Exclusive four pion photoproduction in ultraperipheral Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}=5.02$ 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 $\sqrt{s_{\mathrm{NN}}}=5.02$ TeV is presented for the first time. The cross section, d$\sigma$/d$y$, times the branching ratio ($\rho \to {\pi }^{+}{\pi }^{+}{\pi }^{-}{\pi }^{-}$) is found to be $47.8\pm 2.3(stat.)\pm 7.7(syst.)$ 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 $m_1=1385\pm 14(stat.)\pm 3(syst.)$ MeV/$c^2$, ${\Gamma }_1=431\pm 36(stat.)\pm 82(syst.)$ MeV/$c^2$, $m_2=1663\pm 13(stat.)\pm 22(syst.)$ MeV/$c^2$ and ${\Gamma }_2=357\pm 31(stat.)\pm 49(syst.)$ MeV/$c^2$, respectively. The measured cross sections times the branching ratios are compared to recent theoretical predictions.

arXiv comment24 pages, 3 captioned figures, 3 tables, authors from page 18, figures at http://alice-publications.web.cern.ch/node/10862

References in corpus (18)

• The ALICE TPC, a large 3-dimensional tracking device with fast readout for ultra-high multiplicity events
• The Physics of Ultraperipheral Collisions at the LHC
• STARlight: A Monte Carlo simulation program for ultra-peripheral collisions of relativistic ions
• Higher Quarkonia
• LHC Forward Physics
• Coherent rho^0 Production in Ultra-Peripheral Heavy Ion Collisions
• Imaging the nucleus with high-energy photons
• Photonuclear and Two-photon Interactions at High-Energy Nuclear Colliders
• Measurement of exclusive ${\rho }^0$(770) photoproduction in ultraperipheral pPb collisions at $\sqrt{s_{\mathrm{NN}}}=$ 5.02 TeV
• A study of the centrally produced 4pi channel in pp interactions at 450 GeV/c
• Nuclear shadowing and rho photoproduction
• Selected topics in diffraction with protons and nuclei: past, present, and future
• Distinguishing Hybrids from Radial Quarkonia
• First measurement of coherent ${\rho }^0$ photoproduction in ultra-peripheral Xe-Xe collisions at $\sqrt{{\mathbf{s}}_{\mathbf{NN}}}=5.44$ TeV
• ALICE luminosity determination for Pb$-$Pb collisions at $\sqrt{s_{\mathrm{NN}}}=5.02$ TeV
• Triple Regge exchange mechanisms of four-pion continuum production in the $pp\to pp{\pi }^{+}{\pi }^{-}{\pi }^{+}{\pi }^{-}$ reaction
• Analysis of the pi^+pi^-pi^+pi^- and pi^+pi^0pi^-pi^0 Final States in Quasi-Real Two-Photon Collisions at LEP
• Exclusive four-pion photoproduction in ultra-peripheral heavy-ion collisions at RHIC and LHC energies