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
  landscape
• The Physics of pp?pp
• The Physics of pp2pp
• The pp2pp Experiment
• Status of Data and Analysis
• Future
• Summary

Support by BNL - Department of Energy National
Science Foundation Nuclear Physics grant
0099686 Eastern Europe grant 0105258 Stony Brook
Office of the VP for Research.
Stony Brook, April 22, 2002
2
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
• Total cross section difference Dstot ? stot??
  stot ??
• Differential cross sections ds/dt
• Transverse spin asymmetries (N(t) ? dN/dt)
• AN (Analyzing Power)
• ANN (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,
  t10?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 steeply!

Pomeron Physicsnon-perturbative QCD
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pp?pp Physics

• Elastic scattering (and diffraction) is 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

? trajectory

• for meson trajectories a0 ? 0.0-0.5
• for Elastic scattering a0 ? 1.0 such an 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
  bythe Pomeron
• QCD mediator is a system of gluons with q.n. of
  vacuum (JPC0)At small t?5 GeV2
  calculations are non-perturbative next to
  impossible. Elastic 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 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 indicate trouble with the
  (soft) Pomeron
• Low ?s Spin results (e.g. from AGS) dont fit QCD
  expectations

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pp?pp Physics (contd)

• dip region is determined by the dominant exchange
  amplitudes

Model from A. Donnachie, P.V. Landshoff NP
B231 (1984) 189 (see C. Tang, Thesis SUSB 2001)
Dominant at t1 GeV2 ggg, P, PP
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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
• Expected spin effects

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Spin Physics

• In general spin is sensitive to the mechanism of
  exchange.
• CNI REGION, -t (0.001 0.01) GeV2 ? SINGLE
  SPIN ASYMMETRY EXPECTATION
• leading term of small t AN?d?/dt?2Im ??5
• Interference of hadronic non-flip amplitude with
  electromagnetic spin-flip amplitude produces
  asymmetry (4 5)? in the maximum at ?t?
  0.003 GeV2. This yield to AN is calculable.
• ?
• Base for RHIC polarimetry

FNAL E704 data (1993)
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)
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Spin Physics (cont.)

• SEARCH for spin-flip of Pomeron.
• AN in CNI region is sensitive to hadronic
  spin-flip amplitude due to its interference with
  non-flip electromagnetic amplitude. This term
  (including its phase) may be extracted from
  measured AN (t).
• hadronic spin-flip amplitude accounts for s
  channel helicity noncoservation at high energies.
  helicity-flip term of Pomeron can indicate
• isoscalar anomalous magnetic moment of nucleon
• helicity nonconservation in constituent quark
  gluon vertex
• compact quark pair in proton (diquark quark
  structure).

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Spin physics (cont.)

• DOUBLE TRANSVERSE SPIN ASYMMETRY
• Leading term at small t ANN?d?/dt?2Re ??2
• SEARCH for Odderon.
• ?
• Different (??/2) phases of Pomeron and Odderon
  at t0
• ?
• Enhancement of Odderon contribution to ANN due to
  interference with electromagnetic amplitude
• ?
• Characteristic 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)
f2/f0.05(1i)
f2/f0.05
f2/f0.05i
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TOTAL CROSS SECTION DIFFERENCE

• for transverse polarization ??T (s) ?tot ????
  ? ?tot ????.
• MEDIUM 0.1 ? ?t? ? 1.3 GeV2 REGION
• ?
• Study dynamics of diffractive pp scattering
• Single spin asymmetry AN especially interesting
  in dip region
• From previous measurements
• appearence of negative AN asymmetry near t 1
  GeV2 at Ö-s ?10 GeV
• slow variation in 10 ? Ö-s ? 24 GeV range
• Double spin asymmetry ANN
• ?
• Measurement of differences between spin parallel
  and antiparallel crossections in the whole
  region.
• LARGE ?t? ? 3 GeV2 REGION
• ?
• Test pQCD
• Two gluon (hard Pomeron) and three gluons
  (Odderon) exchanges with point-like quark-gluon
  interaction.
• Small d?/dt with t-8 dependence.

