(a New Proposal to Jefferson Lab 12 Gev -pac34) Measurement of the Semi-inclusive Π and K Electro-production in Dis Regime from Transversely Polarized He Target with the Sbs & Bb Spectrometers in Hall A
An experiment is proposed to measure the Single Spin Asymmetries of the Semi-Inclusive Deep Inelastic Scattering (SIDIS) process ~n(e, e′π±(K±)), using the large-solid-angle Super Bigbite Spectrometer (SBS), the BigBite Spectrometer, and a novel polarized He target that includes alkali-hybrid optical pumping and convection flow to achieve very high luminosity. Both spectrometer arms will utilize GEM-based tracking to accommodate the high rates. The abundant statistics will allow the determination of the Collins and Sivers functions for neutron roughly 10 times more accurate than obtained for proton at HERMES for a detailed grid of the kinematic variables x, p T , and z. Furthermore, by including data taking at two energies, an 8.8 and 11 GeV, we will have data at two values of Q for each bin in x. The azimuthal coverage of our experiment is excellent, and is facilitated by collecting data at a series of neutron polarization directions, always transverse to the beam direction. The SIDIS pions and kaons will be detected over a wide range of the hadron momenta above 2 GeV for the angle between the hadron production and the electron scattering planes up to ±60◦, and the angle between the hadron momenta and the virtual photon momenta up to 60◦. Between the large acceptances of the electron and hadron arms, an electron polarizednucleon luminosity on the level of 4 · 10 cm−2/s, and a target polarization of 65%, we will obtain in a two-month run about 100 times more statistics (after accounting for difference in polarization and dilutions) then was done by the HERMES experiment. The experiment has significant potential for the discovery of new effects in hadron physics.
Transverse Spin Physics at HERMES
Single-spin asymmetries in semi-inclusive pion production are measured by the HERMES experiment for the first time, with a transversely polarised hydrogen target. Two different sine-dependencies are extracted which can be related to the quark distributions transversity h_1(x) and the Sivers function f_1T^perp(x).
Transverse-momentum distributions in a diquark spectator model
All the leading-twist parton distribution functions are calculated in a spectator model of the nucleon, using scalar and axial-vector diquarks. Single gluon rescattering is used to generate T-odd distribution functions. Different choices for the diquark polarization states are considered, as well as a few options for the form factor at the nucleon-quark-diquark vertex. The results are listed in analytic form and interpreted in terms of light-cone wave functions. The model parameters are fixed by reproducing the phenomenological parametrization of unpolarized and helicity parton distributions at the lowest available scale. Predictions for the other parton densities are given and, whenever possible, compared with available phenomenological parametrizations.