Current Status and Prospects of Approved Proton Decay Search Experiments

1. At the Workshop on “Large Detectors for Proton Decay, Supernovae and atmospheric neutrinos and low energy neutrinos from High Intensity Beams” January 16, 2002 Maury Goodman Argonne National Laboratory Soudan 2 // UNO Current Status and Prospects of Approved Proton Decay Search Experiments Maury Goodman – Argonne Lab Large Detector n workshop

2. A Drama in 5 acts Results in PDG book IMB Frejus Kamiokande NUSEX Soudan-1 KGF HPW More recent limits Soudan-2, Super-Kamiokande New limits Super-Kamiokande The discovery of nucleon decay Lessons learned from candidates Approved Experiments ICARUS-600, n telescopes Epilogue Nucleon Decay Maury Goodman – Argonne Lab Large Detector n workshop

3. Limits in the Particle Data Group RPP IMB-3 Kamioka NUSEX Frejus HPW Soudan 1 KGF Act I Maury Goodman – Argonne Lab Large Detector n workshop

4. Best Limits mostly IMB-3 (+Kamiokande) 2 limits from Super-Kamiokande Some high multiplicity and DB=2 & DB=-DL limits from Frejus More Super-Kamiokande and Soudan 2 limits in RPP-2002 (but that’s for Act II) Some inclusive limits from less sensitive experiments Older n Monte Carlos clearly overestimated the n background (oscillations not included) Tendency for ALL Monte Carlos to overestimate background ??? eB often dominated by nuclear effects, which depend on model and not detector. [Would be nice if these were reported separately as e = enuclearedetector] RPP-2000 limits Maury Goodman – Argonne Lab Large Detector n workshop

5. Detector type Exposure (kt-year) Frejus Fe 2.0 HPW H2O <1.0 IMB H2O 11.2 Kamiokande H2O 3.8 KGF Fe <1.0 NUSEX Fe <1.0 Soudan 1 Fe <1.0 Soudan 2 Fe 5.9 Super-Kamiokande H2O 79.3 Nucleon Decay Experiments Maury Goodman – Argonne Lab Large Detector n workshop

6. Limits depend on exposure, candidates and background Exposure is usually the most important [size  time] A Comparison Maury Goodman – Argonne Lab Large Detector n workshop

7. Recent Limits Soudan 2 p→nK+ Other “Super-symmetric” modes h modes High (>2) multiplicity events Super-Kamiokande p→e+p0 Other modes Act II Maury Goodman – Argonne Lab Large Detector n workshop

8. K+ stops at rest and emits 236 MeV/c m+ Requires a visible K (highly ionizing short track) Requires 157 < pm < 315 MeV/c Require a visible muon decay (e = 0.81) All efficiencies * B(K→mn) = 0.090 Also search for K+ →p+p0 (e*B = 0.055) In 5.91 kt-yr 1 candidate Backgrounds: 0.34 n, 0.31 rock t/B > 7.1 * 1031 yr without background subtraction Soudan 2 p→nK+ Maury Goodman – Argonne Lab Large Detector n workshop

9. Monte Carlo decay mode (including nuclear effects) Background from n Monte Carlo Background from “rock” events Examine data, combining appropriate topologies for each decay mode. Soudan 2 Method Maury Goodman – Argonne Lab Large Detector n workshop

10. Use Bigaussian in each pair of variables (a bit better than a box) Soudan 2PDK Analysis Maury Goodman – Argonne Lab Large Detector n workshop

11. K modes Maury Goodman – Argonne Lab Large Detector n workshop

12. P  Maury Goodman – Argonne Lab Large Detector n workshop

13. P  event Maury Goodman – Argonne Lab Large Detector n workshop

14. h modes Maury Goodman – Argonne Lab Large Detector n workshop

15. Great Vertex Resolution Multitrack nucleon decay events “spherical” BUT Fermi motion reduces sphericity Every (em or hadronic) shower has multiple vertices We could not maintain high efficiency with low background. Inclusive analysis of 3 & 4 prongs. For 4 prongs: e(N→l3p) =3.0 ±1.5% 0 candidates (4.56 kt-year) 0.3 background t/B > 6.0 1031 year SoudanMercedes Events Maury Goodman – Argonne Lab Large Detector n workshop

16. CUTS Contained events with >3 prongs 0.7 < Evis < 2.0 GeV pnet/Evis < 0.7 No visible proton No prompt, no-scattering track, L>150cm efficiency 17.5% nuclear efficiency not quite so low because we do not require seeing every p. tFE > 7.0 1031 years (tfree > 1.3 108 s) Background limited at 5.56 kt-years Soudan 2 neutron oscillation Maury Goodman – Argonne Lab Large Detector n workshop

17. p→e+p0 selections: 2 or 3 rings Electron like For 3 ring events, 85 MeV/c2 < mp0 < 185 MeV/c2 800 MeV/c2 < Mtotal < 1050 MeV/c2 Ptotal < 250 MeV/C Zero candidates t/B > 5.0 1033 year !!!!! Super-K p→e+p0 Maury Goodman – Argonne Lab Large Detector n workshop

18. New Limits Super-Kamiokande improved analysis for p →nK+ Act III Maury Goodman – Argonne Lab Large Detector n workshop

19. Require 6.3 MeV g from de-excitement of N15 g hits come before muon Triple coincidence of g, m, decay e For K→p+p0, compare “charge” in and out of a 40 degree cone opposite to direction of p0 Super-K p→nK+ Maury Goodman – Argonne Lab Large Detector n workshop

