1. TAUP2007 1 Searches for nucleon decay and n-n oscillation in Super-Kamiokande Jun Kameda (ICRR, Univ. of Tokyo) for Super-Kamiokande collaboration Sep. 14 th, 2007 TAUP 2007, Sendai, Japan

2. TAUP2007 2 Outline  Introduction of the Super-Kamiokande  Searches for Nucleon decay (p  e + + 0, p     0 )  Search for Neutron-antineutron oscillation  Summary

3. TAUP2007 3 Super-Kamiokande Water Cherenkov detector 50kton (22.5 kton fid.), = 6.02x10 33 neutrons + 7.53x10 33 protons Deep underground (1000m, 2700 m.w.e), Kamioka-mine, Japan. SK-I : 91.6ktyr (Apr.1996-Jul.2001) SK-II: 49.5ktyr (Dec.2002-Oct.2005) SK-III had started from Jul.2006. 39.3m 41.4m SK-I ID 11146 20inch PMTs OD 1885 8-inch PMTs SK-II ID 5182 20inch PMTs Data period: Super-Kamioka Nucleon Decay Experiment 5 countries, 35 institutes ~120 physicist

4. TAUP2007 4 Nucleon decay Searches in Super-Kamiokande  Nucleon decay is the direct evidence of the Grand Unification Theories (GUTs).  Several GUTs predicts several decay modes. (p  e +  0,    0, K +,..)  No positive signal had been observed. Experimental Lifetime lower limits (yr)

5. TAUP2007 5 Nucleon decay (I) p  e + +  0  All visible particles contained  2 or 3 Cherenkov rings  All rings are e-like  no decay electron  85 < M[MeV/c 2 ] <185 (for 3ring)  800 < M tot [MeV/c 2 ] < 1050 & P tot [MeV/c] < 250 Event selection: Efficiency : Super-K I 45.0% (was 42.9%) Super-K II 43.6% (was 42.2%) Improved efficiencies are due to an improved algorithm of separation of the overlapping Cherenkov rings.

6. TAUP2007 6 Total P vs Invariant Mass plots p  e + +  0 SK-I p  e + + 0 MC SK-II No signal was observed in SK-I & SK-II. atm MC Data Eff. 45.0%0.4 event0 event Eff. 43.6%0.04 event0 event 1489.2 days Invariant Mass (MeV/c2) Total P(MeV/c) 798.6 days

7. TAUP2007 7 No Candidate was observed. Estimated B.G. ( osc. considered) SK-I: 0.4, SK-II: 0.04  P /B e  0 > 5.5 x 10 33 years (90 % C.L.) (SK-I)  P /B e  0 > 2.9 x 10 33 years (90 % C.L.) (SK-II) Result of the search for p  e + +  0 (preliminary)  P /B e  0 > 8.4 x 10 33 years (90 % C.L) (SK-I + SK-II)

8. TAUP2007 8 Nucleon decay (II) p   + +  0  All visible particles contained  2 or 3 Cherenkov rings  1 -like  1 decay electron  85 < M[MeV/c 2 ] <185 (for 3ring)  800 < Mtot [MeV/c 2 ] < 1050 & Ptot [MeV/c] < 250 Event selection: Efficiency : Super-K I 35.6% (was 30.6%) Super-K II 35.5% (was 32.1%) ++

9. TAUP2007 9 Result of p   + +  0 (preliminary) SK-I p   + + 0 MC SK-II atm MC Data Eff. 35.6%0.4 event0 event Eff. 35.5%0.2 event0 event 1489.2 days Total P(MeV/c) 798.6 days  P /B e  0 > 4.4 x 10 33 yrs (90 % C.L.) (SK-I)  P /B e  0 > 2.3 x 10 33 yrs (90 % C.L.) (SK-II) No candidates. Invariant Mass(MeV/c 2 )   P /B e  0 > 6.7 x 10 33 years (SK-I + SK-II, 90 % C.L)

10. TAUP2007 10 Summary of nucleon decay search  No positive signals have been observed in any mode.  Obtained lifetime limits: p  e + + 0 : /B > 8.4 x10 33 yr (SK-I+SK-II, preliminary) p   + + 0 : /B > 6.7 x10 33 yr (SK-I +SK-II, preliminary) p +K + : /B > 2.3 x10 33 yr (SK-I), PRD 72, 052007 (2005),  Many other modes (B-L violating modes, etc.) have been searched for in Super-K.

