Experiment Proposal - opera - Infn

We have used functions determined from fits to neutrino charm production data [80, 81]. The charmed
hadron fractions f D 0, f D +, f D
+
s
and f Λ
+
c
are given in [81] as a function of the neutrino energy. Since
the charmed hadrons have different cτ the expected background depends on the values of f h which in
turn are function of the neutrino energy. In the case of the CNGS beam one obtains
f D 0 =0.45 ± 0.14, f D + =0.10 ± 0.03, f D
+
s
=0.18 ± 0.05 and f Λ
+
c
=0.26 ± 0.08
The branching ratios of the charged charmed hadrons have been taken from the PDG [82].
For the special case of quasi-elastic charm production, one has
The background from this process is negligible.
σ(ν µ n → µ − Λ + c )
σ(ν µ N → µ − X) =0.6%
To evaluate the background from single charm production we must treat separately muonic and non
muonic decay channels.
For the electronic and the hadronic charm decay channels the expected background can be written
as follow
N bg = σ c
σ CC
× f C + × ε trigger × ε brick × ε geom × ε vert × ε long
×ε kink × (1 − ε charm
µ ) × ε L(S)
kin
× BR × N DIS
where ε charm
µ is the efficiency in detecting the primary muon in events with a charmed hadron in the
final state and N DIS is the total number of DIS events. The contribution from QE neutrino interactions
is negligible.
For the muonic channel we must account for the fact that the present µ identification algorithm (see
Section 7.2) reconstructs only one muon per event. Therefore, we have three categories of events
• events with the primary muon identified (77.1%);
• events with neither primary nor daughter muon identified (3.6%);
• events with the daughter muon identified (19.3%).
The first category of events does not contribute to the background. The second one contributes to
the background of the hadronic channel. Nevertheless, given the kinematical analysis efficiency and the
small C + → µ + branching ratio, it is completely negligible. The third category of events contributes to
the background only if the charge of the positive muon is either wrongly measured or not measured at
all. Monte Carlo simulations show that only ∼ 6% out of 19.3% of the events with the daughter muon
reconstructed have the charge either not measured or wrongly measured.
186