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Results from T2K Experiment Results from T2K experiment 1. The T2K experiment. The T2K neutrino beamline and the off-axis method The T2K detectors 2. Oscillation analyses results: νe appearance results νμ disappearance results 3. Non-oscillation analyses performed at the near detectors of the T2K 4. Summary and conclusions Magdalena Posiadała-Zezula, University of Warsaw on behalf of the T2K Collaboration Neutrino oscillations Neutrino oscillations are described by the PMNS matrix with : 3 mixing angles, 2 mass differences, 1 complex CP phase δCP with Cij (Sij) representing cosθij (sinθij), where θij is the mixing angle between the generations i and j. flavor eigenstates mass eigenstates −iδ CP ν e 1 0 0 C13 0 S13e C12 S12 0 ν1 0 C S 0 1 0 S C 0 ν µ = 23 23 − 12 12 ν 2 iδ CP ντ 0 −S23 C23 − S13e 0 C13 0 0 1 ν 3 atmospheric and accelerators interference solar and reactors 0 θ ≅ 0 θ ≅ 0 θ23 ≅ 45 13 9 12 34 2 −3 2 δ =? 2 −5 2 Δm32 ≅ 2.4 ×10 eV CP Δm21 ≅ 7.6 ×10 eV € Long baseline accelerator experiments are sensitive to: 2 Atmospheric parameters (θ23, Δ m 32 ) →mainly νμ disappearance € Interference parameters (θ13, δCP) → mainly νe appearance€ Magdalena Posiadała-Zezula, Results from T2K experiment, Miami 2014 University of Warsaw 2 € The T2K experiment Important goals: - precise measurement of θ23 by νμ - measurement of θ13 by νe appearance: disappearance: 2 0.038 2 0.055 sin 2"13 = 0.140 ± 0.032 (N.H.)at 68% C.L. sin θ23 = 0.514 ± 0.056 (N.H.)at 68% C.L. ! € Super-Kamiokande ND280 J-PARC fot. P. Mijakowski Magdalena Posiadała-Zezula, Results from T2K experiment, Miami 2014 University of Warsaw 3 T2K neutrino beamline in J-PARC ~96m length The J-PARC Main Ring (MR) extracts a 30 GeV proton beam every 2-3 seconds. For each acceleration cycle, a beam is extracted to the T2K neutrino beamline as a 5μs spill. Each spill contains 8 bunches. Magdalena Posiadała-Zezula, Results from T2K experiment, Miami 2014 University of Warsaw 4 Beam operation history up to summer 2014 Magdalena Posiadała-Zezula, Results from T2K experiment, Miami 2014 University of Warsaw 5 The off-axis method The T2K experiment employs the off-axis method, which for the first time has been used in search for neutrino oscillations (BNL-E889 proposal). The off-axis method uses the fact that the energy, Eν, of the neutrino emitted at an angle relative to the π (K) direction in a two-body pion (kaon) In T2K, the off-axis angle is set to decay is only weakly dependent on the 2.50 with the neutrino beam energy momentum of the parent meson. at SK peaking at ~0.6 GeV, near the expected first oscillation maximum ( Phys.Rev. D87, 012001, 2013). Magdalena Posiadała-Zezula, Results from T2K experiment, Miami 2014 University of Warsaw 6 The T2K on-axis near detector INGRID The on-axis detector- INGRID 16 cubic modules. Aim: to monitor the ν beam direction by looking at ν interactions with precision better than 1 mrad on a day-by-day basis. The INGRID standard module. 1 module is a sandwich of 10 iron and 11 scintillator planes. It is surrounded by veto scintillator planes. arXiv:1407.4256v2, hep-ex Magdalena Posiadała-Zezula, Results from T2K experiment, Miami 2014 University of Warsaw 7 The T2K off-axis near detector ND280 The ND280 detector is located at 2.5 degrees off axis. The ND280 is placed inside a 0.2 T magnet previously used by the UA1 and NOMAD experiments. The ND280 consists of: 1. π0 detector (P0D); 2. three gas-filled TPC’s for momentum and PID measurement; 3. two fine-grained detectors (FGD’s) as active targets; 4. electromagnetic calorimeter (ECal) for energy measurement and PID; 5. muon detectors (SMRD). Magdalena Posiadała-Zezula, Results from T2K experiment, Miami 2014 University of Warsaw 8 The Super-Kamiokande detector 50 kton water Cherenkov detector (22.5 kton FV) The geometry of the Super-Kamiokande (SK) detector consists of : an inner and an outer detector. 40 m The inner detector (ID ) is a cylindrical structure with ~11k PMTs 40 m The outer detector (OD) contains ~ 2k PMTs. Magdalena Posiadała-Zezula, Results from T2K experiment, Miami 2014 University of Warsaw 9 Super Kamiokande detector- detection principle ν interactions often produce charged particles which may create a cone of Cherenkov photons as they traverse water. When these photons reach the PMTs, they produce a ring-shaped hit pattern which is used to extract information on event vertex position and momenta of particles. νμ-like – well νe-like – defined cone, scattering of e-, sharp ring. “fuzzy” rings. Example of reconstructed events in SK. The white line shows reconstructed cone. Magdalena Posiadała-Zezula, Results from T2K experiment, Miami 2014 University of Warsaw 10 The T2K neutrino flux simulation (Phys.Rev. D87, 012001, 2013). The prediction