11. TAUP2007 11 Search for neutron - anti-neutron oscillation in Oxygen in Super-K I  Several type of (B-L)-violating Gauge theories predicts that neutron spontaneously converts to anti-neutron, and vise versa. (ex. K.S.Babu et al., Phys.Lett.B518(2001) 269-275)  |  B| =2 process. Good test for new physics including GUTs.

12. TAUP2007 12 Expected signals in Water Cherenkov detector  Anti-neutrons quickly pair-annihilates with the surrounding nucleon. Pions ( ~4 ) of several 100MeV/c’s are emitted isotropically, and propagate inside the nuclein                                                                                        anti-n + p anti-n + n n p n p n p      About 2 x nucleon mass energy will be released in the residual nuclei. Branching ratio derived from Bubble Chamber p + d data

13. TAUP2007 13 Typical Event (anti-n+p          ) Multi-Cherenkov ring events are expected. n-nbar MC             Many pions and their secondaries + low energy nuclear fragments

14. TAUP2007 14 0) all visible particles contained a) #of rings >= 2 b) 700< visible energy (MeV) <1300 c) 0< Ptot (MeV/c) <450 d) 750< Mtot (MeV/c 2 ) <1800 # of rings Visible Energy(MeV) Total Momentum (MeV/c) Invariant Mass (MeV/c 2 ) Invariant Mass is smaller than 2xnucleon due to  absorption in &  interaction in nuclear & water Event Selection  10.4% efficiency

15. TAUP2007 15 10.4 % detection efficiency 20 candidates 21.3 background events (osc. effects are included) n-n MC Results of n-n oscillation = 1.77×10 32 yrs ( 90% CL ) (SK-1) (systematic errors are included by Baysian statistics) atm. MC SK-I data Not a spontaneous decay of neutron, but we call the inverse of the event rate is the “ lifetime ” of the neutron in Oxygen. Ptot (MeV/c) Inv. Mass (MeV/c 2 )

16. TAUP2007 16 Systematic uncertainties Possible sources of the systematic uncertainty in experimental and modeling (Pion interactions, n+anti-n annihilation, etc.) are investigated.  -nucleon scattering in nuclear (cross sections, modeling of nuclear, etc) 12.6 % nbar+N Annihilation branching ratio 5.2 % Fermi motion of nucleons 4.2 % Energy scale 1.7 % Asymmetry of gain 4.0 % Cherenkov ring finding 0.6 % Fid.Vol. determination 3.2% Total 15.2% Detection efficiency & Exposure atmospheric flux (flavor ratio, zenith angle dist., spectrum, absolute norm, etc.) 21.5% Neutrino interactions (absolute cross section uncertainties, differential  uncertainties, etc.) 17.8%  -propagations in 16 O (cross sections, 16 O modelings,etc) 2.7% Energy scale 12.0% Asymmetry of gain 9.0 % Cherenkov ring finding 4.3 % Total32.1% B.G rate

17. TAUP2007 17 Comparison with other experimental limits ExperimentSourc e Exposu re(n yr) T bound (10 32 yr)  free (10 8 sec) ILLBeam --- 0.86 Soudan2 56 Fe21.9 0.72 1.3 Frejus 56 Fe 5.0 0.65 1.2 Kamiokande 16 O 3.0 0.43 1.2 IMB 16 O3.0 0.24 0.88 Super-K I 16 O254.5 1.772.36 R (10 23 sec -1 ) --- 1.4 1.0 1.0* Super-K I results includes systematic uncertainty. Bound neutron lifetime can be interpreted to the oscillation time of the free neutron by T bound = R*( free ) 2 * C.B.Dover et al. Phys. Rev. D 27 (1983) 1090

18. TAUP2007 18 Summary  Nucleon decay searches and neutron-antineutron oscillation are reported.  No evidence of nucleon decay, no evidence of n- n oscillation were found. p  e + + 0 : /B > 8.4 x10 33 yr (SK-I+SK-II, preliminary) p   + + 0 : /B > 6.7 x10 33 yr (SK-I +SK-II, preliminary) n-n oscillation:  bound > 1.77x10 32 yr (SK-I, preliminary)  free > 2.36x10 8 sec