Probing Transversity with Interference Fragmentation Function in p p Collisions

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Probing Transversity with Interference
Fragmentation Function in pp Collisions

• Ruizhe Yang, University of Illinois
• (For the PHENIX Collaboration)

PKU-RBRC Workshop on Transverse Spin Physics,
July 2008
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Measurements of quark transversity
Underway
1991
2005
Future
pp
RHIC Collins asym.
STAR, PHENIX, BRAHMS, 20042005 Inclusive AN
E704, 1991 Large forward SSA
RHIC IFF asym.
JParc, RHIC, FAIR Drell-Yan
HERMES 2005, COMPASS 2006 AUT
SIDIS
COMPASS p target
JLab 3He and 12 GeV
BELLE 2006 Collins FF
BELLE IFF
ee-
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Measurement of transversity in pp
Drell-Yan
IFF
Collins
RHIC
RHIC, FAIR
RHIC
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Comparison of IFF and Collins FF
Interference fragmentation function
J. Collins, S.Heppelmann, G. Ladinsky, Nuclear
Physics B, 420 (1994) 565
Matches PHENIX capability better
J. C. Collins, Nucl. Phys. B396, (1993) 161
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Definition of Vectors and Angles
Bacchetta and Radici, PRD70, 094032 (2004)
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Transversity from di-hadron SSA
Physics asymmetry
Hard scattering cross sectionfrom pQCD
Unpolarized quark distribution Known from DIS
IFF Di-hadron FF to be measured in ee-
Transversity to be extracted
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Why di-hadron SSA in pp

• Di-hadron vs single hadron
• Collinear factorization
• No model uncertainties due to kT dependence of FF
  and PDF
• Doesnt need quark momentum
• No need to separate effects like Sivers/Collins
  effects in single hadron measurement
• Completely independent measurement
• Di-hadron measurement in fixed target vs collider
• At higher scale
• sub-leading twist effects suppressed
• factorization assumption better justified

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Ongoing IFF measurement at BELLE (RBRC/Illinois)
IFF sensitivity projection from data
Artru and Collins, Z. Phys. C69, 277 (1996) Boer,
Jakob, and Radici, PRD67, 094003 (2003)
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Models for IFF

• Use partial wave analysis of pp phase shift data
  to model IFF
• Sign change around r mass
• Jaffe, Jin and Tang, PRL 80 (1998) 1166

• Breit-Wigner shape for p wave
• No sign change around r mass
• Trend consistent with HERMES results
• Bacchetta and Radici, Phys. Rev. D 74, 114007
  (2006)

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Polarized pp Collisions at RHIC

• Spin rotators select polarization directions at
  collision points
• Polarimetry with pC and Hjet

Absolute Polarimeter (H jet)
RHIC pC Polarimeters
BRAHMS PP2PP
PHOBOS
Spin Rotators
STAR
PHENIX
Siberian Snakes
Partial Snake
Polarized H- Source 1 mA 70-80 polarization
Strong Snake
Helical Partial Snake
LINAC
AGS
BOOSTER
AGS pC Polarimeter
200 MeV Polarimeter
The RHIC (Relativistic Heavy Ion Collider)
complex at Brookhaven National Laboratory
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PHENIX detectors used for IFF analysis

• Use 2 separate spectrometer arms at central
  rapidity, h lt 0.35
• Azimuthal coverage 90 90
• Electromagnetic Calorimeters
• PbSC PbGl
• High granularity Dh?Df0.01?0.01
• Tracking of charged particles
• Drift chamber, pad chambers
• Beam-beam counter as a luminosity monitor
• Exploit good event selection capability, high
  bandwidth/event rate

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Event selection

• Data taken in 2006
• Integrated luminosity 2.7 pb-1
• Average polarization 51, in radial direction
• Find charge-ordered pairs (hp0), (p0h-), (hh-)
• p0
• PT gt 1 GeV/c
• h/-
• 1 GeV/c lt PT lt 4.7 GeV/c
• Assuming pion mass for all hadrons
• Both particles come from the same detector arm
  (Dh?Df0.7?p/2)
• One particle fires the trigger (EMCal cluster
  with energy gt 1.4 GeV)
• Calculate the asymmetry, extract the analyzing
  power

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vs invariant mass of the pair
Consistent with 0, despite the second bin of p0h-
pairs and the last bin of hh- pairs are 2s from 0
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vs pT of the pair (0.5 lt m lt 0.78)
Soft physics contributions at at low pT, may be
non-neglegible
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vs pT of the pair (0.78 lt m lt 1.0)
Soft physics contributions at at low pT, may be
non-neglegible
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Conclusion and status

• Conclusion
• First measurement of di-hadron SSA in pp
  collisions
• No significant asymmetries have been observed
  with current statistics
• New data available from transverse running in
  2008
• Integrated luminosity 5.2 pb-1
• Average polarization 46

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Future

• Prospects from future large transverse spin data
  sample from PHENIX
• Sub-percent sensitivity possible

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PT and Invariant Mass of Pairs
p0h
p0h-
ph-
PT (GeV/c)
PT (GeV/c)
PT (GeV/c)
p0h
p0h-
ph-
mpp (GeV/c2)
mpp (GeV/c2)
mpp (GeV/c2)
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Particle Reconstruction

• Analyzing data taken in 2006, integrated
  luminosity 2.7 pb-1, polarization 55
• Pairs (p0p), (p0p-), (pp-)
• p0
• Photon cluster (energy, shower shape) from EMCal
• di-photon invariant mass spectrum
• PT gt 1 GeV/c
• p/-
• Momentum measured by bent in magnetic field
• 1 GeV/c lt PT lt 4.7 GeV/c

mgg (GeV/c2)
PT (GeV/c)