First Results of Elastic Scattering of Polarized Protons at RHIC

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First Results of Elastic Scattering of Polarized
Protons at RHIC
Stephen Bültmann Brookhaven National Laboratory


For the pp2pp Collaboration
S. Bültmann, I.H. Chiang, B. Chrien, A. Drees, R.
Gill, W. Guryn, D. Lynn, C. Pearson, P. Pile,
A. Rusek, M. Sakitt, S. Tepikian Brookhaven
National Laboratory, USA J. Chwastowski, B.
Pawlik Institute of Nuclear Physics, Cracow,
Poland M. Haguenauer Ecole Polytechnique/IN2P3
-CNRS, Palaiseau, France A.A. Bogdanov, S.B.
Nurushev, M.F. Runtzo Moscow Engineering
Physics Institute (MEPHI), Moscow, Russia I.G.
Alekseev, V.P. Kanavets, B.V. Morozov, D.N.
Svirida ITEP, Moscow, Russia M. Rijssenbeek,
C. Tang, S. Yeung SUNY at Stony Brook, USA K.
De, N. Guler, J. Li, N. Öztürk University of
Texas at Arlington, USA A. Sandacz Institute
for Nuclear Studies, Warsaw, Poland

• Introduction
• Experimental Setup
• First Results from 2002 Run
• Conclusions
• Outlook (Data from 2003 Run)
• Future Plans

SPIN 2003, Seattle, August 4 - 7, 2003
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The pp2pp Experiment at RHIC
Studies the dynamics and spin dependence of the
hadronic interaction through elastic scattering
of polarized protons in unexplored cms energy
range of 50 GeV lt ?s lt 500 GeV, in the
four-momentum transfer range of 4104 GeV2 ? t
? 1.3 GeV2, covering region of
M
pp2pp

• Coulomb interaction for t lt 103 GeV2
• Measure total cross section stot and access
  imaginary part of scattering amplitude via
  optical theorem
• Hadronic interaction for
  5103 GeV2 ? t ? 1 GeV2
• Measure forward diffraction cone slope b
• First result from 2002 run
• Interference between Coulomb and
  hadronic interaction (CNI-region)
• Measure ratio of real and imaginary part of
  forward scattering amplitude r0 and extract its
  real part using measured stot

Stephen Bültmann BNL

SPIN 2003, Seattle, August 4
7, 2003
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Differential Elastic Cross Section
pp2pp 2002
Nuclear Term
Combined Term
Coulomb Term
DF Coulomb Phase
GE Proton Electric Form Factor
Interference Term
Stephen Bültmann BNL

SPIN 2003, Seattle, August 4
7, 2003
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Backup (Intro Spin Physics with pp2pp)
The helicity amplitudes describe elastic
proton-proton scattering
F1(s,t ) ? ltMgt F2(s,t ) ? ltM--gt F3(s,t
) ? lt-M-gt F4(s,t ) ? lt-M-gt F5(s,t ) ?
ltM-gt
Fn(s,t ) ? lth3 h4 Mh1 h2gt
with hx s-channel helicity
p1 -p2 incoming protons
p3 -p4 scattered
protons F(s,t ) ½ ( F1(s,t ) F3(s,t ) )
Measure
Stephen Bültmann BNL
15th Int. Spin
Physics Symposium at BNL, September 9-14, 2002
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Spin Physics with pp2pp
Single spin asymmetry AN arises in CNI region
from interference of hadronic non-flip amplitude
with electromagnetic spin-flip amplitude
Measure dependence on t to probe for
interference contribution from hadronic spin-flip
amplitude with electromagnetic amplitude
Deviation of t -dependence from calculation
would indicate presence of other interference
terms
N.H. Buttimore, B.Z. Kopeliovich, E. Leader, J.
Soffer, T.L. Trueman, The Spin Dependence of
High-Energy Proton Scattering, PRD 59, 114010
(1999)
Stephen Bültmann BNL

SPIN 2003, Seattle, August 4
7, 2003
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Spin Physics with pp2pp (2)
Measure ANN to find limit on detectable Odderon
contribution to interference between f1 and
f2 Different phases (? ½p) of Pomeron and
Odderon at t 0
for small t
f2 (0.05i 0.05) f1
E. Leader, T.L. Trueman, The Odderon and Spin
Dependence of High-Energy Proton-Proton
Scattering, PRD 61, 077504 (2000)
Stephen Bültmann BNL

SPIN 2003, Seattle, August 4
7, 2003
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Spin Physics with pp2pp (3)
o AGS Data ? CERN Data
Stephen Bültmann BNL

