Measurement of Single Target-Spin Asymmetry in Semi-inclusive Pion Electro-production on a Transversely Polarized 3He Target

Abstract

Parton distribution functions (PDFs) provide important information about the flavor and spin structure of nucleon, which is one of the most fundamental building blocks of nature. Furthermore, they can also shed light on quantum chromodynamics (QCD) in the confinement region. Inclusive deep inelastic scattering (DIS) has been one of the most common tools in accessing PDFs through the measurementof structure functions. Moreover, the cross section in semi-inclusive deep inelastic scattering (SIDIS), which is the product of PDFs and fragmentation functions (FF), which describe the parton hadronization process due to the color force, provides additional information about PDFs. With recent theoretical developments in the framework of the transverse momentum dependent parton distribution functions(TMDs), the importance of SIDIS process have been widely recognized and accepted, since the inclusive DIS will not be able to attain the information of parton transverse momentum.JLab experiment E06-010 is measuring the target single spin asymmetry (SSA) in SIDIS from the n (e, e′π+,−)X reaction with a transversely polarized 3He (effective polarized neutron) target at JLab Hall A with a 5.89 GeV incident electron beam. The kinematic coverage is 0.13 < x < 0.41 and 1.31 < Q2 < 3.1 (GeV2). This experiment represents the first SSA measurement from the SIDIS n (e, e′π±)X process. One of the main objectives of the experiment is to measure the Collins asymmetry,which in turn constrains the "transversity", one of the PDFs whose direct physical interpretation is the probability of finding a transversely polarized parton inside a transversely polarized nucleon. The other main objective of the experiment is to measure the Sivers asymmetry which reveals important information about correlations between the parton transverse momentum and the nucleon spin. The Sivers asymmetry is closely linked to the parton's orbital angular momentum, which is one important piece in understanding the nucleon spin in terms of quark and gluondegrees of freedom. This dissertation will first give an introduction to QCD, SIDIS and currenttheoretical and the experimental status of SSA. Next the experimental setup of E06-010 will be described, followed by the data analysis procedure to extract the Collins/Sivers asymmetries. In the end, the preliminary results from the data analysis will be shown and discussed.