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Recent Nucleon Decay Results from Super-Kamiokande
Jennifer L. RaafBoston University
April 14, 2008
MotivationSuper-Kamiokanden → ν π0 decay searchResults
J.L.Raaf, Boston University APS Meeting, April 14, 2008
Interesting candidate for grand unification:SUSY SO(10) model with B-L violation (by 126 Higgs field)
✦ predicts all neutrino mixings and ratio of in agreement with experimental observations
✦ automatic R-parity conservation ⇒ stable dark matter
✦ prediction of upper limits on some proton decay modesrequires some fine-tuning to make compatible with current experimental limits
Motivation
2
Model can be directly tested by searching for predicted modes!
H.S.Goh, R.N.Mohapatra, S.Nasri, S-P. Ng, Phys Lett B587:105-116 (2004)
∆m2!/∆m2atmos
Imagine a beautiful Adobe Illustrator image here...
J.L.Raaf, Boston University APS Meeting, April 14, 2008
Super-Kamiokande
3
Gifu prefecture, Japan, Kamioka-Mozumi zinc mine1000 meters (2700 meters-water-equivalent)
beneath peak of Mt. Ikeno
Water Cherenkov detector
50 ktons (22.5 ktons fiducial) ultra-pure water7.5 x 1033 protons6.0 x 1033 neutrons
Instrumented with photomultiplier tubes (PMTs)11146 50-cm PMTs in inner region1885 20-cm PMTs in outer region
SK-1, SK-2, and beyond...SK-1: 1996-2001
40% photocathode coverageSK-2: Jan 2003 - Oct 2005
Recovery from accident, 20% photocathode coverageSK-3: May 2006 - present
Restore 40% coverageSK-4:
Replace DAQ electronics, Autumn 2008
J.L.Raaf, Boston University APS Meeting, April 14, 2008
Identifying particle types in Super-K
4
Super-Kamiokande IRun 999999 Sub 0 Ev 4202-11-06:00:12:25
Inner: 3166 hits, 6293 pE
Outer: 0 hits, 0 pE (in-time)
Trigger ID: 0x03
D wall: 1240.0 cm
Fully-Contained Mode
Charge(pe) >26.723.3-26.720.2-23.317.3-20.214.7-17.312.2-14.710.0-12.2 8.0-10.0 6.2- 8.0 4.7- 6.2 3.3- 4.7 2.2- 3.3 1.3- 2.2 0.7- 1.3 0.2- 0.7 < 0.2
+1 subevt
0 500 1000 1500 20000
260
520
780
1040
1300
Times (ns)
2 ringsπ0 → γ γ
1 ringμ+
Simulated p → μ+π0 event
✤ Cherenkov ring IDmuon-like = crisp edgeelectron-like = fuzzy edge
✤ Outer detector (OD) activityclusters of hits in the OD may indicate event due to cosmic ray
✤ Decay electron countlook for electron from muon decay in delayed coincidence with muon ring
1 dot = 1 PMTlarger dot = more light collected
J.L.Raaf, Boston University APS Meeting, April 14, 2008
Nucleon decay: n → ν π0
5
Mono-energetic π0 from n → ν π0 decay (signal) would sit atop a large background of π0’s from atmospheric neutrino interactions in Super-K.
Single π0 event selection:Fully contained in the fiducial volume
(no activity in outer detector)2 electron-like ringsNo decay electronsReconstructed mπ0 85-185 MeV/c2
n → ν π0(signal)
Atmospheric ν(background)
J.L.Raaf, Boston University APS Meeting, April 14, 2008
n → ν π0 Fitting Method
6
Atmospheric ν(background)
χ2 =nbins
∑i=1
(Nobsi −N
expi
(1+∑Nsyserrj=1 f ij · ε j
))2
σ2i+
Nsyserr
∑j=1
(ε jσ j
)2
Nexpi = α · Nνi +β · NNDKi
Minimize χ2 with systematic pull terms to find best fit parameters (α,β):
where
n → ν π0(signal)
Systematic error pull termsπ0 absorptionscatteringcharge exchangedetection efficiency
J.L.Raaf, Boston University APS Meeting, April 14, 2008
Corresponding 90% CL lifetime lower limit:> 7.6 x 1032 years
SK-1 n → ν π0 Results
7
Fit prefers unphysical NDK: -7.5 events90% CL allowed: 15.6 events
χ2/DOF
Unphysical fitPhysical fit
3.90/84.10/8
J.L.Raaf, Boston University APS Meeting, April 14, 2008
SK-2 n → ν π0 Results
8
Fit prefers unphysical NDK: -2.5 events90% CL allowed: 11.7 events
χ2/DOF
Unphysical fitPhysical fit
6.41/86.43/8
Corresponding 90% CL lifetime lower limit:> 5.0 x 1032 years
J.L.Raaf, Boston University APS Meeting, April 14, 2008
SK-1 + SK-2 n → ν π0 Results
9
Fit prefers unphysical NDK: -5.0 events90% CL allowed: 20.2 events
χ2/DOF
Unphysical fitPhysical fit
9.90/1810.02/18
Corresponding 90% CL lifetime lower limit:> 8.8 x 1032 years
J.L.Raaf, Boston University APS Meeting, April 14, 2008
Fitting via χ2 with systematic pull terms allows Super-K to set a lower limit on the decay mode n → ν π0:
SK-1+2 result:
Previous best experimental limit by IMB:
New Super-K limit begins to constrain SO(10) GUTs!
