SearchSearch for Nucleon decays for Nucleon decays

M.MiuraM.Miura

Kamioka Observatory, ICRRKamioka Observatory, ICRR

BLV 2011, GatlinburgBLV 2011, Gatlinburg

ContentsContents

1)1) IntroductionIntroduction

2)2) Super-Kamiokande detectorSuper-Kamiokande detector

3)3) p -> ep -> e++++00 , , ++++00 mode mode

4)4) p -> Kp -> K++++ mode mode

5)5) Other modesOther modes

6)6) SummarySummary

• Nucleon decay experiment is the direct probe for GUTs.• p e+0 (non-SUSY GUTs), p K+ (SUSY-GUTs) are regarded as the dominant mode.• Need large number of nucleons Need large detectors.• Super-Kamiokande data: 22.5kton = 7 x 1033 protons x 10 years run Good detector to investigate nucleon decay !

u

dp

3

~

c~

W

sc

c

~

u uK+

Minimal SU(5) model SUSY SU(5) model

d

u

u e+

d

dc

X

p0

1. Introduction1. Introduction

-

Current Nucleon lifetime limits

Main topics in this talk

pe+0

p+0

pK+-

2. Super-Kamiokande Detector2. Super-Kamiokande DetectorLocation: Kamioka mine, Japan. ~1000 m under ground.Size: 39 m (diameter) x 42 m (height), 50kton water. Optically separated into inner detector (ID) and outer detector (OD, ~2.5 m layer from tank wall.)Photo device: 20 inch PMT (ID), 8 inch PMT (OD, veto cosmic rays).Mom. resolution: 3.0 % for e 1 GeV/c (4.1%: SK-2).Particle ID: Separate into EM shower type (e-like) and muon type (-like) by Cherenkov ring angle and ring pattern.

-like () e-like (e

Nucleon Decay Experiment

96 97 98 99 00 01 02 03 04 05 06 07 08 09 10 11

Accident reconstruction electronics upgrade

SK-4 (~11’Mar 1)Live Time: 763 daysExposure: 46.5kton ・ yr

History of Super-Kamiokande

SK-3Live time: 518 daysExposure: 31.9kton ・ yrID PMT:11146Photo coverage: 40 %

e+0 paper 2007: > 8.2x1033 years (141kton ・year)

This talk: 220 kton ・ year exposure in total

Same

SK-1Livetime: - 1489.2 daysExposure:- 91.7 kton·yrInner PMT: 11146Photo coverage:40 %

SK-2Livetime:- 798.6 daysExposure:- 49.2 kton·yrInner PMT:5182Photo coverage:19 %

K+ paper 2005: > 2.3x1033 years (92kton ・ year)

MC simulations

Proton decay MC <= Efficiency 8 bounded protons in O:

Fermi momentum, binding energy, various nuclear effects are taken into account.

2 free protons: simple two body decay.Atmospheric MC <= BKG for proton decay Flux : Primary cosmic rays make and e.

M.Honda et .al., Phys.Rev. D75 043006(2007)

interaction: NEUT Y.Hayato, Nucl.Phys.Proc.Suppl. 112,171(2002)

3. p3. pee++00 , ,++00 mode mode

0

P

e+ or +

Event features;• e+ ,+and 0 are back-to-back (459 MeV/c) •0 2 s : all particles can be detectable. Reconstruct proton mass and momentum.

Selection;• Fully contained, VTX in fiducail volume.• 2 or 3 ring

e+0 case;• all e-like, w/o decay-e.

+0 case;• one -like with decay-e.

• 85 < M0 < 185 MeV (for 3-ring event) .• 800 < MP < 1050 MeV & Ptot < 250 MeV/c

Selected by simple cuts!

Tot

al m

omen

tum

(M

eV/c

)

No candidate observed.

Blue: PDK MCGreen: ATM MCRed: Data

p+0

pe+0

Open data: Mtot vs Ptot

Mtot

Results of p->e+0, +0

pe+0 p+0

Exp.(kton ・yr)

Eff(%) BKG Data Eff(%) BKG Data

SK1 91.7 44.6±0.7 0.20 0 35.5±0.7 0.23 0

SK2 49.2 43.5±0.7 0.11 0 34.7±0.6 0.11 0

SK3 31.9 45.2±0.7 0.06 0 36.3±0.7 0.08 0

SK4 46.9 45.0±0.7 0.08 0 43.9±0.7 0.17 0

Total 219.7 0.45 0 0.59 0

Lifetime limit (90%C.L,)pe+0: 1.3x1034 years, p+0: 1.1x1034 years

Note 1: In SK2, photo coverage was a half of other periods, but efficiency was almost same.Note 2: In SK4, new electronics was installed and Michel electron tagging was improved. As a result, the efficiency of +0 in SK4 was increased.

e+e

16O->15N

6.3MeV

K+

+

A) K+ -> ++

t

T(dN/dt=max)

Tstart

12ns window

e

Hits

Event features;• K+ is invisible, stops and 2 body decay (P = 236 MeV/c).

Excess in P.• 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

4. p4. p + K+ K++ mode mode-

Open dataBlack: DataRed: ATM MCBlue: PDK MC

No candidates and no excess in P.

Exp.(kton ・yr)

Eff(%) BKG Data

SK1 91.7 7.2±0.1 0.16 0

SK2 49.2 5.8±0.1 0.08 0

SK3 31.9 7.3±0.1 0.04 0

SK4 46.9 8.2±0.1 0.07 0

Total 219.7 0.35 0

N (except SK2)

Black: DataRed: ATM MCBlue: PDK MC

Sys.error (%)

-emission prob. 20.0

Energy scale 2.7

Tstart 8.3

PID 0.6

Ring count 1.4

Water parameter 1.9

Fiducial volume 3.0

Total 22.3

B) 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

M0 P0

Black: Data (w/o dcy-e cut)

Red: Atm. MC

visibleinvisible

No candidates.

