6,785 research outputs found
Measurement of the forward-backward asymmetries in Z->bb and Z->cc decays with leptons
The sample of hadronic Z decays collected by the ALEPH detector at LEP in the years 1991-1995 is analysed in order to measure the forward-backward asymmetries in Z decays to b and c quark pairs. The quark's electric charge is tagged by the charges of electrons and muons produced in b and c semileptonic decays. The separation of the event flavours and of the direct and cascade b semileptonic decays is realised by means of multivariate analyses. The b and c asymmetries are measured simultaneously, and translated, in the framework of the Standard Model, to a determination of the effective electroweak mixing angle
The LHCf experiment at LHC
High Energy Cosmic Ray experiments are providing useful information to understand high energy phenomena in the Universe. However, the uncertainty caused from the poor knowledge of the interaction between very high energy
primary cosmic ray and the Earthâs atmosphere prevents the precise deduction of astrophysical parameters from the observational data. The Large Hadron Collider (LHC) provides the best opportunity for calibrating the hadron interaction models in the most interesting energy range, between 1015 eV and 1017 eV. To constrain the models used in the extensive air shower simulations the measurements of very forward particles are mandatory. Among the LHC experiments, the LHCf experiment has been designed to reach this goal and its capability to measure forward neutral particle produced in p-p interaction will result crucial for a better interpretation of cosmic ray studies. In this paper, the status of the LHCf experiment and preliminary results for 900 GeV data taking are discussed
Nonlocality of Accelerated Systems
The conceptual basis for the nonlocality of accelerated systems is presented.
The nonlocal theory of accelerated observers and its consequences are briefly
described. Nonlocal field equations are developed for the case of the
electrodynamics of linearly accelerated systems.Comment: LaTeX file, no figures, 9 pages, to appear in: "Black Holes,
Gravitational Waves and Cosmology" (World Scientific, Singapore, 2003
The effect of short ray trajectories on the scattering statistics of wave chaotic systems
In many situations, the statistical properties of wave systems with chaotic
classical limits are well-described by random matrix theory. However,
applications of random matrix theory to scattering problems require
introduction of system specific information into the statistical model, such as
the introduction of the average scattering matrix in the Poisson kernel. Here
it is shown that the average impedance matrix, which also characterizes the
system-specific properties, can be expressed in terms of classical trajectories
that travel between ports and thus can be calculated semiclassically.
Theoretical results are compared with numerical solutions for a model
wave-chaotic system
SUSY searches with Opposite Sign Dileptons at CMS
A full simulation study with the detector CMS is presented. The Leptons + Jets + Missing Energy (l = e,) final state for SUSY events is investigated at mSUGRA benchmark point LM1. The end point in the dilepton pair invariant mass distribution is reconstructed and a scan of the plane is performed in order to determine the observability reach
Extreme Value Statistics of Eigenvalues of Gaussian Random Matrices
We compute exact asymptotic results for the probability of the occurrence of
large deviations of the largest (smallest) eigenvalue of random matrices
belonging to the Gaussian orthogonal, unitary and symplectic ensembles. In
particular, we show that the probability that all the eigenvalues of an (NxN)
random matrix are positive (negative) decreases for large N as ~\exp[-\beta
\theta(0) N^2] where the Dyson index \beta characterizes the ensemble and the
exponent \theta(0)=(\ln 3)/4=0.274653... is universal. We compute the
probability that the eigenvalues lie in the interval [\zeta_1,\zeta_2] which
allows us to calculate the joint probability distribution of the minimum and
the maximum eigenvalue. As a byproduct, we also obtain exactly the average
density of states in Gaussian ensembles whose eigenvalues are restricted to lie
in the interval [\zeta_1,\zeta_2], thus generalizing the celebrated Wigner
semi-circle law to these restricted ensembles. It is found that the density of
states generically exhibits an inverse square-root singularity at the location
of the barriers. These results are confirmed by numerical simulations.Comment: 17 pages Revtex, 5 .eps figures include
A trace formula and high energy spectral asymptotics for the perturbed Landau Hamiltonian
A two-dimensional Schr\"odinger operator with a constant magnetic field
perturbed by a smooth compactly supported potential is considered. The spectrum
of this operator consists of eigenvalues which accumulate to the Landau levels.
We call the set of eigenvalues near the 'th Landau level an 'th
eigenvalue cluster, and study the distribution of eigenvalues in the 'th
cluster as . A complete asymptotic expansion for the eigenvalue
moments in the 'th cluster is obtained and some coefficients of this
expansion are computed. A trace formula involving the first eigenvalue moments
is obtained.Comment: 23 page
Method to solve integral equations of the first kind with an approximate input
Techniques are proposed for solving integral equations of the first kind with
an input known not precisely. The requirement that the solution sought for
includes a given number of maxima and minima is imposed. It is shown that when
the deviation of the approximate input from the true one is sufficiently small
and some additional conditions are fulfilled the method leads to an approximate
solution that is necessarily close to the true solution. No regularization is
required in the present approach. Requirements on features of the solution at
integration limits are also imposed. The problem is treated with the help of an
ansatz proposed for the derivative of the solution. The ansatz is the most
general one compatible with the above mentioned requirements. The techniques
are tested with exactly solvable examples. Inversions of the Lorentz, Stieltjes
and Laplace integral transforms are performed, and very satisfactory results
are obtained. The method is useful, in particular, for the calculation of
quantum-mechanical reaction amplitudes and inclusive spectra of
perturbation-induced reactions in the framework of the integral transform
approach.Comment: 28 pages, 1 figure; the presentation is somewhat improved; to be
published in Phys. Rev.
Radiation from perfect mirrors starting from rest and the black body spectrum
We address the question of radiation emission from a perfect mirror that
starts from rest and follows the trajectory z=-ln(cosht) till t->Infinity. We
show that a correct derivation of the black body spectrum via the calculation
of the Bogolubov amplitudes requires consideration of the whole trajectory and
not just of its asymptotic part.Comment: Typos correcte
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