1. Results from PP2PP Experiment at RHIC Andrzej Sandacz XVII th Rencontres de Blois Sołtan Institute for Nuclear Studies, Warsaw on behalf of PP2PP Collaboration Château de Blois, France, May 15-20, 2005

2. Total and Differential Cross Sections, and Polarization Effects in pp Elastic Scattering at RHIC S. Bültmann, I. H. Chiang, R.E. Chrien, A. Drees, R. Gill, W. Guryn*, J. Landgraf, T.A. Ljubičič, D. Lynn, C. Pearson, P. Pile, A. Rusek, M. Sakitt, S. Tepikian, K. Yip Brookhaven National Laboratory, USA J. Chwastowski, B. Pawlik Institute of Nuclear Physics, Cracow, Poland M. Haguenauer Ecole Polytechnique/IN2P3-CNRS, Palaiseau, France A. A. Bogdanov, S.B. Nurushev, M.F Runtzo, M. N. Strikhanov Moscow Engineering Physics Institute (MEPHI), Moscow, Russia I. G. Alekseev, V. P. Kanavets, L. I. Koroleva, B. V. Morozov, D. N. Svirida ITEP, Moscow, Russia S. Khodinov, M. Rijssenbeek, L. Whitehead, S. Yeung SUNY Stony Brook, USA K. De, N. Guler, J. Li, N. Öztürk University of Texas at Arlington, USA A. Sandacz Institute for Nuclear Studies, Warsaw, Poland * spokesman

3. Spin Effects in Elastic Scattering at Collider Energies  Scientific interest Non-perturbative region of QCD ( | t | < 0.05 GeV 2 ) Details of static constituent quark structure of nucleon Some constraints from general principles of Field Theory e.g. allowed growth of single spin-flip / nonflip amplitude ~ ln s as s → ∞ (at fixed t) but spin-flip probes smaller distances ( ~ 0.2 fm ) in nucleon than non-flip interaction ( ~ 1 fm ) If spin-flip present, e.g. compact diquark in the nucleon or anomalous color-magnetic moment of quarks or isoscalar magnetic moment of the nucleon At high energy exchange of Pomeron dominant Pomeron coupling to nucleon spin?

4. 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 non–flip double spin flip spin non–flip double spin flip single spin flip formalism well developed, however not much data ! at high energy only A N measured to some extent Observables cross sections and spin asymmetries also A SS, A SL, A LL

5. Properties of Helicity Amplitudes at Small t and Large s  at small t, due to the conservation of the angular momentum  at large s, mostly unmeasured, but using reasonable assumptions a) extrapolation of experimental data at low energies b) theoretical arguments: factorisation and/or asymptotic dominance of exchanges with definite CP=1 or CP=-1 based on

6. 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 (Kopeliovich & Lapidus) hadronic spin- flip modifies the QED ‘predictions’ hadronic spin-flip usually parametrized as A N & Coulomb Nuclear Interference  1) p  pp had A N (t) needed phenomenological input: σ tot, ρ, δ (diff. of Coulomb-hadronic phases), also for nuclear targets em. and had. formfactors

7. Published A N Measurements in the CNI Region pp Analyzing Power no hadronic spin-flip -t A N (%) E704@FNAL p = 200 GeV/c PRD48(93)3026 E950@BNL p = 21.7 GeV/c PRL89(02)052302 with hadonic spin-flip no hadronic spin-flip pC Analyzing Power r 5 pC  F s had / Im F 0 had Re r 5 = 0.088  0.058 Im r 5 =  0.161  0.226 highly anti-correlated

8. RHIC-Spin Accelerator Complex BRAHMS & PP2PP STAR PHENIX AGS LINAC BOOSTER Pol. Proton Source Spin Rotators 20% Snake Siberian Snakes 200 MeV polarimeter AGS quasi-elastic polarimeter Rf Dipoles RHIC pC “CNI” polarimeters PHOBOS RHIC absolute pH polarimeter Siberian Snakes AGS pC “CNI” polarimeter 5% Snake

9. The Setup of PP2PP

10. Principle of the Measurement Elastically scattered protons have very small scattering angle θ *, hence beam transport magnets determine trajectory scattered protons The optimal position for the detectors is where scattered protons are well separated from beam protons Need Roman Pot to measure scattered protons close to the beam without breaking accelerator vacuum Beam transport equations relate measured position at the detector to scattering angle. x 0,y 0 : Position at Interaction Point Θ* x Θ* y : Scattering Angle at IP x D, y D : Position at Detector Θ x D, Θ y D : Angle at Detector =

11. Elastic Event Identification An elastic event has two collinear protons, one on each side of IP  Inner RP’s used for elastic event reconstruction; higher acceptance  Events with hits in all four RP’s of an arm → full reconstruction of scattered protons momenta → better knowledge of of mean vertex coordinates and beam angles at IP

12. Hit Correlations Before the Cuts After the cuts the background in the final sample is ≈ 0.5% ÷ 2% depending on y (vertical) coordinate Background: inelastic interactions, beam halo and beam-gas interactions example Width mainly due to ε = 15 π mm · mrad  beam emittance  spread of vertex position σ z = 60 cm

13. Elastic Event Selection  match of coordinates on opposite sides of IP; within 3σ for x and y coordinates  hit coordinates in the acceptance area of the detector After the cuts 1.14 million elastic events in t-interval 0.010 ≤ | t | ≤ 0.030 (GeV/c) 2 Loss of elastic events due to the selections < 0.035  events with multiple matches excluded

14. Experimental Determination of A N Use Square-Root-Formulae to calculate spin ( ,  ) and ( ,  ) asymmetries In this formulae luminosities, apparatus asymmetries and efficiencies cancel Wherecan be neglected wrt 1 ( < 0.03 )

15. ε 1 (Φ) whole t range: 0.010 < |t| < 0.030 (GeV/c) 2 ε 1 (Φ) whole t range: 0.010 < |t| < 0.030 (GeV/c) 2 Fit A N cos(  ) dependence to obtain A N Arm A Arm B Statistical errors

16. Preliminary Compared to CNI Prediction without Hadronic Spin-Flip Only statistical errors shown Beam polarization during the data taking in 2003: P Y + P B = 0.88 ± 0.12 Preliminary A N from PP2PP

17. Systematic Errors on A N  luminosities ans detector efficiencies cancel --  background 4.5%  beam positions at the detectors 1.8%  corrections to the standard transport matrices 1.4% (using events detected in all four RP’s)  uncertainties on L x eff and L y eff 6.4%  neglected term with double-spin asymmetries 3.0% All above 8.4% Beam polarization error (preliminary) 13.6% Total systematic 16.0%

18. A N for pp→pp in the CNI Region where t c = -8πα / σ tot, κ is anomalous magnetic moment of the proton fit to measured A N (t) Re r 5, Im r 5

19. r 5 from PP2PP Statistical and systematic errors added in quadratures 13.6% normalisation error due to beam polarisation uncertainty, not included Preliminary Re r 5 = -0.042 ± 0.037, Im r 5 = -0.51 ± 0.59

20. Effect of an Error on the Beam Polarization ( p0 ≡ Re r 5, p1 ≡ Im r 5 )

21. Summary and Outlook  First (preliminary) measurement of A N at a collider energy √s = 200 GeV, small t  A N more than 4σ different from 0  A N systematically ≈ 1σ above CNI curve with no hadronic spin-flip  Possible improvement of accuracy of A N and measurements of double-spin asymmetries at RHIC (A NN, A SS, A LL, A SL ) offer a unique chance to directly probe spin coupling of Pomeron and search for Odderon