Yousef I. Makdisi EIC Meeting Dec 7-8, 2007 Polarized Proton/ Hadron Polarimetry With heavily reliance on the PSTP and RSC presentations K. Boyle, C. Camacho, H. Okada, S. Bazilevsky, I. Nakagawa, G. Bunce, L. Trueman l A preamble: Polarimeter requirements for RHIC Candidate processes for high energy polarimeters l “State of the art?” l What Hurdles? l Further improvements l 3 He polarimetry l Summary

Polarimeter requirements A polarimeter has to satisfy the following: Beam polarization monitor for Physics ( < 5 % ) Several samples over one fill Beam polarization diagnostic and Machine tuning tool Sample on demand and online, fast/within minutes Low systematic errors A large dynamic range & Energy independence Large analyzing power, large cross section, & low background Figure of merit (to optimize) is  A 2 Reasonable Cost Unlike electron polarimeters where processes are calculable, proton reactions rely on experimental verification specially at high energies.

Measuring the beam polarization In accelerators, the stable spin direction is normally vertical (up/down). We measure using a nuclear reaction in a plane that is perpendicular to the polarization direction. N L and N R are the number of scatters to the left and right. A: is the analyzing power of the reaction The statistical error in the measurement for PA << 1 is The polarimeter figure of merit (to optimize) is  A 2  : is the cross section of the reaction

Candidate processes for polarimeters Vs. Energy For transverse beam polarization l pp Elastic scattering l Inclusive Pion Production (significant asymmetry) l p-C elastic scattering in the CNI region (asymmetry few percent) l p-p elastic scattering in the CNI region and Jet targets (similarly)

Asymmetry in pp elastic scattering Vs energy Good analyzing power at low t~0.3 The Analyzing power drops as 1/p Reasonable cross section The cross section fall with energy There are measurements at beam energy of 100 GeV/c with analyzing power of few %

Asymmetry in Inclusive Pion Production Large  + asymmetries were observed at the ZGS using 12 GeV/c beam on hydrogen and deuterium targets in the mid seventies Wisdom had it: polarization effects will disappear at high Energies Large  +/- and  o asymmetries were observed at Fermilab with 200 GeV/c incident polarized proton beam on a hydrogen target For RHIC: we needed to assure the following: The asymmetry is large over the entire RHIC energy range especially at injection A nuclear target does not dilute the asymmetry (A theorist’s warning!!!) The  - asymmetries continue to exhibit the same behavior as  + as they are easier to detect with lower background

Large Asymmetries in inclusive pion production ZGS AGS Fermilab (12 GeV/c) (22 GeV/c) (200 GeV/c) Phys. Lett. B261(1991)201 Phys. Lett. B264(1991)462 Phys. Rev. D.18 (1978) Phys.Rev.D65:092008,2002 This formed the basis of our first design

p-p and p-C elasctic scattering the CNI region The asymmetry is “calculable”: J. Schwinger, Phys. Rev. 69,681 (1946) First suggested by Nural Akchurin (Iowa) l Weak beam momentum dependence l The analyzing power a few percent l High cross section RBRC Workshop (Buttimore, Kopeliovich, Leader, Soffer, Trueman) l The single flip hadronic amplitude Unknown, estimated at ~15 % uncertainty l A simple apparatus (detect the slow recoil protons or ~ 90 0 in the lab) PR D 48 (1993) pC concept test: first at IUCF and later at the AGS Carbon targets to survive the RHIC beam heating Fermilab E704

p-Carbon CNI polarimeters 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 High counting rate, a 2% statistical measurement in <1 min. Analyzing power ~1-2% over the carbon energy range High statistics 10 5 /ch/sec allow bunch to bunch analysis Several measurements per store. Target scans provide beam intensity and polarization profiles Carbon targets: ~10 um, difficult to fabricate, mount, and drive Analysis requires energy and timing calibration and Si dead layer correction per channel Calibrated using the H-Jet at each energy.

