Proton decay sensitivity in future Proton decay sensitivity in future water cherenkov detectorwater cherenkov detector

M.MiuraM.MiuraKamioka Observatory, ICRRKamioka Observatory, ICRR

NNN 2010, ToyamaNNN 2010, Toyama

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ContentsContents

1)1) IntroductionIntroduction2)2) p -> ep -> e++++00 mode mode3)3) p -> Kp -> K++++ mode mode4)4) SummarySummary

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- Proton decay is a breakthrough toward GUTs.- pe+0, K+ are regarded as dominant mode.- The latest results of proton lifetime limit; e+0: 1.2x1034 years @ 206 kton ・ year K+: 3.9x1033 years (14 years since SK start)- Reach 1Megaton ・ year => 56 years more by SK? or construct larger detector.- Cost is bottle neck to construct larger detector. One of dominant is cost for photo sensor. Physics results : as much as possible Cost : as much as low Need optimize photo coverage .

1. Introduction1. Introduction

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In this talk, I made proton decay MC (PDK) and atmospheric MC (ATM) with;

Detector size, PMT(20inch), Electronics, water quality => Same as Super-Kamiokande(SK)

photo coverage 40 %: Current configuration of SK. 20 %: same as SK2 10 %: new one

to study sensitivity for pe+0, K+ .

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2. p->e2. p->e++++00 mode mode

Event features;• e+ and 0 are back-to-back (459 MeV/c) in nucleon rest frame.•0 decays into two s (one may be missed if direction of the other is close to 0).=>2 or 3 e-like ring should be observed. 0 mass should be reconstructed by two rings (3-ring case).=>Proton mass should be reconstructed by all ring and total momentum should be small.

e+0

P

Selection;• Fully contained, VTX in fiducail volume.• 2 or 3 ring and all e-like, w/o decay-electron.• 85 < M0 < 185 MeV (for 3-ring event) .• 800 < MP < 1050 MeV & Ptot < 250 MeV/c

2-1: Event features and selection

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Tot

al m

omen

tum

(MeV

/c)

2-2) Current results (SK1~SK4)T

otal

mom

eutu

m (M

eV/c

)

PDK MC ATM MC Data

Total Mass Total MomentumNo candidate.Data and Atmospheric MC agree well.

Total Mass (MeV)

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SK1 SK2 SK3 SK4Eff(%) 44.6±8.5 43.5±8.3 45.2±8.6 45.0±8.6

BKG(/Mt ・year)

2.13±0.94 2.24±0.99 1.87±0.82 1.62±0.71

Total exposure: 205.7 kton ・ yearLifetime limit: > 1.2x1034 years (90% C.L.)

Photo coverage 40% 20% 40% 40%

In this mode, 40% and 20% are almost same in efficiency and BKG rate.

(±sys.error)

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2-3) Photo coverage study

40% 20 % 10 %

Electron ring 0 rings

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40% 20 % 10 %

Zoom in: 0 rings

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Apply Standard Cuts

Cuts 40 (20)%Eff (%)

10 %Eff (%)

2 or 3ring 73.6 67.6

All e-like 65.5 56.0

85<M0<185 MeV 63.5 49.0

No decay e 62.5 47.5

800<Mtot<1050 MeV&Ptot<250 MeV/c

45.0 27.9

BKG rate 1.62±0.39 2.55±0.57 (stat. only) (/Mton ・ yr)

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Loose efficiency for 10 % photo coverage

Increase fake ring

40 %

20 %

10 %

Poor energy resolution

Tune cuts for 10 % photo coverage11

40 %

20 %

10 %

Cut tuning for e+0

Visible energy for 4th ring

PDK

ATM

0mass

Cut: 85<M0<185 MeV=> 85< M0≤230 MeV

Cut: 2≤ Nring≤3 => 2≤ Nring≤3 .or. (Nring=4&Evis(4)<100 MeV)

PDK

ATM

After tune: Eff = 35.1 %, BKG = 3.47 evts/Mton ・ year

Ring counting thr = 40 MeV&>5% of Eall.

