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OUTLINE of the TALK Description of the experiment Description of analysis

Preliminary Result of A N Measurement in p  p  Elastic Scattering at RHIC, at  s = 200 GeV Włodek Guryn for pp2pp collaboration Brookhaven National Laboratory, Upton, NY, USA. OUTLINE of the TALK Description of the experiment Description of analysis Results and interpretation

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OUTLINE of the TALK Description of the experiment Description of analysis

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  1. Preliminary Result of AN Measurement in pp Elastic Scattering at RHIC, at  s = 200 GeVWłodek Gurynfor pp2pp collaboration Brookhaven National Laboratory, Upton, NY, USA OUTLINE of the TALK Description of the experiment Description of analysis Results and interpretation Where do we go from here?

  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 SUNY Stony Brook, USA K. De, N. Ozturk University of Texas at Arlington, USA A. Sandacz Institute for Nuclear Studies, Warsaw, Poland * spokesman

  3. σtot of gives s dependence of f+ Contributes to the shape of AN Spin Dependence in Elastic Scattering Five helicity amplitudes describe proton-proton elastic scattering Some of the measured quantities are

  4. Source of single spin analyzing power AN Single spin asymmetry AN arises in the CNI region is due to the interference of hadronic non-flip amplitude with electromagnetic spin-flip amplitude (originally called Schwinger asymmetry) Any difference from the above is an indication if other contributions, hadronic spin flip caused by resonance (Reggeon) or vacuum exchange (Pomeron) contributions.

  5. Preliminary 2002 AN = 0.033± 0.018 FNAL E704 • s  20 GeV N. Akchurin et al. PRD 48, 3026 (1993) CNI curve N.H. Buttimore et al. PRD 59,114010 (1999) The world data on AN (pp)

  6. E950 elastic pC J. Tojo et al. PRL 89, 052302 (2002) RHIC/AGS Measurements There will also be results from polarized jet at RHIC

  7. Experimental Determination of AN Use Square-Root-Formulato calculate spin ( ,  ) and false asymmetries (,  .) This formula cancels luminosity dependence and apparatus asymmetries. Since AN is a relative measurement the efficiencies e(t, f) cancel

  8. = 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. x0,y0: Position at Interaction Point Θ*x Θ*y : Scattering Angle at IP xD, yD : Position at Detector ΘxD, ΘyD : Angle at Detector

  9. The Setup

  10. An elastic event has two collinear protons, one on each side of IP • It also has eight Si detector “hits”, four on each side. • Clean trigger: no hits in the other arm and in inelastic counters. • The vertex in (z0) can be reconstructed using ToF. Elastic Event Identification

  11. Acceptance beam pipe shadow Trigger Active area Only “inner” pots used for trigger and analysis, biggest acceptance Analyze the data for the closest position (¾ of all data)

  12. Angle (hit) Correlations Before the CutsEvents with only eight hits Note: the background appears enhanced because of the “saturation” of the main band

  13. Hit selection • Pedestal value, pedestal width (s) and dead channels (only six) were determined; • Valid hit, single strip, has dE/dx > 5s above the pedestal; • Cluster size is  5 consecutive strips above pedestal cut; • Valid hit in the Si plane for event reconstruction: • isa cluster whose dE/dx > 20 ADC counts above pedestal and • iswithin fiducial area of the detector (slide); • has for a y-plane y > 0.2mm from the edge of the detector. • Coordinate for x and y formed from adjacent hits in Sin for each Roman Pot

  14. Elastic Events Display Dave Morse

  15. cm cm Elastic Event Selection IUp Down Corerlations Use the correlation between coordinates from two opposite RPs (RP1U – RP3D) or (RP1D – RP3U) to define candidate tracks. Use natural widths of the distributions - s(x1-x2) vs (x1+x2)

  16. Elastic Event Selection III • After finding matching hits in x and y: • Choose events with one track in x and one track in y and  6hits. • Veto on the Sc signal in the opposite arm, TDC cut. • Choose collinear tracks within 3s in angles. • Plot dN/dt and calculate asymmetries.

