Etude et impact du bruit de fond corrélé pour la mesure de l'angle ...

5.5 Stopping Muon analysis 141
tel-00821629, version 1 - 11 May 2013
Figure 5.22: Comparison between the spatial distributions of SM candidates
(black histograms) and HELN sample obtained by performing o↵-time selection
(violet points). The on-time prompt distributions (top left and right)
shows clear excess of events below the detector chimney, as expected by SM,
while the o↵-time distribution shows events distributed more widely in the
detector, as expected from natural radioactivity gammas. The delayed vertex
distribution (bottom left and right) shows an excess below the chimney
and some others peaks at fixed positions. Such peaks are well reproduced
by the o↵-time selection and are due to LN. The packed distribution is an
artefact of the vertex reconstruction algorithm, which reconstruct the LN
vertex close to the PMT responsible of the light emission.