Transcript B01_yoshida
New results from K2K Makoto Yoshida (IPNS, KEK) for the K2K collaboration NuFACT02, July 4, 2002 London, UK K2K Collaboration High Energy Accelerator Research Organization(KEK) Institute for Cosmic Ray Research(ICRR), University of Tokyo Kobe University Kyoto University Niigata University Okayama University Tokyo University of Science Tohoku University Chonnam National University Dongshin University Korea University Seoul National University Boston University University of California, Irvine University of Hawaii, Manoa Massachusetts Institute of Technology State University of New York at Stony Brook University of Washington at Seattle Warsaw University Soltan Institute for Nuclear Study K2K long baseline neutrino oscillation experiment Kamioka •Super-K 250km KEK n beam line Beam monitor Near detectors • Neutrino beam almost pure nm (98%) <En>~1.3GeV • Near detectors Measure nm flux/spectrum • Far detector Super-Kamiokande (SK) 250 km far from KEK • nm disappearance and ne appearance Neutrino oscillations in K2K nm disappearance probability P(n m n m ) 1 sin 2 (2 ) sin 2 (1.27m2 L / En ) L 250km, m2 3 103 eV 2 Fixed to 250 km En=1.3 GeV Spectrum distortion K2K aims to observe • deficit in number of nm events • distortion of nm spectrum after 250 km travel Super-Kamiokande 41 m • • • • • • 39 m 50kton Water Cherenkov detector 1000m underground 22.5kton fiducial mass Inner detector 11146 PMTs(20’’) Outer detector 1885 PMTs(8’’) Atmospheric n B.G. against K2K ~10-5 events/day in beam spill (1.1ms/2.2s) Neutrino Beam Line @KEK p+Al p+ m+ + nm 12GeV PS 1.1msec / 2.2sec beam spill 6x1012 protons/spill Near neutrino detectors Flux/spectrum Double Horn 250kA x20 nm Pion monitor pp,p after Horn Near to Far flux ratio RFN Near neutrino detectors Muon Range Detector • 1kton water Cherenkov detector (1KT) • Fine Grained Detectors (FGD) • Scintillation fiber tracker (SciFi) • Lead glass calorimeter (LG) • Muon range detector (MRD) same type as SK (25ton fiducial) w/ water target (6ton fiducial) CCQE identification detect electrons from SciFi measure muon momentum n beam monitor (Fe, 330ton fiducial) K2K Results in 2001 GPS 0.2 ΔT TSK TSpill TOF 1.3μ sec 500msec Tspill TSK w/o pre-activity p.e. >200 Fully Contained events in Fiducial Volume (FCFV) 5msec 56 events observed 1.5ms Number of FCFV events (NSK) +7.3 808.0 expected in null oscillation case Probability < 3% T (msec) What’s new • Same data set as in last year • nm spectrum at near site • Oscillation analysis (NSK+ Shape) only NSK in last year • Full error treatment to include correlation Strategy Near site • Number of neutrino events • muon distributions of neutrino events Fit for neutrino spectrum & interaction model Near to Far extrapolation RFN(En) Far site • Total number events • Spectrum shape Event categories for spectrum measurement at near site pm : muon momentum m : muon angle m nm pm m 1KT: single ring m-like FCFV events (1Rm) FGD: single track events proton m nm pm m FGD: QE-like 2-track events proton m nm pm m proton p FGD: nQE-like 2-track events QE and nQE in SciFi 2track events nQE-like QE-like Water Target + Al(20%) Fiducial Mass : 6 ton Em ~150MeV Event Rate ~ 1/1000pulses Fitting Method MC templates Fitted (pm,m) = weighted mean for neutrino spectrum f(En) (8bin) of MC templetes and interaction model (QE/nQE) En QE (MC) nQE(MC) Measured (pm,m) 0 - 0.5 GeV 0.5 - 0.75GeV 0.75 - 1.0GeV • • • • Fitted (pm,m) dist. of 1KT and FGD c2=227 for 197 d.o.f. (90 from 1KT, 137 from FGD) 1KT distributions with fitted results Reasonable fitted distribution CCQE (MC) FGD distributions with fitted results Pm m 1-track m 2-track QE-like 2-track nQE-like Good agreement for ALL sample Neutrino spectrum reconstruction in SK Use single-ring m-like FCFV events (1Rm) Reconstruct neutrino energy assuming CCQE E rec ν m N E μ mμ2 2 m N E μ + pμ cosθμ pm : muon momentum m nm m : muon angle proton Oscillation analysis Data Sets • For number of events (NSK) June ’99-July ’01 FCFV events (56 events) • For spectrum shape Nov ’99-July ’01 1Rm events (29 events) Method-1 Maximum Likelihood method Ltot = Lnorm(f) Lshape(f) Lsyst(f) Normalization term Shape term Nexp= 80.1+6.2-5.4 Constraint term for syst. parameter. (error matrices) Method-2 different treatment of syst. term. Generate many MC samples with syst. parm. changed within error. Ltot = mean value for the MC samples Allowed m2 by NSK and Shape only analysis NSK+Shape Number of Events only Spectrum Shape only NSK and shape analysis indicate the same m2 region for sin22=1 Merged analysis (NSK and Shape) to get allowed region. K2K Allowed region (Shape+Norm) 1.5~3.9x10-3eV2 for sin22=1 @90%CL Consistent with atm. n result cf. Atmospheric n results m2=(1.6~3.9)x10-3 eV2 for sin22=1.0 Shape and NSK @ Best Fit Best fit oscillation parameter (sin22 , m2) method-1 method-2 (1.09, 3.0x10-3eV2) (1.03, 2.8x10-3eV2) Shape only NSK +Shape (1.05, 3.2x10-3eV2) (1.05, 2.7x10-3eV2) normalized by area Null oscillation Best fit method 1 •NSK prediction =54 (obs 56) •KS test prob.(shape)= 79% method 2 •NSK 82% •shape 93% •NSK+shape 50% NSK and Shape are reasonable at best fit point Null Oscillation Probability NSKonly Shape only NSK+Shape method-1 1.3% 15.7% 0.7% method-2 0.7% 14.3% 0.4% Prob. for null oscillation case is less than 1% Conclusion • • • • • • Neutrino spectrum in K2K has been measured by using near detectors Oscillation analysis with number of events and spectrum shape on June99 ~July01 data Analysis for NSK and for shape indicate consistent m2 region for sin22=1 Analysis for NSK+Shape gives m2=1.5~3.9x10-3eV2 for sin22=1 @ 90%CL Null oscillation probability is less than 1% Resume data taking this winter and make statistics 2 times more