Current status and prospects of approved proton decay search experiments
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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.

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Current Status and Prospects of Approved Proton Decay Search Experiments

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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

Current Status and Prospects of Approved Proton Decay Search Experiments

Maury Goodman – Argonne Lab

Large Detector n workshop


Nucleon decay

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


Act i

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


Rpp 2000 limits

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


Nucleon 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

Nucleon Decay Experiments

Maury Goodman – Argonne Lab

Large Detector n workshop


A comparison

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


Act ii

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


Soudan 2 p n k

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


Soudan 2 method

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


Soudan 2 pdk analysis

Use Bigaussian in each pair of variables

(a bit better than a box)

Soudan 2PDK Analysis

Maury Goodman – Argonne Lab

Large Detector n workshop


K modes

K modes

Maury Goodman – Argonne Lab

Large Detector n workshop


Current status and prospects of approved proton decay search experiments

P 

Maury Goodman – Argonne Lab

Large Detector n workshop


P event

P  event

Maury Goodman – Argonne Lab

Large Detector n workshop


H modes

h modes

Maury Goodman – Argonne Lab

Large Detector n 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:

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


Soudan 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 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


Super k p e p 0

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


Act iii

New Limits

Super-Kamiokande improved analysis for p →nK+

Act III

Maury Goodman – Argonne Lab

Large Detector n workshop


Super k p n k

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


Super k limits

Super-K limits

Maury Goodman – Argonne Lab

Large Detector n workshop


Limits

Limits

Maury Goodman – Argonne Lab

Large Detector n 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:

What are the lessons?

What would it take to “discover” nucleon decay?

Act IV

Maury Goodman – Argonne Lab

Large Detector n workshop


Discovery candidates

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


Current status and prospects of approved proton decay search experiments

11 candidates

Lifetime estimate 2.4 1031 years

KGF

Maury Goodman – Argonne Lab

Large Detector n workshop


Frejus candidate

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


Imb3 peak

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


Kamiokande candidate

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


Soudan 68882 746

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


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.

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


Discovery 2

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


Limits 1

“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


Believing low statistics results

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


Act v

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


Currently operating ndk experiments

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

Currently Operating NDK experiments

Maury Goodman – Argonne Lab

Large Detector n 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 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


Icarus1

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


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.

epilogue

Maury Goodman – Argonne Lab

Large Detector n workshop


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