Nucleon Decay Modes Research Articles

Neural-network-driven proton decay sensitivity in the p \u2192 overline{nu} K+ channel using large liquid argon time projection chambers

We report on an updated sensitivity for proton decay via p → overline{nu} K+ at large, dual phase liquid argon time projection chambers (LAr TPCs). Our work builds on a previous study in which several nucleon decay modes have been simulated and analyzed [1]. At the time several assumptions were needed to be made on the detector and the backgrounds. Since then, the community has made progress in defining these, and the computing power available enables us to fully simulate and reconstruct large samples in order to perform a better estimate of the sensitivity to proton decay. In this work, we examine the benchmark channel p → overline{nu} K+, which was previously found to be one of the cleanest channels. Using an improved neutrino event generator and a fully simulated LAr TPC detector response combined with a dedicated neural network for kaon identification, we demonstrate that a lifetime sensitivity of τ /Br (p → overline{nu} K+) > 7 × 1034 years at 90% confidence level can be reached at an exposure of 1 megaton · year in quasi-background-free conditions, confirming the superiority of the LAr TPC over other technologies to address the challenging proton decay modes.

Nucleon and dinucleon decays to leptonic final states in a left-right symmetric model with large extra dimensions

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 varDelta B=-1 and varDelta L=-3, and (b) dinucleon to dilepton decays with varDelta B=-2 and varDelta 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.

SNO+ status and prospects

SNO+ is a multi-purpose experiment whose main goal is to study the nature of the neutrino mass through the observation of neutrinoless double-beta decay. Detection of this rare process would indicate that neutrinos are elementary Majorana particles, proving that lepton number is not conserved. The SNO+ detector will operate in three distinct phases with different target materials: water, pure liquid scintillator and tellurium-loaded liquid scintillator. During the water phase, the external backgrounds were confirmed to be within expectation, new limits on specific channels of invisible nucleon decay modes were set and the Boron-8 solar neutrino flux was measured and confirmed to be compatible with previous measurements. With a completed water phase, SNO+ is moving towards its main Tellurium-loaded phase. Here, we report the status of the experiment, the recent results and the potential of SNO+ for neutrinoless double-beta decay search.

Proton decay: flipped vs. unflipped SU(5)

We analyze nucleon decay modes in a no-scale supersymmetric flipped SU(5) GUT model, and contrast them with the predictions for proton decays via dimension-6 operators in a standard unflipped supersymmetric SU(5) GUT model. We find that these GUT models make very different predictions for the ratios Γ(p → π0μ+)/Γ(p → π0e+), Γ(p → {pi}^{+}overline{nu} )/Γ(p → π0e+), Γ(p → K0e+)/Γ(p → π0e+) and Γ(p → K0μ+)/Γ(p → π0μ+), and that predictions for the ratios Γ(p → π0μ+)/Γ(p → π0e+) and Γ(p → {pi}^{+}overline{nu} )/Γ(p → π0e+) also differ in variants of the flipped SU(5) model with normal- or inverse-ordered light neutrino masses. Upcoming large neutrino experiments may have interesting opportunities to explore both GUT and flavour physics in proton and neutron decays.

B − L violating nucleon decays as a probe of leptoquarks and implications for baryogenesis

We study the effective B−L violating couplings for scalar and vector leptoquarks which can naturally induce dimension seven B−L violating operators leading to very interesting nucleon decay modes such as n→e−π+,e−K+,μ−π+,μ−K+ and p→νπ+. This opens a new window to probe the nature and couplings of the scalar and vector leptoquarks in an ultraviolet model independent way which can provide an orthogonal probe for scalar and vector leptoquark solutions to the recent anomalous B-decay data. Furthermore, we also discuss how these B−L violating interactions can also pave a new way to understand the origin of matter-antimatter asymmetry of the Universe.

