Two-body Decays Research Articles

Universal relations for dilute systems with two-body decays in reduced dimensions

Universal relations for dilute systems with two-body decays in reduced dimensions

Momentum non-conservation in a scalar quantum field theory with a planar θ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\ heta$$\\end{document} interface

Motivated by the recent interest aroused by non-dynamical axionic electrodynamics in the context of topological insulators and Weyl semimetals, we discuss a simple model of the magnetoelectric effect in terms of a θ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\ heta$$\\end{document}-scalar field that interacts through a delta-like potential located at a planar interface. Thus, in the bulk regions the field is constructed by standard free waves with the absence of evanescent components. These waves have to be combined into linear superposition to account for the boundary conditions at the interface in order to yield the corresponding normal modes. Our aim is twofold: first we quantize the θ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\ heta$$\\end{document}-scalar field using the normal modes in the canonical approach and then we look for applications emphasizing the effect of momentum non-conservation due to the presence of the interface. To this end, we calculate the decay of a standard scalar particle into two θ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\ heta$$\\end{document}-scalar particles showing the opening of new decay channels. As a second application, we deal with the two-body scattering of standard charged scalar particles mediated by a θ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\ heta$$\\end{document}-scalar particle, focusing on the momentum non-conserving contribution of the scattering amplitude MNC\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${{\\mathcal {M}}}^{NC}$$\\end{document}. We define a generalization of the usual cross section in order to quantify the emergence of these events. We also study the allowed kinematical region for momentum non-conservation as well as the position of the poles of the amplitude MNC\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${{\\mathcal {M}}}^{NC}$$\\end{document}. Finally, the ratio of the magnitudes between MNC\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${{\\mathcal {M}}}^{NC}$$\\end{document} and the momentum conserving amplitude is discussed in the appropriate region of momentum space.

Washout processes in post-sphaleron baryogenesis from way-out-of-equilibrium decays

We study washout processes in post-sphaleron baryogenesis, a mechanism where the matter–antimatter asymmetry is generated in the decay of exotic particles after the electroweak phase transition. In particular we focus, in a quite model independent way, on those scattering processes that have an amplitude proportional to the CP asymmetry. We find that when the scatterings involve only massless particles, the washouts are very severe for light decaying particles (with masses below a few hundred of GeV) and successful baryogenesis is only possible in a small portion of parameter space. Instead, if even a very light particle participates in these processes, the allowed region of parameter space opens considerably, although the final amount of baryon asymmetry may differ significantly from the expression which is typically used and neglects washouts. Furthermore, we analyze washouts from the non-thermal spectrum of energetic particles produced in cascade decays and indicate in which models they can be relevant.

Reduction of spectroscopic overlap across the Z=8 shell in neutron-rich nuclei

The recent discovery and spectroscopic measurements of O27 and O28 suggests the disappearance of the N=20 shell structure in these neutron-rich oxygen isotopes. We measured one- and two-proton removal cross sections from F27 and Ne29, respectively, extracting spectroscopic factors and comparing them to shell model overlap functions coupled with eikonal reaction model calculations. The invariant mass technique was used to reconstruct the two-body (O24+n) and three-body (O24+2n) decay energies from knockout reactions of F27 (106.2 MeV/u) and Ne29 (112.8 MeV/u) beams impinging on a Be9 target. The one-proton removal from F27 strongly populated the ground state of O26 and the extracted cross section of 3.4−1.5+0.3 mb agrees with eikonal model calculations that are normalized by the shell model spectroscopic factors and account for the systematic reduction factor observed for single nucleon removal reactions within the models used. For the two-proton removal reaction from Ne29 an upper limit of 0.08 mb was extracted for populating states in O27 decaying though the ground state of O26. The measured upper limit for the population of the ground state of O26 in the two-proton removal reaction from Ne29 indicates a significant difference in the underlying nuclear structure of F27 and Ne29.Published by the American Physical Society2024

