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В. Аносов

Joint Institute for Nuclear Research

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S. Gerassimov

Technical University of Munich

A. Amoroso

University of Turin

S. Dasgupta

Istituto Nazionale di Fisica Nucleare, Sezione di Trieste

M. Chiosso

Istituto Nazionale di Fisica Nucleare, Sezione di Torino

B. Parsamyan

A. Alikhanyan National Laboratory

J. Bernhard

University of Würzburg

КЗ

К. Заремба

Warsaw University of Technology

A.M. Kotzinian

Istituto Nazionale di Fisica Nucleare, Sezione di Torino

A. Bressan

University of Trieste

J. Nový

Czech Technical University in Prague

Cooperative Institutions

European Organization for Nuclear Research

891

University of Adelaide

500

University of Aveiro

498

Joint Institute for Nuclear Research

387

A. Alikhanyan National Laboratory

376

Centre National de la Recherche Scientifique

282

Institut National de Physique Nucléaire et de Physique des Particules

222

Istituto Nazionale di Fisica Nucleare, Sezione di Trieste

172

Commissariat à l'Énergie Atomique et aux Énergies Alternatives

155

CEA Paris-Saclay

148

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High-statistics measurement of Collins and Sivers asymmetries for transversely polarised deuterons

arXiv (Cornell University) (2024)

G. D. Alexeev M. Alexeev C. Alice A. Amoroso V. Andrieux

New results are presented on a high-statistics measurement of Collins and Sivers asymmetries of charged hadrons produced in deep inelastic scattering of muons on a transversely polarised $^6$LiD target. The data were taken in 2022 with the COMPASS spectrometer using the 160 \gevv\ muon beam at CERN, balancing the existing data on transversely polarised proton targets. The first results from about two-thirds of the new data have total uncertainties smaller by up to a factor of three compared to the previous deuteron measurements. Using all the COMPASS proton and deuteron results, both the transversity and the Sivers distribution functions of the $u$ and $d$ quark, as well as the tensor charge in the measured $x$-range are extracted. In particular, the accuracy of the $d$ quark results is significantly improved.

Compass

10.48550/arxiv.2401.00309

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Odd and even partial waves of ηπ − and η π − in π − p → η () π − p

C. Adolph A. Amoroso V. Andrieux В. Аносов A. Austregesilo

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Transverse-momentum-dependent multiplicities of charged hadrons in muon-deuteron deep inelastic scattering

Physical review. D/Physical review. D. (2018)

M. Aghasyan M. Alexeev G.D. Alexeev A. Amoroso V. Andrieux

A semi-inclusive measurement of charged hadron multiplicities in deep inelastic muon scattering off an isoscalar target was performed using data collected by the COMPASS Collaboration at CERN. The following kinematic domain is covered by the data: photon virtuality ${Q}^{2}>1\text{ }\text{ }(\mathrm{GeV}/c{)}^{2}$, invariant mass of the hadronic system $W>5\text{ }\text{ }\mathrm{GeV}/{c}^{2}$, Bjorken scaling variable in the range $0.003

Virtual particle

Perturbative QCD

10.1103/physrevd.97.032006

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Citations (59)

Исследование характеристик сборки модулей электромагнитного калометра ECAL0 для эксперимента COMPASS на электронном пучке ускорителя ELSA

В. Аносов Н. Анфимов Й. Барт A. Guskov М. Дзиевицки

Compass

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Observation of $X(3872)$ muoproduction at COMPASS

arXiv (Cornell University) (2017)

M. Aghasyan J. Giarra W. Dünnweber S.A. Mamon P. Sznajder

We have observed exclusive production of the exotic $X(3872)$ hadron in the reaction $\mu^+~N \rightarrow \mu^+ (J\!/\!\psi\pi^+\pi^-)\pi^{\pm}~N'$ using COMPASS data collected with incoming muons of 160~GeV/$c$ and 200~GeV/$c$ momentum. The statistical significance of the $X(3872)$ signal is 6$\sigma$. The shape of the two-pion mass distribution shows disagreement with previous observations. The product of cross section and branching fraction of the $X(3872)$ decay into $J\!/\!\psi\pi\pi$ is determined to be 71$\pm$28(stat)$\pm$39(syst)~pb.

X(3872)

Compass

Sigma

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Contribution of exclusive diffractive processes to the measured azimuthal asymmetries in SIDIS

Nuclear Physics B (2020)

J. Agarwala M. Alexeev G. D. Alexeev A. Amoroso V. Andrieux

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.

