1. DIS 2006 Tsukuba, April 21, 2006 Alessandro Bravar Proton Polarimetry at RHIC Alekseev, A. Bravar, G. Bunce, S. Dhawan, R. Gill, W. Haeberli, H. Huang, O. Jinnouchi, K. Kurita, Y. Makdisi, A. Nass, H. Okada, N. Saito, H. Spinka, E. Stephenson, D. Svirida, T. Wise, J. Wood, A. Zelenski 1. Provide polarization measurements for accelerator 2. Provide polarization measurements for experiments

2. DIS 2006 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  + sizable and known A N – pC elastic scattering in CNI region, A N ~ 1 – 2 %  large statistics > 10 7 events – (very) large   section  fast measurements – requires absolute calibration  polarized gas jet target Physics Asymmetries Single Spin Asymmetries Double Spin Asymmetries measurements

3. DIS 2006 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 Rf Dipoles RHIC pC “CNI” polarimeters PHOBOS RHIC absolute pH polarimeter Siberian Snakes AGS pC “CNI” polarimeter 5% Snake

4. DIS 2006 Alessandro Bravar How It Works ? recoil Carbon polarized beam scattered proton Carbon target t = (p out – p in ) 2 < 0  T kin  2 M C 0.01 < |t| < 0.02 (GeV/c) 2 Polarimetry: Requires large F.o.M: A N 2 x rate for fast measurement (not at any price however, i.e. by increasing the rates) small A N ~ 1 % (far from ideal !)  requires large statistics > 10 7, for d P B ~ few % however too large rates (i.e. thick target, detector area, etc.)  occupancy and pileup  very difficult operation  corrections to measured asymmetries  larger systematic uncertainty Absolute calibration  Polarized Gas Jet target

5. DIS 2006 Alessandro Bravar 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 wide) beam direction 1 3 4 5 6 RHIC  2 rings 2 Si strip detectors (ToF, E C ) 36cm inside RHIC ring @IP12 all Si strips parallel to beam Beam direction

6. DIS 2006 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

7. DIS 2006 Alessandro Bravar pC Systematics RHIC: 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 = 8.5 % (normalization) [P BEAM = 0.386  0.029  0.016] 2 energy scale ~ 50 keV for lowest |t| bin (from detector dead layer) NB these are “external” factors not “intrinsic” limitations Fit with sine function (phase fixed)

8. DIS 2006 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

9. DIS 2006 Alessandro Bravar AGS polarization during acceleration (ramp) raw asymmetry = A N  P B 12+ 36- 36+ G  = 1.91 E beam depolarizing resonances: intrinsic: G  = imperfection: G  = n each point = 50 MeV step 48- red line: simulation of polarization losses assuming constant A N

10. DIS 2006 Alessandro Bravar Bunch by Bunch 110 bunches typical example sometime even nicer than in textbooks

11. DIS 2006 Alessandro Bravar Bunch by Bunch + Spin Patterns high statistics 28 bunches @ injection 110 bunches @ flattop 10 11 p / bunch 110 bunches @ flattop with messed spin pattern

12. DIS 2006 Alessandro Bravar Beam Polarization Profiles … to avoid target location dependencies, sweep the target through the beam => “average” bunch polarization 2 mm intensity profile

13. DIS 2006 Alessandro Bravar Beam Emittance by sweeping the carbon target through the beam ~ 1 sec. measurement

14. DIS 2006 Alessandro Bravar 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

15. DIS 2006 Alessandro Bravar JET Target B A N beam (t )  A N target (t ) for elastic scattering only! P beam = P target.  N beam /  N target

16. DIS 2006 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

17. DIS 2006 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 ~ 1.8  10 6 events for 1.5  10 –3 < -t < 1.0  10 –2 GeV 2 similar statistics for 1.0  10 –2 < -t < 3.0  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 T Kin [MeV]

18. DIS 2006 Alessandro Bravar Energy - Position correlations pp elastic events clearly identified ! number of events (a. u.) T kin   2 (i.e. position 2 ) Energy Position 4 - 36 mm 11 – 181 – 8 not used

19. DIS 2006 Alessandro Bravar Event selections & Backgrounds Strip distribution for energy interval: 1250 – 1750 keV implement the energy / angle correlation in selecting elastic pp events typically, for each energy bin, select 3 to 4 strips per detector Background only from selected channels not from whole detector (4 – 5  smaller !) Total Backgrounds < 8 %:  source < 4%, “interaction” backgrounds < 4 % Si #2 signal background Si #6

20. DIS 2006 Alessandro Bravar P BEAM … P BEAM = 0.392  0.021 (stat)  0.008 (  P TARGET )  0.014 (sys) = 0.392  0.026 2004 ERROR:  P BEAM / P BEAM = 6.6 % 2005, 2006: in progress D P BEAM / P BEAM < 5 % ! tot sys = 0.016 “self calibrating” “Target”:  T – target asymmetry average over beam polarization “Beam”:  B – beam asymmetry average over target polarization ratio  B /  T reduced  2 ~ 1

21. DIS 2006 Alessandro Bravar Summary  fast measurements of P beam in ~ 30 sec.  provides also information on beam properties  steady progress in understanding and addressing systematic issues  “online” precision ~ 10 % (relative)  absolute normalization with a polarized gas JET  during 2004 run with Jet target precision on beam polarization  P BEAM / P BEAM = 6.6 % 2005 – 2006 (in progress):  P BEAM / P BEAM < 5 % !