Transverse Spin and RHIC Probing Transverse Spin in p p Collisions

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Transverse Spin and RHICProbing Transverse Spin
in pp Collisions

• OUTLINE
• Features of RHIC for polarized pp collisions
• Transverse single spin effects in pp
  collisions at ?s200 GeV
• Towards understanding forward p0 cross sections
• Plans for the future

L.C. Bland Brookhaven National Laboratory Transver
se Polarization in Hard Processes Como 7
September 2005
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Installed and commissioned during run 4 To be
commissioned Installed/commissioned in run 5

• Developments for runs 2 (1/02), 3 (3/03 ? 5/03)
  and 4 (4/04 ? 5/03)
• Helical dipole snake magnets
• CNI polarimeters in RHIC,AGS
• ? fast feedback

• b1m operataion
• spin rotators ? longitudinal polarization
• polarized atomic hydrogen jet target

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RHIC Spin Physics Program

• Direct measurement of polarized gluon
  distribution using
• multiple probes
• Direct measurement of anti-quark polarization
  using
• parity violating production of W?
• Transverse spin Transversity transverse spin
  effects
• possible connections to orbital angular
  momentum?

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• Calendar Summary for RHICRun-5 pp Run
• pp commissioning started on March 24, 2005
• pp Physics running, for longitudinal
  polarization, started on April 19, 2005
• 410 GeV Collider dev. data, was May 31st to
  June 3rd
• Transverse polarization was June 13th to June
  16th
• Run ended on June 24, 2005

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RHIC Run-5 Performance
Total for run 9.2 pb-1 delivered 3.1 pb-1
smpled
(nb-1)
Delivered
STAR 2005 Longitudinal Goal
Sampled
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PHENIX Detector

• Philosophy
• High rate capability granularity
• Good mass resolution and particle ID

?0 reconstruction and high pT photon
trigger EMCal ?lt0.38, ??? Granularity ?????
0.01?0.01 Minimum Bias trigger and Relative
Luminosity Beam-Beam Counter (BBC)
3.0lt?lt3.9, ??2?
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(No Transcript)
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STAR detector layout

• TPC -1.0 lt ? lt 1.0
• FTPC 2.8 lt ??? lt 3.8
• BBC 2.2 lt ??? lt 5.0
• EEMC1 lt ? lt 2
• BEMC0 lt ? lt 1
• FPD ? 4.0 3.7

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First AN Measurement at STARprototype FPD results
STAR collaboration Phys. Rev. Lett. 92 (2004)
171801
Similar to result from E704 experiment (vs20
GeV, 0.5 lt pT lt 2.0 GeV/c)
Can be described by several models available as
predictions

• Sivers spin and k? correlation in parton
  distribution functions (initial state)
• Collins spin and k? correlation in fragmentation
  function (final state)
• Qiu and Sterman (initial state) / Koike (final
  state) twist-3 pQCD calculations, multi-parton
  correlations

vs200 GeV, lt?gt 3.8
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Why Consider Forward Physics at a Collider?
Kinematics
Hard scattering hadroproduction
Can Bjorken x values be selected in hard
scattering?

• Assume
• Initial partons are collinear
• Partonic interaction is elastic ? pT,1 ? pT,2

?
Studying pseudorapidity, h-ln(tanq/2),
dependence of particle production probes parton
distributions at different Bjorken x values and
involves different admixtures of gg, qg and qq
subprocesses.
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Simple Kinematic Limits

• Mid-rapidity particle detection
• h1?0 and lth2gt?0
• ? xq ? xg ? xT 2 pT / ?s
• Large-rapidity particle detection
• h1gtgth2
• xq ? xT eh1 ? xF (Feynman x), and
• xg ? xF e-(h1h2)

NLO pQCD (Vogelsang)
1.0 0.8 0.6 0.4 0.2 0.0
qq
fraction
qg
gg
0 10 20 30
pT,p (GeV/c)
? Large rapidity particle production and
correlations involving large rapidity particle
probes low-x parton distributions using valence
quarks
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How can one infer the dynamics of particle
production?Particle production and correlations
near h?0 in pp collisions at ?s 200 GeV
Inclusive p0 cross section
Two particle correlations (h?)
STAR, Phys. Rev. Lett. 90 (2003), nucl-ex/0210033
At vs 200GeV and mid-rapidity, both NLO pQCD
and PYTHIA explains pp data well, down to
pT1GeV/c, consistent with partonic origin
Do they work for forward rapidity?
Phys. Rev. Lett. 91, 241803 (2003) hep-ex/0304038
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Forward p0 production in hadron collider
p0
Ep
p d
qq
EN
qp
p Au
xgp
xqp
qg
EN
(collinear approx.)

