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DOE OSTI2025

Machine-Learning Analysis of Radiative Decays to Dark Matter at the LHC

The search for weakly interacting matter particles (WIMPs) is one of the main objectives of the High Luminosity Large Hadron Collider (HL-LHC). In this work we use Machine-Learning (ML) techniques to explore WIMP radiative decays into a Dark Matter (DM) candidate in a supersymmetric framework. The minimal supersymmetric WIMP sector includes the lightest neutralino that can provide the observed DM relic density through its co-annihilation with the second lightest neutralino and lightest chargino. Moreover, the direct DM detection cross section rates fulfill current experimental bounds and provide discovery targets for the same region of model parameters in which the radiative decay of the second lightest neutralino into a photon and the lightest neutralino is enhanced. This strongly motivates the search for radiatively decaying neutralinos which, however, suffers from strong backgrounds. We investigate the LHC reach in the search for these radiatively decaying particles by means of cut-based and ML methods and estimate its discovery potential in this well-motivated, new physics scenario. We demonstrate that using ML techniques would enable access to most of the parameter space unexplored by other searches.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

NASA NTRS2008

Cross Sections From Scalar Field Theory

A one pion exchange scalar model is used to calculate differential and total cross sections for pion production through nucleon- nucleon collisions. The collisions involve intermediate delta particle production and decay to nucleons and a pion. The model provides the basic theoretical framework for scalar field theory and can be applied to particle production processes where the effects of spin can be neglected.

Norbury, John W.↗

NASA NTRS1992

An obstacle to building a time machine

Gott (1991) has shown that a spacetime with two infinite parallel cosmic strings passing each other with sufficient velocity contains closed timelike curves. An attempt to build such a time machine is discussed. Using the energy-momentum conservation laws in the equivalent (2 + 1)-dimensional theory, the spacetime representing the decay of one gravitating particle into two is explicitly constructed; there is never enough mass in an open universe to build the time machine from the products of decays of stationary particles. More generally, the Gott time machine cannot exist in any open (2 + 1)-dimensional universe for which the total momentum is timelike.

Carroll, Sean M.↗

NASA NTRS1982

Particle physics meets cosmology - The search for decaying neutrinos

The fundamental physical implications of the possible detection of massive neutrinos are discussed, with an emphasis on the Grand Unified Theories (GUTs) of matter. The Newtonian and general-relativistic pictures of the fundamental forces are compared, and the reduction of electromagnetic and weak forces to one force in the GUTs is explained. The cosmological consequences of the curved-spacetime gravitation concept are considered. Quarks, leptons, and neutrinos are characterized in a general treatment of elementary quantum mechanics. The universe is described in terms of quantized fields, the noninteractive 'particle' fields and the force fields, and cosmology becomes the study of the interaction of gravitation with the other fields, of the 'freezing out' of successive fields with the expansion and cooling of the universe. While the visible universe is the result of the clustering of the quark and electron fields, the distribution of the large number of quanta in neutrino field, like the mass of the neutrino, are unknown. Cosmological models which attribute anomalies in the observed motions of galaxies and stars to clusters or shells of massive neutrinos are shown to be consistent with a small but nonzero neutrino mass and a universe near the open/closed transition point, but direct detection of the presence of massive neutrinos by the UV emission of their decay is required to verify these hypotheses.

Henry, R. C.↗

DOE OSTI2024

Search for heavy resonances in final states with four leptons and missing transverse momentum or jets in pp collisions at $\sqrt{s}$ = 13 TeV with the ATLAS detector

