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Search for Nucleon decays

Search for Nucleon decays. M.Miura Kamioka Observatory, ICRR BLV 2011, Gatlinburg. Contents. Introduction Super-Kamiokande detector p -> e + + p 0 , m + + p 0 mode p -> K + + n mode Other modes Summary. 1. Introduction. Nucleon decay experiment is the direct probe for GUTs.

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Search for Nucleon decays

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  1. Searchfor Nucleon decays M.Miura Kamioka Observatory, ICRR BLV 2011, Gatlinburg

  2. Contents • Introduction • Super-Kamiokande detector • p -> e++p0 , m++p0 mode • p -> K++n mode • Other modes • Summary

  3. 1. Introduction • Nucleon decay experiment is the direct probe for GUTs. • p e+p0 (non-SUSY GUTs), p nK+ (SUSY-GUTs) are regarded as the dominant mode. • Need large number of nucleons  Need large detectors. • Super-Kamiokande data: • 22.5kton = 7 x 1033 protons x 10 years run •  Good detector to investigate nucleon decay ! - ~ m u X u ~ nc e+ u ~ u f3 W sc d p u dc ~ p c K+ p0 d d SUSY SU(5) model Minimal SU(5) model

  4. Current Nucleon lifetime limits pe+p0 pm+p0 Main topics in this talk - pnK+

  5. Nucleon Decay Experiment 2. Super-Kamiokande Detector Location: Kamioka mine, Japan. ~1000 m under ground. Size: 39 m (diameter) x 42 m (height), 50kton water. Optically separated into inner detector (ID) and outer detector (OD, ~2.5 m layer from tank wall.) Photo device: 20 inch PMT (ID), 8 inch PMT (OD, veto cosmic rays). Mom. resolution: 3.0 % for e 1 GeV/c (4.1%: SK-2). Particle ID: Separate into EM shower type (e-like) and muon type (m-like) by Cherenkov ring angle and ring pattern. m-like (m) e-like (e, g)

  6. History of Super-Kamiokande reconstruction electronics upgrade Accident • SK-1 • Livetime: • - 1489.2 days • Exposure: • - 91.7 kton·yr • Inner PMT: 11146 • Photo coverage: • 40 % • SK-2 • Livetime: • - 798.6 days • Exposure: • - 49.2 kton·yr • Inner PMT:5182 • Photo coverage: • 19 % SK-3 Live time: 518 days Exposure: 31.9kton・yr ID PMT:11146 Photo coverage: 40 % SK-4 (~11’Mar 1) Live Time: 763 days Exposure: 46.5kton・yr Same e+p0 paper 2007: > 8.2x1033 years (141kton・year) nK+ paper 2005: > 2.3x1033 years (92kton・year) This talk: 220 kton・year exposure in total

  7. MC simulations Proton decay MC <= Efficiency 8bounded protons in O: Fermi momentum, binding energy, various nuclear effects are taken into account. 2 free protons:simple two body decay. Atmospheric n MC <= BKG for proton decay Flux : Primary cosmic rays make nm and ne. M.Honda et .al., Phys.Rev. D75 043006(2007) n interaction: NEUT Y.Hayato, Nucl.Phys.Proc.Suppl. 112,171(2002)

  8. 3. pe+p0 ,m+p0 mode g • Event features; • e+ ,m+and p0are back-to-back (459 MeV/c) • p02gs : all particles can be detectable. •  Reconstruct proton mass and momentum. P p0 g e+or m+ • Selection; • Fully contained, VTX in fiducail volume. • 2 or 3 ring • e+p0 case; • all e-like, w/o decay-e. Selected by simple cuts! • m+p0 case; • one m-like with decay-e. • 85 < Mp0 < 185 MeV (for 3-ring event) . • 800 < MP < 1050 MeV & Ptot < 250 MeV/c

  9. Open data: Mtot vs Ptot Blue: PDK MC Green: ATMn MC Red: Data Mtot pe+p0 Total momentum (MeV/c) pm+p0 No candidate observed.

  10. Results of p->e+p0, m+p0 Note 1: In SK2, photo coverage was a half of other periods, but efficiency was almost same. Note 2: In SK4, new electronics was installed and Michel electron tagging was improved. As a result, the efficiency of m+p0 in SK4 was increased. Lifetime limit (90%C.L,) pe+p0: 1.3x1034 years, pm+p0: 1.1x1034 years

  11. - 4. pn + K+ mode A) K+ -> m++nm • Event features; • K+ is invisible, stops and 2 body decay (Pm = 236 MeV/c). •  Excess in Pm. • Proton in 16O decays and excited nucleus emits 6 MeV g (Prob. 41%, not clear ring). • => Tag g to eliminate BKG. visible ne g 6.3MeV invisible e+ 16O->15N nm m+ K+ nm • Selection: • 1 m-like ring with decay-e. • 215 < Pm < 260 MeV/c • Search Max hit cluster by sliding time window (12ns width); • - 8 < Ng < 60 hits for SK-1,3,4 • 4 < Ng < 30 hits for SK-2 • & • - Tm-Tg < 75 nsec n Tm(dN/dt=max) Hits m e g t 12ns window Tstart

  12. Open data Black: Data Red: ATM MC Blue: PDK MC Ng (except SK2) Black: Data Red: ATM MC Blue: PDK MC No candidates and no excess in Pm.

