Search For Decay Research Articles

Cosmic neutrino background detection in large-neutrino-mass cosmologies

The cosmic neutrino background (CNB) is a definite prediction of the standard cosmological model and its direct discovery would represent a milestone in cosmology and neutrino physics. In this work, we consider the capture of relic neutrinos on a tritium target as a possible way to detect the CNB, as aimed for by the PTOLEMY project. Crucial parameters for this measurement are the absolute neutrino mass ${m}_{\ensuremath{\nu}}$ and the local neutrino number density ${n}_{\ensuremath{\nu}}^{\mathrm{loc}}$. Within the $\mathrm{\ensuremath{\Lambda}}\mathrm{CDM}$ model, cosmology provides a stringent upper limit on the sum of neutrino masses of $\ensuremath{\sum}{m}_{\ensuremath{\nu}}<0.12\text{ }\text{ }\mathrm{eV}$, with further improvements expected soon from galaxy surveys by DESI and EUCLID. This makes the prospects for a CNB detection and a neutrino mass measurement in the laboratory very difficult. In this context, we consider a set of nonstandard cosmological models that allow for large neutrino masses (${m}_{\ensuremath{\nu}}\ensuremath{\sim}1\text{ }\text{ }\mathrm{eV}$), potentially in reach of the KATRIN neutrino mass experiment or upcoming neutrinoless double-beta decay searches. We show that the CNB detection prospects could be much higher in some of these models compared to those in $\mathrm{\ensuremath{\Lambda}}\mathrm{CDM}$, and discuss the potential for such a detection to discriminate between cosmological scenarios. Moreover, we provide a simple rule to estimate the required values of energy resolution, exposure, and background rate for a PTOLEMY-like experiment to cover a certain region in the $({m}_{\ensuremath{\nu}},{n}_{\ensuremath{\nu}}^{\mathrm{loc}})$ parameter space. Alongside this paper, we publicly release a code to calculate the CNB sensitivity in a given cosmological model.

LHC lifetime frontier and visible decay searches in composite asymmetric dark matter models

The LHC lifetime frontier will probe dark sector in near future, and the visible decay searches at fixed-target experiments have been exploring dark sector. Composite asymmetric dark matter with dark photon portal is a promising framework explaining the coincidence problem between dark matter and visible matter. Dark strong dynamics provides rich structure in the dark sector: the lightest dark nucleon is the dark matter, while strong annihilation into dark pions depletes the symmetric components of the dark matter. Dark photons alleviate cosmological problems. Meanwhile, dark photons make dark hadrons long-lived in terrestrial experiments. Moreover, the dark hadrons are produced through the very same dark photon. In this study, we discuss the visible decay searches for composite asymmetric dark matter models. For a few GeV dark nucleons, the LHC lifetime frontier, MATHUSLA and FASER, has a potential to discover their decay when kinetic mixing angle of dark photon is ϵ ≳ 10−4. On the other hand, fixed-target experiments, in particular SeaQuest, will have a great sensitivity to dark pions with a mass below GeV and with kinetic mixing ϵ ≳ 10−4 in addition to the LHC lifetime frontier. These projected sensitivities to dark hadrons in dark photon parameter space are comparable with the future sensitivities of dark photon searches, such as Belle-II and LHCb.

Proton decay in SUSY GUTs

Abstract We review proton decay in the SUSY SU(5) GUTs assuming the mini-split SUSY breaking model. In the mini-split SUSY breaking model, the squark and slepton masses are O(10(2 − 3)) TeV while the gaugino masses are O(1) TeV. As the result, even the minimal SUSY SU(5) GUT is still viable in the model. We present the motivation of the mini-split SUSY model and discuss the future prospects of proton decay searches in the SUSY SU(5) GUTs.

Evaluation of the radon adsorption efficiency of activated carbon fiber using tetrafluoromethane

Abstract The radioactive noble gas radon-222 (222Rn) is one of the most significant background sources in various types of rare event experiments, such as direct dark matter searches, neutrinoless double-beta decay searches, and neutrino experiments. Previously, a method to measure $\rm {}^{222}Rn$ concentration in purified air, argon, and xenon gases at a level of $\rm 1 \, mBq/m^{3}$ was established. Since other detector media are used in these experiments, there is a potential need to expand the study for other types of gases. In this paper the performance of an 80 liter $\rm {}^{222}Rn$ detector filled with tetrafluoromethane ($\rm CF_4$) gas, which is used for a direct dark matter search experiment, NEWAGE, was measured. The calibration factor of the detector for the $\rm CF_4$ gas was measured and its dependence on the absolute humidity was investigated. We also employed activated carbon fiber to evaluate its 222Rn adsorption efficiency in CF4, which was found to be $82.7\pm 0.1(\text{stat.})\pm 2.3(\text{syst.})\%$ at 0.10 MPa. For pressures lower than atmospheric pressure, we found that adsorption efficiency rises with lower pressure, and it is equal to $93.7\pm 0.3(\text{stat.})\pm 3.9(\text{syst.})\%$ at 0.03 MPa.