A search for a new heavy boson produced via gluon-fusion in the four-lepton channel with missing transverse momentum or jets is performed. The search uses proton-proton collision data equivalent to an integrated luminosity of 139 fb -1 at a centre-of-mass energy of 13 TeV collected by the ATLAS detector between 2015 and 2018 at the Large Hadron Collider. This study explores the decays of heavy bosons: R → SH and A → ZH, where R is a CP-even boson, A is a CP-odd boson, H is a CP-even boson, and S is considered to decay into invisible particles that are candidates for dark matter. In these processes, S → invisible and H → ZZ. The Z boson associated with the heavy scalar boson H decays into all decay channels of the Z boson. The mass range under consideration is 390–1300 (320–1300) GeV for the R (A) boson and 220–1000 GeV for the H boson. No significant deviation from the Standard Model backgrounds is observed. The results are interpreted as upper limits at a 95% confidence level on the cross-section times the branching ratio of the heavy resonances.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

NASA NTRS1990

Modeling the dust size distribution in comets with dust fragmentation

A hydrodynamic model was developed of a spherically symmetric dusty gas flow in a cometary atmosphere assuming a single fluid, inviscid, perfect gas. The hydrodynamics for gas and dust, which involves the gas drag force (momentum transfer), heat exchange between gas and dust, photodissociation energy for H2O gas, and radiative heating and cooling terms for dust particles, are solved using the Gear method for stiff, coupled differential equations. Calculations were done with a dust size distribution for radii alpha = 0.01 micron to 10 cm with densities variable with the size. A nucleus size of 4.0 km radius with a density of 0.5 g/cu cm and a total dust-to-gas mass ratio chi = 1 was adopted. There are indications from in situ observations that dust particle fragment into smaller ones. Fragmentation of dust particles was incorporated into the model. This is done by adding source and sink terms in the continuity equations for the dust. Lifetimes for the decay of dust particles were assumed as a function of particle size. It is also assumed that dust particles always fragment only into the next smaller size.

Konno, Ichishiro↗

NASA NTRS1985

Optical radiation from the interaction of energetic atoms, ions, electrons, and photons with surfaces

Heavy particle, electron, and UV photon bombardment of solid surfaces has been recently observed to result in the emission of infrared, visible, and ultraviolet radiation. This effect occurs over a wide range of incident projectile energies. Line radiation arising from transitions between discrete atomic or molecular levels may be attributed to the decay of excited particles which have been sputtered or electronically/chemically desorbed from the surface. Broadband continuum radiation, which is also observed, is believed to arise either from fluorescence of the near surface bulk or from the radiative decay of desorbed excited clusters. Spacecraft, in the ambient near Earth environment, are subject to such bombardment. The dynamics of energetic particle and photon beam interactions with surfaces which lead to surface erosion and glow phenomena will be treated. In addition, projected experimental and theoretical studies of oxygen and nitrogen beam surface interactions on materials characteristic of spacecraft surfaces will be discussed.

Tolk, N. H.↗

NASA NTRS1982

Comets produce submicron particles in the solar system

Observational evidence for the existence of submicron particles issuing from meteor streams and comets is examined. The MTS Explorer 46 carried a meteoroid detector which measured the rate of impact of particles with masses on the order of 10 to the -16th gram. Particle enhancements were observed in association with meteor streams, such as the Taurid and Orionids. The ratio of radiation pressure to gravity is employed to examine the effects of radiation pressure on the particles. When the ratio is higher than one, particles become smaller, unless they are dielectrics. Particles with radii less than 0.1 micron, having a potential of +3.3 V, are projected to have a lifetime of about 3 yr. Several thousands of tons of submicron particles are expected to be produced during a cometary perihelion passage. Launch of a long duration exposure facility with the Shuttle is recommended for studies of the decay of the particles over time.

