Motivation

The specific interest for heavy quark production in heavy ion collisions is due to the chance to study rescattering and energy loss of massive colour charge in quark-gluon plasma. The heavy quarks can be produced due to "pair creation" (leading order diagrams are shown on the top of figure 1), "flavour excitation" (middle of figure 1) and "gluon splittings" (bottom of figure 1). The dominate source of high invariant mass dimuons (M>10 GeV) for the CMS acceptance is expected to be semileptonic BBbar decays. Another process of particular interest is secondary charmonium (B-->J/Psi) production with subsequent decay to dimuons and rate comparable with the rate of primary charmonium yield. The investigation of sensitivity of dimuon spectra to medium-induced effects on heavy quarks and development of methods to separate dimuons from various sources are prior tasks for the current subject.

Participants

I.Lokhtin (SINP MSU), A.Snigirev (SINP MSU)

Main results

1. It has been found for the CMS muon acceptance that the "showering" BBbar pairs give the same order of contribution to high mass dimuon spectra as direct quark pairs. The BBbar pair production from parton showers is dominant mechanism for B-->J/Psi production.
2. We have developed the model of energy loss and rescattering of massive quarks in quark-gluon plasma. On the basic of this model we have created the Monte-Carlo code to simulate medium-induced effects on massive quarks in heavy ion collisions.
3. The sensitivity of dimuon spectra to medium-induced energy loss of heavy quarks has been tested under CMS conditions using developed model. The medium-induced parton rescattering and collisional energy loss is expected to reduce high-mass dimuon rate by factor ~1.5, and the additional radiative energy loss can reduce the rate up to factor ~3-4 (depending on quark production mechanism). Due to different kinematics the high-mass dimuon spectra from direct quarks are more sensitive to the energy loss of b-quarks than dimuons from "showering" quarks. The estimated suppression factor for secondary charmonia ~1.3-2. The estimated nuclear shadowing corrections ~15% for high-mass dimuons from BBbar decays and ~30% for secondary charmonia.
4. Using fast simulation for CMS tracker resolutions and primary vertex finding, we have shown that the recognition of high-mass dimuons from BBbar decays relative to Drell-Yan pairs, as well as the recognition of secondary compared to primary J/Psi's, can be performed using tracker information on the secondary vertex position.

Plans for 2003

Starting development algorithms for (BBbar-->mu+mu-) and (B-->J/Psi-->mu+mu-) reconstruction.