The Gluons spin contribution to the protons spin as seen at RHIC

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The Gluons spin contribution to the protons
spin---as seen at RHIC
G. Bunce Moriond QCD, March 2008
I would like to thank Les Bland, Werner
Vogelsang, Abhay Deshpande, Sasha Bazilevsky,
Matthias Grosse Perdekamp, for their advice and
many plots.
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a history of the strong interaction 1964
quarks to understand the zoo of strongly
interacting particles color quantum number to
describe the O- (sss, S3/2) 1967 quarks are
real! from hard inelastic scattering of
electrons from protons at SLAC 1973 the theory
of QCD quarks and gluons and color
perturbative QCD 1980s to present e-p and
pbar-p colliders beautiful precision tests of
pQCD, unpolarized . 1970s
polarized beams and targets 1988 the spin of
the proton is not carried by its quarks! 1990s to
present confirmed in DIS fixed target
experiments using electrons and muons to probe
the spin structure of the proton 2001 to present
probe the spin structure of the proton using
quarks and gluons (strongly interacting probes
see both the gluons and quarks in the proton)
RHIC
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EMC at CERN J. Ashman et al., NPB 328, 1
(1989) polarized muons probing polarized
protons
proton spin crisis
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(No Transcript)
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DIS
high pT
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Probing ?G in pp Collisions
pp ? hX
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RHIC Polarized Collider
RHIC pC Polarimeters
Absolute Polarimeter (H? jet)
BRAHMS PP2PP
PHOBOS
Siberian Snakes
Siberian Snakes
PHENIX
STAR
Spin Rotators (longitudinal polarization)
Spin Rotators (longitudinal polarization)
Pol. H- Source
LINAC
BOOSTER
Helical Partial Siberian Snake
AGS
200 MeV Polarimeter
AGS pC Polarimeter
Strong AGS Snake
2006 1 MHz collision rate P0.6
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Exquisite Control of Systematics
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ALL
Yellow beam Blue beam
same helicity ? opposite helicity
(P) Polarization (L) Relative Luminosity (N)
Number of pi0s
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RHIC Spin Runs

• P L(pb-1) Results
• 2002 15 0.15 first pol.
  pp collisions!
• 2003 30 1.6 pi0, photon cross
  section,
• A_LL(pi0), 3 PRLs
• 2004 40 3.0 absolute beam
  polarization
• 
  with polarized H jet
• 2005 50 13 large gluon
  pol. ruled out
• (P4 x L 0.8)
• 2006 60 46 first long spin
  run
• (P4 x L 6)
  
• 2007 no
  spin running
• 2008 50 (short)
  run in progress

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RHIC Polarimetry
Jet Polarization

• PHOTO of Jet Pol

? for proton-proton elastic scattering
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Polarization Measurements 2006 Run
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PHENIX and STAR
PHENIX High rate capability High
granularity Good mass resolution and PID Limited
acceptance
STAR Large acceptance with azimuthal
symmetry Good tracking and PID Central and
forward calorimetry
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Cornerstones to the RHIC Spin program
pp ? ? X
0
Mid-rapidity PHENIX
Forward STAR
PRL 97, 152302 (2006)
To appear PRD Rapid, hep-ex-0704.3599
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And Jets and Direct g
pp ? jet X STAR
pp ? ? X PHENIX
PRL 98, 012002 (2007)
PRL 97, 252001 (2006)
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ALL jets
STAR Preliminary Run5 (?s200 GeV)
GRSV Models ?G G ?G(Q21GeV2)1.9 ?G
-G ?G(Q21GeV2)-1.8 ?G 0
?G(Q21GeV2)0.1 ?G std ?G(Q21GeV2)0.4
pT(GeV)
Large gluon polarization scenario is not
consistent with data
Run34 PRL 97, 252001
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ALL ?0
PHENIX Preliminary Run6 (?s200 GeV)
5
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pT(GeV)
GRSV model ?G 0 ?G(Q21GeV2)0.1 ?G
std ?G(Q21GeV2)0.4
Stat. uncertainties are on level to distinguish
std and 0 scenarios?
Run3,4,5 PRL 93, 202002 PRD 73, 091102
hep-ex-0704.3599
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From ALL to ?G (with GRSV)
Calc. by W.Vogelsang and M.Stratmann
?
3 sigma

• std scenario, ?G(Q21GeV2)0.4, is excluded by
  data on gt3 sigma level ?2(std)??2mingt9
• 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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Extending x range is crucial!
Gehrmann-Stirling models
GSC ?G(xgluon 0?1) 1 GRSV-0
?G(xgluon 0?1) 0 GRSV-std ?G(xgluon
0?1) 0.4
Current data is sensitive to ?G for xgluon
0.02?0.3
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Dq-Dq at RHIC via W production
Expected start 2009
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Transverse spin pion A_N--very large forward
asymmetries
AN(p) at 62 GeV
STAR
Kyoto Spin2006
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RHIC Spin Outline
The key points for RHIC Spin are

• Spin structure of proton
• Strongly interacting probes
• -----------
• P60, L2x1031, root(s)200 GeV in 2006
• Polarized atomic H jet absolute P, pp elastic
  physics
• ----------
• Cross sections for pi0, jet, direct photon
  described by pQCD

• Helicity asymmetries sensitivity to gluon spin
  contribution to proton
• ----------
• W boson parity violating production ubar and
  dbar polarizations in proton
• ----------
• Very large transverse spin asymmetries in pQCD
  region
• ----------
• Future transverse spin Drell-Yan

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A Fundamental Test of UniversalityTransverse
Spin Drell Yan at RHIC vs Sivers Asymmetry in
Deep Inelastic Scattering

• Important test at RHIC of recent fundamental QCD
  predictions for the Sivers effect, demonstrating
  attractive vs repulsive color charge forces
• ----------------
• Possible access to quark orbital angular momentum
  
• Requires very high luminosity (RHIC II)
• Both STAR and PHENIX can make important,
  exciting, measurements
• Discussion available at http//spin.riken.bnl.gov/
  rsc/

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Attractive vs Repulsive Sivers Effects Unique
Prediction of Gauge Theory !
DIS attractive
Drell-Yan repulsive
Sivers Dennis Sivers (predicted orbital
angular momentum origin of
transverse asymmetries)
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Experiment SIDIS vs Drell Yan SiversDIS -
SiversDY Probes QCD attraction and QCD
repulsion
HERMES Sivers Results
RHIC II Drell Yan Projections
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Sivers Amplitude
Markus Diefenthaler DIS Workshop Munich, April
2007
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0.1 0.2 0.3 x
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Concluding Remarks

• High luminosity and high polarization achieved!
• --------------
• Delta G direct photon global fits with RHIC,
  DIS new vertex and forward detectors
• --------------
• W boson parity violating production ubar and
  dbar
• --------------
• Very strong theoretical support
• --------------
• Transverse spin renaissance?Drell Yan crucial
  test of our understanding of the underlying
  physics!

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• Spin is one of the most fundamental concepts in
  physics, deeply rooted in Poincare invariance and
  hence in the structure of space-time itself. All
  elementary particles we know today carry spin,
  among them the particles that are subject to the
  strong interactions, the spin ½ quarks and the
  spin 1 gluons. Spin, therefore, plays a central
  role also in our theory of the strong
  interactions, QCD, and to understand spin
  phenomena in QCD will help to understand QCD
  itself.
• To contribute to this understanding is the
  primary goal of the spin physics program at RHIC.