DESY

Virtual particle

10.1016/j.nuclphysb.2020.115039

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Transverse extension of partons in the proton probed in the sea-quark range by measuring the DVCS cross section

Physics Letters B (2019)

R. Akhunzyanov M. Alexeev G. D. Alexeev A. Amoroso V. Andrieux

We report on the first measurement of exclusive single-photon muoproduction on the proton by COMPASS using 160 GeV/c polarised μ+ and μ− beams of the CERN SPS impinging on a liquid hydrogen target. We determine the dependence of the average of the measured μ+ and μ− cross sections for deeply virtual Compton scattering on the squared four-momentum transfer t from the initial to the final proton. The slope B of the t-dependence is fitted with a single exponential function, which yields B=(4.3±0.6stat|sys−0.3+0.1)(GeV/c)−2. This result can be converted into a transverse extension of partons in the proton, 〈r⊥2〉=(0.58±0.04stat|sys−0.02+0.01±0.04model)fm. For this measurement, the average virtuality of the photon mediating the interaction is 〈Q2〉=1.8(GeV/c)2 and the average value of the Bjorken variable is 〈xBj〉=0.056.

Virtual particle

10.1016/j.physletb.2019.04.038

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Citations (34)

Spin Density Matrix Elements in Exclusive $ω$ Meson Muoproduction $^*$

arXiv (Cornell University) (2020)

M. Alexeev G. D. Alexeev A. Amoroso V. Andrieux В. Аносов

We report on a measurement of Spin Density Matrix Elements (SDMEs) in hard exclusive $ω$ meson muoproduction on the proton at COMPASS using 160 GeV/$c$ polarised $ μ^{+}$ and $ μ^{-}$ 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/$c$)$^2$. Here, $Q^2$ denotes the virtuality of the exchanged photon, $W$ the mass of the final hadronic system and $p_T$ the transverse momentum of the $ω$ meson with respect to the virtual-photon direction. The measured non-zero SDMEs for the transitions of transversely polarised virtual photons to longitudinally polarised vector mesons ($γ^*_T \to V_L$) indicate a violation of $s$-channel helicity conservation. Additionally, we observe a sizeable contribution of unnatural-parity-exchange (UPE) transitions that decreases with increasing $W$. The results provide important input for modelling Generalised Parton Distributions (GPDs). In particular, they may allow to evaluate in a model-dependent way the contribution of UPE transitions and assess the role of parton helicity-flip GPDs in exclusive $ω$ production.

Helicity

Virtual particle

Vector meson

Density matrix

10.48550/arxiv.2009.03271

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Citations (1)

Measurement of the cross section for hard exclusive π0 muoproduction on the proton

Physics Letters B (2020)

M. Alexeev G. D. Alexeev A. Amoroso V. Andrieux Н. Анфимов

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 $0.08\,(\text{GeV/}c)^2 < |t| < 0.64\,(\text{GeV/}c)^2$. The average kinematics of the measurement are $\langle Q^2 \rangle =2.0\; {(\text{GeV}/c)^2}$, $\langle \nu \rangle = 12.8\; {\text{GeV}}$, $\langle x_{Bj} \rangle = 0.093 $ and $\langle -t \rangle = 0.256\; {(\text{GeV}/c)^2} $. Fitting the azimuthal dependence reveals a combined contribution by transversely and longitudinally polarised photons of $(8.1 \ \pm \ 0.9_{\text{stat}}{}_{- \ 1.0}^{+ \ 1.1}\big\rvert_{\text{sys}})\,{\text{nb}}/{(\text{GeV}/c)^{2}}$, as well as transverse-transverse and longitudinal-transverse interference contributions of $(-6.0 \pm 1.3_{\text{stat}}{}_{- \ 0.7}^{+ \ 0.7}\big\rvert_{\text{sys}})\,{\text{nb}}/{(\text{GeV}/c)^{2}}$ and $(1.4 \pm 0.5_{\text{stat}}{}_{- \ 0.2}^{+ \ 0.3}\big\rvert_{\text{sys}})\,{\text{nb}}/{(\text{GeV}/c)^{2}}$, respectively. Our results provide important input for modelling Generalised Parton Distributions. In the context of the phenomenological Goloskokov-Kroll model, the statistically significant transverse-transverse interference contribution constitutes clear experimental evidence for the chiral-odd GPD $\overline{E}_T$.

10.1016/j.physletb.2020.135454

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Citations (21)

ATLAS computing technical proposal

A. Airapetian V. Grabsky H. Hakopian A. Vartapetian F. Fares

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Citations (7)