Proton Decay Searches Research Articles

Model of n¯ annihilation in experimental searches for n¯ transformations

Searches for baryon number violation, including searches for proton decay and neutron-antineutron transformation, are expected to play an important role in the evolution of our understanding of beyond Standard Model physics. The neutron-antineutron transformation is a key prediction of certain popular theories of baryogenesis, and the experiments such as the Deep Underground Neutrino Experiment and the European Spallation Source plan to search for this process with bound- and free-neutron systems. Accurate simulation of this process in Monte Carlo will be important for the proper reconstruction and separation of these rare events from background. This article presents developments towards accurate simulation of the annihilation process for use in a cold, free neutron beam for neutron-antineutron searches from antineutron-carbon annihilation, as carbon-12 is the target of choice for the European Spallation Source's NNBar Collaboration. Initial efforts are also made in this paper to perform analogous studies for intra-nuclear transformation searches in argon-40 nuclei, although this latter work will be properly addressed in our next publication.

Gravity waves and proton decay in a flipped SU(5) hybrid inflation model

We revisit supersymmetric hybrid inflation in the context of flipped $SU(5)$ model. With minimal superpotential and minimal K\"ahler potential, and soft SUSY masses of order $(1 - 100)$ TeV, compatibility with the Planck data yields a symmetry breaking scale $M$ of flipped $SU(5)$ close to $(2 - 4) \times 10^{15}$ GeV. This disagrees with the lower limit $M \gtrsim 7 \times 10^{15}$ GeV set from proton decay searches by the Super-Kamiokande collaboration. We show how $M$ close to the unification scale $2\times 10^{16}$ GeV can be reconciled with SUSY hybrid inflation by employing a non-minimal K\"ahler potential. Proton decays into $e^+ \pi^0$ with an estimated lifetime of order $10^{36}$ years. The tensor to scalar ratio $r$ in this case can approach observable values $\sim 10^{-4} - 10^{-3}$.

Determination of trace levels of uranium and thorium in high purity gadolinium sulfate using the ICP-MS with solid-phase chromatographic extraction resin

The new Super-Kamiokande-Gadolinium (SK-Gd) project is an upgrade of the Super-Kamiokande (SK) detector. In the SK-Gd project, 0.2\% Gd$_2$(SO$_4$)$_3$ is loaded into the 50 kton water tank of the SK. One of the main purposes of the project is to discover Supernova Relic Neutrinos. Neutrino measurements and proton decay searches will also be performed in the SK-Gd. In order to measure solar neutrinos with a low energy threshold of $\sim$3.5 MeV in the SK-Gd, the main radioactive contaminations, $^{238}$U and $^{232}$Th, in Gd$_2$(SO$_4$)$_3{\cdot}$8H$_2$O, should be minimized before loading. Our maximum levels for U and Th are 5 mBq (U)/kg (Gd$_2$(SO$_4$)$_3{\cdot}$8H$_2$O) and 0.05 mBq (Th)/kg (Gd$_2$(SO$_4$)$_3{\cdot}$8H$_2$O). In order to measure such low concentrations of U and Th in Gd$_2$(SO$_4$)$_3{\cdot}$8H$_2$O, we developed the solid-phase extraction technique. Using this method, about 90\% or more U and Th could be efficiently extracted while Gd was reduced by a factor of about $10^{4}$. This allowed these radioactivity contaminations to be measured precisely as 0.04 mBq/kg (Gd$_2$(SO$_4$)$_3{\cdot}$8H$_2$O) for U and 0.01 mBq/kg (Gd$_2$(SO$_4$)$_3{\cdot}$8H$_2$O) for Th. We measured three pure Gd$_2$(SO$_4$)$_3{\cdot}$8H$_2$O samples using this method and estimated that the purest one contained $<0.04$ mBq (U)/kg (Gd$_2$(SO$_4$)$_3{\cdot}$8H$_2$O) and 0.06 $\pm$ 0.01 mBq (Th)/kg (Gd$_2$(SO$_4$)$_3{\cdot}$8H$_2$O) by ICP-MS.

Measurement of Neutral-Current K^{+} Production by Neutrinos using MINERvA.

Neutral-current production of K^{+} by atmospheric neutrinos is a background in searches for the proton decay p→K^{+}ν[over ¯]. Reactions such as νp→νK^{+}Λ are indistinguishable from proton decays when the decay products of the Λ are below detection threshold. Events with K^{+} are identified in MINERvA by reconstructing the timing signature of a K^{+} decay at rest. A sample of 201 neutrino-induced neutral-current K^{+} events is used to measure differential cross sections with respect to the K^{+} kinetic energy, and the non-K^{+} hadronic visible energy. An excess of events at low hadronic visible energy is observed relative to the prediction of the neut event generator. Good agreement is observed with the cross section prediction of the genie generator. A search for photons from π^{0} decay, which would veto a neutral-current K^{+} event in a proton decay search, is performed, and a 2σ deficit of detached photons is observed relative to the genie prediction.