Singer, S. F.↗

DOE OSTI2024

Search for X ( 3872 ) → π 0 π 0 χ c 1 , 2

Using 10.1 fb − 1 of e + e − collision data collected by the BESIII detector with center-of-mass energies between 4.15 GeV and 4.30 GeV, we search for the decays X ( 3872 ) → π 0 π 0 χ c 1 , 2 , where the X ( 3872 ) is produced in e + e − → γ X ( 3872 ) . No evidence above 3 σ is found for either decay. Upper limits at the 90% CL on the branching fractions of X ( 3872 ) → π 0 π 0 χ c 1 , 2 normalized to the branching fraction of X ( 3872 ) → π + π − J / ψ are set to be B ( X ( 3872 ) → π 0 π 0 χ c 1 ) / B ( X ( 3872 ) → π + π − J / ψ ) < 1.1 and B ( X ( 3872 ) → π 0 π 0 χ c 2 ) / B ( X ( 3872 ) → π + π − J / ψ ) < 0.5 , taking into account both statistical and systematic uncertainties. Published by the American Physical Society 2024

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

NASA NTRS1990

Numerical simulations of the decay of Martian global dust storms

The decay of Martian global (great) dust storms is investigated. One-dimensional (vertical, static atmosphere) and two-dimensional (latitude-height, steady state circulation) simulations carried out with an aerosol transport-microphysical model indicate that atmospheric motions play a significant role in the observed decay of global dust storms. Spacecraft observations (Mariner 9, Viking) of the 1971 and the two 1977 planet-encircling dust storms have provided suggestions about some characteristics of storm decay. Specifically, the dust particle size distribution is inferred to have remained essentially unchanged for particles with radii between 1 and 10 microns during decay of the 1971 storm, and surface visible opacity declined quasi-exponentially with time in northern midlatitudes during the decay of the two 1977 storms. The results from this investigation indicate that two- and three-dimensional dynamical processes play a significant role the observed decay features of Martian global dust storms. The most important processes are the lofting of dust by vertical motions in the dust source region of the Southern Hemisphere subtropics and a continuing advective resupply of atmospheric dust into the dust sink regions of the Northern Hemisphere. This work has implications for Viking data analyses and future Mars observer observations and requires that the particle size distribution be treated as a time and latitude dependent quantity.

Murphy, James R.↗

NASA NTRS1992

Gamma rays from pion decay - Evidence for long-term trapping of particles in solar flares

The energy spectrum and time dependence of the 50 MeV to 2 GeV gamma rays observed from the 1991 June 11 solar flare are analyzed. It is shown that the emission detected at the late phase of this flare with EGRET on the Compton Gamma-Ray Observatory can be explained by a model in which the bulk of the particles were accelerated during the impulsive phase and subsequently trapped in coronal magnetic loops. The observed spectrum was fit with a combination of pion decay radiation and primary electron bremsstrahlung. The 1991 June 11 data are compared with data for the 1982 June 3 and 1991 June 15 flares from which pion decay emission was also observed. The fact that the fluxes from these three flares are ordered in time in accordance with the predicted time dependence of emission produced by trapped particles provides support for the model.

Mandzhavidze, Natalie↗

DOE OSTI2024

Erratum: Description of the Proton-Decaying 0$^{+}_{2}$ Resonance of the 𝛼 Particle [Phys. Rev. Lett. 131 , 242502 (2023)]

As pointed out by P. Yin, H. Li, A. M. Shirokov, X. Zhao, and J. P. Vary, due to the incorrect normalization of the charge density, our definition of the monopole form factor 𝐹rel⁡(𝑞 2 ) was different from that used in other papers [1,2] by a factor of 1/𝑍. Furthermore, this resulted in the overall incorrect normalization of the monopole form factor in this Letter.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

NASA NTRS1985

Markov-Tree model of intrinsic transport in Hamiltonian systems

A particle in a chaotic region of phase space can spend a long time near the boundary of a regular region since transport there is slow. This 'stickiness' of regular regions is thought to be responsible for previous observations in numerical experiments of a long-time algebraic decay of the particle survival probability, i.e., survival probability approximately t to the (-z) power for large t. This paper presents a global model for transport in such systems and demonstrates the essential role of the infinite hierarchy of small islands interspersed in the chaotic region. Results for z are discussed.