Decays of 1−+ charmoniumlike hybrid using lattice QCD

By extracting the transition amplitudes, we give the first lattice QCD prediction of the two-body decay partial widths of the 1−+ charmoniumlike hybrid ηc1. Given the calculated mass value mηc1=4.329(36) GeV, the ηc1 decay is dominated by the open charm modes D1D¯, D*D,¯ and D*D¯* with partial widths of 258(133), 88(18), and 150(118) MeV, respectively. The coupling of ηc1 to χc1 plus a flavor singlet pseudoscalar is not small, but χc1η decay is suppressed by the small η−η′ mixing angle. The partial width of ηc1→ηcη′ is estimated to be around 1 MeV. We suggest experiments to search for ηc1 in the P-wave D*D¯ and D*D¯* systems. Especially, the polarization of D*D¯* can be used to distinguish the 1−+ product (total spin S=1) from 1−− products (S=0). Published by the American Physical Society 2024

Suppressed atmospheric chemical aging of cooking organic aerosol particles in wintertime conditions

Abstract. Cooking organic aerosol (COA) is one of the major constituents of particulate matter in urban areas. COA is oxidized by atmospheric oxidants such as ozone, changing its physical, chemical and toxicological properties. However, atmospheric chemical lifetimes of COA and its tracers such as oleic acid are typically longer than those that have been estimated by laboratory studies. We tackled the issue by considering temperature. Namely, we hypothesize that increased viscosity of COA at ambient temperature accounts for its prolonged atmospheric chemical lifetimes in wintertime. Laboratory-generated COA particles from cooking oil were exposed to ozone in an aerosol flow tube reactor for the temperature range of −20 to 35 °C. The pseudo-second-order chemical reaction rate constants (k2) were estimated from the experimental data by assuming a constant ozone concentration in the flow tube. The estimated values of k2 decreased by orders of magnitude for lower temperatures. The temperature dependence in k2 was fit well by considering the diffusion-limited chemical reaction mechanism. The result suggested that increased viscosity was likely the key factor to account for the decrease in chemical reactivity at the reduced temperature range, though the idea will still need to be verified by temperature-dependent viscosity data in the future. In combination with the observed global surface temperature, the atmospheric chemical lifetimes of COA were estimated to be much longer in wintertime (> 1 h) than in summertime (a few minutes) for temperate and boreal regions. Our present study demonstrates that the oxidation lifetimes of COA particles will need to be parameterized as a function of temperature in the future for estimating environmental impacts and fates of this category of particulate matter.

Undecay

Unstable particles decay sooner or later, so they are not described by asymptotic one-particle states and they should not be included as independent states in unitarity relations such as the optical theorem. The same applies to any countable collection of unstable particles. We show that the behaviour of unparticle stuff, that is, a continuous collection of particles with different masses and common decay channels, is pretty different: it has a non-vanishing probability of surviving for ever and the corresponding asymptotic states must be taken into account to comply with unitarity. We also discuss compressed spectra and the transition from the discrete to the continuous case.

Testing meson portal dark sector solutions to the MiniBooNE anomaly at the Coherent CAPTAIN Mills experiment

A solution to the MiniBooNE excess invoking rare three-body decays of the charged pions and kaons to new states in the MeV mass scale was recently proposed as a dark-sector explanation. This class of solution illuminates the fact that, while the charged pions were focused in the target-mode run, their decay products were isotropically suppressed in the beam-dump-mode run in which no excess was observed. This suggests a new physics solution correlated to the mesonic sector. We investigate an extended set of phenomenological models that can explain the MiniBooNE excess as a dark sector solution, utilizing long-lived particles that might be produced in the three-body decays of the charged mesons and the two-body anomalous decays of the neutral mesons. Over a broad set of interactions with the long-lived particles, we show that these scenarios can be compatible with constraints from LSND, KARMEN, and MicroBooNE, and evaluate the sensitivity of the ongoing and future data taken by the Coherent CAPTAIN Mills experiment to a potential discovery in this parameter space. Published by the American Physical Society 2024