Improved lower bounds on partial lifetimes for nucleon decay modes

In the framework of a baryon-number-violating effective Lagrangian, we calculate improved lower bounds on partial lifetimes for proton and bound neutron decays, including $p \to \ell^+ \ell'^+ \ell'^-$, $n \to \bar\nu \ell^+ \ell'^-$, $p \to \ell^+ \nu\bar\nu$, and $n \to \bar\nu \bar\nu \nu$, where $\ell$ and $\ell'$ denote $e$ or $\mu$, with both $\ell = \ell'$ and $\ell \ne \ell'$ cases. Our lower bounds are substantially stronger than the corresponding lower bounds from direct experimental searches. We also present lower bounds on $(\tau/B)_{p \to \ell^+\gamma}$, $(\tau/B)_{n \to \bar\nu \gamma}$, $(\tau/B)_{p \to \ell^+ \gamma\gamma}$, and $(\tau/B)_{n \to \bar\nu \gamma\gamma}$. Our method relies on relating the rates for these decay modes to the rates for decay modes of the form $p \to \ell^+ M$ and $n \to \bar\nu M$, where $M$ is a pseudoscalar or vector meson, and then using the experimental lower bounds on the partial lifetimes for these latter decays.

Novel GUT with apparently complete SU(5) multiplets

The perfect fit of the matter fields of the Standard Model (SM) into the $SU(5)$ multiplets has strongly supported the idea of the Grand Unified Theory (GUT) for decades. In this paper, we discuss a novel framework which explains why the SM matter fields form the apparently complete $SU(5)$ multiplets. In the new framework, the apparent matter unification inevitably results from chiral $SU(5)$ gauge theory even if the quarks and leptons are not embedded into the common $SU(5)$ multiplets. We call this class of models the "fake GUT". The novel phenomenological prediction of the fake GUT is more variety of the nucleon decay modes than the conventional GUT, which reflects the rich structure of the origin of the matter fields.

Search for invisible modes of nucleon decay in water with the SNO+ detector

This paper reports results from a search for nucleon decay through 'invisible' modes, where no visible energy is directly deposited during the decay itself, during the initial water phase of SNO+. However, such decays within the oxygen nucleus would produce an excited daughter that would subsequently de-excite, often emitting detectable gamma rays. A search for such gamma rays yields limits of $2.5 \times 10^{29}$ y at 90% Bayesian credibility level (with a prior uniform in rate) for the partial lifetime of the neutron, and $3.6 \times 10^{29}$ y for the partial lifetime of the proton, the latter a 70% improvement on the previous limit from SNO. We also present partial lifetime limits for invisible dinucleon modes of $1.3\times 10^{28}$ y for $nn$, $2.6\times 10^{28}$ y for $pn$ and $4.7\times 10^{28}$ y for $pp$, an improvement over existing limits by close to three orders of magnitude for the latter two.

Physics capabilities of the SNO+ experiment

SNO+ will soon enter its first phase of physics data-taking. The Canadian-based detector forms part of the SNOLAB underground facility, in a Sudbury nickel mine; its location providing more than two kilometres of rock overburden. We present an overview of the SNO+ experiment and its physics capabilities. Our primary goal is the search for neutrinoless double-beta decay, where our expected sensitivity would place an upper limit of 1.9 × 1026 y, at 90% CL, on the half-life of neutrinoless double-beta decay in 130Te. We also intend to build on the success of SNO by studying the solar neutrino spectrum. In the unloaded scintillator phase SNO+ has the ability to make precision measurements of the fluxes of low-energy pep neutrinos and neutrinos from the CNO cycle. Other physics goals include: determining the spectrum of reactor antineutrinos, to further constrain ; detecting neutrinos produced by a galactic supernova and investigating certain modes of nucleon decay.

Understanding the SNO+ Detector

SNO+, a large liquid scintillator experiment, is the successor of the Sudbury Neutrino Observatory (SNO) experiment. The scintillator volume will be loaded with large quantities of 130Te, an isotope that undergoes double beta decay, in order to search for neutrinoless double beta decay. In addition to this search, SNO+ has a broad physics program due to its sensitivity to solar and supernova neutrinos, as well as reactor and geo anti-neutrinos. SNO+ can also place competitive limits on certain modes of invisible nucleon decay during its first phase.The detector is currently undergoing commissioning in preparation for its first phase, in which the detector is filled with ultra pure water. This will be followed by a pure scintillator phase, and then a Tellurium-loaded scintillator phase to search for neutrinoless double beta decay.Here we present the work done to model detector aging, which was first observed during SNO. The aging was found to reduce the optical response of the detector. We also describe early results from electronics calibration of SNO+.

