3,484 research outputs found
A Coverage Study of the CMSSM Based on ATLAS Sensitivity Using Fast Neural Networks Techniques
We assess the coverage properties of confidence and credible intervals on the
CMSSM parameter space inferred from a Bayesian posterior and the profile
likelihood based on an ATLAS sensitivity study. In order to make those
calculations feasible, we introduce a new method based on neural networks to
approximate the mapping between CMSSM parameters and weak-scale particle
masses. Our method reduces the computational effort needed to sample the CMSSM
parameter space by a factor of ~ 10^4 with respect to conventional techniques.
We find that both the Bayesian posterior and the profile likelihood intervals
can significantly over-cover and identify the origin of this effect to physical
boundaries in the parameter space. Finally, we point out that the effects
intrinsic to the statistical procedure are conflated with simplifications to
the likelihood functions from the experiments themselves.Comment: Further checks about accuracy of neural network approximation, fixed
typos, added refs. Main results unchanged. Matches version accepted by JHE
Improved Constraints on the Preferential Heating and Acceleration of Oxygen Ions in the Extended Solar Corona
We present a detailed analysis of oxygen ion velocity distributions in the
extended solar corona, based on observations made with the Ultraviolet
Coronagraph Spectrometer (UVCS) on the SOHO spacecraft. Polar coronal holes at
solar minimum are known to exhibit broad line widths and unusual intensity
ratios of the O VI 1032, 1037 emission line doublet. The traditional
interpretation of these features has been that oxygen ions have a strong
temperature anisotropy, with the temperature perpendicular to the magnetic
field being much larger than the temperature parallel to the field. However,
recent work by Raouafi and Solanki suggested that it may be possible to model
the observations using an isotropic velocity distribution. In this paper we
analyze an expanded data set to show that the original interpretation of an
anisotropic distribution is the only one that is fully consistent with the
observations. It is necessary to search the full range of ion plasma parameters
to determine the values with the highest probability of agreement with the UVCS
data. The derived ion outflow speeds and perpendicular kinetic temperatures are
consistent with earlier results, and there continues to be strong evidence for
preferential ion heating and acceleration with respect to hydrogen. At
heliocentric heights above 2.1 solar radii, every UVCS data point is more
consistent with an anisotropic distribution than with an isotropic
distribution. At heights above 3 solar radii, the exact probability of isotropy
depends on the electron density chosen to simulate the line-of-sight
distribution of O VI emissivity. (abridged abstract)Comment: 19 pages (emulateapj style), 13 figures, ApJ, in press (v. 679; May
20, 2008
Multivariate side-band subtraction using probabilistic event weights
A common situation in experimental physics is to have a signal which can not
be separated from a non-interfering background through the use of any cut. In
this paper, we describe a procedure for determining, on an event-by-event
basis, a quality factor (-factor) that a given event originated from the
signal distribution. This procedure generalizes the "side-band" subtraction
method to higher dimensions without requiring the data to be divided into bins.
The -factors can then be used as event weights in subsequent analysis
procedures, allowing one to more directly access the true spectrum of the
signal.Comment: 17 pages, 9 figure
Heating of the solar wind with electron and proton effects
We examine the effects of including effects of both protons and electrons on the heating of the fast solar wind through two different approaches. In the ïŹrst approach, we incorporate the electron temperature in an MHD turbulence transport model for the solar wind. In the second approach, we adopt more empirically based methods by analyzing the measured proton and electron temperatures to calculate the heat deposition rates. Overall, we conclude that incorporating separate proton and electron temperatures and heat conduction effects provides an improved and more complete model of the heating of the solar wind
Global 3D Simulations of Disc Accretion onto the classical T Tauri Star V2129 Oph
The magnetic field of the classical T Tauri star V2129 Oph can be modeled
approximately by superposing slightly tilted dipole and octupole moments, with
polar magnetic field strengths of 0.35kG and 1.2kG respectively (Donati et al.
