Measuring Transverse Spin Phenomena at PHENIX

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Measuring Transverse Spin Phenomena at PHENIX
RHIC AGS Annual Users Meeting, BNL, June 1-5,
2009

• Ruizhe Yang

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Physics motivation
Spin structure of transversely polarized
proton Define left-right asymetry
Theory Expectation Small asymmetries at high
energies (Kane, Pumplin, Repko, PRL 41,
16891692 (1978) )
AN 10-4 from theory
Experiment E704, Fermilab, 1991
AN 10-1 measured
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Possible origins of large AN
pQCD
Quark Fragmentation
Proton Structure
Collins Effect Correlation between proton
quark spin spin dependent fragmentation
function
Sivers Effect Correlation between proton spin
and quark transverse momentum
Quark transversity
Collins FF
Sivers distribution
J. C. Collins, Nucl. Phys. B396, 161 (1993)
D. Sivers, Phys. Rev. D 41, 83 (1990)
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Global analysis
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Polarized pp at RHIC
RHIC pC Polarimeters
Siberian Snakes
PHOBOS
BRAHMS PP2PP
Siberian Snakes
Spin Flipper
STAR
PHENIX

• 2008 Run
• Large transverse data sample collected
• 2009 Run
• Excellent performance during first 500 GeV run at
  RHIC 10 pb-1
• 200 GeV run ongoingAvg. polarization at 55

Spin Rotators
Partial Snake
Helical Partial Snake
Strong Snake
Polarized Source
LINAC
AGS
BOOSTER
200 MeV Polarimeter
Rf Dipole
AGS Internal Polarimeter
AGS pC Polarimeter
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PHENIX Detector at RHIC

• Central Arms ? lt 0.35
• Identified charged hadrons
• Neutral Pions
• Direct Photon
• J/Psi
• Heavy Flavor

• Muon Arms 1.2 lt ? lt 2.4
• J/Psi
• Unidentified charged hadrons
• Heavy Flavor

• MPC 3.1 lt ? lt 3.9
• Neutral Pions
• Etas

• ZDC h 5.9
• Neutrons

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Cross section measurement

• ?0 Cross-Sections at h 0
• Compare with pQCD calculation
• Agreement at 200 GeV (RHIC)
• Agreement at 62.4 GeV (RHIC)

de Florian, Vogelsang, WagnerPRD 76,094021 (2007)
Bourrely and SofferEur.Phys.J.C36371-374 (2004)
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AN from p0, h/- at central rapidity
PHENIX transverse running in 2005
PHENIX transverse running at 2002
PRL 95, 202001 (2005)
Analysis with high statistics 20062008 data in
progress Smaller statistical uncertainties
(more than factor of 7 improvement)Higher pT
data points possible
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Constrain gluon Sivers effect
p0 AN from PHENIX 2002 data
Anselmino et al, Phys. Rev. D 74, 094011
Upper bound for gluon Sivers function that is
consistent with PHENIX results, assuming
vanishing sea contribution
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Forward p0 AN

• Forward asymmetries contain mixture of
• Sivers
• Transversity x Collins
• PHENIX ?0 results available for ?s62GeV
• Analysis of large 2008 ?s200 GeV dataset AN
  of ?0 and ? 5.2 pb-1, 46 Polarization
• work in progress
• Asymmetries could enter a global analysis on
  transverse spin asymmetries

Process contribution to ?0, ?3.3, ?s200 GeV
PLB 603,173 (2004)
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SSA from di-hadron production

• SSA from Interference Fragmentation Function
  (IFF)
• Measure di-hadron asymmetry with hadron pairs in
  central arm (?0,h) (?0,h-), (h,h-)
• Transversity extraction will become possible
  with Interference Fragmentation Function
  measurement in progress at BELLE(see A. Vossens
  talk in the same session)

• Two different theoretical models gave different
  prediction of mass dependence
• Sign change is not observed in HERMES/COMPASS
  results

Jaffe, Jin and Tang, PRL 80 (1998) 1166
Bacchetta and Radici, Phys. Rev. D 74, 114007
(2006)
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IFF Definition of Vectors and Angles
Bacchetta and Radici, PRD70, 094032 (2004)
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SSA from di-hadron production
No significant asymmetries seen at mid-rapidity.
Added statistics from 2008 running
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SSA from di-hadron production
No significant asymmetries seen at mid-rapidity.
Added statistics from 2008 running
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Sivers effect in di-jet production
Azimuthal distribution of Di-Jet production in
ppBoer and Vogelsang, PRD 69, 094025 (2004)
Counts
Proton SpinkT
Beam is in and out of pageLook at back-to-back
jet opening angles
df
Sensitive to Sivers function only! No
Collins-type effects
Sivers distribution
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Sivers effect in di-hadron production
p0
h/-
Similar analysis possible in different
combinations of rapidity

• PHENIX Result from 2006 data
• Di-hadrons at central rapidities
• Asymmetry consistent with zero
• Analysis with large 2008 data in progress

(Work in progress)
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Sivers effect in heavy flavor production

• D meson production dominated by gluon-gluon
  fusion at RHIC energy
• Sensitive to gluon Sivers effect
• AN measured for muons from D decay (prompt
  muons)
• Smear by decay kinematics

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Sivers effect in J/Y production

• Exploratory measurement of AN J/Psi
• J/Y production mechanism not well understood
• Single spin asymmetries may shed light on
  production mechanism
• Constraints on gluon Sivers function

Yuan, PRD78014024,2008
AN
xF
(Yuan)
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Neutron production at very forward region

• Large negative SSA observed for xFgt0
• Diffractive physics
• Useful for local polarimetry at PHENIX

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Summary and outlook
Figure of merit LP2 (pb-1)
Future high luminosity transverse running at RHIC
(after 2011)

• PHENIX upgrades
• FOCAL 1 lt h lt 3 (2011)
• FVTX h lt 2.4 (2012)
• Heavy flavor
• Precise measurement of Collins effect
• g-jet

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PHENIX upgrades

• Vertex Detectors (2011-2012)
• h lt 2.4
• Heavy flavor tagging
• Separation of c/b
• Jet measurement
• Forward Calorimetery (2012-2013)
• 1 lt h lt 3
• AN ?0, Direct ?, ?-Jet
• Collins-type analyses