Midrapidity forward rapidity

1
Strangeness at RHIC recent results from BRAHMS
Dieter Roehrich UiB for the BRAHMS collaboration

• Midrapidity ? forward rapidity
• Stopping
• Pion and kaon production
• Particle composition at intermediate pt
• Nuclear modification factor

AuAu at ?sNN 130GeV AuAu at ?sNN
200GeV dAu at ?sNN 200GeV pp at ?sNN
200GeV AuAu at ?sNN 62.4GeV
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The BRAHMS experiment
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Net-proton rapidity distribution
dN dy

• RHIC
• central AuAu
• Npart357?8

BRAHMS, PRL, in print nucl-ex/0312023
4
Stopping (1)
5
Stopping (2)
Net-baryon after feed-down neutron corrections
Gaussians in pz
6 order polynomial
Rapidity loss (Npart 357 ? 10)


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Energy loss

• Upper limit to rapidity loss?
• Energy loss

?E 25.7 ? 2.1 TeV ?E/nucleon 72 ? 6 GeV
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Stopping summary

• Net-baryon poor midrapidity region
• dN(net-protons)/dy 7
• Total-baryon rich midrapidity region
• dN(all baryons)/dy ? 65
• Largest observed rapidity loss
• lt?ygt 2
• as large as in pA
• Stopping power
• central AuAu at RHIC 72
• central SS at SPS 58
• pp collisions ? 50

8
Rapidity distributions of identified hadrons
Produced particles Gaussian
shapes Integrating the Gaussians gives
Not corrected for weak decays
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Energy dependence of widths

• Landau hydrodynamics
• Gaussian rapidity distribution
• Observed in hadron - hadron collisions
• Width ? depends only on c.m. energy

• Finite boost-invariant region for thermodynamic
  variables
• Boost-invariant region ? lt 2
• Gaussian rapidity distribution

L.D. Landau, Izv. Akad. Nauk SSSR 17 (1953)
52 P.Carruthers, M.Duong-van, PRD 8 (1973) 859
T. Hirano, Y. Nara, nucl-th/0404039
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Transverse Flow (1)

• Blast Wave fits at y0,1,2,3 (T, ?s, ? free,
  Rmax13fm)

Fix a,T
Fix a,b
Less flow at forward rapidities
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Transverse Flow (2)

• 3D-Hydro
• CGC initial condition
• Ideal massless QGP EoS

nucl-th/0404039
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Corrections for feed-down from weak decays
Towards 4? multiplicity
Pion contamination by neutral kaon decays

• Proton spectra contain approx. 55 of all
  hyperon decays
• Pion spectra contain approx. 35 of all K0S
• Corrected 4? multiplicity

• Integrating the Gaussians and adding unseen
  weak decay products gives Nch 4620 ? 50
• Integrating the pseudo-rapidity spectra gives
  Nch 4790 ? 400

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Strangeness production (1)
Rapidity dependence of K/? ratio
Energy dependence of K/? ratio
no change for
Divergence at higher y
Over the full phase space and corrected for weak
decays K/? 17.0 ? 1.5 (syst) K?/?? 14.2
? 2.0 (syst)
Y lt 1 consistent with Hadron Gas Stat. Model
Phys. Lett. B 518 (2001) 41
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Strangeness production (2)
Energy dependence of K/? ratio at midrapidity

• Preliminary 63 GeV data follow trend

See Djamel Ouerdanes talk on Thursday
afternoon (Parallel session 2)
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Strangeness production (3)
K-/K dependence on p/p
See Michael Murrays talk on Friday
afternoon (Parallel session 4)
63 GeV
BRAHMS, PRL90 (2003) 102301 Tconstant, ?B varies
with y
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Strangeness production (4)

• Input 4? yields into thermal model
• Preliminary weak decay correction
• 4? fit results
• T 153 - 4 MeV
• ?S 0.85 - 0.02
• ?B 96 - 4 MeV
• Midrapidity results
• T 160 - 10 MeV
• ?S ? 1
• ?B ? 25 MeV

F. Becattini
STAR
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Particle Ratios in pp interactions
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Baryon enhancement at intermediate pT

• Midrapidity
• p/? ratio ? 1
• Enhancement compared to pp, dAu
• Forward rapidity
• p/? ratio ? 0.5
• Flow effect?

pp
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Kaons at intermediate pT
preliminary
pp

• Midrapidity Forward rapidity
• K/? ratio increases with transverse momentum
• K/? ratio ? 0.7 at 2 GeV/c

