The pp2pp Experiment at RHIC Elastic Scattering of Polarized Protons

1
The pp2pp Experiment at RHICElastic Scattering
of Polarized Protons

• Michael Rijssenbeek
• Outline
• Preliminaries the people, kinematics, and the
  experimental landscape
• The Physics of pp?pp
• The pp2pp Experiment
• Status of Data and Analysis
• Future
• Summary

Supported by BNL US Department of
Energy National Science Foundation
Nuclear Physics grant 0099686
Eastern Europe grant 0105258 Stony Brook Office
of the VP for Research.
Brookhaven DOE Review, Aug 1, 2002
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The People pp2pp Collaboration

• Total and Differential Cross Sections, and
  Polarization Effects in pp Elastic Scattering at
  RHIC

S. Bueltmann, B. Chrien, A. Drees, R. Gill, W.
Guryn, I. H. Chiang, D. Lynn, 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-CN
RS, 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, P. Yaron, S. Yeung SUNY Stony Brook,
USA K. De, N. Guler, J. Li University of Texas
at Arlington, USA A. Sandacz Institute for
Nuclear Studies, Warsaw, Poland
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Descriptive pp?pp

• Kinematics
• Dynamics
• s-Channel Helicity amplitudes fi (hi is helicity
  of proton i)
• Observables
• cross sections ?tot, ?elastic, ? ?
  Re(A)/Im(A)t0
• s difference DsT ? stot?? stot ??, DsL
• Differential cross sections ds/dt
• Transverse spin asymmetries (N(t) ? dN/dt)
• Analyzing Power
• Double-Spin Correlation parameter

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The Experimental Landscape

• Small t tlt10-3 GeV2
• Coulomb region
• Absolute prediction (direct measurement of L )
• Coulomb-Nuclear Interference (CNI) region,
  t110?3 GeV2 ? ? Re(A)/Im(A)t0 ?
  ?(s)?
• Medium t 10-3lttlt1 GeV2
• Nuclear region
• nuclear slope parameter b(s) and stot(s)
• Diffraction dip at t ? 1 GeV
• destructive interference between different
  exchange amplitudes
• Large t tgt3-6 GeV2
• Perturbative QCD elastic cross section is small
  drops ? t-8 !

PP2PP reach2002
Pomeron Physicsnon-perturbative QCD
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pp?pp Physics

• Elastic scattering (and diffraction) is still
  poorly understood
• Phenomenologically and historically all
  scattering involves exchanges in the s-channel or
  the t-channel
• All non-elastic scattering involves exchanges of
  known (virtual) particles with m2t lt0
• for 0ltlttltlts such scattering is well described
  by Reggeon exchange exchange of families of
  mesons lying on straight trajectories in a
  J(spin) vs m2t plot
• Regge the scattering amplitude A(s,t) goes as
  where ?(t) is the Regge trajectory. Thus

• for meson trajectories a0 ? 0.0-0.5
• for Elastic scattering a0 ? 1.0 such a
  physical object is unknown the
  phenomenological Pomeron
• Pomeron is unlike any other particle !

stot ? s1.01
stot
?s GeV
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pp?pp Physics (contd)

• Elastic and diffractive scattering mediated by
  the Pomeron
• QCD mediator is a system of gluons with q.n. of
  vacuum (JPC0)
• At t?5 GeV2 calculations are
  non-perturbativeElastic scattering probes the
  soft, long-distance behavior of QCD
• QCD is starting to make non-perturbative
  predictions (Lipatov, et al.) predicts
  existence of Odderon (C ?1, a0?1?e) gluonium
  exchange, in addition to Pomeron (C 1, a0?1e)
  exchange.
• Sensitivity to Odderon in CNI (r) and dip
  regions compare to ?pp !
• AN, which is sensitive to the hadronic spin-flip
  in the CNI region, constrains models of nucleon
  structure (e.g. quark-diquark models)
• ANN and AN provide spin amplitude information,
  and will constrain the different exchange
  contributions Odderon/Pomeron.
• Important to verify the t?8 drop at large t
  (perturbative prediction).
• Recent HERA (small x) and TeVatron (RapGap
  events) results A soft vs hard Pomeron?
• Low ?s Spin results (e.g. from AGS) dont fit QCD
  expectations

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Physics Range of pp2pp
TeVatron data are inconsistent!

• RHIC unexplored region in pp energy
• Highest pp energy so far?s 63 GeV (ISR)
• Next highest ?s 14 TeV (LHC)
• Compare to?pp at ?s 62.8, 540, 630, 1800 GeV
• Odderon contribution has opposite sign in?pp !
• Spin measurements are available only at low ?s ?
  24 GeV
• pp2pp s-range
• 50 ? ?s ? 500 GeV
• pp2pp t-range from Coulomb to beyond Dip
• 4104?t?1.5 GeV2

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Physics of pp2pp

• RHIC has the UNIQUE capability for colliding
  POLARIZED proton beams, further elucidating the
  exchange dynamics
• Beam energy between 25 and 250 GeV
• Transverse, Longitudinal polarization
• Polarization up to 70
• Polarization can be chosen on a bunch-by-bunch
  basis (eliminates detection systematics!)

