Virtual Photon Tagged Jets

Camelia Mironov

The study of the new state of matter created at RHIC will continue at the LHC with investigations of the properties of this matter. High transverse momentum jets are a key measurement in this sense. While traversing the medium, the partons which will subsequently fragment into jets will loose energy through collisions and radiation and thus their properties will be modified. By measuring these modifications, we gain information about the properties of the medium.

We will present preliminary studies on possible jet measurement at LHC using the leptonic decay of a high transverse momentum virtual photon (gamma*) in association with a hadronic jet. The interested production channels are two: q+qbar -> gamma* + q (annihilation process) and g+q -> gamma* + q( Compton scattering) followed by gamma* -> l- + l+ and qg -> jet. The total energy of the jet is highly correlated to that of gamma*. The jet can be considered in this case as tagged (i.e. a gamma*-tag) with a known energy. Based on energy conservation between gamma* (who's energy is not modified by the medium) and the jet (who does suffer energy loss in the medium), a precise energy loss measurement can be done, which allows for a determination of the momentum fraction of the far side hadrons (i.e. the fragmentation function).