1. Rola spinu w elastycznym rozpraszaniu pp i pC w RHIC-u Andrzej Sandacz Seminarium Fizyki Wielkich Energii UW Warszawa, 4 marca 2005

2. Why interesting to study spin effects in elastic scattering?  Scientific interest Non-perturbative region of QCD ( | t | < 0.05 GeV 2 ) Details of static constituent quark structure of nucleon Constraints from general principles of Field Theory e.g. single spin-flip / nonflip amplitude ~ ln s as s → ∞ 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  Practical interest - beam polarimetry at RHIC Pomeron coupling to nucleon spin?

3. can be traced back to

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) Cross Sections expressed in terms of spin non–flip double spin flip spin non–flip double spin flip single spin flip ?  M  formalism well developed, however not much data ! only A N studied / measured to some extent observables: 3 cross sections 5 spin asymmetries

5. 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 

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” interpreted in terms of Pomeron spin – flip and parametrized as A N & Coulomb Nuclear Interference  1) p  pp had A N (t)

7. Some 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 pp 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. Polarimetry : Impact on RHIC Spin Physics  measured spin asymmetries normalized by P B to extract Physics Spin Observables  RHIC Spin Program requires  P beam / P beam ~ 0.05  normalization  scale uncertainty  polarimetric process with large  and known A N – pC elastic scattering in CNI region, A N ~ 1 – 2 % – fast measurements – requires absolute calibration  polarized gas jet target Physics Asymmetries Single Spin Asymmetries Double Spin Asymmetries measurements recoil

10. The Road to P beam with the JET target Requires several independent measurements 0 JET target polarization P target (Breit-Rabi polarimeter) 1 A N for elastic pp in CNI region: A N = - 1 / P target  N ’ 2 P beam = 1 / A N  N ” 1 & 2 can be combined in a single measurement: P beam / P target = -  N ’ /  N ” “ self calibration” works for elastic scattering only 3 CALIBRATION: A N pC for pC CNI polarimeter in covered kinematical range: A N pC = 1 / P beam  N ”’ (1 +) 2 + 3 measured simultaneously with several insertions of carbon target 4 BEAM POLARIZATION: P beam = 1 / A N pC  N ”” to experiments at each step pick-up some measurement errors: transfer calibration measurement expected precision

11. the JET ran with an average intensity of 1  10 17 atoms / sec the JET thickness of 1  10 12 atoms/cm 2 record intensity target polarization cycle +/0/- ~ 500 / 50 / 500 sec polarization to be scaled down due to a ~3% H 2 background: P target ~ 0.924 ± 0.018 (current understanding) no depolarization from beam wake fields observed ! JET target polarization & performance 0.94 0.96 0.98 pol. minus polarization plus polarization 2.5 h time

12. Recoil Si spectrometer 6 Si detectors covering the blue beam => MEASURE energy (res. < 50 keV) time of flight (res. < 2 ns) scattering angle (res. ~ 5 mrad) of recoil protons from pp  pp elastic scattering HAVE “design” azimuthal coverage one Si layer only  smaller energy range  reduced bkg rejection power B A N beam (t )  A N target (t ) for elastic scattering only! P beam =  P target.  N beam /  N target

13. Recoil particle ID ; Correlation of TOF and Energy TOF ns  TOF< +/-8 ns width line prompt events calibration alpha source ( 241 Am, 5.486 MeV) T R MeV GeV/c 2 1 02 Mp TRTR

14. Forward scattering particle ID ; Correlation of Energy and position (ch  ) vertical strips  ch#  recoil angle #1 #16 #1 #16 Ch#116 T R MeV 241 Am  TOF < +/-8 ns TOF vs T R Si detector of 16channels #1 #16 #4 TRTR TOF analysis

15. ONLINE  statistical errors only no background corrections no dead layer corrections no systematic studies no false asymmetries studies no run selection “ONLINE” measured asymmetries & Results data divided into 3 p energy energy bins “Target”: average over beam polarization “Beam”: average over target polarization an example: 750 < E REC < 1750 keV  P beam  = 37 %  2 %  P beam (pC CNI)  = 38 % No major surprises ? (statistical errors only !) blue beam with alternating bunch polarizations:    … good uniformity from run to run (stable JET polarization) JET polarization reversed each ~ 5 min. 1 run ~ 1 hour work in progress !

