Dijet Double Longitudinal Spin Asymmetry A_LL in Proton-proton collisions at √s = 200 GeV

Tai Sakuma

Preliminary Results

The longitudinal double spin asymmetry A_LL of the dijet production in polarized proton-proton collisions at 200 GeV at the mid-rapidity |η| ≤ 0.8 was measured. A_LL was measured as a function of the dijet invariant mass M_jj.

The A_LL was measured as the ratios of the spin sorted dijet yields with the corrections for the relative luminosity and polarizations:

Four false asymmetries, which should vanish, were measured for a systematic check of the data. Two single spin asymmetries and two wrong-sign spin asymmetries were consistent with zero within the statistical uncertainties.

The largest systematic uncertainty is the trigger bias, which is the uncertainty in the changes of A_LL from the parton level to the detector level. This was evaluated using the MC events with several polarized parton distributions which are compatible with the current experimental data: DSSV, GRSV std, and the GRSV series with ΔG from -0.45 to 0.3. In this evaluation, in order to calculate A_LL with the unpolarized event generator Pythia, the MC events were wighted by the products of the spin asymmetries of the parton distributions and parton-level cross sections.

The result is consistent with a theoretical prediction based on the DSSV polarized parton distributions, which indicates the dijet A_LL will be a promising channel to constrain the polarized gluon distribution when we collect more statistics.

Analysis Detail

Please, visit this site for the detail: http://people.physics.tamu.edu/sakuma/star/jets/c100926_dijets_asym/s0000_index_001/prelim.php