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Charged Particle Production at High Rapidity in p+p collisions at RHIC. Ramiro Debbe. Outline of presentation. Brief description of the measurement. - PowerPoint PPT Presentation
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CIPANP2006 High Energy Hadron 1-June-2006
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Charged Particle Production at High Rapidity in p+p collisions at RHIC
Ramiro Debbe
CIPANP2006 High Energy Hadron 1-June-2006
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Outline of presentation
Brief description of the measurement.
These are the first measurements of identified charged particle production at this energy (200 GeV) at high rapidity (y~3)
Comparison of spectra and NLO pQCD calculations.
Will describe the measurement of the p/+ ratio at high rapidity.
CIPANP2006 High Energy Hadron 1-June-2006
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CC
3.25<<5.25
The data at forward rapidities were collected with FS at 4º ( ~3) and 2.3º (~3.4)
CIPANP2006 High Energy Hadron 1-June-2006
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•Covers ~70% of pp inelastic cross-section (41mb)• 3.25 < || < 5.25 range• Vertex resolution (z)~ 1.6cm • ±40cm in z used in the analysis
CIPANP2006 High Energy Hadron 1-June-2006
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We use Pythia 6.326 to extract the trigger bias introduced on the yields and translate them into differential cross-sections normalized to total inelastic (41 mb )
Total: Msel=0 and exclude elastic events.
NSD: semi hard QCD 2->2, SDA, SDB, DD, low Pt and at least one hit in both CC
Correction for trigger bias.
GEANT3 has CC FFS and BFS
CIPANP2006 High Energy Hadron 1-June-2006
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Particle Identification is done with BRAHMS RICH
One angle setting, several (6) magnetic field settings
Radiator gas with high index of refraction.
Radius resolution: 1.2 %
Efficiency 97%
CIPANP2006 High Energy Hadron 1-June-2006
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p+p identified spectra at high rapidity
Built with data from 4 and 2.3 degrees and up to six magnetic field settings.
Geometrical acceptance corrections applied as well as absorption and decay in flight.
Trigger bias (~20%) is also corrected. Normalization to total inelastic cross-section (41 mb)
BRAHMS Preliminary
Red : positive particles
Blue empty: negative particles
CIPANP2006 High Energy Hadron 1-June-2006
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Comparison of measurement and NLO pQCD calculations
The fragmentation functions differ by the amount of g-> The data points toward a dominance of gluon-gluon and gluon-quark below 10 GeV/c
NLO pQCD can reproduce the data at RHIC energies. This is a strong indication that the correct description of this should be done with partonic degrees of freedom
CIPANP2006 High Energy Hadron 1-June-2006
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√s=23.3GeV √s=52.8GeV
NLO-pQCD can reproduce y~0 hadron production at ISR but fails at higher rapidities.
Neutral pion production at small angles
at ISR
Lloyd et al.
PRL 45 89 (1980)
Bourrely and Soffer Eur. Phys. J. C36 371-374 (2004)
xF xF
Ed3
dp3 [
b/G
e V3 ]
Ed3
dp3 [
b/G
e V3 ]
Data-pQCD difference at pT=1.5GeV
CIPANP2006 High Energy Hadron 1-June-2006
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NLO pQCD for proton+anti-proton compared to data
A recent update of the KKP fragmentation function is used for this comparison: AKK where g->p has increased relevance.
The AKK function does well at y=0 (STAR p+p) where the ratio anti-p/p~1 can be seen as consistent with dominance of gg or gq processes, but in my opinion is not appropriate for high rapidities because of the small value of the p/p ratio.
CIPANP2006 High Energy Hadron 1-June-2006
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STAR 0 at high rapidity
FPD: Lead-glass arrays 3.4<<4.0 on both sides of collision.
Spectra at 3.3 and 3.8 obtained with a smaller FPD
arXiv:nucl-ex/0602011KKP frag. func. has higher g-> than Kretzer
CIPANP2006 High Energy Hadron 1-June-2006
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NLO pQCD comparisons to data
Calculations done by W. Vogelsang. Only one scale =pT and the same fragmentation functions as used for the PHENIX comparison.
KKP FF does a better job compared to Kretzer, can we extend the conclusion about gg and gq dominance at these rapidities?
BRAHMS Preliminary
KKP has only 0 frag. Modifications were needed to calculate charged pions
CIPANP2006 High Energy Hadron 1-June-2006
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Particle/anti-particle ratios at y=3.0 and NLO comparisons
The NLO calculation reproduces the data closely, the pion ratio does not have corrections from weak decays (we estimate that the correction will be small).
CIPANP2006 High Energy Hadron 1-June-2006
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Ratios p/+ at y=3.0 and 3.3 The -/+ ratio is consistent with dominance of valence quarks (at high pT) at these rapidities.
The difference between protons and anti-protons indicates another mechanism besides fragmentation (as AKK) that puts so many protons at high pT at this rapidities.
Red: proton/+ Blue: p/ -
BRAHMS Preliminary
Small p/p ratio eliminates possible strong gluon -> p or p fragmentation (p/p~1)
e+e- p+pbar/++ - ALEPH
CIPANP2006 High Energy Hadron 1-June-2006
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Summary and outlook
BRAHMS has measured, for the first time, identified charged particle production at high rapidity.
NLO pQCD calculations describe well the pion and kaon production with a favored set of fragmentation functions known as KKP. These agreements imply a dominance of g q and g g processes at these high rapidities as was the case for the measurements of neutral pions at mid-rapidity.
The behavior of protons around y=3 cannot be explained with NLO calculation and the abundance of protons (with respect to positive pions) at high pT is an open question.