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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 487 records · Page 27
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

Relic abundance of MeV millicharged particles

The relic abundance of light millicharged particles (MCPs) with the electric charge e′ = 5 × 10{sup –5}e and with the mass slightly below or above the electron mass is calculated. The abundance depends on the mass ratio η = m{sub X}/m{sub e} and for η < 1 can be high enough to allow MCPs to be the cosmological dark matter or to make a noticeable contribution to it. On the other hand, for η ≳ 1 the cosmological energy density of MCPs can be quite low, Ω{sub X}h{sub 0}{sup 2} ≈ 0.02 for scalar MCPs, and Ω{sub X}h{sub 0}{sup 2} ≈ 0.001 for spin 1/2 fermions. But even the lowest value of Ω{sub X}h{sub 0}{sup 2} is in tension with several existing limits on the MCP abundances and parameters. However, these limits have been derived under some natural or reasonable assumptions on the properties of MCPs. If these assumptions are relaxed, a patch in the mass–charge plot of MCPs may appear, permitting them to be dark matter particles.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2019

Holistic Description of the Lepton Sector

A sequence of necessary actions for the formulation of free leptonic equations (Dirac algorithm) is established. A complete and closed set of equations for the description of massive and massless, charged and neutral, stable and unstable leptons is obtained within a unified algorithmic approach. The Lorentz invariance and covariance of the newly derived equations is as rigorous as for the Dirac equation. All the established facts together explain the exceptional role of the structure of lepton equations that serves as a carrier of the properties of the observed particles.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
NASA NTRS2001

Monte Carlo track structure for radiation biology and space applications

Over the past two decades event by event Monte Carlo track structure codes have increasingly been used for biophysical modelling and radiotherapy. Advent of these codes has helped to shed light on many aspects of microdosimetry and mechanism of damage by ionising radiation in the cell. These codes have continuously been modified to include new improved cross sections and computational techniques. This paper provides a summary of input data for ionizations, excitations and elastic scattering cross sections for event by event Monte Carlo track structure simulations for electrons and ions in the form of parametric equations, which makes it easy to reproduce the data. Stopping power and radial distribution of dose are presented for ions and compared with experimental data. A model is described for simulation of full slowing down of proton tracks in water in the range 1 keV to 1 MeV. Modelling and calculations are presented for the response of a TEPC proportional counter irradiated with 5 MeV alpha-particles. Distributions are presented for the wall and wall-less counters. Data shows contribution of indirect effects to the lineal energy distribution for the wall counters responses even at such a low ion energy.

NASA Center JSC↗
DOE OSTI2013

One needs positive signatures for detection of Dark Matter

One believes there is huge amount of Dark Matter particles in our Galaxy which manifest themselves only gravitationally. There is a big challange to prove their existence in a laboratory experiment. To this end it is not sufficient to fight only for the best exclusion curve, one has to see an annual recoil spectrum modulation—the only available positive direct dark matter detection signature. A necessity to measure the recoil spectra is stressed.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2015

Wavefront analysis of the laser beam propagating through a turbid medium

Laser beam propagation through a scattering suspension of polystyrene microspheres in distilled water is studied theoretically and experimentally. The dependence of wavefront aberrations on the particle concentration is investigated. The existence of symmetric wavefront aberrations of the laser beam passed through a turbid medium is shown. (light scattering)

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2013

Classical and quantum discrete dynamical systems

We study deterministic and quantum dynamics from a constructive “finite” point of view, since the introduction of the continuum or other actual infinities in physics poses severe conceptual and technical difficulties, and while all of these concepts are not really needed in physics, which is in fact an empirical science. Particular attention is paid to the symmetry properties of discrete systems. For a consistent description of the symmetries of dynamical systems at different time instants and the symmetries of various parts of such systems, we introduce discrete analogs of gauge connections. These gauge structures are particularly important to describe the quantum behavior. The symmetries govern the fundamental properties of the behavior of dynamical systems. In particular, we can show that the moving soliton-like structures are inevitable in a deterministic (classical) dynamical system, whose symmetry group breaks the set of states into a finite number of orbits of the group. We demonstrate that the quantum behavior is a natural consequence of symmetries of dynamical systems. This behavior is a result of the fundamental inability to trace the identity of indistinguish-able objects during their evolution. Information is only available on invariant statements and values related with such objects. Using general mathematical arguments, any quantum dynamics can be shown to reduce to a sequence of permutations. The quantum interferences occur in the invariant subspaces of permutation representations of the symmetry groups of dynamical systems. The observables can be expressed in terms of permutation invariants. We also show that in order to describe quantum phenomena it is sufficient to use cyclotomic fields—the minimal extensions of natural numbers suitable for quantum mechanics, instead of a non-constructive number system—the field of complex numbers. The finite groups of symmetries play the central role in this review. In physics there is an additional reason for such groups to be of interest. Numerous experiments and observations in particle physics point to the importance of finite groups of relatively low orders in a number of fundamental processes. The origin of these groups has no explanation within presently recognized theories, such as the Standard Model.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2019

