Yoshihisa OBAYASHI (KEK - IPNS) ne appearance search Yoshihisa OBAYASHI (KEK - IPNS) May 30, 2001 Yoshihisa OBAYASHI

nm to ne oscillation search Three Active Neutrino & Mass Degeneration Scenario (Dm212<<Dm213~Dm223) Present Limit: sin22q13>10-1@Dm2~3x10-3eV2 Obtained by CHOOZ (PALO VERDE) experiment Neutrino Beam is Essentially Pure nm (nm : ne~100:0.2@peak) Optimum neutrino energy: below 1GeV May 30, 2001 Yoshihisa OBAYASHI

Appearance Signal ne Q.E.ne C.C. interaction No hadron No recoiled proton ring Single electron shower Single Fussy Ring Cherenkov Angle ~ 42o En can be reconstructed e+- shower ne May 30, 2001 Yoshihisa OBAYASHI

BG(1): nm C.C. interaction Sharp Ring Edge Cherenkov Angle < 42o Good PID (atm. n study) Easy to reject nm m May 30, 2001 Yoshihisa OBAYASHI

n n p0→2g BG(2): N.C. p0 production 2 showers p0→2g Not Reproduce En If 2 rings overlap or A ring is too weak single ring like Not Reproduce En n n p0→2g 2 showers May 30, 2001 Yoshihisa OBAYASHI

ne selection SK Atmn official selection (single-ring e-like): Fully Contained (No Anti-counter Activity) Only one ring is reconstructed PID likelihood is e-like (Showering) Evis > 100MeV No Muon Decay Electron Dm2=3x10-3eV2, sin22qme=0.05 Number of events for JHF(0.77MW) 5yr exposure to Super-Kamiokande(22.5kt) nmC.C. nmN.C. Beam ne Osc’d ne Generated 10713.6 4080.3 292.1 301.6 1ring e-like 14.3 247.1 68.4 203.7 red. eff. 0.1% 6.1% 23.4% 67.5% We need to reject more! May 30, 2001 Yoshihisa OBAYASHI

Tight e/p0 separation Shower direction w.r.t. beam cosqne: g from p0 tend to have a forward peak Force to find 2nd ring and… E(g2)/E(g1+g2): Large for BG Likelihood diff. between 1-ring and 2-rings Invariant mass: Small for ne May 30, 2001 Yoshihisa OBAYASHI

Expected Backgrounds & Signal Dm2=3x10-3eV2, sin22qme=0.05 Number of events for JHF(0.77MW) 5yr exposure to Super-Kamiokande(22.5kt) nmC.C. nmN.C. Beam ne Osc’d ne Generated 10713.6 4080.3 292.1 301.6 1ring e-like 14.3 247.1 68.4 203.7 red. eff. 0.1% 6.1% 23.4% 67.5% e/p0 sep. 3.5 23.0 21.9 152.2 red.eff. 0.03% 0.6% 7.5% 50.4% .4<En<1.2 1.8 9.3 11.1 123.2 0.02% 0.2% 3.8% 40.8% May 30, 2001 Yoshihisa OBAYASHI

Expected Signal & BG distribution Reconstruct En as Quasi-Elastic interaction Apply Energy Cut 0.4GeV< E <1.2GeV (OAB2o) OAB2o 5year May 30, 2001 Yoshihisa OBAYASHI

Sensitivity for Mixing Angle sin22qme sensitivity May 30, 2001 Yoshihisa OBAYASHI

Sensitivities Sensitive down to sin22qme~3x10-3 @Dm2=3x10-3eV2 By tuning En, sensitive down to sin22qme~5x10-3 in all allowed Dm2atm sin22q13~1x10-2 @90% C.L. May 30, 2001 Yoshihisa OBAYASHI

Comparison to Other Projects MINOS: High En ntCC→t→e may be a serious BG OPERA(,ICARUS) Tuned to find nt appearance More high En Small Far Detector JHF neutrino has highest sensitivity in ne appearance search May 30, 2001 Yoshihisa OBAYASHI

Summary ~1 GeV neutrino beam + SK(Water Cherenkov) is a good solution to search: 0.01 < sin22q13 < 0.1 @ Dm2atm. Expected sensitivity: sin22q13~ 0.01 @ 90%C.L. ne appearance sensitivity of JHFnu+SK is higher than MINOS, OPERA. May 30, 2001 Yoshihisa OBAYASHI