DIS 2006 TSUKUBA April 21, 2006 Alessandro Bravar Spin Dependence in Polarized Elastic Scattering in the CNI Region A. Bravar, I. Alekseev, G. Bunce, S. Dhawan, R. Gill, H. Huang, W. Haeberli, O. Jinnouchi, K. Kurita, Y. Makdisi, A. Nass, H. Okada, N. Saito, H. Spinka, E. Stephenson, D. Svirida, T. Wise, J. Wood, A. Zelenski

D I S Alessandro Bravar RHIC beams + internal targets  fixed target mode  s ~ 14 GeV The Elastic Process: Kinematics recoil proton or Carbon (polarized) proton beam scattered proton polarized proton target or Carbon target essentially 1 free parameter: momentum transfer t = (p 3 – p 1 ) 2 = (p 4 – p 2 ) 2 <0 + center of mass energy s = (p 1 + p 2 ) 2 = (p 3 – p 4 ) 2 + azimuthal angle  if polarized !  elastic pp kinematics fully constrained by recoil proton only !

D I S Alessandro Bravar Helicity Amplitudes for spin ½ ½  ½ ½ Scattering process described in terms of Helicity Amplitudes  i All dynamics contained in the Scattering Matrix M (Spin) Cross Sections expressed in terms of spin non–flip double spin flip spin non–flip double spin flip single spin flip ?  M  identical spin ½ particles formalism well developed, however not much data ! only A N studied / measured to some extent observables: 3  -sections 5 spin asymmetries

D I S Alessandro Bravar The Very Low t Region around t ~  10  3 (GeV/c) 2 A hadronic  A Coulomb  INTERFERENCE CNI = Coulomb – Nuclear Interference scattering amplitudes modified to include also electromagnetic contribution hadronic interaction described in terms of Pomeron (Reggeon) exchange electromagnetic single photon exchange  = |A hadronic + A Coulomb | 2 unpolarized  clearly visible in the cross section d  /dtcharge polarized  “left – right” asymmetry A N magnetic moment + P 

D I S Alessandro Bravar the left – right scattering asymmetry A N arises from the interference of the spin non-flip amplitude with the spin flip amplitude (Schwinger) in absence of hadronic spin – flip contributions A N is exactly calculable (Lapidus & Kopeliovich): hadronic spin- flip modifies the QED “predictions” interpreted in terms of Pomeron spin – flip and parametrized as A N & Coulomb Nuclear Interference  1) p    pp had A N (t)

D I S Alessandro Bravar polarimeters

D I S Alessandro Bravar p  p   p p

D I S Alessandro Bravar p  p  pp and p  p   pp with a Polarized Gas Jet Target RHIC polarized Proton beams polarized gas JET target A N beam (t )  A N target (t ) for elastic scattering only! P beam = P target.  B /  T

D I S Alessandro Bravar The Atomic H Beam Source separation magnets (sextupoles) H 2 dissociator Breit-Rabi polarimeter focusing magnets (sextupoles) RF transitions holding field magnet recoil detectors ToF, E REC ;  REC record beam intensity 100% eff. RF transitions focusing high intensity B-R polarimeter P target ~ ± OR P z + OR P z - H = p + + e -

D I S Alessandro Bravar pp elastic data collected Hor. pos. of Jet cts. = 2.5 mm Number of elastic pp events FWHM ~ 6 mm as designed recoil protons unambiguously identified ! CNI peak A N 1 < E REC < 2 MeV prompt events and beam-gas  source calibration recoil protons elastic pp  pp scattering background 118 cts. subtracted JET Profile: measured selecting pp elastic events ToF vs E REC correlation T kin = ½ M R (dist/ToF) 2  ToF <  8 ns

D I S Alessandro Bravar TDC vs ADC individual channels Energy - Position correlations T kin   2 (i.e. position 2 ) pp elastic events clearly identified ! fully absorbed protons punch through protons recoil energy punch through recoil protons position

D I S Alessandro Bravar not corrected for the magnetic field M X 2 [GeV 2 ] Mp2Mp2 inelastic threshold number of events (a. u.) FWHM ~ 0.1 GeV 2 M 2 X (GeV 2 ) proton M 2 X distribution 80 cm from target convoluted with spectrometer Resolution  M 2 X 2  M 2 X ~ 0.1 GeV 2 Missing Mass M X 100 GeV M2XM2XM2XM2X simulations

D I S Alessandro Bravar A N for p  p  100 GeV no need of a hadronic spin – flip contribution to describe these data no hadronic spin-flip Re r 5 =  Im r 5 =  in the simplest assumption: spin-flip prop. to non-flip ampli. source of systematic errors: 1  P TARGET = 2 % 2 from backgrounds & event selection <  false asymmetries: small similar to statistical errors  2 ~ 13 / 14 d.o.f. (11 / 12) hep-ex/

D I S Alessandro Bravar A NN for p  p   100 GeV preliminary source of sys. errors: 1  P T 2 = 3 % 2 from backgrounds and event selections ~ rel. luminosity ~ similar to stat. errors A NN basically 0  double spin – flip amplitudes (  2 and  4 ) are very small / do not contribute in this region statistical errors only

D I S Alessandro Bravar p  C  p C

D I S Alessandro Bravar A N for p  C  100 GeV no hadronic spin-flip with hadronic spin-flip “forbidden” asymmetries systematic uncertainty best fit with hadronic spin-flip Kopeliovich – Truemann model PRD64 (01) hep-ph/ r 5 pC  F s had / Im F 0 had preliminary statistical errors only spread of r 5 values from syst. uncertainties 1  contour

D I S Alessandro Bravar A N p  C  pC: Energy Dependence A N (%) Beam Energy (GeV) preliminary data t = GeV 2 t = GeV 2 t = GeV 2 t = GeV 2 statistical errors only E ? Asymptotic regime No energy dependence ? only statistical errors shown normalization errors: ~ 10 % (at 3.9) ~ 15 % (at 6.5) ~ 20 % (at 21.7) systematic errors: < 20 % - backgrounds - pileup - RF noise

D I S Alessandro Bravar Summary  measured A N pp and A NN pp for elastic pp  pp scattering at 100 GeV with very high accuracy (statistical and systematic) – |t| range: < |t| < (GeV/c) 2  A N data well described by CNI – QED predictions (Schwinger – Lapidus) these data do not require a hadronic spin-flip term A NN ~ 0 over whole range with no “structure” (i.e. t – dependence)  measured A N pC for elastic pC  pC scattering at 100 GeV (RHIC) – zero crossing around |t| ~ 0.03 (GeV/c) 2  pC data require substantial hadronic spin-flip !  measured A N pC for pC  pC scattering over 3.5 < E b < 24 GeV (AGS) – E b < 10 GeV/c: almost no t dependence & departure from “CNI” shape