Quantum decay in renormalizable field theories: Quasiparticle formation, Zeno and anti-Zeno effects

In a renormalizable theory the survival probability of an unstable quantum state features divergences as a consequence of the rapid growth of the density of states with energy. Introducing a high energy cutoff Λ, the transient dynamics during a time scale ≃1∕Λ describes the renormalization of the bare into a “quasiparticle” state which decays on longer time scales. During this early transient the decay law features Zeno behavior e{sup −(t∕t{sub Z}){sup 2}} with the Zeno time-scale t{sub Z}∝1∕Λ{sup 3∕2}. We introduce a dynamical renormalization framework that allows to separate consistently the dynamics of formation of the quasiparticle state and its decay on longer time scales by introducing a renormalization time scale along with alternative “schemes”. The survival probability obeys a renormalization group equation with respect to this scale. We find a transient suppression of the decay law for large Lorentz factor as a consequence of the narrowing of the phase space for decay different from the usual time dilation. In the presence of higher mass thresholds, the energy uncertainty associated with transient dynamics leads to an anti Zeno enhancement with a transient acceleration of the decay into heavier particles. There remains memory of the transient effects in the survival probability even at long time. We discuss possible consequences of these effects in cosmology.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2016

Is it possible to discover a dark matter particle with an accelerator?

The paper contains description of the main properties of the galactic dark matter (DM) particles, available approaches for detection of DM, main features of direct DM detection, ways to estimate prospects for the DM detection, the first collider search for a DM candidate within an Effective Field Theory, complete review of ATLAS results of the DM candidate search with LHC RUN I, and less complete review of “exotic” dark particle searches with other accelerators and not only. From these considerations it follows that one is unable to prove, especially model-independently, a discovery of a DM particle with an accelerator, or collider. One can only obtain evidence on existence of a weakly interacting neutral particle, which could be, or could not be the DM candidate. The current LHC DM search program uses only the missing transverse energy signature. Non-observation of any excess above Standard Model expectations forces the LHC experiments to enter into the same fighting for the best exclusion curve, in which (almost) all direct and indirect DM search experiments permanently take place. But this fighting has very little (almost nothing) to do with a real possibility of discovering a DM particle. The true DM particles possess an exclusive galactic signature—annual modulation of a signal, which is accessible today only for direct DM detection experiments. There is no way for it with a collider, or accelerator. Therefore to prove the DM nature of a collider-discovered candidate one must find the candidate in a direct DM experiment and demonstrate the galactic signature for the candidate. Furthermore, being observed, the DM particle must be implemented into a modern theoretical framework. The best candidate is the supersymmetry, which looks today inevitable for coherent interpretation of all available DM data.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2015

Light mediators in dark matter direct detections

In an extended effective operator framework, we investigate in detail the effects of light mediators on the event spectra of dark matter (DM)-nucleus scatterings. The presence of light mediators changes the interpretation of the current experimental data, especially the determination of DM particle mass. We show by analytic and numerical illustrations that in general for all the operators relevant to spin-independent scatterings, the DM particle mass allowed by a given set of experimental data increases significantly when the mediator particle becomes lighter. For instance, in the case of CDMS-II-Si experiment, the allowed DM particle mass can reach ∼50 (100) GeV at 68% (90%) confidence level, which is much larger than ∼10 GeV in the case with contact interactions. The increase of DM particle mass saturates when the mediator mass is below O(10) MeV. The upper limits from other experiments such as SuperCDMS, CDMSlite, CDEX, XENON10/100, LUX, PandaX etc. all tend to be weaker toward high DM mass regions. In a combined analysis, we show that the presence of light mediators can partially relax the tension in the current results of CDMS-II-Si, SuperCDMS and LUX.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2014

