Transverse momentum dependence of semi-inclusive pion production

H Mkrtchyan,P Mckee,N El Khayari,M Ungaro,H Breuer,T Angelescu,E Schulte,X Jiang,M Wang,K Hafidi,J Roche,P Markowitz,N Kalantarians,R Ent,L Gan,J Reinhold,A Ahmidouch,T Ostapenko,V Kubarovsky,D Day,Y Liang,R Asaturyan,A Uzzle,L Yuan,D Gaskell,N Benmouna,S Vidakovic,G Niculescu,E Hungerford,S Malace,M Jones,T Horn,C Bertoncini,B Moziak,T Dodario,C Smith,Y Li,I Niculescu,S Danagoulian,T Navasardyan,G Warren,B Wojtsekhowski,J Arrington,E Segbefia,L Tang,V Tadevosyan,X Zheng,W Hinton,D Dutta,P Stoler,H.P Blok,W Vulcan ,O K Baker ,S H Connell ,D Meekins ,W Boeglin ,M M Dalton ,S E Rock ,Yanou Cui ,V V Frolov ,K S Joo ,J Dunne ,P Bosted ,R J Holt ,A N Villano ,G R Smith ,F R Wesselmann ,James Kelly ,M E Christy ,C Keppel ,S A Wood ,G M Huber ,Elizabeth J Mcgrath ,H Fenker ,P E Reimer ,G S Adams ,Chang Xu ,A K Opper ,Haibin Zhu

doi:10.1016/j.physletb.2008.05.047

Abstract

Cross sections for semi-inclusive electroproduction of charged pions (π±) from both proton and deuteron targets were measured for 0.2<x<0.5, 2<Q2<4 GeV2, 0.3<z<1, and Pt2<0.2 GeV2. For Pt<0.1 GeV, we find the azimuthal dependence to be small, as expected theoretically. For both π+ and π−, the Pt dependence from the deuteron is found to be slightly weaker than from the proton. In the context of a simple model, this implies that the initial transverse momenta width of d quarks is larger than for u quarks and, contrary to expectations, the transverse momentum width of the favored fragmentation function is larger than the unfavored one.

Highlights

Much is known about the light-cone momentum fraction, x, and virtuality scale, Q2, dependence of the up and down quark parton distribution functions (PDFs) in the nucleon
The process of semi-inclusive deep-inelastic lepton scattering (SIDIS), lN → lhX has been shown to factorize [5], in the high energy limit, into lepton-quark scattering followed by quark hadronization
The probability of producing a pion with a transverse momentum Pt relative to the virtual photon (q) direction is described by a convolution of the quark distribution fucntions and pt-dependent fragmentation functions D+(z, pt) and D−(z, pt), where pt is the transverse momentum of the the pion relative to the quark direction, with the imposed condition Pt = zkt + pt

Summary

Introduction

Cross sections for semi-inclusive electroproduction of charged pions (π±) from both proton and deuteron targets were measured for 0.2 < x < 0.5, 2 < Q2 < 4 GeV2, 0.3 < z < 1, and Pt2 < 0.2 GeV2. In the context of a simple fit, the initial transverse momenta of d quarks tends to be larger than for u quarks, while the transverse momentum width of the favored fragmentation function is slightly larger than that of the unfavored function.

Results

Conclusion