Coherent $\rho^0$ photoproduction in ultra-peripheral Pb--Pb collisions at $\mathbf{\sqrt{\textit{s}_{\rm NN}}} = 2.76$ TeV

J. Adam , R. Vernet (1) , A. Baldisseri (2) , H. Borel (2) , J. Castillo Castellanos (2) , J.L. Charvet (2) , A. Lardeux (2) , H. Pereira Da Costa (2) , A. Rakotozafindrabe (2) , I. Belikov (3) , B. Hippolyte (3) , C. Kuhn (3) , A. Maire (3) , L. Molnar (3) , C. Roy (3) , X. Sanchez Castro (3) , V. Barret (4) , N. Bastid (4) , A. Batista Camejo (4) , P. Crochet (4) , P. Dupieux (4) , S. Li (4) , X. Lopez (4) , F. Manso (4) , S. Porteboeuf-Houssais (4) , P. Rosnet (4) , B. Vulpescu (4) , Laurent Aphecetche (5) , Guillaume Batigne (5) , B. Erazmus (5) , Magali Estienne (5) , Marie Germain (5) , J. Martin Blanco (5) , Gines Martinez Garcia (5) , L. Massacrier (5) , D.A. Moreira De Godoy (5) , A. Morreale (5) , Philippe Pillot (5) , L. Ronflette (5) , Y. Schutz (5) , Alexandre Shabetai (5) , Diego Stocco (5) , M. Wang (5) , J. Zhu (5) , C. Cheshkov (6) , B. Cheynis (6) , L. Ducroux (6) , J.-Y. Grossiord (6) , B. Teyssier (6) , R. Tieulent (6) , A. Uras (6) , G. Conesa Balbastre (7) , J. Faivre , C. Furget (7) , R. Guernane (7) , S. Kox (7) , J.S. Real (7) , C. Silvestre (7) , A. Vauthier (7) , Z. Conesa Del Valle (8) , I. Das (8) , B. Espagnon (8) , C. Hadjidakis (8) , I. Lakomov (8) , C. Suire (8) , J. D. Tapia Takaki (8) , L. Valencia Palomo (8)

1 CC-IN2P3 - Centre de Calcul de l'IN2P3
2 IRFU - Institut de Recherches sur les lois Fondamentales de l'Univers
3 IPHC - Institut Pluridisciplinaire Hubert Curien
4 LPC - Laboratoire de Physique Corpusculaire - Clermont-Ferrand
5 SUBATECH - Laboratoire SUBATECH Nantes
6 IPNL - Institut de Physique Nucléaire de Lyon
7 LPSC - Laboratoire de Physique Subatomique et de Cosmologie
8 IPNO - Institut de Physique Nucléaire d'Orsay

We report the first measurement at the LHC of coherent photoproduction of $\rho^0$ mesons in ultra-peripheral Pb-Pb collisions. The invariant mass and transverse momentum distributions for $\rho^0$ production are studied in the $\pi^+ \pi^-$ decay channel at mid-rapidity. The production cross section in the rapidity range $|y|<0.5$ is found to be $\mathrm{d}\sigma/\mathrm{d}y = 425 \pm 10 \, (\mathrm{stat.})$ $^{+42}_{-50} \, (\mathrm{sys.})$ mb. Coherent $\rho^0$ production is studied with and without requirement of nuclear breakup, and the fractional yields for various breakup scenarios are presented. The results are compared with those from lower energies and with model predictions based on the Glauber model and the color dipole model. The measured cross section is found to be inconsistent with a scaling of the $\gamma$-nucleon cross section using the Glauber model.

Domaines: Physique Nucléaire Expérimentale [nucl-ex]; Physique des Hautes Energies - Expérience [hep-ex]

J. Adam, R. Vernet, A. Baldisseri, H. Borel, J. Castillo Castellanos, et al.. Coherent $\rho^0$ photoproduction in ultra-peripheral Pb--Pb collisions at $\mathbf{\sqrt{\textit{s}_{\rm NN}}} = 2.76$ TeV. Journal of High Energy Physics, 2015, 09, pp.095. ⟨10.1007/JHEP09(2015)095⟩. ⟨in2p3-01139191⟩