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Nuclear Modification Factor

• Transverse momentum spectra of charged hadrons
  and identified particles at different rapidities
  (0 lt y lt 3.2)
• Nuclear modification factor
• Rapidity dependence of RdAu and RAu helps to
  distinguish final from initial state effects and
  to disentangle different initial conditions

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Arsene et al. PRL2003
Nuclear Modification Factor AuAu

• Large high pT suppression in central AuAu
• Even larger suppression at forward rapidity

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Are Pions and Protons suppressed?
?0
?2.2
preliminary

• Pions are suppressed at all rapidities
• Protons are not suppressed up to pt 3 GeV/c
• Very strong pion suppression at forward rapidity

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Nuclear Modification Factor dAu
charged hadrons

• High pT enhancement in dAu collisions at
  ?sNN200 GeV
• Comparing AuAu to dAu at midrapidity
• ? Strong effect of dense medium
• ? Partonic energy loss

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Nuclear Modification Factor
Cronin effect Initial state multiple scattering
leading to Cronin enhancement (RAAgt1)

• Midrapidity
• dAu
• Central AuAu
• Forward rapiditiesWhere do shadowing/ gluon
  saturation effects come in?

Jet-quenching

• Shadowing/saturation
• depletion of low-x partons
• due to
• - coherent multiple scattering
• gluon saturation
• e.g. Color Glass Condensate (CGC)

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RdAu at different Pseudorapidities
BRAHMS Submitted to PRL, March 2004

• Cronin-like enhancement at ?0
• Clear suppression as ? changes from 0 to 3.2
• But ratio of dn/d? exhibits similar trend

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Centrality Dependence of Enhancement/Suppression
in dAu

• Change of RCP from mid- to forward rapidities is
  stronger for central collisions than for
  semi-peripheral collisions

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CGC Saturation Model (1)

• CGC describes dn/d? and predicts
• But HIJING and AMPT also do well

Nucl.Phys. A 730 (2004) 448
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CGC Saturation Model (2)

• CGC model describes RdAu and RCP
• Suppression comes in at y gt 0.2

D. Kharzeev, Y.V. Kovchegov, K. Tuchin,
hep-ph/0405054 (2004)
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Spare
BUT (1) - Pseudorapidity Distribution in dAu

• Multiplicity in dAu scales with Npart
• Enhanced production for ? lt 0
• Suppression for ? gt 0
• Modification effects for soft pions, not only for
  high pT
• Same observation at SPS (NA35, NA49)

PHOBOS data P. Steinberg, QM 2004
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Spare
BUT (2) - RpA at SPS energies

• NA49 data
• 200 GeV pPb
• as we go forward R decreases
• B. Boimska, PhD thesis
• Warsaw Institute forNuclear Studies, May04

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BUT (3) - pQCD Models (1)

• pQCD-improved parton model
• Glauber-type collision geometry
• Nuclear shadowing
• Nuclear multiscattering

G.G. Barnafoldi, G. Papp, P. Levai, G. Fai,
nucl-th/0404012 (2004)
See also R. Vogt, hep-ph/0405060 (2004)

• Increasing strength of standard nuclear shadowing
  with increasing ?
• Including nuclear multiscattering ? reasonable
  agreement between data and pQCD

See also R. Vogt, hep-ph/0405060 (2004)
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Summary

• Central AuAu collisions
• Stopping rapidity shift of 2 units
• 72 of energy available for particle production
• Gaussian rapidity distributions
• 4? yields
• Rapidity dependence of K/? ratio
• Energy dependence of K/? ratio (total yields)
• Baryon enhancement at intermediate pT
• Nuclear modification
• Strong pion suppression at all rapidities - even
  stronger at large ?
• Protons are not suppressed up to pT 3 GeV/c
• dAu collisions
• Nuclear modification
• Cronin-like enhancement at ?0
• Clear suppression as ? changes from 0 to 3.2
• Indication of shadowing/saturation?

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The BRAHMS Collaboration

• I.Arsene10,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, 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
• 1Brookhaven National Laboratory, USA, 2IReS and
  Université Louis Pasteur, Strasbourg, France
• 3Jagiellonian University, Cracow, Poland,
  4Institute of Nuclear Physics, Cracow, Poland
• 5Johns Hopkins University, Baltimore, USA, 6New
  York University, USA
• 7Niels Bohr Institute, Blegdamsvej 17, University
  of Copenhagen, Denmark
• 8Texas AM University, College Station. USA,
  9University of Bergen, Norway
• 10University of Bucharest, Romania, 11University
  of Kansas, Lawrence,USA
• 12 University of Oslo Norway