Blue: PDK MCRed: ATM MCBlack: Data

Exp.(kton ・yr)

Eff(%) BKG Data

SK1 91.7 6.5±0.1 0.46 0

SK2 49.2 5.3±0.1 0.33 0

SK3 31.9 6.6±0.1 0.14 0

SK4 46.9 7.9±0.1 0.31 0

Total 219.7 1.24 0

Ebk vs EresOpen data

Ebk

Black: DataRed: ATM MCBlue: PDK MC

Sys. error (%)

-N crs in water 5.0

Energy scale 2.5

PID 2.1

Ring count 4.0

Water parameter 2.8

Fiducial volume 3.0

Total 8.3

p K+ Combined lifetime limit (90% CL): > 4.0 x1033 yrs @219.7 ktont ・ yr

-

5. Other modes5. Other modes

n

0

e+

+

-

+

p

Nucleon => lepton + meson(using 141 kt ・ year data)

•Consistent with BKG for all modes.•Most of them give the most stringent limits in the world.

B-L conserving mode

B-L violating mode

• ne-K+

e+e

e-

K+: =12ns

+

n

Search for e (330 MeV/c) and (236 MeV/c) with time difference.

Data: SK1~SK2, 141 kton ・ yearEff.: 11 % for SK1, 8.4 % for SK2BKG: 0.3 events OBS: 1 event

Lifetime limit: > 0.99x1033 years

• ppK+K+(B=2) - K+ can be seen (~800 MeV/c).-Distance of Vertices of K+ decay: ~2.6 m-Use Boosted Decision Tree technique.

Data: SK1, 91.6 kton ・ yearEff.: 12.6% BKG: 0.3 events OBS: 0 event

Lifetime limit: > 1.7x1032 years

+

K+ K+

6. Summary6. Summary• Fruitful nucleon decay results from Super-Fruitful nucleon decay results from Super-

Kamiokande.Kamiokande.• We could We could not find any evidences not find any evidences of nucleon decay.of nucleon decay.• We calculated nucleon lifetime limits with 90 % C.L.We calculated nucleon lifetime limits with 90 % C.L.

pp e e++00: > 1.3x10: > 1.3x103434 yrs yrs

++00: > 1.1x10: > 1.1x103434 yrs yrs

KK++: > 4.0x10: > 4.0x103333 yrs yrs• Other mode both (B-L) conserving and violating Other mode both (B-L) conserving and violating

modes are also studied.modes are also studied.

-

Future prospects• Need larger volume detector

(Megaton class).

Ex. Hyper-Kamiokande project (fiducail volume 0.56 Mton, 20 % photo coverage)

• Sensitivity with HK 10 years run;

e+0: 1.3x1035 year

K+: 2.5x1034 year

Cover most of major models!Cover most of major models!

pe+0

pK+

-

-

Letter of Intent: Hyper-Kaiokande Experiment arXiv:1109.3262 [hep-ex]

Backup

Q. What are BKG for e+0 mode ?Contribution to BG

CCQE 28%

CC single 32%

CC multi 19%

other CC 2%

NC 19%

+N -> lepton+N*; N*->N’+mesone CC case, e and ±, 0 are out-going particles.

+N -> lepton+Pe case, e and P are out-going particles and P interacts in water and make secondary 0.

Estimation from 1kt water detector by using K2K beam(~10Mton ・ year equivalent)

)()(63.1 45.051.0

42.033.0 sysstat

Phys.Rev.D77,032003(2008)

Background rate: 1.6±0.4 events/Mton ・ year by MC

Agree well !

Systematic error for e+0 (Efficiency)

Systematic error pe+0 p+0

-N effect 15 % 15 %

NN-correlation 7 % 7 %

Fermi motion 8 % 8 %

Detector 4.4 % 4.6 %

Total 19 % 19 %

Q. What are BKG for K+ mode ?

K+->++N -> lepton+N*; N*->N’+meson: 44%

Resonance N* decays into K+.

+N -> charged lepton+P: 17 %

Low P lepton, High P proton => VTX mis-reconstructed

K+->+

+N -> lepton+N*; N*->N’+meson: 63%

-Resonance N* decays into K+.- N* decays into 0 and charged lepton goes backward of 0.

Detail of ne-K+

e+e

e-

K+: =12ns

+

n

Selection:• FCFV 2R, e+ with decay-e• 250< Pe< 400 MeV/c,

200< P < 280 MeV/c,

• T-Te > 6 nsec

Detail of ppK+ K+

+

K+ K+

Distance between K+ decay points

K+ momentum

BDT output

nn oscillation in SK

• Exposure: 24.5x10Exposure: 24.5x103333 neutrons neutrons ・・ years years

(SK-1 data only) (SK-1 data only)

• No evidence.No evidence.

• Oscillation time for free neutron:Oscillation time for free neutron:

2.44x102.44x1088 sec sec

(theoretical suppression factor: 1.0x10(theoretical suppression factor: 1.0x102323 sec sec-1-1))

arXiv:1109.4227arXiv:1109.4227

-

Schematic view of the HK detector

Discovery potential with 3 ; pe+0: 5.7x1034 years pK+: 1.0x1034 years Sensitivity with 90 % C.L: pe+0: 1.3x1035 years pK+: 2.5x1034 years

p e+0