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Absolute polarimetry at RHIC

Absolute polarimetry at RHIC. How to measure absolute beam polarization? Polarized hydrogen atomic gas jet target system Recoil spectrometer and analysis A N results from RUN4 Beam polarization measurements from RUN5 Next step towards the best accuracy. Hiromi Okada (BNL)

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Absolute polarimetry at RHIC

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  1. Absolute polarimetry at RHIC • How to measure absolute beam polarization? • Polarized hydrogen atomic gas jet target system • Recoil spectrometer and analysis • AN results from RUN4 • Beam polarization measurements from RUN5 • Next step towards the best accuracy Hiromi Okada (BNL) I. Alekseev, A. Bravar, G. Bunce, S. Dhawan, O. Eyser, R. Gill, W. Haeberli, O. Jinnouchi, A. Khodinov, K. Kurita, Z. Li, Y. Makdisi, I. Nakagawa, A. Nass, S. Rescia, N. Saito, E. Stephenson, D. Svirida, T. Wise, A. Zelenski

  2. How to measure beam polarization ? : raw asymmetry AN: analyzing power RHIC Spin Program requires Our mission  achieve 5% measurement Statistical issue

  3. How to choose an ideal interaction for polarimeter ? A • Non-zero AN • large cross section • Common detector set up for different beam momentum. • Injection 24GeV/c, flattop 100GeV/c ~ 250GeV/c Elastic scattering process pA pA in very small -t region. Our case: A is proton or Carbon. Polarized Proton beam • In the region of -t ~ 10-3 (GeV/c)2, Coulomb interaction and Nuclear interaction become same size and Interfere each other (CNI). AN is expected to be large!

  4. H-Jet polarimeter pp pp AGS pC polarimeter pC pC RHIC pC polarimeter pC pC Beam AGS and RHIC polarimeter complex IP12 • ONLINE monitor, • Fill by Fill beam polarization (OFFLINE). • Calibration for RHIC pC polarimeter (OFFLINE) • Wednesday 15:40~ • Y. Makdisi

  5. Road to fill by fill Pbeam (OFFLINE) Ptarget from BRP target , beam H-jet polarimeter RHIC pC polarimeter • Details of pC pol. are … • Today 16:00 ~ • A. Bazilevsky • B. Morozov • Thursday 9:00~ • I. Nakagawa <Pbeam> from H-Jet-polarimeter beampC • AN of pp pp • Physics motivation. • Confirmation of the system works well. Effective ANpC of RHIC pC-polarimeter Fill by fill beam polarizations for experiments

  6. Method to get <Pbeam> Forward scattered proton RHIC proton beam • Beam and target are both protons, AN should be same. • Ptarget is measured by BRP precisely. H-jet target recoil proton • Minimize systematic uncertainty by using the same system ! • Checking AN, we confirm our system works properly. How precisely we know AN?

  7. Understanding of AN before 2004 Physics motivation: Precise AN data in CNI region • Unpredictable • Parameter r5 Expected to be dominant and calculable. E704, FNAL 200 GeV/c Phys. Rev. D 48, 3026 (1993) Spin-orbit interaction from the motion of the neutron magnetic moment in the nuclear-coulomb field (Schwinger 1948) Re r5= 0.02 r5= 0 Re r5= 0.02 1st term 0.001 0.001

  8. Polarized atomic hydrogen gas jet target system (H-jet-target system) • Brief history • April 2002 • Atomic Beam Source trajectory calculation completed. Magnets ordered. • January 2002 • Wisconsin Univ. and BNL design details. • January 2003 • Chambers for Jet ordered. • March 2004 • H-jet system installed and completed commissioning run successfully! • Very stable 2005, 2006 long runs! • Polarization • Profile • Thickness • Stability • Very rapid assembly sequence by super professional team! • Wednesday 9:00~ • W. Haeberli

  9. target H-jet-target system • Height: 3.5 m • Weight: 3000 kg • Entire system moves along x-axis 10 ~ +10 mm to adjust collision point with RHIC beam. Recoil proton RHIC proton beam IP12

  10. H-jet-target system |1> |2> H = p++e |1> |2> |3> |4> Hyper fine structure H2 desociater Separating Magnet (Sextuples) Atomic Beam Source RF transitions (WFT or SFT) P+ OR P Scattering chamber Holding magnet |1> |3> |2> |4> Breit-Rabi Polarimeter Separating magnet 2nd RF-transitions for calibration |1> |2> Ion gauge Ion gauge

  11. Target polarization Nuclear polarization of the atoms measured by BRP: 95.8%  0.1% Nuclear polarization Correct H2, H2O contamination. Divided by factor 1.037 1 day Ptarget = 92.4%  1.8% Polarization cycle (+/ 0/  ) = (500/50/500) seconds Very stable for entire run period !

  12. Target profile and thickness Target profile • Target size in collision pointFWHM = 6.5 mm • Guarantee required angle resolution  ~ 5 mrad • Target thickness along z-axis: (1.3  0.2 )1012 atoms/cm2 Achieve designed values! Measurements were done by using 2.0 mm diameter compression tube

  13. Recoil detector can detect H-Jet-target ! Using 2.0 mm diameter compression tube Using RHIC-beam and Recoil detector • Fix RHIC proton beam position (diameter  ~1mm). • Move H-Jet-target system for every 1.5 mm step. Find the best collision point !

