OPERA Experiment Research Articles

Superluminal neutrinos: an OPERA in three acts

Abstract In September 2011 the OPERA experiment at the Gran Sasso Laboratory, Italy announced that they had evidence that the neutrinos in the CERN-to-Gran-Sasso (CNGS) beam line were travelling very slightly faster than the speed of light. If true this would have ranked among the most important discoveries of the 21st century. In the event it was not true and was rapidly discredited. This paper explains what the measurement entailed, the responses to it and the eventual explanation, and discusses whether the initial publication and the subsequent reactions were appropriate.

Resetting of nuclear emulsions by erasing noises formed during storage: Mechanism and application

The resetting of a nuclear emulsion is one of the most important technologies for the start of its new era and was realized in the OPERA experiment. Since the OPERA experiment was carried out several months after the production of its nuclear emulsion layers, AgBrI grains in the layers were exposed to ionizing particles before experiments, and formed latent image centers as noises on their surfaces. The technology to reset the emulsion layers was needed and achieved by the refresh treatment, which erased the latent image centers by enhancing their fading under the condition with high humidity at high temperature in the presence of 5-methyl-benzotriazole (5-MBT). While the treatment is being applied to other experiments with nuclear emulsions, its mechanism has not yet been made clear. Taking into account the fact that 5-MBT played a central role for the effect of the treatment, this study has been undertaken to reveal the mechanism of the treatment by focusing on the behavior of 5-MBT. It has been revealed that the irreversible phase transition of 5-MBT for the formation of epitaxial silver salt nanoparticles of 5-MBT anions at the corners of the AgBrI grains during the treatment enhances the detachment of a silver ion from a latent image center on a site with electric charge of +1/2, thus making the center to bear the electric charge of −1/2 and unstable against oxidation. Ideas have been proposed to make the treatment available for other experiments with nuclear emulsions.

Bad stats: A regular series exploring slip-ups, snafus and salutary lessons from the world of statistics: The OPERA experiment versus Einstein

Bad stats: A regular series exploring slip-ups, snafus and salutary lessons from the world of statistics: The OPERA experiment versus Einstein

The JUNO experiment Top Tracker

The main task of the Top Tracker detector of the neutrino reactor experiment Jiangmen Underground Neutrino Observatory (JUNO) is to reconstruct and extrapolate atmospheric muon tracks down to the central detector. This muon tracker will help to evaluate the contribution of the cosmogenic background to the signal. The Top Tracker is located above JUNO’s water Cherenkov Detector and Central Detector, covering about 60% of the surface above them. The JUNO Top Tracker is constituted by the decommissioned OPERA experiment Target Tracker modules. The technology used consists in walls of two planes of plastic scintillator strips, one per transverse direction. Wavelength shifting fibres collect the light signal emitted by the scintillator strips and guide it to both ends where it is read by multianode photomultiplier tubes. Compared to the OPERA Target Tracker, the JUNO Top Tracker uses new electronics able to cope with the high rate produced by the high rock radioactivity compared to the one in Gran Sasso underground laboratory. This paper will present the new electronics and mechanical structure developed for the Top Tracker of JUNO along with its expected performance based on the current detector simulation.

Radiological Characterization Studies for the CNGS Dismantling

A comprehensive study of the radiological CNGS (CERN Neutrinos to Gran Sasso Experiment) environment characterization is presented. It comprises the evaluation of the residual dose rates of the most relevant standalone beam line equipment, such as the target and horn, as well as overall dose levels in the cavern before and after dismantling. Furthermore, the radionuclide inventories of the main objects to be dismantled were calculated by the Monte Carlo FLUKA code and ActiWiz. The latter is particularly important for transport and waste management. Moreover, we present benchmarking measurements of residual dose rates in the experimental cavern, staying in good agreement with simulation predictions. Additional measurements, as well as FLUKA and ActiWiz studies, allowed for assessing the concrete composition of the cavern’s walls and floor and the shielding blocks. The resulting refined composition allowed for evaluating more precisely the radionuclide inventories and residual dose rates expected before and after the dismantling in the CNGS target area. This was particularly important for the evaluation of the dismantling cost and the substantial savings due to the reusage of the majority of the concrete blocks. Finally, contamination measurements in the accessible parts of the area also are included. All the results discussed are crucial for determining the requirements, planning, and costs of the CNGS dismantling.

Updated constraints on sterile neutrino mixing in the OPERA experiment using a new νe identification method

Abstract This paper describes a new νe identification method specifically designed to improve the low-energy ($\lt {30}\, {\rm GeV}$) νe identification efficiency attained by enlarging the emulsion film scanning volume with the next-generation emulsion readout system. A relative increase of 25–70% in the νe low-energy region is expected, leading to improvements in the OPERA sensitivity to neutrino oscillations in the framework of the 3 + 1 model. The method is applied to a subset of data where the detection efficiency increase is expected to be more relevant, and one additional νe candidate is found. The analysis combined with the ντ appearance results improves the upper limit on sin 22θμe to 0.016 at 90% C.L. in the MiniBooNE allowed region $\Delta m^2_{41} \sim {0.3}\, {\rm eV}^{2}$.