Search for trilepton nucleon decay via p→e+νν and p→μ+νν in the Super-Kamiokande experiment.

The trilepton nucleon decay modes p→e+νν and p→μ+νν violate |Δ(B-L)| by two units. Using data from a 273.4 kt yr exposure of Super-Kamiokande a search for these decays yields a fit consistent with no signal. Accordingly, lower limits on the partial lifetimes of τp→e+νν>1.7×10(32) years and τp→μ+νν>2.2×10(32) years at a 90% confidence level are obtained. These limits can constrain Grand Unified Theories which allow for such processes.

Realistic fermion masses and nucleon decay rates in supersymmetric SU(5) with vectorlike matter

We show that by adding a vectorlike $5+\overline{5}$ pair of matter fields to the spectrum of the minimal renormalizable supersymmetric $SU(5)$ theory the wrong relations for fermion masses can be corrected, while being predictive and consistent with proton lifetime limits. Threshold correction from the vectorlike fields improves the unification of gauge couplings compared to the minimal model. It is found that for supersymmetric spectra lighter than 3 TeV, which would be testable at the LHC, at least some of the nucleon decay modes should have partial lifetimes shorter than about $2\ifmmode\times\else\texttimes\fi{}{10}^{34}$ years, which is within reach of ongoing and proposed experiments.

Search for nucleon decay into charged antilepton plus meson in Super-Kamiokande I and II

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.

Science from detection of neutrinos from supernovae

The neutrinos emitted from supernovae contain information about the physics of stellar collapse and of the nature of the neutrinos themselves. Several large detectors exist that will be capable of observing some subset of those neutrinos. In addition, we have designed OMNIS, the Observatory for Multiflavour NeutrInos from Supernovae. OMNIS will detect the neutrinos from (a) neutral-current interactions from νe, νμ, , ντ and , and (b) charged-current interactions from high-momentum νe, with lead nuclei. It will utilize two types of detectors: (1) lead slabs alternating with vertical planes of neutron detectors, in which neutrons produced by neutrino–lead interactions will be detected, and (2) lead perchlorate, in which both the resulting neutrons and Cerenkov light will be detected. OMNIS will measure neutrino masses below 100 eV, provide new information on MSW or vacuum oscillations from νμ/ντ to νe, especially to Θ13, and possibly diagnose the process of collapse to a black hole. It will observe the late-time evolution of the neutrino distributions, and possibly see predicted late-time effects, e.g. a phase transition from neutron-star matter to kaon-condensed matter or quark matter. OMNIS is also sensitive to some modes of nucleon decay that should make it possible to improve significantly on present limits for those modes. Of crucial importance to OMNIS is an experiment, using neutrinos from a stopped pion beam, to determine the flavour and energy-dependent response of lead to neutrinos. This will provide important input into cross section calculations for which few data currently exist. We plan to perform this experiment using one of the lead perchlorate detector modules from OMNIS.

Supernovae neutrinos and the r-process and ν-processes of nucleosynthesis

The neutrinos emitted from supernovae contain information both about the physics of stellar collapse and of the nature of the neutrinos. Several detectors exist that will be capable of observing some subset of those neutrinos. To complement these detectors, we have designed OMNIS, the Observatory for Multiflavor NeutrInos from Supernovae. OMNIS will provide new information on stellar collapse and neutrino transformations, possibly diagnose the process of collapse to a black hole, and observe the late-time evolution of the neutrino distributions. OMNIS' ability to measure the spectra of the neutrinos will have an important effect on our understanding of the r- and ν-processes of nucleosynthesis. OMNIS is also sensitive to some modes of nucleon decay that could significantly improve present limits.

THE SEARCH FOR NUCLEON DECAY AT SUPER-KAMIOKANDE

We have analyzed 1144 days of Super-Kamiokande data for 13 of the more than 40 possible nucleon decay modes. We have studied p→e+π0, and twelve other two particle B-L conserving decay modes including those with kaons that are preferred in supersymmetric theories. Most modes are currently free of candidate events. In all cases the number of candidates is consistent with atmospheric neutrino induced backgrounds. We have calculated 90% confidence level single sided lower limits on the lifetime of the neutron and proton (divided by the unknown branching ratio) for the studied modes. All of our lower limits are higher than previous best limits by a factor of 2-10. Our limit for p→e+π0 is now 4.4×1033 years.