SPIN 2003, Seattle, August 4
7, 2003
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Birds Eye View of RHIC
Stephen Bültmann BNL

SPIN 2003, Seattle, August 4
7, 2003
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Principle of Measurement

Elastically forward scattered protons have very
small scattering angle ? Beam transport magnets
determine trajectory of beam and scattered
protons Scattered protons need to be well
separated from the beam protons Need Roman Pot
to measure scattered protons close to beam
Beam transport equations relate measured
position at detector to scattering angle
x a11 x0 Leff ?x ? Optimize so
that a11 small and Leff large ?x
a12 x0 a22 ?x ? x0 can be calculated
by measuring ?x (2nd RP)


Similar equations for y-coordinate Neglect terms
mixing x- and y-coordinate in above equations
Stephen Bültmann BNL

SPIN 2003, Seattle, August 4
7, 2003
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Backup (Beam Transport)
S. Tepikian
pp2pp RP Position
Stephen Bültmann BNL
Spin 2003,
Seattle, August 4 - 7, 2003
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pp2pp Experimental Setup
Roman Pot Station with Detectors ( used in 2002
and 2003 )
Need special tune of accelerator and detectors
approaching the proton beams closely via Roman
Pots to measure very small angles of elastically
scattered protons Two pairs of silicon microstrip
detectors measuring (x,y) coordinates with 100 mm
pitch plus one trigger scintillator per Roman
Pot One Roman Pot above and below the beam for
each Roman Pot Station
Roman Pot above beam
RP Station used in 2003
to IR
Roman Pot below beam
Inelastic Detectors Four planes of
scintillation counters on either side of
Interaction Region (IR) detecting particles from
inelastically scattered protons
Stephen Bültmann BNL

SPIN 2003, Seattle, August 4
7, 2003
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Silicon Detector Assembly
T
Silicon Wafer
Tooling Balls
Detector Package with 4 Planes (viewed from
reverse side)
Stephen Bültmann BNL

SPIN 2003, Seattle, August 4
7, 2003
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Engineering Run 2002
Conditions 14 hour run with high ß 10 m beam
tune beam momentum p 100 GeV/c 55 proton
bunches per beam beam scraped to emittance e ? 12
p 10-6 m and beam intensity I ?
51011 protons beam polarization P 0.24
(preliminary) Closest approach of first detector
strip to beam 15 mm ? 15 sbeam ? tmin
-410-3 GeV2 Collected 300,000 elastic
scattering events
Results of 2002 Data Analysis Extraction of
diffraction cone slope b Calculation of single
spin asymmetry AN
Correlation between the horizontal coordinate as
measured by the detectors on either side of the
interaction region
Stephen Bültmann BNL

SPIN 2003, Seattle, August 4
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Beam Angular Divergence
Good agreement between width of ?x and ?y
distributions for measured and simulated events
with emittance of e 12 p 10-6 m ??x
? 150 µrad ??y ? 70 µrad
??y
??x
N. Öztürk
N. Öztürk
Stephen Bültmann BNL

SPIN 2003, Seattle, August 4
7, 2003
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Elastic Hit Pattern
Hit distribution of scattered protons within
3s-correlation cut reconstructed using the
nominal beam transport Agreement between Monte
Carlo simulation and data
Stephen Bültmann BNL

SPIN 2003, Seattle, August 4
7, 2003
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t -?-Acceptance
t - ( pbeam ? ) 2 ? azimuthal angle
Find region in t - and ?-space with full
acceptance coverage and high statistics
Acceptance
Arm A
Depends on detector position
45º lt f lt 135º
Depends on beam transport element positions
N. Öztürk
Stephen Bültmann BNL

SPIN 2003, Seattle, August 4
7, 2003
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Extracting b from t -Distribution
Fit t -distribution with
4 p ( a GE 2 ) 2

C

t2



fixing stot 51.6 mb and r 0.13 and keeping b
as a free parameter in range 0.010 GeV2 ? t
? 0.019 GeV2 results in b ( 16.3 ?
1.6 ) GeV-2
Stephen Bültmann BNL

SPIN 2003, Seattle, August 4
7, 2003
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Systematic Error

• Monte Carlo simulation to evaluate contributions
  to systematic error due to
• Beam emittance
• Vertex position and spread
• Beam transport matrix elements
• Initial beam angle ( largest single source with
  Db 0.8 GeV-2 )
• Resulting systematic error Db 0.9 GeV-2
• Studied sensitivity to stot and r (
  indicating small correlation with b )
• Dstot 4mb ?
  Db ? 0.1 GeV-2
• Dr 0.02 ?
  Db ? 0.3 GeV-2

