ASYMMETRIES ANALYSIS FROM THE FORWARD ANGLE PART OF THE G0 EXPERIMENT

Abstract

The possible role of the strange quarks in the spin structure of the nucleon has spawned a great deal of interest in the study of the contribution of strange quarks to the electromagnetic (EM) structure of the nucleon. Weak neutral form factors arising from the Z{sup 0} coupling of the electron to the proton, in addition to the usual electromagnetic form factors, give access to G{sub E}{sup s} and G{sub M}{sup s}: contributions of the strange quarks to the nucleon EM form factors. Various collaborations (SAMPLE at Bates, HAPPEX and G0 at Jefferson Lab, PVA4 at MAMI) have performed parity-violating electron scattering experiments in order to measure the strange quark form factors. In these high luminosity experiments, longitudinally-polarized electron beams are scattered off unpolarized targets of protons or deuterons; the resulting asymmetry in cross sections measured between the two beam helicity states is a simple function of G{sub E}{sup s} and G{sub M}{sup s}. Measurements at different angles and/or on different targets are necessary to separate the electric and magnetic strange quark form factors. The G0 collaboration has built a dedicated large acceptance apparatus which allows measurements of the asymmetry both at forward and backward angles off LH2 and LD2.more » As a result, the collaboration will be able to separately extract G{sub E}{sup s} and G{sub M}{sup s} over a range of four momentum transfer Q{sup 2} from 0.3 to 0.8 (GeV/c){sup 2} when the entire experimental program in Hall C at Jefferson Lab is completed. The first phase of the experiment (forward angle configuration) which is sensitive to linear combinations of the two strange quark form factors over the whole range of Q{sup 2}, was completed in May 2004; progress on the analysis set will be reported.« less