searches for nucleon decay and n-n oscillation in super-kamiokande
DESCRIPTION
Searches for nucleon decay and n-n oscillation in Super-Kamiokande. Jun Kameda (ICRR, Univ. of Tokyo) for Super-Kamiokande collaboration Sep. 14 th , 2007 TAUP 2007, Sendai, Japan. Outline. Introduction of the Super-Kamiokande Searches for Nucleon decay (p e + + p 0 , p m + +p 0 ) - PowerPoint PPT PresentationTRANSCRIPT
TAUP2007 1
Searches for nucleon decay and n-n oscillation
in Super-Kamiokande
Jun Kameda (ICRR, Univ. of Tokyo)
for Super-Kamiokande collaborationSep. 14th, 2007
TAUP 2007, Sendai, Japan
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Outline
Introduction of the Super-Kamiokande Searches for Nucleon decay
(pe++0, p0) Search for Neutron-antineutron oscillatio
n Summary
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Super-Kamiokande
• Water Cherenkov detector• 50kton (22.5 kton fid.), = 6.02x1033 neutrons + 7.53x1033 protons• Deep underground (1000m, 2700 m.w.e), Kamioka-mine, Japan.
SK-I : 91.6ktyr (Apr.1996-Jul.2001)SK-II: 49.5ktyr (Dec.2002-Oct.2005)SK-III had started from Jul.2006.
39.3m
41.4m
SK-IID 11146 20inch PMTsOD 1885 8-inch PMTsSK-IIID 5182 20inch PMTs
Data period:
Super-Kamioka Nucleon Decay Experiment
5 countries, 35 institutes~120 physicist
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Nucleon decay Searchesin Super-Kamiokande
Nucleon decay is the direct evidence of the Grand Unification Theories (GUTs).
Several GUTs predicts several decay modes. (pe+0,0,K+,..)
No positive signal had been observed.
Experimental Lifetime lower limits (yr)
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Nucleon decay (I) p e+ + 0
All visible particles contained 2 or 3 Cherenkov rings All rings are e-like no decay electron 85 < M[MeV/c2] <185 (for 3ring) 800 < Mtot [MeV/c2] < 1050
& Ptot [MeV/c] < 250
Event selection:
Efficiency : Super-K I 45.0% (was 42.9%)Super-K II 43.6% (was 42.2%)
Improved efficiencies are due to an improvedalgorithm of separation of the overlapping Cherenkov rings.
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Total P vs Invariant Mass plots p e+ + 0
SK-ISK-I
p e++0 MC
SK-IISK-II
No signal was observed in SK-I & SK-II.
atm MC Data
Eff. 45.0% 0.4 event 0 event
Eff. 43.6% 0.04 event 0 event
1489.2days
Invariant Mass (MeV/c2)
Total P(MeV/c)
798.6days
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• No Candidate was observed.• Estimated B.G. ( osc. considered) SK-I: 0.4, SK-II: 0.04• P/Be0 > 5.5 x 1033 years (90 % C.L.) (SK-I) • P/Be0 > 2.9 x 1033 years (90 % C.L.) (SK-II)
Result of the search for p e+ + 0 (preliminary)
P/Be0 > 8.4 x 1033 years (90 % C.L)
(SK-I + SK-II)
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Nucleon decay (II) p + + 0
All visible particles contained 2 or 3 Cherenkov rings 1 -like 1 decay electron 85 < M[MeV/c2] <185 (for 3ring) 800 < Mtot [MeV/c2] < 1050
& Ptot [MeV/c] < 250
Event selection:
Efficiency : Super-K I 35.6% (was 30.6%)Super-K II 35.5% (was 32.1%)
+
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Result of p + + 0 (preliminary)
SK-ISK-I
p ++0 MC
SK-IISK-II
atm MC Data
Eff. 35.6% 0.4 event 0 event
Eff. 35.5% 0.2 event 0 event
1489.2days
Total P(MeV/c)
798.6days
•P/Be0 > 4.4 x 1033 yrs (90 % C.L.) (SK-I)
• P/Be0 > 2.3 x 1033 yrs (90 % C.L.) (SK-II)
No candidates. Invariant Mass(MeV/c2)
P/Be0 > 6.7 x 1033 years (SK-I + SK-II, 90 % C.L)
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Summary of nucleon decay search
No positive signals have been observed in any mode.
