Spin 2004

1
Spin Dependence in Elastic Scatteringin the CNI
Region pp pp pC pC

• A. Bravar, I. Alekseev, G. Bunce, S. Dhawan, R.
  Gill,
• H. Huang, W. Haeberli, G. Igo, O. Jinnouchi, A.
  Khodinov,
• K. Kurita, Z. Li, Y. Makdisi, A. Nass, H. Okada,
  S. Rescia,
• N. Saito, H. Spinka, E. Stephenson, D. Svirida,
  D. Underwood,
• C. Whitten, T. Wise, J. Wood, A. Zelenski

2
The Elastic Process Kinematics
scattered proton
(polarized) proton beam
RHIC beams internal targets º fixed target
mode Ö s 14 GeV
polarized proton target or Carbon target
recoil proton or Carbon
essentially 1 free parameter momentum transfer
t (p3 p1)2 (p4 p2)2 lt0 center of mass
energy s (p1 p2)2 (p3 p4)2 azimuthal
angle j if polarized ! Þ elastic pp kinematics
fully constrained by recoil proton only !
3
Helicity Amplitudes for spin ½ ½ ½ ½
Scattering process described in terms of Helicity
Amplitudes fi All dynamics contained in the
Scattering Matrix M (Spin) Cross Sections
expressed in terms of
spin nonflip double spin flip spin
nonflip double spin flip single spin flip
observables 3 -sections 5 spin asymmetries
identical spin ½ particles
formalism well developed, however not much data
! only AN studied / measured to some extent
4
The Very Low t Region
around t -10-3 (GeV/c)2 Ahadronic
ACoulomb Þ INTERFERENCE CNI Coulomb Nuclear
Interference

• scattering amplitudes modified to include also
  electromagnetic contribution
• hadronic interaction described in terms of
  Pomeron (Reggeon) exchange
• electromagnetic single photon exchange
• s Ahadronic ACoulomb2
• unpolarized Þ clearly visible in the cross
  section ds/dt charge
• polarized Þ left right asymmetry
  AN magnetic moment

g

P
5
AN Coulomb Nuclear Interference
the left right scattering asymmetry AN arises
from the interference of the spin non-flip
amplitude with the spin flip amplitude
(Schwinger) in absence of hadronic spin
flip contributions AN is exactly calculable
(Kopeliovich Lapidus) hadronic spin- flip
modifies the QED predictions interpreted in
terms of Pomeron spin flip
and parametrized as
µ(m-1)p µspphad
AN (t)
6
can be traced back to
7
Some AN measurements in the CNI region
pC Analyzing Power
E950_at_BNL p 21.7 GeV/c PRL89(02)052302
pp Analyzing Power

E704_at_FNAL p 200 GeV/c PRD48(93)3026
no hadronic spin-flip
with hadonic spin-flip
AN()
no hadronic spin-flip
r5pC µ Fshad / Im F0had Re r5 0.088
0.058 Im r5 -0.161 0.226 highly
anti-correlated
-t
8
RHIC pp accelerator complex
RHIC pC CNI polarimeters

absolute pH polarimeter
BRAHMS PP2PP
PHOBOS
RHIC
PHENIX
Siberian Snakes
STAR
Siberian Snakes
Spin Rotators
5 Snake
LINAC
BOOSTER
AGS quasi-elastic polarimeter
AGS
Pol. Proton Source
AGS pC CNI polarimeter
200 MeV polarimeter
Rf Dipoles
20 Snake
9
Polarimetry Impact on RHIC Spin Physics
Single Spin Asymmetries
Physics Asymmetries
recoil
Double Spin Asymmetries
measurements

• measured spin asymmetries normalized by PB to
  extract Physics Spin Observables
• RHIC Spin Program requires DPbeam / Pbeam 0.05
• normalization Þ scale uncertainty
• polarimetric process with large s and known AN
• pC elastic scattering in CNI region, AN 1 2
• fast measurements
• requires absolute calibration polarized gas jet
  target

10
The Road to Pbeam with the JET target

• Requires several independent measurements
• 0 JET target polarization Ptarget (Breit-Rabi
  polarimeter)
• 1 AN for elastic pp in CNI region AN - 1 /
  Ptarget eN
• 2 Pbeam 1 / AN eN
• 1 2 can be combined in a single measurement
  Pbeam / Ptarget - eN / eN
• self calibration works for elastic scattering
  only
• 3 CALIBRATION ANpC for pC CNI polarimeter in
  covered kinematical range
• ANpC 1 / Pbeam eN
• (1 ) 2 3 measured simultaneously with several
  insertions of carbon target
• 4 BEAM POLARIZATION Pbeam 1 / ANpC eN to
  experiments
• at each step pick-up some measurement errors

expected precision
transfer calibration measurement
11
pp p p
12
pp pp and pp pp with a Polarized Gas Jet
Target
polarized gas JET target

