Speaker
Description
The intense photon fluxes of relativistic nuclei provide an opportunity to study photonuclear interactions in ultra-peripheral collisions. Exclusive final states of vector mesons can be studied in the process γ + A → meson + A. The measurement of photoproduced π+π−π+π− final states in ultra-peripheral Pb–Pb collisions at √sNN = 5.02 TeV is presented for the first time. The cross section, dσ/dy, times the branching ratio is measured in the rapidity interval |y| < 0.5 and compared to recent theoretical predictions. The invariant mass distribution is not well described with a single Breit-Wigner resonance, so the production of two independent excited resonances, ρ(1450) and ρ(1700), and their interference is considered. The values of the masses and widths of the resonances are found to be in a good agreement with the PDG values. The mixing angle between the two resonances is also extracted from the fits to the invariant mass spectra.
