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The charge-conjugation and parity-reversal (CP) symmetry of fundamental particles is a symmetry between matter and antimatter. Violation of this CP symmetry was first observed in 1964 1 , and CP violation in the weak interactions of quarks was soon established 2 . Sakharov proposed 3 that CP violation is necessary to explain the observed imbalance of matter and antimatter abundance in the Universe. However, CP violation in quarks is too small to support this explanation. So far, CP violation has not been observed in non-quark elementary particle systems. It has been shown that CP violation in leptons could generate the matter–antimatter disparity through a process called leptogenesis 4 . Leptonic mixing, which appears in the standard model’s charged current interactions 5 , 6 , provides a potential source of CP violation through a complex phase δ CP , which is required by some theoretical models of leptogenesis 7 – 9 . This CP violation can be measured in muon neutrino to electron neutrino oscillations and the corresponding antineutrino oscillations, which are experimentally accessible using accelerator-produced beams as established by the Tokai-to-Kamioka (T2K) and NOvA experiments 10 , 11 . Until now, the value of δ CP has not been substantially constrained by neutrino oscillation experiments. Here we report a measurement using long-baseline neutrino and antineutrino oscillations observed by the T2K experiment that shows a large increase in the neutrino oscillation probability, excluding values of δ CP that result in a large increase in the observed antineutrino oscillation probability at three standard deviations (3 σ ). The 3 σ confidence interval for δ CP , which is cyclic and repeats every 2π, is [−3.41, −0.03] for the so-called normal mass ordering and [−2.54, −0.32] for the inverted mass ordering. Our results indicate CP violation in leptons and our method enables sensitive searches for matter–antimatter asymmetry in neutrino oscillations using accelerator-produced neutrino beams. Future measurements with larger datasets will test whether leptonic CP violation is larger than the CP violation in quarks. The T2K experiment constrains CP symmetry in neutrino oscillations, excluding 46% of possible values of the CP violating parameter at a significance of three standard deviations; this is an important milestone to test CP symmetry conservation in leptons and whether the Universe’s matter–antimatter imbalance originates from leptons.

The Fourier harmonics, v 2 and v 3 of negative pions are measured at center-of-mass energy per nucleon pair of s NN = 17.3 GeV around midrapidity by the CERES/NA45 experiment at the CERN SPS in 0–30% central PbAu collisions with a mean centrality of 5.5%. The analysis is performed in two centrality bins as a function of the transverse momentum p T from 0.05 GeV/ c to more than 2 GeV/ c . This is the first measurement of the v 3 1 / 3 / v 2 1 / 2 ratio as a function of transverse momentum at SPS energies, that reveals, independently of the hydrodynamic models, hydrodynamic behavior of the formed system. For p T above 0.5 GeV/ c , the ratio is nearly flat in accordance with the hydrodynamic prediction and as previously observed by the ATLAS and ALICE experiments at the much higher LHC energies. The results are also compared with the SMASH-vHLLE hybrid model predictions, as well as with the SMASH model applied alone.

The Fourier harmonics,$$v_2$$v 2 and$$v_3$$v 3 of negative pions are measured at center-of-mass energy per nucleon pair of$$\\sqrt{s_{\\textrm{NN}}}$$s NN = 17.3 GeV around midrapidity by the CERES/NA45 experiment at the CERN SPS in 0–30% central PbAu collisions with a mean centrality of 5.5%. The analysis is performed in two centrality bins as a function of the transverse momentum$$\\mathrm {p_{\\textrm{T}}}$$p T from 0.05 GeV/ c to more than 2 GeV/ c . This is the first measurement of the$$v^{1/3}_{3}/v^{1/2}_{2}$$v 3 1 / 3 / v 2 1 / 2 ratio as a function of transverse momentum at SPS energies, that reveals, independently of the hydrodynamic models, hydrodynamic behavior of the formed system. For$$\\mathrm {p_{\\textrm{T}}}$$p T above 0.5 GeV/ c , the ratio is nearly flat in accordance with the hydrodynamic prediction and as previously observed by the ATLAS and ALICE experiments at the much higher LHC energies. The results are also compared with the SMASH-vHLLE hybrid model predictions, as well as with the SMASH model applied alone.

