arXiv subjects

Jan Matousek

Publications and source records attributed to Jan Matousek.

5 recordsLinked to original sources

arXiv2026

Measurements of transverse-momentum dependent effects in semi-inclusive DIS at COMPASS

Its cornerstone were studies of hadron production in deep inelastic scattering (DIS), which can be interpreted in the transverse-momentum-dependent (TMD) factorisation framework, allowing to access the distributions of polarisation and transverse momentum of quarks within the nucleon in the language of TMD PDFs, and the hadronisation in terms of TMD fragmentation functions. The data collected with a liquid hydrogen target in 2016-2017 will soon bring new information on the transverse momentum and may allow for the first time to extract the transverse polarisation of quarks within an unpolarised nucleon described by the Boer-Mulders function. The unique data collected with a transversely polarised deuteron target have already improved the knowledge of the d-quark transversity (transverse counterpart of the helicity PDF), reducing the uncertainties by a factor of 2.5 at large Bjorken x, and are yet to yield a number of interesting results.

hep-ex↗

arXiv2022

Azimuthal Asymmetries in Unpolarised Semi-Inclusive DIS at COMPASS

In semi-inclusive deep inelastic scattering (SIDIS) the non-zero transverse momentum of partons induces azimuthal dependence of the cross-section. For unpolarised nucleon, three azimuthal modulations that can be related to different combinations of twist-two or higher twist transverse momentum dependent PDFs and fragmentation functions arise: the so-called Cahn effect reflected in $\cos\phi_\mathrm{h}$ modulation, the $\cos2\phi_\mathrm{h}$ term related to the Boer--Mulders PDF and $\sin\phi_\mathrm{h}$ twist-three effect known as beam-spin asymmetry. In 2016 and 2017, the COMPASS experiment at CERN collected a large sample of SIDIS events using a longitudinally polarised 160~GeV/$c$ muon beam scattering on a liquid hydrogen target. Amplitudes of the aforementioned azimuthal modulations have been extracted from part of the data. A new procedure has been developed to subtract a background coming from the decay of diffractively produced vector mesons. The results presented in this talk qualitatively agree with earlier COMPASS results obtained with an isoscalar target.

hep-ex↗

arXiv2019

Measurement of the azimuthal modulations of hadrons in unpolarised SIDIS

In 2016 and 2017 COMPASS has collected a considerable amount of deep inelastic scattering events with a 160 GeV/c muon beam and a liquid hydrogen target. An analysis of 4 % of these data has allowed to extract preliminary results on the amplitudes of three azimuthal modulations, $A_{UU}^{\cos\phi_h}$, $A_{UU}^{\cos2\phi_h}$ and $A_{LU}^{\sin\phi_h}$. The first two are particularly important since they carry information on the intrinsic transverse momentum $\vec{k}_T$ of the quarks and on the correlations between the quark spin and $\vec{k}_T$, expressed by the Boer-Mulders TMD PDFs. They show strong kinematic dependence as a function of the Bjorken variable $x$, of the fraction of virtual photon energy carried by the hadron $z$ and of the component $P_{hT}$ of the hadron momentum orthogonal to the virtual photon direction, thus confirming the results of previous measurements. Also, as was recently shown by COMPASS, hadrons coming from decay of diffractively produced vector mesons give significant contribution to the amplitudes in certain kinematic regions, explaining in part the kinematic dependencies and helping the interpretation of the measurements. The effect on the published COMPASS $^6$LiD data is discussed.

hep-ex↗

arXiv2018

Weighted transverse spin asymmetries in 2015 COMPASS Drell-Yan data

Muon pairs created in the Drell-Yan process of a negative pion beam of 190 GeV/c momentum impinging on a transversely polarised NH$_3$ target were detected with the COMPASS spectrometer at CERN in 2015. In addition to the extraction of the transverse spin asymmetries (TSAs) from these data, a complementary analysis of the TSAs weighted by powers of the dimuon momentum $q_T$ has been performed and is presented in this paper. In the transverse momentum dependent parton distribution functions (TMD PDFs) formalism, the $q_T$-weighted TSAs can be interpreted in terms of products of the TMD PDFs of the beam pion and of the transversely polarised target proton, unlike the conventional TSAs, which are interpreted as their convolutions. This allowed us to make a straightforward comparison with the expectation based on the weighted Sivers asymmetry measured in the SIDIS process. In a similar way, the Boer-Mulders function of the pion and proton can be obtained as well.

hep-ex↗

arXiv2017

Measurement of $q_T$-weighted TSAs in 2015 COMPASS Drell-Yan data

In the polarised Drell-Yan experiment at the COMPASS facility at CERN the beam of negatively-charged pions with 190 GeV/c momentum and intensity about $10^8$ pions/s interacted with transversely polarised NH$_3$ target. Muon pairs produced in Drell-Yan process (DY) were detected. Recently, the first ever Transverse Spin Asymmetries (TSAs) measurement in DY has been presented by COMPASS. A complementary analysis of the TSAs weighted by powers of the dimuon transverse momentum $q_T$ are presented. In the Transverse Momentum Dependent (TMD) PDF formalism, the $q_T$-weighted TSAs can be written in terms of products of the TMD PDFs of two colliding hadrons, unlike the conventional TSAs, which are their convolutions over quarks transverse momenta. The results are compared in a straightforward way with the weighted Sivers asymmetry in the SIDIS process, released by COMPASS in 2016.

hep-ex↗