Search for Higgs boson decays into a pair of pseudoscalar particles in the bbμμ final state with the ATLAS detector in pp collisions at s=13 TeV

This paper presents a search for decays of the Higgs boson with a mass of 125 GeV into a pair of new pseudoscalar particles, $H\rightarrow aa$, where one $a$-boson decays into a $b$-quark pair and the other into a muon pair. The search uses 139 fb$^{-1}$ of proton-proton collision data at a center-of-mass energy of $\sqrt{s}=13$ TeV recorded between 2015 and 2018 by the ATLAS experiment at the LHC. A narrow dimuon resonance is searched for in the invariant mass spectrum between 16 GeV and 62 GeV. The largest excess of events above the Standard Model backgrounds is observed at a dimuon invariant mass of 52 GeV and corresponds to a local (global) significance of $3.3 \sigma$ ($1.7 \sigma$). Upper limits at 95% confidence level are placed on the branching ratio of the Higgs boson to the $bb\mu\mu$ final state, $\mathcal{B}(H\rightarrow aa\rightarrow bb\mu\mu)$, and are in the range $\text{(0.2-4.0)} \times 10^{-4}$, depending on the signal mass hypothesis.

Search for rare alpha and double beta decays of Yb isotopes to excited levels of daughter nuclei

A search for alpha and double beta decays of ytterbium isotopes was performed with an ultra low-background high purity germanium detector at Gran Sasso Underground Laboratory (Italy). A 194.7 g Yb_2(C_2O_4)_3 powder sample was measured for 11.3 days with a total Yb exposure of 1.25 kgtimes day. Half-life limits for alpha -decay modes of ^{168}mathrm Yb, ^{170}mathrm Yb, ^{171}mathrm Yb, ^{172}mathrm Yb, ^{173}mathrm Yb, ^{174}mathrm Yb and ^{176}mathrm Yb into the first excited states have been obtained between 6times 10^{14} years and 2times 10^{16} years. These are the first experimental constraints of these decay modes. Double electron capture of ^{168}mathrm Yb and double beta decay of ^{176}mathrm Yb into the first excited 2^+ and 0^+ states could be excluded with limits between 1times 10^{14} years to 8times 10^{16} years. This improves the experimental information on some of the decay modes compared to previous constraints.

Search for exotic decays of the Higgs boson into b overline{b} and missing transverse momentum in pp collisions at sqrt{s} = 13 TeV with the ATLAS detector

A search for the exotic decay of the Higgs boson (H) into a b overline{b} resonance plus missing transverse momentum is described. The search is performed with the ATLAS detector at the Large Hadron Collider using 139 fb−1 of pp collisions at sqrt{s} = 13 TeV. The search targets events from ZH production in an NMSSM scenario where H → {overset{sim }{chi}}_2^0{overset{sim }{chi}}_1^0 , with {overset{sim }{chi}}_2^0 → a{overset{sim }{chi}}_1^0 , where a is a light pseudoscalar Higgs boson and {overset{sim }{chi}}_{1,2}^0 are the two lightest neutralinos. The decay of the a boson into a pair of b-quarks results in a peak in the dijet invariant mass distribution. The final-state signature consists of two leptons, two or more jets, at least one of which is identified as originating from a b-quark, and missing transverse momentum. Observations are consistent with Standard Model expectations and upper limits are set on the product of cross section times branching ratio for a three-dimensional scan of the masses of the {overset{sim }{chi}}_2^0 , {overset{sim }{chi}}_1^0 and a boson.

Search for the radiative {Xi}_b^{-} \u2192 \u039e\u2212\u03b3 decay

The first search for the rare radiative decay {Xi}_b^{-} → Ξ−γ is performed using data collected by the LHCb experiment in proton-proton collisions at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of 5.4 fb−1. The {Xi}_b^{-} → Ξ−J/ψ channel is used as normalization. No {Xi}_b^{-} → Ξ−γ signal is found and an upper limit of mathcal{B} ( {Xi}_b^{-} → Ξ−γ) < 1.3 × 10−4 at 95% confidence level is obtained.

