Natalia Katrynska

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• Physics at Forward Rapidities
• BRAHMS Experiment at RHIC

Natalia Katrynska Smoluchowski Institute of
Physics Jagiellonian University for the BRAHMS
Collaboration
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Outline

• Overview of BRAHMS detector setup.
• A few details of analysis process.
• Nuclear Modification Factor in dAu collisions
  for different centralities and rapidities _at_
  200 GeV.
• 4. Forward like-particle ratios of pions, kaons
  and protons
• _at_ 62.4 GeV and 200 GeV.
• 5. The invariant yield distributions of
  identified hadrons.
• 6. Limiting fragmentation in pp collisions.
• 7. Summary.

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Broad RAnge Hadron Magnetic Spectrometers at RHIC
Colliding systems _at_ 62.4 and 200 GeV
AuAu CuCu
BRAHMS
PHOBOS
PHENIX
STAR
d Au
p p
RICH detector situated in Forward Spectrometer
allows to identify high momentum particles
(e-,µ-/, p-/, K-/, p)
ToF
placed before RICH measures hadrons with lower
velocity.
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Some details of data analysis
1. Particle identification of pions, kaons and
protons. 2. Applied corrections for
efficiency, weak-decays, absorption in
materials . 3. The data was corrected for
geomet- rical acceptance.
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dAu Collisions _at_ 200 GeV
PRL 93 (2004) 242303
Nuclear medium effects
Cronin enhancement for y 0
suppression at high p T
expected Color Glass Condensate state (gluon
saturation) at forward
rapidity (low x) ?
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RdAu for Identified Particles
E.J.Kim, H.Yang, INCP2007
Although there is a limitation in pT to
determine the nuclear modification factor at
BRAHMS experiment the suppression of R dAu is
clearly visible for forward rapidities for pions,
kaons and protons for 0-30 centrality bin. For
peripheral centrality the value of factor is
comparable with midrapidity region. At
midrapidity, at pT 2 GeV/c , for both
centralities R dAu of protonos reaches value gt
1.5.
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Forward Like-Particle Ratios _at_ 200 GeV
p p collisions
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Pions and Protons Production
p p collisions _at_ 200 GeV
The protons over antiprotons yield excess
causes a noticeable difference between the p/p-
and p/p . That high p/p at high pT is a
puzzle , especially with reference to the baryon
number transport considering as a soft low pT
phenomena.
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Particle Ratios _at_ 62.4 GeV
p p collisions
The difference between protons and
antiprotons yield seen _at_ 200 GeV, at
lower energy increses by an order of the
magnitude.
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Comparison of p/p ratio
p p collisions
A remarkable value for the p/p (pT) ratio
is observed at ? 3.2 in p p collisions _at_
62.4 GeV. This value is considerably different
from the value measured _at_ 200 GeV. The increase
of p/p with increasing y is seen in the wide
range of rapidity.
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Invariant Cross Section vs. NLO Calculations
p p collisions _at_ 200 GeV
PRL 98 (2007) 252001
factorization normalization scales µ µF
µR pT CTEQ6 parton distribution functions


KKP modified to obtain FFs for specific charges
Dpu (1z)Dp0u
Dp0u 1/2Dp- pu z fraction of the
parton momentum carried by the hadron
Dpu function fragmenting u quarks
into positive pions
AKK - FFs reproduce
well STAR data at y0 gt at high y gluons
fragmenting into anti-/protons gt 80
for pT lt 5 GeV/c
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Invariant Cross Section vs. NLO Calculations
F. Videbaek, Winter Workshop on
Nuclear Dynamics, 2007
p p collisions _at_ 62.4 GeV
factorization normalization scales µ µF
µR pT

