Semi-inclusive charged-pion electroproduction off protons and deuterons: Cross sections, ratios, and access to the quark-parton model at low energies

Abstract

A large set of cross sections for semi-inclusive electroproduction of charged pions (π ± ) from both proton and deuteron targets was measured. The data are in the deep-inelastic scattering region with invariant mass squared W 2 > 4 GeV 2 (up to ≈ 7 GeV 2 ) and range in four-momentum transfer squared 2 < Q 2 < 4 (GeV/c) 2 , and cover a range in the Bjorken scaling variable 0.2 < x < 0.6. The fractional energy of the pions spans a range 0.3 < z < 1, with small transverse momenta with respect to the virtual-photon direction, P 2 t < 0.2 (GeV/c) 2 . The invariant mass that goes undetected, Mx or W ′ , is in the nucleon resonance region, W ′ < 2 GeV. The new data conclusively show the onset of quark-hadron duality in this process, and the relation of this phenomenon to the high-energy factorization ansatz of electron-quark scattering and subsequent quark → pion production mechanisms. The x, z and P 2 t dependences of several ratios (the ratios of favored-unfavored fragmentation functions, charged pion ratios, deuteron-hydrogen and aluminum-deuteron ratios for π + and π − ) have been studied. The ratios are found to be in good agreement with expectations based upon a high-energy quark-parton model description. We find the azimuthal dependences to be small, as compared to exclusive pion electroproduction, and consistent with theoretical expectations based on tree-level factorization in terms of transverse-momentum-dependent parton distribution and fragmentation functions. In the context of a simple model, the initial transverse momenta of d quarks are found to be slightly smaller than for u quarks, while the transverse momentum width of the favored fragmentation function is about the same as for the unfavored one, and both fragmentation widths are larger than the quark widths.

Investigations into the flavor dependence of partonic transverse momentum

“…In any case, we remark that the average kinematics of the experiment taken into consideration in Refs. [24,26] are different from Hermes (see also the discussion in Ref. [58]).…”

“…This is a landmark achievement in the knowledge of the internal structure of hadrons. Earlier data already gave some indications, but were limited in the variety of targets, or final-state hadrons, or multidimensional coverage (see, e.g., [22][23][24][25][26]). The Compass collaboration has recently released similar data [27].…”

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

“…In Figure 14, the h þ multiplicities are compared to the π þ semi-inclusive cross section measured by the E00-18 experiment [31] at Jefferson Lab. The measurement by the E00-18 was performed at hzi ¼ 0.55 and hxi ¼ 0.32 in the range 2 ðGeV=cÞ 2 < Q 2 < 4 ðGeV=cÞ 2 .…”

Unpolarized SIDIS Cross Section from a 3 He Target

“…While it has been shown that the evolution effect is expected to be significant, most of the existing studies used the simple formalism (GPM) described in section 2. While factorization originates in the high energy limit (Q Λ QCD or Q M nucleon ) [12,60], and at low Q 2 the description with hadronic degrees of freedom is more widely used [28], the applicability of the quark-parton model with factorization in the modest Q 2 ranges has been observed in the quark-hadron duality [64,65].…”