Conclusions
10
τB.R.
> 1.12×1032 years
τB.R.
> 8.8×1032 years
Imagine another Adobe Illustrator image here...
extras
J.L.Raaf, Boston University APS Meeting, April 14, 2008
Standard Model (SM)Represented by product of symmetry groups SU(3) x SU(2) x U(1)
Local gauge symmetries responsible for forces that mediate EM, weak, and strong interactions
Finite but unobservably long proton lifetime due to baryon number (B) conservation Introduced empirically!Other conserved quantities (e.g., electrical charge) result from gauge symmetries
Nucleon Decay
12
Grand Unified Theories (GUTs)Motivated partly by desire to constrain quantities that are seemingly arbitrary in SM
Attempt to unify the 3 fundamental interactions: coupling constants that describe strong, weak, and EM forces unified at large energies⇒ fundamental forces are low energy manifestations of a single unified force
Many GUTs result in proton lifetime ranges accessible to current experiments
e.g., MSSM
J.L.Raaf, Boston University APS Meeting, April 14, 2008
Super-KamiokandeRun 999999 Sub 0 Ev 1702-11-06:00:06:33
Inner: 3594 hits, 9239 pE
Outer: 1 hits, 1 pE (in-time)
Trigger ID: 0x03
D wall: 398.4 cm
Fully-Contained Mode
Charge(pe) >26.723.3-26.720.2-23.317.3-20.214.7-17.312.2-14.710.0-12.2 8.0-10.0 6.2- 8.0 4.7- 6.2 3.3- 4.7 2.2- 3.3 1.3- 2.2 0.7- 1.3 0.2- 0.7 < 0.2
0 500 1000 1500 20000
240
480
720
960
1200
Times (ns)
Simulated event
1 ringe+
2 ringsπ0 → γ γ
Decay mode: p → e+ π0
13
Selection Criteria3 e-like rings (1 from e+, 1 or 2 from π0 decay)no decay electrons85 < mπ < 185 MeV/c2 (3-ring events only)0 < pp < 250 MeV/c800 < mp < 1050 MeV/c2
SK-ISK-II
Selection criterion
Dete
ctio
n ef
ficie
ncy
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
nring e-like decay e ! mass mp pp
Efficiency (%)
SK-1 40.8
SK-2 42.2
J.L.Raaf, Boston University APS Meeting, April 14, 2008
Super-KamiokandeRun 999999 Sub 0 Ev 1702-11-06:00:06:33
Inner: 3594 hits, 9239 pE
Outer: 1 hits, 1 pE (in-time)
Trigger ID: 0x03
D wall: 398.4 cm
Fully-Contained Mode
Charge(pe) >26.723.3-26.720.2-23.317.3-20.214.7-17.312.2-14.710.0-12.2 8.0-10.0 6.2- 8.0 4.7- 6.2 3.3- 4.7 2.2- 3.3 1.3- 2.2 0.7- 1.3 0.2- 0.7 < 0.2
0 500 1000 1500 20000
240
480
720
960
1200
Times (ns)
Simulated p → e+π0 event
1 ringe+
2 ringsπ0 → γ γ
Event Signatures
14
Super-Kamiokande IRun 999999 Sub 0 Ev 4202-11-06:00:12:25
Inner: 3166 hits, 6293 pE
Outer: 0 hits, 0 pE (in-time)
Trigger ID: 0x03
D wall: 1240.0 cm
Fully-Contained Mode
Charge(pe) >26.723.3-26.720.2-23.317.3-20.214.7-17.312.2-14.710.0-12.2 8.0-10.0 6.2- 8.0 4.7- 6.2 3.3- 4.7 2.2- 3.3 1.3- 2.2 0.7- 1.3 0.2- 0.7 < 0.2
+1 subevt
0 500 1000 1500 20000
260
520
780
1040
1300
Times (ns)
2 ringsπ0 → γ γ
1 ringμ+
Simulated p → μ+π0 event
μ+π0 selection2 or 3 rings, 1 μ-like
(1 from μ+, 1 or 2 from π0 decay)1 decay electron85 < mπ < 185 MeV/c2
(for 3-ring events only)pp < 250 MeV/c800 < mp < 1050 MeV/c2
e+π0 selection2 or 3 e-like rings
(1 from e+, 1 or 2 from π0 decay)no decay electrons85 < mπ < 185 MeV/c2
(for 3-ring events only)pp < 250 MeV/c800 < mp < 1050 MeV/c2
J.L.Raaf, Boston University APS Meeting, April 14, 2008
Decay mode: p → e+ π0
15
SK-I atmospheric !
Proton mass (MeV/c2)
Prot
on m
omen
tum
(MeV
/c)
0
200
400
600
800
1000
0 200 400 600 800 1000 1200
SK-I e+!0
Proton mass (MeV/c2)
Prot
on m
omen
tum
(MeV
/c)
0
200
400
600
800
1000
0 200 400 600 800 1000 1200
SK-I data
Proton mass (MeV/c2)
Prot
on m
omen
tum
(MeV
/c)
0
200
400
600
800
1000
0 200 400 600 800 1000 1200
SK-ISK-II
Selection criterion
Dete
ctio
n ef
ficie
ncy
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
nring e-like decay e ! mass mp pp