Search

An event topology with two secondary vertices compatible with the decay of short-lived particles was found in the analysis of neutrino interactions in the OPERA target. The observed topology is compatible with tau neutrino charged current (CC) interactions with charm production and neutrino neutral current (NC) interactions with c c ¯ pair production. However, other processes can mimic this topology. A dedicated analysis was implemented to identify the underlying process. A Monte Carlo simulation was developed and complementary procedures were introduced in the kinematic reconstruction. A multivariate analysis technique was used to achieve an optimal separation of signal from background. Most likely, this event is a ν τ CC interaction with charm production, the tau and charm particle decaying into 1 prong and 2 prongs, respectively. The significance of this observation is evaluated. [ABSTRACT FROM AUTHOR]

The OPERA experiment, designed to perform the first observation of $$\nu _\mu \rightarrow \nu _\tau $$ oscillations in appearance mode through the detection of the $$\tau $$ leptons produced in $$\nu _\tau $$ charged current interactions, has collected data from 2008 to 2012. In the present paper, the procedure developed to detect $$\tau $$ particle decays, occurring over distances of the order of $$1~\mathrm{mm}$$ from the neutrino interaction point, is described in detail and applied to the search for charmed hadrons, showing similar decay topologies as the $$\tau $$ lepton. In the analysed sample, 50 charm decay candidate events are observed while $$54\pm 4$$ are expected, proving that the detector performance and the analysis chain applied to neutrino events are well reproduced by the OPERA simulation and thus validating the methods for $$\nu _\tau $$ appearance detection. [ABSTRACT FROM AUTHOR]

The OPERA detector, designed to search for $$\nu _{\mu } \rightarrow \nu _{\tau }$$ 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. [ABSTRACT FROM AUTHOR]

Section Analysis, line 9: sub-sample of 818 events becomes sub-sample of 817 events. [ABSTRACT FROM AUTHOR]

Direct Dark Matter searches are nowadays one of the most fervid research topics with many experimental efforts devoted to the search for nuclear recoils induced by the scattering of Weakly Interactive Massive Particles (WIMPs). Detectors able to reconstruct the direction of the nucleus recoiling against the scattering WIMP are opening a new frontier to possibly extend Dark Matter searches beyond the neutrino background. Exploiting directionality would also prove the galactic origin of Dark Matter with an unambiguous signal-to-background separation. Indeed, the angular distribution of recoiled nuclei is centered around the direction of the Cygnus constellation, while the background distribution is expected to be isotropic. Current directional experiments are based on gas TPC whose sensitivity is limited by the small achievable detector mass. In this paper we present the discovery potential of a directional experiment based on the use of a solid target made of newly developed nuclear emulsions and of optical read-out systems reaching unprecedented nanometric resolution. [ABSTRACT FROM AUTHOR]