Coherent photoproduction of ρ0 vector mesons in ultra-peripheral Pb-Pb collisions at $$ \sqrt{{\mathrm{s}}_{\mathrm{NN}}} $$ = 5.02 TeV

A bstract Cross sections for the coherent photoproduction of ρ 0 vector mesons in ultra-peripheral Pb-Pb collisions at $$ \sqrt{{\mathrm{s}}_{\mathrm{NN}}} $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msqrt> <mml:msub> <mml:mi>s</mml:mi> <mml:mi>NN</mml:mi> </mml:msub> </mml:msqrt> </mml:math> = 5 . 02 TeV are reported. The measurements, which rely on the π + π − decay channel, are presented in three regions of rapidity covering the range |y| &lt; 0 . 8. For each rapidity interval, cross sections are shown for different nuclear-breakup classes defined according to the presence of neutrons measured in the zero-degree calorimeters. The results are compared with predictions based on different models of nuclear shadowing. Finally, the observation of a coherently produced resonance-like structure with a mass around 1.7 GeV/ c 2 and a width of about 140 MeV/ c 2 is reported and compared with similar observations from other experiments.

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