Proton Decay Search with Hanohano
The following estimates the sensitivity of Hanohano to the proton decay mode predicted
by SUSY p → ν + K+. If no events are observed during a 100 kt-y exposure with
negligible background, then a partial lifetime limit of τ/B > 9.6 x 1033 y is set. The
comparable limit from Super-K using a 92 kt-y exposure is τ/B > 2.3 x 1033 y.
Super-K fiducial volume is 22.6 kt about 2.5 times greater than the present design for 9 kt
Hanohano fiducial. The number of protons per kt in water and scintillating oil is almost
the same (see rough calculation below). Super-K detection efficiency is 17% about 4
times lesser than the expected 65% for Hanohano. So overall a 9 kt Hanohano is 1.5
times more effective at searching for this proton decay mode than is the 23 kt Super-K.
Some rough calculations with references follow.
Scintillating Oil:
Composition of scintillating oil is about CH2 –
This gives 14 g/mole molecular weight or 2.3 x 10-23 g/molecule.
1 kt (109 g) has 4.3 x 1031 molecules of CH2 –
With 8 protons per molecule this gives 3.4 x 1032 protons per kt.
Hypothetical Hanohano: 10 years of exposure of 10 kt gives 3.4 x 1034 proton-years.
Detection efficiency in scintillating oil is 65% (T. Marrodan Undagoitia et al., Phys. Rev.
D72 (2005) 075014).
Partial lifetime limit (90% C.L.) for 100 kt-y exposure of scintillating liquid is τ/B > (3.4
x 1034 x 0.65) / 2.3 = 9.6 x 1033 y
Water Cherenkov:
Composition of water is H2OThis gives 18 g/mole molecular weight or 3.0 x 10-23 g/molecule.
1 kt (109 g) has 3.3 x 1031 molecules of H2O –
With 10 protons per molecule this gives 3.3 x 1032 protons per kt.
Super-K exposure of 92 kt-y gives 3.1 x 1034 proton-years.
Detection efficiency in water is only 17% because K+ is below Cherenkov threshold.
Super-K uses 92 kt-y exposure to set limit of τ/B > 2.3 x 1033 y (K. Kobayashi et al.,
Phys. Rev. D72 (2005) 052007).