Meiss, J. D.↗

DOE OSTI2024

Search for Neutral Heavy Scalars in ttZ Events Using 13 TeV pp Collisions at CMS

This thesis presents a search for a heavy pseudoscalar particle, A, which decays into a lighterscalar, H, and a Z boson within the Two-Higgs-Doublet Model (2HDM). We focus on Zboson decays to leptons, with H decays into a t t ̄ pair. The search uses the Asimov dataset–a theoretical dataset generated to predict the expected results for discovery and exclusion based on conditions from proton-proton collisions at the LHC, atintegrated luminosity of 138f b−1, as recorded by the CMS detector. The analysis focuses on events with three charged leptons, two of which come from the Z boson decay and one from a top quark decay. The expected results suggest the search has high sensitivity, showing discovery potential across much of the 2HDM Type-II parameter space, with possible deviations from the Standard Model background exceeding 5σ significance. The search sets upper limits on the cross-section times branching ratio, assuming narrow particle widths, for A masses up to 2100 GeV and H masses up to 1900 GeV. The results are interpreted in the 2HDM Type-II framework to exclude certain regions of parameter space at the 95% confidence level as a function of particle masses and variables such as tanβ and cos(β−α). The findings highlight the potential reach implications of future search in this parameter region.

Rudrabhatla, Sahithi [Illinois U., Chicago]↗

NASA NTRS1978

Prediction of solar energetic particle event histories using real-time particle and solar wind measurements

The comparatively well-ordered magnetic structure in the solar corona during the decline of Solar Cycle 20 revealed a characteristic dependence of solar energetic particle injection upon heliographic longitude. When analyzed using solar wind mapping of the large scale interplanetary magnetic field line connection from the corona to the Earth, particle fluxes display an approximately exponential dependence on heliographic longitude. Since variations in the solar wind velocity (and hence the coronal connection longitude) can severely distort the simple coronal injection profile, the use of real-time solar wind velocity measurements can be of great aid in predicting the decay of solar particle events. Although such exponential injection profiles are commonplace during 1973-1975, they have also been identified earlier in Solar Cycle 20, and hence this structure may be present during the rise and maximum of the cycle, but somewhat obscured by greater temporal variations in particle injection.

Roelof, E. C.↗

DOE OSTI2025

Stability of superconducting strings

We investigate the stability of superconducting strings as bound states of strings and fermion zero modes at both the classical and quantum levels. The dynamics of these superconducting strings can result in a stable configuration, known as a vorton . We mainly focus on global strings, but the majority of the discussion can be applied to local strings. Using lattice simulations, we study the classical dynamics of superconducting strings and confirm that they relax to the vorton configuration through Nambu-Goldstone boson radiation, with no evidence of over-shooting that would destabilize the vorton. We explore the tunneling of fermion zero modes out of the strings. Both our classical analysis and quantum calculations yield consistent results: the maximum energy of the zero mode significantly exceeds the fermion mass, in contrast to previous literature. Additionally, we introduce a world-sheet formalism to evaluate the decay rate of zero modes into other particles, which constitute the dominant decay channel. We also identify additional processes that trigger zero-mode decay due to non-adiabatic changes of the string configuration. In these decay processes, the rates are suppressed by the curvature of string loops, with exponential suppression for large masses of the final states. We further study the scattering with light charged particles surrounding the string core produced by the zero-mode current and find that a wide zero-mode wavefunction can enhance vorton stability.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

NASA NTRS1991

Gamma Ray Observatory (GRO) Prelaunch Mission Operations Report (MOR)

