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Register a new userSearch for Nucleon and Dinucleon Decays with an Invisible Particle and a Charged Lepton in the Final State at the Super-Kamiokande Experiment
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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.
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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.
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.
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.
The trilepton nucleon decay modes $p rightarrow e^+ u u$ and $p rightarrow mu^+ u u$ violate $|Delta (B - L)|$ by two units. Using data from a 273.4 kiloton year exposure of Super-Kamiokande a search for these decays yields a fit consistent with no signal. Accordingly, lower limits on the partial lifetimes of $tau_{p rightarrow e^+ u u} > 1.7 times 10^{32}$ years and $tau_{p rightarrow mu^+ u u} > 2.2 times 10^{32}$ years at a $90 % $ confidence level are obtained. These limits can constrain Grand Unified Theories which allow for such processes.
The existence of dark matter has been established in astrophysics. However, there are no dark matter candidates in the Standard Model~(SM). If the dark matter particles or their mediator can not interact with SM fermions or gauge bosons, the Higgs boson is the only portal to the dark matter. We present a simulation study to search for invisible decays of the Higgs boson at the ILC with the ILD detector.
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