Measurement of the double-spin asymmetry ALL for inclusive multi-γ pair production with 200 GeV/ c polarized proton beam and polarized proton target

Abstract

The invariant double-differential cross section, E 1E 2d 6σ / d p 3 1d p 3 2 , and the double-spin asymmetry, A LL , for inclusive multi-γ pair production in which γ-rays came from neutral mesons were measured with a 200 GeV/ c longitudinally-polarized proton beam and a longitudinally-polarized proton target. Most of the multi-γ pairs comes from two-jet type events which are sensitive to partonic interaction. The A LL values were found to be consistent with zero. The invariant double-differential cross section for inclusive π 0 π 0 production was also measured. These measured cross sections are consistent with LUND Monte Carlo simulations. Using the LUND Monte Carlo simulation package with the Carlitz-Kaur model of spin dependent distribution functions of valence quarks, the A LL values have been compared with theoretical predictions of gluon polarization, ΔG/ G. The results put restrictions on the size of ΔG/ G in the region of 0.05 ⪅ x ⪅ 0.35.