New limits on double-beta decay of ^{190}Pt and ^{198}Pt

A search for double-beta decay of ^{190}Pt and ^{198}Pt with emission of gamma -ray quanta was realized at the HADES underground laboratory with a 148 g platinum sample measured by two ultralow-background HPGe detectors over 8946 h. The isotopic composition of the platinum sample has been measured with high precision using inductively coupled plasma mass spectrometry. New lower limits for the half-lives of ^{190}Pt relative to different channels and modes of the decays were set on the level of lim T_{1/2}sim 10^{14}–10^{16} year. A possible exact resonant 0nu KN transition to the 1,2 1326.9 keV level of ^{190}Os is limited for the first time as T_{1/2} ge 2.5 times 10^{16} year. A new lower limit on the double-beta decay of ^{198}Pt to the first excited level of ^{198}Hg was set as T_{1/2} ge 3.2times 10^{19} year, one order of magnitude higher than the limit obtained in the previous experiment.

Scintillation light detection in the 6-m drift length ProtoDUNE Dual Phase liquid argon TPC

The Deep Underground Neutrino Experiment (DUNE) is a leading-edge experiment for long-baseline neutrino oscillation studies, neutrino astrophysics and nucleon decay searches. ProtoDUNE-Dual Phase (DP) is a 6 × 6 × 6 m3 liquid argon time-projection-chamber (LArTPC) operated at the CERN Neutrino Platform in 2019–2020 as a prototype of the DUNE far detector. In ProtoDUNE-DP, the scintillation and electroluminescence light produced by cosmic muons in the LArTPC is collected by photomultiplier tubes placed up to 7 m away from the ionizing track. In this paper, we present the performance of the ProtoDUNE-DP photon detection system, comparing different wavelength-shifting techniques and the use of xenon-doped LAr as a promising option for future large LArTPCs. The scintillation light production and propagation processes are analyzed and compared to simulations, improving understanding of the liquid argon properties.

Scintillation light detection in the 6-m drift-length ProtoDUNE Dual Phase liquid argon TPC

DUNE is a dual-site experiment for long-baseline neutrino oscillation studies, neutrino astrophysics and nucleon decay searches. ProtoDUNE Dual Phase (DP) is a 6 times 6 times 6 m^3 liquid argon time-projection-chamber (LArTPC) that recorded cosmic-muon data at the CERN Neutrino Platform in 2019–2020 as a prototype of the DUNE Far Detector. Charged particles propagating through the LArTPC produce ionization and scintillation light. The scintillation light signal in these detectors can provide the trigger for non-beam events. In addition, it adds precise timing capabilities and improves the calorimetry measurements. In ProtoDUNE-DP, scintillation and electroluminescence light produced by cosmic muons in the LArTPC is collected by photomultiplier tubes placed up to 7 m away from the ionizing track. In this paper, the ProtoDUNE-DP photon detection system performance is evaluated with a particular focus on the different wavelength shifters, such as PEN and TPB, and the use of Xe-doped LAr, considering its future use in giant LArTPCs. The scintillation light production and propagation processes are analyzed and a comparison of simulation to data is performed, improving understanding of the liquid argon properties.

SNO+

SNO+ is an operating liquid scintillator neutrino detector. Filling with liquid scintillator was completed in April 2021. Previously, SNO+ took water-filled data and also made measurements of backgrounds during scintillator partial-fill. These measurements (included physics results) enable SNO+ to quantify backgrounds for our final objective, the search for neutrinoless double beta decay when tellurium is loaded in the liquid scintillator detector at 0.5% by weight. This article highlights several measurements made by SNO+ and summarizes the status and outlook of the experiment.

Astroparticle physics in DUNE with the X-ARAPUCA detectors

DUNE is a long-baseline accelerator experiment in construction at Fermilab and SURF (South Dakota). The scientific program encompasses the investigation of long-baseline neutrino oscillation, with a focus on the study of the CP violation and neutrino mass hierarchy, along with high sensitivity searches for rare events, such as the observation of supernova neutrino bursts and the search for proton decay. The DUNE far detector consists of four liquid Argon TPCs located deep underground, paired with a Photon Detection System. In the present article we will discuss the role of the PDS in the search of the aforementioned rare events and the latest results in terms of technological achievements obtained by the PDS Consortium.

Enrico Bellotti: a leader in underground physics

Enrico Bellotti: a leader in underground physics

Status of 48Ca double beta decay search in CANDLES

We study a strategy to reduce veto-time in the search for neutrino-less double-beta decay (0υββ) with CANDLES-III system. We develop a new likelihood analysis and apply it to our new Run010 data. We show that we can increase the un-vetoed live-time by 11.8%. Thanks to this improvements, We expect to increase a limit on the life-time of 0υββ by a factor of three by analyzing both Run009 and Run010 data.