  14. Recoil detector set up • Analysis • 1. Recoil proton kinetic energy correction • 2. Elastic event selection • Raw asymmetry

  15. H-jet target Si detectors (8cm  5cm)3 L-R sides Strip runs along RHIC beam axis 1ch width = 4mm (400strips) recoil proton L = 0.8 m RHIC proton beam Channel # relates to recoil angle R,5 mrad pitch. Each channel measures kinetic energyTRand TOF. IP12

  16. Read out electronics Three left-right pairs of Si detectors ・ 96 read-out channels ・ 96 charge-sensitive preamplifiers RHIC-ring, IP12Recoil spectrometer • Signal shaping • Wave Form Digitizer • DAQ-PC Counting room 55 m twisted pair cables (category 5)

  17. Ch#14 Ch#3 Ch#4 Ch#6 Ch#15 Ch#9 Ch#7 Ch#8 Ch#10 Ch#13 Ch#16 Ch#5 Ch#11,12 Ch#2 Ch#1 Ch#1-16 • source for energy calibration • 241Am(5.486 MeV) R How to identify elastic events ? Ch#  R, R big  TR big  fast protons Forward scattered proton proton beam proton target recoil proton #16 Ch#1 Array of Si detectors measures TR & ToF of recoil particles. Channel # corresponds to recoil angle R. 2 correlations (TR & ToF ) and (TR & R )  the elastic process

  18. Recoil proton kinetic energy corrections • -t = 2mpTR • Measured deposit energy = kinetic energy ; 1< TR <7 MeV • Energy loss correction in “the entrance-window” for low energy recoil protons: TR < 1 MeV. • Punch through correction for high energy recoil protons: TR > 7 MeV. Recoil protons SiO2 Al electrode Entrance-window p+ Fiducial Volume Full deposit n Al anode Punch-through

  19. Recoil proton identification Recoil protons : |ToFcal. ToF| < 8 nsec Blue area: |ToFcalToF| 8 nsec Red line:expected spectrum from ToF and TR resolutions

  20. Inelastic threshold Forward scattered proton identification Select proper 2 ~3 channels for each TR bin. Blue area: ”selected” channels Red line: Expected spectrum from TRand R resolutions Channel#

  21. Raw-asymmetry calculation of selected elastic events • Calculation is done using square-root formula • target :Based on H-Jet target polarization sign. (sign changes every 500 seconds) • beam :Based on beam polarization sign. (sign changes every bunch) • Sort with -t (=2mpTR) • Apply background correction, RBG: 2~3% (RHIC-beam origin)

  22. AN from RUN4

  23. AN at 100 GeV/c 3.9 M events Unpredictable Parameterized with r5 • Errors on the data points are statistics only. • Components of systematic uncertainty • - Acceptance asymmetry • - Background correction • - Elastic event selection |r5| =0 • Set r5 as free parameter: •  2/ndf = 11.1/12 •  |r5| is consistent with zero at 100GeV/c ! PLB 638 (2006), 450-454 • Compare measured AN and expected curve with |r5| =0  2/ndf = 13.4/14. • Tool itself has a beautiful AN and described from first principle QED explanation at 100 GeV/c.

  24. AN at 24 GeV/c preliminary 0.8 M events Set r5 as free parameter  Im r5 = 0.108  0.074  Re r5 = 0.006  0.031 2/ndf = 2.87/7 |r5|=0 • Compare measured AN and expected curve with |r5| =0  2/ndf = 35.5/9. • r5 has s dependence ?  Not improbable in theory.

  25. Contribution to theoretical understanding of AN Prediction: AN at 24GeV/c Input: ANpC at 24GeV/c, 100GeV/c ANpp at 100GeV/c AN 24GeV/c Data vs. prediction AN Prediction by L. Trueman (BNL) -t (GeV/c)2

  26. Beam polarization results from RUN5

  27. Raw asymmetries from RUN5 Blue beam 2.9M events Yellow beam 3.7M events AN ANPtarget Run5 statistics Yellow: 5.3 M events Blue: 4.2 M events

  28. Source of systematic uncertainty • Total systematic uncertainty (relative) : 2.9% • Background effect : 2.1 % •  Next slide • Unpolarized fraction of Jet-target : 2.0 % •  H2, H2O contamination

  29. Upper limit of systematic uncertainty from background effects two strips eight strips 4  background target, beamreflect anincrease in background. beam / target is onlyweakly affected! Systematic uncertainty from background effects TR (MeV)

  30. RUN5 Absolute beam polarization at 100GeV/c P(target) = 92.4%  1.8% stat. sys. P(blue beam) = 49.3%  1.5%  1.4% P(yellow beam)= 44.3%  1.3%  1.3% Achieve goal !!

  31. Next step towards the best accuracy • More data in RUN6 ! • Yellow: 10.7 M events, Blue 8.2 M events (100GeV/c). • Expected statistical uncertainty is about 1%. • Remaining systematic uncertainty is unpolarized fraction of H-Jet target. • Currently 2% • Improvement is ongoing….. Sunrise at Montauk

  32. Pol’ H-Jet on CERN COURIEROct. 2005! courierhttp://www.cerncourier.com/main/article/45/8/15 Thank you!

  33. pppp vs. pCpC in RHIC-ring

  34. Stopping power Stopping power of  particle in silicon (dE/dx) Hamamatsu-type: d1=2.69  0.06 m, d2=1.79  0.06 m BNL-type: < 0.2 m

  35. two peak spectrum • Calibration  sources; 241Am (EAm =5.486 MeV), 148Gd (EGd = 3.183 MeV) Hamamatsu-type E~0.06 keV BNL-type Am1 or Gd1 Am2 or Gd2 E~0.06 keV d1,d2 Hamamatsu-type

  36. Atomic beam intensity (1.24 0.2)1017 atoms/sec at 75K nozzle temperate Atomic beam velocity 1560002000 cm/sec FWHM 0.65cm Thickness ~1.21012 atoms/cm2 Holding magnet 120mT

  37. Brief history of recoil detector set up R #16 y #16 Ch#1 z x Ch#1

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