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 $\gamma$ + A → meson + A. The measurement of photoproduced $\pi^+\pi^− \pi^+ \pi^−$ final states in ultra-peripheral Pb–Pb collisions at √sNN = 5.02 TeV is presented for the first time. The cross section, d$\sigma$/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, $\rho$(1450) and $\rho$(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.
