Recent Nucleon Decay Results from Super-Kamiokande

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1 Recent Nucleon Decay Results from Super-Kamiokande Jennifer L. Raaf Boston University April 14, 28 Motivation Super-Kamiokande n ν π decay search Results

2 Motivation Interesting candidate for grand unification: SUSY SO(1) model with B-L violation (by 126 Higgs field) predicts all neutrino mixings and ratio of experimental observations H.S.Goh, R.N.Mohapatra, S.Nasri, S-P. Ng, Phys Lett B587: (24) m 2 / m 2 atmos automatic R-parity conservation stable dark matter in agreement with prediction of upper limits on some proton decay modes requires some fine-tuning to make compatible with current experimental limits Model can be directly tested by searching for predicted modes! Imagine a beautiful Adobe Illustrator image here... J.L.Raaf, Boston University 2

3 Super-Kamiokande Gifu prefecture, Japan, Kamioka-Mozumi zinc mine 1 meters (27 meters-water-equivalent) beneath peak of Mt. Ikeno Water Cherenkov detector 5 ktons (22.5 ktons fiducial) ultra-pure water 7.5 x 1 33 protons 6. x 1 33 neutrons Instrumented with photomultiplier tubes (PMTs) cm PMTs in inner region cm PMTs in outer region SK-1, SK-2, and beyond... SK-1: % photocathode coverage SK-2: Jan 23 - Oct 25 Recovery from accident, 2% photocathode coverage SK-3: May 26 - present Restore 4% coverage SK-4: Replace DAQ electronics, Autumn 28 J.L.Raaf, Boston University 3

4 Identifying particle types in Super-K Super-Kamiokande I Run Sub Ev ::12:25 Inner: 3166 hits, 6293 pe Outer: hits, pe (in-time) Trigger ID: x3 D wall: 124. cm Fully-Contained Mode Charge(pe) > <.2 Simulated p μ + π event 2 rings π γ γ 1 ring μ subevt Cherenkov ring ID muon-like = crisp edge electron-like = fuzzy edge Outer detector (OD) activity clusters of hits in the OD may indicate event due to cosmic ray Decay electron count look for electron from muon decay in delayed coincidence with muon ring 26 1 dot = 1 PMT larger dot = more light collected Times (ns) J.L.Raaf, Boston University 4

5 Nucleon decay: n ν π Mono-energetic π from n ν π decay (signal) would sit atop a large background of π s from atmospheric neutrino interactions in Super-K. n ν π (signal) Single π event selection: Fully contained in the fiducial volume (no activity in outer detector) 2 electron-like rings No decay electrons Reconstructed mπ MeV/c 2 Atmospheric ν (background) J.L.Raaf, Boston University 5

6 χ 2 = nbins i=1 n ν π Fitting Method Minimize χ 2 with systematic pull terms to find best fit parameters (α,β): ( ( )) Ni obs N exp i 1 + N 2 syserr j=1 f j i ε ) j 2 σ 2 i + N syserr j=1 ( ε j σ j where N exp i = α N ν i + β N NDK i Atmospheric ν (background) n ν π (signal) Systematic error pull terms π absorption scattering charge exchange detection efficiency J.L.Raaf, Boston University 6

7 SK-1 n ν π Results χ 2 /DOF Unphysical fit Physical fit 3.9/8 4.1/8 Fit prefers unphysical NDK: -7.5 events 9% CL allowed: 15.6 events Corresponding 9% CL lifetime lower limit: > 7.6 x 1 32 years J.L.Raaf, Boston University 7

8 SK-2 n ν π Results Unphysical fit Physical fit χ 2 /DOF 6.41/8 6.43/8 Fit prefers unphysical NDK: -2.5 events 9% CL allowed: 11.7 events Corresponding 9% CL lifetime lower limit: > 5. x 1 32 years J.L.Raaf, Boston University 8

