New searches for muonphilic particles at proton beam dump spectrometers
Not Available
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
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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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Measurement of the Centrality Dependence of the Dijet Yield in p + Pb Collisions at s NN = 8.16 TeV with the ATLAS Detector
ATLAS measured the centrality dependence of the dijet yield using 165 nb − 1 of p + Pb data collected at s NN = 8.16 TeV in 2016. The event centrality, which reflects the p + Pb impact parameter, is characterized by the total transverse energy registered in the Pb-going side of the forward calorimeter. The central-to-peripheral ratio of the scaled dijet yields, R CP , is evaluated, and the results are presented as a function of variables that reflect the kinematics of the initial hard parton scattering process. The R CP shows a scaling with the Bjorken x of the parton originating from the proton, x p , while no such trend is observed as a function of x Pb . This analysis provides unique input to understanding the role of small proton spatial configurations in p + Pb collisions by covering parton momentum fractions from the valence region down to x p ∼ 10 − 3 and x Pb ∼ 4 × 10 − 4 . © 2024 CERN, for the ATLAS Collaboration 2024 CERN
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Generalized Ginsparg-Wilson relations
We give a general derivation of Ginsparg-Wilson relations for both Dirac and Majorana fermions in any dimension. These relations encode continuous and discrete chiral, parity and time-reversal anomalies and will apply to the various classes of free-fermion topological insulators and superconductors (in the framework of a relativistic quantum field theory in Euclidean spacetime). We show how to formulate the exact symmetries of the lattice action and the relevant index theorems for the anomalies. Published by the American Physical Society 2024
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Pressure anisotropy and radial stress balance in the Jovian neutral sheet
By examining particle and magnetic field data from the Voyager 1 and 2 spacecraft, signatures were found indicating that the (greater than about 28 keV) particle pressure parallel to the magnetic field is greater than the pressure perpendicular to the field within the nightside neutral sheet (three nightside neutral sheet crossings, with favorable experimental conditions, were used). By incorporating the pressure anisotropy into the calculation of radial forces within the hightside neutral sheet, it is found that (1) force balance is approximately achieved and (2) the anisotropy force term provides the largest contribution of the other particle forces considered (pressure gradients and the corotation centrifugal force). With regard to the problem of understanding the balance of radial forces within the dayside neutral sheet (McNutt, 1984; Mauk and Krimigis, 1987), the nightside pressure anisotropy force is larger than the dayside pressure gradient forces at equivalent radial distances; however, a full accounting of the dayside regions remains to be achieved.
Paranicas, C. P.↗
Wilsonian effective potentials and closed string field theory
We investigate Wilsonian effective field theory as a model for the construction of the tachyon potential and nonperturbative vacua in closed string field theory. In a number of cases we are able to find the effective potential exactly, and observe what appear to be universal features. We find that the effective field theory contains the same nonperturbative vacuum structure as the bare Lagrangian, though this information is encoded less efficiently as the distance scale of the effective field theory is increased. The implication is that closed string field theory plausibly contains information about the nonperturbative vacuum structure of string theory, in spite of its similarities to effective field theory. We also truncate the effective potential at a fixed power of the field and investigate how the global structure of the effective potential may be approximated via Padé resummation. Qualitative comparisons suggest that computation of the eighth to sixteenth order closed string vertex should be enough to obtain reliable results for the closed string field theory action evaluated on the tachyon field.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Analysis of the 31 Oct 1972 interplanetary shock wave and associated unusual phenomena
We analyze in detail the disturbed time period Oct. 31-Nov. 1, 1972 using magnetic field, plasma, and energetic particle data as well as magnetic field data. In particular, we discuss an interplanetary forward shock wave accompanied by a traditional shock-spike event in the energetic particles, a large tangential discontinuity correlated with a geomagnetic storm main phase, and a reverse interplanetary shock. This forward and reverse shock pair was caused by a 2N solar flare which occurred some 47 hours earlier. We also discuss an unusual rarefaction in the solar wind following (and probably related to) the shock pair, wherein the Alfven Mach number abruptly decreased from about 4.5 to about 1.5, allowing the earth's bow shock to move outward at least 20 earth radii beyond its nominal position.
Ipavich, F. M.↗
Computer simulation of the velocity diffusion of cosmic rays
Monte Carlo simulation experiments were performed in order to study the velocity diffusion of charged particles in a static turbulent magnetic field. By following orbits of particles moving in a large ensemble of random magnetic field realizations with suitable chosen statistical properties, a pitch-angle diffusion coefficient is derived. Results are presented for a variety of particle rigidities and rms random field strengths and compared with the predictions of standard quasi-linear theory and the nonlinear partially averaged field theory.