  17. Before ToF After ToF Calculation of Scattering Angle • Using matched hits scattering angels can be calculated. • Use transport and and average (x0, y0) and beam angles obtained from vectors reconstructed using all eight RPs. • Make z-vertex correction using ToF.

  18. s(DQx) = 130 mrad s(DQx) = 100 mrad s(DQy) = 70 mrad Collinearity:DQx before and after z-correction, and DQy

  19. Event Yields after Cuts

  20. Useful t-interval [0.011,0.029] (Gev/c)2 dN/dt

  21. F angle distributions for spin combinations

  22. Where is very small Determination of AN • Use Square-Root-Formulato calculate raw asymmetries. • It cancels cancel luminosity dependence and effects of apparatus asymmetries. • It uses ,  bunch combinations. Since AN is a relative measurement the efficiencies e(t, f) cancel

  23. AN(j) PRELIMINARY PRELIMINARY j [deg] j [deg] Arm AArm B Preliminary Results: Full bin 0.011 < -t < 0.029 (GeV/c)2 Fit AN cos(j) dependence to obtain AN

  24. One point for full t-interval [0.011,0.029] Two points for two half intervals PRELIMINARY PRELIMINARY Results: PYellow+ PBlue = 0.67 (central value) and CNI curve (stot,r from world data, B from pp2pp result) Preliminary Note: a) PYellow+ PBlue = 0.67 can vary by ± 15% ( a working number); b) Systematic effects due to the beam transport uncertainty are small compared to the beam polarization uncertainty.

  25. PRELIMINARY PRELIMINARY Results: comparison with CNIdifferent polarizations and CNI parameters Curves show dependence of CNI on stot, r and B

  26. Preliminary Prediction using E704 and E950 dataLarry Trueman LT: The predictions are very uncertain because E704 makes a very large contribution with large errors to the Regge parameters. The upper curve has Regge contribution and the Pomeron coupling set to zero. Here t = 0.02 + 0.01i. Not much change  in the curve. Note that the f/a2 is the dominant Regge contribution and this leads to a very large energy dependence, especially to Re(t), in going from 704 energy to RHIC energy. At s = 400 GeV2, t = 0.1281 + 0.0285 i

  27. Kopeliovich - Povh prediction Mod.Phys.Lett. A13:3033-3038,1998 This Exp. Preliminary Preliminary CNI Theoretical Interpretation: Boris Kopeliovich Assume the non-flip Re f+/ Im f+ = p/2*e=0.15, where e ~ 0.1, is the power of s in energy dependence of stot. 1) The dashed curve is calculation with central values for r5 as was published by E950. Need for energy dependence of r5 2) The dash-dotted uses Im r5= 0.12, from pp and pp data at low energies. (BK SPIN2002 and hep-ph/0211061.) The phase is assumed to be the same as for the non-flip amplitude, i.e. Re r5/Im r5=0.15. 4) Solid curve assumes r5 rising as se, Regge Model of stot i.e. the spin-flip amplitude rises as s2e and results in: a) Im r5=  0.24 ( twice that at low energy.) b) Re r5=p/2*2e*Im r5=  0.075.

  28. Summary • We have measured the single spin analyzing power AN in polarized pp elastic scattering at s = 200 GeV, highest to date, in t-range [0.011,0.29] (GeV/c)2. • The AN is  4-5s from zero (statistical error.) • The AN is  2s away from a CNI curve, which does not have hadronic spin flip amplitude. • We discussed interpretation of the result by Larry Trueman and Boris Kopeliovich. (there is clear s dependence in r5, a hadronic spin flip is present.) • In order to understand better underlying dynamics one needs to map s and t-dependence of AN and also measure other spin related variables ANN…. • RHIC is a great and unique place to do this physics and we have a plan how to do it and do it better!

  29. dN/dt x-y Full acceptance at s 200 GeV Without IPM and kicker With IPM and kicker Future Possibility – Big Improvement

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