recent results from brahms from y=0 to y=3 i. g. bearden niels bohr institute university of...

Recent Results from BRAHMS

from y=0 to y=3I. G. BeardenNiels Bohr Institute

University of Copenhagen, Denmark

Quark Matter 2002, July 18-24, Nantes, France

for the

BRAHMS COLLABORATION

I.G.Bearden, Niels Bohr Institute 20 July 2002

BRAHMS

The BRAHMS CollaborationI.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, Poland5Johns Hopkins University, Baltimore, USA, 6New York University, USA

7Niels Bohr Institute, Blegdamsvej 17, University of Copenhagen, Denmark8Texas A&M University, College Station. USA, 9University of Bergen, Norway 10University of Bucharest, Romania, 11University of Kansas, Lawrence,USA

12 University of Oslo Norway

I.G.Bearden, Niels Bohr Institute 20 July 2002

BRAHMS

The BRAHMS Experiment

95°

30°

30°

15°

2.3°

I.G.Bearden, Niels Bohr Institute 20 July 2002

BRAHMS

Determination of Collision Vertex, Centrality

I.G.Bearden, Niels Bohr Institute 20 July 2002

BRAHMS

Sys. Error :

10%

8%

0-5%

5-10%

10-20

Multiplicity density @ 200GeV

100AGeV+100 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.

I.G.Bearden, Niels Bohr Institute 20 July 2002

BRAHMS

Limiting fragmentation

Shift data to beam frame of reference

PRL 88 (2002) 2002301 BRAHMS

PLB 523 (2001) 227 BRAHMS

Phys Rev C (2000)62 014903

Moving awayfrom

midrapidity particle productio

nlooks like

SPS

I.G.Bearden, Niels Bohr Institute 20 July 2002

BRAHMS

dNch/d: Comparison to Models

SNN=200GeV

AMPT

High density QCDgluon saturationKharzeev and Levin,PLB523(2001)79

Differences forPeripheral Collisions but Small effect !

I.G.Bearden, Niels Bohr Institute 20 July 2002

BRAHMSMRS

FORWARD

I.G.Bearden, Niels Bohr Institute 20 July 2002

BRAHMS

PID in BRAHMS

MRSTOF

FSTOF

FSTOF+C1

RICH

I.G.Bearden, Niels Bohr Institute 20 July 2002

BRAHMS

Ratios are (relatively) easy...

Ratios could vary in pt, and in yNarrow 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 centralitySee poster for details of the analysis!

4o

8o

12o

I.G.Bearden, Niels Bohr Institute 20 July 2002

BRAHMS

Particle/Particle vs rapidity

BRAHMS, submitted to PRL12/07/02 nucl-ex/0207006

I.G.Bearden, Niels Bohr Institute 20 July 2002

BRAHMS

BRAHMS, submitted to PRL12/07/02 nucl-ex/0207006

Becattini: T=170, s=1

PBM (PhysLettB518

(2000)41) predicts y=0

ratios almost exactly

K-/K+=

exp(2s/T)(pbar/p)1/3

K- /K+=(pbar/p)1/4 is

a fit to the data points

I.G.Bearden, Niels Bohr Institute 20 July 2002

BRAHMS

Top 10% central

K+ p cross~1.2GeV/

cP pion cross

>2GeV/c?

I.G.Bearden, Niels Bohr Institute 20 July 2002

BRAHMS

Not surprisingly, the antiparticle spectra don’t look much different...at y=0!

I.G.Bearden, Niels Bohr Institute 20 July 2002

BRAHMS

,p cross1.2 GeV/c

p>K overcovered pT

Only small part of high rapidity data analyzed...so far.

I.G.Bearden, Niels Bohr Institute 20 July 2002

BRAHMS

Pbar , K- yield lowerthan p, K+

Pbar,- cross at higher pT

I.G.Bearden, Niels Bohr Institute 20 July 2002

BRAHMS

Inverse pT Slope

vs. mass...

Nb: all fits are in pt, oversame range for all particles,

at all rapidities

I.G.Bearden, Niels Bohr Institute 20 July 2002

BRAHMS

Strangeness : ratio K/

I.G.Bearden, Niels Bohr Institute 20 July 2002

BRAHMS

y = 3 similar to SPS

Strangeness : K/ systematics

I.G.Bearden, Niels Bohr Institute 20 July 2002

BRAHMS

I.G.Bearden, Niels Bohr Institute 20 July 2002

BRAHMS

p and pbar yields0-10%: BRAHMS Preliminary SNN=200 GeV: 0-10% Central

y = 0

y=0.8

I.G.Bearden, Niels Bohr Institute 20 July 2002

BRAHMS

p and pbar at y=2.9BRAHMS Preliminary

antiprotonYield =10.5 0.8 1.6 (Inverse pt slope =325.517.3)

proton Yield = 33.7 1.8 5.1

(Inverse pt slope = 341.8 13.8

I.G.Bearden, Niels Bohr Institute 20 July 2002

BRAHMS

Net protons, first shot...

BRAHMS Preliminary

d2N/dpTdy

I.G.Bearden, Niels Bohr Institute 20 July 2002

BRAHMS

Net protons vs Rapidity!

I.G.Bearden, Niels Bohr Institute 20 July 2002

BRAHMS

Can we kill models?

Points scaled by 2

I.G.Bearden, Niels Bohr Institute 20 July 2002

BRAHMS

Q’AMPT

I.G.Bearden, Niels Bohr Institute 20 July 2002

BRAHMS

High pt

y=0

y=0 High pt

y=2.2

C.E.Jørgensen Parallel session I today.

I.G.Bearden, Niels Bohr Institute 20 July 2002

BRAHMS

Future plans...• Analyze complete data set at high

rapidity – Better pt coverage– (slightly) higher y

• Spectra, yields for 1<y<3• Source size at mid, forward rapidity• p+p data • Longer term...

– Upgrades better high pt PID in MRS

I.G.Bearden, Niels Bohr Institute 20 July 2002

BRAHMS

Summary• K-/K+, pbar/p ratios fall off with rapidity• Universal correlation between K-/K+ and pbar/p• K-/- decreases from 0.15 (y=0) to 0.1(y=3)• Inverse slope decreases with rapidity• Measured dN/dy over 3 units of rapidity.• Dramatic increase in net protons at y=3Low to high chemical potential from y=0 to

y=3Net baryon central plateau (y=0 to almost y=2)Significant transparency

I.G.Bearden, Niels Bohr Institute 20 July 2002

BRAHMS

Radius versus Momentum

Zoom in

RICH used for PIDp>15GeV/cK>8 GeV/c>4 GeV/c