Obtained lifetime limits: pe++0 : /B > 8.4 x1033 yr (SK-I+SK-II, preliminary) p++0 : /B > 6.7 x1033 yr (SK-I +SK-II, preliminary) p+K+ : /B > 2.3 x1033yr (SK-I), PRD 72, 052007 (2005),
Many other modes (B-L violating modes, etc.) have been searched for in Super-K.
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Search for neutron - anti-neutron oscillation
in Oxygen in Super-K I
Several type of (B-L)-violating Gauge theories predicts that neutron spontaneously converts to anti-neutron, and vise versa. (ex. K.S.Babu et al., Phys.Lett.B518(2001) 269-275)
|B| =2 process.Good test for new physicsincluding GUTs.
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Expected signals in Water Cherenkov detector
Anti-neutrons quickly pair-annihilates with the surrounding nucleon.
Pions (<n>~4 ) of several 100MeV/c’s are emitted isotropically, and propagate inside the nuclein
anti-n + p anti-n + n
np
np
np
About 2 x nucleon mass energy will be released in the residual nuclei.
Branching ratio derived fromBubble Chamber p + d data
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Typical Event (anti-n+p )
Multi-Cherenkov ring events are expected.
n-nbar MC
Many pions andtheir secondaries+ low energynuclear fragments
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0) all visible particles containeda) #of rings >= 2b) 700< visible energy (MeV) <1300c) 0< Ptot (MeV/c) <450d) 750< Mtot (MeV/c2) <1800
# of rings
Visible Energy(MeV) Total Momentum (MeV/c) Invariant Mass (MeV/c2)
Invariant Mass is smaller than 2xnucleondue to absorption in & interactionin nuclear & water
Event Selection
10.4% efficiency
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10.4 % detection efficiency
20 candidates
21.3 background events (osc. effects are included)
n-n MC
Results ofn-n oscillation
limit
1T
bound
= 1.77×1032 yrs ( 90% CL ) (SK-1)
(systematic errors are included by Baysian statistics)
atm. MC
SK-I data
Not a spontaneous decay of neutron,but we call the inverse of the event rateis the “lifetime” of the neutron in Oxygen.
Ptot
(MeV
/c)
Inv. Mass (MeV/c2)
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Systematic uncertaintiesPossible sources of the systematic uncertainty in experimental and modeling (Pion interactions, n+anti-n annihilation, etc.) are investigated.
-nucleon scattering in nuclear(cross sections, modeling of nuclear, etc)
12.6 %
nbar+N Annihilation branching ratio
5.2 %
Fermi motion of nucleons 4.2 %
Energy scale 1.7 %
Asymmetry of gain 4.0 %
Cherenkov ring finding 0.6 %
Fid.Vol. determination 3.2%
Total 15.2%
Detection efficiency & Exposureatmospheric flux(flavor ratio, zenith angle dist., spectrum, absolute norm, etc.)
21.5%
Neutrino interactions(absolute cross section uncertainties, differential uncertainties, etc.)
17.8%
-propagations in 16O(cross sections, 16O modelings,etc)
2.7%
Energy scale 12.0%
Asymmetry of gain 9.0 %
Cherenkov ring finding 4.3 %
Total 32.1%
B.G rate
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Comparison with other experimental limits
Experiment Source
Exposure(n yr)
Tbound
(1032yr)
free
(108sec)
ILL Beam --- --- 0.86Soudan2 56Fe 21.9 0.72 1.3Frejus 56Fe 5.0 0.65 1.2Kamiokande
16O 3.0 0.43 1.2
IMB 16O 3.0 0.24 0.88Super-K I 16O 254.5 1.77 2.36
R(1023sec-1)
---
1.4
1.4
1.0
1.0
1.0*
Super-K I results includes systematic uncertainty.
Bound neutron lifetime can be interpreted to the oscillation time of the free neutron by Tbound = R*(free)2
* C.B.Dover et al. Phys. Rev. D 27 (1983) 1090
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Summary
Nucleon decay searches and neutron-antineutron oscillation are reported.
No evidence of nucleon decay, no evidence of n-n oscillation were found.
pe++0 : /B > 8.4 x1033 yr (SK-I+SK-II, preliminary)p++0 : /B > 6.7 x1033 yr (SK-I +SK-II, preliminary) n-n oscillation: bound> 1.77x1032 yr (SK-I, preliminary)
free> 2.36x108 sec