Spin effects in large rapidity neutral pion production at STAR

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Spin effects in large rapidity neutral pion
production at STAR
OGAWA, Akio
For Collaboration

• STAR experiment and Forward Pion Detector
• Forward physics in hadron collider
• Analyzing power with transverse polarized proton
  beams
• Conclusions and outlook

• Trieste Italy

12 Oct 2004
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The Collaboration
Solenoid Tracker At RHIC
522 collaborators 51 institutions 12 countries
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STAR Detector
TPC -1.0 lt ? lt 1.0 Forward-TPC 2.8 lt ??? lt
3.8 BBC 2.2 lt ??? lt 5.0 FPD ? 4.1 and
3.6

• Upgraded Forward ?? Detector (FPD)
• Pb-glass EM calorimeter
• (from IHEP Protovino, used in E704)
• Shower-Maximum Detector (SMD)
• Preshower

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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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Forward p0 Inclusive Cross Section

• STAR data at
• ??? 3.8 (hep-ex/0310058, Phys. Rev. Lett. 92
  (2004) 171801)
• ??? 3.3 (hep-ex/0403012, Preliminary)
• NLO pQCD calculations at fixed ? with equal
  factorization and renormalization scales pT
• Solid and dashed curves differ primarily in the
  g ? ? fragmentation function

STAR data consistent with Next-to-Leading Order
pQCD calculations in contrast to data at lower ?s
(Bourrely and Soffer, Eur.Phys.J. C36 (2004)
371-374)
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• PYTHIA (with detector effects) predicts
• S grows with ltxFgt and ltpT,pgt
• ss decrease with ltxFgt and ltpT,pgt
• PYTHIA prediction agrees with data
• Larger intrinsic kT required to fit data
• Another check for understanding of the process
• Tool for spin and low x gluon physics (in d-Au)

STAR Preliminary
25ltEplt35GeV
STAR Preliminary
45ltEplt55GeV
Statistical errors only
nucl-ex/0408004
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Large Analyzing Powers at RHIC

• First measurement of AN for forward p0 production
  at ?s200GeV

• Similar to FNAL E704 result at ?s 20 GeV
• In agreement with several models including
  different dynamics

STAR collaboration, hep-ex/0310058, Phys. Rev.
Lett. 92 (2004) 171801

• Sivers spin and k? correlation in initial state
  (related to orbital angular momentum?)
• Collins Transversity distribution function
  spin-dependent fragmentation function
• ? suppressed? (hep-ph/0408356)
• Qiu and Sterman (initial-state) / Koike
  (final-state) twist-3 pQCD calculations

First shown at spin2002

• pT dependence?
• xFlt0?
• AN with mid-rapidity correlation?

• Spin dependence in jet?
• Heavy flavors??
• Related to gluon saturation???

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Mass resolution 20MeV We understand gain 2
level Efficiencies is almost purely geometrically
determined
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RHIC Run3 data analysis for FPD
RHIC-Run3 (2003 May) Polarization 30 0.5/pb
with transverse pol. in 2 weeks (0.4/pb with
longitudinal pol. In 2 weeks)
Polarization is measured by RHIC pC CNI
polarimeter FPD East North South Cross
ratio method FPD West South Single arm
measurement Relative luminosity R
is measured by BBC ? J.
Kiryluks talk 2 measurements are consistent
? averaged
Left
Negative xF p0
Positive xF p0
Polarized beam
Unpolarized beam
Right
positive AN more p0 going left to polarized
beam
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Measurement of AN for forward p0 production at
?s200GeV
Statistical error only for lthgt4.1

• Positive AN at large positive xF has been
  confirmed
• Larger significance to be non-zero positive
  than published data
• The first measurement of negative xF AN has been
  done, and is consistent with zero
• ? Sensitive to twist-3 gluon-gluon correlation

STAR Preliminary
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Conclusions

• Forward hadron production at hadron-hadron
  collider selects high-x (thus high polarization)
  quark low-x gluon scatterings
• Inclusive cross section is consistent with NLO
  pQCD calculations and PYTHIA(LO pQCD parton
  showers)
• Di-hadron correlation with large rapidity
  interval in pp agree with PYTHIA prediction
• Analyzing power for forward p0 mesons at large
  positive xF was found to be positive
• The first measurement of negative xF AN has been
  done, and is consistent with zero
• More (Cross section at lthgt4.1, ATT, ALL,
  correlations with other detectors) on the way

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Outlook
Current FPD

• Disentangling the dynamics of AN via
• Higher precision AN measurement vs xF and pT
• AN with mid rapidity correlation
• Forward jet
• Proposal for forward calorimeter upgrade
• Heavy mesons and direct photons
• Low x gluons in nuclei
• Mid rapidity jets
• Di-jet kT balance ? gluon Sivers function
• Inside jet particle correlation ? Collins
  function Transversity
• ALLfor forward p0 gluon polarization at low x

h4.2
h3.2
2.4m square 1500 cells
h2.5

• Tomorrow 13th(wed) evening
• RHIC upgrade session

RHIC run for 2005 starts in November (next
month) First long physics run for pp, with
P50, starting 2005 Jan Plans for some data
taking with transverse spin _at_ STAR after
longitudinal spin data taking