9 SK-1 + SK-2 n ν π Results Unphysical fit Physical fit χ 2 /DOF 9.9/18 1.2/18 Fit prefers unphysical NDK: -5. events 9% CL allowed: 2.2 events Corresponding 9% CL lifetime lower limit: > 8.8 x 1 32 years J.L.Raaf, Boston University 9

10 Conclusions Fitting via χ 2 with systematic pull terms allows Super-K to set a lower limit on the decay mode n ν π : SK-1+2 result: τ B.R. > years Previous best experimental limit by IMB: τ B.R. > years New Super-K limit begins to constrain SO(1) GUTs! Imagine another Adobe Illustrator image here... J.L.Raaf, Boston University 1

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12 Nucleon Decay Standard Model (SM) Represented by product of symmetry groups SU(3) x SU(2) x U(1) Local gauge symmetries responsible for forces that mediate EM, weak, and strong interactions Finite but unobservably long proton lifetime due to baryon number (B) conservation Introduced empirically! Other conserved quantities (e.g., electrical charge) result from gauge symmetries Grand Unified Theories (GUTs) Motivated partly by desire to constrain quantities that are seemingly arbitrary in SM Attempt to unify the 3 fundamental interactions: coupling constants that describe strong, weak, and EM forces unified at large energies fundamental forces are low energy manifestations of a single unified force e.g., MSSM Many GUTs result in proton lifetime ranges accessible to current experiments J.L.Raaf, Boston University 12

13 Super-Kamiokande Run Sub Ev ::6:33 Inner: 3594 hits, 9239 pe Outer: 1 hits, 1 pe (in-time) Trigger ID: x3 D wall: cm Fully-Contained Mode Decay mode: p e + π 1.9 Charge(pe) > <.2 Simulated event 2 rings π γ γ 1 ring e Detection efficiency SK-I SK-II nring e-like decay e! mass m p p p Selection criterion Times (ns) Selection Criteria 3 e-like rings (1 from e +, 1 or 2 from π decay) no decay electrons 85 < mπ < 185 MeV/c 2 (3-ring events only) < pp < 25 MeV/c 8 < mp < 15 MeV/c 2 Efficiency (%) SK SK J.L.Raaf, Boston University 13

14 Event Signatures Super-Kamiokande Run Sub Ev ::6:33 Inner: 3594 hits, 9239 pe Outer: 1 hits, 1 pe (in-time) Trigger ID: x3 D wall: cm Fully-Contained Mode Charge(pe) > <.2 Simulated p e + π event 2 rings π γ γ 1 ring e + Super-Kamiokande I Run Sub Ev ::12:25 Inner: 3166 hits, 6293 pe Outer: hits, pe (in-time) Trigger ID: x3 D wall: 124. cm Fully-Contained Mode Charge(pe) > <.2 Simulated p μ + π event 2 rings π γ γ 1 ring μ subevt e + π selection 2 or 3 e-like rings (1 from e +, 1 or 2 from π decay) no decay electrons 85 < mπ < 185 MeV/c 2 (for 3-ring events only) pp < 25 MeV/c 8 < mp < 15 MeV/c Times (ns) μ + π selection 2 or 3 rings, 1 μ-like (1 from μ +, 1 or 2 from π decay) 1 decay electron 85 < mπ < 185 MeV/c 2 (for 3-ring events only) pp < 25 MeV/c 8 < mp < 15 MeV/c Times (ns) J.L.Raaf, Boston University 14

15 Decay mode: p e+ π SK-I atmospheric! Proton mass (MeV/c ) 1 12 SK-I data 1 Proton momentum (MeV/c) 8 SK-I e+! 1 Proton momentum (MeV/c) Proton momentum (MeV/c) 1 Proton mass (MeV/c ) Proton mass (MeV/c2).9 Detection efficiency SK-I SK-II.1 nring e-like decay e! mass mppp Selection criterion J.L.Raaf, Boston University 15