e+ e- annihilation into J/psi + J/psi

Recent measurements by the Belle Collaboration of the exclusive production of two charmonia in e(+)e(-) annihilation differ substantially from theoretical predictions. We suggest that a significant part of the discrepancy can be explained by the process e(+)e(-)-->J/psi+J/psi. Because the J/psi+J/psi production process can proceed through fragmentation of two virtual photons into two cc pairs, its cross section may be larger than that for J/psi+eta(c) by about a factor of 3.7, in spite of a suppression factor alpha(2)/alpha(2)(s) that is associated with the QED and QCD coupling constants.     

Search for the invisible decay of J/psi in psi(2S) --> pi(+)pi(-) J/psi

Using psi(2S) --> pi(+)pi(-) J/psi events in a sample of 14.0 x 10(6) psi(2S) decays collected with the BES-II detector, a search for the decay of the J/psi to invisible final states is performed. No signal is found, and an upper limit at the 90% confidence level is determined to be 1.2 x 10(-2) for the ratio B(J/psi --> invisible)/B(J/psi-->mu(+)mu(-)). This is the first search for J/psi decays to invisible final states.     

J/psi production in quark-gluon plasma

We study J/psi production at RHIC and LHC energies with both initial production at energies reached and the BNL Relativistic Heavy Ion Collider (RHIC) and CERN Large Hadron Collider (LHC) with regeneration. We solve the coupled set of transport equations for the J/psi distribution in phase space and the hydrodynamic equation for evolution of quark-gluon plasma. At RHIC, continuous regeneration is crucial for the J/psi momentum distribution while the elliptic flow is still dominated by initial production. At energies reached at the LHC energy, almost all the initially created J/psis are dissociated in the medium and regeneration dominates the J/psi properties.     

J/psi suppression in nucleus-nucleus collisions

We propose a model for calculating J/psi suppression in high-energy hadron-nucleus and nucleus-nucleus collisions. We factorized the process into a production of the cc- pairs convoluted with a transition probability into the observed J/psi mesons. As the produced cc- pairs exit the nuclear matter, multiple scattering increases the square of the relative momentum between the c and c- such that some pairs are transmuted into open charm states. With only one parameter, the energy gained by the produced cc- pair per unit length in the nuclear medium, our model can fit all observed J/psi suppression data in hadron-nucleus and nucleus-nucleus collisions.     

Possible solution of the J/psi production puzzle

We argue that the s-channel cut contribution to J/psi hadroproduction can be significantly larger than the usual cut contribution of the color-singlet mechanism, which is known to underestimate the experimental measurements. A scenario accounting for intermediate cc[over ] interactions is proposed that reproduces the data at low and midrange transverse momenta P_(T) from the Fermilab Tevatron and BNL Relativistic Heavy Ion Collider. The J/psi produced in this manner are polarized predominantly longitudinally.