Recent Results from BRAHMS from y0 to y3

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Recent Results from BRAHMSfrom y0 to y3
I. G. Bearden
Niels Bohr Institute University of Copenhagen,
Denmark
for the BRAHMS
COLLABORATION
Quark Matter 2002, July 18-24, Nantes, France
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The BRAHMS Collaboration
I.G. Bearden7, D. Beavis1, C. Besliu10, Y.
Blyakhman6, J.Brzychczyk4, B. Budick6, H.
Bøggild7 , C. Chasman1, C. H. Christensen7, P.
Christiansen7, J.Cibor4, R.Debbe1, E. Enger12, J.
J. Gaardhøje7, M. Germinario7 , K. Grotowski4 ,
K. Hagel8, O. Hansen7, A.K. Holme12, H. Ito11,
E. Jacobsen7, A. Jipa10, J. I. Jordre10, F.
Jundt2, C.E.Jørgensen7, R. Karabowicz4 , T.
Keutgen9, E. J. Kim5, T. Kozik3, T.M.Larsen12, J.
H. Lee1, Y. K.Lee5, G. Løvhøjden2, Z. Majka3, A.
Makeev8, B. McBreen1, M. Mikkelsen12, M. Murray8,
J. Natowitz8, B.S.Nielsen7, K. Olchanski1, D.
Ouerdane7, R.Planeta4, F. Rami2, D. Roehrich9,
B. H. Samset12, D. Sandberg7, S. J. Sanders11,
R.A.Sheetz1, Z.Sosin3, P. Staszel7, T.S.
Tveter12, F.Videbæk1, R. Wada8, A.Wieloch3 and I.
S. Zgura10 1Brookhaven National Laboratory,
USA, 2IReS and Université Louis Pasteur,
Strasbourg, France 3Jagiellonian University,
Cracow, Poland, 4Institute of Nuclear Physics,
Cracow, Poland 5Johns Hopkins University,
Baltimore, USA, 6New York University, USA 7Niels
Bohr Institute, Blegdamsvej 17, University of
Copenhagen, Denmark 8Texas AM University,
College Station. USA, 9University of Bergen,
Norway 10University of Bucharest, Romania,
11University of Kansas, Lawrence,USA 12
University of Oslo Norway
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The BRAHMS Experiment
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Determination of Collision Vertex, Centrality
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Multiplicity density _at_ 200GeV

• 100AGeV100 AGeV
• ? N(ch)d?
• 4630
• Central 0-5
• dN(ch)/d? (?0) 632
• FWHM of distribution
• ?? 7.5? 0.5

For details, see the BRAHMS poster by S. Sanders,
H. Ito.
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Limiting fragmentation
Moving away from midrapidity particle
production looks like SPS
PLB 523 (2001) 227 BRAHMS
PRL 88 (2002) 2002301 BRAHMS
Phys Rev C (2000)62 014903
Shift data to beam frame of reference
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dNch/d? Comparison to Models
AMPT High density QCD gluon saturation Kharzeev
and Levin, PLB523(2001)79
?SNN200GeV
Differences for Peripheral Collisions but Small
effect !
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FORWARD 1lthlt3.6
MRS -0.5lthlt1
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PID in BRAHMS
MRS TOF
FS TOF C1
RICH
FS TOF
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Ratios are (relatively) easy...
Ratios could vary in pt, and in y Narrow y bins,
look vs pt
geometric acceptance same for particles and
antiparticles, so correction is not needed.
For given B field, angular setting, compare ()
and (-) polarity
Normalize to number of triggers, and --bingo!--
ratios....
No dependence on transverse momentum or
centrality See poster for details of the analysis!
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Particle/Particle vs rapidity
BRAHMS, submitted to PRL 12/07/02 nucl-ex/0207006
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Becattini T170, gs1 PBM (PhysLettB518 (2000)41)
predicts y0 ratios almost exactly K-/K exp(2m
s/T)(pbar/p)1/3 K- /K(pbar/p)1/4 is a fit to
the data points
BRAHMS, submitted to PRL 12/07/02 nucl-ex/0207006
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Not surprisingly, the antiparticle spectra dont
look much different...at y0!
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Only small part of high rapidity data
analyzed...so far.
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Inverse pT Slope vs. mass...
Nb all fits are in pt, over same range for all
particles, at all rapidities
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Strangeness ratio K/?

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Strangeness K/? systematics
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p and pbar yields
0-10 BRAHMS Preliminary ?SNN200 GeV 0-10
Central
y0.8
y 0
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p and pbar at y2.9
BRAHMS Preliminary
proton Yield 33.7 ?1.8 ? 5.1 (Inverse
pt slope 341.8 ? 13.8
antiproton Yield 10.5 ? 0.8 ?1.6 (Inverse pt
slope 325.5?17.3)
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Net protons, first shot...
d2N/dpTdy
BRAHMS Preliminary
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Net protons vs Rapidity!
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Can we kill models?
Points scaled by 2
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Q
AMPT
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High pt y0
y0 High pt y2.2
C.E.Jørgensen Parallel session I today.
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Future plans...

• Analyze complete data set at high rapidity
• Better pt coverage
• (slightly) higher y
• Spectra, yields for 1ltylt3
• Source size at mid, forward rapidity
• pp data
• Longer term...
• Upgrades better high pt PID in MRS

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Summary

• K-/K, pbar/p ratios fall off with rapidity
• Universal correlation between K-/K and pbar/p
• K-/p- decreases from 0.15 (y0) to 0.1(y3)
• Inverse slope decreases with rapidity
• Measured dN/dy over 3 units of rapidity.
• Dramatic increase in net protons at y3
• ? Low to high chemical potential from y0 to y3
• ?Net baryon central plateau (y0 to almost y2)
• ?Significant transparency

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Radius versus Momentum
RICH used for PID pgt15GeV/c Kgt8 GeV/c pgt4 GeV/c