We report an early result from the ICARUS experiment on the search for a ν μ → ν e signal due to the LSND anomaly. The search was performed with the ICARUS T600 detector located at the Gran Sasso Laboratory, receiving CNGS neutrinos from CERN at an average energy of about 20 GeV, after a flight path of ∼730 km. The LSND anomaly would manifest as an excess of ν e events, characterized by a fast energy oscillation averaging approximately to with probability . The present analysis is based on 1091 neutrino events, which are about 50 % of the ICARUS data collected in 2010–2011. Two clear ν e events have been found, compared with the expectation of 3.7±0.6 events from conventional sources. Within the range of our observations, this result is compatible with the absence of a LSND anomaly. At 90 % and 99 % confidence levels the limits of 3.4 and 7.3 events corresponding to oscillation probabilities and are set respectively. The result strongly limits the window of open options for the LSND anomaly to a narrow region around (Δ m 2 ,sin 2 (2 θ )) new =(0.5 eV 2 ,0.005), where there is an overall agreement (90 % CL) between the present ICARUS limit, the published limits of KARMEN and the published positive signals of LSND and MiniBooNE Collaborations.

The observation of the recent electron neutrino appearance in a muon neutrino beam and the high-precision measurement of the mixing angle $\\theta _{13}$ have led to a re-evaluation of the physics potential of the T2K long-baseline neutrino oscillation experiment. Sensitivities are explored for CP violation in neutrinos, non-maximal $\\sin ^22\\theta _{23}$, the octant of $\\theta _{23}$, and the mass hierarchy, in addition to the measurements of $\\delta _{{\\rm CP}}$, $\\sin ^2\\theta _{23}$, and $\\Delta m^2_{32}$, for various combinations of $\\nu$-mode and $\\bar {\\nu }$-mode data-taking.With an exposure of $7.8\\times 10^{21}$ protons-on-target, T2K can achieve 1$\\sigma$ resolution of 0.050 (0.054) on $\\sin ^2\\theta _{23}$ and $0.040\\ (0.045)\\times 10^{-3}\\,\\rm {eV}^2$ on $\\Delta m^2_{32}$ for 100% (50%) neutrino beam mode running assuming $\\sin ^2\\theta _{23}=0.5$ and $\\Delta m^2_{32} = 2.4\\times 10^{-3}\\,\\hbox {eV}^2$. T2K will have sensitivity to the CP-violating phase $\\delta _{\\rm {CP}}$ at 90% C.L. or better over a significant range. For example, if $\\sin ^22\\theta _{23}$ is maximal (i.e. $\\theta _{23}=45^\\circ$) the range is $-115^\\circ \\lt \\delta _{\\rm {CP}}\\lt -60^\\circ$ for normal hierarchy and $+50^\\circ \\lt \\delta _{\\rm {CP}}\\lt +130^\\circ$ for inverted hierarchy. When T2K data is combined with data from the NO$\\nu$A experiment, the region of oscillation parameter space where there is sensitivity to observe a non-zero $\\delta _{{\\rm CP}}$ is substantially increased compared to if each experiment is analyzed alone.

A bstract During May 2012, the CERN-CNGS neutrino beam has been operated for two weeks for a total of ~1.8 × 10 17 p.o.t., with the proton beam made of bunches, few ns wide and separated by 100 ns. This beam structure allows a very accurate time of flight measurement of neutrinos from CERN to LNGS on an event-by-event basis. Both the ICARUS-T600 PMT-DAQ and the CERN-LNGS timing synchronization have been substantially improved for this campaign, taking advantage of additional independent GPS receivers, both at CERN and LNGS as well as of the deployment of the “White Rabbit” protocol both at CERN and LNGS. The ICARUS-T600 detector has collected 25 beam-associated events; the corresponding time of flight has been accurately evaluated, using all different time synchronization paths. The measured neutrino time of flight is compatible with the arrival of all events with speed equivalent to the one of light: the difference between the expected value based on the speed of light and the measured value is δt = tof c −tof ν  = 0.10 ± 0.67 stat.  ± 2.39 syst.  ns. This result is in agreement with the value previously reported by the ICARUS Collaboration, δt  = 0.3 ± 4.9 stat.  ± 9.0 syst.  ns, but with improved statistical and systematic accuracy.