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Sensitivity curve for e+0 search (90% CL)

40 % (~20%)

10 %Preliminary

1035 year ~4 Megaton ・ year for 40(20) % photo coverage ~9 Megaton ・ year for 10 % photo coverage

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2. p-> 2. p-> + K+ K++ mode modeK+: below cherenkov threshold. Use decay products of K+.

Method A) K+ -> ++

e+e

K+: =12ns+

P

visibleinvisible

Event features;• Proton => K+(below Č thrs.)+. • K+ most ｌｙ stops and decays into + (236 MeV/c)+(Br.64%).=> Monochromatic

Selection:• 1 -like ring with decay-e (except method-B).

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Current results (SK1-SK4)

No excess in Data.Agree with ATM .

Black: DataRed: ATMn MCBlue: PDK MC

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e+e

16O->15N

6.3MeV

K+

+

B) K+ -> ++ with prompt

t

T(dN/dt=max)

Tstart (dN/dt=0)

12ns window

e

Hits

Event features;• Proton in 16O decays and excited nucleus emits 6 MeV (Prob. 41%, not clear ring).=> Tag to eliminate BKG.

Selection:• 1 -like ring with decay-e.• 215 < P < 260 MeV/c• Search Max hit cluster by sliding time window (12ns width); - 8 < N < 60 hits for SK-1,3,4 4 < N < 30 hits for SK-2 & - T-T < 75 nsec

visibleinvisible

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Current results (SK1-SK4)

No candidate.

SK1,SK3,SK4 merged plot

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C) K+ -> ++

K++

e+

0

+

e

205 MeV/c

Event features;• Br. 21 %.•and are back-to-back and have 205 MeV/c.•P+ is just above Č thres.(not clear ring).

=> Search for monochromatic 0 with backward activities.

Selection:• 2 e-like rings with decay-e.• 85 < M0 < 185 MeV.• 175 < P0 < 250 MeV/c.• Ebk: visible energy sum in 140-180 deg. of 0 dir, Eres: in 90-140 deg. 7< Ebk < 17 MeV & Eres < 12 MeV

Eres

Ebk

visibleinvisible

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Current results (SK1-SK4)

No candidate.

SK1,SK3,SK4 merged plot

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SK-1 SK-2 SK-3 SK-4Eff.(%) 7.2±1.6 5.8±1.3 7.3±1.6 8.2±1.7

BKG/Mt ・yr

1.69±0.57 1.64±0.55 1.33±0.45 1.53±0.51

Current results (SK1-SK4)K+ -> ++ with prompt

SK-1 SK-2 SK-3 SK-4Eff.(%) 6.5±0.6 5.3±0.5 6.6±0.6 7.9±0.6

BKG/Mt ・yr

4.97±1.56 6.67±2.09 4.35±1.36 6.53±2.04

K+ -> ++

Total exposure: 205.7 kton ・ yearLifetime limit: > 3.9x1033 years (90% C.L.)

Decay-e tagging improved by new electronics.

(±sys.error)

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3-2) Photo coverage study

40 % 20 % 10 %

ring (236 MeV/c, Evis~50 MeV)

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Apply Standard Cuts: K+ -> ++ with prompt 　　　 * 2<N<15 is applied to 10% MC

Cuts Eff.40 % PC

Eff.20 %PC

Eff.10 %PC

FC1R 57.2 % 57.2 49.0

Decay-e 56.8 56.5 42.6

P 52.9 51.5 34.2

Le<200cm 51.8 49.0 28.5

Goodness>0.6 50.6 47.3 26.5

N&T 8.2 7.1 3.6

BKG 1.5 1.6 12.1/Megaton ・ yr

8 times larger !