  13. B) K+ -> p++p0 • Event features; • Br. 21 %. • p0and p+ are back-to-back and have 205 MeV/c. • Pp+ is just above Č thres. • (not clear ring). ne nm p+ Eres e+ visible K+ Ebk invisible m+ nm g => Search for monochromatic p0 with backward activities. p0 205 MeV/c g Black: Data (w/o dcy-e cut) Red: Atm. MC • Selection: • 2 e-like rings with decay-e. • 85 < Mp0 < 185 MeV. • 175 < Pp0 < 250 MeV/c. • Ebk: visible energy sum in 140-180 deg. of • p0 dir, • Eres: in 90-140 deg. • 7< Ebk < 17 MeV & Eres < 12 MeV Mp0 Pp0

  14. Open data No candidates. Ebk vs Eres Blue: PDK MC Red: ATM MC Black: Data Black: Data Red: ATM MC Blue: PDK MC Ebk - p nK+Combined lifetime limit (90% CL): > 4.0 x1033 yrs @219.7 ktont・yr

  15. 5. Other modes B-L conserving mode Nucleon => lepton + meson (using 141 kt・year data) p0 h r0 w p e+ m+ + n p- r- • Consistent with BKG for all modes. • Most of them give the most stringent limits in the world.

  16. B-L violating mode • ne-K+ Search for e (330 MeV/c) and m (236 MeV/c) with time difference. ne e+ Data: SK1~SK2, 141 kton・year Eff.: 11 % for SK1, 8.4 % for SK2 BKG: 0.3 events OBS: 1 event Lifetime limit: > 0.99x1033 years e- n nm m+ K+: t=12ns nm • - K+ can be seen (~800 MeV/c). • Distance of Vertices of K+ decay: • ~2.6 m • -Use Boosted Decision Tree technique. • ppK+K+(DB=2) m+ p+ K+ K+ g Data: SK1, 91.6 kton・year Eff.: 12.6% BKG: 0.3 events OBS: 0 event Lifetime limit: > 1.7x1032 years (p0) g nm

  17. 6. Summary • Fruitful nucleon decay results from Super-Kamiokande. • We could not find any evidences of nucleon decay. • We calculated nucleon lifetime limits with 90 % C.L. p e+p0: > 1.3x1034 yrs m+p0: > 1.1x1034 yrs nK+: > 4.0x1033 yrs • Other mode both (B-L) conserving and violating modes are also studied. -

  18. Future prospects pe+p0 • Need larger volume detector (Megaton class). Ex. Hyper-Kamiokande project (fiducail volume 0.56 Mton, 20 % photo coverage) • Sensitivity with HK 10 years run; e+p0: 1.3x1035 year nK+: 2.5x1034 year  Cover most of major models! - pnK+ - Letter of Intent: Hyper-Kaiokande Experiment arXiv:1109.3262 [hep-ex]

  19. Backup

  20. Q. What are BKG for e+p0 mode ? n+N -> lepton+N*; N*->N’+meson ne CC case, e and p±, p0 are out-going particles. n+N -> lepton+P ne case, e and P are out-going particles and P interacts in water and make secondary p0. Background rate: 1.6±0.4 events/Mton・year by MC Estimationfrom 1kt water detector by using K2K n beam (~10Mton・year equivalent) Phys.Rev.D77,032003(2008) Agree well !

  21. Systematic error for e+p0 (Efficiency)

  22. Q. What are BKG for nK+ mode ? K+->n+m K+->p++p0 n+N -> lepton+N*; N*->N’+meson: 44% n+N -> lepton+N*; N*->N’+meson: 63% Resonance N* decays into K+. • Resonance N* decays into K+. • N* decays into p0 and charged lepton goes backward of p0. n+N -> charged lepton+P: 17 % Low P lepton, High P proton => VTX mis-reconstructed

  23. Detail of ne-K+ ne • Selection: • FCFV 2R, e+m with decay-e • 250< Pe< 400 MeV/c, • 200< Pm < 280 MeV/c, • Tm-Te > 6 nsec e+ e- n nm m+ K+: t=12ns nm

  24. Detail of ppK+ K+ m+ p+ K+ K+ g (p0) Distance between K+ decay points g nm BDT output K+ momentum

  25. nn oscillation in SK - • Exposure: 24.5x1033 neutrons・years (SK-1 data only) • No evidence. • Oscillation time for free neutron: 2.44x108 sec (theoretical suppression factor: 1.0x1023 sec-1) arXiv:1109.4227

  26. Schematic view of the HK detector

  27. Discovery potential with 3s; pe+p0: 5.7x1034 years pnK+: 1.0x1034 years Sensitivity with 90 % C.L: pe+p0: 1.3x1035 years pnK+: 2.5x1034 years p e+p0

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