Midrapidity vs forward rapidities

1
Properties of matter at forward rapidities
Dieter Roehrich University of Bergen BRAHMS
collaboration

• Midrapidity vs forward rapidities
• Nuclear modification factors
• RAA and RCP
• charged hadrons
• identified particles (?, p)
• pp reference
• dAu
• AuAu, CuCu

2
Nuclear modification factors

• Definitions
• Rd(A)A ? RCP
• Rd(A)A isospin effects, canonical strangeness
  suppression
• RCP collective effects in peripheral
  collisions, undefined collision geometry
  in peripheral collisions

central
peripheral
peripheral
central
3
Kinematics
1

• RHIC example
• At 4 (y3 for pions) and pT1 GeV/c one can
  reach values as low of x2 10-4
• This is a lower limit, not a typical value most
  of the data collected at 4 would have x20.01

2?1 process
yrapidity of (xL, k) system
2
Guzev, Strikman, and Vogelsang (hep-ph/0407201)
4
Reference pp midrapidity (1)

• NLO pQCD can reproduce the data at RHIC
  energies
• The fragmentation functions differ by the
  amount of g-gt?

5
Reference pp midrapidity (2)
NLO pQCD for protonanti-proton

• A recent update of the KKP fragmentation
  function AKK (flavor-dependent FFs of light
  quarks)

6
Reference pp forward rapidity (1)
STAR ?0 at high rapidity

• KKP FF higher g-gt? than Kretzer

nucl-ex/0602011
7
Reference pp forward rapidity (2)
Identified particle spectra Red positive
particles Blue negative particles
BRAHMS Preliminary

• Trigger bias (20) has been corrected
• Normalization to total inelastic cross-section
  (41 mb)

8
Reference pp forward rapidity (3)
BRAHMS Preliminary
Calculations done by W. Vogelsang. Only one scale
?pT and the same fragmentation functions as used
for the PHENIX comparison.
KKP has only ?0 frag. Modifications were needed
to calculate charged pions

• NLO pQCD describes data also at forward
  rapidities

9
Reference pp forward rapidity (4)
Ratios p/? at y3.0 and 3.3

• Excess of positive pions ratio -gt1/2
  (valence quark counting)
• Small p/p ratio eliminates possible strong g
  -gt p or p fragmentation
• The difference between protons and
  anti-protons indicates another mechanism
  besides fragmentation (as AKK) that puts so
  many protons at high pT.

BRAHMS Preliminary
Red proton/? Blue antiproton/ ?-
ee- ppbar/? ?- ALEPH
10
Conclusions (pp)

• NLO pQCD describes data at all rapidities
• Modified FFs
• But large proton/pion ratio at intermediate pt
  and high y?

11
Charged hadrons RdAu at different
pseudorapidities
BRAHMS PRL 93, 242303 (2004)

• Cronin-like enhancement at ?0
• Consistent with PHOBOS at ?1
• Clear suppression as ? changes from 0 to 3.2

PHOBOS, PHYS. REV. C70 (2004) 061901(R)
12
Charged hadrons centrality dependence of
enhancement/suppression in dAu
BRAHMS PRL 93, 242303 (2004)

• Consistent with PHENIX at ?1.4-2.2 and STAR at
  ?2.5-4.0
• Change of RCP from mid- to forward rapidities is
  stronger for central collisions than for
  semi-peripheral collisions

S.S.Adler et al. (PHENIX), Phys. Rev. Lett. 94
(2005) 082302
B. Mohanty (STAR), QM2005 (1B)
13
RdAu and RCP(dAu) pions, ? (y0)

• RdAu
• Almost no Cronin effect
• RdAu consistent with 1
• RCP
• Strong Cronin effect

?
?0
M. Tannenbaum (PHENIX), 2005 RHICAGS Annual
Users Meeting
K. Adcox et al. (PHENIX), Nucl. Phys. A757 (2005)
184
14
RdAu ?0 (?4)