Low-scale baryogenesis from three-body decays

Baryogenesis at the TeV scale from CP-violating decays of a massive particle requires some way to avoid the washouts from processes closely related to the existence of CP violation. Baryogenesis from three-body decays (instead of two-body decays) has been proposed as a way for TeV scale baryogenesis. In this work we revisit this statement and show that, although three-body-decay models can provide interesting alternatives to address other kind of difficulties faced by low-scale baryogenesis, the generic problem due to the washouts proportional to the CP asymmetry persists. Therefore, as in two-body-decay models, the mass of the decaying particle cannot be below ∼10 TeV unless some mechanism to avoid these kinds of washouts is implemented. Published by the American Physical Society 2024

Robust bounds on ALP dark matter from dwarf spheroidal galaxies in the optical MUSE-Faint survey

Nearby dwarf spheroidal galaxies are ideal targets in the search for indirect dark matter (DM) signals.In this work, we analyze MUSE spectroscopic observations of a sample of five galaxies, composed of both classical and ultra-faint dwarf spheroidals. The goal is to search for radiative decays of axion-like particles (ALPs) in the mass range of 2.7–5.3 eV. After taking into account the uncertainties associated with the DM spatial distribution in the galaxies, we derive robust bounds on the effective ALP-two-photon coupling.They lie well below the QCD axion band and are significantly more constraining than limits from other probes, in the relevant mass range.We also test the possible presence of a positive signal, concluding that none of the wavelength channels selected for this analysis, i.e., not affected by large background contamination, is exhibiting such evidence.

Weakly interacting Bose gas with two-body losses

We study the many-body dynamics of weakly interacting Bose gases with two-particle losses. We show that both the two-body interactions and losses in atomic gases may be tuned by controlling the inelastic scattering process between atoms by an optical Feshbach resonance. Interestingly, the low-energy behavior of the scattering amplitude is governed by a single parameter, i.e. the complex ss-wave scattering length a_cac. The many-body dynamics are thus described by a Lindblad master equation with complex scattering length. We solve this equation by applying the Bogoliubov approximation in analogy to the closed systems. Various peculiar dynamical properties are discovered, some of them may be regarded as the dissipative counterparts of the celebrated results in closed Bose gases. For example, we show that the next-order correction to the mean-field particle decay rate is to the order of |n a_c^{3}|^{1/2}|nac3|1/2, which is an analogy of the Lee-Huang-Yang correction of Bose gases. It is also found that there exists a dynamical symmetry of symplectic group Sp(4,\mathbb{C})(4,ℂ) in the quadratic Bogoliubov master equation, which is an analogy of the SU(1,1) dynamical symmetry of the corresponding closed system. We further confirmed the validity of the Bogoliubov approximation by comparing its results with a full numerical calculation in a double-well toy model. Generalizations of other alternative approaches such as the dissipative version of the Gross-Pitaevskii equation and hydrodynamic theory are also discussed in the last.

Comparing models for a unitary black hole S matrix

This paper compares features, challenges, and puzzles of different models for a unitary black hole S-matrix, focusing on both recent nonisometric models, as well as “nonviolent unitarization,” which is based on new quantum interactions of a black hole. As a foundation for comparison, the description of real-time Hawking evolution is first overviewed, including leading effects of gravitational dressing and backreaction. Connection is then made to qubit models for evolution, and some technology is outlined to facilitate their description. Important features of both nonisometric models and nonviolent unitarization are investigated in qubit models, which illustrate essential differences between the respective approaches. The nonisometric models present puzzles for understanding evolution of internal outgoing excitations, which can be excited by interactions such as particle decay. Qubit models for nonviolent unitarization are further developed, and nicely illustrate aspects of that approach. Some remaining questions in generalizing to more complete models for evolution are discussed. Published by the American Physical Society 2024

Observational constraints on the parameterization of particle dry deposition over bare cropland

