Towards Matter-Antimatter Balance at RHIC Antiparticle-to-particle ratios measured by BRAHMS Djamel Ouerdane Niels Bohr Institute XL International Winter Meeting on Nuclear Physics Bormio, January 21-26, 2002 BRAHMS
Jan 09, 2016
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