• STAR
• RdAu at high ?
• Strong suppression
• Larger than h- - isospin effect

G. Rakness (STAR), DIS 2005 nucl-ex/0602011
15
RdAu and RCP(dAu) pions and protons (y0)

• RdAu and RCP show Cronin effect
• Effect seems to be larger for baryons than for
  mesons

C. Mironov (STAR), 2005 RHICAGS Annual Users
Meeting and D. Pal (PHENIX), QM2005, sect. 1a
16
RdAu and RCP(dAu) pions and protons (y3.2)
BRAHMS preliminary
F. Videbaek (BRAHMS), DIS2005

• RdAu
• Strong suppression for ?-
• Enhancement for antiprotons ? different from RCP
• RCP
• Suppression for both pions and protons at forward
  rapidity

?
p
H. Yang (BRAHMS), QM2005 (poster 36)
17
RdAu pions and protons (y3)

• RdAu
• Suppression for ? and K
• No suppressions for protons
• RCP
• Suppression for both pions and protons at forward
  rapidity

18
Experimental facts dAu at RHIC (1)

• At midrapidity
• Cronin enhancement observed for several particle
  species in RdAu and RCP (magnitude differs by
  a factor of 2)
• RCP(Cronin peak) ? RdAu(Cronin peak)
• Cronin effect (baryons) gt Cronin effect (mesons)
• At forward rapidities
• Increasing suppression of charged hadrons, h-,
  ?-, ?0with increasing (pseudo)rapidity
• RCP suppression of protons and antiprotons
• RdAu no suppressionen of protons

19
Experimental facts dAu at RHIC (2)

• Ratio of dn/d?(dAu) / dn/d?(pp) exhibits a
  similar suppression trend

• Enhanced production for ? lt 0
• Suppression for ? gt 0
• Modification effects all pions, not only at high
  pT

P. Steinberg (PHOBOS), QM 2004
?
20
Experimental facts dAu at SPS (1)
Ratio of dn/dy(dAu) / dn/dy(NN) exhibits a
similar suppression trend

• Enhanced production for ? lt 0
• Suppression for ? gt 0
• Limiting fragmentation

NA35
T. Alber et al. (NA35), Eur. Phys. J. C 2, 643
(1998)
21
Experimental facts dAu (pPb) at SPS (2)
dAu
B. Boimska (NA49), PhD thesis, Warzaw (2004)
pPb

• Increasing suppression with increasing xF
• Pattern similar for pions and antiprotons,
  different for protons

Similar trend at the AGS R. Debbe et al.
(BRAHMS) CINPP proceedings (2005)
22
Stopping and particle production in p(d)-A at SPS

• Large momentum degradation of projectile in
  central pA by multiple collisions
• Very different from pp

S. Brodsky et al., PRL 39 (1977) 1120
NA49
NA35

• Pion production at forward rapidities independent
  of target

23
Initial and final effects - dAu

• Initial effects
• Wang, Levai, Kopeliovich, Accardi
• Especially at forward rapidities
• Eskola, Kolhinen, Vogt, Nucl. Phys. A696 (2001)
  729-746
• HIJING
• D.Kharzeev et al., PLB 561 (2003) 93
• Others
• B. Kopeliovich et al., hep-ph/0501260
• J. Qiu, I, Vitev,hep-ph/0405068
• R. Hwa et al., nucl-th/0410111
• D.E. Kahana, S. Kahana, nucl-th/0406074

Cronin effect Initial state elastic multiple
scattering leading to Cronin enhancement (RAAgt1)
broaden pT
Nuclear shadowing depletion of low-x partons
Gluon saturation depletion of low-x gluons due
to gluon fusion Color Glass Condensate (CGC)
Suppression due to dominance of projectile
valence quarks, energy loss, coherent multiple
scattering, energy conservation, parton
recombination, ...
24
CGC saturation model (1)

• CGC describes dn/d? and ?0 inv. CS at forward
  rapidities

Data BRAHMS, submitted to PRL, nucl-ex/0401025
Data B. Mohanty (STAR), QM2005
Model A. Dumitru, A. Hayashigaki, J.
Jalilian-Marian, hep-ph/0506308
Model Kharzeev, Levin, Nardi. Nucl. Phys. A 730
(2004) 448
25
CGC saturation model (2)

