# Presentation: 620678

## Correlations between J/ψ and charged hadrons

- Chun Zhang / Jiangyong Jia

## 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.

## Imaginations 

- Hard Gluon

- c

- cbar

- Jpsi

- CSM : pT is largely balanced by the hard gluon

- COM : pT is largely from initial kT

- Jpsi

## 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.

## J () – h correlation

## Run3 PP J/ψ

## Run3 PP J/ψ pT 

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

## 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.

## J (ee) – h correlation

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

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

- Mass distribution for same sign and opposite sign

## 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

- 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

## 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)

- The mixed event is almost flat due to the decay kinematics (<pT> is small comparing to Jpsi mass)

- Mixed event

- All triggers

- Background triggers

## 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

- 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

## 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 !