Spin%20at%20RHIC%20Present%20Status%20and%20Future%20Plans

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Spin at RHICPresent Status and Future Plans

• OUTLINE
• Spin at RHIC how its done, why its done, and
  who does it
• Status of ALL measurements at RHIC sensitivity
  to DG
• Status of transverse single-spin asymmetries at
  RHIC
• Future plans

L.C. Bland, BNL IWHSS08, Torino 2 April 2008
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RHIC Spin CollaborationConfederation of Groups
Involved in the Effort

• Accelerator Physicists
• Primarily BNL Collider-Accelerator Department
• RHIC spin is a successful accelerator physics
  experiment
• Essential contributions from RIKEN for spin at
  RHIC
• RHIC Experiments (PHENIX,STAR,BRAHMS)
• RIKEN / RBRC, University and National Laboratory
  groups
• RHIC spin planning fully integrated in experiment
  collaborations
• Polarimetry
• Primarily BNL effort, with detailees from RHIC
  experiments
• Essential measurements required for RHIC spin
  results
• Theory
• RIKEN / RBRC, University and National Laboratory
  groups
• RHIC spin results require QCD global analyses to
  extract physics

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RHIC Spin Goals - I
How is the proton built from its known quark and
gluon constituents? As with atomic and nuclear
structure, this is an evolving understanding
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RHIC Spin Goals - IIUnderstanding the Origin of
Proton Spin
Understanding the origin of proton spin helps to
understand its structure
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RHIC Spin Goals - III Milestones and Other
Objectives

• Direct measurement of polarized gluon
  distribution (DG) using multiple probes
• Direct measurement of flavor identified
  anti-quark polarization using parity violating
  production of W?
• Transverse spin connections to partonic orbital
  angular momentum (Ly) and transversity (dS)

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RHIC Spin Probes - IPolarized proton collisions
/ hard scattering probes of DG
Describe pp particle production at RHIC energies
(?s ? 62 GeV) using perturbative QCD at Next to
Leading Order, relying on universal parton
distribution functions and fragmentation functions
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RHIC Spin Probes - IIUnpolarized cross sections
as benchmarks and heavy-ion references
Good agreement between experiment and theory ?
calibrated hard scattering probes of proton spin
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RHIC As a Polarized Collider
2005 Pblue 49.3 /- 1.5 /- 1.4
Pyellow 44.3 /- 1.3 /- 1.3
DP/P 4.2 (goal5) 2006 1 MHz collision
rate Polarization0.6 (online)
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RHIC Run-6
Plot by Phil Pile
An extraordinary Run-6!
Average Polarization 60!
Outstanding luminosity and polarization
performance from RHIC for polarized proton
collisions at ?s 200 GeV
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PHENIX Detector

• p0/g/h detection
• Electromagnetic Calorimeter (PbSc/PbGl)
• High pT photon trigger to collect p0's, hs, gs
• Acceptance hlt0.35, f 2 x p/2
• High granularity (1010mrad2)
• p/ p-
• Drift Chamber (DC) for Charged Tracks
• Ring Imaging Cherenkov Detector (RICH)
• High pT charged pions (pTgt4.7 GeV).
• Relative Luminosity
• Beam Beam Counter (BBC)
• Acceptance 3.0lt hlt3.9
• Zero Degree Calorimeter (ZDC)
• Acceptance 2 mrad
• Local Polarimetry
• ZDC
• Shower Maximum Detector (SMD)

EMCal
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Run-6 STAR detector layout

• Detectors used for jets
• Time Projection Chamber, ?lt1.4 Tracking
• Barrel EM Calorimeter, ?lt1 Triggering
  Calorimetry
• Endcap EM Calorimeter, 1.09lt?lt2 Triggering
  Calorimetry
• Beam-Beam Counters, 3.4lt?lt5 Triggering,
  Luminosity, local Polarimetry

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Longitudinal Two-Spin (ALL)
Status of probing for gluon polarization
via measurements of ALLfor midrapidity jet,p0
production
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ALL ?0
5
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pT(GeV)
GRSV model ?G 0 ?G(Q21GeV2)0.1 ?G
std ?G(Q21GeV2)0.4
Statistical uncertainties now to the point of
distinguishing std and 0 scenarios?
Run3,4,5 PRL 93, 202002 PRD 73, 091102
hep-ex-0704.3599
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From pT to xgluonmidrapidity neutral pion ALL

• Each pT bin corresponds to a wide range in
  xgluon, heavily overlapping with other pT bins
• Data are not sensitive to variation of ?G(xgluon)
  within our x range
• Quantitative analysis needs to assume some
  ?G(xgluon) shape

log10(xgluon)

• NLO pQCD for ?0, 2lt pT lt 9 GeV/c ? 0.02 lt xgluon
  lt 0.3
• GRSV model ?G(0.02 lt xgluonlt 0.3) 0.6?G(0 lt
  xgluon lt 1 )

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Constraining ?G from p0 ALLSimilar approach as
used for jets
Calculations by W.Vogelsang and M.Stratmann
?