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Physics of pp2pp (contd)

• Single Transverse Spin Asymmetry (Analyzing
  Power) AN
• Interference of hadronic non-flip amplitude with
  electromagnetic spin-flip amplitude produces
  calculable asymmetry (maximum 4 at t 0.003
  GeV2)
• Option for RHIC polarimetry

FNAL E704 data (1993)
pp2pp simulation (2003)(C. Tang, Thesis
SUSB,2001)
Projectedpp2pp 2002
N.H. Buttimore, B.Z. Kopeliovich, E. Leader, J.
Soffer, T.L. Trueman, The Spin Dependence of
High-Energy Proton Scattering, PR D59 114010
(1999)

• Measure the Pomeron spin-flip amplitude
• hadronic spin-flip amplitude accounts for
  schannel helicity non-conservation at high
  energy helicity-flip term of Pomeron can
  indicate
• isoscalar anomalous magnetic moment of nucleon
• helicity non-conservation in constituent
  quarkgluon vertex
• diquarkquark structure of nucleon

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Physics of pp2pp (contd)

• Double Transverse Spin Asymmetry ANN
• Search for the Odderon
• Different (??/2) phases of Pomeron and Odderon
  at t0 Enhanced Odderon contribution to ANN due
  to interference with one-photon
  exchangeCharacteristic peak near t 0.002
  GeV2

E. Leader, T.L. Trueman, The Odderon and Spin
Dependence of High-Energy Proton-Proton
Scattering, PR D61 077504 (2000)
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Physics of pp2pp (contd)

• dip region several dominant exchange amplitudes
• Study dynamics of diffractive pp scattering P,
  PP, ggg
• Single spin asymmetry AN especially interesting
  in dip regionprevious measurements
• appearance of negative AN asymmetry near t 1
  GeV2 at Ös ?10 GeV
• slow variation in 10 ? Ös ? 24 GeV range
• Compare pp with?pp, e.g.

Model from A. Donnachie, P.V. Landshoff , NP
B231 (1984) 189. (see C.
Tang, Thesis SUSB 2001)
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The pp2pp Detectors

24 Scintillation Counter planes 2.5???5.5
z
x
Roman PotStation 1
LinearSlide
Station 2 (uninstrumented)
Vacuum
Bellows
UHVChamber
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Roman Pot Si Detector Package

• 4 planes of 400 µm Silicon microstrip detectors
  (BNL Instrum. Div.)
• 2 X- and 2 Y-detectors 4.5 x 7.5 cm2
• Closest proximity to the beam 1.4 mm
• 8 mm trigger scintillator, 2 PMT readout

Al strips 512 (Y), 768 (X), 70µm wide100 µm
pitch
implanted resistors
Trigger Scintillator
1st strip?edge 490 µm
guard ring
bias ring
SVX2E (DØ)(and DØ Readout Controller)
Silicon Sensor (backside)
Tooling Balls
Si Detector Package
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January 2002 Run

• Engineering run January 2002
• pbeam 100 GeV/c
• 1 Roman pot station in per arm, inelastic
  detector around Interaction Point (IP)
• Pots at 57 m from IP, Leff,y 23 m
• Kinematics range 0.005 lt t lt 0.02 GeV2
• Run
• 4 hours commissioning on 1/19/02
• 14 hours of data on 1/24/02
• excellent beam quality emittance 10p?mm?mrad
  after scraping
• Estimated Polarization 25
• 100 efficient data taking
• Collected 974k events (30 elastic triggers)
• Data will primarily be used to study detector
  performance and to prepare for data run in 2003
• High quality of data will yield publishable
  physics !

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Data Analysis

• We are analyzing the 2002 data
• Calibration
• Precision survey of detector
• Calibration of Si channels (pedestals/gain) to
  optimize hit recognition
• Determine trigger efficiency
• Determine Si efficiency in x and y planes using
  elastics
• Acceptance calculation
• Data detector fiducial regions with high
  acceptance
• Simulations analytical, Geant using measured
  transport matrix
• Background determination
• Select events using cuts in corrected
  collinearity distribution
• Calculate beam halo, diffractive, and random
  backgrounds
• Determine differential dN/dt as a function of t
  and extract nuclear slope b and possibly AN

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Hit Patterns

• Raw Detector X-Y hit positions (no alignment
  applied)100k triggerstight elastics (1 hit
  in each plane)

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Hit Correlations

• Arm-Arm Correlations

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Plans

• 2003
• 2 More stations
• ?s 200 GeV
• Extend to smaller t 10?3 ? t ? 0.02 GeV2
• stot, selastic, b, AN, ANN
• More statistics!
• 2004-2005
• ?s 500 GeV
• Small t 410?4 ? t ? 0.13 GeV2
• stot , selastic, r, b, AN, ANN, and absolute L !
• Large t 0.1 ? t ? 1.3 GeV2
• Dip region and its spin dependence

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Summary

• pp2pp will measure spin-dependent elastic
  proton-proton scattering in a new kinematic
  region RHIC Spin is UNIQUE Facility for
  this!
• pp2pp probes the Pomeron (Odderon)
• Large distance QCD
• Transition to pQCD
• First engineering run successful
• Working on 2002 physics results nuclear slope,
  AN(N)
• Next (2003-2005) finish building experiment and
  complete physics program
• UNIQUE opportunities at RHIC for pp?pp over the
  next few years