The NASA Astrophysics Program is an endeavor to understand the origin and fate of the universe, to understand the birth and evolution of the large variety of objects in the universe, from the most benign to the most violent, and to probe the fundamental laws of physics by examining their behavior under extreme physical conditions. These goals are pursued by means of observations across the entire electromagnetic spectrum, and through theoretical interpretation of radiations and fields associated with astrophysical systems. Astrophysics orbital flight programs are structured under one of two operational objectives: (1) the establishment of long duration Great Observatories for viewing the universe in four major wavelength regions of the electromagnetic spectrum (radio/infrared/submillimeter, visible/ultraviolet, X-ray, and gamma ray), and (2) obtaining crucial bridging and supporting measurements via missions with directed objectives of intermediate or small scope conducted within the Explorer and Spacelab programs. Under (1) in this context, the Gamma Ray Observatory (GRO) is one of NASA's four Great Observatories. The other three are the Hubble Space Telescope (HST) for the visible and ultraviolet portion of the spectrum, the Advanced X-ray Astrophysics Facility (AXAF) for the X-ray band, and the Space Infrared Telescope Facility (SIRTF) for infrared wavelengths. GRO's specific mission is to study the sources and astrophysical processes that produce the highest energy electromagnetic radiation from the cosmos. The fundamental physical processes that are known to produce gamma radiation in the universe include nuclear reactions, electron bremsstrahlung, matter-antimatter annihilation, elementary particle production and decay, Compton scattering, synchrotron radiation. GRO will address a variety of questions relevant to understanding the universe, such as: the formation of the elements; the structure and dynamics of the Galaxy; the nature of pulsars; the existence of black holes; the possible existence of large amounts of antimatter, energetic and explosive phenomena occurring in galactic nuclei; the origin of the cosmic diffuse background; particle acceleration in the Sun, stars and stellar systems; processes in supernovae; and the origin and evolution of the universe itself.

Source record↗

NASA NTRS1997

Characterization of Aircraft Produced Soot and Contrails Near the Tropopause

Participation in the SUCCESS project primarily involved development and deployment of specific instruments for characterizing jet aircraft exhaust emissions as particulates and their subsequent evolution as contrail particles, either liquid or solid, as cirrus. Observations can be conveniently considered in two categories - close or distant from the aircraft. Thus close to the aircraft the exhaust is mixing through the engine turbulence with a much drier and colder environment and developing water/ ice supersaturation along the trail depending on circumstances (near field), whereas distant from the aircraft (far field) the exhaust has cooled essentially to ambient temperature, the turbulence has decayed and any particle growth or evaporation is controlled by the prevailing ambient conditions. Intermediate between these two regions the main aircraft vortices form (one on each side of the aircraft) which tend to inhibit mixing under some conditions, a region extending from a few aircraft lengths to sometimes a hundred times this distance. Our approach to the problem lay in experience gained in characterizing the smoke from hydrocarbon combustion in terms of its cloud forming properties and its potential influence on the radiation properties of the smoke and subsequent cloud from the viewpoint of reduction (absorbtion and scattering ) of solar radiation flux leading to significant global cooling (Hudson et al 1991; Hallett and Hudson 1991). Engine exhaust contains a much smaller proportion of the fuel carbon than is sometimes present in ordinary combustion (less than 0.01% compared with 10%) and influences condensation in quite different ways, to be characterized by the Cloud Condensation Nucleus, CCN - supersaturation spectrum. The transition to ice is to be related to the dilution of solution droplets to freeze by homogeneous nucleation at temperatures somewhat below -40C (Pueschel et al 1998). The subsequent growth of ice particles depends critically on temperature, supersaturation and to some extent pressure, as is demonstrated in an NSF funded project being carried out in parallel with the work reported here. As will be discussed below, nucleation processes themselves and also exhaust impurities also influence the growth of ice particles and may control some aspects of growth of ice in contrails. Instrumentation was designed to give insight into these questions and to be flown on the NASA DC- 8 as a platform. In addition a modest program was undertaken to investigate the properties of laboratory produced smoke produced under controlled conditions from the viewpoint of forming both CCN and CN. The composition of the smoke could inferred from a thermal characterization technique; larger particles were captured by formvar replicator for detailed analysis; ice particles were captured and evaporated in flight on a new instrument, the cloudscope, to give their mass, density and impurity content.

Hallett, John↗