Charged mesons in Au Au interactions at 62.4 AGeV

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Charged mesons in AuAu interactions at 62.4 AGeV

• Ionut Arsene for the BRAHMS Collaboration
• University of Oslo, Norway
• University of Bucharest, Romania

2
Experimental overview (1)
Broad RAnge Hadron Magnetic Spectrometer
Two small solid angle spectrometers (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.
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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).

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Data and phase space coverage
Due to the limited acceptance of the detectors,
only a part from the phase space is covered.
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Pt spectra (1)

• The Pion Pt spectra is well fitted with a power
  law function of the form f(Pt) (1Pt/P0)-r
• The fitted exponent decrease with centrality.

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Pt spectra (2)

• Kaons Pt spectra at mid-rapidity.
• The spectra is fitted with a Boltzman function.

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Mean Pt for pions and kaons

• ltPtgt constant around mid-rapidity and slightly
  decrease at forward rapidities.
• ltPtgt at y0
• pions 425 MeV/c
• kaons 650 MeV/c
• Bottom figure BRAHMS 200 AGeV

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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.

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Particle ratios (2)

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

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Particle ratios (3)

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

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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.

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K/pi ratios at 200 AGeV

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

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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)
52 P.Carruthers, M.Duong-van, PRD 8 (1973) 859
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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)

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The BRAHMS Collaboration

• I.Arsene12,10,I.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,J. J. Gaardhøje7,M.
  Germinario7, K. Hagel8,
• O. Hansen7, H. Ito11, E. Jacobsen7, A.
  Jipa10, J. I. Jordre10, F. Jundt2,
• C.E.Jørgensen7, E. J. Kim5, T. Kozik3,
  T.M.Larsen12, J. H. Lee1, Y. K.Lee5,
• G. Løvhøjden2, Z. Majka3, A. Makeev8, B.
  McBreen1, M. Murray8, J. Natowitz8,
• B. Neuman11,B.S.Nielsen7, K. Olchanski1, D.
  Ouerdane7, R.Planeta4, F. Rami2,
• D. Roehrich9, C.Ristea7, O.Ristea10, B. H.
  Samset12, S. J. Sanders11, I. S. Sgura10,
  R.A.Sheetz1, Z.Sosin3, P. Staszel7, T.S.
  Tveter12, F.Videbæk1, R. Wada8
  ,A.Wieloch3,Z. Yin9
• 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 AM University, College Station. USA,
• 9 University of Bergen, Norway
• 10 University of Bucharest, Romania,