Sept.03 C. Sterner (TAUP03) 1

ExperimentalReview of ProtonDecay

Chris SternerUniversity of California, Irvine

Super-Kamiokande

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Outlinen Soudan 2

u nK+, m+K0

n Super-Kamiokandeu e+p0, nK+

u Future status

u see S. Mine talk for Background study

n Nucleon Disappearance

(Frejus, SNO, LXe DAMA,

Borexino CTF)

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15N

Parent Proton

Parent NucleusPossible daughter particles(visible and invisible) of varioustheorized modes

e+ p0 ( 5 x 1032 yr . )

Possible daughter nucleiwhich may decay

gamma

Beta, alpha?

16O

nK+ ( 2 x 1033 yr. )

Completely invisible decay modes? ( 1028 yr. )

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Soudan 2Iron Tracking Calorimeter @ Soudan, Minnesota, USAActive outer shield of proportional tubes Argon-CO2 drift tubes

~3 cm spatial resolution Allows resolution of:

shower vs. gamma showerproton track vs. pion/muon

963 tons (770 fiducial) 4.41 kiloton-years fiducial exposure2090 m.w.e. depth

Ref.: Phys. Rev. D, 61, 072004 Phys. Rev D, 62, 092003 NIM Phys Rev A 376, p36

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,pKKnmn+++ÆÆSoudan 2:

K+

e+

m+ E x BR (m+ n) = 9.0%Background Exp’d = .40Candidate events = 1

(3.56 kt-yr exposure)

•2 Charged tracks•K range > 50cm•28 < m range < 58 cm•Decay electron

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Soudan 2:

0,pKKnpp+++ÆÆ

K+

p+

p0

•2 tracks and 2 showers•K range < 50 cm•100 < MK < 660 MeV/c2

•80 < Pp+ < 400 MeV/c•40 < Pp0 < 390 MeV/c•10 < Mp0 < 290 MeV/c2 E x BR (p+p0) = 5.5%

Background Exp’d = 1.14Candidate events = 0(3.56 kt-yr exposure)

Combined T/B(nK+) Limit = 4.3 x 1031 yr. (90%)

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0spKm+ÆSoudan 2:

p p

m

•3 charged tracks ( ) or 1 track and 3-4 showers ( )•Invariant mass Cut•Total momentum Cut•K0 Invariant mass Cut•K0 Total momentum Cut

0sKpp+-Æ

000sKppÆ

E x BR = 22%Background Exp’d = .80 Candidate EventsT/B Limit = 1.5 x 1032 yr. (90%)

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Soudan 2: Summary

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Super-Kamiokande IWater cherenkov detector @ Kamioka, JapanOuter detector veto sheild11146 50cm Photomultiplier Tubes (PMTs)

Energy resolution DE/E = 3% (1GeV e,m)Vertex resolution = 15 cm (e+p0)Particle ID : 99% 1 ring shower (e-like)

vs. 1 ring non-showering (m-like)

50 kton H2O (22.5 kton fiducial)1489 days (91.6 kton-yr exposure)2700 m.w.e depth

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Super-K: 0pep+Æ

•2 or 3 e-like cherenkov rings•If 3 rings then 85 < Mp0 < 185 MeV/c2

•No decay electron•800 < Mproton < 1050 MeV/c2

•PTOT < 250 MeV/c

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Super-K: 0pep+Æ

91.6 kt-yr exposure (1489 days SK-I)

E = 40%Background Exp’d = 0.2Candidate events = 0

T/B (e+p0) = 5.4 x 1032 yr. (90%)

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16O Nucleon decay kinematics in MC•Nuclear potential•Fermi motion•Nuclear medium effect correlated decay (~10% of decays)

Yamazaki & Akaishi. PLB 453.

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•Method I •1 m – like cherenkov ring•1 decay electron•Proton rejection cut•215 < Pm < 260 MeV/c•Fit of spectrum atm n and signal

T/B (p nK+, spectrum) = 4.2 x 1032 yr. (90%)

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Super-K: ,pKKnmn+++ÆÆ

, Spectrum search

91.6 kt-yr exposure (1489 days SK-I)

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Super-K: •Method II

,pKKnmn+++ÆÆ, Prompt gamma search

•1 m –like•1 decay electron•Proton rejection cut•215 < Pm < 260 MeV/c•Prompt gamma tag

T/B (p nK+, prompt g) = 11.4 x 1032 yr. (90%)

Æ

E x BR (nK+) = 8.6%Background Exp’d = 0.70 candidate events

g

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Super-K:

π0 π+ Residual

0,pKKnpp+++ÆÆ

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Super-Kamiokande I: Summary

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Super-Kamiokande II

Nov. 2001 implosion damaged SK-IInner detector PMTs redistributed11146 PMTs 5182 PMTs (47% of original)40% photocathode coverage 19% now

@pdk energy vertex, energy, PID resolution should be okayprompt gamma tag less efficient, but possible

Detector running now (Dec. 2002 - )Super-K III full strength detector for 2006.

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Proton Disappearance:SNO [Zdesenko & Tretyak, Phys. Lett. B 553(2003) 135-140.]

1000 ton of D2OProton disappearance D ? + nneutron capture on D2O, 35ClT/B (p ?) Limit = 3.5 x 1028 yr.

DAMA @ Gran Sasso [Phys. Lett. B 493 (2000) 12-18.]6.5 kg Liquid 129Xe scintillator + 3 EMI PMTsSearch for decay of possible daughter nuclei T/B (p ?) Limit = 1.9 x 1024 yr.

Borexino Counting Test Facility4 ton Liquid scintillator T/B (p ?) Limit = 1.2 x 1026 yr.

Frejus T/B (n 3ne) Limit = 3.0 x 1025 yr.

[Learned, Reines, Soni. Phys. Rev. Lett. 43 (1979)]

T/B (n 3ne) Limit = 5.0 x 1026 yr.

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Conclusions:Present generation of nucleon decay experiments finds no excess

of candidates

SK back online

Continue to search with other physics goals (atm n, solar n, dark matter, supernova n, accelerator n, relic and reactor n?)