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

Abstract

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 ðGeV=cÞ 2 , invariant mass of the hadronic system W > 5 GeV=c 2 , Bjorken scaling variable in the range 0.003 < x < 0.4, fraction of the virtual photon energy carried by the hadron in the range 0.2 < z < 0.8, and square of the hadron transverse momentum with respect to the virtual photon direction in the range 0.02 ðGeV=cÞ 2 < P 2 hT < 3 ðGeV=cÞ 2 . The multiplicities are presented as a function of P 2 hT in three-dimensional bins of x, Q 2 , z and compared to previous semi-inclusive measurements. We explore the small-P 2 hT region, i.e. P 2 hT < 1 ðGeV=cÞ 2 , where hadron transverse momenta are expected to arise from nonperturbative effects, and also the domain of larger P 2 hT , where contributions from higher-order perturbative QCD are expected to dominate. The multiplicities are fitted using a single-exponential function at small P 2 hT to study the dependence of the average transverse momentum hP 2 hT i on x, Q 2 and z. The power-law behavior of the multiplicities at large P 2 hT is investigated using various functional forms. The fits describe the data reasonably well over the full measured range.

Measurement of the azimuthal modulations of hadrons in unpolarized SIDIS

“…The fraction of the final-state hadrons originating from the diffractive vector meson (DVM) decays in the SIDIS hadron sample has been estimated in an earlier work [5] using two Monte Carlo (MC) simulations: LEPTO to generate SIDIS events and HEPGEN [9] for the diffractive ρ 0 and φ events. To get the fraction in the bins of the azimuthal asymmetries, which are different from Ref.…”

“…To get the fraction in the bins of the azimuthal asymmetries, which are different from Ref. [5], a parametrisation has been used. Only the ρ 0 , giving the dominant contribution, has been considered.…”

“…Ref. [5]) that part of the hadron sample used for COMPASS multiplicity and azimuthal asymmetry analyses originates from the diffractive production of vector mesons (ρ 0 , φ, ω) that decay into lighter hadrons. This process, which can be described by the fluctuation of the virtual photon into a vector meson that interacts with the nucleon via multiple-gluon exchange, can not be taken into account in the usual TMD PDF interpretation outlined above.…”

Power corrections in semi-inclusive deep inelastic scatterings at fixed target energies

“…In this kinematic regime where Q 2 P 2 h T 1/fm 2 , similar to the inclusive DIS, SIDIS cross section can be factorized into a product of perturbatively calculable lepton-parton scattering at the hard scale Q, corresponding transverse momentum dependent (TMD) parton distribution functions (or simply, TMDs), φ i/P (x, k T , µ 2 ) with k T being the active parton's transverse momentum perpendicular to the direction of the colliding hadron of momentum P , and TMD fragmentation functions (FFs), D j→h (z, p T , µ 2 ) with the emergent hadron-type h carrying momentum fraction between z and z + dz of the fragmenting parton of momentum p and p T being the parton's transverse momentum off the direction of the observed final-state hadron of momentum P h , where i, j = {q,q, g} represent the active parton flavors [9,10]. In terms of this TMD factorization formalism, with the corrections of O(P h T /Q), lepton-hadron SIDIS is an excellent process to probe three-dimensional (3D) confined motion of quarks and gluons inside a bound proton, and has been actively pursued by experimental programs at all lepton-hadron scattering facilities, such as COMPASS at CERN [11] and various experiments at Jefferson Lab [12], as well as the future Electron-Ion Collider (EIC) [13].…”

Charged hadron fragmentation functions from collider data

“…First, the charged hadrons SIDIS multiplicities measured by the COMPASS Collaboration [67, 68] could be included in our analysis of unidentified charged-hadron FFs in order to achieve flavour separation. This is possible thanks to the sensitivity of the SIDIS observable to different FF combinations as compared to SIA and pp .…”