New limits on nucleon decay modes to neutrinos

Abstract New limits on neutron decay to 3 and 5 neutrinos based on Kamioka data [1] are derived by evaluating the bremsstrahlung photon emission probability during decay. One finds that τ(n → 3ν) BR > 2.3 10 27 yr(90% CL) and τ(n → 5ν) BR > 1.7 10 27 yr(90% CL) .

Dominance of the nucleon decay K-channels in PLR invariant SO(10)

RH rotations of the fermionic mass matrices are not observable in the standard model, but dictate the details of the proton decay in GUTs. $P_{LR}$ symmetry in the two light families leads to a full RH mixing. We give two versions of suitable broken $P_{LR}$ invariant SO(10) which leads to nucleon decay modes similar to those of SUSY-GUTs with rates in the range of observability of superKamiokande and ICARUS.

Nucleon decay in non-minimal supersymmetric SO(10)

Evaluation of nucleon decay modes and branching ratios in a non-minimal supersymmetric SO(10) grand unified theory is presented. The non-minimal GUT considered is the supersymmetrised version of the ‘realistic’ SO(10) model originally proposed by Harvey, Reiss and Ramond, which is realistic in that it gives acceptable charged fermion and neutrino masses within the context of a phenomenological fit to the low-energy standard model inputs. Despite a complicated Higgs sector, the SO(10) 10 Higgs superfield mass insertion is found to be the sole contribution to the tree-level F-term governing nucleon decay. The resulting dimension-5 operators that mediate nucleon decay give branching ratio predictions parameterised by a single parameter, the ratio of the Yukawa couplings of the 10 to the fermion generations. For parameter values corresponding to a lack of dominance of the third family self-coupling, the dominant nucleon decay modes are p → K + + ν μ and n → K 0 + ν μ as expected. Further, the charged muon decay modes are enhanced by two orders of magnitude over the standard minimal SUSY SU(5) predictions, thus predicting a distinct spectrum of ‘visible’ modes. These charged muon decay modes, along with p → π + + ν μ and n → π 0 + ν μ , which are moderately enhanced over the SUSY SU(5) prediction, suggest a distinguishing fingerprint of this particular GUT model, and if nucleon decay is observed at Super-KAMIOKANDE the predicted branching ratio spectrum can be used to determine the validity of this ‘realistic’ SO(10) SUSY GUT model.

Low-mass right-handed gauge bosons, proton decay, and other observable predictions in SU(8)L x SU(8)R and SU(16).

The prospects of an alternative method of decoupling the parity and SU(2){sub {ital R}} breaking are reexamined under the constraints of CERN LEP measurements in the minimal chains of SU(8){sub {ital L}}{times}SU(8){sub {ital R}} and SU(16) grand unified theories. Including the uncertainties in the input parameters, one chain permits the SU(2){sub {ital L}}{times}SU(2){sub {ital R}}{times}SU(4){sub {ital C}}-breaking scale {ital M}{sub {ital C}}=10{sup 5.6{plus_minus}0.6} GeV leading to the {Delta}({ital B}{minus}{ital L})={minus}2 nucleon-decay modes possibly accessible to the ongoing experiments and observable branching ratios for rare kaon decays. Uncertainties in the Higgs scalar masses near {ital M}{sub {ital C}} result in wider ranges of predictions on the proton lifetime and mixing times for {ital n}-{ital {bar n}} and {ital H}-{ital {bar H}} oscillations. In a separate chain the SU(2){sub {ital L}}{times}SU(2){sub {ital R}}{times}U(1){sub {ital B}{minus}{ital L}}{times}SU(3){sub {ital C}}-breaking scale corresponding to the masses of right-handed gauge bosons could be {ital M}{sub {ital R}}=10{sup 2.8{plus_minus}0.7} GeV, which seems to be the lowest value predicted so far in a non-SUSY GUT consistent with minimal fine-tuning of parameters.