Absolute polarimetry at RHIC 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 1.How to measure absolute beam polarization? 2.Polarized hydrogen atomic gas jet target system 3.Recoil spectrometer and analysis 4.A N results from RUN4 5.Beam polarization measurements from RUN5 6.Next step towards the best accuracy

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

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

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

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

 Beam and target are both protons, A N should be same.  P target is measured by BRP precisely. Method to get RHIC proton beam Forward scattered proton H-jet target recoil proton  Minimize systematic uncertainty by using the same system !  Checking A N, we confirm our system works properly. How precisely we know A N ?

Physics motivation: Precise A N data in CNI region Unpredictable Parameter r 5 Re r 5 = 0.02 r 5 = 0 Re r 5 =  0.02 E704, FNAL 200 GeV/c Phys. Rev. D 48, 3026 (1993) Understanding of A N before Expected to be dominant and calculable. 1st term Spin-orbit interaction from the motion of the neutron magnetic moment in the nuclear-coulomb field (Schwinger 1948)

Polarized atomic hydrogen gas jet target system Polarization Profile Thickness Stability 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! Very rapid assembly sequence by super professional team!  Wednesday 9:00~  W. Haeberli (H-jet-target system)

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

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

Target polarization Correct H 2, H 2 O contamination. Divided by factor P target = 92.4%  1.8% 1 day Nuclear polarization of the atoms measured by BRP: 95.8%  0.1% Nuclear polarization Very stable for entire run period ! Polarization cycle (+/ 0/  ) = (500/50/500) seconds

Target profile and thickness Target profile Target size in collision point FWHM = 6.5 mm Guarantee required angle resolution  ~ 5 mrad Target thickness along z-axis: (1.3  0.2 )  atoms/cm 2 Achieve designed values! Measurements were done by using 2.0 mm diameter compression tube

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

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

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

Read out electronics Three left-right pairs of Si detectors ・ 96 read-out channels ・ 96 charge-sensitive preamplifiers RHIC-ring, IP12 Recoil spectrometer Counting room 1.Signal shaping 2.Wave Form Digitizer 3.DAQ-PC 55 m twisted pair cables (category 5)

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

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

Recoil protons : |ToF cal.  ToF| < 8 nsec Blue area: |ToF cal  ToF|  8 nsec Red line:expected spectrum from ToF and T R resolutions Recoil proton identification

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

 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 (=2m p T R )  Apply background correction, R BG : 2~3% (RHIC-beam origin) Raw-asymmetry calculation of selected elastic events

A N from RUN4

Compare measured A N and expected curve with |r 5 | =0   2 /ndf = 13.4/14. Tool itself has a beautiful A N and described from first principle QED explanation at 100 GeV/c. PLB 638 (2006), A N at 100 GeV/c |r 5 | =0 Set r 5 as free parameter:   2 /ndf = 11.1/12  |r 5 | is consistent with zero at 100GeV/c ! Unpredictable Parameterized with r 5  Errors on the data points are statistics only.  Components of systematic uncertainty - Acceptance asymmetry - Acceptance asymmetry - Background correction - Background correction - Elastic event selection - Elastic event selection 3.9 M events

A N at 24 GeV/c  Compare measured A N and expected curve with |r5| =0   2 /ndf = 35.5/9.  r 5 has  s dependence ?  Not improbable in theory. 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

Contribution to theoretical understanding of A N Input: A N pC at 24GeV/c, 100GeV/c A N pp at 100GeV/c Prediction: A N at 24GeV/c -t (GeV/c) 2 ANAN Prediction by L. Trueman (BNL) A N 24GeV/c Data vs. prediction

Beam polarization results from RUN5

Yellow beam 3.7M events Blue beam 2.9M events Raw asymmetries from RUN5 Run5 statistics Yellow: 5.3 M events Blue: 4.2 M events ANAN A N  P target

Total systematic uncertainty (relative) : 2.9% Background effect : 2.1 %  Next slide Unpolarized fraction of Jet-target : 2.0 %  H 2, H 2 O contamination Source of systematic uncertainty

Upper limit of systematic uncertainty from background effects  target,  beam reflect an increase in background.  beam /  target is only weakly affected! eight strips T R (MeV) two strips 4  background Systematic uncertainty from background effects

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

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

Pol’ H-Jet on CERN COURIER Oct. 2005! courierhttp:// Thank you!

pp  pppC  pC pp  pp vs. pC  pC in RHIC-ring H-Jet polarimeterRHIC pC polarimeter TargetPolarized atomic hydrogen gas jet target Ultra thin carbon ribbon Event rate14 Hz2M Hz operationcontinuously1 minutes every ~2 hours ANAN Measured precisely  BRP gives P target  self-calibration Limited accuracy  needs calibration with H-jet polarimeter RoleAbsolute beam pol. measurement, Calibration for RHIC pC polarimeter ONLINE monitor, Fill by Fill beam polarization for experimental groups

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

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

Atomic beam intensity (1.24  0.2)  atoms/sec at 75K nozzle temperate Atomic beam velocity  2000 cm/sec FWHM 0.65cm Thickness: 1.24**10 17 /(1.56*0.65*10 5 ) Thickness ~1.2  atoms/cm 2 Holding magnet 120mT

Brief history of recoil detector set up RR Ch#1 #16 Ch#1 #16 x y z RUN2004 Spring: Commissioning run 2005, 2006 Long physics run beamBlue beam only Blue/ yellow beam alternatively -t range (GeV/c) < -t < < -t < 0.009