The Ridge Associated with the Nearside Jet

1
The Ridge Associated with the Near-side Jet in
High Energy-Heavy-Ion Collisions
Cheuk-Yin Wong Oak
Ridge National Laboratory

• Introduction
• The momentum kick model the near-side ridge
  data
• The nature of the early parton rapidity plateau
• The nature of (jet parton)-(medium parton)
  collisions
• for jet partons with pTlt10 GeV
• Conclusions

C.Y.Wong, Phy.Rev.C76,054908(07) C.Y.Wong,
Chin.Phys.Lett.25,3936(08) C.Y.Wong,
J.Phys.G35,104085(08) C.Y.Wong, Phys.
Rev.C78,064905(08) C.Y.Wong, arXiv0901.0726(PRC,
in press) C.Y.Wong, arXiv0903.3879(09)
2
What is the near-side ridge ?
near-side jet
associated particle
away-side jet

• Occurrence of a near-side jet
• We detect associated particles in coincidence
  with the jet
• We measure the f and ? of these associated
  particles,
• ?ff (associated particle)- f (jet
  trigger)
• ??? (associated particle) - ? (jet
  trigger)
• The probability distribution in ?f- ?? is in the
  form of
• a ridge and a peak

3
Many Ridge Models

• C.Y.Wong,Phy.Rev.C76,054908(07)Chin.Phys.Lett.25
  ,3936(08)Phys.Rev.C78,064905(08)J.
  Phys.G35,104085(08)arXiv0901.0726(PRC,in
  press)arXiv0903.3879.
• S.A.Voloshin, Phys. Lett. B632, 490 (06)
• E. Shuryak, Phys.Rev.C76, 047901 (07)
• V. S. Pantuev, arxiv0710.1882(07)
• C. B. Chiu and R.C. Hwa, Phys. Rev. C76, 047901
  (08)
• N. Armesto, C. A. Salgado, U. A. Wiedemann,
  Phys.Rev.C76,054908(07)
• A.Dumitru,Y.Nara,B.Schenke,M.Strickland,
  Phys.Rev.C78,024909(08)
• A.majumder,B.Mueller,and S.A.Bass, Phys. Rev.
  Lett. 99, 042301 (07)
• R.Mizukawa,T.Hirano,M.Isse,Y.Nara,A.Ohnishi,J.Phys
  .G35,104083(08)
• S.Gavin,L.McLerran,G.Moschelle,arXiv0806.4718
• A. Dumitru,F. Gelis, L. McLerran, and R.
  Venugoplan, Nucl.Phys.A810,91(09)
• Y.Hama and collaborators,
• many more

4
Gomel, Belarus, September 8, 2009
0-10
Ridge yield
Jet yield
B/M
5
Experimental data implies that ridge particles
are medium partons kicked by the jet

• Ridge yield increases with increasing
  N_participants
• Ridge yield nearly independent of the jet trigger
  properties
• Tjet gt Tridge gt Tbulk
• B/MridgeB/Mbulk, but B/Mjet ? B/Mbulk
• ? ridge particles are medium partons
• 5. ?f 0 implies that the ridge particles
  acquire additional longitudinal momentum from the
  jet.
• ? ridge particles and the jet are related
  by collisions
• Ridge particles nearly flat in ??
• ? the flat ?? comes from the ridge
  particles momentum distribution before they are
  kicked by the jet

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Momentum kick model

• Ridge particles are medium partons kicked by the
  jet.

Significance of the Momentum kick model

• It provides valuable information on
• The early parton momentum distribution
• The nature of the collision between the jet and
  the medium parton

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Schematic picture of the momentum kick model
C.Y.Wong, Phys. Rev.C78,064905(08)
8
The momentum distribution in the momentum kick
model consists of two components
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The ridge is the initial distribution shifted by
the kick

• The kicked final partons subsequently
  materialize as hadrons by parton-hadron duality
• The shape of the ridge particle distribution
  depends on the initial parton momentum
  distribution and the longitudinal momentum kick
  qL.

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Initial parton momentum distribution
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The observed distribution in the momentum kick
model is a sum of ridge and jet components
We need the pp near-side jet data
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The pp near-side jet data can be described by
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pp near-side jet data (open blue circles)
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Momentum kick model gives the correct prediction
for PHOBOS
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pttrig
ptassoc
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Shape of early parton momentum distribution
19
Early parton rapidity distribution has a plateau
structure
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Important physical parameters extracted from
near-side ridge data at s1/2200 GeV

• The rapidity distribution of early partons has a
  plateau structure
• qL0.8-1.0 GeV, longitudinal momentum kick per
  parton-parton collision
• fR ltNkgt 3.0-3.8 for the most central AuAu
  collisions
• The inverse slope T for early partons is
  intermediate between Tjet and Tbulk

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We find rapidity plateau structures in early
parton distributions

• Rapidity plateau structures appear in many
  multi-particle production processes
• Theoretically, a rapidity plateau is expected in
  QED2 fragmentation, which mimics particle
  production in QCD as a q and a qbar pull away
  from each other at high energies.
• Experimentally, a rapidity plateau has been
  observed in high energy ee- annihilation,
• and pp collisions.

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Rapidity plateaus occur in ee- and pp collisions
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Early parton rapidity distribution is
intermediate between those of pp and AA
collisions
This is consistent with the direction of the
evolution of the parton rapidity distributions.
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Question on the early parton rapidity plateau

• Classical string fragmentation such as the Lund
  Model stipulates that there is a longitudinal
  distance and momentum ordering
• particles with large rapidity are produced
  late in time
• Jet parton and medium parton collisions take
  place in an early stage. Partons with large
  rapidities may not be produced for the jet to
  collide
• The resolution of this puzzle may rely on the
  quantum treatment of the production process

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Wigner function of particle production in QED2
C.Y.Wong,arXiv0903.3879
26
Wigner function of produced bosons
Bosons of different rapidities are produced
simultaneously at t0
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Is qL1 GeV per kick compatible with other
parton-parton properties?
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Hadron-hadron elastic scattering data gives a
0.3 fm
Schiz et al. PRD 24, 26 (1981)
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Transverse correlation length a extracted from
the momentum kick model is compatible with those
from other non-perturbative treatment of
parton-parton scattering as the exchange of a
pomeron.
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Conclusions

• The ridge particles associated with the near-side
  jet can be described as medium partons kicked by
  the jet
• They carry information on the early parton
  momentum distribution and the momentum kick.
• The early parton momentum distribution has a
  rapidity plateau structure with a thermal-like
  transverse momentum distribution
• The magnitude of the longitudinal momentum kick
  gained by the parton per collision is 1 GeV,
  which is also the momentum loss by the jet per
  parton-parton collision in a jet-parton
  collision.