Abstract We report a measurement of the flux-integrated $\\nu_{\\mu}$ charged-current cross sections on water, hydrocarbon, and iron in the T2K on-axis neutrino beam with a mean neutrino energy of 1.5 GeV. The measured cross sections on water, hydrocarbon, and iron are $\\sigma^{\\rm{H_{2}O}}_{\\rm{CC}} = (0.840\\pm 0.010(\\mathrm{stat.})^{+0.10}_{-0.08}(\\mathrm{syst.}))\\times10^{-38}\\,\\mathrm{cm}^2$/nucleon, $\\sigma^{\\rm{CH}}_{\\rm{CC}} = (0.817\\pm 0.007(\\mathrm{stat.})^{+0.11}_{-0.08}(\\mathrm{syst.}))\\times10^{-38}\\,\\mathrm{cm}^2$/nucleon, and $\\sigma^{\\rm{Fe}}_{\\rm{CC}} = (0.859\\pm 0.003(\\mathrm{stat.})^{+0.12}_{-0.10}(\\mathrm{syst.}))\\times10^{-38}\\,\\mathrm{cm}^2$/nucleon, respectively, for a restricted phase space of induced muons: $\\theta_{\\mu}<45^{\\circ}$ and $p_{\\mu}>$0.4 GeV/$c$ in the laboratory frame. The measured cross section ratios are ${\\sigma^{\\rm{H_{2}O}}_{\\rm{CC}}}/{\\sigma^{\\rm{CH}}_{\\rm{CC}}} = 1.028\\pm 0.016(\\mathrm{stat.})\\pm 0.053(\\mathrm{syst.})$, ${\\sigma^{\\rm{Fe}}_{\\rm{CC}}}/{\\sigma^{\\rm{H_{2}O}}_{\\rm{CC}}} = 1.023\\pm 0.012(\\mathrm{stat.})\\pm 0.058(\\mathrm{syst.})$, and ${\\sigma^{\\rm{Fe}}_{\\rm{CC}}}/{\\sigma^{\\rm{CH}}_{\\rm{CC}}} = 1.049\\pm 0.010(\\mathrm{stat.})\\pm 0.043(\\mathrm{syst.})$. These results, with an unprecedented precision for the measurements of neutrino cross sections on water in the studied energy region, show good agreement with the current neutrino interaction models used in the T2K oscillation analyses.

Liquid Argon Time Projection Chamber (LAr TPC) detectors offer charged particle imaging capability with remarkable spatial resolution. Precise event reconstruction procedures are critical in order to fully exploit the potential of this technology. In this paper we present a new, general approach to 3D reconstruction for the LAr TPC with a practical application to the track reconstruction. The efficiency of the method is evaluated on a sample of simulated tracks. We present also the application of the method to the analysis of stopping particle tracks collected during the ICARUS T600 detector operation with the CNGS neutrino beam.

An extension of the new standard model, by introducing a mixing of the low mass “active” neutrinos with heavy ones, or by any model with lepton flavor violation, is considered. This leads to non-orthogonal neutrino production and detection states and to modifications of neutrino oscillations in both vacuum and matter. The possibility of the discovery of such effects in current and future neutrino oscillation experiments is discussed. First order approximation formulas for the flavor transition probabilities in constant density matter, for all experimentally available channels, are given. Numerical calculations of flavor transition probabilities for two sets of new physics parameters describing a single “effective” heavy neutrino state, both satisfying present experimental constraints, have been performed. Two energy ranges and several baselines, assuming both the current (±2σ) and the expected future errors (±3%) of the neutrino oscillation parameters are considered, keeping their present central values. It appears that the biggest potential of the discovery of the possible presence of any new physics is pronounced in oscillation channels in which νe and νē are not involved at all, especially for two baselines, L=3000 km and L=7500 km, which for other reasons are also called “magic” for future Neutrino Factory experiments.

The ICARUS collaboration has demonstrated, following the operation of a 600 ton (T600) detector at shallow depth, that the technique based on liquid argon time projection chambers is now mature. The study of rare events, not contemplated in the standard model, can greatly benefit from the use of this kind of detectors. In particular, a deeper understanding of atmospheric neutrino properties will be obtained thanks to the unprecedented quality of the data ICARUS provides. However if we concentrate on the T600 performance, most of the νμ charged current sample will be partially contained, due to the reduced dimensions of the detector. In this article, we address the problem of how well we can determine the kinematics of events having partially contained tracks. The analysis of a large sample of atmospheric muons collected during the T600 test run demonstrates that, in case the recorded track is at least one meter long, the muon momentum can be reconstructed by an algorithm that measures the multiple Coulomb scattering along the particle’s path. Moreover, we show that momentum resolution can be improved by almost a factor two using an algorithm based on the Kalman filtering technique.