1. СПИН – 05 Д У Б Н А Септ. 29, 2005 Alessandro Bravar Spin Dependence in Polarized p  p  pp & p  C  pC Elastic Scattering in the CNI Region A. Bravar, I. Alekseev, G. Bunce, S. Dhawan, R. Gill, H. Huang, W. Haeberli, G. Igo, O. Jinnouchi, K. Kurita, Y. Makdisi, A. Nass, H. Okada, N. Saito, H. Spinka, E. Stephenson, D. Svirida, C. Whitten, T. Wise, J. Wood, A. Zelenski

2. С П И Н 0 5 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 !

3. С П И Н 0 5 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

4. С П И Н 0 5 Alessandro Bravar Cross Sections in Terms of Cross Sections in Terms of  i total  section differential  section longitudinal  section transverse  section optical theorem unpolarized: avarage over all initial states (  and  ) and sum over all final states ( , ,  ) polarized: study specific spin configurations

5. С П И Н 0 5 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 

6. С П И Н 0 5 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)

7. С П И Н 0 5 Alessandro Bravar can be traced back to

8. С П И Н 0 5 Alessandro Bravar 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

9. С П И Н 0 5 Alessandro Bravar polarimeters

10. С П И Н 0 5 Alessandro Bravar 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

11. С П И Н 0 5 Alessandro Bravar 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 % – fast measurements – requires absolute calibration  polarized gas jet target Physics Asymmetries Single Spin Asymmetries Double Spin Asymmetries measurements recoil

12. С П И Н 0 5 Alessandro Bravar p  p   p p

13. С П И Н 0 5 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

14. С П И Н 0 5 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 record beam intensity 100% eff. RF transitions focusing high intensity B-R polarimeter OR P z + OR P z - H = p + + e -

15. С П И Н 0 5 Alessandro Bravar 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

16. С П И Н 0 5 Alessandro Bravar The Polarized Jet Target under development Dissociator stage Baffle location Sextupoles 1-4 Sextupoles 5-6 Profile measurement BRP vacuum vessel Electronics racks Turbo pump controllers Dissociator RF systems Vac. gauges monitors Target chamber & beam pipe adapters Recoil spectrometer silicon detectors

17. С П И Н 0 5 Alessandro Bravar 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

18. С П И Н 0 5 Alessandro Bravar Kinematics R ; E R ; tof S essentially 1 free parameter: t (+  )  elastic pp kinematics fully constrained by recoil proton only ! measure position and energy of recoil  R & t t : 0.001 – 0.02 GeV 2  R : 1 – 5 degrees T kin : 0.5 – 10 MeV p R : 30 – 140 MeV |t| : 0.001 – 0.02 GeV 2  R : 1 – 5 degrees T kin : 0.5 – 10 MeV p R : 30 – 140 MeV/c tof : 100 – 20 nsec (@ 1m)  additional kinematical constraint R & E R  m beam (M X ); tof & E R  m target

19. С П И Н 0 5 Alessandro Bravar Jet-Target Holding Magnetic Field (1.0)  Bdl ~ 0 displacement (cm) B z (Gauss) p = 30 MeV/c (|t|~10 -3 ) p = 100 MeV/c (|t|~10 -2 ) + - + 1.0 kGauss Helmholtz coils almost no effect on recoil proton trajectories: left – right hit profiles & left – right acceptances almost equal (also under reversal of holding field)

20. С П И Н 0 5 Alessandro Bravar pp elastic data collected Hor. pos. of Jet 10000 cts. = 2.5 mm Number of elastic pp events FWHM ~ 6 mm as designed recoil protons unambiguously identified ! 100 GeV ~ 3  10 6 events for 1.5  10 –3 < -t < 3.5  10 –2 GeV 2 24 GeV ~ 300 k events 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

21. С П И Н 0 5 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

22. С П И Н 0 5 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 2 @ 100 GeV M2XM2XM2XM2X simulations

23. С П И Н 0 5 Alessandro Bravar A N for p  p  pp @ 100 GeV preliminary source of systematic errors: 1  P TARGET = 2 % 2 from backgrounds & event selections <  0.0016 3 false asymmetries: small similar to statistical errors

24. С П И Н 0 5 Alessandro Bravar A N for p  p  pp @ 100 GeV preliminary data compared to CNI prediction [  TOT = 38.5 mbarn,  = -0.07,  = 0.02]  2 ~ 12 / 14 d.o.f. no need of a hadronic spin – flip contribution to describe these data no hadronic spin-flip

25. С П И Н 0 5 Alessandro Bravar and with the hadronic spin-flip term preliminary Im r 5 = 0.002  0.029 Re r 5 = -0.006  0.007  2 /ndf = 10 / 12 uncertainty on the  (  =  0.03) parameter can change at the same level with hadronic spin-flip stat + sys errors used in fits hadronic spin – flip contribution consistent with zero (1  level) in the simplest assumption: spin-flip prop. to non-flip ampli.

