Ramiro Debbe for the BRAHMS collaboration Physics Department
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Transcript of Ramiro Debbe for the BRAHMS collaboration Physics Department
Kolkata India 8-12 February 2005
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Ramiro Debbe
for the BRAHMS collaborationPhysics Department
BRAHMS Overview
5th International Conference on Physics and Astrophysics of
Quark Gluon Plasma
Kolkata India 8-12 February 2005
Outline of the presentation
• A brief summary of particle production in Au-Au collisions at √sNN= 200GeV.
• Intermediate Pt physics. Pt suppression and the formation of an opaque dense medium and will discuss its behavior as function of rapidity and centrality.
• Summary
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The BRAHMS Detector
MRS
FFS
BFS
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TMA
INEL
ZDC ZDCBB BB
multiplicity [a.u.]
Event characterization
The centrality of the collision for the results that will be presented is defined as fractions of the total multiplicity measured with the TMA in -2<<2
The centrality of Au-Au collisions can also be defined with the ZDC and BB or TMA correlations.
Our triggers are defined with the ZDC and BB, p+p and d+Au collisions were triggered with the INEL detectors.
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Charged particle production
This is one of the first measurements at RHIC with a multiplicity density unexpectedly low. It may indicate the high degree of coherence in high energy A+A collisions.
It already shows a bell shape and a slow growth as function of centrality.
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Rapidity Densities in Au-Au at sNN = 200 GeV
Integrated multiplicities (Gaussian fit)
N() ~ 1780N(+) ~ 1760N(K+) ~ 290N(K) ~ 240N(pbar)~ 85
0 1 2 3 4 5rapidity
Total number of +K+p > 4000 (consistent with thedNch/d measurement)
nucl-ex/0403050
The longitudinal expansion does not modify much the shapes of the thermal source or the PDF of the colliding ions.
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Particle Yields
n
T
p
pA
−
⎟⎟⎠
⎞⎜⎜⎝
⎛+
0
1
Pions: power law Protons: Gaussian
⎥⎦
⎤⎢⎣
⎡−
2
2
2exp
σTpA
Top
5%
cen
tral
collisio
ns
Kaons: exponential
⎟⎠
⎞⎜⎝
⎛ −−
T
mmA Texp
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Transverse Dynamics
,K,p spectra described byblast wave modelWe see a weak rapidity dependence of both T and
K
p
BRAHMS preliminary
Kinetic frezze out temp. T115 Mev, T0.7c at y=0• Flow velocity decreases with rapidity. Lower density lower pressure less flow• Temperature increases. Lower density faster freeze out higher temperature
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Baryon number transportEven at this high energy, there is a non-zero net proton at mid-rapidity.
Baryon junctions can have a small-x component that would bring baryon number to mid-rapidity.
No weak decay corrections
Once the corrections are included: nB=2.03±0.08np
Au+Au s=200GeV 0-10% central
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Rapidity loss
The average rapidity loss at RHIC energies does not scale as the ones measured at lower energy values.
PRL 93, 1020301, (2003) 73±6% of the beam energy available for particle production
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Energy Balance
• Fit , K and p distributions (dN/dy and mT vs y) total energy of , K and p • Assume reasonable distribution for particles we don’t detect (0,n,…)• Calculate the total energy…
∑ ∫ ⎥⎦
⎤⎢⎣
⎡=
specieTtotal dy cosh(y)m
dydN E
NB: the method is verysensitive to the tails of the dN/dy dist. (10-15%) k+k-
pi+
pi-
pi0
lbar
k0bar
p
pbar
l
nbark0
n
?
35 TeV (EbeamNpart)of which 25 TeV are carried by produced particles.
p : 3108 p : 428K+ : 1628K- : 1093+: 5888- : 6117
0 : 6004n : 3729n : 513K0 : 1628K0 : 1093 : 1879 : 342
Energy (in GeV)
sum: 33.4 TeVproduced: 24.8TeV
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Strangeness production
Mid-rapidity RHIC is well beyond the “resonance gas” of CERN. It appears that the production of K- and K+ is becoming “similar” .
At forward rapidities, the baryon chemical potential has grown by ~ 5 and we may be entering again a CERN like system.
Integrated
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Particle abundances and statistical models
For a fixed chemical freeze out temperature. The ratios of anti-particle to particle correlate along the Becattini et al. calculation based on their statistical model.
s =0
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Results from p+p collisions
We found remarkable similarity in the baryon number transport in Au+Au and p+p collisions as seen in the anti-proton/proton ratio.
The Au+Au results were extracted from 0-20% central events.
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0000NN = -= -0.08 +- 0.005 +- 0.08 +- 0.005 +- [0.015] in 0.17 < x[0.015] in 0.17 < xFF < 0.32< 0.32
0000NN = = +0.05 +- 0.005 +- +0.05 +- 0.005 +- [0.015] in 0.17 < x[0.015] in 0.17 < xFF < < 0.320.32
An = /P with P ~40-45% = (N+ /L+ - N-/L-) / (N+ /L+ + N-/L-)
Transverse Spin Asymmetries An
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PT suppression can be related to two possible mechanisms:
Modification of the wave function in the initial state
Cronin type enhancement by coherent multiple scattering at y~0
Quantum evolution at high rapidity. Gluon emmission tamed by fusion. dNg/d(ln1/x) = s (2Ng - Ng2)
The growth of the numerator in RABor Rcp is slower than that of the denominator.
