A
bstract
In spring 2012 CERN provided two weeks of a short bunch proton beam dedicated to the neutrino velocity measurement over a distance of 730 km. The OPERA neutrino experiment at the ...underground Gran Sasso Laboratory used an upgraded setup compared to the 2011 measurements, improving the measurement time accuracy. An independent timing system based on the Resistive Plate Chambers was exploited providing a time accuracy of ~1 ns. Neutrino and anti-neutrino contributions were separated using the information provided by the OPERA magnetic spectrometers. The new analysis profited from the precision geodesy measurements of the neutrino baseline and of the CNGS/LNGS clock synchronization. The neutrino arrival time with respect to the one computed assuming the speed of light in vacuum is found to be δ
t
ν
≡
T OF
c
−
T OF
ν
= (0.6±0.4 (
stat
.)±3.0 (
syst
.)) ns and
ns for ν
μ
and
, respectively. This corresponds to a limit on the muon neutrino velocity with respect to the speed of light of −1.8 × 10
−6
< (
v
ν
−
c
)/
c
< 2.3 × 10
−6
at 90% C.L. This new measurement confirms with higher accuracy the revised OPERA result.
The OPERA detector, designed to search for $\nu_{\mu} \to \nu_{\tau}$ oscillations in the CNGS beam, is located in the underground Gran Sasso laboratory, a privileged location to study TeV-scale ...cosmic rays. For the analysis here presented, the detector was used to measure the atmospheric muon charge ratio in the TeV region. OPERA collected charge-separated cosmic ray data between 2008 and 2012. More than 3 million atmospheric muon events were detected and reconstructed, among which about 110000 multiple muon bundles. The charge ratio $R_{\mu} \equiv N_{\mu^+}/N_{\mu^-}$ was measured separately for single and for multiple muon events. The analysis exploited the inversion of the magnet polarity which was performed on purpose during the 2012 Run. The combination of the two data sets with opposite magnet polarities allowed minimizing systematic uncertainties and reaching an accurate determination of the muon charge ratio. Data were fitted to obtain relevant parameters on the composition of primary cosmic rays and the associated kaon production in the forward fragmentation region. In the surface energy range 1-20 TeV investigated by OPERA, $R_{\mu}$ is well described by a parametric model including only pion and kaon contributions to the muon flux, showing no significant contribution of the prompt component. The energy independence supports the validity of Feynman scaling in the fragmentation region up to $200$ TeV/nucleon primary energy.
The OPERA neutrino experiment in the underground Gran Sasso Laboratory (LNGS) was designed to perform the first detection of neutrino oscillations in direct appearance mode in the νμ → ντ channel, ...the ντ signature being the identification of the τ-lepton created in its charged current interaction. The hybrid apparatus consists of a large mass emulsion film lead target complemented by electronic detectors. Placed in the LNGS, it is exposed to the high-energy long-baseline CERN Neutrino beam to Gran Sasso (CNGS) 730 km away from the neutrino source. The observation of a first ντ candidate event was reported in 2010. In this paper, we discuss the result of the analysis of the data taken during the first two years of operation (2008-2009) underlining the major improvements brought to the analysis chain and to the Monte Carlo simulations. The statistical significance of the one event observed so far is then evaluated to 95%.
A first result of the search for \numu $\rightarrow$ \nue oscillations in the OPERA experiment, located at the Gran Sasso Underground Laboratory, is presented. The experiment looked for the ...appearance of \nue in the CNGS neutrino beam using the data collected in 2008 and 2009. Data are compatible with the non-oscillation hypothesis in the three-flavour mixing model. A further analysis of the same data constrains the non-standard oscillation parameters $\theta_{new}$ and $\Delta m^2_{new}$ suggested by the LSND and MiniBooNE experiments. For large $\Delta m^{2}_{new}$ values ($>$0.1 eV$^{2}$), the OPERA 90% C.L. upper limit on sin$^{2}(2\theta_{new})$ based on a Bayesian statistical method reaches the value $7.2 \times 10^{-3}$.
The OPERA neutrino experiment is designed to perform the first observation of neutrino oscillations in direct appearance mode in the $\nu_\mu \to \nu_\tau$ channel, via the detection of the ...$\tau$-leptons created in charged current $\nu_\tau$ interactions. The detector, located in the underground Gran Sasso Laboratory, consists of an emulsion/lead target with an average mass of about 1.2 kt, complemented by electronic detectors. It is exposed to the CERN Neutrinos to Gran Sasso beam, with a baseline of 730 km and a mean energy of 17 GeV. The observation of the first $\nu_\tau$ candidate event and the analysis of the 2008-2009 neutrino sample have been reported in previous publications. This work describes substantial improvements in the analysis and in the evaluation of the detection efficiencies and backgrounds using new simulation tools. The analysis is extended to a sub-sample of 2010 and 2011 data, resulting from an electronic detector-based pre-selection, in which an additional $\nu_\tau$ candidate has been observed. The significance of the two events in terms of a $\nu_\mu \to \nu_\tau$ oscillation signal is of 2.40 $\sigma$.
The OPERA detector, designed to search for
ν
μ
→
ν
τ
oscillations in the CNGS beam, is located in the underground Gran Sasso laboratory, a privileged location to study TeV-scale cosmic rays. For the ...analysis here presented, the detector was used to measure the atmospheric muon charge ratio in the TeV region. OPERA collected charge-separated cosmic ray data between 2008 and 2012. More than 3 million atmospheric muon events were detected and reconstructed, among which about 110000 multiple muon bundles. The charge ratio
R
μ
≡
N
μ
+
/
N
μ
-
was measured separately for single and for multiple muon events. The analysis exploited the inversion of the magnet polarity which was performed on purpose during the 2012 Run. The combination of the two data sets with opposite magnet polarities allowed minimizing systematic uncertainties and reaching an accurate determination of the muon charge ratio. Data were fitted to obtain relevant parameters on the composition of primary cosmic rays and the associated kaon production in the forward fragmentation region. In the surface energy range 1–20 TeV investigated by OPERA,
R
μ
is well described by a parametric model including only pion and kaon contributions to the muon flux, showing no significant contribution of the prompt component. The energy independence supports the validity of Feynman scaling in the fragmentation region up to
200
TeV/nucleon primary energy.
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