Atmospheric neutrinos and proton decay in Super-Kamiokande and Hyper-Kamiokande

Super-Kamiokande is a 50 kton water Cherenkov detector, which has been in operation since 1996. Super-Kamiokande atmospheric neutrino data have a preference for the normal neutrino mass hierarchy (Δχ2=χNH2−χIH2=−4.3) when the constraints from reactor neutrino experiments are included. The search for tau neutrino appearance from neutrino oscillations has resulted in a 4.6σ exclusion of the hypothesis of no tau appearance. Hyper-Kamiokande is a proposed next-generation water Cherenkov detector, which will be a natural extension of Super-Kamiokande. The proposed experiment will have two cylindrical tanks containing 520 kton of water in total. Hyper-K will search for CP violation using the neutrino beam from J-PARC, and will have a broad physics program including studies of atmospheric neutrinos, supernova burst neutrinos, geo-neutrinos and searches for proton decay.

Underground physics with DUNE

The Deep Underground Neutrino Experiment (DUNE) is a project to design, construct and operate a next-generation long-baseline neutrino detector with a liquid argon (LAr) target capable also of searching for proton decay and supernova neutrinos. It is a merger of previous efforts of the LBNE and LBNO collaborations, as well as other interested parties to pursue a broad programme with a staged 40-kt LAr detector at the Sanford Underground Research Facility (SURF) 1300 km from Fermilab. This programme includes studies of neutrino oscillations with a powerful neutrino beam from Fermilab, as well as proton decay and supernova neutrino burst searches. In this paper we will focus on the underground physics with DUNE.

Super-PINGU for measurement of the leptonic CP-phase with atmospheric neutrinos

We explore a possibility to measure the CP-violating phase δ using multimegaton scale ice or water Cherenkov detectors with low, (0.2-1) GeV, energy threshold assuming that the neutrino mass hierarchy is identified. We elaborate the relevant theoretical and phenomenological aspects of this possibility. The distributions of the ν μ (track) and ν e (cascade) events in the neutrino energy and zenith angle (E ν − θ z ) plane have been computed for different values of δ. We study properties and distinguishability of the distributions before and after smearing over the neutrino energy and zenith angle. The CP-violation effects are not washed out by smearing, and furthermore, the sensitivity to δ increases with decrease of the energy threshold. The ν e events contribute to the CP-sensitivity as much as the ν μ events. While sensitivity of PINGU to δ is low, we find that future possible upgrade, Super-PINGU, with few megaton effective volume at (0.5-1) GeV and e.g. after 4 years of exposure will be able to disentangle values of δ = π/2, π, 3π/2 from δ = 0 with “distinguishability” (∼ significance in σ’s) S tot = (3 − 8), (6 − 14), (3 − 8) correspondingly. Here the intervals of S σot are due to various uncertainties of detection of the low energy events, especially the flavor identification, systematics, etc. Super-PINGU can be used simultaneously for the proton decay searches.

Future Prospects of Super-kamiokande and Hyper-kamiokande

The Super-Kamiokande detector has been obtaining data since 1996 and has produced many important physics re- sults, including measurements of oscillations in atmospheric, solar and accelerator neutrinos. This paper discusses the prospects for Super-Kamiokande over the next 10 years and the capabilities of the next-generation experiment, Hyper-Kamiokande. Indeed, the T2K and reactor neutrino experiments have established that the mixing angle θ13 is relatively large, and therefore measurements of the CP phase using a large scale accelerator neutrino experiment such as Hyper-Kamiokande are possible. In addition, since Hyper-Kamiokande is a multi-purpose detector, studies of the mass hierarchy using atmospheric neutrinos, searches for proton decay and measurements of astrophysical neutrinos can also be performed.

Beta decay to continuum states: the case of11Be

Beta decay in exotic nuclei can lead to multi-particle final states. This contri- bution discusses briefly what decay mechanisms may enter in such decays and presents, on behalf of the IS541 collaboration at ISOLDE/CERN, preliminary data from a search for the beta-delayed proton decay of the halo nucleus 11 Be.

Status and New Ideas Regarding Liquid Argon Detectors

Large (up to ∼100 kt) liquid argon (LAr) time-projection chamber detectors are presently being considered for proton decay searches and neutrino astrophysics, as well as for far detectors for the next generation of long-baseline neutrino oscillation experiments that aim to determine neutrino mass hierarchy and search for CP violation in the leptonic sector. These detectors rely on the capabilities to assemble large volumes of LAr in ultrahigh-purity conditions, possibly in an underground environment, and to achieve relatively long drifts for the ionization charge. Several proposals have been developed, each of which takes a different approach to the design of the cryogenic vessels and has different scales of modularity to reach the final mass dictated by physics. New detector concepts, with innovative designs of readout electronics and novel methods for the readout of the ionization charge and scintillation light, have been proposed.

Design and operation of ARGONTUBE: a 5 m long drift liquid argon TPC

The Liquid Argon Time Projection Chamber (LArTPC) is a prime type of detector for future large-mass neutrino observatories and proton decay searches. In this paper we present the design and operation, as well as experimental results from ARGONTUBE, a LArTPC being operated at the AEC-LHEP, University of Bern. The main goal of this detector is to prove the feasibility of charge drift over very long distances in liquid argon. Many other aspects of the LArTPC technology are also investigated, such as a voltage multiplier to generate high voltage in liquid argon (Greinacher circuit), a cryogenic purification system and the application of multi-photon ionization of liquid argon by a UV laser. For the first time, tracks induced by cosmic muons and UVlaser beam pulses have been observed and studied at drift distances of up to 5 m, the longest reached to date.

