factor of two in the region $x\lesssim 0.02$. A next-to-leading order QCD fit to the $g_1$ world data is performed. It leads to a new determination of the quark spin contribution to the nucleon spin, $ΔΣ$ ranging from 0.26 to 0.36, and to a re-evaluation of the first moment of $g_1^{\rm p}$. The uncertainty of $ΔΣ$ is mostly due to the large uncertainty in the present determinations of the gluon helicity distribution. A new evaluation of the Bjorken sum rule based on the COMPASS results for the non-singlet structure function $g_1^{\rm NS}(x,Q^2)$ yields as ratio of the axial and vector coupling constants $|g_{\rm A}/g_{\rm V}| = 1.22 \pm 0.05~({\rm stat.}) \pm 0.10~({\rm syst.})$, which validates the sum rule to an accuracy of about 9\%.
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Submitted 31 March, 2015;
originally announced March 2015.
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Measurement of radiative widths of $a_2(1320)$ and $π_2(1670)$
Authors:
C. Adolph,
R. Akhunzyanov,
M. G. Alekseev,
G. D. Alexeev,
A. Amoroso,
V. Andrieux,
V. Anosov,
A. Austregesilo,
B. Badelek,
F. Balestra,
J. Barth,
G. Baum,
R. Beck,
Y. Bedfer,
A. Berlin,
J. Bernhard,
K. Bicker,
J. Bieling,
R. Birsa,
J. Bisplinghoff,
M. Bodlak,
M. Boer,
P. Bordalo,
F. Bradamante,
C. Braun
, et al. (184 additional authors not shown)
Abstract:
The COMPASS Collaboration at CERN has investigated the reaction $π^- γ\rightarrow π^-π^-π^+$ embedded in the Primakoff reaction of $190~\textrm{GeV}$ pions scattering in the Coulomb field of a lead target, $π^- \text{Pb} \rightarrow π^-π^-π^+ \text{Pb}$. Exchange of quasi-real photons is selected by isolating the sharp Coulomb peak observed at momentum transfer below $0.001~(\text{GeV}/c)^2$. Usin…
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The COMPASS Collaboration at CERN has investigated the reaction $π^- γ\rightarrow π^-π^-π^+$ embedded in the Primakoff reaction of $190~\textrm{GeV}$ pions scattering in the Coulomb field of a lead target, $π^- \text{Pb} \rightarrow π^-π^-π^+ \text{Pb}$. Exchange of quasi-real photons is selected by isolating the sharp Coulomb peak observed at momentum transfer below $0.001~(\text{GeV}/c)^2$. Using a partial-wave analysis the amplitudes and relative phases of the $a_2(1320)$ and $π_2(1670)$ mesons have been extracted, and the Coulomb and the diffractive contributions have been disentangled. Measuring absolute production cross sections we have determined the radiative width of the $a_2(1320)$ to be $Γ_0(a_2(1320) \rightarrow πγ) = (358 \pm 6_{\textrm{stat}} \pm 42_{\textrm{syst}})~\textrm{keV}$. As the first measurement, $Γ_0(π_2(1670) \rightarrow πγ) = (181 \pm 11_{\textrm{stat}} \pm 27_{\textrm{syst}})~\textrm{keV} \cdot (\textrm{BR}^{\textrm{PDG}}_{f_2 π}/\textrm{BR}_{f_2 π})$ is obtained for the radiative width of the $π_2(1670)$, where in this analysis the branching ratio $\textrm{BR}^{\textrm{PDG}}_{f_2 π}=0.56$ has been used. We compare these values to previous measurements and theoretical predictions.
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Submitted 11 March, 2014;
originally announced March 2014.
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A high-statistics measurement of transverse spin effects in dihadron production from muon-proton semi-inclusive deep-inelastic scattering
Authors:
C. Adolph,
R. Akhunzyanov,
M. G. Alekseev,
Yu. Alexandrov,
G. D. Alexeev,
A. Amoroso,
V. Andrieux,
V. Anosov,
A. Austregesilo,
B. Badelek,
F. Balestra,
J. Barth,
G. Baum,
R. Beck,
Y. Bedfer,
A. Berlin,
J. Bernhard,
R. Bertini,
K. Bicker,
J. Bieling,
R. Birsa,
J. Bisplinghoff,
M. Bodlak,
M. Boer,
P. Bordalo
, et al. (196 additional authors not shown)
Abstract:
A measurement of the azimuthal asymmetry in dihadron production in deep-inelastic scattering of muons on transversely polarised proton (NH$_{3}$) targets are presented. They provide independent access to the transversity distribution functions through the measurement of the Collins asymmetry in single hadron production. The data were taken in the year $2010$ with the COMPASS spectrometer using a…
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A measurement of the azimuthal asymmetry in dihadron production in deep-inelastic scattering of muons on transversely polarised proton (NH$_{3}$) targets are presented. They provide independent access to the transversity distribution functions through the measurement of the Collins asymmetry in single hadron production. The data were taken in the year $2010$ with the COMPASS spectrometer using a $160\,\mbox{GeV}/c$ muon beam of the CERN SPS, increasing by a factor of about three the available statistics of the previously published data taken in the year $2007$. The measured sizeable asymmetry is in good agreement with the published data. An approximate equality of the Collins asymmetry and the dihadron asymmetry is observed, suggesting a common physical mechanism in the underlying fragmentation.
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Submitted 30 January, 2014;
originally announced January 2014.
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Hadron Transverse Momentum Distributions in Muon Deep Inelastic Scattering at 160 GeV/$c$
Authors:
C. Adolph,
M. G. Alekseev,
V. Yu. Alexakhin,
Yu. Alexandrov,
G. D. Alexeev,
A. Amoroso,
V. Andrieux,
A. Austregesilo,
B. Badelek,
F. Balestra,
J. Barth,
G. Baum,
Y. Bedfer,
A. Berlin,
J. Bernhard,
R. Bertini,
K. Bicker,
J. Bieling,
R. Birsa,
J. Bisplinghoff,
M. Boer,
P. Bordalo,
F. Bradamante,
C. Braun,
A. Bravar
, et al. (186 additional authors not shown)
Abstract:
Multiplicities of charged hadrons produced in deep inelastic muon scattering off a $^6$LiD target have been measured as a function of the DIS variables $x_{Bj}$, $Q^2$, $W^2$ and the final state hadron variables $p_T$ and $z$. The $p_T^2$ distributions are fitted with a single exponential function at low values of $p_T^2$ to determine the dependence of $\langle p_T^2 \rangle$ on $x_{Bj}$, $Q^2$,…
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Multiplicities of charged hadrons produced in deep inelastic muon scattering off a $^6$LiD target have been measured as a function of the DIS variables $x_{Bj}$, $Q^2$, $W^2$ and the final state hadron variables $p_T$ and $z$. The $p_T^2$ distributions are fitted with a single exponential function at low values of $p_T^2$ to determine the dependence of $\langle p_T^2 \rangle$ on $x_{Bj}$, $Q^2$, $W^2$ and $z$. The $z$-dependence of $\langle p_T^2 \rangle$ is shown to be a potential tool to extract the average intrinsic transverse momentum squared of partons, $\langle k_{\perp}^2 \rangle$, as a function of $x_{Bj}$ and $Q^2$ in a leading order QCD parton model.
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Submitted 31 May, 2013;
originally announced May 2013.