Correlations between J and charged hadrons

1
Correlations between J/? and charged hadrons

• Chun Zhang / Jiangyong Jia

2
Motivation how J/? is produced

• Gluon Gluon fusion(GG) and Gluon
  Fragmentation(GF) are the main mechanisms for
  charm pair(ccbar) production at RHIC energy.
• The produced ccbar needs to radiate gluons in
  order to get ride of color and to form a J/? . It
  can radiate one hard gluon?(Color Singlet Model)
  or many soft gluons(Color Octet Model).
• We think we may be able to discriminate these
  different productions by looking the azimuth
  correlation between the J/? and the hadrons
  produced in the same collisions, in other words,
  how the momentum of high pT J/? is balanced.

3
Imaginations
CSM pT is largely balanced by the hard gluon
Hard Gluon
c
cbar
Jpsi
COM pT is largely from initial kT
Jpsi
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Expectations we need simulations

• If GFCSM, azimuth correlation on away side,
  and the peak is expected to be wide, and may not
  center at 180 degree.
• If GFCOM, azimuth correlation on away side and
  one may see near side peak.
• If GGCSM, azimuth correlation on away side.
• If GGCOM, no away side peak, and one may see
  near side peak.
• All above speculations assumes all the particles
  correlated are from the same collisions. Proton
  Proton collisions are the best. But dAu and CuCu
  may doable.

5
J/y (mm) h correlation
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Run3 PP J/?
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Run3 PP J/? pT
Mass widow is from 2.4 GeV/c2 to 4.0 GeV/c2
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Azimuth Correlation between J/? in muon arms and
charged hadrons in central arms

• Trigger particle is the J/? in muon arms.
• Associated particles are the charged hadrons in
  central arms
• Mass widows is from 2.4 to 4.0 GeV.
• Hint of away side correlation ?
• pT cut for associated particles is 100 MeV/c.
• This measurement is sensitive to GF/CSM.
• Opposite sign as foreground and same sign as
  background and correlation function is normalized
  to per trigger yield.

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J/y (ee) h correlation
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Mass distribution for same sign and opposite sign

• Combined statistics from RUN3 pp and dAu
• Good run list and electron ID cut from analysis
  note 258

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• Trigger particle Jpsi background, where
  background can be estimated by like-sign ee pair
• Thus to get the true same event Df distribution
  for Jpsi, we need to subtract two correlation
  function, I.e subtract like-sign h Df from
  Trigger h Df distribution

Same event
All triggers
Background triggers
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• We need to do the similar subtraction for the
  mixed event pairs
• The mixed event is almost flat due to the decay
  kinematics (ltpTgt is small comparing to Jpsi mass)

Mixed event
All triggers
Background triggers
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• Comparing the Like-sign subtracted foreground and
  Like-sign subtracted mixed event Df distribution
• No apparent jet like correlation can be seen.
• We would like to go higher pT in both trigger
  JPsi and associated hadrons, where the GF
  contribution is more dominate

14
Summary

• We are currently statistic limited.
• We would like to study the correlation as
  function of J/? and hadron pT.
• Run5 CuCu, there are 10000 J/?.
• Run5 PP, we look forward !