2nd International Workshop on the critical point and the onset of deconfinement

Charged mesons in Au+Au interactions at 62.4 AGeV

Ionut Arsene for the BRAHMS Collaboration University of Oslo, Norway

University of Bucharest, Romania

2nd International Workshop on the critical point and the onset of deconfinement

Experimental overview (1)

Broad RAnge Hadron Magnetic Spectrometer

Two small solid anglespectrometers (FS and MRS)that can rotate from 2.3 to 30 degrees (FS) and from 30 to 90 degrees (MRS) provide very good PID over a wide range of rapidity and Pt.

2nd International Workshop on the critical point and the onset of deconfinement

Experimental overview(2)

Top: MRS PID curves. The pions/kaons are well separated up to 2 GeV/c, and kaons/protons up to 3-4 GeV/c

Bottom: PID plot from the RICH detector. RICH extends the particle identification to ~10GeV/c (pi/K) and ~25 GeV/c (K/p).

2nd International Workshop on the critical point and the onset of deconfinement

Data and phase space coverage

Due to the limited acceptance of the detectors, only a part from the phase space is covered.

2nd International Workshop on the critical point and the onset of deconfinement

Pt spectra (1)

The Pion Pt spectra is well fitted with a power law function of the form f(Pt) ~ (1+Pt/P0)^{-r}

The fitted exponent decrease with centrality.

2nd International Workshop on the critical point and the onset of deconfinement

Pt spectra (2)

Kaons Pt spectra at mid-rapidity.

The spectra is fitted with a Boltzman function.

2nd International Workshop on the critical point and the onset of deconfinement

Mean Pt for pions and kaons

<Pt> constant around mid-rapidity and slightly decrease at forward rapidities.

<Pt> at y=0: pions: ~425 MeV/c kaons: ~650 MeV/c Bottom figure: BRAHMS

200 AGeV

2nd International Workshop on the critical point and the onset of deconfinement

Particle ratios (1)

the pi-/pi+ ratio is ~1 on the entire rapidity range;

the K-/K+ ratio is ~0.9 around mid-rapidity and decrease at forward rapidities.

2nd International Workshop on the critical point and the onset of deconfinement

Particle ratios (2)

pi-/pi+ and K-/K+ ratios as a function of Pt.

2nd International Workshop on the critical point and the onset of deconfinement

Particle ratios (3)

Energy dependence of K/pi ratio at midrapidity (left)Energy dependence of K/pi ratio at midrapidity (left) Rapidity dependence of K/pi ratios (right)Rapidity dependence of K/pi ratios (right) The error bars in the right figure are statistical only.The error bars in the right figure are statistical only.

2nd International Workshop on the critical point and the onset of deconfinement

Particle ratios (4)

Preliminary K/pi ratios as a function

of Pt. K/pi ratio increase with

transverse momentum. At 1 GeV/c the ratios

are ~0.4.

2nd International Workshop on the critical point and the onset of deconfinement

K/pi ratios at 200 AGeV

Midrapidity & Forward rapidity K/pi ratio ~0.4 at 1GeV/c and ~ 0.7 at 2 GeV/c

2nd International Workshop on the critical point and the onset of deconfinement

Energy dependence of widths

Landau hydrodynamics Gaussian rapidity

distribution The widths

depend only on c.m. energy

L.D. Landau, Izv. Akad. Nauk SSSR 17 (1953) 52P.Carruthers, M.Duong-van, PRD 8 (1973) 859

2nd International Workshop on the critical point and the onset of deconfinement

Summary

Pt spectra for mesons Gaussian rapidity distributions 4 yields C.M. energy dependence of widths and K-/K+ ratios Pt dependence of the and K-/K+ ratios Rapidity dependence of K/ ratios Pt dependence of K/ratios Energy dependence of K/ ratio (total yields)

2nd International Workshop on the critical point and the onset of deconfinement

The BRAHMS Collaboration

I.Arsene[12,10],I.G. Bearden[7], D. Beavis[1], C. Besliu[10], Y. Blyakhman[6], J.Brzychczyk[4], B. Budick[6],H. Bøggild[7] ,C. Chasman[1], C. H. Christensen[7], P. Christiansen[7],

J.Cibor[4],R.Debbe[1],J. J. Gaardhøje[7],M. Germinario[7], K. Hagel[8], O. Hansen[7], H. Ito[11], E. Jacobsen[7], A. Jipa[10], J. I. Jordre[10], F. Jundt[2],

C.E.Jørgensen[7], E. J. Kim[5], T. Kozik[3], T.M.Larsen[12], J. H. Lee[1], Y. K.Lee[5], G. Løvhøjden[2], Z. Majka[3], A. Makeev[8], B. McBreen[1], M. Murray[8], J. Natowitz[8], B. Neuman[11],B.S.Nielsen[7], K. Olchanski[1], D. Ouerdane[7], R.Planeta[4], F. Rami[2],

D. Roehrich[9], C.Ristea[7], O.Ristea[10], B. H. Samset[12], S. J. Sanders[11], I. S. Sgura[10], R.A.Sheetz[1], Z.Sosin[3], P. Staszel[7], T.S. Tveter[12], F.Videbæk[1], R. Wada[8] ,A.Wieloch[3],Z. Yin[9]

[1] Brookhaven National Laboratory, USA, [2] IReS and Université Louis Pasteur, Strasbourg, France

[3] Jagiellonian University, Cracow, Poland, [4] Institute of Nuclear Physics, Cracow, Poland[5] Johns Hopkins University, Baltimore, USA,

[6] New York University, USA[7] Niels Bohr Institute, Blegdamsvej 17, University of Copenhagen, Denmark

[8] Texas A&M University, College Station. USA, [9] University of Bergen, Norway

[10] University of Bucharest, Romania, [11] University of Kansas, Lawrence,USA

[12] University of Oslo Norway