1,021 research outputs found
The Nuclear Reactions in Standard BBN
Nowadays, the Cosmic Microwave Background (CMB) anisotropies studies
accurately determine the baryon fraction omega_b, showing an overall and
striking agreement with previous determinations of omega_b obtained from Big
Bang Nucleosynthesis (BBN). However, a deeper comparison of BBN predictions
with the determinations of the primordial light nuclides abundances shows
slight tensions, motivating an effort to further improve the accuracy of
theoretical predictions, as well as to better evaluate systematics in both
observations and nuclear reactions measurements. We present some results of an
important step towards an increasing precision of BBN predictions, namely an
updated and critical review of the nuclear network, and a new protocol to
perform the nuclear data regression.Comment: 4 pp.,4figs. Few typos corrected and updated refs. to match the
version appearing in the proceedings of Conference ``Nuclei in the Cosmos
VIII'', Vancouver, BC, Canada, 19-23 Jul 2004, published in Nucl. Phys.
Bayesian model comparison applied to the Explorer-Nautilus 2001 coincidence data
Bayesian reasoning is applied to the data by the ROG Collaboration, in which
gravitational wave (g.w.) signals are searched for in a coincidence experiment
between Explorer and Nautilus. The use of Bayesian reasoning allows, under well
defined hypotheses, even tiny pieces of evidence in favor of each model to be
extracted from the data. The combination of the data of several experiments can
therefore be performed in an optimal and efficient way. Some models for
Galactic sources are considered and, within each model, the experimental result
is summarized with the likelihood rescaled to the insensitivity limit value
(`` function''). The model comparison result is given in in terms of
Bayes factors, which quantify how the ratio of beliefs about two alternative
models are modified by the experimental observationComment: 16 pages, 4 figures. Presented at the GWDAW2002 conference, held in
Kyoto on Dec.,2002. This version includes comments by the referees of CQG,
which has accepted the paper for pubblication in the special issue of the
conference. In particular, note that in Eq. 12 there was a typeset error. As
suggested by one of the referees, a uniform prior in Log(alpha) has also been
considere
Bayesian Inference in Processing Experimental Data: Principles and Basic Applications
This report introduces general ideas and some basic methods of the Bayesian
probability theory applied to physics measurements. Our aim is to make the
reader familiar, through examples rather than rigorous formalism, with concepts
such as: model comparison (including the automatic Ockham's Razor filter
provided by the Bayesian approach); parametric inference; quantification of the
uncertainty about the value of physical quantities, also taking into account
systematic effects; role of marginalization; posterior characterization;
predictive distributions; hierarchical modelling and hyperparameters; Gaussian
approximation of the posterior and recovery of conventional methods, especially
maximum likelihood and chi-square fits under well defined conditions; conjugate
priors, transformation invariance and maximum entropy motivated priors; Monte
Carlo estimates of expectation, including a short introduction to Markov Chain
Monte Carlo methods.Comment: 40 pages, 2 figures, invited paper for Reports on Progress in Physic
The history of mass assembly of faint red galaxies in 28 galaxy clusters since z=1.3
We measure the relative evolution of the number of bright and faint (as faint
as 0.05 L*) red galaxies in a sample of 28 clusters, of which 16 are at 0.50<=
z<=1.27, all observed through a pair of filters bracketing the 4000 Angstrom
break rest-frame. The abundance of red galaxies, relative to bright ones, is
constant over all the studied redshift range, 0<z<1.3, and rules out a
differential evolution between bright and faint red galaxies as large as
claimed in some past works. Faint red galaxies are largely assembled and in
place at z=1.3 and their deficit does not depend on cluster mass, parametrized
by velocity dispersion or X-ray luminosity. Our analysis, with respect to
previous one, samples a wider redshift range, minimizes systematics and put a
more attention to statistical issues, keeping at the same time a large number
of clusters.Comment: MNRAS, 386, 1045. