2024/04/11 by ALICE Collaboration
#FOS: Physical sciences #High Energy Physics - Experiment (hep-ex) #Nuclear Experiment (nucl-ex)
paper · doi:10.48550/arxiv.2404.07542
The intense photon fluxes from relativistic nuclei provide an opportunity to study photonuclear interactions in ultraperipheral collisions. The measurement of coherently photoproduced π+π-π+π- final states in ultraperipheral Pb-Pb collisions at √sNN=5.02 TeV is presented for the first time. The cross section, dσ/dy, times the branching ratio (ρ→ π+ π+ π- π-) is found to be 47.8±2.3~\rm(stat.)±7.7~\rm(syst.) mb in the rapidity interval |y| < 0.5. The invariant mass distribution is not well described with a single Breit-Wigner resonance. The production of two interfering resonances, ρ(1450) and ρ(1700), provides a good description of the data. The values of the masses (m) and widths (Γ) of the resonances extracted from the fit are m1=1385±14~\rm(stat.)±3~\rm(syst.) MeV/c2, Γ1=431±36~\rm(stat.)±82~\rm(syst.) MeV/c2, m2=1663±13~\rm(stat.)±22~\rm(syst.) MeV/c2 and Γ2=357 ±31~\rm(stat.)±49~\rm(syst.) MeV/c2, respectively. The measured cross sections times the branching ratios are compared to recent theoretical predictions.