489 research outputs found
A likelihood method to cross-calibrate air-shower detectors
We present a detailed statistical treatment of the energy calibration of
hybrid air-shower detectors, which combine a surface detector array and a
fluorescence detector, to obtain an unbiased estimate of the calibration curve.
The special features of calibration data from air showers prevent unbiased
results, if a standard least-squares fit is applied to the problem. We develop
a general maximum-likelihood approach, based on the detailed statistical model,
to solve the problem. Our approach was developed for the Pierre Auger
Observatory, but the applied principles are general and can be transferred to
other air-shower experiments, even to the cross-calibration of other
observables. Since our general likelihood function is expensive to compute, we
derive two approximations with significantly smaller computational cost. In the
recent years both have been used to calibrate data of the Pierre Auger
Observatory. We demonstrate that these approximations introduce negligible bias
when they are applied to simulated toy experiments, which mimic realistic
experimental conditions.Comment: 10 pages, 7 figure
Traveling waves for nonlinear Schr\"odinger equations with nonzero conditions at infinity, II
We prove the existence of nontrivial finite energy traveling waves for a
large class of nonlinear Schr\"odinger equations with nonzero conditions at
infinity (includindg the Gross-Pitaevskii and the so-called "cubic-quintic"
equations) in space dimension . We show that minimization of the
energy at fixed momentum can be used whenever the associated nonlinear
potential is nonnegative and it gives a set of orbitally stable traveling
waves, while minimization of the action at constant kinetic energy can be used
in all cases. We also explore the relationship between the families of
traveling waves obtained by different methods and we prove a sharp nonexistence
result for traveling waves with small energy.Comment: Final version, accepted for publication in the {\it Archive for
Rational Mechanics and Analysis.} The final publication is available at
Springer via http://dx.doi.org/10.1007/s00205-017-1131-
Influence of Low Energy Hadronic Interactions on Air-shower Simulations
Experiments measuring cosmic rays above an energy of 10^14 eV deduce the
energy and mass of the primary cosmic ray particles from air-shower
simulations. We investigate the importance of hadronic interactions at low and
high energies on the distributions of muons and electrons in showers on ground.
In air shower simulation programs, hadronic interactions below an energy
threshold in the range from 80 GeV to 500 GeV are simulated by low energy
interaction models, like Fluka or Gheisha, and above that energy by high energy
interaction models, e.g. Sibyll or QGJSJet. We find that the impact on shower
development obtained by switching the transition energy from 80 GeV to 500 GeV
is comparable to the difference obtained by switching between Fluka and
Gheisha.Comment: 4 pages, 6 figures, ISVHECRI 200
The Air Microwave Yield (AMY) experiment - A laboratory measurement of the microwave emission from extensive air showers
The AMY experiment aims to measure the microwave bremsstrahlung radiation
(MBR) emitted by air-showers secondary electrons accelerating in collisions
with neutral molecules of the atmosphere. The measurements are performed using
a beam of 510 MeV electrons at the Beam Test Facility (BTF) of Frascati INFN
National Laboratories. The goal of the AMY experiment is to measure in
laboratory conditions the yield and the spectrum of the GHz emission in the
frequency range between 1 and 20 GHz. The final purpose is to characterise the
process to be used in a next generation detectors of ultra-high energy cosmic
rays. A description of the experimental setup and the first results are
presented.Comment: 3 pages -- EPS-HEP'13 European Physical Society Conference on High
Energy Physics (July, 18-24, 2013) at Stockholm, Swede
On the symmetry of minimizers
For a large class of variational problems we prove that minimizers are
symmetric whenever they are .Comment: 17 pages, to appear in Arch. Rational Mech. Anal.; added Example 7
and some reference
Measurement of the lateral distribution function of UHECR air showers with the Pierre Auger Observatory
We describe how the lateral distribution function (LDF) is measured using the large sample of events recorded with the surface detector (SD) array and with a small sample observed with the fluorescence detectors (FD). For hybrid events, in which SD and FD measurements of the same shower are available, the core position is much better constrained than for SD-onlyevents, thus providing an important cross-check on the LDF determined from SD measurements alone.
