Experiment Proposal - opera - Infn

Table 25: Expected background from hadron reinteractions. The contribution as a function of the track
multiplicity at the primary vertex is also given. The numbers are normalised to 10 6 DIS events.
Events HM LM Short Total
ν µ NC 2.1 0.6 4.1 6.8
ν µ CC 2.3 ≪ 0.1 2.0 4.3
Total 4.4 0.6 6.1 11.1
Table 26: Expected background for the different channels. The numbers are normalised to 10 6
events.
DIS
τ → e τ → µ τ → h Total Error
Long: charm 7.0 1.4 7.0 15.4 ±15%
Long: ν e CC
and π 0 0.2 - - 0.2 ±10%
Long: µ scatt. - 5.0 - 5.0 ±50%
Long: had. reint. - - 5.0 5.0 ±50%
Long total 7.2 6.4 12.0 25.6 -
Short: charm 1.1 - (1.3) 1.1 ±15%
Short: ν e CC
and π 0 0.1 - - 0.1 ±10%
Short:had.reint. - - (6.1) (6.1)
Short Total 1.2 - - 1.2
Total 8.4 6.4 12.0 26.8
This background has been evaluated by simulating 1 × 10 7 NC and CC events with GEANT 3.21.
The results are shown in Table 25.
Hadron reinteractions can also contribute to the τ → µ channel when a hadron, produced either in
ν µ NC or ν µ CC interactions with the muon not identified, is misidentified as a muon (see Section 7.3.5).
The evaluation of this background is in progress.
Data on hadronic reinteractions are being analysed [88, 89]. An experimental evaluation of the reinteraction
background is expected soon. In the present situation of the analysis and given the large Monte
Carlo uncertainties, we presently assume a 50% error on this background.
7.5 Sensitivity to ν µ ↔ ν τ oscillations
For the evaluation of the sensitivity of the experiment we assumed the τ detection efficiencies given in
Section 7.3.11 and the backgrounds in Table 26, with the referred to uncertainties.
Since we do not plan to replace with new bricks those which are removed for the event analysis, but
rather with peripheral bricks, the mass of the detector decreases as a function of the exposure time. In
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