Baryon Number Violation

Abstract

This report, prepared for the Community Planning Study -Snowmass 2013 -summarizes the theoretical motivations and the experimental efforts to search for baryon number violation, focussing on nucleon decay and neutron-antineutron oscillations. Present and future nucleon decay search experiments using large underground detectors, as well as planned neutron-antineutron oscillation search experiments with free neutron beams are highlighted. OverviewBaryon Number, B, is observed to be an extremely good symmetry of Nature. The stability of ordinary matter is attributed to the conservation of baryon number. The proton and the neutron are assigned B = +1, while their antiparticles have B = −1, and the leptons and antileptons all have B = 0. The proton, being the lightest of particles carrying a non-zero B, would then be absolutely stable if B is an exactly conserved quantum number. Hermann Weyl formulated the principle of conservation of baryon number in 1929 primarily to explain the stability of matter [1]. Weyl's suggestion was further elaborated by Stueckelberg [2] and Wigner [3] over the course of the next two decades. The absolute stability of matter, and the exact conservation of B, however, have been questioned both on theoretical and experimental grounds. Unlike the stability of the electron which is on a firm footing as a result of electric charge conservation

Two loop unification of non-SUSY SO(10) GUT with TeV scalars

“…through more complicated symmetry breaking chains. 2 Here we use the normalization for the hypercharge so that…”

“…In this paper, we compute the two loop beta function and show that this model unifies to two loop order around 10 15 GeV. We then compute the proton lifetime, taking into account threshold effects and show that these effects place it above the Super Kamiokande limit [2].…”

“…For our purposes, we will focus solely on the * tdanielbrennan@physics.rutgers.edu first process as it is the dominant decay channel for this class of models assuming that there is small flavor mixing [22]. By measuring this decay, the latest experiments have placed the lifetime of the proton on the order of 10 34 years [2,21]. This places a strong constraint on the class of physical theories, providing a minimum requirement for all GUT models.…”

Nucleon decay in the deuteron

“…If it is not associated to a local, gauge symmetry, B is expected to be violated in extensions of the SM to higher energies. In fact, proton decay is an outstanding prediction of Grand Unified Theories, in which the strong, weak, and electromagnetic interactions unify at an ultrahigh scale of the order of 10 16 GeV [1]. At present, the lower bounds on the proton lifetime for the two important decay channels p → π 0 + e + and p → π + + ν are 1.6 • 10 34 y and 3.9 • 10 32 y at 90% confidence level, respectively [2,3].…”

Dinucleon and Nucleon Decay to Two-Body Final States with no Hadrons in Super-Kamiokande

“…Since B is an accidental symmetry in the Standard Model (SM) of particle physics, observation of B violation would imply new physics beyond the Standard Model. Many theoretical extensions of the SM allow violation of B and/or lepton number, L, and predict experimentally observable processes (see reviews in [2] and [3]). The searches for ten such B-violating processes via nucleon or dinucleon decay in Super-Kamiokande are detailed in this Letter.…”