• Large rapidity p production (hp4) probes
  asymmetric partonic collisions
• Mostly high-x valence quark low-x gluon
• 0.3 lt xqlt 0.7
• 0.001lt xg lt 0.1
• ltzgt nearly constant and high 0.7 0.8
• Large-x quark polarization is known to be large
  from DIS
• Directly couple to gluons A probe of low x
  gluons

NLO pQCD Jaeger,Stratmann,Vogels
ang,Kretzer
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xF and pT range of FPD data
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pp?p0X cross sections at 200 GeV

• The error bars are point-to-point systematic and
  statistical errors added in quadrature
• The inclusive differential cross section for p0
  production is consistent with NLO pQCD
  calculations at 3.3 lt ? lt 4.0
• The data at low pT are more consistent with the
  Kretzer set of fragmentation functions, similar
  to what was observed by PHENIX for p0 production
  at midrapidity.

D. Morozov (IHEP), XXXXth Rencontres de Moriond
- QCD, March 12 - 19, 2005
NLO pQCD calculations by Vogelsang, et al.
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STAR -FPD Preliminary Cross Sections
Similar to ISR analysis J. Singh, et al Nucl.
Phys. B140 (1978) 189.
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PYTHIA a guide to the physics
Forward Inclusive ?? Cross-Section
Subprocesses involved
qg
gg and qg ? qgg
STAR FPD
Soft processes

• PYTHIA prediction agrees well with the inclusive
  ?0 cross section at ??3-4
• Dominant sources of large xF ?? production from
  
• q g ? q g (2?2) ? ?? X
• q g ? q g g (2?3) ? ?? X

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Single Spin AsymmetryDefinitions

• Definition
• ds?(?) differential cross section of p0 then
  incoming proton has spin up(down)

• Two measurements
• Single arm calorimeter
• R relative luminosity (by BBC)
• Pbeam beam polarization
• Two arms (left-right) calorimeter
• No relative luminosity needed

positive AN more p0 going left to polarized beam
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Caveats -RHIC CNI Absolute polarization
still preliminary. -Result Averaged over
azimuthal acceptance of detectors.
-Positive XF (small angle scattering of the
polarized proton).
Run 2 Published Result.
Run 3 Preliminary Result. -More Forward
angles. -FPD Detectors. - 0.25 pb-1 with
Pbeam27
Run 3 Preliminary Backward Angle Data. -No
significant Asymmetry seen. (Presented at
Spin 2004 hep-ex/0502040)
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New Physics at high gluon density

• Shadowing. Gluons hidingbehind other gluons.
  Modificationof g(x) in nuclei. Modified
  distributionsneeded by codes that hope to
  calculateenergy density after heavy ion
  collision.
• Saturation Physics. New phenomena associated
  with large gluon density.
• Coherent gluon contributions.
• Macroscopic gluon fields.
• Higher twist effects.
• Color Glass Condensate

Edmond Iancu and Raju Venugopalan, review for
Quark Gluon Plasma 3, R.C. Hwa and X.-N. Wang
(eds.), World Scientific, 2003 hep-ph/0303204.
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? Dependence of RdAu
G. Rakness (Penn State/BNL), XXXXth Rencontres
de Moriond - QCD, March 12 - 19, 2005
See also J. Jalilian-Marian, Nucl. Phys. A739,
319 (2004)

• From isospin considerations, p p ? h? is
  expected to be suppressed relative to d nucleon
  ? h? at large ? Guzey, Strikman and Vogelsang,
  Phys. Lett. B 603, 173 (2004)
• Observe significant rapidity dependence similar
  to expectations from a toy model of RpA within
  the Color Glass Condensate framework.

