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A.Bazilevsky Brookhaven National Laboratory For the RHIC Polarimetry Group

Measurements of the analyzing power in pp elastic scattering in the CNI region for different beam energies at RHIC. A.Bazilevsky Brookhaven National Laboratory For the RHIC Polarimetry Group. Scattering of ½ ½ → ½ ½. Scattering process described in terms of helicity amplitudes  i

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A.Bazilevsky Brookhaven National Laboratory For the RHIC Polarimetry Group

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  1. Measurements of the analyzing power in pp elastic scattering in the CNI region for different beam energies at RHIC A.Bazilevsky Brookhaven National Laboratory For the RHIC Polarimetry Group

  2. Scattering of ½ ½ → ½ ½ Scattering process described in terms of helicity amplitudes i All dynamics contained in the Scattering Matrix M spin non–flip double spin flip spin non–flip double spin flip single spin flip Some observables: At very low –t ~10-3 (GeV/c)2 : FHadronic FCoulomb  Coulomb-Nuclear Interference (CNI)  Interference term in physics observables

  3. AN @ CNI The left-right asymmetry (AN) arises from the interference of the spin non-flip amplitude with spin flip amplitude Kopeliovich&Lapidus (1974) • AN is exactly calculable in the absence of hadronic spin- flip • With phenomenological input: tot, , B • Hadronic spin- flip modifies the QEDcalculation • Its contribution described by

  4. AN pp2pp: PLB632 (2006) 167 E704: PRD48 (1993) 3026 s=200 GeV s=19.4 GeV Hjet@RHIC: PLB 638 (2006) 450 Hjet@RHIC: PRD 79, 094014(2009) Hadronic spin flip! s=13.7 GeV s=6.7 GeV

  5. Absolute Polarimeter (H jet) RHIC pC Polarimeters Siberian Snakes BRAHMS & PP2PP (p) RHIC PHENIX (p) STAR (p) Siberian Snakes Spin Rotators Solenoid Snake LINAC BOOSTER Pol. Proton Source 500 mA, 400 ms AGS Warm Snake 200 MeV Polarimeter AC Dipole AGS pC CNI Polarimeter Cold Snake HJet @ RHIC Polarized atomic hydrogen gas jet target HJet p RHIC p I ~1017atoms / sec D ~ 1012atoms/cm2 P ~ 0.96

  6. Identification of Elastic Events ToF vs Energy Forward scattered proton proton beam proton target recoil proton Energy vs Channel # YELLOW beam BLUE beam Array of Si detectors measures TR&ToFof recoil proton Channel # corresponds to recoil angle R Correlations (TR & ToF ) and (TR & R )  the elastic process

  7. AN measurements Left-Right asymmetry is calculated using square root formula (cancels acceptance and luminosity effects) • Target polarization: • P~0.96 • Flips sign every ~10min In each recoil proton Ekin bin (-t = 2MpEkin) • Corrections/uncertainties • Background in side strips shows no asymmetry => dilutes signal AN (4-8%) • H-Jet molecular background (~3%) may additionally dilute signal AN (if not fully present in side strips) • Energy correction (Si dead layer) • Variations due to event selection • Total syst. uncertainty: 4-6% Signal strips Ekin=2.0-2.5 MeV Side strips

  8. Hjet: AN AN is beam energy independent for 0.002 < –t < 0.008 (GeV/c)2 PRD 79, 094014(2009) PLB 638 (2006) 450

  9. N. H. Buttimore et. al. Phys. Rev. D59, 114010 (1999) r5 fit AN = f (Re r5, Im r5) 1, 2, 3 1, 2, 3 Re r5 = -0.055 Im r5 = -0.016 Re r5 = -0.002 Im r5 = -0.005 Ep=31 GeV (s=7.7 GeV) Ep=250 GeV (s=21.7 GeV) r5=0 r5=0 r5 non-zero at >2.5 r5 zero within 1

  10. r5 1 contours s=19.4 GeV (E704) Very precise data from HJet@RHIC Non zero hadronic spin flip contribution to AN observed al low energies, s<8 GeV Hadronic spin flip contribution from higher energy data, s>13 GeV consistent with 0 s=21.7 GeV s=13.7 GeV s=7.7 GeV s=6.7 GeV s=200 GeV (pp2pp) Much improved pp2pp data in I.Alekseev’s talk

  11. Summary • HJetpolarimeter at RHIC is a key device for proton beam polarizations measurements which in parallel (for free!) provides precise measurements of ANvs–t in pp elastic scattering in CNI region for s= 7–22 GeV • Statistical errors are small (~2% in each –t bin) • Dominant uncertainties are systematic; background studies are necessary to improve systematic uncertainties • More data are expected in future RHIC runs in the same s range and possibly with extended acceptance in –t • Data indicate on the hadronic spin flip contribution to AN at low energies, s<8 GeV

  12. Backups

  13. N. H. Buttimore et. al. Phys. Rev. D59, 114010 (1999) r5 fit • tc = -8πα/ σtot, σtotis total cross section • κ is anomalous magnetic moment of the proton •  is the ratio of the real to imaginary parts of forward (non-flip) elastic amplitude • b is exp slope of had. elastic cross section: Relative phase between the Coulomb and hadronic amplitudes

  14. B, , tot tot B From PDG  = Re T / Im T From PDG

  15. Hadronic spin flip contribution Ep=100 GeV Im(r5)= -0.2,0,+0.2 Ep=100 GeV Re(r5)= -0.05,0,+0.05 r5=0 Ep=24 GeV Ep=31 GeV Ep=100 GeV Ep=250 GeV

  16. With Syst. errors Only stat. errors Ep=250 GeV (s=21.7 GeV)  0 within 1 0 within 1 Ep=31 GeV (s=7.7 GeV)  0 at ~2.5 0 at>5

  17. HJet Left-right asymmetry in elastic scattering: Interference between electromagnetic and hadronic amplitudes in the Coulumb-Nuclear Interference (CNI) region Forward scattered proton Beam and target are both protons RHIC proton beam H-jet target recoil proton <5% Ptarget is provided by Breit Rabi Polarimeter

  18. |1> |2> H = p++e HJet target system |1> |2> |3> |4> Hyper fine structure H2 desociater Separating Magnet (Sextuples) Atomic Beam Source RF transitions (WFT or SFT) P+ OR P Scattering chamber Holding magnet |1> |3> |2> |4> Breit-Rabi Polarimeter Separating magnet 2nd RF-transitions for calibration |1> |2> Ion gauge Ion gauge

  19. HJet Target asymmetry vs TR Run4 Blue  Run5 Blue  Run5 Yellow  Run6 Blue  Run6 Yellow

  20. HJet: Example from Run6 εtarget εbeam Polarization vs fill Measures average over beam profile polarization with fill-by-fill stat. uncertainty ~10% Data accumulated for a few fills provide normalization for pC polarimeter with uncertainty <5%

  21. pC Analyzing Power Run04 zero hadronic spin-flip With hadronic spin-flip (E950) Phys.Rev.Lett.,89,052302(2002) unpublished Ebeam = 100 GeV pC: AN Elastic scattering: interference between electromagnetic and hadronic amplitudes in the Coulumb-Nuclear Interference (CNI) region Ebeam = 21.7GeV

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