Transcript Polarized Proton/ Hadron Polarimetry

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
 A preamble:
Polarimeter requirements for RHIC
Candidate processes for high energy polarimeters
 “State of the art?”
 What Hurdles?
 Further improvements
 3He polarimetry
 Summary
Yousef I. Makdisi
EIC Meeting
Dec 7-8, 2007
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 A2
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.
1 NL  NR
P
A NL  NR
NL and NR 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
P 
1
A
1
NL  NR
The polarimeter figure of merit (to optimize) is A2
: is the cross section of the reaction
Candidate processes for polarimeters Vs. Energy
For transverse beam polarization

pp Elastic scattering

Inclusive Pion Production (significant asymmetry)

p-C elastic scattering in the CNI region (asymmetry few percent)

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
(12 GeV/c)
Phys. Rev. D.18 (1978) 3939-3945
AGS
(22 GeV/c)
Phys.Rev.D65:092008,2002
Fermilab
(200 GeV/c)
Phys. Lett. B261(1991)201
Phys. Lett. B264(1991)462
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)
 Weak beam momentum dependence
 The analyzing power a few percent
 High cross section
Leader, Soffer, Trueman)
The single flip hadronic amplitude
Unknown, estimated at ~15 % uncertainty
 A simple apparatus
(detect the slow recoil protons or carbon
@ ~ 900 in the lab)

PR D 48 (1993) 3026-3036
RBRC Workshop (Buttimore, Kopeliovich,
Fermilab
E704
pC concept test: first at IUCF and later at the AGS
Carbon targets to survive the RHIC beam heating
p-Carbon CNI polarimeters
1 N left  N right
PB  

AN N left  N right
0.01 < |t| < 0.02 (GeV/c)2
polarized
beam
Carbon
target
recoil
Carbon
scattered
proton
t = (pout – pin)2 < 0
 Tkin  2 MC
•High counting rate, a 2% statistical measurement in <1 min.
•Analyzing power ~1-2% over the carbon energy range
•High statistics 105/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
6
1
beam
direction
Ultra thin Carbon ribbon
Target
(3.5mg/cm2, 5-10 mm wide)
5
2
4
3
30cm
Si strip detectors
(ToF, EC)
Beam direction
all Si strips
parallel to beam
•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”)
•45o detectors: sensitive to vertical and radial components of Pbeam and
unphysical asymmetries
p-Carbon CNI RHIC
TOF, ns
Tkin= ½ MR(dist/ToF)2
Typical mass reconstruction
non-relativistic kinematics
Carbon
Prompts
Alpha
Alpha
Prompts
EC, keV
110 bunches@ flattop messed spin pattern
C*
a
Carbon
MR, GeV
The RHIC Polarized Hydrogen Jet Target
•pumps 1000 l/sec compression 106 for H
•Nozzle Temperature 70K
•Sextupoles 1.5T pole field and 2.5T/cm grad.
Hyperfine states
(1),(2),(3),(4)
•RF transitions SFT (1.43GHz) WFT (14MHz)
•Holding field 1.2 kgauss B/B = 10-3
•vacuum 10-8Torr jet on / 10-9 Torr jet off.
•Molecular Hydrogen contamination 1.5%
•Overall nuclear polarization dilution of 3%
•Jet beam intensity 12.4 x 1016 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.
(1),(2)
Pz+ : (1),(4)
SFT ON (2)(4)
Pz- : (2),(3)
WFT ON (1)(3)
Pz0:
(1),(2),(3),(4)
(SFT&WFT ON )
Target polarization
Nuclear polarization
Nuclear polarization of the
atoms measured by BRP:
95.8%  0.1%
Correct H2, H2O contamination.
Divide with factor 1.037
1 day
Polarization cycle
(+/ 0/  ) = (300/30/300) seconds
Ptarget = 92.4%  1.8%
Pt arg et
Pt arg et
 2%
No depolarization due to beam bunching observed
Stream of offline analysis
Ptarget from BRP
target , beam
Pbeam by H-Jet-polarimeter
AN of pp pp
1. Confirmation of the
system works well.
2. Physics motivation.
H-jet polarimeter
RHIC pC polarimeter
beampC
Effective ANpC of RHIC
pC-polarimeter
Fill by fill beam polarizations
for experiments
Recoil Silicon Strip Spectrometer
For p-p elastic scattering only:
N  N