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Constraining the x-values probed in hadronic
scattering
Guzey, Strikman, and Vogelsang, Phys. Lett. B
603, 173 (2004).
Log10(xGluon)

• Collinear partons
• x pT/?s (eh1 eh2)
• x? pT/?s (e?h1 e?h2)

• FPD ? ? 4.0
• TPC and Barrel EMC ? lt 1.0
• Endcap EMC 1.0 lt ? lt 2.0
• FTPC 2.8 lt ??? lt 3.8

CONCLUSION Measure two particles in the final
state to constrain the x-values probed
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Back-to-back Azimuthal Correlationswith large ??
Fit ???????????LCP normalized distributions and
with Gaussianconstant
Beam View
Top View
Trigger by forward ??
??

• E? gt 25 GeV
• ???? ? 4

Coicidence Probability 1/radian

• Midrapidity h? tracks in TPC
• -0.75 lt ??lt 0.75
• Leading Charged Particle(LCP)
• pT gt 0.5 GeV/c

???????????LCP
S Probability of correlated event under
Gaussian B Probability of un-correlated event
under constant ?s Width of Gaussian
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• PYTHIA (with detector effects) predicts
• S grows with ltxFgt and ltpT,?gt
• ?s decrease with ltxFgt and ltpT,?gt
• PYTHIA prediction agrees with pp data
• Larger intrinsic kT required to fit data

25ltE?lt35GeV
45ltE?lt55GeV
Statistical errors only
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Plans for the Future
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STAR Forward Meson Spectrometer

• NSF Major Research Initiative (MRI) Proposal
• submitted January 2005
• hep-ex/0502040

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STAR detector layout with FMS

• TPC -1.0 lt ? lt 1.0
• FTPC 2.8 lt ??? lt 3.8
• BBC 2.2 lt ??? lt 5.0
• EEMC1 lt ? lt 2
• BEMC-1 lt ? lt 1
• FPD ? 4.0 3.7

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Three Highlighted Objectives In FMS
Proposal(not exclusive)

1. A d(p)Au?p0p0X measurement of the parton model
   gluon density distributions xg(x) in gold nuclei
   for 0.001lt x lt0.1. For 0.01ltxlt0.1, this
   measurement tests the universality of the gluon
   distribution.
2. Characterization of correlated pion cross
   sections as a function of Q2 (pT2) to search for
   the onset of gluon saturation effects associated
   with macroscopic gluon fields. (again d-Au)
3. Measurements with transversely polarized protons
   that are expected to resolve the origin of the
   large transverse spin asymmetries in reactions
   for forward ?? production. (polarized pp)

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Frankfurt, Guzey and Strikman, J. Phys. G27
(2001) R23 hep-ph/0010248.

• constrain x value of gluon probed by high-x
  quark by detection of second hadron serving as
  jet surrogate.
• span broad pseudorapidity range (-1lthlt4) for
  second hadron ? span broad range of xgluon
• provide sensitivity to higher pT for forward p0
  ? reduce 2?3 (inelastic) parton process
  contributions thereby reducing uncorrelated
  background in Df correlation.

Pythia Simulation
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Disentangling Dynamics of Single Spin
AsymmetriesSpin-dependent particle correlations
Collins/Hepplemann mechanism requires
transversity and spin-dependent fragmentation
Sivers mechanism asymmetry is present for forward
jet or g
Large acceptance of FMS will enable disentangling
dynamics of spin asymmetries
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New FMS Calorimeter Lead Glass From FNAL E831 804
cells of 5.8cm?5.8cm?60cm Schott F2 lead glass
Loaded On a Rental Truck for Trip To BNL
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FPD Physics for Run6
We intend to stage a large version of the FPD to
prove our ability to detect direct photons.
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How do we detect direct photons?

