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Correlations between J/ ψ and charged hadrons

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.

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Correlations between J/ ψ and charged hadrons

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  1. Correlations between J/ψ and charged hadrons Chun Zhang / Jiangyong Jia

  2. 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.

  3. GF : pT is balanced from back to back jets c cbar GG : pT is from initial kT of gluons c cbar Imaginations CSM : pT is largely balanced by the hard gluon Hard Gluon c cbar Jpsi COM : pT is largely from initial kT Jpsi

  4. 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.

  5. J/y (mm) – h correlation

  6. Run3 PP J/ψ

  7. Run3 PP J/ψ pT Mass widow is from 2.4 GeV/c2 to 4.0 GeV/c2

  8. 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.

  9. J/y (ee) – h correlation

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

  11. 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

  12. 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

  13. 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/ψ and hadron pT. • Run5 CuCu, there are ~10000 J/ψ. • Run5 PP, we look forward !

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