Measurement of the Analyzing Power of Proton-Carbon Elastic Scattering in the Cni Region at Rhic

Abstract

The single transverse spin asymmetry, A N , of the p-carbon elastic scattering process in the Coulomb Nuclear Interference (CNI) region was measured using an ultra thin carbon target and polarized proton beam in the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory (BNL). In 2004, data were collected to calibrate the p-carbon process at two RHIC energies (24 GeV, 100 GeV). A N was obtained as a function of momentum transfer −t. The results were fit with theoretical models which allow us to assess the contribution from a hadronic spin flip amplitude.The elastic scattering of polarized protons off nuclei at RHIC energies (24 − 250 GeV) provides information on a spin dependent hadronic spin-flip amplitude. In the Coulomb-Nuclear Interference (CNI) region, i.e. 0.005 < −t < 0.05 (GeV/c) 2 where t = (p out − p in ) 2 ≈ −2M C T kin < 0, the single transverse spin asymmetry, A N , of p-carbon elastic scattering is used to measure the beam polarization in RHIC. The data also provide physics information on the spin dependent hadronic contribution to the transverse asymmetry. For very small angle scattering, the elastic process dominates, and experimentally the elastic events are cleanly identified by measuring the recoil carbons for polar angles near 90• in the laboratory frame. In the CNI region, the electromagnetic and hadronic helicity amplitudes are comparable in size. A non-zero A N arises mainly from the interference between the coulomb spin-flip amplitude (which generates the anomalous magnetic moment of the proton) and the hadronic non spin-flip amplitude. This interference term, called 'pure CNI' is precisely determined from QED calculation. However, a contribution to A N can also come from the other interference term from the hadronic spin flip amplitude (coupling with the 1

Probing the Pomeron spin structure with Coulomb-nuclear interference

“…Double-dot-dashed blue and solid red curves correspond to Eikonal approximation without, ( 24)-( 25), and with, ( 29)- (30), absorptive corrections, respectively. In both cases, r pA 5 = 0; data for pC scattering at 100 GeV are from [30].…”

“…Black dotted curve presents Born approximation, Equations (9)-(10) and (14)-(15). Double-dot-dashed blue and solid red curves correspond to Eikonal approximation without, (24)-(25), and with, (29)-(30), absorptive corrections, respectively. In both cases, r…”

Coulomb-Nuclear Interference in Polarized pA Scattering

“…Double-dot-dashed blue and solid red curves correspond to Eikonal approximation without, ( 24) and ( 25), and with, ( 29) and (30), absorptive corrections, respectively. In both cases, r pA 5 = 0; data for pC scattering at 100 GeV are from [29].…”