Status of the analysis of FPD data from Run6

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Status of the analysis of FPD data from Run6
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SPIN06 Abstract
Measurements of Transverse Spin Effects with the
Forward Pion Detector of STAR

• Status of the analysis of Run6 data
• AN(xF,pT) for p0 at vs200 GeV
• p0 production in forward region at vs62 GeV
• Jet-like events

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Transverse spin runs at STAR with forward
calorimetry 2001?2006
sampled
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Motivation for AN measurements in pp ? p0 X
W.Vogelsang http//www.npl.uiuc.edu/rseidl/worksh
ops/TransverseSpin_RHICAGS06/Vogelsang.pdf
U.dAlesio
Phenomenological models expect that p0 analyzing
power decreases with increasing pT
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Cell-by-cell calibration

• gains are determined from
• p0 peak position in 2? invariant
• mass distributions sorted by
• high towers
• accuracy of the calibration is
• at the level of 2

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Energy-dependent corrections
p0 peak position depends on the energy due to
energy leakages and ADC granularity (dedicated
MC study has been done)
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Run-dependent corrections
The FPD response vary with time/beam conditions
used for spin sorting
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Detector acceptance

• Strong correlation between xF
• and pT in the individual detectors
• Broader pT range in xF bins
• when combining data at
• lt?gt3.2 and 3.7

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Details of data analysis

• Event selection

30 fills, 467 runs gt 13.8M 2? events in four
matrices
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Details of data analysis
Analyzing power is measured by cross-ratio
method with two-arms (left-right) detector

Width of the distributions is generally consistent
with statistics
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p0 AN at vs200 GeV xF-dependence

• AN at positive xF grows with
• increasing xF
• AN at negative xF is consistent
• with zero
• Run 6 data at lt?gt3.7 are
• consistent with previous
• measurements

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AN(pT) at xF gt 0.4 (Run 35)
hep-ex/0512013
Online calibration of CNI polarimeter
Data are consistent with the 1/pT expectation of
pQCD
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AN(pT) in xF-bins (Run 6)

• Combined Run6 data at lt?gt3.2
• and 3.7
• No decrease with increasing pT
• is seen for the p0 analyzing
• power

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Summary

• In Run 6, 6.8 pb-1 of data with average beam
  polarization 60
• has been acquired in pp collisions at vs200
  GeV
• Sizable transverse single spin asymmetry is
  observed for
• forward rapidity inclusive p0 production at
  lt?gt3.2 and 3.7
• AN at positive xF grows with increasing
  xF
• AN at negative xF is consistent with
  zero
• No decrease of AN with increasing pT is
  seen in the explored range
• No systematic effects have been
  revealed besides threshold effect
• in the data at lt?gt3.2 accuracy of
  the measurements is driven
• by the statistics
• Run 6 preliminary results at vs200 GeV are
  ready for release?
• Additional study of systematic errors is to
  be done for
• the publication

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Summary

• Toward SPIN06
• re-analysis of Run 3 and Run 5 data with
  the same cuts as for Run 6
• to cover broader pT range
• theoreticians have been contacted hope
  to get predictions/calculations
• for the AN in the FPD kinematic region
• Analysis of the data at vs62 GeV is underway
• Still to do jet-like events
• simulation has been started
• calibration of the FPD outer matrices
  needs to be completed

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Backup
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Correlation between FPD gains and BBC rates
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Data to simulations comparison
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pp ? p0 X cross sections at vs200 GeV
nucl-ex/0602011

• The error bars are statistical plus
  point-to-point systematic
• Consistent with NLO pQCD calculations at 3.3 lt ?
  lt 4.0
• Data at low pT trend from KKP fragmentation
  functions toward Kretzer. PHENIX observed
  similar behavior at mid-rapidity.

NLO pQCD calculations by Vogelsang et al.
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Separated xF and pT dependence
Similar to ISR analysis J. Singh et al., Nucl.
Phys. B140, 189 (1978).
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distributions in pT bins