N  N
 beam  AN  Pbeam
 target   AN  Ptarget
 beam
Pbeam  
 Ptarget
 target
Results of AN in the CNI region @ 100 GeV/c

A N  Im 
|r5| =0
H. Okada et al., PLB 638
(2006), 450-454
em
SF

had
NF

had*
SF

em
NF


had 2
NF
AN Results at Lower RHIC Energies
preliminary
0.8 M events
24 GeV/c
Set r5 as free parameter
 Im r5 = 0.108  0.074
 Re r5 = 0.006  0.031
2/ndf = 2.87/7
|r5|=0
5 M events
31 GeV/c
The analyzing power vs energy seems constant !
2005 Polarimeters Normalization Summary
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( 1.01 +/- .031 +/- .029 +/- .005)
Blue
P/P(profile)=4.0%
Yellow
P(blue)/P(blue) = 5.9%
A_N(05)=A_N(04)x( 1.02 +/- .028 +/- .029 +/- .022)
P/P(profile)=4.1%
P(yellow)/P(yellow) = 6.2%
[P(blue) x P(yellow) ]/[P_b x P_y] = 9.4%
Goal:
10%
p-Crabon raw asymmetry @ 100 GeV
X-90
X-45
Good agreement btw X90 vs. X45
X-average
Radial asymmetry
Cross asymmetry
False asymmetry ~0
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
Target asymmetry in Jet-Pol
JetTarget
Run6 Blue
Run6 Yellow
Run5 Blue
Run5 Yellow
TRecoil (MeV)
Jet performance is very stable through the Years
Background is small and its effect on JetTarget is small
 Beam polarization is measured reliably by Jet-Pol
pC vs HJet 2006
Fill Number
Hurdles-Monitoring and Analysis
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)
FY05
Bravar
Analysis
I. Nakagawa (RIKEN/RBRC)
K.O. Eyser (UCR)
FY06
Bravar, 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
The molecular hydrogen fraction represents the largest uncertainty 2%.
 Better handle on this measurement
 Assess vs the jet profile
 Effort is underway to measure in situ using beam luminescence
 A better handle on backgrounds from incident beam-gas scattering as well as
from the opposite beam.
 Measure An vs the jet beam profile
 Simultaneous measurements with both beams.
 How close can we get the two beams
 What is the resultant background
 Acceptance issues
 Improve the jet Pbeam measurement per fill (currently 10% in 6 hrs.)
 Increase silicon t-range acceptance
 Open up the holding field magnet aperture

Hurdles pC polarimeters
Data handling:
 Improve the silicon “effective dead layer” analysis for better stability as
this directly impacts the effective analyzing power.
 Decouple the Time of Flight and Energy determination
 Measure the dead layer using a carbon beam from the Tandem
Beam profile and polarization profile
 Installed a better target drive mechanism
 Improved the target mounting and positioning mechanism
 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
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.
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.

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

Fill and collide bunches with different polarization states:

Measure the beam polarization on a bunch by bunch basis
Measure the Luminosity for each bunch
Measure the asymmetries for each type of bunch crossing
Reconfigure the bunch combinations by recogging the beams
Flip the beam polarization




p-3He Elastic Scattering (from L. Trueman)
pol. p--3He
p—pol 3He
No Hadron helicity flip
Hadron helicity flip
Looking Ahead
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)

Replace the polarized hydrogen jet target with two unpolarized hydrogen targets. (proposed
by Bravar)
 Increase the jet density several fold resulting in better statistical accuracy within a fill.
 With higher number of bunches planned for EIC, this represents a lower sensitivity to
rate compared to carbon targets.

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.
 Need to adjust to the more restricted bunch spacing


p-Carbon polarimeters will be needed for profile / polarization measurements
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 3He
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.
BRAHMS(p)
Absolute Polarimeter (H jet) RHIC pC Polarimeters
Siberian Snakes
Spin flipper
PHENIX (p)
STAR (p)
Spin Rotators
(longitudinal polarization)
Spin Rotators
Solenoid Partial Siberian Snake (longitudinal polarization)
LINAC
Pol. H Source
200 MeV Polarimeter
BOOSTER
AGS
Helical Partial
Siberian Snake
AGS Polarimeters
Strong AGS Snake