Exclusive four pion photoproduction in ultraperipheral Pb-Pb collisions at $\sqrt{s_{\rm NN}} = 5.02$ TeV (2404.07542v1)
Abstract: The intense photon fluxes from relativistic nuclei provide an opportunity to study photonuclear interactions in ultraperipheral collisions. The measurement of coherently photoproduced $\pi+\pi-\pi+\pi-$ final states in ultraperipheral Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}=5.02$ TeV is presented for the first time. The cross section, d$\sigma$/d$y$, times the branching ratio ($\rho\rightarrow \pi+ \pi+ \pi- \pi-$) is found to be $47.8\pm2.3~\rm{(stat.)}\pm7.7~\rm{(syst.)}$ 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, $\rho(1450)$ and $\rho(1700)$, provides a good description of the data. The values of the masses ($m$) and widths ($\Gamma$) of the resonances extracted from the fit are $m_{1}=1385\pm14~\rm{(stat.)}\pm3~\rm{(syst.)}$ MeV/$c2$, $\Gamma_{1}=431\pm36~\rm{(stat.)}\pm82~\rm{(syst.)}$ MeV/$c2$, $m_{2}=1663\pm13~\rm{(stat.)}\pm22~\rm{(syst.)}$ MeV/$c2$ and $\Gamma_{2}=357 \pm31~\rm{(stat.)}\pm49~\rm{(syst.)}$ MeV/$c2$, respectively. The measured cross sections times the branching ratios are compared to recent theoretical predictions.
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