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HIGH P(T) SUPRESSION AT FORWARD RAPIDITIES IN
AUAU AT \/sNN 200 GeV Catalin Ristea NBI
XXXXth Rencontres de Moriond March 12-19 2005
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Intro
- high pt particles are produced from the
fragmentation of jets resulting in hard
scatterings.- loose energy by gluon
bremsstrahlung sensitive to the properties of
the traversed medium jet quenching.
Brahms PRL 91(2003)

- peripheral collisions have minimum collective
effect gt similar to pp collisions.
- models describing the suppression take into
account gluon saturation, gluon shadowing,
parton recombination, jet-quenching.- Cronin
enhancement.
XXXXth Rencontres de Moriond March 12-19 2005
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Identified hadrons at y 0
Phenix PRC69 (2004)
Particle dependent nuclear modification factor
observed at mid-rapidity - pions are strongly
suppressed - protons are not suppressed, but
even enhanced - possible explanations... What
about higher rapidities ?
XXXXth Rencontres de Moriond March 12-19 2005
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Brahms setup
Brahms two arm magnetic spectrometers providing
good momentum resolution and hadron
identification capabilities over a wide
rapidity range
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Acceptances and pt spectra (AuAu)
- small solid angle 6 msr for MRS and 0.5 msr
for FS - map out the particle phase-space by
collecting data with many different spectrometer
settings - average spectrum - corrections
- inclusive pt spectra for nonidentified h and
h- at ? 3.2 - power-low shape, where the vast
majority of particles are produced in the pt
region below 2 GeV/c - steeper at higher ?
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High pt suppression
Brahms PRL 91(2003)
- approximate binary scaling in semi-peripheral
collisions - strong suppression in central
collisions (f. 4) - similar behaviour at ? 0 and
2.2 -gt source extended to ? 2 - longitudinal
expansion at y gt0 - Rcp similar to Raa (no
medium effect in semi-peripheral colls.) - most
systematic errors cancel out in Rcp - the
suppression can not be explained by hadronic
energy loss
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Summary
Central AuAu collisions Strong pion suppression
at all rapidities - even stronger at large ? At
??3.2, suppression of all hadrons, with Rcp(p) gt
Rcp(K) gt Rcp(?) Centrality dependence dAu
collisions Cronin-like enhancement at ?0 Clear
suppression as ? changes from 0 to 3.2 CGC models
can describe the enhancement/suppression effects
in dAu Strong suppression in central AuAu
collisions due to final state effects ? Partonic
energy loss More data still to be included We
have data to be analysed even at higher y/? (3,
2.3 degs 3.5)
XXXXth Rencontres de Moriond March 12-19 2005