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


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


The BRAHMS Detector

MRS

FFS

BFS


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.


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.


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


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


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


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


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


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


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


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.


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


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


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)

X. N. Wang et al.


Invariant yields of charged particles in Au+Au and d+Au


Arsene et al.PRL 91 2003

R=Rcp(=2.2)/Rcp(=0)


RAuAu of Pions and Protons

=0=2.2

Preliminary

It is clear that baryons have a different behavior. No feed down corrections applied


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


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.


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


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,)


Particle identification in d-Au collisions


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?


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


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


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


• 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


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.


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-


p/ ratiosBRAHMS Preliminary

Ramiro Debbe for the BRAHMS collaboration Physics Department

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