Y
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pT suppression cont.
Energy loss in a medium formed after the collision :
Energy loss is encoded in the fragmentation of the final state parton. The number of interactions (each emitting a gluon) depends on the density of the medium.
Gluon density of the formed medium (rapidity dependent)
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Invariant yields of charged particles in Au+Au and d+Au
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Arsene et al.PRL 91 2003
R=Rcp(=2.2)/Rcp(=0)
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RAuAu of Pions and Protons
=0=2.2
Preliminary
It is clear that baryons have a different behavior. No feed down corrections applied
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d+Au nuclear modification factor
The absence of suppression in d+Au at y=0 and back-to-back correlations have been considered necessary conditions to the formation of a dense and opaque medium; the suppression seen in Au+Au is a final state effect.
But the possibility of a saturated Au cannot be excluded
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Spectra from d-Au and p-p collisions
Upper panels show an outline of the data used construct the spectra. At each angle, one or several magnetic field settings were used.
Spectra are acceptance and detector efficiency corrected, other corrections as momentum resolution and binning effects were not included.
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PRL 94 (2004)Cronin like enhancement at Cronin like enhancement at =0.=0.
Clear suppression as Clear suppression as changes up to 3.2 changes up to 3.2
Same ratio made with dn/dSame ratio made with dn/d follows the follows the low plow pTT R RdAudAu
RdAu as function of rapidity
Minimum bias with
<< Ncoll> = 7.2> = 7.2±0.3
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Rcp ratios At =0 the central events have the ratio systematically above that of semi-central events. We see a reversal of behavior as we study events at =3.2
Rcp
1/<Ncoll central> NABcentral(pT,
1/<Ncoll periph> NAB
periph(pT,)
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Particle identification in d-Au collisions
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Identified particles in d-Au at =3.2
80% of the negative charged particles at =3 are pions
Many protons in the most forward d+Au. Is this beam fragmentation?
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RdAu for anti-protons and pions (min bias)
This will not be the first time baryons show a different nuclear modification factor.
PHENIX reported such difference at y=0 in AuAu and dAu systems
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Nuclear modification factor RAuAu
- different centrality classesEnergy dependence (SPSRHIC) pT=3-4GeV/c
pT=3-4GeV/c40-60%20-40%10-20%0-10%
RAuAu at sNN = 62.4 GeV
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Strong centrality dependence:
Rcp(0-10%) < Rcp(20-40%)
No significant h dependence
in 0<h<3.2
Maximum at pT~2GeV/c
Rcp(+) > Rcp(-)
Systematic Errors
- 10-15% overall
- 10% p-by-p
~3.2
~2.2~0
BRAHMS PRL 91 (2003)
BRAHMS Preliminary
Rcp of charged hadrons at ~3.2
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• Data
BRAHMS Preliminary
±K±
p,pbar
Suppression for all particles
maximum at pT~2GeV/c
Rcp(+) ~ Rcp(-) for p, K, p
Rcp(p) > Rcp(K) > Rcp(p)
Rcp for Identified particles at y~3
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Summary
• We have now a wide view of bulk particle production in Au+Au collisions. There are no extended plateaus in the density distributions, ~ 70% of the beam energy is made available for particle production in central Au+Au.
• Forward physics has proved to be a fertile ground for discovery and an important ingredient of our understanding of the new medium formed at RHIC.
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The BRAHMS Collaboration
I.Arsene10,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,J. J. Gaardhøje7,M. Germinario7, K. Hagel8, O. Hansen7, H. Ito11, E. Jacobsen7, A. Jipa10, J. I. Jordre10, F. Jundt2,
C.E.Jørgensen7, E. J. Kim5, T. Kozik3, T.M.Larsen12, J. H. Lee1, Y. K.Lee5, G. Løvhøjden2, Z. Majka3, A. Makeev8, B. McBreen1, M. Murray8, J. Natowitz8, B. Neuman11,B.S.Nielsen7, K. Olchanski1, D. Ouerdane7, R.Planeta4, F. Rami2,
D. Roehrich9, B. H. Samset12, S. J. Sanders11, I. S. Sgura10, R.A.Sheetz1, Z.Sosin3, P. Staszel7, T.S. Tveter12, F.Videbæk1, R. Wada8 ,A.Wieloch3,Z. Yin9
1Brookhaven National Laboratory, USA, 2IReS and Université Louis Pasteur, Strasbourg, France3Jagiellonian University, Cracow, Poland, 4Institute of Nuclear Physics, Cracow, Poland
5Johns Hopkins University, Baltimore, USA, 6New York University, USA7Niels Bohr Institute, Blegdamsvej 17, University of Copenhagen, Denmark
8Texas A&M University, College Station. USA, 9University of Bergen, Norway 10University of Bucharest, Romania, 11University of Kansas, Lawrence,USA
12 University of Oslo Norway
- 12 institutions-
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p/ ratiosBRAHMS Preliminary
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