A Holistic Understanding of Scientific Methodology: The Cases of the CMS and OPERA Experiments

AbstractPhilosophers of science are divided over the interpretations of scientific normativity. Larry Laudan defends a sort of goal-directed rules for scientific methodology. In contrast, Gerard Doppelt thinks methodological rules are a mixed batch of rules in that some are goal-oriented hypothetical rules and others are goal-independent categorical rules. David Resnik thinks that the debate between them is at a standstill now. He further thinks there are certain rules, such as the rule of consistency which is goal independent. However, he proposes a holistic understanding of the scientific methodology. Taking a thread from Resnik, the present paper also advocates a holistic understanding of the scientific methodology. Given that many scientific practices deal with systems, the focus will be given to the systems by assuming each as a constellation of methodological norms. By taking each system as a set of mutually supportive methodological rules whose instrumental values underwrite the coherence relation among them, the paper aims to provide what could be a viable holistic epistemological account that can explain scientific normativity at work in a scientific system. The paper will lay down specific holistic criteria for understanding the scientific methodology. They will be used to show how a holistic account could satisfactorily account for the success of the Compact Muon Solenoid (CMS) experiment in discovering the Higgs boson and how the holistic account can account for the instrumental error behind the apparent faster-than-light neutrino anomaly of the Oscillation Project with Emulsion-t Racking Apparatus (OPERA) experiments respectively.

Ordinary Versus Novel Particle With the Example of Their Spontaneous Transition

The bicubic equation of particle limiting velocity formalism yields three solutions c1, c2 and c3, (primary, secondary and tertiary) limiting velocities in terms of the congruent parameter  which is defined in terms of m, v, and E, respectively being particle mass, velocity and energy. The bicubic equation discriminant D is given in terms of the congruent parameter z(m). When one has z2(m) ≤ 1 with the discriminant satisfying D ≤ 0 then we are talking about limiting velocities of ordinary particles. Good examples are the relativistic particles such as electron, neutrino,etc., with luminal limiting velocity c3 = c and calculated superluminal c2, and imaginary superluminal c1, all corresponding to the real particle energy. On the specific level, the situations like these, we discuss in the muon neutrino velocities with the OPERA detector and the electron velocities from the 2010 Grab Nebula Flare. The z(m) = 1 value separates the ordinary particles from novel particles, associated with D ⪰ 0 and z2 ⪰ 1 with new novel particle limiting velocity solutions c1, c2 and c3 which depend, in addition to z(m), also on the congruent angle α(m), nonlinearly related to z(m). These solutions are discussed on the newly defined sterile neutrino which here is modeled as an ordinary particle with z2 ⪯ 1 spontaneously transiting via z(m) = 1 into the modeled novel sterile neutrino with z2 ⪰ 1. All ordinary and novel particles limiting velocities carry real particle energies; the ordinary particle limiting velocity solutions being in quadratic forms, while the novel particle limiting velocity solutions being respectively, in quadratic complex form, linear complex form, and just congruent angle α complex quadratic form.

OPERA tau neutrino charged current interactions

The OPERA experiment was designed to discover the vτ appearance in a vμ 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 vμ beam with a baseline of 730 km, collecting a total of 1.8·1020 protons on target. The OPERA Collaboration eventually assessed the discovery of vμ→vτ oscillations with a statistical significance of 6.1 σ by observing ten vτ CC interaction candidates. These events have been published on the Open Data Portal at CERN. This paper provides a detailed description of the vτ data sample to make it usable by the whole community.

The major achievements of the OPERA experiment and its legacy

The OPERA experiment was designed to discover the [Formula: see text] appearance in a pure [Formula: see text] beam, resulting from neutrino oscillations. The detector, located in the underground Gran Sasso Laboratory, consisted of an emulsion/lead target complemented by electronic detectors and was exposed, from 2008 to 2012, to the (CERN Neutrinos to Gran Sasso (CNGS)) beam, an almost pure [Formula: see text] beam with a baseline of 730 km, collecting a total of [Formula: see text] protons on target. OPERA was unique in its capability of detecting all three neutrino flavors. OPERA discovered [Formula: see text] oscillations in appearance mode with a significance of [Formula: see text]. In this review, we report the major achievements of the OPERA experiment and its legacy in the nuclear emulsion technology.

Antimatter, Anti-Space, Anti-Time

The article shows that the special theory of relativity (STR) created in the last century was based on postulates due to the lack of the required experimental information and turned out to be incorrect, as its principle of light speed non-exceedance was refuted by studies of special processes in linear electric circuits in the 21st century. And thus, it made obsolete the unsuccessful OPERA and ICARUS experiments carried out at the Large Hadron Collider. Therefore, an alternative version of the STR has been proposed. Its relativistic formulas imply the existence of numerous mutually invisible parallel universes and antiverses. It is explained how they can be seen. There is anti-matter, as well as anti-space and anti-time in antiverses in the same quantities as matter, space and time in universes.

First observation of a tau neutrino charged current interaction with charm production in the OPERA experiment

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 coverline{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 nu _{tau } 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.