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Physics of pp2pp (contd)

• Double Transverse Spin Asymmetry
  ANNEnhancement of the odderon
  contribution to ANN(t) due to interference with
  one-photon exchange.

f2/f0.05(1i)
f2/f0.05
f2/f0.05 i
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)

• Single Transverse Spin Asymmetry (Analyzing
  Power) AN

pp2pp simulation(C. Tang, Thesis SUSB,2001)
FNAL E704 data (1993)
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)
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Physics of pp2pp(contd)
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 Dip
• 4104?t?1.5 GeV2

PP2PP
50
500
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Additional Physics with pp2pp

• With the same experimental setup
• Single and Double Diffractive physics
• Use other light ions e.g. p?d, p?a
• increase t-range into perturbative QCD region
• t ? 3 GeV2
• Needs additional tracking instrumentation near IP

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The RHIC-Spin Collider

• The RHIC Spin complex

e 10 ? mm mrad with scraping
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The pp2pp Detectors

• Location of small-angle detectors (Roman
  Pots)
• Roman Pot detector package

pp2pp Elastic and Inelastic detectors (January
2002)
24 Scintillation Counter planes 2.5???5.5
to Readout and DAQ
Roman Pot
P
P
Trigger Counters Silicon Detectors
SVX Electronics
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Experimental Technique

• independence of vertex position
• parallel-to-point focussing ydet a11y ?
  a12?ywith a11 ?(?/?) cosy? ?siny
  a12 Leff,y ?(??) siny ( at
  interaction point)optimum a110, Leff large
  sit at y(z) (n ? ½)?, n0,1,2, and ?? 0,
  ? largethen ydet Leff,y ?y
• limit on minimum tmin
• ?min dmin/Leff, tmin (?min pbeam)2 with
  dmin k ?y d0, k ? 15 ?y
  ?(??mp/6pbeam), d0 distance to 1st detector
  strip with Leff ? ?(??) and dmin ? k ?y
• tmin ? k2? mppbeam/6?
• maximize ? minimize k (and d0) and ?

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Roman Pot Stations

• Each Roman Pot station
• Contains two Roman Pots with detector packages
• Precision motion with CNC Linear Slide

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Roman Pot Design

• Roman Pot
• Thinnest possible bottom (0.8 mm) to closely
  approach the beam (minimize d01.8 mm)
• 300µm thin beam windows reduce interactions and
  beam blow-up

PMTs
LV regulation
Trigger Counters
Silicon Detectors
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Si Detector Package

• 4 planes of 400 µm Silicon microstrip detectors
  (BNL Instrum. Div.)
• 4.5 x 7.5 cm2 sensitive area
• good resolution, low occupancy
• Redundancy 2X- and 2Y-detectors
• Closest proximity to the beam 14 mm
• 8 mm trigger scintillator with two PMT readout
  behind Silicon planes

Al strips 512 (Y), 768 (X), 70µm wide100 µm
pitch
implanted resistors
1st strip?edge 490 µm
guard ring
bias ring
Trigger Scintillator
Si Detector Package
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January 2002 Run

• Engineering run January 2002
• pbeam 100 GeV/c
• 1 Roman pot station in each arm, plus 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 5p?mm?mrad
  after scraping
• Estimated Polarization 25
• 100 efficient data taking
• Collected 974k events (60 elastic triggers)
• Data will primarily be used to study detector
  performance and to prepare for data run in 2003
• High quality of data will provide 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
• From data detector fiducial regions with high
  acceptance
• From 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

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Hit Patterns

• Detector X-Y hit positionsonline100k
  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 small t 410?4 ? t ? 0.02 GeV2
• stot, r, b, AN, ANN, and absolute L !
• More statistics!
• 2004
• ?s 500 GeV
• Small t 410?4 ? t ? 0.13 GeV2
• stot, 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.
• pp2pp probes the Pomeron(Odderon) Large distance
  QCD
• First engineering run successful
• Working on first physics results nuclear slope,
  AN(N)
• Next finish building experiment to complete
  physics program
• Exciting opportunities at RHIC for pp2pp in next
  few years

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Si Tests

• Si Tests
• Noise Examples of noise distributions
  (RMS)
• Source test