of the flux and spectrum of neutrinos at the T2K detectors (INGRID, ND280 and SK) is based on : 1) FLUKA generation – simulation of p+C interactions in the target 2) JNUBEAM simulation- tracking exiting particles from the target. The simulation and its associated uncertainties are driven by: a) primary beam profile measurements, b) measurements of the horns magnetic fields, c) hadron production data and re-weighting, including NA61/SHINE measurements from 2007 run: (Phys.Rev. C85, 035210, 2012, Phys.Rev. C84, 034604, 2011). Fluxes at INGRID, ND280 and SK Magdalena Posiadała-Zezula, Results from T2K experiment, Miami 2014 University of Warsaw 11 NA61/SHINE at CERN SPS Large-acceptance hadron spectrometer. The main tracking and particle identification devices are large- volume TPCs and ToF. Two TPCs are located between coils of the two superconducting magnets (1.14 Tm) Two types of measurements were done for T2K: 31GeV/c protons on: 1). Thin target (4%λint)- studies of primary interactions 2). Replica of the T2K target (1.9λint)- production of all hadrons along the target Year Thin target Replica target Status registered no of events registered no of events 2007 6.3 x105 used by T2K 2.3x105 Published 2009 4.4x106 2.4x106 Being analyzed 2010 - 1x107 Under Calibration Magdalena Posiadała-Zezula, Results from T2K experiment, Miami 2014 University of Warsaw 12 Possible improvements with 2009 NA61 data with thin target data: with T2K replica target data, better coverage, new hadronic measurements tested on 2007 data Magdalena Posiadała-Zezula, Results from T2K experiment,Nucl.Instrum.Meth.A701, Miami 2014 2013 University of Warsaw 13 TheT2K predicted ν flux Flux is mainly composed of νμ Contamination fromνe is ~1.2% Total uncertainty on T2K flux is ~10-15% Main uncertainty on flux predictions still comes from hadronic interactions - it will be improved with the 2009 NA61 results <Eν>≈0.6 GeV <Eν>≈0.6 GeV Magdalena Posiadała-Zezula, Results from T2K experiment, Miami 2014 University of Warsaw 14 Oscillation analysis procedure in T2K Neutrino Flux prediction : • Hadron production data from SK NA61/SHINE Fit to ND280 data constrains ND280 flux and cross section parameters expected ν sample νμ μ νe (νμ) νe (νμ) sample enhanced in events for candidates enhanced CC event unosc. selected in CC candidates spectra in in DATA events MC in DATA MC Cross section models: • Interaction generator (NEUT) • External data (MiniBooNE) Extraction of the oscillation parameters Magdalena Posiadała-Zezula, Results from T2K experiment, Miami 2014 University of Warsaw 15 Systematic uncertainties- impact of the ND280 measurements Strong reduction of the systematic uncertainties to the event rate at SK, thanks to the ND280 data Systematic sources νμ νe sample sample [%] [%] ν flux and w/o ND280 meas. 21.8 26.0 cross section w ND280 meas. 2.7 3.1 ν cross sections due to difference 5.0 4.7 of target between near and far detector Final or secondary hadronic 3.0 2.4 interactions Super-K detector 4.0 2.7 Total w/o ND280 meas 23.5 26.8 w/ ND280 meas. 7.7 6.8 Magdalena Posiadała-Zezula, Results from T2K experiment, Miami 2014 University of Warsaw 16 Super-Kamiokande event selection Fully Contained, 1 ring events inside the fiducial volume of the SK detector μ–like: e–like: pe > 100 MeV/c pμ > 200 MeV/c NO Michel electron Michel electron less than 2 π0 rejection μ -like PID Erec < 1250 MeV, e-like PID 120 events observed 28 events observed expected 446±23 (syst) expected 4.9±0.6 (syst) Magdalena Posiadała-Zezula, Results from T2K experiment, Miami 2014 University of Warsaw 17 νe appearance results Phys.Rev.Lett. 112 (2014) 061802 The neutrino oscillation parameters are obtained using maximum likelihood fit in (pe, θe) Results are consistent with independent analysis based on neutrino reconstructed energy Erec Best fit value : θ ν 2 +0.038 The (pe, e) distribution for e sin 2"13 = 0.140#0.032 for N.H. and $CP = 0 candidate-events with MC predictions. 7.3σ significance to non-zero θ13 ! Discovery of νe appearance !!! T2K has made the first observation of νe in νμ beam Magdalena Posiadała-Zezula, Results from T2K experiment, Miami 2014 University of Warsaw 18 νμ disappearance analysis Phys.Rev.Lett. 112 (2014) 181801 World leading measurement for θ23 ! For the first time, the mixing angle θ23 is better constrained by an accelerator experiment than by atmospheric neutrinos. Fit to data made using 3 flavor framework for oscillations. Maximal mixing is favored 2 +0.055 sin "23 = 0.514#0.056 for N.H. ! Magdalena Posiadała-Zezula, Results from T2K experiment, Miami 2014 University of Warsaw 19 Joint νμ-νe fit and δCP constrains A joint fit is needed because of the correlations between mixing parameters: θ13, θ23, δCP and others;
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