Stephen Bültmann BNL

SPIN 2003, Seattle, August 4
7, 2003
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Result Forward Cone Slope b Value
b 16.3 ? 1.6 (stat.) ? 0.9 (sys.) GeV-2
Stephen Bültmann BNL

SPIN 2003, Seattle, August 4
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Bunch Interaction Pattern
Two beams of 55 bunches each Bunches filled with
transversely polarized protons Polarization
state, up or down, was selected on Bunch-By-Bunch
basis for each beam separately
Bunch interaction patterns ?? ?? ??
?? ?0 ? ?
Crossings with empty bunches were used for
background estimates Bunch dependent inelastic
count rate can potentially be used for relative
normalization of elastic count rate in asymmetry
calculation
Stephen Bültmann BNL

SPIN 2003, Seattle, August 4
7, 2003
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Analyzing Power AN
Combine asymmetry measurements with either
polarized proton beam and double-spin asymmetry
of both beams to obtain
Use Square-Root-Formula to cancel luminosity
dependence of count rates and obtain
-
? N?? (p - f ) N?? (f )
? N?? (p - f ) N ??(f )
?N

? N?? (p - f ) N?? (f )
? N?? (p - f ) N ??(f )
Stephen Bültmann BNL

SPIN 2003, Seattle, August 4
7, 2003
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Raw Asymmetry ?N
Fit ?N / cos ? AN ( Pblue Pyellow )
0.016 0.007
Preliminary
Using preliminary estimate for measured
polarization of Pblue Pyellow 0.24
0.10 we obtain AN 0.033
0.018
Stephen Bültmann BNL

SPIN 2003, Seattle, August 4
7, 2003
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False Asymmetry ?f
Assign polarization of interacting bunches
according to a random number and treat resulting
polarization sorted count rates like the raw
asymmetry ?N Fit results in ?f / cos ?
0.000 0.007
Stephen Bültmann BNL

SPIN 2003, Seattle, August 4
7, 2003
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Conclusions

• We had a successful engineering run in 2002
• Beam was set up efficiently for pp2pp running
  conditions
• Detectors and trigger were efficient
• MC Simulation reproduces features of the data
• We made the first measurement of the forward
  slope value b 16.3 1.6 (stat.) 0.9 (sys.)
  GeV-2 at ?s 200 GeV for 0.010 GeV2 ? t ?
  0.019 GeV2
• We measured the raw asymmetry eN for
  proton-proton elastic scattering in the range
  0.010 GeV2 ? t ? 0.020 GeV2 to be eN 0.016
  0.007

Stephen Bültmann BNL

SPIN 2003, Seattle, August 4
7, 2003
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Comparison of Runs 2002 and 2003

• 2002 2003
• Proton intensity / beam 0.51012 1.91012
• Number of bunches 55 55
• Proton polarization (prelim.) 0.24 0.37
• Beam tune ß 10 m 10 m
• Beam momentum 100 GeV 100 GeV
• Number of elastic events 300,000 3 Million
• Expected statistical errors (on single data
  point)
• db 1.60 0.35
• deN 0.007 0.001
• dstot - 5 10
• Improvement of systematic error due to
• Measurement of local angle with Roman Pot station
  set added in 2003
• Improved beam optics measurement
• Van der Meer beam scans for luminosity
  measurement

Stephen Bültmann BNL

SPIN 2003, Seattle, August 4
7, 2003
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Future Running with existing Setup

• Change beam optics from ß 10 m to ß 20 m
• Increase kinematic region to lower t of 0.003
  GeV2 lt t lt 0.02 GeV2
• Measure at different beam energies in range 50
  GeV ? ?s ? 500 GeV
• Determine ?s -dependence
• Establish agreement between RHIC data and
  existing data at lower energies in region below
  ?s lt 60 GeV

Physics Goal Pomeron and
possibly Odderon contribution to spin-dependent
hadronic interaction
Achievable Goals with Expanded Experimental
Setup Beam tune of ß 100 m to reach lowest t
? Measure stot directly and
improved fit range for r Roman Pot stations
between DX and D0 magnets to reach highest t gt
1 GeV2 ? Measure AN with predicted values as
large as 0.15 if Pomeron contributes ? Confirm
previously observed sign change of AN at lower
energies
Measure AN over extended t -range and at
different energies Measure ANN (high statistics,
polarization) Measure r , stot , and b
Stephen Bültmann BNL

SPIN 2003, Seattle, August 4
7, 2003