Experimental SearchesExperimental Searches for Proton Decayfor Proton ecay

Ed Kearns Boston University

generalitiesnnbar oscillationproton decay modes

- results from Super-K- background studies

photocathode coverage- photocathode coverage

looking forward

Experiments as

sExperiments represented with best

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2007‐Oct‐03 Ed Kearns – NNN07 – Proton Decay Review 2

Antileptonl    plus meson modes

IMB h t i PDGIMB has most in PDG(for now)

Super-K has only p ysearched for favored channels (for now)

Iron tracking detectors Iron tracking detectors can compete in very few modes (too small)

There are good reasons to cover many of these modes…

2007‐Oct‐03 Ed Kearns – NNN07 – Proton Decay Review 3

Beyondilantilepton

plusmeson

And we should search And we should search broadly and not be constrained by favored theories. We are testing fundamental symmetries– always worthwhile.

2007‐Oct‐03 Ed Kearns – NNN07 – Proton Decay Review 4

… what else??

Super‐Kamiokande22.5 kton fiducial volume 7.5×1033 p + 6×1033 n

SK-I: 1996-200111146 50-cm inner PMTs , 40% coverage1885 20-cm outer PMTs

SK-II: Jan 2003-Oct 2005Recovery from accident5182 50-cm inner PMTsAcrylic + FRP protectivey pOuter detector fully restored

SK-III: May 2006-Restored 40% coveragegOuter detector segmented (top | barrel | bottom)

SK-future: Replace all electronics - 2008

2007‐Oct‐03 Ed Kearns – NNN07 – Proton Decay Review 5

pAdd Gadolinium - 20??

Neutron – antineutron Oscillation

Antineutron annihilates with nearby n or pEnergy release ~ 2× nucleon massEnergy release ~ 2× nucleon massHigh multiplicity ~ 4π/eventIsotropic distribution

i l i l i f b bbl h b d

+ − 2%+ 0 1%

n p+ n n+Final state simulation from bubble chamber data

π+

π− π0

π0γγ

γ γ

π+π− 2%

π0π0 1.52%π+π−π0 6.48%

π+π−π0π0 11%

π+π0 1%

π+π0π0 8%

π+π0π0π0 10%

π+π+π−π0 22%

π+

π0 γγ

π+π−π0π0π0 28%

2π+ 2π− 7%

2π+ 2π−π0 24%

2π+π−2π0 36%

2π+ π−ω 16%

3π+ 2π−π0 7%

2007‐Oct‐03 Ed Kearns – NNN07 – Proton Decay Review 6

π+ π−ω 10%

2π+ 2π−π0π0 10%

Example n-nbar simulated event

2007‐Oct‐03 Ed Kearns – NNN07 – Proton Decay Review 7

Event SelectionFully-contained, fiducial volumeOptimize ε/√BG

(a) #of rings >= 2(a) #of rings >= 2(b) 700 < visible energy < 1300 MeV (c) low net momentum: 0< Ptot < 450 MeV/c(d) high mass: 750 < Mt t < 1800 MeV/c2(d) high mass: 750 Mtot 1800 MeV/c

# of rings

2007‐Oct‐03 Ed Kearns – NNN07 – Proton Decay Review 8

8Visible Energy (MeV) Net Momentum (MeV/c) Total Mass (MeV/c2)

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Results:

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10.4 % detection efficiencysys. uncertainty 15.2%(mostly intranuclear scattering)

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(mostly intranuclear scattering)

21.3 background eventsν osc. effects are included um

(MeV

/c)

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ν osc. effects are includedsys. uncertainty 32%(mostly flux, cross sections)

Net

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entu

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20 candidates1

boundτ =Γ

= 1.77×1032 yrs ( 90% CL)

N

0

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limitbound Γ

y ( )

23 1 8/( 1 10 ) 2.36 10freeR s T sτ −= × = > ×

2007‐Oct‐03 Ed Kearns – NNN07 – Proton Decay Review 9

9

0

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200 400 600 800 1000 1200 1400 1600 18008 ILL Reactor Expt: 0.86 10f

freecf T s> ×

• Fully contained, Fiducial volume• 2 or 3 rings

Event selection criteria:

g• All rings are e-like• π0 mass 85-185 MeV/c2

• No µ-decay electrons2• Mass range 800-1050 MeV/c2

• Net momentum < 200 MeV/c

2007‐Oct‐03 Ed Kearns – NNN07 – Proton Decay Review 10

0.4 BG evts=

45.0%ε =SK1

inar

ySu

per-K

Pre

limi

43.6%ε =

SK2SK2

2007‐Oct‐03 Ed Kearns – NNN07 – Proton Decay Review 11

0.04 BG evts=

0 h lSK1

p→e+π0 Search Results

SK-I SK-IIDetection efficiency 45.0% 43.6Background estimate 0.40 0.04gExposure 1489.2 d

(91.6 kt⋅yr)798.6 d (49.1 kt⋅yr)

Data 0 0Lifetime limit (90% CL) 5.5×1033 yr 2.9×1033yr

SK233 (90% CL)/ 8 4 10BR >

Super-K Preliminary

33 (90% CL)/ 8.4 10 BR yrτ > ×

2007‐Oct‐03 Ed Kearns – NNN07 – Proton Decay Review 12

Background prediction:g p(a) data vs MC(b) independent MC code 

2007‐Oct‐03 Ed Kearns – NNN07 – Proton Decay Review 13

Consistent BG estimate of 0.21 evts/100 kt.yr

Direct measurement of proton d  b k d  i  K K decay background using K2K beam (1KT near detector)

