RECENT RESULTS IN K2K EXPERIMENT Shimpei YAMAMOTO (Kyoto Univ.) 10 th ICEPP 16-FEB-2004 Shimpei YAMAMOTO (Kyoto Univ.) 10 th ICEPP 16-FEB-2004

10th ICEPP 2 JAPAN: 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 KOREA: Chonnam National University Dongshin University / Korea University Seoul National University U.S.A.: 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 POLAND: Warsaw University / Solton Institute Since 2002 JAPAN: Hiroshima University, Osaka University CANADA: TRIUMF / University of British Columbia EUROPE: Rome / Saclay / Barcelona / Valencia / Geneva RUSSIA: INR-Moscow K2K collaboration

10th ICEPP 3 OutlineOutline K2K & neutrino oscillation Recent status & results –  → x oscillation analysis – e appearance –New near detector “SciBar” Prospects Summary K2K & neutrino oscillation Recent status & results –  → x oscillation analysis – e appearance –New near detector “SciBar” Prospects Summary

10th ICEPP 4 K2K LBL oscillation exp. KEKSK 1kt SciFi MRD LG(K2K-I) SciBar(K2K-II)  Near Detectors =1.3GeV L=250km (fixed) 98%   Super-Kamiokande(SK) 50kt water cherenkov detector (22.5kt fid. vol.) beamline beamline Beam monitor

10th ICEPP 5 Neutrino Oscillation in K2K oscillation prob.: Aiming results: –Reduction of events –Distortion of  spectrum – e appearance  osci. parameters (sin 2 2θ,Δm 2 ) –Near to far extrapolation –Rate & spectrum null oscillation w/ oscillation

10th ICEPP 6 Neutrino Beamline p+Al        +  e + + e (1.3%) +  (0.5%) double horm: high eff. of  collection Pion monitor: near/far flux ratio Muon monitor: beam intensity & direction Fast extraction every 2.2secFast extraction every 2.2sec Beam spill 1.1usBeam spill 1.1us

10th ICEPP 7 Near Detectors (ND) fiducial fiducial 1kt Water Cherenkov detector (KT) 25 ton same type as SK Scintillation Fiber tracker (SciFi) 6 ton detect protons  QE/nQE Muon Range Detector (MRD) ~700 ton (Fe) beam monitor Lead Glass calorimeter (LG) detect electrons from SciFi K2K-I Mar,1999 – Jul,2001 Mar,1999 – Jul,2001 SKI (11146PMTs) SKI (11146PMTs) | SK accident SK accident |K2K-II Dec,2002 – Dec,2002 – SKII (~5200PMTs) SKII (~5200PMTs) LG removed LG removed SciBar (Oct,2003 -) SciBar (Oct,2003 -)

10th ICEPP 8 Delivered protons on target 5~6x10 12 (protons per pulse) 10/7 12/21 6/23 12/23 ‘99 ‘00 ‘01‘02‘03 K2K-IIK2K-I 9.5x10 19 POT (8.4x10 19 for analysis)

10th ICEPP 9 K2K event selection in SK T spill T SK GPS T Spill : Abs. time of spill start T SK : Abs. time of SK event TOF: 0.83ms (KEK to Kamioka) No Decay-e HE Trig. FC: fully contained (No activity in Outer Detector) FV: 22.5kt Fiducial Volume Expected atm. BG ~2x10 -3 within 1.5  s. 1.5  s  500  sec  5  sec FCFV 72 events Jun.’99 – Apr.’ x proton on target K2K-I + part of K2K-II

10th ICEPP 10 K2K events in SK Jun.1999~Apr.2003 K2K-I (56 events) K2K-II (+16 events)

 → X oscillation analysis (K2K-I)  → X oscillation analysis (K2K-I)

10th ICEPP 12 Analysis flow –N SK : Number of FCFV events –S SK (E rec ) : E rec distribution (shape) of 1R  Num. of events & Observed (p ,   ) distributionsNum. of events & Observed (p ,   ) distributions  Neutrino FluxNeutrino Flux Fit  spectrum & interaction modelFit  spectrum & interaction model – f near (E ) (8 bins) – nQE/QE ratio – Error matrix (to include correlation) Near to Far extrapolation: R FN (E ) Near site site Use Maximum Likelihood Fit in (sin 2 2 ,  m 2 )

10th ICEPP 13 Reconstruction of E Reconstruction of E   proton  pp Use single-ring  -like FCFV (1R  ) eventsUse single-ring  -like FCFV (1R  ) events Assume QE int. and reconstruct EAssume QE int. and reconstruct E ( ~50% of K2K 1R  events are CCQE ) E

10th ICEPP 14 interaction (~1GeV) interaction (~1GeV) Charged current quasi-elastic scat, (CCQE) pion productions (nonQE) p  : muon momentum   : muon angle   proton  pp   nucleon  pp  ※ E can be reconstructed from P  and  . from P  and  . 1kt : single ring  -like FCFV SciFi: QE-like 2track single track (proton invisible) single track (proton invisible) 1kt : single/multi ring FCFV SciFi: nonQE-like 2track

10th ICEPP 15 1KT : P  <1.5GeV/c, 4  acceptance – –1-ring  -like(1R  ) fully contained in Fid.25ton(FC) : 22,476ev. SciFi : P  >1GeV/c,   <60deg. – –1-track  -like : 5963ev. – –2-track QE-like (  p <25deg.) : 764ev. – –2-track nonQE-like (  p >30deg.) : 1288ev. PIMON – –  (p,  ) distribution ⇒ Neutrino Spectrum (>1GeV) Fitting Parameters E  : 8 bins, nonQE/QE ratio Spectrum nonQE-like QE-like

