Figure 1

Opposite-sign dimuon invariant mass spectra for the p-Pb (top) and Pb-p (bottom) data samples, together with the result of a fit For the fits shown here, Crystal Ball functions (shown as dashed lines) and a variable-width Gaussian have been used for the resonances and the background,respectively. The $\chi^{2}$/ndf refers to the goodness of the signal and background combined fit in the displayed mass range.