Setup for pC scattering – the RHIC polarimeters Ultra thin Carbon ribbon Target (3.5  g/cm 2, 5-10  m wide) beam direction Si strip detectors (ToF, E C ) 30cm all Si strips parallel to beam Beam direction Recoil carbon ions detected with Silicon strip detectors Readout by specially designed Waveform digitizers 72 channels read out channel (each channel is an “independent polarimeter”) 45 o detectors: sensitive to vertical and radial components of Pbeam and unphysical asymmetries

p-Carbon CNI RHIC E C, keV TOF, ns Typical mass reconstruction Carbon Alpha C*   Prompts Alpha Carbon Prompts M R, GeV T kin = ½ M R (dist/ToF) 2 non-relativistic kinematics 110 flattop messed spin pattern

The RHIC Polarized Hydrogen Jet Target Hyperfine states (1),(2),(3),(4) (1),(2) Pz+ : (1),(4) SFT ON (2)  (4) Pz- : (2),(3) WFT ON (1)  (3) Pz0: (1),(2),(3),(4) (SFT&WFT ON ) Hyperfine state (1),(2),(3),(4) pumps 1000 l/sec compression 106 for H Nozzle Temperature 70K Sextupoles 1.5T pole field and 2.5T/cm grad. RF transitions SFT (1.43GHz) WFT (14MHz) Holding field 1.2 kgauss  B/B = vacuum Torr jet on / Torr jet off. Molecular Hydrogen contamination 1.5% Overall nuclear polarization dilution of 3% Jet beam intensity 12.4 x H atoms /sec Jet beam polarization 92.4% +/- 1.8% Jet beam size 6.6 mm FWHM In 2006 the Jet measured the beam to jet polarization ratio to 10% per 6-hr. store.

Target polarization Correct H 2, H 2 O contamination. Divide with factor P target = 92.4%  1.8% 1 day Nuclear polarization of the atoms measured by BRP: 95.8%  0.1% Nuclear polarization Polarization cycle (+/ 0/  ) = (300/30/300) seconds No depolarization due to beam bunching observed

P target from BRP P beam by H-Jet-polarimeter Effective A N pC of RHIC pC-polarimeter Fill by fill beam polarizations for experiments A N of pp  pp 1.Confirmation of the system works well. 2.Physics motivation. Stream of offline analysis  target,  beam  beam pC H-jet polarimeter RHIC pC polarimeter

Recoil Silicon Strip Spectrometer For p-p elastic scattering only:

H. Okada et al., PLB 638 (2006), Results of A N in the CNI 100 GeV/c |r 5 | =0

A N Results at Lower RHIC Energies Set r 5 as free parameter  Im r 5 =    Im r 5 =    Re r 5 =    Re r 5 =     2 /ndf = 2.87/7   2 /ndf = 2.87/7 preliminary |r 5 |=0 0.8 M events 24 GeV/c 31 GeV/c The analyzing power vs energy seems constant ! 5 M events

2005 Polarimeters Normalization Summary  P(blue)/P(blue) = 5.9%  P(yellow)/P(yellow) = 6.2%  [P(blue) x P(yellow) ]/[P_b x P_y] = 9.4% A_N(2005) = A_N(2004) x (S +/-  A(jet stat)/A +/-  A(jet syst)/A +/-  A(pC syst)/A) A_N(05)=A_N(04)x( / / /-.005)  P/P(profile)=4.0% A_N(05)=A_N(04)x( / / /-.022)  P/P(profile)=4.1% Goal: 10% Blue Yellow

p-Crabon raw 100 GeVX-90X-45 X-average Cross asymmetry Radial asymmetry False asymmetry ~0 Good agreement btw X90 vs. X45 Regular polarimeter runs (every 2 hours) --measurements taken simultaneously with Jet -target --very stable behavior of measured asymmetries --  P = 3% per measurement (20 M events, 30 s)

H-Jet Performance at 100 GeV Run6 Blue Run6 Yellow Run5 Blue Run5 Yellow Target asymmetry in Jet-Pol T Recoil (MeV)  Jet Target Jet performance is very stable through the Years Background is small and its effect on  Jet Target is small  Beam polarization is measured reliably by Jet-Pol

pC vs HJet 2006 Fill Number

Hurdles-Monitoring and Analysis l The RHIC polarimetry comprises two separate but connected experiments and analyses requiring a significant collaborative effort and coordination. FY 04 pC polarimeter Jet Coordinator A. Bravar (BNL, Phys) Analysis O. Jinnouchi (RIKEN/RBRC) H. Okada (Kyoto) FY05Bravar AnalysisI. Nakagawa (RIKEN/RBRC)K.O. Eyser (UCR) FY06Bravar, Nakagawa Analysis S. Bazilevsky (RBRC)K. Boyle (USB) C. M. Camacho (LANL) H. Liu (LANL) Online A. Hoffman (MIT)R. Gill (BNL-Phys) Monitoring A. Dion (SBU) Zelenski & YM(BNL-CAD) FY08 Bazilevsky, B. Morozov (BNL, Phys) It takes over a year to produce the final results