Search for long-lived neutral particles decaying into lepton jets in proton-proton collisions at $ \sqrt{s}=8 $ TeV with the ATLAS detector

Several models of physics beyond the Standard Model predict neutral particles that decay into final states consisting of collimated jets of light leptons and hadrons (so-called “lepton jets”). These particles can also be long-lived with decay length comparable to, or even larger than, the LHC detectors’ linear dimensions. This paper presents the results of a search for lepton jets in proton-proton collisions at the centre-of-mass energy of $ \sqrt{s}=8 $ TeV in a sample of 20.3 fb collected during 2012 with the ATLAS detector at the LHC. Limits on models predicting Higgs boson decays to neutral long-lived lepton jets are derived as a function of the particle’s proper decay length.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2019

FCC Physics Opportunities

This volume of the Conceptual Design Report is dedicated to an overview of the FCC physics potential. It focuses on the most significant targets of the potential FCC research programme but, for the sake of space, not covering a large body of science that will nevertheless be accessible (and which is documented in various other reports, listed in the Appendix). The studies presented here, in addition to setting plausible targets for the FCC achievements, have helped in making the choice of the colliders’ parameters (energy, luminosity) and their operation plans. Furthermore, these studies contributed to the deinition of the critical detector features and parameters, as described in Volumes 2 and 3 of the CDR. While at first discussing the targets of each collider separately, the second part of this volume puts their synergy and complementarity in perspective, underscoring the added benefit to science brought by the unity and coherence of the whole programme. In addition to summarising the outcome of the work done during this CDR phase of the FCC physics studies, for the benefit of the whole particle physics community, this document is intended to stimulate an expert discussion of the FCC physics potential, in the context of the forthcoming review of the European Strategy for Particle Physics.

43 PARTICLE ACCELERATORS↗
DOE OSTI2016

An estimation of photon scattering length in tetraphenyl-butadiene

Tetraphenyl-butadiene (TPB) is a wavelength shifting material that can absorb ultraviolet photons and emit blue photons. It is used in the detection of vacuum ultraviolet (VUV) photons, for which typical photo-sensors, such as most photomultiplier tubes (PMT) and silicon photomultipliers (SiPM), do not have any quantum efficiency. The secondary blue light is emitted isotropically, however, due to scattering within the material, its angular distribution upon exiting the material can not be easily predicted. In this work, we describe a procedure for estimating the scattering length of blue light in TPB, by measuring and modeling the angular distribution as a function of layer thickness. The experiment consists of shining 254nm light at various thicknesses of TPB deposited on fused silica, and measuring the intensity of blue light using SiPMs on either side of the sample. We simulate light propagation within the sample to estimate the light yield and compare that to the data, which allows us to estimate mean scattering length for photons in TPB to be in the range 2–3 µm, with some preference for a central value of 2.75 µm.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2018

Search for neutrinoless β + EC decay of Te 120 with CUORE-0

Here, we have performed a search for neutrinoless $\beta^{+}\hspace{-0.2em}EC$ decay of $^{120}$Te using the final CUORE-0 data release. We describe a new analysis method for the simultaneous fit of signatures with different event topology, and of data subsets with different signal efficiency, obtaining a limit on the half-life of the decay of $T_{1/2}>1.6\cdot10^{21}$ yr at $90\%$ CI. Combining this with results from Cuoricino, a predecessor experiment, we obtain the strongest limit to date, corresponding to $T_{1/2}>2.7\cdot10^{21}$ yr at $90\%$ CI.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2014

Extracting TMDs from CLAS12 data

We present studies of double longitudinal spin asymmetries in semi-inclusive deep inelastic scattering using a new dedicated Monte Carlo generator, which includes quark intrinsic transverse momentum within the generalized parton model based on the fully differential cross section for the process. Additionally we employ Bessel-weighting to the MC events to extract transverse momentum dependent parton distribution functions and also discuss possible uncertainties due to kinematic correlation effects.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