• Isolate photons by having sensitivity to partner
  in decay of known particles
• p0??? M0.135 GeV BR98.8
• K0 ? p0p0 ??? ?? 0.497 31
• ?? ?? 0.547
  39
• ?? p0 ? ??? ? 0.782
  8.9
• Detailed simulations underway

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Where do decay partners go?
m p0(h) di-photon parameters zgg
E1-E2/(E1E2) fgg opening angle Mm 0.135
GeV/c2 (p0) Mm0.548 GeV/c2 (h)

• Gain sensitivity to direct photons by making
  sure we have high probability to catch decay
  partners
• This means we need dynamic range, because
  photon energies get low (0.25 GeV), and
  sufficient area (typical opening angles few
  degrees at our h ranges).

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Sample decays on FPD
With FPD module size and electronic dynamic
range, have gt95 probability of detecting second
photon from p0 decay.
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Timeline for the Baseline RHIC Spin Program
Ongoing progress on developing luminosity and
polarization
Research Plan for Spin Physics at RHIC
(2/05)

• Program divides into 2 phases
• s200 GeV with present detectors for gluon
  polarization (?g) at higher x transverse
  asymmetries
• ?s500 GeV with detector upgrades for ?g at lower
  x W production

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Summary / Outlook

• Large transverse single spin asymmetries are
  observed for large rapidity p0 production for
  polarized pp collisions at ?s 200 GeV
• AN grows with increasing xF for xFgt0.35
• AN is zero for negative xF
• Large rapidity p0 cross sections for pp
  collisions at ?s 200 GeV is in agreement with
  NLO pQCD, unlike at lower ?s. Particle
  correlations are consistent with expectations of
  LO pQCD ( parton showers).
• Large rapidity p0 cross sections and particle
  correlations are suppressed in dAu collisions at
  ?sNN200 GeV, qualitatively consistent with
  parton saturation models.
• Plan partial mapping of AN in xF-pT plane in
  RHIC run-5
• Propose increase in forward calorimetry in STAR
  to probe low-x gluon densities and establish
  dynamical origin of AN (complete upgrade by
  10/06).

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Backups
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Towards establishing consistency between FPD
(p0)/BRAHMS(h-)

• Extrapolate xF dependence at pT2.5 GeV/c to
  compare with BRAHMS h- data. Issues to consider
• lthgt of BRAHMS data for 2.3ltpTlt2.9 GeV/c bin.
  From Fig. 1 of PRL 94 (2005) 032301 take lthgt3.07
  ? ltxFgt0.27
• p-/h- ratio?
• Results appear consistent but have insufficient
  accuracy to establish pp?p-/p0 isospin effects

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Systematics
Measurements utilizing independent calorimeters
consistent within uncertainties

• Systematics
• Normalization uncertainty 16
• position uncertainty (dominant)
• Energy dependent uncertainty 13 - 27
• energy calibration to 1 (dominant)
• background/bin migration correction
• kinematical constraints

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FPD Detector and ?º reconstruction

• robust di-photon reconstructions with FPD in
  dAu collisions on deuteron beam side.
• average number of photons reconstructed
  increases by 0.5 compared to pp data.

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dAu ? p0p0X, pseudorapidity correlations with
forward p0 HIJIING 1.381 Simulations

• increased pT for forward p0 over run-3 results
  is expected to reduce the background in Df
  correlation
• detection of p0 in interval -1lthlt1 correlated
  with forward p0 (3lthlt4) is expected to probe
  0.01ltxgluonlt0.1 ? provides a universality test of
  nuclear gluon distribution determined from DIS
• detection of p0 in interval 1lthlt4 correlated
  with forward p0 (3lthlt4) is expected to probe
  0.001ltxgluonlt0.01 ? smallest x range until eRHIC
• at dAu interaction rates achieved at the end of
  run-3 (Rint30 kHz), expect 9,700?200 (5,600?140)
  p0-p0 coincident events that probe
  0.001ltxgluonlt0.01 for no shadowing
  (shadowing) scenarios.

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STAR Forward Calorimetry Recent History and Plans

• Prototype FPD proposal Dec 2000
• Approved March 2001
• Run 2 polarized proton data (published 2004
  spin asymmetry and cross section)
• FPD proposal June 2002
• Review July 2002
• Run 3 data pp dAu (Preliminary An Results)
• FMS Proposal Complete Forward EM
  Coverage(hep-ex/0502040).

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Students prepare cells at test Lab at BNL