Dataset of tau neutrino interactions recorded by the OPERA experiment

We describe the dataset of very rare events recorded by the OPERA experiment. The events represent tracks of particles associated with tau neutrino interactions coming from the transformation of muon neutrinos due to a process known as neutrino oscillations. The events have been published on the CERN Open Data Portal. We describe the dataset semantics and the interactive event display visualisation tool accompanying the data release.

Annual modulation of the atmospheric muon flux measured by the OPERA experiment

The OPERA experiment, designed to search for νμ→ντ oscillations, reached its main goal by observing the appearance of ντ in the CNGS νμ beam. Thanks to its location in the underground Gran Sasso laboratory, under 3800 m.w.e., it has also been exploited as an observatory for TeV muons produced by cosmic rays in the atmosphere. In this paper the preliminary measurement of the annual modulation of the atmospheric muon flux with the OPERA detector is reported.

More results from the OPERA experiment

The OPERA experiment reached its main goal by proving the appearance of tau-neutrinos in the CNGS muon-neutrino beam. A total sample of 5 candidates fulfilling the analysis defined in the proposal was detected with a S/B ratio of about ten allowing to reject the null hypothesis with a significance of 5.1 σ. The search was extended to ½T-like interactions failing the kinematical analysis defined in the experiment proposal, to obtain a statistically enhanced, lower purity, signal sample. One such interesting neutrino interaction showing a double vertex topology with a high probability of being a tau-neutrino interaction with charm production will be reported. Based on the enlarged data sample the estimation of (math) in appearance mode is presented. The search for ½e interactions has been extended over the full data set with a more than twofold increase in statistics with respect to published data. The analysis of the νμ → νe channel is updated and the implications of the electron-neutrino sample in the framework of the 3+1 sterile model is discussed. An analysis of the νμ → ντ oscillations in the framework of the sterile neutrino model has also been performed.

New results from the OPERA experiment in the CNGS neutrino beam

A new analysis of full OPERA data set was performed, based on looser selection criteria and multivariate approach. Oscillation parameters and tau neutrino cross-section have been determined with a reduced statistical uncertainty, and the discovery of tau neutrino appearance is confirmed at 6.1σ level. Moreover, the search for electron neutrino events has been extended to the full dataset, exploiting an improved method for the electron neutrino energy estimation. New limits have been set in the 3+1 neutrino model.

Measurement of the cosmic ray muon flux seasonal variation with the OPERA detector

The OPERA experiment discovered muon neutrino into tau neutrino oscillations in appearance mode, detecting tau leptons by means of nuclear emulsion films. The apparatus was also endowed with electronic detectors with tracking capability, such as scintillator strips and resistive plate chambers. Because of its location in the underground Gran Sasso laboratory, under 3800 m.w.e., the OPERA detector has also been used as an observatory for TeV muons produced by cosmic rays in the atmosphere. In this paper the measurement of the single muon flux modulation and its correlation with the seasonal cycle of atmospheric temperature is reported.

Final results on neutrino oscillation parameters from the OPERA experiment in the CNGS beam

The OPERA experiment has conclusively observed the appearance of tau neutrinos in the muon neutrino CNGS beam. Exploiting the OPERA detector capabilities, it was possible to isolate high purity samples of $\nu_{e}$, $\nu_{\mu}$ and $\nu_{\tau}$ charged current weak neutrino interactions, as well as neutral current weak interactions. In this Letter, the full dataset is used for the first time to test the three-flavor neutrino oscillation model and to derive constraints on the existence of a light sterile neutrino within the framework of the $3+1$ neutrino model. For the first time, tau and electron neutrino appearance channels are jointly used to test the sterile neutrino hypothesis. A significant fraction of the sterile neutrino parameter space allowed by LSND and MiniBooNE experiments is excluded at 90% C.L. In particular, the best-fit values obtained by MiniBooNE combining neutrino and antineutrino data are excluded at 3.3 $\sigma$ significance.

Final results of the OPERA experiment on ντ appearance and the OPERA “legacy”

OPERA (Oscillation Project with Emulsion tRacking Apparatus) was a long-baseline experiment at the INFN Gran Sasso laboratory (LNGS) designed to search for νμ → ντ oscillations in appearance mode. It took data from 2008 to 2012 with the CNGS neutrino beam from CERN. In 2015, after the detection of five ντ candidates with a signal-to-background ratio of ∼ 10, the discovery of ντ appearance in the CNGS beam was announced with 5.1σ significance. After having reached the experiment main goal, the selection of ντ candidates has been extended by loosening the selection criteria and applying a multivariate approach for events identification, in order to improve the statistical uncertainty in the measurement of the oscillation parameters and of ντ properties. Future experiments that will take advantage of the improvements done by OPERA in the use of nuclear emulsions will also be described.

Exploring new physics from ντ events in OPERA

We analyze in details the impact of the 10 ντ events seen in the OPERA experiment [1] in constraining the Non Standard Interaction parameter εμτ affecting neutrino propagation in matter and the allowed parameter space of models with one sterile neutrino of the 3+1 type.