Target Single-spin Asymmetries Research Articles

TMDs studied in semi-inclusive deep inelastic scattering at HERMES

The HERMES measured azimuthal amplitudes of cross sections and their transverse target single spin asymmetries for hadron productions in semi-inclusive deep inelastic scattering. From the extracted amplitudes, novel parton distribution functions can be studied. The recent results related to Sivers and Boer–Mulders distribution functions are discussed.

Nucleon transversity study using a polarized 3He target in Hall A at JLab

A first measurement of Single target Spin Asymmetry (SSA) from semi-inclusive electro-production of charged pions from a transversely polarized 3He target in Deep-Inelastic-Scattering kinematics was completed in Hall A at Jefferson Lab in early 2009. Such SSA will allow for an extraction of the much desired information on the Collins and Sivers asymmetry from the “neutron” in order to probe the quark transversity distributions. Future 11 GeV measurements at Jefferson Lab in Hall A using a solenoid magnetic detector system is being planned.

Latest HERMES results on transverse spin effects in hadron structure and formation⋆

Transverse target single-spin asymmetries in semi-inclusive deep inelastic scattering allow to study the so-called Collins and Sivers mechanisms. The first one connects the poorly known fundamental transversity distribution function, describing the transverse spin-polarization of quarks in a transversely polarized proton, to the Collins fragmentation function, describing spin-orbit correlations in the hadron formation process. The second one is sensitive to the Sivers function, which correlates the intrinsic transverse momentum of quarks with the proton’s spin orientation and is related to the orbital angular momentum of quarks. Preliminary results on azimuthal single target-spin asymmetries in semi-inclusive electro-production of pions and kaons at the HERMES experiment are presented. The full data set collected with a transversely polarized hydrogen target was analyzed providing the HERMES most precise results on the Collins and Sivers azimuthal moments.

Neutron transversity measurement at Jefferson Lab with a polarized 3He target

A first measurement of single target spin asymmetry (SSA) from semi-inclusive electroproduction of charged pions from a transversely polarized 3He target in deep-inelastic-scattering kinematics will take data in Hall A at Jefferson Lab in 2008. Such SSA will allow for an extraction of the much desired information on the Collins and Sivers asymmetry from the “neutron” in order to probe the quark transversity distributions. The experiment will be a coincidence measurement with the BigBite spectrometer detecting the scattered electrons and the left-arm HRS spectrometer detecting the charged pions. The prospect of future 11 GeV measurements at Jefferson Lab in Hall A using a solenoid magnetic detector system is also discussed in this talk.

Single target-spin asymmetry in semi-inclusive deep inelastic scattering on a transversely polarized nucleon target

We use a new set of Collins functions to update a previous prediction on the azimuthal asymmetries of pion production in a semi-inclusive deep-inelastic scattering process on a transversely polarized nucleon target. We find that the calculated results can give a good explanation to the HERMES experiment with the new parametrization, and this can enrich our knowledge of the fragmentation process. Furthermore, with two different approaches of distribution and fragmentation functions, we present a prediction on the azimuthal asymmetries of pion and kaon production at the kinematics region of the experiments E06010 and E06011 planned at Jefferson Lab. It is shown that the results are insensitive to the models for the pion case. However, the results for kaon production are sensitive to different approaches of distribution and fragmentation functions. This is helpful to clarify some points in the study of the azimuthal spin asymmetries and fragmentation functions in hadronization processes.

New observables in longitudinal single-spin asymmetries in semi-inclusive DIS

We analyze longitudinal beam and target single-spin asymmetries in semi-inclusive deep inelastic scattering and in jet deep inelastic scattering, including all possible twist-3 contributions as well as quark mass corrections. We take into account the path-ordered exponential in the soft correlators and show that it leads to the introduction of a new distribution and a new fragmentation function contributing to the asymmetries.

Parton distributions in light-cone gauge: where are the final-state interactions?

We show that the final-state interaction effects in the single target spin asymmetry discovered by Brodsky et al. can be reproduced by either a standard light-cone gauge definition of the parton distributions with a prescription for the light-cone singularities consistent with the light-cone gauge link, or a modified light-cone gauge definition with a gauge link involving the gauge potential at the spatial infinity.

DVCS and exclusive meson production at HERMES

Experimental data on the first measurement of single beam-spin asymmetry in Deeply Virtual Compton scattering (DVCS) and single target-spin asymmetry in the hard exclusive pion production from hydrogen target at HERMES are presented. The results obtained are discussed in the framework of Generalized Parton Distribution (GPD) functions of the nucleon.

Investigation of single spin asymmetries in [formula omitted] electroproduction

The azimuthal single target-spin asymmetries for π + production in semi-inclusive deep inelastic scattering of leptons off longitudinally polarized protons are evaluated using two main approaches available in the literature. It is shown that the approximation where the twist-2 transverse quark spin distribution in the longitudinally polarized nucleon is small enough to be neglected leads to a consistent description of all existing asymmetries observed by the HERMES experiment.

Perturbative contribution to the sinφ asymmetry in inclusive π + electroproduction

We consider the sinφ single target-spin asymmetry in deep-inelastic π + inclusive electroproduction off a longitudinally polarized target. We show that at larger transverse momentum of the outgoing hadron the evaluated asymmetry decreases if one takes into account the first order α S perturbative contribution to the cross section, integrated over the azimuthal angle. This leads to good agreement with recent HERMES data.

Single-spin azimuthal asymmetries in the “Reduced twist-3 approximation”

We consider the single-spin azimuthal asymmetries recently measured at the HERMES experiment for charged pions produced in semi-inclusive deep inelastic scattering of leptons off longitudinally polarized protons. Guided by the experimental results and assuming a vanishing twist-2 transverse quark spin distribution in the longitudinally polarized nucleon, denoted as “reduced twist-3 approximation”, a self-consistent description of the observed single-spin asymmetries is obtained. In addition, predictions are given for the z dependence of the single target-spin asymmetry.

Single target-spin asymmetries in semi-inclusive pion electroproduction on longitudinally polarized protons

We evaluate the single-spin sinΦ h and sin2 Φ h azimuthal asymmetries in the semi-inclusive pion production in deep inelastic lepton scattering off longitudinally polarized proton target in the HERMES kinematics. A good agreement with the HERMES data is a achieved using only the twist-2 distribution and fragmentation functions.