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