Exclusive photoproduction of excited ρmesons decaying to four pions in ultraperipheral Pb-Pb collisions at √sNN=5.02 TeV

Abstract

The intense photon fluxes from relativistic nuclei provide an opportunity to study photonuclear interactions in ultraperipheral collisions. In particular, it allows for the investigations of excited, light-flavour vector mesons. The measurement of coherently photoproduced pi(+)pi(-)pi(+)pi(-) final states in ultraperipheral Pb-Pb collisions at root s(NN) = 5.02 TeV is presented for the first time. The cross section, d sigma/dy, times the branching ratio (rho -> pi(+)pi+pi(-)pi(-)) is found to be 47.8 +/- 2.3 (stat.) +/- 7.7 (syst.) mb in the rapidity interval |y| < 0.5. The invariant mass distribution is not well described with a single Breit-Wigner resonance without an interference term. Including interference with a non-resonant contribution results in the mass and width values being too far from those reported in PDG, while the production of two interfering resonances, rho(1450) and rho(1700), also provides a good description of the data. The values of the masses (m) and widths (Gamma) of the resonances extracted from the fit assuming two interfering resonances are m(1) = 1385 +/- 14 (stat.) +/- 3 (syst.) MeV/c(2), Gamma(1) = 431 +/- 36 (stat.) +/- 82 (syst.) MeV/c(2), m2 = 1663 +/- 13 (stat.) +/- 22 (syst.) MeV/c(2) and Gamma(2) = 357 +/- 31 (stat.) +/- 49 (syst.) MeV/c(2), respectively. The measured cross sections times the branching ratios are compared to recent theoretical predictions.