15.9 Mt⋅yr CC, 4.5 Mt⋅yr NC

NEUT

0 0 42 0 4

NUANCE

2007‐Oct‐03 Ed Kearns – NNN07 – Proton Decay Review 14

0 +0.42 0.45-0.33 0.51 BG = 1.63 (stat) (sys.) evts/Mt yre π+ +

− ⋅

p→µ+π0 Search Resultsp µ

SK-I SK-II

Detection efficiency 35.6% 35.5%

B k d i 0 4 0 2Background estimate 0.4 0.2

Exposure 1489.2 d (91.6 kt⋅yr)

798.6 d (49.1 kt⋅yr)

Data 0 0

2007‐Oct‐03 Ed Kearns – NNN07 – Proton Decay Review 15

Data 0 0

Lifetime limit (90% CL) 6.7×1033 yr (combined)

2007‐Oct‐03 Ed Kearns – NNN07 – Proton Decay Review 16

2007‐Oct‐03 Ed Kearns – NNN07 – Proton Decay Review 17

0p Kν π π+ +→ →

2007‐Oct‐03 Ed Kearns – NNN07 – Proton Decay Review 18

p→Κ+ν SearchS i i ll i f ll

Re-optimization SK-I SK-II

SK-I Sensitive to collection of smallamount of light (few # hits).

for SK-II

Nhit γ (prompt gamma) 7-60 hits 5-30 hitsBackwards light (π+π0) 40-100 p.e. 20-50 p.e.Plus a few other cuts such as light outside cone, proton rejection cuts

SK-II: Efficiency ↓, background ↑, need more work !

SK-I33/ 2 3 10B yrτ > ×/ 2.3 10

(SK-I, 90% CL)B yrτ > ×

2007‐Oct‐03 Ed Kearns – NNN07 – Proton Decay Review 19

40% or 20% Photon Coverage?Super-K I (40% coverage) Super-K II (20% coverage)

Sub-GeV vertex resolution 26 cm (e-like) / 23 cm (µ-like) 30 cm (e-like) / 29 cm (µ-like)

Sub-GeV particle mis-ID 0.81% (e-like) / 0.70% (µ-like) 0.69% (e-like) / 0.96% (µ-like)

Sub-GeV momentum resolution 4.8% (e-like) / 2.5% (µ-like) 6.3% (e-like) / 4.0% (µ-like)

p→e+π0 signal efficiency 45.0 ±1.3 ±6.7% 42.2 ±1.2 ±6.5%p g y

p→ e+π0 background 0.4 (±35%) events/100kty 0.04 (±35%) events/100kty

p→ K+ν, γ tag signal efficiency 8.4±0.1 ±1.7% 4.7±0.1 ±1.0%

p→ K+ν, γ tag background 0.72 (±28%) events/100kty 1.4 (±30%) events/100kty

p→ K+ν, π+π0 signal efficiency 5.5 ±0.1 ±0.7% 5.7 ±0.1 ±0.4%

p→ K+ν π+π0 background 0 59(±28%) events/100kty 1 0(±30%) events/100ktyp→ K ν, π π background 0.59(±28%) events/100kty 1.0(±30%) events/100kty

T2K CCνe likelihood effic. 83.7% (±0.1% stat) 84.8 %

T2K BG likelihood effic. 21.3 % 21.5 %

2007‐Oct‐03 Ed Kearns – NNN07 – Proton Decay Review 20

Preliminary numbers, for comparison purposes. Final published efficiencies and BG may differ.

2007‐Oct‐03 Ed Kearns – NNN07 – Proton Decay Review 21

Beyond Super-K:NNN

2007‐Oct‐03 Ed Kearns – NNN07 – Proton Decay Review 22

ass

duci

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l to

fidro

porti

onPr

2007‐Oct‐03 Ed Kearns – NNN07 – Proton Decay Review 23

ICARUS T600 Status: installed in Gran Sasso Lab.Expected to start in Expected to start in early-mid 2008

2007‐Oct‐03 Ed Kearns – NNN07 – Proton Decay Review 24

0p e π+→500 kt WC

pet

ime

SK I+II

SK1

SK2SK3+

oton

life

IMB

pr

2007‐Oct‐03 Ed Kearns – NNN07 – Proton Decay Review 25

p K ν+→100 kt LAr

pet

ime 500 kt WC

oton

life

SK3SK I

pr SK1

IMB

2007‐Oct‐03 Ed Kearns – NNN07 – Proton Decay Review 26

Summary & Conclusion

New nnbar result from Super-K (no evidence for)competes with best free neutron experiment

Updated searches for e+π0, µ+π0

no evidenceno evidencebackground estimate under control20% photocoverage is quite adequate

20% photocoverage is challenging for K+νp g g gand probably any mode requiring small numbers of hits

and I’m sure we will hear more about the prospectsand I m sure we will hear more about the prospectsfor the next generation. What will they be? When will they start?

2007‐Oct‐03 Ed Kearns – NNN07 – Proton Decay Review 27