1. BRAHMS overview Paweł Staszel,
Marian Smoluchowski Institute of Physics
Jagiellonian University
for the BRAHMS Collaboration
Quark Matter
Budapest, 4 – 9 August, 2005

2. The Relativistic Heavy Ion Collider
BRAHMS
PHOBOS
STAR
PHENIX
Au+Au
d+Au
p+p
energies:
sNN=200GeV,
sNN=62GeV
Cu+Cu

3. Outline Detector setup.
General (bulk) characteristics of nucleus-nucleus reactions.
Elliptic flow (for 200).
Baryon to meson ratios.
High pT suppression.
Summary.

4. Broad Range Hadron Magnetic Spectrometers
Tile Ring 1
Flow Ring 2
Si Ring 1

5. Particle identification summary
7.5 GeV/c
5.5 GeV/c
4.0 GeV/c
3.5 GeV/c
K / p
4.5 GeV/c
3.0 GeV/c
2.5 GeV/c
2.0 GeV/c
K/
TOF2
TOF1
TOFW2
TOFW
2  cut
0<<1
C4 Threshold (MRS):
 / K separation 9 GeV/c
RICH (FS):
 / K separation 20 GeV/c
Proton ID up to 35 GeV/c
1.5<<4

6. Charged Particle Multiplicity
Energy density: Bjorken 1983
eBJ = 3/2 (<Et>/ pR2t0) dNch/d
assuming formation time t0=1fm/c:
>5.0 GeV/fm3 for 200 GeV
>4.4 GeV/fm3 for 130 GeV
>3.7 GeV/fm3 for 62.4 GeV

7. K/ energy dependence, AuAu
Ionat Arsene, poster #126
200GeV
62GeV

8.  Anti-particle to particle ratios Chemical freeze-out
BRAHMS PRELIMINARY
BRAHMS PRELIMINARY
It is not true for p+p
pbar/p verus K-/K+ : good statistical model description with B= B(y) with T~170MeV
But this describes also energy depencency at y=0  only B controls the state of matter
STAR and NA47 measures pbar/p versus
-/+
At 200 GeV: -/+ = 1.0, K-/K+ = 0.95, pbar/p = 0.75
At 62 GeV: -/+ = 1.0, K-/K+ = 0.84, pbar/p = 0.45,
At |y|<1 matterantimatter

9. Kinetic freeze-out: AuAu @ 200GeV
BRAHMS preliminary
Flow velocity increases with centrality.
Temperature decreases with centrality.
the same anti-correlation is observed
versus y:
Flow velocity decreases with rapidity.
Temperature increases with rapidity
Comparing 200GeV and 62GeV data
In the same Npart bin, we see reduction in
flow by ~10% and no change in T
Lower density 
lower pressure  less flow
faster freeze out  higher temperature
Oana Ristea poster #50

10. Elliptic flow (v2) No v2(pT) rapidity dependence AuAu @200GeV =0 =1
=3.2 dN
ddpt 2
(1 + 2v1cos + 2v2(,pt)cos2) dN
ddptd =
Hiro Ito, parallel sem. 2b, Fri.

11. pbar/- ratios vs. centrality and  (parton recombination)
Smooth increase from peripheral to central in AuAu at sNN = 200 GeV
Centrality dependence is stronger at midrapidity than forward rapidity
The maximum is shifted to low pT at forward rapidity

12. p/pi ratios vs pt (parton recombination, hydro)
no significant difference between y=0 and y~1
flow/mass effect ?

13. pbar/- scaling with Npart
sNN=200GeV
Strong rapidity
dependence
CuCu data consistent with AuAu for the same Npart pp
Eun-Joo Kim, parallel sem. 1b Fri. pp

14. K/ ratios at =3.1, Au+Au @200GeV

15. High pt Suppression  Jet Quenching
Particles with high pt’s (above ~2GeV/c)
are primarily produced in hard scattering
processes early in the collision q
hadrons
leading
particle
leading particle
Schematic view of jet production
p+p experiments  hard scattered
partons fragment into jets of hadrons
In A-A, partons traverse the medium
 Probe of the dense and hot stage
If QGP  partons will lose a large
part of their energy
(induced gluon radiation)
 suppression of jet production
 Jet Quenching
Experimentally  depletion of the high pt region in hadron spectra

