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

138 5. Correlated background
5.5 Stopping Muon analysis
tel-00821629, version 1 - 11 May 2013
Stopping muon background is due to muons entering in the ID through the
chimney, stopping and then decaying. The ionization energy deposited by
the muon before stopping and the delayed Michel electron emitted upon
muon decay mimic, respectively, the prompt and the delayed events generated
by an ¯⌫ e . The time correlation between prompt and delayed events
is expected to be of the order of the muon live time, ⌧ µ ' 2.2 µs, since the
Michel electron deposit quickly its energy in the scintillator.
The acceptance conditions which allow a muon to enter the chimney and to
deposit energy without being identified by the muon tagging are very strict,
as already discussed above. For this reason, the IVT strategy developed to
tag FN with high e ciency is not expected to have the same performance
with SM, then a di↵erent strategy has been adopted.
The energy spectrum of the Michel electron emitted in the muon decay extends
from 0 MeV up to ⇠ 60 MeV, but only ⇠ 1% 1 of the total is emitted
with an energy of [6, 12] MeV and is expected to generate correlated background.
Since the ionization energy lost by the muon before stopping is not
expected to be correlated with the energy by which the Michel electron is
emitted, a di↵erent delayed energy window is adopted.
The SM are separated from the FN by requiring the time correlation between
prompt and delayed events to be t