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Comparison some distributions

|VTXrec-VTXtrue| (1R events)

20 %66 cm

40 %44 cm

10 %91 cm

N

40 %

20 %

10 %

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After tuningCut 2 < N < 15 3 < N <15Eff. 3.6 % 2.7 %BKG 12.1 2.1 events/Megaton ・ year

Cut tuning for N

PDK MC

ATM MC

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Cuts Eff.40 % PC

Eff.20 %PC

Eff.10 %PC

FC2Ree 17.8 % 17.0 15.4

Decay-e 13.2 13.3 10.5

M0 12.4 12.1 8.5

P0 10.5 10.0 6.2

Eres&Ebk 7.9 6.7 3.0

Apply Standard Cuts: K+ -> ++

BKG 6.5 6.7 8.4/Megaton ・ yr

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Comparison some distributions

40 %

20 %

10 %

40 %

20 %

10 %

EresEbk

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After tuningCut 7< Ebk < 17 MeV 7 < Ebk <20 MeVEff. 3.0 % 3.4 %BKG 8.4 8.6 events/Megaton ・ year

Cut parameter tuning for Ebk

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10 32

10 33

10 34

10 35

10 36

10 37

10 - 2 10 - 1 1 10 10 2 10 3

E xposure (M egaton year)

Parti

al Lif

etim

e (ye

ars)

p K + s ens it ivity (90 C L )

S uper- K limit206ktyr3.9 x 10 33 yrs (90 C L )

Sensitivity curve for K+ search (90% CL)

40%

20%10%Preliminary

1034 year ~1 Megaton ・ year for 40 % photo coverage ~1.2 Megaton ・ year for 20 % photo coverage ~7 Megaton ・ year for 10 % photo coverage

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Sensitivity curve with each method

40 % 20 % 10 %

Red: MergedBlue: prompt Green: +0

Black: P spectrum

Prompt method is dominant in each case.

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Improve tagging with better PMT

NNo , or overlap with tail.

Should have hit (by vector cuts)

Better QE can recover efficiency.

Crude estimation of QE effect

Should study PMT performance(QE, dark rate, T-resolution, e.t.c.)

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Red hist x 2 Factor

ta

ggin

g ef

f (%

)

20 % coverage

10% coverage

Eff. for N cut

• Study for Study for proton decay sensitivity proton decay sensitivity by changing by changing photo photo coveragecoverage (tank size, 20inch PMT are same as SK). (tank size, 20inch PMT are same as SK).

• Rough estimate required exposureRough estimate required exposureee++00 10 103535yearyear: ~9Mt: ~9Mt ・・ year exposure for 10 % coverageyear exposure for 10 % coverage

~4Mt~4Mt ・・ year for 40 (20) % year for 40 (20) %

40% 20% 10%(preliminary)Eff(%) BKG

/Mt ・yr

Eff(%) BKG/Mt ・yr

Eff(%) BKG/Mt ・yr

e+0 45.0 1.6 (same as 40%) 35.1 3.5

K+: 8.2 1.5 7.1 1.6 2.7 2.1

K+:+0 7.9 6.5 6.7 6.7 3.4 8.6

4. Summary4. Summary

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KK++ 10 103434yearyear: ~7Mt: ~7Mt ・・ year exposure for 10 % coverageyear exposure for 10 % coverage ~1Mt~1Mt ・・ year for 40 (20) %year for 40 (20) %

Next StepNext Step• Improve reconstruction tools.Improve reconstruction tools.• Investigate Investigate PMT performance.PMT performance.

- QE- QE

- Dark rate- Dark rate- PMT size- PMT size- T resolution- T resolution- …….- …….

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Backup

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K+ -> ++ with prompt

Decay-e PID

40 %

19 %

10 %

40 %

19 %

10 %

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K+ -> ++ with prompt

P L-e

40 %

19 %

10 %

40 %

19 %

10 %

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Should study PMT performance(QE, dark rate, T-resolution, PMT size…)

Example 2: decrease dark rateSimple MC: 236 MeV/c

N

Black: 5.3kHz default)Red: 3.0 kHz

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