NNN02 16 January, 2002 CERN Maury Goodman – Argonne Lab Large Detector workshop Current Status and Prospects of Approved Proton Decay Search Experiments 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

NNN02 16 January, 2002 CERN Maury Goodman – Argonne Lab Large Detector workshop Nucleon Decay A Drama in 5 acts I. Results in PDG book  IMB Frejus Kamiokande NUSEX Soudan-1 KGF HPW II. More recent limits  Soudan-2, Super-Kamiokande III. New limits  Super-Kamiokande IV. The discovery of nucleon decay  Lessons learned from candidates V. Approved Experiments  ICARUS-600, telescopes Epilogue

NNN02 16 January, 2002 CERN Maury Goodman – Argonne Lab Large Detector workshop Act I Limits in the Particle Data Group RPP  IMB-3  Kamioka  NUSEX  Frejus  HPW  Soudan 1  KGF

NNN02 16 January, 2002 CERN Maury Goodman – Argonne Lab Large Detector workshop RPP-2000 limits  Best Limits mostly IMB-3 (+Kamiokande)  2 limits from Super-Kamiokande  Some high multiplicity and  B=2 &  B=-  L 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 Monte Carlos clearly overestimated the background (oscillations not included)  Tendency for ALL Monte Carlos to overestimate background ???   B often dominated by nuclear effects, which depend on model and not detector. [Would be nice if these were reported separately as  =  nuclear  detector ]

NNN02 16 January, 2002 CERN Maury Goodman – Argonne Lab Large Detector workshop Nucleon Decay Experiments Detector type Exposure (kt-year) Frejus Fe 2.0 HPW H 2 O <1.0 IMB H 2 O 11.2 Kamiokande H 2 O 3.8 KGF Fe <1.0 NUSEX Fe <1.0 Soudan 1 Fe <1.0 Soudan 2 Fe 5.9 Super-Kamiokande H 2 O 79.3

NNN02 16 January, 2002 CERN Maury Goodman – Argonne Lab Large Detector workshop A Comparison  Limits depend on exposure, candidates and background  Exposure is usually the most important [size  time]

NNN02 16 January, 2002 CERN Maury Goodman – Argonne Lab Large Detector workshop Act II Recent Limits  Soudan 2  p→ K +  Other “Super-symmetric” modes   modes  High (>2) multiplicity events  Super-Kamiokande  p→e +  0  Other modes

NNN02 16 January, 2002 CERN Maury Goodman – Argonne Lab Large Detector workshop Soudan 2 p→ K +  K + stops at rest and emits 236 MeV/c  +  Requires a visible K (highly ionizing short track)  Requires 157 < p  < 315 MeV/c  Require a visible muon decay (  = 0.81)  All efficiencies * B(K→  ) =  Also search for K + →     (  *B = 0.055)  In 5.91 kt-yr  1 candidate  Backgrounds: 0.34, 0.31 rock   /B > 7.1 * yr without background subtraction

NNN02 16 January, 2002 CERN Maury Goodman – Argonne Lab Large Detector workshop Soudan 2 Method  Monte Carlo decay mode (including nuclear effects)  Background from Monte Carlo  Background from “rock” events  Examine data, combining appropriate topologies for each decay mode.

NNN02 16 January, 2002 CERN Maury Goodman – Argonne Lab Large Detector workshop Soudan 2 PDK Analysis  Use Bigaussian in each pair of variables (a bit better than a box)

NNN02 16 January, 2002 CERN Maury Goodman – Argonne Lab Large Detector workshop K modes

NNN02 16 January, 2002 CERN Maury Goodman – Argonne Lab Large Detector workshop P   

NNN02 16 January, 2002 CERN Maury Goodman – Argonne Lab Large Detector workshop P    event

NNN02 16 January, 2002 CERN Maury Goodman – Argonne Lab Large Detector workshop  modes

NNN02 16 January, 2002 CERN Maury Goodman – Argonne Lab Large Detector workshop Soudan Mercedes Events 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:  (N→ l  3  =3.0 ±1.5% 0 candidates (4.56 kt-year) 0.3 background  /B > year

NNN02 16 January, 2002 CERN Maury Goodman – Argonne Lab Large Detector workshop Soudan 2 neutron oscillation CUTS  Contained events with >3 prongs  0.7 < E vis < 2.0 GeV  p net /E vis < 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 .   FE > years (  free > s)  Background limited at 5.56 kt-years

NNN02 16 January, 2002 CERN Maury Goodman – Argonne Lab Large Detector workshop Super-K p→e +  0  p→e +  0 selections:  2 or 3 rings  Electron like  For 3 ring events, 85 MeV/c 2 < m  0 < 185 MeV/c 2  800 MeV/c 2 < M total < 1050 MeV/c 2  P total < 250 MeV/C  Zero candidates   /B > year  !!!!!

