Ramiro Debbe

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BRAHMS Overview
5th International Conference on Physics and
Astrophysics of Quark Gluon Plasma
Ramiro Debbe for the BRAHMS collaboration Physics
Department
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Outline of the presentation

• A brief summary of particle production in Au-Au
  collisions at vsNN 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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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
-2lt?lt2
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,
pp and dAu 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 AA 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
nucl-ex/0403050
Integrated multiplicities (Gaussian fit) N(??)
1780 N(?) 1760 N(K) 290 N(K?)
240 N(pbar) 85
Total number of ?Kp gt 4000 (consistent with
the dNch/d? measurement)
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
Top 5 central collisions
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Transverse Dynamics
?,K,p spectra described by blast wave model We
see a weak rapidity dependence of both T and ?
?
K
p

• Kinetic frezze out temp. T?115 Mev, ?T?0.7c at
  y0
• Flow velocity decreases with rapidity.
• Lower density ? lower pressure ? less flow
• Temperature increases.
• Lower density ? faster freeze out ? higher
  temperature

BRAHMS preliminary
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Baryon number transport
Even 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 nB2.030.08np
AuAu ?s200GeV 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.
736 of the beam energy available for particle
production
PRL 93, 1020301, (2003)
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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 dont detect (?0,n,?)
• Calculate the total energy

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Strangeness production
Integrated
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.
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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 pp collisions
We found remarkable similarity in the baryon
number transport in AuAu and pp collisions as
seen in the anti-proton/proton ratio.
The AuAu results were extracted from 0-20
central events.
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Transverse Spin Asymmetries An

• An e /P with P 40-45
• (N /L - N-/L-) / (N /L N-/L-)

ltegt 0.022 gt AN 0.05 - 0.005 - 0.015 in
0.17 lt xF lt 0.32
ltegt -0.035 gt AN -0.08 - 0.005 - 0.015 in
0.17 lt xF lt 0.32
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PT suppression can be related to two possible
mechanisms
Modification of the wave function in the initial
state
Y
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.
Cronin type enhancement by coherent multiple
scattering at y0
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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 AuAu
and dAu
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RhRcp(h2.2)/Rcp(h0)
Arsene et al.PRL 91 2003
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RAuAu of Pions and Protons
?0
Preliminary
?2.2
It is clear that baryons have a different
behavior.
No feed down corrections applied
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dAu nuclear modification factor
The absence of suppression in dAu at y0 and
back-to-back correlations have been considered
necessary conditions to the formation of a dense
and opaque medium the suppression seen in AuAu
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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RdAu as function of rapidity
Cronin like enhancement at ?0. Clear suppression
as ? changes up to 3.2 Same ratio made with dn/d?
follows the low pT RdAu
PRL 94 (2004)
Minimum bias with lt Ncollgt 7.20.3
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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
1/ltNcoll centralgt NABcentral(pT,h)
Rcp
1/ltNcoll periphgt NABperiph(pT,h)
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Particle identification in d-Au collisions
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Identified particles in d-Au at ?3.2
Many protons in the most forward dAu. Is this
beam fragmentation?
80 of the negative charged particles at ?3 are
pions
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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 y0 in AuAu and dAu
systems
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RAuAu at ?sNN 62.4 GeV
Nuclear modification factor RAuAu - different
centrality classes
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Rcp of charged hadrons at ?3.2
BRAHMS Preliminary

• Strong centrality dependence
• Rcp(0-10) lt Rcp(20-40)
• No significant h dependence
• in 0lthlt3.2
• Maximum at pT2GeV/c
• Rcp() gt Rcp(-)
• Systematic Errors
• - 10-15 overall
• - 10 p-by-p

h3.2
h2.2
h0
BRAHMS PRL 91 (2003)
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Rcp for Identified particles at y3
BRAHMS Preliminary
p
K

• Suppression for all particles
• maximum at pT2GeV/c
• Rcp() Rcp(-) for p, K, p
• Rcp(p) gt Rcp(K) gt Rcp(p)

p,pbar

• Data

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Summary

• We have now a wide view of bulk particle
  production in AuAu collisions. There are no
  extended plateaus in the density distributions,
  70 of the beam energy is made available for
  particle production in central AuAu.
• 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
- 12 institutions-

• 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, 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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p/p ratios
BRAHMS Preliminary
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