[Segmento extraído de la ponencia]Facultad de Ciencias Exacta
2022 report from the Auger-TA working group on UHECR arrival directions
After over 60 years, the powerful engines that accelerate ultra-high-energy
cosmic rays (UHECRs) to the formidable energies at which we observe them from
Earth remain mysterious. Assuming standard physics, we expect UHECR sources to
lie within the local Universe (up to a few hundred~Mpc). The distribution of
matter in the local Universe is anisotropic, and we expect this anisotropy to
be imprinted on the distribution of UHECR arrival directions. Even though
intervening intergalactic and Galactic magnetic fields deflect charged UHECRs
and can distort these anisotropies, some amount of information on the
distribution of the sources is preserved. In this proceedings contribution, we
present the results of the joint Pierre Auger Observatory and Telescope Array
searches for (a) the largest-scale anisotropies (the harmonic dipole and
quadrupole) and (b) correlations with a sample of nearby starburst galaxies and
the 2MRS catalogue tracing stellar mass within~250~Mpc. This analysis updates
our previous results with the most recent available data, notably with the
addition of 3~years of new Telescope Array data. The main finding is a
correlation between the arrival directions of ~of
UHECRs detected with ~EeV by~Auger or with~~EeV by~TA
and the positions of nearby starburst galaxies on a
~angular scale, with a
~post-trial significance, up from obtained in our
previous study.Comment: proceedings of the 6th International Symposium on Ultra High Energy
Cosmic Rays (UHECR2022), 3-7 October 2022, L'Aquila, Ital
A search for point sources of EeV photons
Measurements of air showers made using the hybrid technique developed with
the fluorescence and surface detectors of the Pierre Auger Observatory allow a
sensitive search for point sources of EeV photons anywhere in the exposed sky.
A multivariate analysis reduces the background of hadronic cosmic rays. The
search is sensitive to a declination band from -85{\deg} to +20{\deg}, in an
energy range from 10^17.3 eV to 10^18.5 eV. No photon point source has been
detected. An upper limit on the photon flux has been derived for every
direction. The mean value of the energy flux limit that results from this,
assuming a photon spectral index of -2, is 0.06 eV cm^-2 s^-1, and no celestial
direction exceeds 0.25 eV cm^-2 s^-1. These upper limits constrain scenarios in
which EeV cosmic ray protons are emitted by non-transient sources in the
Galaxy.Comment: 28 pages, 10 figures, accepted for publication in The Astrophysical
Journa
Search for transient optical counterparts to high-energy IceCube neutrinos with Pan-STARRS1
In order to identify the sources of the observed diffuse high-energy neutrino
flux, it is crucial to discover their electromagnetic counterparts. IceCube
began releasing alerts for single high-energy ( TeV) neutrino
detections with sky localisation regions of order 1 deg radius in 2016. We used
Pan-STARRS1 to follow-up five of these alerts during 2016-2017 to search for
any optical transients that may be related to the neutrinos. Typically 10-20
faint ( mag) extragalactic transients are found within the
Pan-STARRS1 footprints and are generally consistent with being unrelated field
supernovae (SNe) and AGN. We looked for unusual properties of the detected
transients, such as temporal coincidence of explosion epoch with the IceCube
timestamp. We found only one transient that had properties worthy of a specific
follow-up. In the Pan-STARRS1 imaging for IceCube-160427A (probability to be of
astrophysical origin of 50 %), we found a SN PS16cgx, located at 10.0'
from the nominal IceCube direction. Spectroscopic observations of PS16cgx
showed that it was an H-poor SN at z = 0.2895. The spectra and light curve
resemble some high-energy Type Ic SNe, raising the possibility of a jet driven
SN with an explosion epoch temporally coincident with the neutrino detection.
However, distinguishing Type Ia and Type Ic SNe at this redshift is notoriously
difficult. Based on all available data we conclude that the transient is more
likely to be a Type Ia with relatively weak SiII absorption and a fairly normal
rest-frame r-band light curve. If, as predicted, there is no high-energy
neutrino emission from Type Ia SNe, then PS16cgx must be a random coincidence,
and unrelated to the IceCube-160427A. We find no other plausible optical
transient for any of the five IceCube events observed down to a 5
limiting magnitude of mag, between 1 day and 25 days after
detection.Comment: 20 pages, 6 figures, accepted to A&
Reconstruction of inclined air showers detected with the Pierre Auger Observatory
We describe the method devised to reconstruct inclined cosmic-ray air showers
with zenith angles greater than detected with the surface array of
the Pierre Auger Observatory. The measured signals at the ground level are
fitted to muon density distributions predicted with atmospheric cascade models
to obtain the relative shower size as an overall normalization parameter. The
method is evaluated using simulated showers to test its performance. The energy
of the cosmic rays is calibrated using a sub-sample of events reconstructed
with both the fluorescence and surface array techniques. The reconstruction
method described here provides the basis of complementary analyses including an
independent measurement of the energy spectrum of ultra-high energy cosmic rays
using very inclined events collected by the Pierre Auger Observatory.Comment: 27 pages, 19 figures, accepted for publication in Journal of
Cosmology and Astroparticle Physics (JCAP
- …