NNN02 16 January, 2002 CERN Maury Goodman – Argonne Lab Large Detector workshop Act III New Limits  Super-Kamiokande improved analysis for p → K +

NNN02 16 January, 2002 CERN Maury Goodman – Argonne Lab Large Detector workshop Super-K p→ K +  Require 6.3 MeV  from de-excitement of N 15   hits come before muon  Triple coincidence of , decay e  For K→      compare “charge” in and out of a 40 degree cone opposite to direction of  0

NNN02 16 January, 2002 CERN Maury Goodman – Argonne Lab Large Detector workshop Super-K limits

NNN02 16 January, 2002 CERN Maury Goodman – Argonne Lab Large Detector workshop Limits

NNN02 16 January, 2002 CERN Maury Goodman – Argonne Lab Large Detector workshop Act IV 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: 1. What are the lessons? 2. What would it take to “discover” nucleon decay?

NNN02 16 January, 2002 CERN Maury Goodman – Argonne Lab Large Detector workshop Discovery /Candidates  IMB – many early candidates were neutron modes  KGF – quoted lifetimes  Low background candidates (at one time)  Frejus e +   Kamiokande     Soudan 2 e    “peak” at 1 GeV

NNN02 16 January, 2002 CERN Maury Goodman – Argonne Lab Large Detector workshop KGF  11 candidates  Lifetime estimate years

NNN02 16 January, 2002 CERN Maury Goodman – Argonne Lab Large Detector workshop Frejus Candidate  Candidate p→e +  0  →       Event 1378/460  Background estimate (<<10%)  Presented as candidate at conferences  Not published as a candidate (N C =0)

NNN02 16 January, 2002 CERN Maury Goodman – Argonne Lab Large Detector workshop IMB3 peak  Two events in peak with p net < 450 MeV  Both candidates for e    0  Background 0.7

NNN02 16 January, 2002 CERN Maury Goodman – Argonne Lab Large Detector workshop Kamiokande candidate  p→     Background < 0.08 (in the one mode)  Candidate used to set a limit  Well ruled out by Super- Kamiokande

NNN02 16 January, 2002 CERN Maury Goodman – Argonne Lab Large Detector workshop Soudan  Candidate for e   E vis = 1030 MeV, p net = 330 Mev/c  No background in MC  Also could be , e   The nuclear efficiency is quite low (3%).  If really nulceon decay, expect multiprong excess. UPON FURTHER ANALYSIS  Not a candidate as e  kinematically   preferred (further from box)  Background grew from ~0 to 0.3

NNN02 16 January, 2002 CERN Maury Goodman – Argonne Lab Large Detector workshop Discovery-1 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.   background Monte Carlo matches data.  Other internal consistency checks pass  No conflict with previous experiments.

NNN02 16 January, 2002 CERN Maury Goodman – Argonne Lab Large Detector workshop Discovery-2  Can nucleon decay be discovered with two events?  …  All the same criteria apply, people will use their own “Bayesian prior.”

NNN02 16 January, 2002 CERN Maury Goodman – Argonne Lab Large Detector workshop Limits-1 “Bias” in analyzing data can work both ways. In the Soudan 2 K+ 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.

NNN02 16 January, 2002 CERN Maury Goodman – Argonne Lab Large Detector workshop Believing Low Statistics results? Compare:  DONUT emulsion  Discovery of .  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 0    Mod. Phys. Lett A ) 2002   events (after fit) [Background ~2.0]  3.1  PDG method

NNN02 16 January, 2002 CERN Maury Goodman – Argonne Lab Large Detector workshop Act V Currently Operating Experiments Future Approved Experiments  ICARUS (600 ton version)  telescopes (for monopole catalyzed nucleon decay)

NNN02 16 January, 2002 CERN Maury Goodman – Argonne Lab Large Detector workshop Currently Operating NDK experiments (please note - this list is in alphabetical order.)

NNN02 16 January, 2002 CERN Maury Goodman – Argonne Lab Large Detector workshop ICARUS  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  Great electron identification and other pattern recognition leads to very low backgrounds  e +  0 has an efficiency of 37% with no background (1 Megaton year)  Cuts: One  0  one e, E p < 100 MeV, 0.93 < E total < 0.97 GeV [45% of  0 are absorbed]  K+ has an efficiency of 97%  Cuts: One K, no  0, no e’s, no  ’s, no  ±, E total < 0.8 GeV

NNN02 16 January, 2002 CERN Maury Goodman – Argonne Lab Large Detector workshop ICARUS Value of running T600  With great background rejection, a new small detector can only improve on modes with large background.   + is such a mode  T600 will verify both the predicted background levels and the anticipated detector efficiencies.

NNN02 16 January, 2002 CERN Maury Goodman – Argonne Lab Large Detector workshop epilogue (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.