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Coherent psi (2S) photo-production in ultra-peripheral Pb-Pb collisions at s(NN)=2.76TeV

We have performed the first measurement of the coherent psi(2S) photo-production cross section in ultraperipheral Pb-Pb collisions at the LHC. This charmonium excited state is reconstructed via the psi(2S) -> l(+)l(-) and ->(2S) -> J/psi pi(+)pi(-) decays, where the J/psi decays into two leptons. The analysis is based on an event sample corresponding to an integrated luminosity of about 22 mu b(-1). The cross section for coherent psi(2S) production in the rapidity interval -0.9 < y < 0.9is d sigma(coh)(psi(2S))/dy = 0.83 +/- 0.19 (stat+syst) mb. The psi(2S) to J/psi coherent cross section ratio is 0.34(-0.07)(+0.08)(stat+syst). The obtained results are compared to predictions from theoretical models.

j/psi photoproduction ; transverse-momentum ; mesons ; hera ; lhc ; tev ; electroproduction ; particles ; e(+)e(-) ; psi (2S) ; ultra-periphera ; Pb-Pb ; 2.76TeV

ALICE Collaboration