Towards Matter-Antimatter Balance at RHICAntiparticle-to-particle ratios measured by BRAHMS

Djamel Ouerdane Niels Bohr Institute

XL International Winter Meeting on Nuclear PhysicsBormio, January 21-26, 2002

BRAHMS

Djamel Ouerdane - Niels Bohr Institute 2BRAHMS

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, I. S. Sgura10, 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, 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

Djamel Ouerdane - Niels Bohr Institute 3BRAHMS

Outline of the talk

• BRAHMS : what, where, when ? • Data reconstruction : Collision vertex and centrality

Particle identification

• Antiparticle to particle ratios (Au+Au at 200 GeV) Centrality and Transverse Momentum dependence

Ratios as a function of rapidity

• Summary and things to come

Djamel Ouerdane - Niels Bohr Institute 4BRAHMS

Year 2001 achievements

Physics running from July 7 to November 26 More than 15 G events recorded with BRAHMS

Au+Au at GeV200NNs

BRAHMS at The Relativistic Heavy Ion Collider

BRAHMSBRAHMS

Djamel Ouerdane - Niels Bohr Institute 5BRAHMS

BRAHMS Acceptance

Tra

nsv

erse

mom

entu

m [

GeV

/c]

Rapidity

• PID in MRS via TOFW

• PID in FS via TOF1, C1, TOF2 and RICH

Particle IDentification

Djamel Ouerdane - Niels Bohr Institute 6BRAHMS

Determination of Collision Vertex

z ?

• Combining hits in TPM1: 0.2 cmz

z• Δt in BBC measurements : 0.65 cm

BBL BBR

Djamel Ouerdane - Niels Bohr Institute 7BRAHMS

Determination of Collision CentralityEnergy deposit Multiplicity Centrality

Silicon Strips

Plastic Scintillator Tiles

Djamel Ouerdane - Niels Bohr Institute 8BRAHMS

Matched in the magnet gap

Tracking in the Spectrometers

Tracks reconstructed in Tracking Chambers (TPCs and DCs)

Bending of tracks momentum of particles (p = qB)

Djamel Ouerdane - Niels Bohr Institute 9BRAHMS

Vertex

Beam Line

D1 magnet gap

D2 magnet gapT2

T1Front-ForwardSpectrometer

TPM1

D5 magnet gap

TPM2

Mid-rapiditySpectrometer

How does a real event look ?

Djamel Ouerdane - Niels Bohr Institute 10BRAHMS

K separation up to p 2 GeV/c

PID with the Time-of-flight Wall TOFW (MRS)

125 scintillator slats

Momentum [GeV/c]q

1

Tim

e of

Flig

ht a

t 4.5

m [

ns]

Tof resolution : 100 ps

1

12

22

pm

Djamel Ouerdane - Niels Bohr Institute 11BRAHMS

PID in the front-forward spectrometer (FFS)

Time-of-flight wall H1 (40 slats – PMT time resolution σ 65 ps)

TOF resolution : 85 ps

0 2 4 6-2-4-61/q momentum [GeV/c]

30

32

34

36

38TOF [ns]

C1 π threshold

Threshold Cherenkov C1(π momentum threshold 2.7 GeV/c K momentum threshold 8.7 GeV/c)

p/K separation up to p 6 GeV/c

Djamel Ouerdane - Niels Bohr Institute 12BRAHMS

Time-of-flight wall H232 scintillator slats18 meters from nominal vertexTOF resolution: 85 ps

Pion-veto by the RICH

PID in the back forward spectrometer (BFS)

Djamel Ouerdane - Niels Bohr Institute 13BRAHMS

Proton acceptance (TOFW and H1 only)

Djamel Ouerdane - Niels Bohr Institute 14BRAHMS

No sign of Pt or centrality dependence

Antiparticle to Particle Ratios vs Pt and centralityin 197Au+197Au reaction at 200 GeVNNs

BRAHMS Preliminary

Pions 1Kaons 0.92Protons 0.75

BRAHMS Preliminary

Pions 1Kaons 0.92Protons 0.75

Djamel Ouerdane - Niels Bohr Institute 15BRAHMS

Rapidity dependence – pions and kaons( 200 GeV)NNs

Kaons

)KΛpp(p

)N(K)N(K

)N(K

)N(K

)N(K

appair

pair-

Pions

Djamel Ouerdane - Niels Bohr Institute 16BRAHMS

)()(

)(

)(

)(

otherpair

pair

pNpN

pN

pN

pN

Baryon transport … orpair production?

We need the yields!

Rapidity dependence – proton ratio( 200 GeV)NNs

Djamel Ouerdane - Niels Bohr Institute 17BRAHMS

Energy Systematics (y=0)

- towards matter-antimatter balance….

Protons Kaons

Djamel Ouerdane - Niels Bohr Institute 18BRAHMS

Net protons at midrapidity

* Assuming 14% more pbar (cf. dN/dη, BRAHMS sub to PRL dec.2001) and 0.75.

NNs 200 GeV (30) (23) (7)*

)(/)( pNpN

* NA49 QM99 & Phys. Rev. Lett. 82, 2471 (1999)

NNs 17 GeV 31 5 26*

* PHENIX nucl-ex/0112006

NNs 130 GeV 29 20 9*

)()(

)(

)(

)(

otherpair

pair

pNpN

pN

pN

pN

N(p) )pN( )pN( -N(p)CM Energy

Djamel Ouerdane - Niels Bohr Institute 19BRAHMS

Antiparticle-to-particle ratios in Au+Au at GeV200NNs

• Ratios nearly independent of Pt and centrality

• Present models do not reproduce RHIC data

• Measured , and - for p and K this is the highest so far observed in HI collisions

)p(N/)p(N )K(N/)K(N )(N/)(N

• Strong energy dependence of p and k ratios (towards matter-antimatter balance at RHIC)

• Strong rapidity dependence of p ratio - consistent with high transperancy scenario (but Bjorken limit not reached)

+ - + +

Djamel Ouerdane - Niels Bohr Institute 20BRAHMS

And more to comeComparison between Au+Au and p+p at 200 GeVΝΝσ

Particle yields