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Correlations between J/ψ and charged hadrons

Chun Zhang / Jiangyong Jia

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Motivation how J/ψ 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/ψ . 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/ψ and the hadrons produced in the same collisions, in other words, how the momentum of high pT J/ψ is balanced.

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Imaginations

ccbar

GF : pT is balanced from back to back jets

c

cbar

GG : pT is from initial kT of gluons

Hard Gluon

c

cbar Jpsi

CSM : pT is largely balanced by the hard gluon

COM : pT is largely from initial kT

Jpsi

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Expectations we need simulations

• If GF+CSM, azimuth correlation on away side, and the peak is expected to be wide, and may not center at 180 degree.• If GF+COM, azimuth correlation on away side and one may see near side peak.• If GG+CSM, azimuth correlation on away side.• If GG+COM, 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.

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J () – h correlation

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Run3 PP J/ψ

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Run3 PP J/ψ pT

Mass widow is from 2.4 GeV/c2 to 4.0 GeV/c2

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Azimuth Correlation between J/ψ in muon arms and charged hadrons in central arms

• Trigger particle is the J/ψ 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 (ee) – h correlation

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• Combined statistics from RUN3 pp and dAu

• Good run list and electron ID cut from analysis note 258

Mass distribution for same sign and opposite sign

• Using the Jpsi candidates in mass widow 3-3.2 GeV to get a good signal/bg ratio

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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 distribution for Jpsi, we need to subtract two correlation function, I.e subtract like-sign – h from Trigger – h 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 (<pT> 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 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

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Summary

• We are currently statistic limited.

• We would like to study the correlation as function of J/ψ and hadron pT.

• Run5 CuCu, there are ~10000 J/ψ.

• Run5 PP, we look forward !