Kaiser, T. B.↗
Computer simulation of the velocity diffusion of cosmic rays
Monte Carlo simulation experiments have been performed in order to study the velocity diffusion of charged particles in a static turbulent magnetic field. By following orbits of particles moving in a large ensemble of random magnetic field realizations with suitably chosen statistical properties, a pitch-angle diffusion coefficient is derived. Results are presented for a variety of particle rigidities and rms random field strengths and compared with the predictions of standard quasi-linear theory and the nonlinear partially averaged field theory.
Kaiser, T. B.↗
Digital PIV Measurements of Acoustic Particle Displacements in a Normal Incidence Impedance Tube
Acoustic particle displacements and velocities inside a normal incidence impedance tube have been successfully measured for a variety of pure tone sound fields using Digital Particle Image Velocimetry (DPIV). The DPIV system utilized two 600-mj Nd:YAG lasers to generate a double-pulsed light sheet synchronized with the sound field and used to illuminate a portion of the oscillatory flow inside the tube. A high resolution (1320 x 1035 pixel), 8-bit camera was used to capture double-exposed images of 2.7-micron hollow silicon dioxide tracer particles inside the tube. Classical spatial autocorrelation analysis techniques were used to ascertain the acoustic particle displacements and associated velocities for various sound field intensities and frequencies. The results show that particle displacements spanning a range of 1-60 microns can be measured for incident sound pressure levels of 100-130 dB and for frequencies spanning 500-1000 Hz. The ability to resolve 1 micron particle displacements at sound pressure levels in the 100 dB range allows the use of DPIV systems for measurement of sound fields at much lower sound pressure levels than had been previously possible. Representative impedance tube data as well as an uncertainty analysis for the measurements are presented.
Humphreys, William M., Jr.↗
Low energy (10eV to 10 keV) equatorial particle fluxes and soft particle fluxes near the equator
Several spectra are shown that represent one rotation of ISIS-1. Spectra 1, 2, 3, represent particles moving down the field line into northern ionosphere and spectra 4, 5, 6 represent particles moving up field lines towards the magnetic equator. The former are direct fluxes and the latter are albedo fluxes. The spectra observed are remarkably similar to these observed in the auroral zone. The direct fluxes exhibit a relative maximum in the few keV range and the albedo a power low spectrum with increased fluxes at low energies. Examination of concurrent topside sounder data on ISIS-1 revealed a positive correlation between a region of turbulent ionosphere and particle fluxes. This ionospheric condition is referred to as equatorial spread F and has been studied extensively with bottomside ionospheric sounders and backscatter radars. The perigee of ISIS crossed the magnetic equator at four local times (0400, 1000, 1600, 2100) during the lifetime of the particle spectrometer. No fluxes were observed at 0400 and 1000 local time. At 1600 a few instances of particles were observed. At 2100 essentially all passes included detectable equatorial fluxes. This is in agreement with the frequency of occurence of equatorial spread F.
Winningham, J. D.↗
Energetic particles in the vicinity of a possible neutral line in the plasma sheet
Combined plasma, magnetic field, and energetic particle data obtained from ISEE-1 in the geomagnetic tail during two successive energetic particle burst events are presented. The behavior of protons with energies of more than about 100 keV is very different from that of the 30-100 keV protons which represent the suprathermal tail of the plasma sheet distribution. The more energetic ions appear on a time scale of several minutes following a northward turning of the tail magnetic field. At about the same time the plasma measurements show a velocity of about 200 km/s in the tailward direction. From these results, it is argued that two successive magnetic neutral lines are created well within the plasma sheet and move close to the satellite position in the earthward direction. The extent of the neutral line is then limited to the dusk side of the tail.
Moebius, E.↗
Particle Acceleration and Radiation associated with Magnetic Field Generation from Relativistic Collisionless Shocks
Shock acceleration is an ubiquitous phenomenon in astrophysical plasmas. Plasma waves and their associated instabilities (e.g., the Buneman instability, two-streaming instability, and the Weibel instability) created in the shocks are responsible for particle (electron, positron, and ion) acceleration. Using a 3-D relativistic electromagnetic particle (REMP) code, we have investigated particle acceleration associated with a relativistic jet front propagating through an ambient plasma with and without initial magnetic fields. We find only small differences in the results between no ambient and weak ambient magnetic fields. Simulations show that the Weibel instability created in the collisionless shock front accelerates particles perpendicular and parallel to the jet propagation direction. While some Fermi acceleration may occur at the jet front, the majority of electron acceleration takes place behind the jet front and cannot be characterized as Fermi acceleration. The simulation results show that this instability is responsible for generating and amplifying highly nonuniform, small-scale magnetic fields, which contribute to the electron s transverse deflection behind the jet head. The "jitter" radiation from deflected electrons has different properties than synchrotron radiation which is calculated in a uniform magnetic field. This jitter radiation may be important to understanding the complex time evolution and/or spectral structure in gamma-ray bursts, relativistic jets, and supernova remnants.