• CGC model describes RdAu and RCP
• Suppression comes in at y gt 0.6

D. Kharzeev, Y.V. Kovchegov, K. Tuchin,
hep-ph/0405054 (2004)
26
pQCD models (1)

• pQCD-improved parton model
• Glauber-type collision geometry
• Nuclear shadowing
• Initial state incoherent multiple scattering

G.G. Barnafoldi, G. Papp, P. Levai, G. Fai,
nucl-th/0404012 (2004)
see also A. Arcadi, M. Gyulasy, nucl-th/0402101
(2004)

• Increasing strength of standard nuclear shadowing
  with increasing ?
• ? reasonable agreement between RdAu and pQCD
• but underestimation of centrality dependence of
  RCP

see R. Vogt, hep-ph/0405060 (2004), Phys. Rev.
C70 (2004) 064902
See also R. Vogt, hep-ph/0405060 (2004)
27
pQCD models (2)

• NLO pQCD calculations
• Nuclear shadowing
• Multiple scattering

nucl-ex/0602011 and references therein

• STAR data
• Nuclear shadowing cannot explain the suppression
  in RdAu for neutral pions at ?4

See also R. Vogt, hep-ph/0405060 (2004)
28
pQCD models (3)

• Coherent multiple scattering of a parton with the
  remnants of the nucleus in the final state

J.W.Qiu, I.Vitev, hep-ph/0405068

• Low pT suppression which grows with rapidity and
  centrality
• Disappearence of the nuclear modification at high
  pT

29
Phenomenological models (1)
B. Kopeliovich et al., hep-ph/0501260

• Suppression at large xF
• Forward region is dominated by the fragmentation
  of valence quarks
• Induced energy loss via increased gluon
  bremsstrahlung in cold nuclear matter
• Momentum conservation forbids particle production
  at xF ?1

30
Phenomenological models (2a)
K. Tywoniuk, I. Arsene, L. Bravina, A.B.
Kaidalov, QM2005, poster 241

• Gluonic shadowing in GRIBOV-REGGE FIELD THEORY
• GRFT links shadowing in A-A collisions to
  diffraction
• Input data from H1 and ZEUS on diffraction (NLO
  QCD) ? gluonic nPDF
• Assumptions
• high-pT particles come from jets
• no rapidity dependence in Cronin effect
• Result Suppression at forward rapidities is
  mostly due to gluonic shadowing

31
Phenomenological models (2b)
NA49 data
K. Tywoniuk, I. Arsene, L. Bravina, A.B.
Kaidalov QM2005, poster 241

• Gluonic shadowing in GRIBOV-REGGE FIELD THEORY
  at SPS
• Although present at SPS energies, gluonic
  shadowing cannot explain the magnitude of the
  effect
• Shadowing due to valence quarks will dominate in
  this kinematical region
• Final state multiple scattering and energy loss?

See also I.Vitev, 2005 RHICAGS Annual Users
Meeting T.Goldman, M.Johnson, J.W.Qiu, I.Vitev,
in preparation
32
Conclusions (dAu)

• Suppression phenomena at RHIC and SPS
• Variety of processes can result in suppression
• Quality of data is insufficient for ruling out
  models

33
Final state effects AA collisions
Gallmeister et al., PRC67 (2003)
044905 Fries, Muller, Nonaka, Bass,
nucl-th/0301078Lin, Ko, PRL89 (2002)
202302 R. Hwa et al., nucl-th/0501054 Gyula
ssy, Wang, Vitev, Baier, Wiedemann e.g.
nucl-th/0302077
Hadronic absorption of fragments
Parton recombination (up to moderate pT)
Energy loss of partons in dense matter
34
RAA ?0,? and direct photons - AuAu at 200
GeV (y0)

• PHENIX
• Direct photons
• no suppression
• Large suppression for ?0,? in central AuAu at
  high pT

