Su Houng Lee

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J/y Dissociation cross section in Vacuum and QGP

• Su Houng Lee
• Yonsei University
• Seoul , Korea

• Introduction on dissociation cross section in
  different models
• Progress in QCD calculations LO and NLO
• Dissociation due to thermal gluons and quarks

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Quarkonium Haron interaction in QCD
Important because a) J/y suppression is a
signature of QGP in Heavy Ion collision b)
J/y suppression can occur through dissociation
by hadrons in later stages of HIC,
need to know J/y hadron cross section
c) Recent lattice show J/y will survive in QGP
up to 2 T_c. need to know J/y parton
cross section
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J/y hadron cross section
mb
1. Effective model
s1/2 (GeV)
2. Quark exchange model
3. LO pert QCD
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Progress in QCD calculations

• LO and NLO

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Basics in Heavy Quark system
1. Heavy quark propagation
Perturbative treatment are possible because
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2. System with two heavy quarks
Perturbative treatment are possible when
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Perturbative treatment are possible when
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Historical perspective on Quarkonium Haron
interaction in QCD

• Peskin (79), Bhanot and Peskin (79)
• a) From OPE
• b) Binding energy e0 gtgt L
• Kharzeev and Satz (94,96) , Arleo et.al.(02,04)
• a) Rederive, target mass correction
• b) Application to J/y physics in HIC

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Rederivation of Peskin formula using
Bethe-Salpeter equation (Lee,Oh 02)
Resum Bound state by Bethe-Salpeter Equation
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NR Power counting in Heavy bound state
1. Perturbative part
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LO Amplitude
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However, near threshold, LO result is expected
to have large correction
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NLO Amplitude
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NLO Amplitude
Collinear divergence when q10. Cured by mass
factroization
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Mass factorization
Gluons whose kcos q1 lt Q scale, should be
included in parton distribution function
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NLO Amplitude
Higher order in g counting
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Application to Upsilon dissociation cross section
Fit quark mass and coupling from fitting to
coulomb bound state gives
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Total cross section for Upsilon by nucleon NLO
vs LO
NLO
NLO/LO
LO
Large higher order corrections Even larger
correction for charmonium
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What do we learn from NLO calculation ?
1. Large NLO correction near threshold, due
to log terms
2. Dissociation by quarks are less than 10
of that by gluons
ltlt
Quenched lattice results at finite temperature
are reliable
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Total cross section gluon vs quark effects
With thermal mq mg 200 MeV
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Effective Thermal cross section gluon vs quark
effects
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Effective Thermal width gluon vs quark effects
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Summary

• We reported on the QCD NLO Quarkonium-hadron
  dissociation cross section.
• ? Large correction even for upsilon
  system, especially near threshold

2. The corrections becomes smaller with
thermal quark and gluon mass of larger than 200
MeV ? The thermal widht of J/y becomes
1 GeV at T600 MeV
3. The dissociation cross section due to
quarks are less than 10 of that due to the
gluons. ? The quenched lattice
calculation of the mass and width of J/y at
finite temperature should be reliable.
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Example
LO QCD
Total cross section for open charm
CM energy
Meson exchange model Wei, Ko, Lee (03)
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LO ressult for y gluon, y-gluon dissociation
(Oh, Kim, Lee (02))
LO ressult for y nucleon, y-nucleon
dissociation (Oh, Kim, Lee (02))