Dry deposition affects the removal rates and lifetimes of atmospheric particles. Bare cropland, a surface cover type representing cultivated land after harvesting and ploughing, is widespread around the world, but the parameterizations of dry deposition velocity for this land type have not been well constrained. In this study, we integrate existing observational data of particle dry deposition for bare cropland to constrain the corresponding parameterization scheme. Considering that strong disparities exist between the calculated dry deposition velocity from existing parameterizations and the observations, a range of empirical parameters employed are adjusted to best match the model simulations with the observations. The results from the revised parameterization match much more closely with the observations for the different particle sizes than those obtained when using the existing one. As a result, particles smaller than 0.5 μm in diameter exhibit a decrease in dry deposition velocity by roughly one order of magnitude, while that of larger particles increase. Among the processes contributing to the dry deposition, the impaction and interception are dominant for particles with aerodynamic diameters between 0.1 and 10 μm, due to the roughness characteristics and large clod size of bare cropland, in contrast to smooth bare soils. Applying our revised scheme in an atmospheric chemical transport model over the North China Plain leads to a general increase in PM2.5 mass concentrations across the domain, reaching up to 11.2% over the croplands. Particularly, the number concentrations of particle in Aitken and accumulation modes are increased by 12.9% and 16.8%, respectively. The associated increase in cloud condensation nuclei concentrations reaches as high as 39.6%.

Improved Energy Valley Optimizer with Levy Flight for Optimization Problems

Energy Valley Optimizer (EVO) is one of the recent metaheuristic algorithms. It draws inspiration from advanced principles in physics related to particle stability and decay modes. This paper presents a new Energy Valley Optimizer (EVO) and levy flights that are hybrid to improve the EVO in solving optimization problems. Levy flight is one of the most important randomization techniques. Fifteen mathematical test functions (five unimodal functions, four multimodal functions, and six composite functions) are solved with the proposed algorithm. We also compare our results with previous results of metaheuristic algorithms. The statistical results show that the results of the Levy Energy Valley Optimizer (LEVO) outperform other algorithms in almost all mathematical test functions.

Search for supersymmetry in final states with disappearing tracks in proton-proton collisions at s=13 TeV

A search is presented for charged, long-lived supersymmetric particles in final states with one or more disappearing tracks. The search is based on data from proton-proton collisions at a center-of-mass energy of 13 TeV collected with the CMS detector at the CERN LHC between 2016 and 2018, corresponding to an integrated luminosity of 137 fb−1. The search is performed over final states characterized by varying numbers of jets, b-tagged jets, electrons, and muons. The length of signal-candidate tracks in the plane perpendicular to the beam axis is used to characterize the lifetimes of wino- and Higgsino-like charginos produced in the context of the minimal supersymmetric standard model. The dE/dx energy loss of signal-candidate tracks is used to increase the sensitivity to charginos with a large mass and thus a small Lorentz boost. The observed results are found to be statistically consistent with the background-only hypothesis. Limits on the pair-production cross section of gluinos and squarks are presented in the framework of simplified models of supersymmetric particle production and decay, and for electroweakino production based on models of wino and Higgsino dark matter. The limits presented are the most stringent to date for scenarios with light third-generation squarks and a wino- or Higgsino-like dark matter candidate capable of explaining the observed dark matter relic density. © 2024 CERN, for the CMS Collaboration 2024 CERN

Gauge and scalar boson mediated proton decay in a predictive SU(5) GUT model

We assess proton decay signatures in the simplest viable SU(5) model with regard to constraints on parameters governing the Standard Model fermion mass spectrum. Experimental signals for all eight two-body proton decay processes result from exchange of two gauge bosons, a single scalar leptoquark, or their combination. Consequently, it enables us to delve into an in-depth anatomy of proton decay modes and anticipate future signatures. Our findings dictate that observing a proton decay into p→π0e+ indicates gauge boson mediation, with the potential for observation of p→η0e+ mode. Alternatively, if decay is through the p→K+ν¯ process, it is mediated by a scalar leptoquark, possibly allowing the observation of p→π0μ+. Detection of both p→π0e+ and p→K+ν¯ could enhance p→π0μ+ through constructive interference. The model predicts inaccessibility of p→π+ν¯, p→η0μ+, p→K0e+, and p→K0μ+, regardless of the dominant mediation type, in the coming decades. In summary, through a comprehensive analysis of proton decay signals, gauge coupling unification, and fermion masses and mixing, we both accurately and precisely constrain the parameter space of the SU(5) model in question. Published by the American Physical Society 2024