Technical Hurdles-Jet Target l The molecular hydrogen fraction represents the largest uncertainty 2%. n Better handle on this measurement n Assess vs the jet profile n Effort is underway to measure in situ using beam luminescence l A better handle on backgrounds from incident beam-gas scattering as well as from the opposite beam. l Measure An vs the jet beam profile l Simultaneous measurements with both beams. n How close can we get the two beams n What is the resultant background n Acceptance issues l Improve the jet P beam measurement per fill (currently 10% in 6 hrs.) n Increase silicon t-range acceptance n Open up the holding field magnet aperture

Hurdles pC polarimeters Data handling: l Improve the silicon “effective dead layer” analysis for better stability as this directly impacts the effective analyzing power. l Decouple the Time of Flight and Energy determination l Measure the dead layer using a carbon beam from the Tandem Beam profile and polarization profile l Installed a better target drive mechanism l Improved the target mounting and positioning mechanism l New target mounts allow alternating between vertical and horizontal targets within one fill Vacuum issues with target changing Borozov: Replace the silicon strips with APDs w/ better energy resolution. A test in the AGS polarimeter is planned for this run.

Molecular Hydrogen Component l With the jet off the beam line, we measured the hydrogen component with a modified 12 mm - wide QMA which covers the full jet profile. The molecular hydrogen fraction comprised 1.5 % -> 3% nuclear dilution assuming the molecular hydrogen is unpolarized. l We repeated the measurement using an electron beam to ionize the jet beam and a magnet to analyze the outcome. This indicated a similar H2 content. But we could not reproduce the cross section that is quoted in the literature. l We are currently engaging to measure the same in situ using the proton beam luminescence and a CCD camera. We have seen the atomic hydrogen lines but not the molecular line. A spectrometer was installed this year and will attempt the same during the upcoming polarized proton run. The effort will continue as this represents the largest systematic error from the jet.

Systematics l Fill and collide bunches with different polarization states: l Measure the beam polarization on a bunch by bunch basis l Measure the Luminosity for each bunch l Measure the asymmetries for each type of bunch crossing l Reconfigure the bunch combinations by recogging the beams l Flip the beam polarization

p- 3 He Elastic Scattering (from L. Trueman) pol. p-- 3 He p—pol 3 He No Hadron helicity flip Hadron helicity flip

Looking Ahead l The polarized jet target will map the analyzing power in pp elastic scattering at various RHIC energies from 24 GeV/c (injection) to 250 Gev/c (top energy) l Replace the polarized hydrogen jet target with two unpolarized hydrogen targets. (proposed by Bravar) l Increase the jet density several fold resulting in better statistical accuracy within a fill. l With higher number of bunches planned for EIC, this represents a lower sensitivity to rate compared to carbon targets. l Recoil elastic protons traverse a significant path in the silicon compared to recoil carbon. The dead layer correction represents a minimal hurdle to the jet analysis. l Need to adjust to the more restricted bunch spacing l p-Carbon polarimeters will be needed for profile / polarization measurements l We need guidance as to what accuracy is required for EIC physics; how many sigma away or scale issues.

Summary Proton polarimetery at high energies is NOT an easy task. p-Carbon CNI polarimeters form the main stay now in the AGS and RHIC. The polarized H-Jet target provided a calibration of the polarimeters at any energy. The goal of 5% at 100 GeV was achieved should do the same at any RHIC energy. The challenge is still ahead for closer bunch spacing at eRHIC, and to reduce the H-Jet molecular Hydrogen error below 2%. We have just started (PSTP2007) to look at 3 He A workshop is planned in conjunction with SPIN 2008 When it comes to proton polarimetry at high energies: we have come a long way!! We have a long way to go if the goals set at the 1-2 % level.