Midrapidity vs forward rapidities

1
Nuclear modification factors at forward
rapidities
Dieter Roehrich University of Bergen

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

• NLO pQCD calc. (W. Vogelsang)

h-
5
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)
6
RdAu ?0 (?4)

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

G. Rakness (STAR), DIS 2005
7
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)
8
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
9
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
10
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)
11
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-,
  ?-, ?0, J/? with increasing (pseudo)rapidity
• RCP suppression of protons and antiprotons
• RdAu enhancement of antiprotons

12
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
?
13
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)
14
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)
15
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

16
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, ...
17
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
18
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)
19
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)
20
pQCD models (2)

• 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

21
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

22
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

23
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
24
Conclusions (dAu)

• Cronin effect
• Experimental situation needs clarification
• Initial or final state effect?
• Suppression phenomena at RHIC and SPS
• Variety of processes can result in suppression
• Quality of data is insufficient for ruling out
  models
• Outlook
• Back-to-back azimuthal correlations with large
  ??
• Low energy dAu run at RHIC a unique chance

25
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
26
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
27
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
28
Matter at forward rapidity (y?3)
dn/dy drops by a factor of 3
BRAHMS, Phys. Rev. Lett. 94 (2005) 162301
J.I. Jørdre (BRAHMS), PhD thesis (2004)
I. Arsene (BRAHMS), QM2005, poster 126
29
RCP vs RAuAu identified hadrons
AuAu at 200 GeV (?3.2)

• RAuAu
• mass dependence
• RCP
• constant suppression

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

R. Karabowicz (BRAHMS), QM2005, section 1b
30
RAuAu identified hadrons AuAu at 200 GeV
midrapidity vs ?3.2
pions
protons

• NO change of RAuAu with rapidity

R. Karabowicz (BRAHMS), QM2005, section 1b
31
CGC 3d-hydro jet
PRC 68 (2003) Hirano and Nara

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

• Little change of RAuAu(pions) with rapidity

32
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. ?
33
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 ?

34
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?
• Outlook
• Connection to flowRAA(pt, ?)