519 research outputs found
Accelerator Measurements of Magnetically Induced Radio Emission from Particle Cascades with Applications to Cosmic-Ray Air Showers
For 50 years, cosmic-ray air showers have been detected by their radio emission. We present the first laboratory measurements that validate electrodynamics simulations used in air shower modeling. An experiment at SLAC provides a beam test of radio-frequency (rf) radiation from charged particle cascades in the presence of a magnetic field, a model system of a cosmic-ray air shower. This experiment provides a suite of controlled laboratory measurements to compare to particle-level simulations of rf emission, which are relied upon in ultrahigh-energy cosmic-ray air shower detection. We compare simulations to data for intensity, linearity with magnetic field, angular distribution, polarization, and spectral content. In particular, we confirm modern predictions that the magnetically induced emission in a dielectric forms a cone that peaks at the Cherenkov angle and show that the simulations reproduce the data within systematic uncertainties
Mesonic screening masses at high temperature and finite density
We compute the first perturbative correction to the static correlation
lengths of light quark bilinears in hot QCD with finite quark chemical
potentials. The correction is small and positive, with mu-dependence depending
on the relative sign of chemical potentials and the number of dynamical
flavors. The computation is carried out using a three-dimensional effective
theory for the lowest fermionic Matsubara mode. We also compute the full
correlator in free theory and find a rather complicated general mu-dependence
at shorter distances. Finally, rough comparisons with lattice simulations are
discussed.Comment: 24 pages, 5 figures, JHEP style. Minor corrections and
clarifications, version to appear in JHE
Picosecond timing of Microwave Cherenkov Impulses from High-Energy Particle Showers Using Dielectric-loaded Waveguides
We report on the first measurements of coherent microwave impulses from
high-energy particle-induced electromagnetic showers generated via the Askaryan
effect in a dielectric-loaded waveguide. Bunches of 12.16 GeV electrons with
total bunch energy of GeV were pre-showered in tungsten, and
then measured with WR-51 rectangular (12.6 mm by 6.3 mm) waveguide elements
loaded with solid alumina () bars. In the 5-8 GHz
single-mode band determined by the presence of the dielectric in the waveguide,
we observed band-limited microwave impulses with amplitude proportional to
bunch energy. Signals in different waveguide elements measuring the same shower
were used to estimate relative time differences with 2.3 picosecond precision.
These measurements establish a basis for using arrays of alumina-loaded
waveguide elements, with exceptional radiation hardness, as very high precision
timing planes for high-energy physics detectors.Comment: 16 pages, 15 figure
Measurements and Modeling of Near-Surface Radio Propagation in Glacial Ice and Implications for Neutrino Experiments
We present measurements of radio transmission in the 100 MHz range
through a m deep region below the surface of the ice at Summit
Station, Greenland, called the firn. In the firn, the index of refraction
changes due to the transition from snow at the surface to glacial ice below,
affecting the propagation of radio signals in that region. We compare our
observations to a finite-difference time-domain (FDTD) electromagnetic wave
simulation, which supports the existence of three classes of propagation: a
bulk propagation ray-bending mode that leads to so-called "shadowed" regions
for certain geometries of transmission, a surface-wave mode induced by the
ice/air interface, and an arbitrary-depth horizontal propagation mode that
requires perturbations from a smooth density gradient. In the non-shadowed
region, our measurements are consistent with the bulk propagation ray-bending
mode both in timing and in amplitude. We also observe signals in the shadowed
region, in conflict with a bulk-propagation-only ray-bending model, but
consistent with FDTD simulations using a variety of firn models for Summit
Station. The amplitude and timing of our measurements in all geometries are
consistent with the predictions from FDTD simulations. In the shadowed region,
the amplitude of the observed signals is consistent with a best-fit coupling
fraction value of % (0.06% in power) or less to a surface or horizontal
propagation mode from the bulk propagation mode. The relative amplitude of
observable signals in the two regions is important for experiments that aim to
detect radio emission from astrophysical high-energy neutrinos interacting in
glacial ice, which rely on a radio propagation model to inform simulations and
perform event reconstruction.Comment: 14 pages, 13 figures, version accepted to PR
Debye screening in strongly coupled N=4 supersymmetric Yang-Mills plasma
Using the AdS/CFT correspondence, we examine the behavior of correlators of
Polyakov loops and other operators in N=4 supersymmetric Yang-Mills theory at
non-zero temperature. The implications for Debye screening in this strongly
coupled non-Abelian plasma, and comparisons with available results for thermal
QCD, are discussed.Comment: 21 pages, 5 figures, significantly expanded discussion of Polyakov
loop correlator and static quark-antiquark potentia
Development Toward a Ground-Based Interferometric Phased Array for Radio Detection of High Energy Neutrinos
The in-ice radio interferometric phased array technique for detection of high
energy neutrinos looks for Askaryan emission from neutrinos interacting in
large volumes of glacial ice, and is being developed as a way to achieve a low
energy threshold and a large effective volume at high energies. The technique
is based on coherently summing the impulsive Askaryan signal from multiple
antennas, which increases the signal-to-noise ratio for weak signals. We report
here on measurements and a simulation of thermal noise correlations between
nearby antennas, beamforming of impulsive signals, and a measurement of the
expected improvement in trigger efficiency through the phased array technique.
We also discuss the noise environment observed with an analog phased array at
Summit Station, Greenland, a possible site for an interferometric phased array
for radio detection of high energy neutrinos.Comment: 13 Pages, 14 Figure
Accelerator measurements of magnetically-induced radio emission from particle cascades with applications to cosmic-ray air showers
For fifty years, cosmic-ray air showers have been detected by their radio
emission. We present the first laboratory measurements that validate
electrodynamics simulations used in air shower modeling. An experiment at SLAC
provides a beam test of radio-frequency (RF) radiation from charged particle
cascades in the presence of a magnetic field, a model system of a cosmic-ray
air shower. This experiment provides a suite of controlled laboratory
measurements to compare to particle-level simulations of RF emission, which are
relied upon in ultra-high-energy cosmic-ray air shower detection. We compare
simulations to data for intensity, linearity with magnetic field, angular
distribution, polarization, and spectral content. In particular, we confirm
modern predictions that the magnetically induced emission in a dielectric forms
a cone that peaks at the Cherenkov angle and show that the simulations
reproduce the data within systematic uncertainties.Comment: 5 pages, 7 figure
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