20. Super-K limits Maury Goodman – Argonne Lab Large Detector n workshop

21. Limits Maury Goodman – Argonne Lab Large Detector n workshop

22. The Discovery of Nucleon Decay(?!) “Seek, and ye shall find…” There have been interesting candidates from most detectors, some called signals at various times. Let’s review some of these “discoveries”. The goal is not to titillate, but to ask: What are the lessons? What would it take to “discover” nucleon decay? Act IV Maury Goodman – Argonne Lab Large Detector n workshop

23. IMB – many early candidates were neutron modes KGF – quoted lifetimes Low background candidates (at one time) Frejus e+r Kamiokande m+h Soudan 2 eppp IMB3 “peak” at 1 GeV Discovery/Candidates Maury Goodman – Argonne Lab Large Detector n workshop

24. 11 candidates Lifetime estimate 2.4 1031 years KGF Maury Goodman – Argonne Lab Large Detector n workshop

25. Candidate p→e+r0(→p+p-) Event 1378/460 Background estimate (<<10%) Presented as candidate at conferences Not published as a candidate (NC=0) Frejus Candidate Maury Goodman – Argonne Lab Large Detector n workshop

26. Two events in peak with pnet < 450 MeV Both candidates for ep0p0 Background 0.7 IMB3 peak Maury Goodman – Argonne Lab Large Detector n workshop

27. p→m+h Background < 0.08 (in the one mode) Candidate used to set a limit Well ruled out by Super-Kamiokande Kamiokande candidate Maury Goodman – Argonne Lab Large Detector n workshop

28. Candidate for eppp Evis = 1030 MeV, pnet = 330 Mev/c No background in MC Also could be mppp, emmp, mmmp The nuclear efficiency is quite low (3%). If really nulceon decay, expect multiprong excess. UPON FURTHER ANALYSIS Not a candidate as eppp kinematically mppp preferred (further from box) Background grew from ~0 to 0.3 Soudan 68882-746 Maury Goodman – Argonne Lab Large Detector n workshop

29. Can nucleon decay be discovered with one event? Probably not. But one event with sufficiently low background in an understood detector should be taken seriously iff: Some theoretical motivation for that mode Probability of background is low integrated over all modes studied. n background Monte Carlo matches n data. Other internal consistency checks pass No conflict with previous experiments. Discovery-1 Maury Goodman – Argonne Lab Large Detector n workshop

30. Can nucleon decay be discovered with two events? … All the same criteria apply, people will use their own “Bayesian prior.” Discovery-2 Maury Goodman – Argonne Lab Large Detector n workshop

31. “Bias” in analyzing data can work both ways. In the Soudan 2 nK+ analysis, we had one event which matched the kinematics very well. Upon close scrutiny, the muon track was found to be heavily ionizing and was called a proton (and removed from the sample). This would be reasonable if we HAD called this a signal. But such a-posteriori analysis causes some (hopefully small) immeasurable bias in the efficiency. Limits-1 Maury Goodman – Argonne Lab Large Detector n workshop

32. Compare: DONUT emulsion Discovery of nt. 4 events; [Background 0.41 ± 0.15] Near expected cross section NuTeV anomaly {Helium bag vertices} Neutralino or heavy lepton decay? 3 events; [Background <0.30] Assymetry doesn’t match decay idea Heidelberg 0nbb (Mod. Phys. Lett A16 2409-2420) 2002 8.3 events (after fit) [Background ~2.0] 3.1s PDG method Believing Low Statistics results? Maury Goodman – Argonne Lab Large Detector n workshop

33. Currently Operating Experiments ------------------------------------------------ Future Approved Experiments ICARUS (600 ton version) n telescopes (for monopole catalyzed nucleon decay) Act V Maury Goodman – Argonne Lab Large Detector n workshop

34. (please note - this list is in alphabetical order.) Currently Operating NDK experiments Maury Goodman – Argonne Lab Large Detector n workshop

35. ICARUS 600 ton detector will be operating next year in LNGS Capabilities of larger liquid argon detectors will be covered in other talks. The initial physics program of ICARUS is described at http://www.cern.ch/icarus/publications.html Great electron identification and other pattern recognition leads to very low backgrounds e+p0 has an efficiency of 37% with no background (1 Megaton year) Cuts: One p0, one e, Ep < 100 MeV, 0.93 < Etotal < 0.97 GeV [45% of p0 are absorbed] nK+ has an efficiency of 97% Cuts: One K, no p0 , no e’s, no m’s, no p±, Etotal < 0.8 GeV ICARUS Maury Goodman – Argonne Lab Large Detector n workshop

36. Value of running T600 With great background rejection, a new small detector can only improve on modes with large background. np+ is such a mode T600 will verify both the predicted background levels and the anticipated detector efficiencies. ICARUS Maury Goodman – Argonne Lab Large Detector n workshop

37. (My) Conclusion Super-Kamiokande has set a number of impressive limits on nucleon decay. I look forward to more analysis of other modes in Super-Kamiokande. Prospects for significant improvement in sensitivity in the short term is low. I look forward to new Large Detectors for Proton Decay, Supernovae and atmospheric neutrinos and low energy neutrinos from High Intensity Beams. epilogue Maury Goodman – Argonne Lab Large Detector n workshop