16. this expt. E704@FNAL A N for p  p  pp @ 100 GeV data in this t region being analyzed preliminary data (from this expt. only) fitted with CNI prediction [  TOT = 38.5 mbarn,  = 0,  = 0] fitted with: N  f CNI N – “normalization factor” N = 0.98  0.03  2 ~ 5 / 7 d.o.f. the errors shown are statistical only (see previous slide) no need of a hadronic spin – flip contribution to describe these data however, sensitivity on  5 had in this t range low no hadronic spin-flip

17. Setup for pC scattering – the RHIC polarimeters  recoil carbon ions detected with Silicon strip detectors  2   72 channels read out with WFD (increased acceptance by 2)  very large statistics per measurement (~ 20  10 6 events) allows detailed analysis – bunch by bunch analysis – channel by channel (each channel is an “independent polarimeter”) – 45 o detectors : sensitive to vertical and radial components of P beam  unphysical asymmetries Ultra thin Carbon ribbon Target (3.5  g/cm 2,10  m) beam direction 1 3 4 5 6 RHIC  2 rings 2 Si strip detectors (ToF, E C ) 30cm inside RHIC ring @IP12

18. Event Selection & Performance - very clean data, background < 1 % within “banana” cut - good separation of recoil carbon from  (C*   X) and prompts may allow going to very high |t| values -  (Tof) <  10 ns (    ~ 1 GeV) - very high rate: 10 5 ev / ch / sec E C, keV TOF, ns Typical mass reconstruction Carbon Alpha C*  Prompts Alpha Carbon Prompts M R, GeV M R ~ 11 GeV   ~ 1 GeV T kin = ½ M R (dist/ToF) 2 non-relativistic kinematics

19. Raw asymmetry (t) @ 100 GeV (RHIC) X-90X-45 X-average Regular calibration measurements Cross asymmetry Radial asymmetry False asymmetry ~0 higher –t range False asymmetry ~0 good agreement btw X90 vs. X45 0.020.01 0.02 0.03 0.04 -t (GeV/c) 2 Regular polarimeter runs measurements taken simultaneously with Jet -target very stable behavior of measured asymmetries Polarimeter dedicated runs (high -t) Signal attenuation (x1/2) to reach higher – t Normalized at overlap region to regular runs Zero crossing measured with large significance preliminary

20. A N for p  C  pC @ 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) 034004 hep-ph/0305085 r 5 pC  F s had / Im F 0 had preliminary statistical errors only spread of r 5 values from syst. uncertainties 1  contour

21. The Setup of PP2PP

22. 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 =

23. Elastic Event Identification An elastic event has two collinear protons, one on each side of IP 1.It also has eight Si detector “hits”, four on each side. 2.Clean trigger: no hits in the other arm and in inelastic counters. 3.The vertex in (z 0 ) can be reconstructed using ToF.

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

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

26. Systematic error ~ 15% (icluding 12.5% incertainty on beam polarisation)

27. Brief summary on A N experimental results at CNI region pp (E704, 1993) pp (RHIC jet, 2004) pp (PP2PP, 2004) 19 pC (E950, 2002) pC (RHIC Cpol,2004) 14 200 6 14 0.002 – 0.05 0.001 – 0.009 0.01 – 0.03 0.009 – 0.045 0.007 – 0.05 0.01 0.002 < 0.001 0.004 √s [GeV]-t range [GeV 2 ] typical ΔA N Both pC results consistent; 5% single spin-flip contribution, significantly different from 0 Both low energy pp results consistent; do not require spin-flip pp result at collider energy indicate spin-flip Another spin puzzle ?

28. A consistent theoretical description of the data ( T.L. Trueman )  Regge poles model, dominant contributions P, f, ω, a 2, ρ exchanges I = 0I = 1  Fit to unpolarized pp and ppbar data → g 0 P, g 0 f, g 0 ω, g 0 a, g 0 ρ ( s, t )  pC polarised I = 0 exchanges only Assumption: λ P, λ f, λ ω real, energy independent pC data → λ P = 0.09 ± 0.014, λ f = –0.30 ± 0.02, λ ω = 0.19 ± 0.10  pp polarised jet data all five exchanges contribute ‘degeneracy’: ( f, a 2 ) → R+ ( C = +1 ) and ( ω, ρ ) → R- ( C = -1 ) λ P = 0.09 (fixed), jet data → λ R+ = –0.32, λ R- = 1.09 compensation by ρ contribution (mostly) → almost no net spin-flip  pp at collider contributions of all Reggeons but Pomeron decrease ~ 10 % spin-flip due to Pomeron exchange expected

29. Summary and outlook  New precise data on A N in pp and pC scattering at small t from RHIC Small but significantly different from 0 spin-flip contribution, even at  (Model dependent) estimate of Pomeron single spin-flip contribution 0.09 ± 0.02  Possible results from RHIC in future  A N in increased energy range up to √s = 500 GeV  double-spin asymmetry A NN sensitive to hypothetical Odderon (C = -1 partner of Pomeron)  moderate t (0.15 – 1.5 GeV 2 ) dramatic spin dependence seen in pp scattering at low energies  large t ( > 2 GeV 2 ) ~ t -8 √s = 200 GeV 3 vector exchanges (gluons/ color singlets) between pairs of quarks