Long-lived particle decays at the proposed MATHUSLA experiment

We carefully study the decay and reconstruction of long-lived particle (LLP) decays in the proposed MATHUSLA LLP detector for the HL-LHC. Our investigations are focused on three LLP benchmark models. MATHUSLA’s primary physics target is represented by hadronically decaying LLPs with mass above ∼10 GeV, produced in exotic Higgs decays. We also investigate GeV-scale scalar and right-handed neutrino LLPs, which are the target of many other proposed experiments. We first introduce a public astim code to allow for efficient signal-only studies of LLP decays in MATHUSLA and general external LLP detectors. For each of our benchmark scenarios, we carefully simulate LLP production and decay, and make our simulation library publicly accessible for future investigations and comparisons with other experiments. We then systematically study the geometric acceptance of MATHUSLA for LLP decays in these scenarios, and present updated sensitivity projections that include these acceptances. Our results show that the idealized reach of MATHUSLA computed in earlier studies is mostly realized. We also investigate possible ways of increasing the signal acceptance using the inherent geometric flexibility of the FastSim, which will provide useful inputs for realistic experimental and engineering optimization of the detector in the future. Published by the American Physical Society 2024

Search for a massless particle beyond the Standard Model in the Σ+ → p + invisible decay

A massless particle beyond the Standard Model is searched for in the two-body decay Σ+→p+invisible using (1.0087±0.0044)×1010J/ψ events collected at a center-of-mass energy of s=3.097GeV with the BESIII detector at the BEPCII collider. No significant signal is observed, and the upper limit on the branching fraction B(Σ+→p+invisible) is determined to be 3.2×10−5 at the 90% confidence level. This is the first search for a flavor-changing neutral current process with missing energy in hyperon decays which plays an important role in constraining new physics models.

Predicting the XRISM dark matter decay signal in the Milky Way halo

ABSTRACT Dark matter may be detected in X-ray decay, including from the decay of the dark matter particles that make up the Milky Way (MW) halo. We use a range of density profiles to compute X-ray line intensity profiles, with a focus on the resonantly produced sterile neutrino dark matter candidate. Compared to the Navarro–Frenk–White density profile, we show that using an adiabatically contracted halo profile suppresses the line intensity in the halo outskirts and enhances it in the Galactic Centre (GC), although this enhancement is eliminated by the likely presence of a core within 3 kpc. Comparing our results to MW halo observations, other X-ray observations, and structure formation constraints implies a sterile neutrino mixing angle parameter s11 ≡ sin 2(2θ) × 1011 ∼ [3, 4] (particle lifetime $\tau _{28}\equiv \tau /(10^{28}\rm {s})\sim [1.0,1.3]$), which is nevertheless is strong tension with some reported non-detections. We make predictions for the likely decay flux that the X-Ray Imaging and Spectroscopy Mission (XRISM) satellite would measure in the GC, plus the Virgo and Perseus clusters, and outline further steps to determine whether the dark matter is indeed resonantly produced sterile neutrinos as detected in X-ray decay.

A numerical research on transient transport of high-temperature particles associated with air gouging process

The high-temperature particles produced by air gouging processes are common pollutants in cleaning workshops, which could endanger workers’ health. In this research, a two-way coupled Eulerian-Lagrangian method based on discrete phase modelling (DPM) was used to investigate the transport characteristics of high-temperature particles generated from air gouging processes. The particle group in the movement was divided into core zone and boundary zone, and the kinetic mechanism of particles in different zones was analysed. The results show particles in the boundary zone are more susceptible to the vortex entrainment effect than particles in the core zone, and some particles could be moved from the vortex diffusion zone to the vortex recirculation zone. The smaller the particle size, the better the followability to the hot airflow. The slower the temperature decay of particles, the more significant the thermophoresis effect, which could enhance the diffusion behaviour of the small particles. By analysing the average residence time of particles in the breathing zone, the influence of different factors on the average vertical diffusion height [Formula: see text] of particles is summarized, and a nonlinear regression prediction model of [Formula: see text] is established. The results can contribute to health risk assessment and industrial ventilation design.