Limits on muon-neutrino to tau-neutrino oscillations induced by a sterile neutrino state obtained by OPERA at the CNGS beam

The OPERA experiment, exposed to the CERN to Gran Sasso $\nu_\mu$ beam, collected data from 2008 to 2012. Four oscillated $\nu_\tau$ Charged Current interaction candidates have been detected in appearance mode, which are consistent with $\nu_\mu \to \nu_\tau$ oscillations at the atmospheric $\Delta m^2$ within the "standard" three-neutrino framework. In this paper, the OPERA $\nu_\tau$ appearance results are used to derive limits on the mixing parameters of a massive sterile neutrino.Comment: 11 pages, 4 figures; reference to Planck result updated in the Introduction. Submitted to JHE

Determination of a time-shift in the OPERA set-up using high energy horizontal muons in the LVD and OPERA detectors

The purpose of this work is to report the measurement of a time-shift in the OPERA set-up in a totally independent way from Time Of Flight (TOF) measurements of CNGS neutrino events. The LVD and OPERA experiments are both installed in the same laboratory: LNGS. The relative position of the two detectors, separated by an average distance of ~ 160 m, allows the use of very high energy horizontal muons to cross-calibrate the timing systems of the two detectors, using a TOF technique which is totally independent from TOF of CNGS neutrino events. Indeed, the OPERA-LVD direction lies along the so-called "Teramo anomaly", a region in the Gran Sasso massif where LVD has established, many years ago, the existence of an anomaly in the mountain structure, which exhibits a low m. w. e. thickness for horizontal directions. The "abundant" high-energy horizontal muons (nearly 100 per year) going through LVD and OPERA exist because of this anomaly in the mountain orography. The total live time of the data in coincidence correspond to 1200 days from mid 2007 until March 2012. The time coincidence study of LVD and OPERA detectors is based on 306 cosmic horizontal muon events and shows the existence of a negative time shift in the OPERA set-up of the order of deltaT(AB) = - (73 \pm 9) ns when two calendar periods, A and B, are compared. This result shows a systematic effect in the OPERA timing system from August 2008 until December 2011. The size of the effect is comparable with the neutrino velocity excess recently measured by OPERA. It is probably interesting not to forget that with the MRPC technology developed by the ALICE Bologna group the TOF world record accuracy of 20 ps was reached. That technology can be implemented at LNGS for a high precision determination of TOF with the CNGS neutrino beams of an order of magnitude smaller than the value of the OPERA systematic effect

More results from the OPERA experiment

The OPERA experiment reached its main goal by proving the appearance of vτ in the CNGS vμ beam. Five vτ candidates were detected with a S/B ratio of ∼ 10, allowing to reject the null hypothesis at 5.1σ. The search has been extended by loosening the selection criteria in order to improve the statistical uncertainty. One of the vτ candidates selected with the new strategy shows a double vertex topology and, after a dedicated multivariate analysis, is compatible with being a vTτ interaction with charm production. Based on the enlarged data sample the estimation of Δm223 in appearance mode is being performed. The search for ve interactions has been extended over the full data set with a more than twofold increase in statistics: data are compatible with the non-oscillation hypothesis in the three-flavour mixing model. The implications of the electron neutrino sample in the framework of the 3+1 sterile mode will lead to exclusion limits on sin2 2θμe. Finally, the analysis of the annual modulation of cosmic muons is introduced

OPERA tau neutrino charged current interactions

The OPERA experiment was designed to discover the v(tau) appearance in a v(mu) beam, due to neutrino oscillations. The detector, located in the underground Gran Sasso Laboratory, consisted of a nuclear photographic emulsion/lead target with a mass of about 1.25 kt, complemented by electronic detectors. It was exposed from 2008 to 2012 to the CNGS beam: an almost pure v(mu) beam with a baseline of 730 km, collecting a total of 1.8 center dot 10(20) protons on target. The OPERA Collaboration eventually assessed the discovery of v(mu)-> v(tau) oscillations with a statistical significance of 6.1 sigma by observing ten v(tau) CC interaction candidates. These events have been published on the Open Data Portal at CERN. This paper provides a ydetailed description of the v(tau) data sample to make it usable by the whole community

Study of charged hadron multiplicities in charged-current neutrino-lead interactions in the OPERA detector (vol 78, 62, 2018)

Erratum to: Eur. Phys. J. C (2018) 78:6

Determination of a time-shift in the OPERA set-up using high-energy horizontal muons in the LVD and OPERA detectors

The purpose of this work is to report the measurement of a time-shift in the OPERA setup in a way totally independent of the Time-Of-Flight (TOF) measurements of CNGS neutrino events and without the need to know the distance between the two laboratories, CERN and LNGS, where the neutrinos are produced and detected, respectively. The LVD and OPERA experiments are both installed in the same laboratory: LNGS. The relative position of the two detectors, separated by an average distance of similar to 160 m, allows the use of very high-energy horizontal muons to cross-calibrate the timing systems of the two detectors, using a TOF technique, which, as stated above, is totally independent of the TOF of CNGS neutrino events. Indeed, the OPERA-LVD direction lies along the so-called "Teramo anomaly", a region in the Gran Sasso massif where LVD has established, many years ago, the existence of an anomaly in the mountain structure, which exhibits a low m.w.e. thickness for horizontal directions. The "abundant" high-energy horizontal muons (nearly 100 per year) going through LVD and OPERA exist because of this anomaly in the mountain orography. The total live time of the data in coincidence between the two experiments correspond to 1200 days from mid 2007 until March 2012. The time coincidence study of LVD and OPERA detectors is based on 306 cosmic-horizontal-muon events and shows the existence of a negative time-shift in the OPERA set-up of the order of Delta t(AB) = -(73 +/- 9) ns when two calendar periods, A and B, are compared. The first, A, goes from August 2007 to August 2008 plus the period from January 2012 to March 2012; the second period, B, goes from August 2008 to December 2011. This result shows a systematic effect in the OPERA timing system present from August 2008 until December 2011. The size of the effect, in terms of the cosmic horizontal muons TOF, is comparable with the neutrino velocity excess recently measured by OPERA. It is probably interesting not to forget that with the MRPC technology developed by the ALICE Bologna group the TOF world record accuracy of 20 ps was reached. This technology can be implemented at LNGS for a high-precision determination of TOF with the CNGS neutrino beams. If new experiments are needed for the study of neutrino velocities they must be able to detect effects an order of magnitude smaller than the value of the OPERA systematic effect

Erratum to: Study of charged hadron multiplicities in charged-current neutrino–lead interactions in the OPERA detector (The European Physical Journal C, (2018), 78, 1, (62), 10.1140/epjc/s10052-017-5509-y)

Section Analysis, line 9: sub-sample of 818 events becomes sub-sample of 817 events

Discovery of \u3c4 Neutrino Appearance in the CNGS Neutrino Beam with the OPERA Experiment

The OPERA experiment was designed to search for \u3bd\u3bc \u2192 \u3bd\u3c4 oscillations in appearance mode, i.e., by detecting the \u3c4 leptons produced in charged current \u3bd\u3c4 interactions. The experiment took data from 2008 to 2012 in the CERN Neutrinos to Gran Sasso beam. The observation of the \u3bd\u3bc \u2192 \u3bd\u3c4 appearance, achieved with four candidate events in a subsample of the data, was previously reported. In this Letter, a fifth \u3bd\u3c4 candidate event, found in an enlarged data sample, is described. Together with a further reduction of the expected background, the candidate events detected so far allow us to assess the discovery of \u3bd\u3bc \u2192 \u3bd\u3c4 oscillations in appearance mode with a significance larger than 5\u3c3