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1.
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Exotic meson $\pi_1(1600)$ with $J^{PC} = 1^{-+}$ and its decay into $\rho(770)\pi$
/ COMPASS Collaboration
We study the spin-exotic $J^{PC} = 1^{-+}$ amplitude in single-diffractive dissociation of 190 GeV$/c$ pions into $\pi^-\pi^-\pi^+$ using a hydrogen target and confirm the $\pi_1(1600) \to \rho(770) \pi$ amplitude, which interferes with a nonresonant $1^{-+}$ amplitude. We demonstrate that conflicting conclusions from previous studies on these amplitudes can be attributed to different analysis models and different treatment of the dependence of the amplitudes on the squared four-momentum transfer and we thus reconcile their experimental findings. [...]
arXiv:2108.01744; CERN-EP-2021–162.-
2022-01-01 - 30 p.
- Published in : Phys. Rev. D 105 (2022) 012005
Fulltext: 2108.01744 - PDF; PhysRevD.105.012005 - PDF;
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2.
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Probing transversity by measuring $\Lambda$ polarisation in SIDIS
/ Alexeev, M.G. ; Alexeev, G.D. (Dubna, JINR) ; Amoroso, A. ; Andrieux, V. ; Anosov, V. (Dubna, JINR) ; Augsten, K. ; Augustyniak, W. (NCBJ, Warsaw) ; Azevedo, C.D.R. (Aveiro U.) ; Badełek, B. (Warsaw U.) ; Balestra, F. et al.
/COMPASS
Based on the observation of sizeable target-transverse-spin asymmetries in single-hadron and hadron-pair production in Semi-Inclusive measurements of Deep Inelastic Scattering (SIDIS), the chiral-odd transversity quark distribution functions $h_1^q$ are nowadays well established. Several possible channels to access these functions were originally proposed. [...]
arXiv:2104.13585; CERN-EP-2021-072.-
Geneva : CERN, 2022-01-10 - 18 p.
Draft (restricted): PDF; Fulltext: CERN-EP-2021-072 - PDF; 2104.13585 - PDF;
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3.
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Spin Density Matrix Elements in Exclusive $\omega$ Meson Muoproduction $^*$
/ COMPASS Collaboration
We report on a measurement of Spin Density Matrix Elements (SDMEs) in hard exclusive $\omega$ meson muoproduction on the proton at COMPASS using 160 GeV/$c$ polarised $ \mu ^{+}$ and $ \mu ^{-}$ beams impinging on a liquid hydrogen target. The measurement covers the range 5.0 GeV/$c^2$ $< W <$ 17.0 GeV/$c^2$, with the average kinematics $\langle Q^{2} \rangle=$ 2.1 (GeV/$c$)$^2$, $\langle W \rangle= 7.6$ GeV/$c^2$, and $\langle p^{2}_{\rm T} \rangle = 0.16$ (GeV/$c$)$^2$. [...]
arXiv:2009.03271; CERN-EP-2020-169.-
Geneva : CERN, 2021-02-05 - 22 p.
- Published in : Eur. Phys. J. C 81 (2021) 126
Article from SCOAP3: PDF; Draft (restricted): PDF; Fulltext: 2009.03271 - PDF; CERN-EP-2020-169 - PDF;
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4.
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A Triangle Singularity as the Origin of the $a_1(1420)$
/ Alexeev, G.D. (Dubna, JINR) ; Alexeev, M.G. (Turin U. ; INFN, Turin) ; Amoroso, A. (Turin U. ; INFN, Turin) ; Andrieux, V. (CERN ; Illinois U., Urbana) ; Anosov, V. (Dubna, JINR) ; Antoshkin, A. (Dubna, JINR) ; Augsten, K. (Dubna, JINR ; CTU, Prague) ; Augustyniak, W. (NCBJ, Warsaw) ; Azevedo, C.D.R. (Aveiro U.) ; Badełek, B. (Warsaw U.) et al.
The COMPASS experiment recently discovered a new isovector resonance-like signal with axial-vector quantum numbers, the $a_1(1420)$, decaying to $f_0(980)\pi$. With a mass too close to and a width smaller than the axial-vector ground state $a_1(1260)$, it was immediately interpreted as a new light exotic meson, similar to the $X$, $Y$, $Z$ states in the hidden-charm sector. [...]
arXiv:2006.05342; CERN-EP-2020-104.-
Geneva : CERN, 2021-08-18 - 21 p.
- Published in : Phys. Rev. Lett.