16. Charged hadron invariant spectra
Scaled N+N reference
RAA =
Yield(AA)
NCOLL(AA)  Yield(NN)
Nuclear Modification Factor
RAA<1  Suppression relative to
scaled NN reference
SPS:
data do not show suppression
enhancement (RAA>1) due to initial state
multiple scattering (“Cronin Effect”)
Yield(0-10%)/NCOLL(0-10%)
RCP =
Yield(40-60%)/NCOLL(40-60%)

17. Au+Au: comparison 200 GeV between 62 GeV
Brahms preliminary
200 GeV
Catalin Ristea, poster #4
62 GeV
(pp reference is based on ISR collider data)

18. Two systems comparison @ 62.4GeV
Brahms preliminary
Cu+Cu
Truls M. Larsen, parallel sem. 3a Fri.
Au+Au

19. RCP dependence on  for AuAu @200 GeV and 62.4 GeV
weak  dependence at 200 GeV…
…but greater suppression approaching beam rapidity at 63 GeV.
peripheral collision  pp collision

20. RCP and RAA for identified hadrons at y~3.1, Au+Au @ 200GeV
protons
pions
kaons

21. RAA versus centrality for identified hadrons

22. ….more on RAA rapidity dependence
Radek Karabowicz parallel sem. 1b Fri.

23. Parton spectrum using pp reference spectrum
Strong energy absorption model from a static 2D matter source. (Insprired by A.Dainese (Eur.Phys.J C33,495) and A.Dainese , C.Loizides and G.Paic (hep-ph/ ) )
Parton spectrum using pp reference spectrum
Parton energy loss DE ~ q.L**2
q adjusted to give observed RAA at h~1.
The change in dN/dh will result in slowly rising RAA .
The modification of reference pp spectrum causes the RAA to be approximately constant as function of h .

24. RdAu and RAA for anti-protons and pions @200
BRAHMS PRELIMINARY
suppression for p- but stronger for AuAu
both RdA and RAA show enhancement for p-bar

25. Summary Large hadron multiplicities
 Almost a factor of 2 higher than at SPS energy( higher )
 Much higher than pp scaled results( medium effects)
Identified hadron spectra
 Good description by statistical model
 Large transverse flow consistent with high initial density
v2(pt) is seem to not depend on rapidity
p/
 show strong  dependency
 for given energy depend only on Npar
High-pT
 suppression increases with energy for given centrality bin
 weak dependency on rapidity of RAA which is consistent with surface
jet emission
 RCP can hide or enhance nuclear effects
 At y=3.2 RAA shows larger suppression than RdA

26. The BRAHMS Collaboration
I.Arsene7, I.G. Bearden6, D. Beavis1, S. Bekele6 , C. Besliu9, B. Budick5,
H. Bøggild6 , C. Chasman1, C. H. Christensen6, P. Christiansen6, R. Clarke9, R.Debbe1,
J. J. Gaardhøje6, K. Hagel7, H. Ito10, A. Jipa9, J. I. Jordre9, F. Jundt2, E.B. Johnson10,
C.E.Jørgensen6, R. Karabowicz3, E. J. Kim4, T.M.Larsen11, J. H. Lee1, Y. K. Lee4,
S.Lindal11, G. Løvhøjden2, Z. Majka3, M. Murray10, J. Natowitz7, B.S.Nielsen6,
D. Ouerdane6, R.Planeta3, F. Rami2, C. Ristea6, O. Ristea9, D. Röhrich8,
B. H. Samset11, D. Sandberg6, S. J. Sanders10, R.A.Sheetz1, P. Staszel3,
T.S. Tveter11, F.Videbæk1, R. Wada7, H. Yang6, Z. Yin8, and I. S. Zgura9
1Brookhaven National Laboratory, USA, 2IReS and Université Louis Pasteur, Strasbourg, France
3Jagiellonian University, Cracow, Poland,
4Johns Hopkins University, Baltimore, USA, 5New York University, USA
6Niels Bohr Institute, University of Copenhagen, Denmark
7Texas A&M University, College Station. USA, 8University of Bergen, Norway
9University of Bucharest, Romania, 10University of Kansas, Lawrence,USA
11 University of Oslo Norway
48 physicists from 11 institutions

27. Limiting Fragmentation
Shift the dNch/d distribution by the beam rapidity, and scale by Npart. Lines up with lower energy  limiting fragmentation
Au+Au sNN=200GeV (0-5% and 30-40%)
Au+Au sNN=130GeV (0-5%)
Pb+Pb sNN=17GeV (9.4%)