nnn02 16 january, 2002 cern maury goodman – argonne lab large detector workshop current status and...
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16 January, 2002 CERN
Maury Goodman – Argonne Lab
Large Detector workshop
NNN02NNN02Current Status and
Prospects of Approved Proton
Decay Search ExperimentsAt the Workshop on
“Large Detectors for Proton Decay, Supernovae and atmospheric neutrinos
and low energy neutrinos from High Intensity Beams”
January 16, 2002Maury Goodman
Argonne National Laboratory
Soudan 2 // UNO
16 January, 2002 CERN
Maury Goodman – Argonne Lab
Large Detector workshop
NNN02NNN02Nucleon 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
16 January, 2002 CERN
Maury Goodman – Argonne Lab
Large Detector workshop
NNN02NNN02Act I
Limits in the Particle Data Group RPP IMB-3 Kamioka NUSEX Frejus HPW Soudan 1 KGF
16 January, 2002 CERN
Maury Goodman – Argonne Lab
Large Detector workshop
NNN02NNN02RPP-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 = nucleardetector]
16 January, 2002 CERN
Maury Goodman – Argonne Lab
Large Detector workshop
NNN02NNN02Nucleon Decay Experiments
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
16 January, 2002 CERN
Maury Goodman – Argonne Lab
Large Detector workshop
NNN02NNN02A Comparison
Limits depend on exposure, candidates and background
Exposure is usually the most important [size time]
16 January, 2002 CERN
Maury Goodman – Argonne Lab
Large Detector workshop
NNN02NNN02Act II
Recent Limits
Soudan 2 p→K+
Other “Super-symmetric” modes modes High (>2) multiplicity events
Super-Kamiokande p→e+0
Other modes
16 January, 2002 CERN
Maury Goodman – Argonne Lab
Large Detector workshop
NNN02NNN02Soudan 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→) = 0.090 Also search for K+ → (*B = 0.055) In 5.91 kt-yr
1 candidate Backgrounds: 0.34 , 0.31 rock
/B > 7.1 * 1031 yr without background subtraction
16 January, 2002 CERN
Maury Goodman – Argonne Lab
Large Detector workshop
NNN02NNN02Soudan 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.
16 January, 2002 CERN
Maury Goodman – Argonne Lab
Large Detector workshop
NNN02NNN02Soudan 2PDK Analysis
Use Bigaussian in each pair of variables
(a bit better than a box)
16 January, 2002 CERN
Maury Goodman – Argonne Lab
Large Detector workshop
NNN02NNN02SoudanMercedes 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→l3 =3.0 ±1.5% 0 candidates (4.56 kt-year) 0.3 background /B > 6.0 1031 year
16 January, 2002 CERN
Maury Goodman – Argonne Lab
Large Detector workshop
NNN02NNN02Soudan 2 neutron oscillation
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 .
FE > 7.0 1031 years (free > 1.3 108 s) Background limited at 5.56 kt-years
16 January, 2002 CERN
Maury Goodman – Argonne Lab
Large Detector workshop
NNN02NNN02 Super-K p→e+0
p→e+0 selections:2 or 3 ringsElectron likeFor 3 ring events, 85 MeV/c2 < m
0
< 185 MeV/c2 800 MeV/c2 < Mtotal < 1050 MeV/c2
Ptotal < 250 MeV/C
Zero candidates /B > 5.0 1033 year
!!!!!
16 January, 2002 CERN
Maury Goodman – Argonne Lab
Large Detector workshop
NNN02NNN02Act III
New Limits
Super-Kamiokande improved analysis for p →K+
16 January, 2002 CERN
Maury Goodman – Argonne Lab
Large Detector workshop
NNN02NNN02Super-K p→K+
Require 6.3 MeV from de-excitement of N15
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
16 January, 2002 CERN
Maury Goodman – Argonne Lab
Large Detector workshop
NNN02NNN02Act 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?
16 January, 2002 CERN
Maury Goodman – Argonne Lab
Large Detector workshop
NNN02NNN02Discovery/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
16 January, 2002 CERN
Maury Goodman – Argonne Lab
Large Detector workshop
NNN02NNN02KGF
11 candidates Lifetime estimate 2.4 1031 years
16 January, 2002 CERN
Maury Goodman – Argonne Lab
Large Detector workshop
NNN02NNN02Frejus Candidate
Candidate p→e+0→ Event 1378/460 Background estimate (<<10%) Presented as candidate at conferences Not published as a candidate (NC=0)
16 January, 2002 CERN
Maury Goodman – Argonne Lab
Large Detector workshop
NNN02NNN02IMB3 peak
Two events in peak with pnet < 450 MeV
Both candidates for e0
Background 0.7
16 January, 2002 CERN
Maury Goodman – Argonne Lab
Large Detector workshop
NNN02NNN02Kamiokande candidate
p→ Background < 0.08 (in the one
mode) Candidate used to set a limit Well ruled out by Super-
Kamiokande
16 January, 2002 CERN
Maury Goodman – Argonne Lab
Large Detector workshop
NNN02NNN02Soudan 68882-746
Candidate for e Evis = 1030 MeV, pnet = 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
16 January, 2002 CERN
Maury Goodman – Argonne Lab
Large Detector workshop
NNN02NNN02Discovery-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.
16 January, 2002 CERN
Maury Goodman – Argonne Lab
Large Detector workshop
NNN02NNN02Discovery-2
Can nucleon decay be discovered with two events?
…All the same criteria apply, people
will use their own “Bayesian prior.”
16 January, 2002 CERN
Maury Goodman – Argonne Lab
Large Detector workshop
NNN02NNN02Limits-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.
16 January, 2002 CERN
Maury Goodman – Argonne Lab
Large Detector workshop
NNN02NNN02Believing Low Statistics results?
Compare:
DONUT emulsionDiscovery 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 0Mod. Phys. Lett A16 2409-2420) 2002events (after fit) [Background ~2.0]
3.1 PDG method
16 January, 2002 CERN
Maury Goodman – Argonne Lab
Large Detector workshop
NNN02NNN02Act V
Currently Operating Experiments
------------------------------------------------
Future Approved Experiments
ICARUS (600 ton version)
telescopes (for monopole catalyzed nucleon decay)
16 January, 2002 CERN
Maury Goodman – Argonne Lab
Large Detector workshop
NNN02NNN02Currently Operating NDK
experiments
(please note - this list is in alphabetical order.)
16 January, 2002 CERN
Maury Goodman – Argonne Lab
Large Detector workshop
NNN02NNN02ICARUS
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+0 has an efficiency of 37% with no background (1 Megaton year) Cuts: One 0one e, Ep < 100 MeV,
0.93 < Etotal < 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 ±, Etotal <
0.8 GeV
16 January, 2002 CERN
Maury Goodman – Argonne Lab
Large Detector workshop
NNN02NNN02ICARUS
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.
16 January, 2002 CERN
Maury Goodman – Argonne Lab
Large Detector workshop
NNN02NNN02epilogue
(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.