Figure 1

Primary vertex distributions for the analyzed events The left panel shows the distributions along the beam axis. Selected events (full symbols) are required to have a reconstructed primary vertex with $|z|< 10 cm$ The right panel corresponds to the directions perpendicular to the beam axis: horizontally(i.e. $x$-direction, squares and full line) and vertically (i.e. $y$-direction, triangles and dashed line).