Nishikawa, K.↗
Wave production in an ultrarelativistic electron-positron plasma
In this paper we calculate the eigenmodes associated with an ultrarelativistic electron-positron beam traversing a low-energy electron-positron plasma under physical conditions that may exist along open magnetic field lines above pulsar polar caps. We assume that both beam and plasma are cold and charge neutral, and that magnetic field strength and particle density decrease as the cube of (1/R). In the superstrong magnetic fields near the stellar surface where cyclotron frequencies exceed plasma frequencies, electrostatic waves and associated transverse low-frequency waves are driven unstable by the two-stream type particle distribution. At larger distances above the stellar surface the slow beam cyclotron wave is driven unstable. At even greater radial distance (approximately when particle energy density exceeds magnetic energy density) both the Ordinary and Alfven modes become unstable. All of these instabilities can lead to generation of radiation. If the particle distribution as generated at the stellar surface, assumed to consist of two streams, is modified only by plasma effects, then electrostatic and associated transverse waves may only be unstable near the stellar surface. The beam cyclotron mode which is driven by a two-stream or an inverted particle distribution may be stable.
Hardee, P. E.↗
Signs of pseudo-Dirac neutrinos in SN1987A data
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72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Time- and Space-Varying Neutrino Mass Matrix from Soft Topological Defects
Not Available
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Upstream particle events close to the bow shock and 200 earth radii upstream - ISEE-1 and ISEE-3 observations
Two energetic particle events (28 keV - 145 keV) upstream of the earth's bow shock have been investigated with two identical experiments of the Max-Planck-Institut/University of Maryland on ISEE-1 and ISEE-3. Close to the bow shock the particle distribution is more or less isotropic and indicates strong scattering of these particles in the upstream wave field. At ISEE-3 the particles move essentially scatter-free from the general bow shock direction. The temporal evolution of the particle bursts is discussed in terms of the interplanetary magnetic field topology and the scattering conditions.
Scholer, M.↗
The Portable Ice Nucleation Experiment (PINE): a new online instrument for laboratory studies and automated long-term field observations of ice-nucleating particles
Atmospheric ice-nucleating particles (INPs) play an important role in determining the phase of clouds, which affects their albedo and lifetime. A lack of data on the spatial and temporal variation of INPs around the globe limits our predictive capacity and understanding of clouds containing ice. Automated instrumentation that can robustly measure INP concentrations across the full range of tropospheric temperatures is needed in order to address this knowledge gap. In this study, we demonstrate the functionality and capacity of the new Portable Ice Nucleation Experiment (PINE) to study ice nucleation processes and to measure INP concentrations under conditions pertinent for mixed-phase clouds, with temperatures from about -10 to about -40°C. PINE is a cloud expansion chamber which avoids frost formation on the cold walls and thereby omits frost fragmentation and related background ice signals during the operation. The development, working principle and treatment of data for the PINE instrument is discussed in detail. We present laboratory-based tests where PINE measurements were compared with those from the established AIDA (Aerosol Interaction and Dynamics in the Atmosphere) cloud chamber. Within experimental uncertainties, PINE agreed with AIDA for homogeneous freezing of pure water droplets and the immersion freezing activity of mineral aerosols. Results from a first field campaign conducted at the Atmospheric Radiation Measurement (ARM) Southern Great Plains (SGP) observatory in Oklahoma, USA, from 1 October to 14 November 2019 with the latest PINE design (a commercially available PINE chamber) are also shown, demonstrating PINE's ability to make automated field measurements of INP concentrations at a time resolution of about 8 min with continuous temperature scans for INP measurements between -10 and -30°C. During this field campaign, PINE was continuously operated for 45 d in a fully automated and semi-autonomous way, demonstrating the capability of this new instrument to also be used for longer-term field measurements and INP monitoring activities in observatories.
54 ENVIRONMENTAL SCIENCES↗
Cloud microstructure as determined by an optical cloud particle spectrometer.
Use of an improved single-particle light-scattering instrument for measurement of cloud microstructure in field studies. Cloud particle size and number information is measured over 12 sizing intervals, in the range from 4 to 85 microns in diameter. The microstructure can be observed in real time and with a spatial resolution not previously reported. The general features of water cloud droplet size and number distributions are consistent with previous direct capture and replication studies. The transition from water to ice phase regions in cumuliform clouds can be inferred from dramatic changes observed in the distribution features. Results are also presented for stratus and cirrus cloud penetrations.
Ryan, R. T.↗