The Other STARPHENIX Discrepancy Differences in the f analyses

1
The Other STAR-PHENIX DiscrepancyDifferences
in the f analyses

• Charles Maguire
• Vanderbilt University
• L/H PWG meeting August 25, 2005

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Outline

• Numerical statement of Run2 discrepancy
• Update from QM05 presentations
• Systematic comparisons of Run2 data
• Its not just a one data point error effect
  (Rafelski conjecture)
• Action plan for further studies
• Plans for eventual contact again with STAR (and
  Rafelski?)
• Previous short contact before QM04, no resolution

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Current Status of the Run2 DiscrepancyLooking at
the integrated yield numbers dN/dy

• Publications from Run2 AuAu data at 200 GeV
• STAR in PL B 612 (April 2005) 181-189
• PHENIX in PR C 72 (July 2005) 014903
• One common centrality bin and minimum bias
  datacan be directly compared using exponential
  fitting

Run2 discrepancy factors for dN/dy 1.69
/- 0.27 (0 - 10 centrality) 1.79 /- 0.13
(minimum bias)
statisticalerrors only
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Update from QM05 Presentations

• Both STAR and PHENIX presented Run4 yield results
• Both stated that their Run4 results agreed with
  their Run2 resultsBy inference the integrated
  yield discrepancy persists for Run4
• Questions were asked about the STAR-PHENIX
  discrepancyObvious interest in getting this
  discrepancy resolved
• STAR had a back-up slide not shown quoting a
  Rafelski et al. preprintwhich questioned the
  lowest PHENIX mT data point in 0-10
  centrality(that back-up slide will be shown
  later in this presentation)
• STAR and PHENIX presented the first v2 results
  for the f
• STARs result tended to be higher than PHENIXs
  result but the error bars are too large to
  conclude that there is a discrepancy
• The yield discrepancy may diminish the credence
  of the v2 quotes ?
• PHENIX declined to show RdAu results for the f
• STAR declined to show Run4 RAA results for the f
  but PHENIX did show Run4 RAA results claiming f
  suppression
• In its Run2 paper STAR had shown an absence of
  suppression for the f

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Minimum Bias Data Comparison I
Two data sets are plottedThe two sets of data
are fitted by exponential functions. The same
mT range is used in both fits,omitting low mT
STAR points No significant change in
STAR results as compared with using their full
minimum bias mT range
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Minimum Bias Data Comparison II
Same data sets are plottedSame mT range used
but omitting lowest mT PHENIX data point Slight
changes in both dN/dy values, but the discrepancy
ratio is still the same at 1.7 /- 0.2
(statistical) The fact that STAR and PHENIX
disagree at the intermediate pT values means that
STAR doesnt see f suppression but PHENIX does
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Most Central Bin Data Comparison I
The 0-10 data sets are plottedSame mT range
used including lowest mT PHENIX data point but
omitting the lowest STAR mT points No
significant change in STARs result as compared
with using all their data.
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Most Central Bin Data Comparison II
The 0-10 data sets are plotted.Same mT fit
range used but dropping lowest mT PHENIX data
point. Significant changes in STARs results
with just one more data point omittedT jumps
from 344 to 395 MeV dN/dy drops from 6.77 to
4.84 STARs lowest 6 mT data points appear to be
on a different exponential line compared to the
highest 6 mT points in the 0-10 bin. This was
not the case for the min bias bin issue of
STARs kink analysis for higher pT kaons? No
significant change from PHENIXs original result
with lowest mT point. Discrepancy ratio becomes
1.3 /- 0.3
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RAA and RCP From Run2 STAR (PLB figure)
STAR sees almost the same RCP 0.5 for the f as
PHENIX in the Run2 data
STAR sees no RAA suppression for the f in the
0-5 centrality bin from Run2 for the pT range
1.5 to 3.4 GeV/c
STAR sees RAA 1.5 enhancement for the f in the
60-80 centrality bin for the pT range 1.5 to 3.4
GeV/c
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RAA and RCP from Run4 PHENIX (QM05 prelim
figures)
PHENIX claims RAA 0.4 suppression for the f in
the 0-10 centrality bin for the pT range 1.5 to
2.1 GeV/c comparable to effect seen in the
p0Suppression decreases in the 60-90 bin,
again comparable to the p0 RCP for the f
comparable to what STAR has published for Run2
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Unshown STAR Backup Slide from QM05(but it
shows what they are thinking)
Johann Rafelski etc. nucl-th/0412072
Rafelski et al. conjecture that the lowest PHENIX
mT data point is a factor of 1.5 too low and this
drives the low dN/dy value for PHENIX. Since
STAR has more low mT data, then STARs result is
more believable
0 - 10 centralitySTAR data
0 - 10 centralityPHENIX data
My opinion (see next slide)By using a linear
plot Rafelski et al. obscure the difference in
normalization at the higher mT points. Rafelski
et al. also ignore the minimum bias data
discrepancy.
0 - 10 centralitySTAR and PHENIX
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Checking the Rafelski et al Conjecture Johann
Rafelski etc. nucl-th/0412072
Rafelski et al. conjecture that the lowest PHENIX
mT data point is a factor of 1.5 too low and this
drives the low dN/dy value for PHENIX. Since
STAR has more low mT data, then STARs result is
more believable
Actual fact Only if all of PHENIXs data points
were increased by a factor of 1.5 would there be
agreement with STARs results.A change of 1.5
in just the lowest PHENIX mT data point gives
very little change in the fit result for dN/dy
and T. Changes are actually well within the fit
uncertainties.
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Question about RdAu for the f in PHENIX Values
appear to be systematically low?
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Possible mistakes made by PHENIX analysis

• Numerical error
• Simplest explanation is that there is a
  persistent numerical mistakeof order 1.5 in
  computing final yield values
• Difficult to believe since there have been more
  than one independent analyses of the yield values
  (UCR, WIS, and VU) for Run2 and Run4
• Monte Carlo error fiducial volume
• Real dead areas not completely accounted for in
  simulation
• Difficult to believe since there have been
  extensive real vs MC acceptance checks in both
  East and West Arms
• Such an error would affect all analyses, but
  pairs worse than singles
• Monte Carlo error radiation length
• Assume PISA omits a significant 1-2 radiation
  lengthwould have to be after DC/PC1 in view of
  photon conversion studies
• Increased absoprtion would attenuate lower
  momentum kaon
• Assumption needs to be systematically studied
  with PISA changes
• Would also want to check the effect on the proton
  acceptances

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Initial List of Action Items

• Embedding for Run4
• The embedding effort for Run4 was not completed
  in time for QM05
• Dedicated embedding effort needs to be resumed
  for Run4
• Who will do it and where?
• Monte Carlo radiation length checks
• Will first check current sensitivity, e.g. how
  much energy is being lost by kaons and protons
  traversing all the way to the EMCal or TOF?
• Will add 1 and 2 additions at the PC1 region
• Checks will be made on proton and kaon
  acceptances (CFM will oversee this)
• Monte Carlo fiducial volume re-checks
• There are gaping holes in the the Dch acceptance
  which arerun dependent. Are these being
  properly accounted?
• Any serious fiducial volume change affects all
  analyses
• Schedule for external contacts with STAR and
  Rafelski et al.?
• Want to avoid the issue being settled by a
  theory preprint
• Should we send a work-in-progress set of plots
  to each?