10th ICEPP 16 SciFi p  /   1-track  2-track QE-like 2-track nQE-like  PP

10th ICEPP 17 1kt p  /   p  and   distributions of 1kt 1ring  -like FCFV events PP 

10th ICEPP 18 Allowed region (  → X ) Allowed region Use both Number of events + Spectrum shape (June ’99 – July ’01)(Nov. ’99 – July ’01) Null oscillation probability: less than 1%. Null oscillation probability: less than 1%.  m 2 =1.5~3.9 x 10-3 eV 2, sin 2 2  =1(90%CL)  m 2 =1.5~3.9 x 10-3 eV 2, sin 2 2  =1(90%CL) 68% 90% 99% exp 56 obs ↔ Normalized by area reconstructed E Expectation w/o oscillation Best Fit Best fit point 2.8x10 -3

10th ICEPP 19 Comparison w/ SK result 90% C.L. K2K SK

Search for e appearance (K2K-I)

10th ICEPP 21 Search for e appearance Fully contained – Single ring – e-like (ring pattern and opening angle) (ring pattern and opening angle) Visible energy>100MeV – w/o decay electrons Ring pattern Opening angle To be submitted for publication data  MC NC of   MC e MC

10th ICEPP 22 Data reduction summary DATA SETJune’99 – July’01 (4.8×10 19 POT) DATA SET: June’99 – July’01 (4.8×10 19 POT) DAT A  MCbeam e MCsignal e MC (CC) sin 2 2   e =1,  m 2 =2.8x10 -3 eV w/o decay-e FCFV Single ring PID (e-like) Evis>100Me V NC:87% CC1  :7% CCm  4% CCQE:2% electron candidate: 1 event (obs.) 2.4 events (exp.) 2.4 events (exp.)

10th ICEPP 23 Excluded region   → e ) sin 2 2   e  m 2 (eV 2 ) K2K(90%CL) CHOOZ(90%CL) e disappearance e disappearance SK atm. SK atm. allowed (90%CL)

Near Detector Upgrade

10th ICEPP 25 SciBar detector Spec. & analysis status will be presented by following talkers.  Upgrade near detector to explore low E region (after removal of LG) Fine segmented scintillator trackerFine segmented scintillator tracker Scintillator target & fully activeScintillator target & fully active ~ Working well !!

10th ICEPP 26 ProspectsProspects K2K-II is running stablyK2K-II is running stably ━ flux in low energy region by SciBar ━SciFI flux measurement using PID ━Improvement of Near/Far extrapolation (Harp) ━K2K events in SK-II New results of oscillation analysis come soon !

10th ICEPP 27 SummarySummary K2K-I data has been analyzed so far:K2K-I data has been analyzed so far: –  → x oscillation analysis Null oscillation prob: less than 1% Null oscillation prob: less than 1%  m 2 =1.5~3.9 x eV 2 2  =1(90%CL) (consistent w/ atm. )  m 2 =1.5~3.9 x eV 2 2  =1(90%CL) (consistent w/ atm. ) – e appearance search 1 e candidate (consistent with BG) 1 e candidate (consistent with BG) K2K-II running stablyK2K-II running stably –New near detector SciBar –Low energy neutrino –K2K events in SK-II –New results of oscillation analysis will come soon K2K-I data has been analyzed so far:K2K-I data has been analyzed so far: –  → x oscillation analysis Null oscillation prob: less than 1% Null oscillation prob: less than 1%  m 2 =1.5~3.9 x eV 2 2  =1(90%CL) (consistent w/ atm. )  m 2 =1.5~3.9 x eV 2 2  =1(90%CL) (consistent w/ atm. ) – e appearance search 1 e candidate (consistent with BG) 1 e candidate (consistent with BG) K2K-II running stablyK2K-II running stably –New near detector SciBar –Low energy neutrino –K2K events in SK-II –New results of oscillation analysis will come soon

supplementssupplements

10th ICEPP 29 Pion monitor Measure Momentum / Angle Dist. of π’s Just after Horn/Target +Well known π Decay Kinematics +Well Defined Decay Volume Geometry ⇒ Predict ν μ Energy Spectrum at Near Site Far Site ν μ Flux Ratio (Far/Near) as a Function of Neutrino Energy Ring Image Gas Cherenkov Detector (Index of Refraction is Changeable) To Avoid Severe Proton Beam Background, ν μ Energy Information above 1GeV is Available (β of 12GeV Proton ~ β of 2GeV π)

10th ICEPP 30 Muon monitor Behind beam dump  sensitive to initially high energy  (>5.5GeV) Provide fast (spill-by-spill) monitoring of Intensity  targeting/horn stability Profile  beam direction Segmented Ionization Chamber Silicon Pad Detector Array

10th ICEPP 31 Stability of Neutrino spectrum measurement by the Pion monitor Energy and angle of muons produced in the CC interactions by MRD

10th ICEPP 32 e candidate event e candidate event

10th ICEPP 33 Method of flux fitting (ND)  2 =227 for 197 d.o.f. (90 from 1kt, 137 from FGD) for fitted (p    ) dist. of 1KT and FGD (124 data points) 0 ~0.5 GeV 0.5 ~0.75GeV 0.75 ~1.0GeV E QE(MC) non-QE(MC) neutrino spectrum  (E ) and interaction model (QE/non-QE ratio). Fit the parameters. Measured (p    ) 7bins 8bins pp  pp  Prepare MC templates  (E ), QE/non-QE ratio …

10th ICEPP 34 Contribution of sys. errors on spectrum Total Spec.nQE/QESpec.+nQE/QE F/N  SK SK Escale