Experiment Proposal - opera - Infn

Table 29: 90% CL limits on ∆m 2 defining the OPERA allowed region for full mixing. In the three
columns we assume to observe a number of events corresponding to the best fit and to the 90% CL limits
given bt Super-Kamiokande.
True value 1.5 × 10 −3 eV 2 3.2 × 10 −3 eV 2 5.0 × 10 −3 eV 2
Upper limit 2.1 × 10 −3 eV 2 3.8 × 10 −3 eV 2 5.6 × 10 −3 eV 2
Lower limit 0.8 × 10 −3 eV 2 2.6 × 10 −3 eV 2 4.3 × 10 −3 eV 2
(Upper-Lower)/True 41% 19% 12%
detection of ν τ appearance. However, we point out that additional constraints can be extracted from the
reconstruction of the event topology and that, therefore, additional decay channels may be included in
the analysis, such as muonic and hadronic τ decays in the lead (short kinks) or a specific ρ search in the
hadronic channel. The determination of the oscillation parameters may therefore be improved.
7.7 Additional physics subjects
7.7.1 Search for ν µ ↔ ν e oscillations
Because of the very good electron identification, OPERA is also sensitive to ν µ ↔ ν e oscillations. Together
with the ν µ ↔ ν τ appearance search this measurement allows to perform an analysis of neutrino
oscillation with three-flavour mixing.
A background source for the ν µ ↔ ν e search is the ∼ 1% ν e (¯ν e ) contamination of the ν µ beam.
Another one is given by electrons from the Dalitz decay of neutral pions produced in ν µ NC interactions
(π 0 → e + e − γ) and photon to electron conversions in the lead plates (π 0 → 2γ followed by γN →
e + e − N). The latter contribution is reduced by selecting neutrino interactions with one identified electron
(positron) of measured energy greater than a given threshold. The contamination from pions misidentified
as electrons has to be included as well.
The statistical error on the background estimate determines the sensitivity of the measurement of
the oscillation parameters together with systematic errors due to the uncertainty on the ν e content of
the beam and on the number of pseudo-prompt electrons produced by π 0 ’s.
The calculation of the detection efficiency, of the background and of the sensitivity is in progress. An
estimate of the sensitivity has been given in [6], showing the capability of detecting ν µ ↔ ν e oscillations.
7.7.2 Oscillation search through NC/CC ratio measurement
The expected performance of the detector target as a calorimeter for shower energy measurement and
the presence of spectrometers for the identification and the momentum determination of muons allow a
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