• GRSV-std scenario, ?G(Q21GeV2)0.4, is
  excluded by data on gt3s level
• Only exp. stat. uncertainties are included (the
  effect of syst. uncertainties is expected to be
  small in the final results)
• Theoretical uncertainties are not included

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Jet reconstruction in STAR

• Midpoint cone algorithm (Adapted from
  Tevatron II - hep-ex/0005012 )
• Seed energy 0.5 GeV
• Cone radius in ?-?
• R0.4 (2005)
• R0.7 (2006)
• Splitting/merging fraction f0.5

Data jets MC
jets
Geant
Detector
Pythia
Particle
Use PythiaGEANT to quantify detector response
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Final 2005 Inclusive ALLjets Results
hep-ex arXiv0710.2048
0.2 lt ? lt 0.8

• Data are compared to predictions within the GRSV
  framework with several input values of ?G.

B. Jager et.al, Phys.Rev.D70, 034010
GRSV-std

• The inclusive measurements give sensitivity to
  gluon polarization over a broad momentum range

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Constraining DG from jet production ALLBefore
global analyses

• Compute ALL in NLO pQCD varying integral DG, but
  maintaining GRSV shape
• Perform ?2 analysis between calculations and
  measured jet ALL

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Run 2006 Data

• Improved FOM
• Luminosity 2 ? 4.7 pb-1
• Polarization 50 ? 60 (online polarization)
• Barrel EMC ? coverage 0,1 ? -1,1
• In addition
• Jet Cone Radius 0.4 ? 0.7
• -0.7 lt ?jet axis lt 0.9
• Neutral Energy Fraction lt 0.85
• Increased trigger thresholds
• Inclusion of Endcap EMC towers
• Improved tracking at large ?

STAR Preliminary
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2006 Inclusive ALLjets
-0.7 lt ? lt 0.9
GRSV curves with cone radius 0.7 and -0.7 lt ? lt
0.9
ALL systematics (x 10 -3)
Reconstruction Trigger Bias -1,3 (pT dep)
Non-longitudinal Polarization 0.03 (pT dep)
Relative Luminosity 0.94
Backgrounds 1st bin 0.5 Else 0.1
pT systematic ?6.7

• Using jet patch trigger (??x?? 1x1 patch of
  towers) only
• Statistical uncertainties are 3-4 times smaller
  than 2005 in high pT region (pTgt13 GeV/c)

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2006 Inclusive ALLjets
Theoretical uncertainties not included
GRSV DIS best fit0.24 1? -0.45 to 0.7 PRD 63,
094005 (2001)

• Within GRSV framework
• ?g_std excluded with 99 CL
• ?glt-0.7 excluded with 90 CL

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Summary of ALL Measurements

• Data accumulated through RHIC run 6 for inclusive
  ?0 and jet ALL has reached high statistical
  significance to constrain ?G in the limited x
  range (0.02?0.3)
• ?G is found to be consistent with zero, to date
• Theoretical uncertainties (x dependence) are
  significant

• Future Plans for Probing DG
• Improve statistical precision of midrapidity
  p0,jet ALL measurements and extend measurements
  to higher pT
• Determine x-dependence of DG via correlation
  measurements jet1jet2 and gjet
• Extend gluon-x range probed to lower x via
  measurements of ALL at larger rapidity and higher
  ?s
• Global analysis in NLO pQCD of RHIC data and
  HERMES,COMPASS data

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Transverse Single-Spin Asymmetries (AN)
Probing for orbital motion within transversely
polarized protons
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Expectations from Theory
What would we see from this gedanken experiment?
F?0 as mq?0 in vector gauge theories, so AN
mq/pT or,AN 0.001 for pT 2 GeV/c Kane,
Pumplin and Repko PRL 41 (1978) 1689
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A Brief History
?s20 GeV, pT0.5-2.0 GeV/c

• QCD theory expects very small (AN10-3)
  transverse SSA for particles produced by hard
  scattering.

• The FermiLab E-704 experiment found strikingly
  large transverse single-spin effects in p?p
  fixed-target collisions with 200 GeV polarized
  proton beam (??s 20 GeV).

• ??0 E704, PLB261 (1991) 201.
• ??/- - E704, PLB264 (1991) 462.