KKP modified as for pp system _at_
200 GeV
observed
rapid changes with different rapidities at high
pT (xF up to 0.5)

although
at high pT it seems that the fit falls down
below data there is still good agreement
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Net-proton Distribution
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J. Phys. G Part. Phys. 8 August 2007 S619-S622
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Net-proton dN/dy in dAu Collisions _at_ 200 GeV
H. Yang, QM2008, oral presentaion
Going from midrapidity to forward rapidity
there is no sigificant alteration - taking
errors under consideration - for the most
central dAu collisions. For more
peripherial reactions for rapidity y 3 it is
noticeable the difference of proton and
antiproton production in comparison with
midrapidity regime.
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Limiting Fragmentation
for Elementary Reactions
A remarkable overlap of dN/dy
distributions at all energies (pp _at_ 200 GeV,
ybeam 5.3 pp _at_ 62.4 GeV, ybeam 4.2)
appears when viewed in their projectile frame.
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Summary
dAu collisions
It is observed a significant suppression of
the yield of charged hadrons compared to pp
collisions at forward rapidities. Due to
limitation in pT it is difficult to specify the
character of particular particle in forward
regime. The results _at_ 200 GeV indicate that
the simple quark-diquark breaking mechanism is
not sufficient to characterize particles yields
in the whole considered interval of rapidity.
It seems that NLO pQCD rationally describe the
mesons (pions and kaons) production distributions
at high rapidity in relativistic elementary
collisions. The updated AKK FFs reflect the
invariant cross section for anti-/proton the
unexpected excess of protons over antiprotons
(p/p 0.1 at y 3.3) yield suggests it may not
be related to baryon transport number. Forward
particle production _at_ 62.4 GeV has a similar
tendency, but with stronger effect.
pp collisions
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BRAHMS Collaboration
I. C. Arsene12, I. G. Bearden7, D. Beavis1, S.
Bekele12, C. Besliu10, B. Budick6, H. Bøggild7,
C. Chasman1, C. H. Christensen7, P.
Christiansen7, H.Dahlsgaard7, R. Debbe1, J. J.
Gaardhøje7, K. Hagel8, H. Ito1, A. Jipa10,
E.B.Johnson11, J. I. Jørdre9, C. E. Jørgensen7,
R. Karabowicz5, N. Katrynska5 ,E. J. Kim11, T. M.
Larsen7, J. H. Lee1, Y. K. Lee4,S. Lindahl12, G.
Løvhøiden12, Z. Majka5, M. J. Murray11,J.
Natowitz8, C.Nygaard7, B. S. Nielsen7, D.
Ouerdane7, D.Pal12, F. Rami3, C. Ristea8, O.
Ristea11, D. Röhrich9, B. H. Samset12, S. J.
Sanders11, R. A. Scheetz1, P. Staszel5, T. S.
Tveter12, F. Videbæk1, R. Wada8, H. Yang9, Z.
Yin9, I. S. Zgura2 , A. Qviller7 1. Brookhaven
National Laboratory, Upton, New York, USA 2.
Institute of Space Science, Bucharest - Magurele,
Romania 3. Institut Pluridisciplinaire Hubert
Curien et Université Louis Pasteur, Strasbourg,
France 4. Johns Hopkins University, Baltimore,
USA 5. M. Smoluchowski Institute of Physics,
Jagiellonian University, Krakow, Poland 6. New
York University, New York, USA 7. Niels Bohr
Institute, University of Copenhagen, Copenhagen,
Denmark 8. Texas AM University, College Station,
Texas, USA 9. University of Bergen, Department of
Physics and Technology, Bergen, Norway 10.
University of Bucharest, Romania 11. University
of Kansas, Lawrence, Kansas, USA 12. University
of Oslo, Department of Physics, Oslo, Norway
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back-up slides
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RCP for dAu Collisions _at_ 200 GeV
PRL 93 (2004) 242303
at ? 0 central-peripheral ratio larger than
semicentral-peripheral increased role of
Cronin-like multiple scattering effects at ?
3.2 more central ratio is lower suppression
mechanism depends on the centraliy collision
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Limiting Fragmentation
in AuAu Collisions _at_ 62.4 and 200 GeV
Viewing from the rest frame of one of the
nuclei with simultaneously substracting
calculated value of target baryons (grey bands)
for heavy ions collisions at RHIC (BRAHMS) and
SPS (NA49).
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