current status and prospects of approved proton decay search experiments

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




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




NNN02NNN02Act I

Limits in the Particle Data Group RPP IMB-3 Kamioka NUSEX Frejus HPW Soudan 1 KGF




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]




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




NNN02NNN02A Comparison

Limits depend on exposure, candidates and background

Exposure is usually the most important [size time]




NNN02NNN02Act II

Recent Limits

Soudan 2 p→K+

Other “Super-symmetric” modes modes High (>2) multiplicity events

Super-Kamiokande p→e+0

Other modes




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




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.




NNN02NNN02Soudan 2PDK Analysis

Use Bigaussian in each pair of variables

(a bit better than a box)




NNN02NNN02K modes




NNN02NNN02P




NNN02NNN02P event




NNN02NNN02 modes




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




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




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

!!!!!




NNN02NNN02Act III

New Limits

Super-Kamiokande improved analysis for p →K+




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




NNN02NNN02Super-K limits




NNN02NNN02Limits




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?




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




NNN02NNN02KGF

11 candidates Lifetime estimate 2.4 1031 years




NNN02NNN02Frejus Candidate

Candidate p→e+0→ Event 1378/460 Background estimate (<<10%) Presented as candidate at conferences Not published as a candidate (NC=0)




NNN02NNN02IMB3 peak

Two events in peak with pnet < 450 MeV

Both candidates for e0

Background 0.7




NNN02NNN02Kamiokande candidate

p→ Background < 0.08 (in the one

mode) Candidate used to set a limit Well ruled out by Super-

Kamiokande




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




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.




NNN02NNN02Discovery-2

Can nucleon decay be discovered with two events?

…All the same criteria apply, people

will use their own “Bayesian prior.”




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.




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




NNN02NNN02Act V

Currently Operating Experiments

------------------------------------------------

Future Approved Experiments

ICARUS (600 ton version)

telescopes (for monopole catalyzed nucleon decay)




NNN02NNN02Currently Operating NDK

experiments

(please note - this list is in alphabetical order.)




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




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.




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.

current status and prospects of approved proton decay search experiments

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