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Two of the Explanations for Large Transverse
SSASpin-correlated kT
initial state
final state
Require experimental separation of Collins and
Sivers contributions
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Transverse Single-Spin AsymmetriesWorld-wide
experimental and theoretical efforts

• Transverse single-spin asymmetries are observed
  in semi-inclusive deep inelastic scattering with
  transversely polarized proton targets
• ? HERMES (e) COMPASS (m) and planned at JLab
• Collins fragmentation function is observed in
  hadron-pair production in ee- collisions (BELLE)
• Intense theory activity underway

SPIRES-HEP search title including
Transverse spin, Transversity,
single spin
Total number 625 (19682006) Experimental
results 14
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Spin Effects in the Forward DirectionStatus
prior to RHIC run 6
J. Adams et al. (STAR), PRL 92 (2004) 171801 and
PRL 97 (2006) 152302

• Transverse SSA persist at large xF at RHIC
  energies where unpolarized cross sections are
  calculable

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STAR Results vs. Di-Jet Pseudorapidity Sum Run-6
Result
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High Precision Analyzing Powers
(2003 ? 2006)
B.I. Abelev, et al, hep-ex/0801.2990
? Precision measurements at ?s 200 GeV provide
stringent contraints on the models
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High Precision Analyzing Powers
(2003 ? 2006)
B.I. Abelev, et al, hep-ex/0801.2990
? No model fully describes the precision
data More experimental (and theoretical) work
needed
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PHENIX Goes ForwardFirst results with muon
piston calorimeter from run 6p?p?p0X, ?s 62
GeV
Transverse SSA persists with similar
characteristics over a broad range of collision
energy (20 lt ?s lt 200 GeV)
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Summary Transverse Single Spin Asymmetry (SSA)
Measurements

• Feynman-x dependence of large-rapidity pion
  production shows large transverse SSA at RHIC
  energies, where cross sections are described by
  NLO pQCD
• Feynman-x dependence of large-rapidity transverse
  SSA are consistent with theoretical models
  (Sivers effect ? orbital motion / twist-3
  calculations)
• The pT dependence of large-rapidity p0 transverse
  SSA does not follow theoretical expectations
• Direct measurement of spin-correlated kT (Sivers
  effect) via midrapidity di-jet spin asymmetries
  completed in RHIC run 6 and found consistent with
  zero.
• Cancellations found in theory calculations
  subsequent to measurements also expect small
  di-jet spin asymmetries at midrapidity.

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Future RHIC Spin Plans

• Measure parity violation for W? production to
  determine flavor dependence of quark and
  antiquark polarization.
• Requires completion of PHENIX muon trigger
  upgrade and STAR forward tracking for charge sign
  discrimination.

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Plans for Transverse Polarization
MeasurementsRHIC run 8 and beyond

• Experimental separation of Collins and Sivers
  effects via transverse single-spin asymmetry
  measurements for large rapidity p-p production
• Extend measurements of transverse single spin
  asymmetries from hadron production to prompt
  photon production, including away-side
  correlations
• Develop RHIC experiments for a future measurement
  of transverse single spin asymmetries for
  Drell-Yan production of dilepton pairs

Transverse-Spin Drell-Yan Physics at RHIC L.
Bland, S.J. Brodsky, G. Bunce, M. Liu, M.
Grosse-Perdekamp, A. Ogawa, W. Vogelsang, F.
Yuan http//spin.riken.bnl.gov/rsc/write-up/dy_fin
al.pdf
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Forward Meson SpectrometerQuantifying possible
color glass condensate viaforward p0 and
correlations in dAu versus pp at ?sNN200 GeV
North FMS half before sealing
pp data at ?s 200 GeV also acquired Recorded
8 pb-1 in run 8
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Sivers in SIDIS vs Drell Yan
Transverse-Spin Drell-Yan Physics at RHIC L.
Bland, S.J. Brodsky, G. Bunce, M. Liu, M.
Grosse-Perdekamp, A. Ogawa, W. Vogelsang, F.
Yuan http//spin.riken.bnl.gov/rsc/write-up/dy_fin
al.pdf

• Important test at RHIC of the fundamental QCD
  prediction of the non-universality of the Sivers
  effect!
• requires very high luminosity ( 250pb-1)

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Non-universality of Sivers Asymmetries Unique
Prediction of Gauge Theory !
Simple QED example
Drell-Yan repulsive
DIS attractive
Same in QCD
As a result
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Experiment SIDIS vs Drell Yan SiversDIS -
SiversDY Test QCD Prediction of
Non-Universality
HERMES Sivers Results
RHIC Drell Yan Projections
0
Sivers Amplitude
Markus Diefenthaler DIS Workshop Munchen, April
2007
0
0.1 0.2 0.3 x
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Rapidity and Collision Energy
Large rapidity acceptance required to probe
valence quark Sivers function
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Backup
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Benchmarking Simulations
pp ? J/?X ? ll-X, ?s200 GeV
PHENIX, hep-ex/0611020
mm- 1.2lthlt2.2
ee- hlt0.35
J/? is a critical benchmark that must be
understood before Drell-Yan
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Dilepton Backgrounds
Drell-Yan
J/?
?
?
Isolation needed to discriminate open heavy
flavor from DY