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New results from K2K

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

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New results from K2K

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  1. New results from K2K Makoto Yoshida (IPNS, KEK) for the K2K collaboration NuFACT02, July 4, 2002 London, UK

  2. 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 forNuclear Study

  3. K2K long baseline neutrino oscillation experiment • 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 • Kamioka • Super-K 250km • KEK • n beam line • Beam monitor • Near detectors

  4. Neutrino oscillations in K2K nm disappearance Fixed to 250 km probability En=1.3 GeV Spectrum distortion • K2K aims to observe • deficit in number of nmevents • distortion ofnm spectrum • after 250 km travel

  5. Super-Kamiokande • 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) 41 m 39 m

  6. Neutrino Beam Line @KEK p+Al  p+  m+ + nm • Near neutrino detectors • Flux/spectrum 12GeV PS 1.1msec / 2.2sec beam spill 6x1012 protons/spill 200m Double Horn 250kA  x20 nm Pion monitor pp,qp after Horn Near to Far flux ratio RFN

  7. Near neutrino detectors Muon Range Detector • 1kton water Cherenkov detector (1KT) same type as SK (25ton fiducial) • Fine Grained Detectors (FGD) • Scintillation fiber tracker (SciFi) w/ water target (6ton fiducial) • CCQE identification • Lead glass calorimeter (LG) detect electrons from SciFi • Muon range detector (MRD) measure muon momentum • nbeammonitor (Fe, 330ton fiducial)

  8. K2K Results in 2001 GPS Tspill TSK 500msec w/o pre-activity p.e. >200 Fully Contained events in Fiducial Volume (FCFV) Number of FCFV events (NSK) 5msec 56 events observed 80 expected in null oscillation case Probability < 3% 1.5ms DT (msec)

  9. 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

  10. 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

  11. Event categories for spectrum measurement at near site pm : muon momentum 1KT: single ring m-like FCFV events (1Rm) FGD: single track events qm : muon angle pm m nm qm proton pm m nm qm FGD: QE-like 2-track events proton pm m nm qm FGD: nQE-like 2-track events proton p

  12. QE and nQE in SciFi 2track events Water Target + Al(20%) Fiducial Mass : 6 ton DEm~150MeV Event Rate ~ 1/1000pulses nQE-like QE-like

  13. Fitting Method MC templates for neutrino spectrum f(En)(8bin) and interaction model (QE/nQE) Fitted (pm,qm) = weighted mean of MC templetes En QE (MC) nQE(MC) Measured (pm,qm) 0 - 0.5 GeV 0.5 - 0.75GeV 0.75 - 1.0GeV Fitted (pm,qm) dist. of 1KT and FGD c2=227 for 197 d.o.f. (90 from 1KT, 137 from FGD) • • • •

  14. 1KT distributions with fitted results Reasonable fitted distribution

  15. FGD distributions with fitted results CCQE (MC) qm Pm 1-track m 2-track QE-like 2-track nQE-like Good agreement for ALL sample

  16. pm : muon momentum m nm qm : muon angle proton Neutrino spectrum reconstruction in SK Use single-ring m-like FCFV events (1Rm) Reconstruct neutrino energy assuming CCQE

  17. 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 • Nexp= 80.1+6.2-5.4 Shape term 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

  18. Allowed Dm2 by NSK and Shape only analysis NSK+Shape Number of Events only Spectrum Shape only NSK and shape analysis indicate the same Dm2 region for sin22q=1 Merged analysis (NSK and Shape) to get allowed region.

  19. K2K Allowed region (Shape+Norm) 1.5~3.9x10-3eV2 for sin22q=1 @90%CL Consistent with atm. n result • cf. Atmospheric n results • Dm2=(1.6~3.9)x10-3 eV2 • for sin22q=1.0

  20. Shape and NSK @ Best Fit Best fit oscillation parameter (sin22q , Dm2) method-1 method-2 Shape only (1.09, 3.0x10-3eV2) (1.05, 3.2x10-3eV2) NSK +Shape (1.03, 2.8x10-3eV2) (1.05, 2.7x10-3eV2) normalized by area • method 1 • NSK prediction =54 (obs 56) • KS test prob.(shape)= 79% • method 2 • NSK 82% • shape 93% • NSK+shape 50% Null oscillation Best fit NSK and Shape are reasonable at best fit point

  21. Null Oscillation Probability method-1 method-2 NSKonly 1.3% 0.7% Shape only 15.7% 14.3% NSK+Shape 0.7% 0.4% Prob. for null oscillation case is less than 1%

  22. 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 Dm2 region for sin22q=1 • Analysis for NSK+Shape gives Dm2=1.5~3.9x10-3eV2 for sin22q=1@ 90%CL • Null oscillation probability is less than 1% • Resume data taking this winter and make statistics 2 times more

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