Draft (restricted): PDF; Fulltext: CERN-EP-2020-104 - PDF; 2006.05342 - PDF;
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5.
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Antiproton over proton and K$^-$ over K$^+$ multiplicity ratios at high $z$ in DIS
/ COMPASS Collaboration
The $\bar{\rm p} $ over p multiplicity ratio is measured in deep-inelastic scattering for the first time using (anti-) protons carrying a large fraction of the virtual-photon energy, $z>0.5$. The data were obtained by the COMPASS Collaboration using a 160 GeV muon beam impinging on an isoscalar $^6$LiD target. [...]
arXiv:2003.11791; CERN-EP-2020-041.-
Geneva : CERN, 2020-07-02 - 19 p.
- Published in : Phys. Lett. B 807 (2020) 135600
Article from SCOAP3: PDF; Draft (restricted): PDF; Fulltext: CERN-EP-2020-041 - PDF; 2003.11791 - PDF; Fulltext from publisher: PDF;
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6.
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Contribution of exclusive diffractive processes to the measured azimuthal asymmetries in SIDIS
/ COMPASS Collaboration
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. [...]
arXiv:1912.10322; CERN-EP-2019-286.-
Geneva : CERN, 2020-07 - 13 p.
- Published in : Nucl. Phys. B 956 (2020) 115039
Article from SCOAP3: PDF; Draft (restricted): PDF; Fulltext: 1912.10322 - PDF; CERN-EP-2019-286 - PDF;
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7.
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COMPASS++/AMBER: Proposal for Measurements at the M2 beam line of the CERN SPS Phase-1: 2022-2024
/ Adams, B ; Aidala, C A ; Alexeev, G D ; Alexeev, M G ; Amoroso, A ; Andrieux, V ; Anfimov, N V ; Anosov, V ; Antoshkin, A ; Augsten, K et al.
The Compass++/Amber (proto-)collaboration proposes to establish a “New QCD facility at the M2 beam line of the CERN SPS” and perform in phase-1, i.e. [...]
CERN-SPSC-2019-022 ; SPSC-P-360.
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2019.
Fulltext
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8.
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Measurement of the cross section for hard exclusive $\pi^0$ leptoproduction
/ COMPASS Collaboration
We report on a measurement of hard exclusive $\pi^0$ muoproduction on the proton by COMPASS using 160 GeV/$c$ polarised $\mu^+$ and $\mu^-$ beams of the CERN SPS impinging on a liquid hydrogen target. From the average of the measured $\mu^+$ and $\mu^-$ cross sections, the virtual-photon proton cross section is determined as a function of the squared four-momentum transfer between initial and final proton in the range $0.08\,(\text{GeV/}c)^2 < |t| < 0.64\,(\text{GeV/}c)^2$. [...]
arXiv:1903.12030; CERN-EP-2019-049.-
2020-06-10 - 9 p.
- Published in : Phys. Lett. B 805 (2020) 135454
Article from SCOAP3: PDF; Fulltext: PDF; Fulltext from publisher: PDF;
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9.
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A New QCD facility at the M2 beam line of the CERN SPS: COMPASS++/AMBER
/ Adams, B. (Chicago U., EFI ; Xonics Inc.) ; Aidala, C.A. (Michigan U.) ; Akhunzyanov, R. (Dubna, JINR) ; Alexeev, G.D. (Dubna, JINR) ; Alexeev, M.G. (Turin U.) ; Amoroso, A. (Turin U. ; INFN, Turin) ; Andrieux, V. (Illinois U., Urbana) ; Anfimov, N.V. (Dubna, JINR) ; Anosov, V. (Dubna, JINR) ; Antoshkin, A. (Dubna, JINR) et al.
In this Letter of Intent, we propose a broad experimental programme for the ``New QCD facility at the M2 beam line of the CERN SPS''. [...]
arXiv:1808.00848 ; CERN-SPSC-2019-003 ; SPSC-I-250 ; SPSC-I-250.
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2019. - 91 p.
Full text - Fulltext
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10.
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Measurement of $P_T$-weighted Sivers asymmetries in leptoproduction of hadrons
/ COMPASS Collaboration
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. [...]
arXiv:1809.02936; CERN-EP-2018-242.-
Geneva : CERN, 2019-03 - 20 p.
- Published in : Nucl. Phys. B 940 (2019) 34-53
Article from SCOAP3: PDF; Draft (restricted): PDF; Fulltext: CERN-EP-2018-242 - PDF; 1809.02936 - PDF;
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