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Register a new userDinucleon and Nucleon Decay to Two-Body Final States with no Hadrons in Super-Kamiokande
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Using 0.37 megaton$cdot$years of exposure from the Super-Kamiokande detector, we search for 10 dinucleon and nucleon decay modes that have a two-body final state with no hadrons. These baryon and lepton number violating modes have the potential to probe theories of unification and baryogenesis. For five of these modes the searches are novel, and for the other five modes we improve the limits by more than one order of magnitude. No significant evidence for dinucleon or nucleon decay is observed and we set lower limits on the partial lifetime of oxygen nuclei and on the nucleon partial lifetime that are above $4times 10^{33}$ years for oxygen via the dinucleon decay modes and up to about $4 times 10^{34}$ years for nucleons via the single nucleon decay modes.
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A search for dinucleon decay into pions with the Super-Kamiokande detector has been performed with an exposure of 282.1 kiloton-years. Dinucleon decay is a process that violates baryon number by two units. We present the first search for dinucleon decay to pions in a large water Cherenkov detector. The modes $^{16}$O$(pp) rightarrow$ $^{14}$C$pi^{+}pi^{+}$, $^{16}$O$(pn) rightarrow$ $^{14}$N$pi^{+}pi^{0}$, and $^{16}$O$(nn) rightarrow$ $^{14}$O$pi^{0}pi^{0}$ are investigated. No significant excess in the Super-Kamiokande data has been found, so a lower limit on the lifetime of the process per oxygen nucleus is determined. These limits are: $tau_{pprightarrowpi^{+}pi^{+}} > 7.22 times 10^{31}$ years, $tau_{pnrightarrowpi^{+}pi^{0}} > 1.70 times 10^{32}$ years, and $tau_{nnrightarrowpi^{0}pi^{0}} > 4.04 times 10^{32}$ years. The lower limits on each mode are about two orders of magnitude better than previous limits from searches for dinucleon decay in iron.
Search results for nucleon decays $p rightarrow e^+X$, $p rightarrow mu^+X$, $n rightarrow ugamma$ (where $X$ is an invisible, massless particle) as well as dinucleon decays $np rightarrow e^+ u$, $np rightarrow mu^+ u$ and $np rightarrow tau^+ u$ in the Super-Kamiokande experiment are presented. Using single-ring data from an exposure of 273.4 kton $cdot$ years, a search for these decays yields a result consistent with no signal. Accordingly, lower limits on the partial lifetimes of $tau_{p rightarrow e^+X} > 7.9 times 10^{32}$ years, $tau_{p rightarrow mu^+X} > 4.1 times 10^{32}$ years, $tau_{n rightarrow ugamma} > 5.5 times 10^{32}$ years, $tau_{np rightarrow e^+ u} > 2.6 times 10^{32}$ years, $tau_{np rightarrow mu^+ u} > 2.2 times 10^{32}$ years and $tau_{np rightarrow tau^+ u} > 2.9 times 10^{31}$ years at a $90 % $ confidence level are obtained. Some of these searches are novel.
Baryon number violation appears in many contexts. It is a requirement for baryogenesis and is a consequence of Grand Unified Theories (GUTs), which predict nucleon decay. Nucleon decay searches provide the most direct way to test baryon number conservation and also serve as a unique probe of GUT scale physics around $10^{14-16}$ GeV. Such energies cannot be reached directly by accelerators. However, they can be explored indirectly at large underground water Cherenkov (WC) experiments, which due to the size of their fiducial volume are highly sensitive to nucleon decays. We review searches for baryon number violating processes at the state of the art WC detector, the Super-Kamiokande. Analyses of the typically dominant non-SUSY and SUSY nucleon decay channels such as $p rightarrow (e^+, mu^+) pi^0$ and $p rightarrow u K^+$, as well as more exotic searches, will be discussed. Presented studies set the worlds best limits, which circumvent the allowed parameter space of theoretical models
We consider baryon-number-violating nucleon and dinucleon decays to leptonic final states in the context of a left-right symmetric (LRS) model with large extra dimensions. Specifically, we study (a) nucleon to trilepton decays with $Delta B=-1$ and $Delta L=-3$, and (b) dinucleon to dilepton decays with $Delta B=-2$ and $Delta L=-2$. In the LRS model, $B-L$ is gauged and is spontaneously broken by a Higgs vacuum expectation value $v_R$, which characterizes the scale at which processes violating $B-L$ occur. We show that together with the lower bound on $v_R$ from experimental limits on $n$-$bar n$ oscillations, constraints from searches for other nucleon decay modes imply sufficient suppression of these nucleon to trilepton and dinucleon to dilepton decay modes in this model to agree with experimental bounds.
Searches for a nucleon decay into a charged anti-lepton (e^+ or {mu}^+) plus a light meson ({pi}^0, {pi}^-, {eta}, {rho}^0, {rho}^-, {omega}) were performed using the Super-Kamiokande I and II data. Twelve nucleon decay modes were searched for. The total exposure is 140.9 kiloton cdot years, which includes a 91.7 kiloton cdot year exposure (1489.2 live days) of Super-Kamiokande-I and a 49.2 kiloton cdot year exposure (798.6 live days) of Super-Kamiokande-II. The number of candidate events in the data was consistent with the atmospheric neutrino background expectation. No significant evidence for a nucleon decay was observed in the data. Thus, lower limits on the nucleon partial lifetime at 90% confidence level were obtained. The limits range from 3.6 times 10^31 to 8.2 times 10^33 years, depending on the decay modes.
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