Search for the Invisible Decay of Neutrons with KamLAND

Abstract

The Kamioka Liquid scintillator Anti-Neutrino Detector is used in a search for single neutron or twoneutron intranuclear disappearance that would produce holes in the s-shell energy level of 12 C nuclei. Such holes could be created as a result of nucleon decay into invisible modes (inv), e.g., n ! 3 or nn ! 2 . The deexcitation of the corresponding daughter nucleus results in a sequence of space and timecorrelated events observable in the liquid scintillator detector. We report on new limits for one-and twoneutron disappearance: n ! inv > 5:8 10 29 years and nn ! inv > 1:4 10 30 years at 90% C.L. These results represent an improvement of factors of 3 and >10 4 over previous experiments.

Improved upper limits on baryon-number violating dinucleon decays to dileptons

“…where the final inequality follows from the fact that P nn,J =0 < 1. Even without inserting an estimated value for the suppression factor due to P nn,J =0 , our bound (21) is stronger than the direct limits on these two decays, which are (from the SuperKamiokande experiment) [20]:…”

“…For comparison, there is a bound from a direct search by the KamLAND experiment 1 , namely [21] (τ /B) nn→inv. > 1.4 × 10 30 yr (26) per 12 C nucleus, where "inv."…”

Baryon-number-violating nucleon and dinucleon decays in a model with large extra dimensions

“…These limits include (τ /B) p→e + xx > 0. 58 [20], where here x denotes an unobserved neutral, weakly interacting fermion with negligibly small mass that does not decay in the detector. Thus, for ex-ample, the lower limit on (τ /B) for the decay p → ℓ + xx applies to all of the decays p → ℓ +νν′ (with ∆L = −3), p → ℓ + νν ′ (with ∆L = −1), and p → ℓ + νν ′ (with ∆L = 1) for ℓ + = e + or µ + , and similarly, the lower bound on n → xxx applies to all neutron decays to combinations of (anti)neutrinos with ∆L ranging from ∆L = −3 to ∆L = +3.…”

“…Then the decay rate for one of the three dinucleon-todilepton decays (1.5)-(1.8) is 20) where S is a symmetry factor, S = 1/2 for decays with identical leptons in the final state and R 2 is the phasespace factor.…”

Neutrino Physics with SNO+

“…SNO+ is expecting to improve the current best limit set by KamLAND [6] by almost an order of magnitude to about 8.2×10 30 and 9.1×10 30 years on the neutron and proton invisible decay mode respectively.…”