2007). Here we construct a numerical model of V2129 Oph incorporating this
result and simulate accretion onto the star. Simulations show that the disk is
truncated by the dipole component and matter flows towards the star in two
funnel streams. Closer to the star, the flow is redirected by the octupolar
component, with some of the matter flowing towards the high-latitude poles, and
the rest into the octupolar belts. The shape and position of the spots differ
from those in a pure dipole case, where crescent-shaped spots are observed at
the intermediate latitudes. Simulations show that if the disk is truncated at
the distance of 6.2 R_* which is comparable with the co-rotation radius, 6.8
R_*, then the high-latitude polar spots dominate, but the accretion rate
obtained from the simulations is about an order of magnitude lower than the
observed one. The accretion rate matches the observed one if the disk is
disrupted much closer to the star, at 3.4 R_*. However, the octupolar belt
spots strongly dominate. Better match has been obtained in experiments with a
dipole field twice as strong. The torque on the star from the
disk-magnetosphere interaction is small, and the time-scale of spin evolution,
2 x10^7-10^9 years is longer than the 2x10^6 years age of V2129 Oph. The
external magnetic flux of the star is strongly influenced by the disk: the
field lines connecting the disk and the star inflate and form magnetic towers
above and below the disk. The potential (vacuum) approximation is still valid
inside the Alfv\'en (magnetospheric) surface where the magnetic stress
dominates over the matter stress.Comment: 15 pages, 15 figures, after major revision, added 3 figures, 2
tables. Accepted to MNRA
On the presentation of the LHC Higgs Results
We put forth conclusions and suggestions regarding the presentation of the
LHC Higgs results that may help to maximize their impact and their utility to
the whole High Energy Physics community.Comment: Conclusions from the workshops "Likelihoods for the LHC Searches",
21-23 January 2013 at CERN, "Implications of the 125 GeV Higgs Boson", 18-22
March 2013 at LPSC Grenoble, and from the 2013 Les Houches "Physics at TeV
Colliders" workshop. 16 pages, 3 figures. Version 2: Comment added on the
first publication of signal strength likelihoods in digital form by ATLA
Global 3D Simulations of Disc Accretion onto the classical T Tauri Star BP Tauri
The magnetic field of the classical T Tauri star BP Tau can be approximated
as a superposition of dipole and octupole moments with respective strengths of
the polar magnetic fields of 1.2 kG and 1.6 kG (Donati et al. 2008). We adopt
the measured properties of BP Tau and model the disc accretion onto the star.
We observed in simulations that the disc is disrupted by the dipole component
and matter flows towards the star in two funnel streams which form two
accretion spots below the dipole magnetic poles. The octupolar component
becomes dynamically important very close to the star and it redirects the
matter flow to higher latitudes. The spots are meridionally elongated and are
located at higher latitudes, compared with the pure dipole case, where
crescent-shaped, latitudinally elongated spots form at lower latitudes. The
position and shape of the spots are in good agreement with observations. The
disk-magnetosphere interaction leads to the inflation of the field lines and to
the formation of magnetic towers above and below the disk. The magnetic field
of BP Tau is close to the potential only near the star, inside the
magnetospheric surface, where magnetic stress dominates over the matter stress.
A series of simulation runs were performed for different accretion rates. They
show that an accretion rate is lower than obtained in many observations, unless
the disc is truncated close to the star. The torque acting on the star is about
an order of magnitude lower than that which is required for the rotational
equilibrium. We suggest that a star could lose most of its angular momentum at
earlier stages of its evolution.Comment: 11 pages, 13 figures, submitted to MNRA
Roles of Fast-Cyclotron and Alfven-Cyclotron Waves for the Multi-Ion Solar Wind
Using linear Vlasov theory of plasma waves and quasi-linear theory of
resonant wave-particle interaction, the dispersion relations and the
electromagnetic field fluctuations of fast and Alfven waves are studied for a
low-beta multi-ion plasma in the inner corona. Their probable roles in heating
and accelerating the solar wind via Landau and cyclotron resonances are
quantified. We assume that (1) low-frequency Alfven and fast waves have the
same spectral shape and the same amplitude of power spectral density; (2) these
waves eventually reach ion cyclotron frequencies due to a turbulence cascade;
(3) kinetic wave-particle interaction powers the solar wind. The existence of
alpha particles in a dominant proton/electron plasma can trigger linear mode
conversion between oblique fast-whistler and hybrid alpha-proton cyclotron
waves. The fast-cyclotron waves undergo both alpha and proton cyclotron
resonances. The alpha cyclotron resonance in fast-cyclotron waves is much
stronger than that in Alfven-cyclotron waves. For alpha cyclotron resonance, an
oblique fast-cyclotron wave has a larger left-handed electric field
fluctuation, a smaller wave number, a larger local wave amplitude, and a
greater energization capability than a corresponding Alfven-cyclotron wave at
the same wave propagation angle \theta, particularly at < \theta <
. When Alfven-cyclotron or fast-cyclotron waves are present, alpha
particles are the chief energy recipient. The transition of preferential
energization from alpha particles to protons may be self-modulated by
differential speed and temperature anisotropy of alpha particles via the
self-consistently evolving wave-particle interaction. Therefore, fast-cyclotron
waves as a result of linear mode coupling is a potentially important mechanism
for preferential energization of minor ions in the main acceleration region of
the solar wind.Comment: 29 pages, 10 figures, 3 tables. Accepted for publication in Solar
Physic
The Machine Learning Landscape of Top Taggers
Based on the established task of identifying boosted, hadronically decaying
top quarks, we compare a wide range of modern machine learning approaches.
Unlike most established methods they rely on low-level input, for instance
calorimeter output. While their network architectures are vastly different,
their performance is comparatively similar. In general, we find that these new
approaches are extremely powerful and great fun.Comment: Yet another tagger included
Measuring the Higgs Sector
If we find a light Higgs boson at the LHC, there should be many observable
channels which we can exploit to measure the relevant parameters in the Higgs
sector. We use the SFitter framework to map these measurements on the parameter
space of a general weak-scale effective theory with a light Higgs state of mass
120 GeV. Our analysis benefits from the parameter determination tools and the
error treatment used in new--physics searches, to study individual parameters
and their error bars as well as parameter correlations.Comment: 45 pages, Journal version with comments from refere
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