26. С П И Н 0 5 Alessandro Bravar A NN for p  p   pp @ 100 GeV preliminary source of systematic errors: 1  P T 2 = 3 % 2 from backgrounds and event selections ~ 0.001 3 rel. luminosity ~ 0.001 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

27. С П И Н 0 5 Alessandro Bravar p  C  p C

28. С П И Н 0 5 Alessandro Bravar Setup for pC scattering – the RHIC polarimeters  recoil carbon ions scattered around 90 o detected with Silicon strip detectors polar acceptance  ± 1.5 o around 90 o  2   72 channels read out with WFD  very large cross section  very fast measurements statistics per measurement (~ 20  10 6 events) allows detailed analysis beam direction 1 3 4 5 6 RHIC  2 rings 2 Si strip detectors (ToF, E C ) ~36cm inside RHIC ring @IP12 Ultra thin Carbon ribbon Target (3.5  g/cm 2, < 10  m)

29. С П И Н 0 5 Alessandro Bravar DAQ and WFD ADC 3  140 MHz synchronized to accelerator clocks bunch  -ing  “start” TDC “online” analysis of waveform performed beteween consecutive bunch  -ing  PH, tot Q, t.o.f.; full waveform (JET) ~50ns ~100mV FPGA onboard memory  t ~ 2 ns  E < 50 keV DAQ PC 20  10 6 events in 20 seconds  deadtimeless DAQ system can accept, analyze, and store 1 event / each bunch  -ing Wave Form Digitizer = peak sensing ADC, CFD, … common to the pC and JET DAQ system

30. С П И Н 0 5 Alessandro Bravar Si Detector design and energy loss at t ~ -0.01 (GeV/c) 2, Energy of recoil Carbon E kin ~ few 100 keV ( E kin = -t / 2M C ) range in Silicon, only fraction of micrometer substantial fraction of Carbon energy lost in entrance window (up to 50%)  correct E kin for energy loss  energy scale error important to minimize energy losses in entrance window of detector active area 24 x 12 mm 2 thickness 400  twelve 2 mm wide DC coupled strips top view of Si strip p + implants ~150 nm deep charge collection Al electrodes n type Si wafer n + implants and Al backplane

31. С П И Н 0 5 Alessandro Bravar 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

32. С П И Н 0 5 Alessandro Bravar A N p  C  pC at 3.9, 6.5, 9.7 & 21.7 GeV only statistical errors are shown normalization errors: ~ 10 % (at 3.9) ~ 15 % (at 6.5) ~ 20 % (at 21.7) systematic errors: < 20 % - backgrounds - pileup - RF noise recoil Carbon energy (keV) p = 3.9 GeV p = 21.7 GeV p = 9.7 GeV preliminary 2003 + 2004 data CNI peak ~ 4 %  P B  ~ 73 %  P B  ~ 65 %  P B  ~ 47 % p = 6.5 GeV A N (%) momentum transfer –t (GeV 2 /c 2 )  P B  ~ 60 % statistical errors only (AGS)

33. С П И Н 0 5 Alessandro Bravar A N p  C  pC: Energy Dependence A N (%) Beam Energy (GeV) preliminary 2003 + 2004 data t = - 0.01 GeV 2 t = - 0.02 GeV 2 t = - 0.03 GeV 2 t = - 0.04 GeV 2 statistical errors only only statistical errors are shown systematic errors as for previous slide E ? Asymptotic regime No energy dependence ?

34. С П И Н 0 5 Alessandro Bravar 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

35. С П И Н 0 5 Alessandro Bravar pC Systematics: each detector channel covers same t range  72 independent measurements of A N width ~ stat. error single meas. channel by channel raw asymmetry sources of systematic uncertainties: 1  P BEAM = 7.8 % (normalization) [P BEAM = 0.386  0.030, stat. error] 2 energy scale ~ 50 keV for lowest |t| bin (from “energy correction”) NB these are “external” factors not “intrinsic” limitations Fit with sine function (phase fixed)

36. С П И Н 0 5 Alessandro Bravar 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

37. С П И Н 0 5 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: 0.0015 < |t| < 0.035 (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