B. Cole (PHENIX), QM2005
35
RAuAu vs RCP identified hadrons AuAu at
200 GeV (y0)

• RAuAu
• baryons are enhanced
• mesons are suppressed

• RCP
• baryons suppressed gt 2.5 GeV/c
• mesons suppressed gt 1.5 GeV/c

J. Dunlop (STAR), QM2005
36
Matter at forward rapidity (1)
dn/dy drops by a factor of 3
BRAHMS, Phys. Rev. Lett. 94 (2005) 162301
J.I. Jørdre (BRAHMS), PhD thesis (2004)
37
Matter at forward rapidity (2)
SPS-like hadron chemistry
p/p
62.4 GeV
62.4 GeV
Drastic change of antiproton/pion ratio
38
RAuAu charged hadrons AuAu at 200 GeV

• NO change of RAuAu with rapidity

39
RCP vs RAuAu identified hadrons
AuAu at 200 GeV (?3.2)

• RCPconstantsuppression
• RAuAumass dependence

• Large difference in RAuAu vs RCP for
  (anti-)protons

40
RAuAu identified hadrons AuAu at 200 GeV
midrapidity vs ?3.2
pions
protons

• NO change of RAuAu with rapidity

41
RAuAu vs Npart pions AuAu at 200 GeV
midrapidity vs ?3.2

• Stronger volume dependence of RAuAu at forward
  rapidity

42
CGC 3d-hydro jet rapidity dependence
PRC 68 (2003) Hirano and Nara

• CGC 3d-hydro-dynamic simulation with jet (2?2
  pQCD/ PYTHIA)

• Little change of RAuAu(pions) with rapidity

43
CGC 3d-hydro jet

• Why?

PRC 68 (2003) Hirano and Nara

• CGC initial parton distribution drops by a factor
  of 2 at ?3.2

• Different time evolution of the thermalized
  parton density at ?3.2 ? less jet energy loss

• Steeper slope of pQCD components at ?3.2

Is 2. cancelled by 3. ?
44
Surface emission
Dainese, Loizides, Paic, Eur. Phys. J. C38 (2005)
461

• Medium at RHIC is so dense that only particles
  produced close to the surface can escape
• Can corona effect mask the lower parton density
  at ?3.2 ?

45
Conclusions (AuAu)

• Nuclear modification
• Strong pion suppression at all rapidities
• Protons are enhanced at all rapidities (RAuAu)
  and moderate pT
• No dependence of RAuAu on rapidity
• Accidental effect? Surface emission?

46
The BRAHMS Collaboration
I.Arsene7, I.G. Bearden6, D. Beavis1, S. Bekele6
, C. Besliu9, B. Budick5, H. Bøggild6 , C.
Chasman1, C. H. Christensen6, P. Christiansen6,
R. Clarke9, R.Debbe1, J. J. Gaardhøje6, K.
Hagel7, H. Ito10, A. Jipa9, J. I. Jordre9, F.
Jundt2, E.B. Johnson10, C.E.Jørgensen6, R.
Karabowicz3, E. J. Kim4, T.M.Larsen11, J. H.
Lee1, Y. K. Lee4, S.Lindal11, G. Løvhøjden2, Z.
Majka3, M. Murray10, J. Natowitz7, B.S.Nielsen6,
D. Ouerdane6, R.Planeta3, F. Rami2, C. Ristea6,
O. Ristea9, D. Röhrich8, B. H. Samset11, D.
Sandberg6, S. J. Sanders10, R.A.Sheetz1, P.
Staszel3, T.S. Tveter11, F.Videbæk1, R. Wada7,
H. Yang6, Z. Yin8, and I. S. Zgura9 1Brookhaven
National Laboratory, USA, 2IReS and Université
Louis Pasteur, Strasbourg, France 3Jagiellonian
University, Cracow, Poland, 4Johns Hopkins
University, Baltimore, USA, 5New York University,
USA 6Niels Bohr Institute, University of
Copenhagen, Denmark 7Texas AM University,
College Station. USA, 8University of Bergen,
Norway 9University of Bucharest, Romania,
10University of Kansas, Lawrence,USA 11
University of Oslo Norway