RHIC polarized proton beams
13
The Atomic H Beam Source
H2 dissociator
H p e-
separation magnets (sextupoles)

RF transitions
focusing magnets (sextupoles)
OR
Pz OR Pz-
recoil detectors
record beam intensity 100 eff. RF
transitions focusing high intensity B-R
polarimeter
Breit-Rabi polarimeter
holding field magnet
14
JET target polarization performance

• the JET ran with an average intensity of 11017
  atoms / sec
• the JET thickness of 1 1012 atoms/cm2
  record intensity
• target polarization cycle
• /0/- 500 / 50 / 500 sec
• polarization to be scaled down due to a 3 H2
  background
• Ptarget 0.924 0.018
• (current understanding)
• no depolarization from beam
• wake fields observed !

minus polarization
0.94 0.96 0.98 pol.
plus polarization
time
2.5 h
15
The Polarized Jet Target under development
Electronics racks
Dissociator stage
Baffle location
Vac. gauges monitors
Sextupoles 1-4
Turbo pump controllers
Sextupoles 5-6
Dissociator RF systems
Profile measurement
BRP vacuum vessel
Target chamber beam pipe adapters
Recoil spectrometer silicon detectors
16
Recoil Si spectrometer
ANbeam (t ) - ANtarget (t ) for elastic
scattering only! Pbeam - Ptarget . eNbeam /
eNtarget
6 Si detectors covering the blue beam gt MEASURE
energy (res. lt 50 keV) time of
flight (res. lt 2 ns) scattering angle (res.
5 mrad) of recoil protons from pp pp elastic
scattering

• HAVE design
• azimuthal coverage
• one Si layer only
• smaller energy range
• reduced bkg rejection power

17
Jet-Target Holding Magnetic Field (1.0)
Helmholtz coils

almost no effect on recoil proton
trajectories left right hit profiles left
right acceptances almost equal (also under
reversal of holding field)
18
pp elastic data collected
ToF vs EREC correlation Tkin ½ MR(dist/ToF)2
recoil protons elastic pp ?pp scattering
JET Profile measured selecting pp elastic events
FWHM 6 mm as designed
D ToF lt 8 ns
background 118 cts. subtracted
Number of elastic pp events
CNI peak AN 1 lt E REC lt 2 MeV
? source calibration
Hor. pos. of Jet 10000 cts. 2.5 mm
prompt events and beam-gas

• recoil protons unambiguously identified !
• 100 GeV 1.8 106 events for 1.5 103 lt -t lt
  1.0 102 GeV2
• similar statistics for 1.0 102 lt -t lt 3.0
  102 GeV2
• 24 GeV 300 k events

19
Energy - Position correlations
Tkin µ q2 (i.e. position2)

fully absorbed protons
punch through recoil protons
recoil energy
punch through protons
position
pp elastic events clearly identified !
TDC vs ADC individual channels
20
Missing Mass MX2 _at_ 100 GeV
Mp2
not corrected for the magnetic field
simulations
M2X distribution 80 cm from target convoluted
with spectrometer Resolution DM2X 0.1 GeV2
FWHM 0.1 GeV2
number of events (a. u.)
DM2X
inelastic threshold
M2X (GeV2)
proton
MX2 GeV2
21
AN for pp pp _at_ 100 GeV
preliminary
statistical errors only
source of systematic errors 1 D PTARGET 2
(normalization error) 2 from backgrounds lt
0.0015 3 false asymmetries small
22
AN for pp pp _at_ 100 GeV
data (from this expt. only) fitted with CNI
prediction sTOT 38.5 mbarn, r 0, d
0 fitted with N f CNI N
normalization factor N 0.98 0.03 c2 5 / 7
d.o.f. the errors shown are statistical
only (see previous slide)
no hadronic spin-flip
preliminary
data in this t region being analyzed
no need of a hadronic spin flip contribution to
describe these data however, sensitivity on f5had
in this t range low
23
ONLINE measured asymmetries Results
ONLINE º statistical errors only no
background corrections no dead layer
corrections no systematic studies no false
asymmetries studies no run selection
data divided into 3 p energy energy bins
an example 750 lt EREC lt 1750 keV
Target average over beam polarization Beam
average over target polarization
work in progress !
blue beam with alternating bunch polarizations
?? ?? ?? good uniformity from run to
run (stable JET polarization) JET polarization
reversed each 5 min.
1 run 1 hour

• á Pbeam ñ 37 2
• á Pbeam (pC CNI) ñ 38
• No major surprises ?
• (statistical errors only !)

