You are here

Coherent photoproduction of $ρ^{0}$ vector mesons in ultra-peripheral Pb-Pb collisions at $\sqrt{s_{\rm NN}} = 5.02$ TeV

Cross sections for the coherent photoproduction of $\rho^{0}$ vector mesons in ultra-peripheral Pb-Pb collisions at $ \sqrt{s_{\mathrm{NN}}}= 5.02$ TeV are reported. The measurements, which rely on the $\pi^+\pi^-$ decay channel, are presented in three regions of rapidity covering the range $|y|<~0.8$. 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.

 

Submitted to: JHEP
e-Print: arXiv:2002.10897 | PDF | inSPIRE

Figures

Figure 1

. Correlation between the energy distributions of the ZNA and ZNC detectors for events selected for the analysis (left). Energy distribution in each single detector (right).
[png]   [pdf]   [eps]
[png]   [pdf]   [eps]

Figure 3

. Invariant mass distribution of pion pairs with the different components of the fit represented by lines. See text for details
[png]   [pdf]   [eps]

Figure 4

. Invariant mass (left) and transverse momentum (right) distributions of pion pairs at large invariant masses. The lines correspond to the fit components described in the text. The symbols depict the signal and like-sign background distributions
[png]   [pdf]   [eps]
[png]   [pdf]   [eps]

Figure 5

. Cross section for the coherent photoproduction of $\Rz$ vector mesons in Pb--Pb UPC as a function of rapidity for no forward-neutron selection (top left), and for the 0n0n (top right), 0nXn (bottom left) and XnXn (bottom right) classes. The lines show the predictions of the different models described in the text
[png]   [pdf]   [eps]
[png]   [pdf]   [eps]
[png]   [pdf]   [eps]
[png]   [pdf]   [eps]