The Selena Neutrino Experiment

Imaging sensors made from an ionization target layer of amorphous selenium (aSe) coupled to a silicon complementary metal-oxide-semiconductor (CMOS) active pixel array for charge readout are a promising technology for neutrino physics. The high spatial resolution in a solid-state target provides unparalleled rejection of backgrounds from natural radioactivity in the search for neutrinoless ββ decay and for solar neutrino spectroscopy with 82Se. We present results on the ionization response of aSe measured from the photoabsorption of 122 keV γ rays in a single-pixel device. We report on the progress in the fabrication and testing of the first prototype imaging sensors based on the Topmetal II − pixelated CMOS charge readout chip. We explore the scientific reach of a large neutrino detector with the proposed technology based on our experimental understanding of the sensor performance.

Prospects for searching new Double Beta Decay physics with KamLAND-Zen 800

Two-neutrino double beta decay (2υββ) is a rare second-order weak radioactive decay process. It has been observed in neutrinoless double beta decay (0υββ) search experiments. Precise observation of 2υββ is essential to reduce the theoretical uncertainty in the calculation of nuclear matrix elements required to obtain the effective Majorana mass from a lifetime of 0υββ. Also, 2υββ itself is interesting because new physics could be hiding in the energy spectrum, such as for example, Majoron emission mode 0υββ and 2υββ with neutrino self-interaction. KamLAND-Zen 800 is an experiment to search for 0υββ of 136Xe with a large ultra-pure liquid scintillator detector, KamLAND. KamLAND-Zen 800 has been observing 745 kg of xenon gas at 91% enriched in 136Xe since 2019, providing a high statistics 2υββ decay sample. We describe the potential for new physics searches in 2υββ with KamLAND-Zen 800.

Direct measurement of topological information for Cherenkov lights using HUNI-ZICOS detector

The topological information of Cherenkov light emitted from low energy electron was directly measured by HUNI-ZICOS detector. A 1.484 MeV electron with fixed direction to the center of hemispherical surface of the detector was generated by Compton back scattering with 100 degree from 88Y 1.836 MeV gamma. The observed averaged angle of Cherenkov light emitted from this electron was clustered around 40 degree assuming the vertex position to be at the center of truncated icosahedron photomultiplier jig. It was not Cherenkov angle around 47 degree as obtained by old simulation and the vertex to be the center of light yield for hitted photomultiplier. According to the HUNI-ZICOS simulation, the averaged angle of Cherenkov light was also clustered around 40 degree. On the other hands, the simulated averaged angle of scintillation was clustered around 49 degree, which is consistent with the averaged value of angle between the direction to center of hemisphere surface and each photomultiplier from the center of the jig. The obtained hitmap seemed to have same non flat structure as that of simulation due to Cherenkov ring. This is an evidence that Cherenkov lights emitted from 1.484 MeV electron should really have their topology. Therefore, we concluded that we will be able to reduce 208Tl background using the averaged angle for 96 Zr neutrinoless double beta decay search.

The neutrinoless double beta decay CROSS experiment: demonstrator with surface sensitive bolometers

The CROSS experiment is proposing to use a new technology of surface sensitive bolometers for low-background neutrinoless double beta decay searches. Efficient rejection of surface α and β events will allow to reach background in the region of interest below than 10−4 cnts/keV/kg/yr. The isotopes of interest, which are 130Te and 100Mo, are investigated with TeO2 and Li2MoO4 bolometers. The surface sensitivity is achieved thanks to the evaporation of thin metallic film on the crystal surface that modifies the pulse shape of near-surface events. An investigation of various pulse shape parameters was performed. The analysis shows that one of the best parameters for discrimination is the integrated area of the raw signal both for TeO2 and Li2MoO4 with Pd-Al (10 nm - 100 nm) bi-layer.

The cosmic muon-induced background for the LEGEND-1000 alternative site at LNGS

The in-situ production of long-lived radio-isotopes by cosmic muon interactions may generate a non-negligible background for rare event searches in the deep subsurface. The delayed decay of 77(m)Ge has been identified as the dominant in-situ cosmogenic contributor for a neutrinoless double-beta decay search with 76Ge. The future ton-scale LEGEND-1000 experiment requires a total background of ≤ 10−5 cts/(keV-kg-yr). Dedicated Monte Carlo studies of the 77(m)Ge background at the alternative LNGS site were performed. The addition of passive neutron moderators, in combination with a delayed coincidence strategy, results in a background contribution of 8.6 × 10−7 cts/(keV.kg.yr) with an additional dead time of < 9%.