Run 6 Dijet Double Longitudinal Spin Asymmetry (Tai Sakuma)

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

Tai Sakuma

Preliminary Results

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

The ALL 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 ALL 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 ALL 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 double longitudinal spin asymmetry ALL for the dijet production as a function of dijet mass Mjj.

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

Analysis Detail

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