Transversity distributions from difference asymmetries in semi-inclusive DIS

V Barone,F Bradamante,G Sbrizzai,J Matousek,A Moretti,A Kerbizi,A Martin,A Bressan

doi:10.1103/physrevd.99.114004

Abstract

In recent years information on the transversity distribution $h_1$ has been obtained combining the Collins asymmetry results from semi-inclusive deep inelastic scattering (SIDIS) data on transversely polarized nucleon targets with the information on the fragmentation function of a transversely polarized quark from the asymmetries measured in $e^+e^-$ annihilation into hadrons. An alternative method was proposed long time ago, which does not require the $e^+e^-$ data, but allows one to get ratios of the $u$ and $d$ quark transversity distributions from the SIDIS data alone. The method utilizes the ratio of the difference of the Collins asymmetries of positively and negatively charged hadrons produced on transversely polarized proton and deuteron targets. We have applied this method to the COMPASS proton and deuteron data, and extracted the ratio $h_1^d/h_1^u$. The results are compared to those obtained in a previous point--by--point extraction based both on SIDIS and $e^+e^-$ data.

Highlights

Much interest has been dedicated to the transversity distribution in the past 20 years
In recent years information on the transversity distribution h1 has been obtained by combining the Collins asymmetry results from semi-inclusive deep inelastic scattering (SIDIS) data on transversely polarized nucleon targets with the information on the fragmentation function of a transversely polarized quark from the asymmetries measured in eþe− annihilation into hadrons
We have determined for the first time the transverse-spin difference asymmetries of positively and negatively charged hadrons using the SIDIS p and d COMPASS data

Summary

INTRODUCTION

Much interest has been dedicated to the transversity distribution in the past 20 years. Over the last decade singlespin asymmetries clearly related to the transversity distribution function have been measured in semi-inclusive deep inelastic scattering (SIDIS) on transversely polarized nucleons, namely, in DIS processes in which at least one hadron of the current jet is detected In these processes the cross section exhibits a spin-dependent azimuthal modulation that can be expressed in terms of a convolution of the transversity PDF and a fragmentation function (FF) which is chiral odd, guaranteeing the cross section to be chirally even. An alternative way to measure transversity from the Collins asymmetries alone is via the so-called “difference asymmetries,” which allow extracting combinations of the u and d quark transversity without knowing the Collins FF This method was proposed a long time ago [22,23,24] to access the helicity PDFs and has been used by the SMC Collaboration [25].

CROSS SECTIONS AND DIFFERENCE ASYMMETRIES

MONTE CARLO STUDIES

RESULTS

CONCLUSION