Decoupling can revive minimal supersymmetric SU(5)

We revisit proton decay via the color-triplet Higgs multiplets in the minimal supersymmetric grand unified model with heavy sfermions. Although the model has been believed to be excluded due to the too short lifetime of proton, we have found that it is possible to evade the experimental constraints on the proton decay rate if the supersymmetric particles have masses much heavier than the electroweak scale. With such heavy sfermions, the 126GeV Higgs boson is naturally explained, while they do not spoil the gauge coupling unification and the existence of dark matter candidates. Since the resultant proton lifetime lies in the regions which may be reached in the future experiments, proton decay searches may give us a chance to verify the scenario as well as the supersymmetric grand unified models.

Enhancement of proton decay rates in supersymmetric SU(5) grand unified models

In the supersymmetric grand unified theories (SUSY GUTs), gauge bosons associated with the unified gauge group induce proton decay. We investigate the proton decay rate via the gauge bosons in the SUSY GUTs under the two situations; one is with extra vector-like multiplets, and the other is with heavy sfermions. It is found that the proton lifetime is significantly reduced in the former case, while in the latter case it is slightly prolonged. Determination of the particle contents and their mass spectrum below the GUT scale is important to predict the proton lifetime. The proton decay searches have started to access to the 1016GeV scale.

θ13and proton lifetime in a minimalSO(10)×S4model of flavor

In a recent paper, a minimal supersymmetric (SUSY) SO(10)xS_4 based unified model of flavor for quarks and leptons was proposed with two 10 and one 126 contributing to fermion masses. An important aspect of this model is that Yukawa couplings emerge dynamically from minimization of the flavon potential, thereby reducing the number of parameters considerably. We make a detailed numerical analysis of this model for fermion mixings including SUSY threshold effects at the TeV scale and type-I corrections to a type-II dominant seesaw for neutrino masses. This is a single-step breaking model with SUSY SO(10) broken at the Grand Unified Theory (GUT)-scale of 2x10^16 GeV to the Minimal Supersymmetric Standard Model (MSSM). The minimal model has only 11 parameters, and therefore, the charged fermion fits predict the masses (up to an overall scale) and mixings in the neutrino sector. We present correlations for the different predictions in the neutrino mixing parameters. The recent experimental "large" \theta_{13} value of \sim 9 degrees can be obtained by a simple extension of the minimal model. We also find that proton decay mode p -> K^+\bar{\nu}_\mu has a partial lifetime of \sim10^34 yrs, which is within reach of the next round of planned proton decay searches. The successful fit for fermion masses requires the Higgs mass to be below 129 GeV in this model. If the Higgs mass lies between 120-128 GeV, as suggested by the recent LHC data, we find a lower limit on the light stop mass of 755 (211) GeV for \mu>0 (<0).

Identification of Neutron Produced from v Interactions with Water and Its Physics Application at Super-Kamiokande IV

With the electronics upgrade in 2008, the fourth phase of Super-Kamiokande(SK) is now capable of identifying neutrons from neutrino interactions with water. A detailed study has been conducted in determining the detection efficiency and background probability. An analysis of neutron production in atmospheric neutrino data is presented, together with a preliminary result of background study for the supernova relic neutrino(SRN) study. Also discussed are prospects of future SRN searches and possible improvement of background rejection for proton decay searches with neutron identification - potentially gadolinium-enhanced - in SK and beyond.

Recent proton decay results from Super-Kamiokande

Recent experimental limits on the search for proton decay are presented. Data from Super-Kamiokande, a water Cherenkov detector with a fiducial volume of 22,500 tons of ultra pure water, are used in the analysis. Analyses from SK-I (40% photomultiplier coverage) plus SK-II (20% photomultiplier coverage) are reported with results from p→e+π0, p→μ+π0, and p→ν¯K+.

Maurice Goldhaber

Maurice Goldhaber

GLACIER and related R&D

Liquid argon detectors, with mass up to 100 kton, are being actively studied in the context of proton decay searches, neutrino astrophysics and for the next generation of long baseline neutrino oscillation experiments to study the neutrino mass hierarchy and CP violation in the leptonic sector. The proposed Giant Liquid Argon Charge Imaging ExpeRiment (GLACIER) offers a well defined conceptual design for such a detector. In this paper we present the GLACIER design and some of the R&D activities pursued within the GLACIER.

LENA: Low Energy Neutrino Astronomy

We focus on the physics potential of a large liquid scintillation detector in the field of low energy neutrino astrophysics. Proton decay search and long baseline oscillations will be discussed briefly at the end.

Results from massive underground detectors on solar and atmospheric neutrino studies and proton decay searches

Massive underground detectors have been playing important roles in particle and astro-particle physics. Results from massive underground detectors on solar and atmospheric neutrino studies and proton decay searches are reviewed.