24
pC p C
25
Setup for pC scattering the RHIC polarimeters
beam direction
inside RHIC ring _at_IP12
Ultra thin Carbon ribbon Target (3.5mg/cm2 ,10mm)
1
6
5
2
Si strip detectors (ToF, EC)
3
4
30cm
RHIC 2 rings

• recoil carbon ions detected with Silicon strip
  detectors
• 2 72 channels read out with WFD (increased
  acceptance by 2)
• very large statistics per measurement ( 20 106
  events) allows detailed analysis
• bunch by bunch analysis
• channel by channel (each channel is an
  independent polarimeter)
• 45o detectors sensitive to vertical and radial
  components of Pbeam
• unphysical asymmetries

26
Event Selection Performance

• - very clean data, background lt 1 within
  banana cut
• - good separation of recoil carbon from a (C a
  X) and prompts
• may allow going to very high t values
• D (Tof) lt 10 ns (Þ sM 1 GeV)
• very high rate 105 ev / ch / sec

27
AN pC pC at 3.9, 6.5, 9.7 21.7 GeV
(AGS)
momentum transfer t (GeV2/c2)
only statistical errors are shown normalization
errors 10 (at 3.9) 15 (at 6.5)
20 (at 21.7) systematic errors lt 20
- backgrounds - pileup - RF noise
CNI peak 4
p 3.9 GeV
AN ()

preliminary 2003 2004 data
áPBñ 73
p 6.5 GeV
áPBñ 65
p 9.7 GeV
áPBñ 60
p 21.7 GeV
áPBñ 47
statistical errors only
recoil Carbon energy (keV)
28
AN pC pC Energy Dependence
only statistical errors are shown systematic
errors as for previous slide
t - 0.01 GeV2 t - 0.02 GeV2 t - 0.03 GeV2
t - 0.04 GeV2
AN ()
preliminary 2003 2004 data
Asymptotic regime
E ?
No energy dependence ?
statistical errors only
Beam Energy (GeV)
29
Raw asymmetry (t) _at_ 100 GeV (RHIC)
Regular calibration measurements
good agreement btw X90 vs. X45
Radial asymmetry
Cross asymmetry
preliminary
0.02
0.03
0.04
False asymmetry 0
-t (GeV/c)2
0.02
0.01
-t (GeV/c)2

• Polarimeter dedicated runs (high -t)
• Signal attenuation (x1/2) to reach higher t
• Normalized at overlap region to regular runs
• Zero crossing measured with large significance

• Regular polarimeter runs
• measurements taken simultaneously with Jet
  -target
• very stable behavior of measured asymmetries

30
pC Systematics
each detector channel covers same t range 72
independent measurements of AN
width stat. error single meas.
channel by channel raw asymmetry
Fit with sine function (phase fixed)
sources of systematic uncertainties 1 D PBEAM
7.8 (normalization) PBEAM 0.386 0.030,
stat. error 2 energy scale 50 keV for lowest
t bin (from detector
dead layer) NB these are external
factors not intrinsic limitations
31
AN for pC pC _at_ 100 GeV
r5pC µ Fshad / Im F0had
statistical errors only
1 s contour
preliminary
no hadronic spin-flip
spread of r5 values from syst. uncertainties
with hadronic spin-flip
best fit with hadronic spin-flip Kopeliovich
Truemann model PRD64 (01) 034004 hep-ph/0305085
systematic uncertainty
forbidden asymmetries
32
Summary

• measured ANpp for elastic pp pp scattering at
  100 GeV with very high accuracy (statistical and
  systematic)
• t range 0.0015 lt t lt 0.010 (GeV/c)2
• soon AN in t range of 0.010 lt t lt 0.030
  (GeV/c)2
• soon ANN in same t range (stat. err. 2.5
  larger)
• pp data well described by CNI QED predictions
  (S LK)
• no need for a hadronic spin-flip term
• measured ANpC for elastic pC pC scattering at
  100 GeV (RHIC)
• zero crossing around t 0.03 (GeV/c)2
• pC data require substantial hadronic spin-flip !
• measured ANpC for pC pC scattering over 3.5 lt
  Eb lt 24 GeV (AGS)
• Eb lt 10 GeV/c almost no t dependence departure
  from CNI shape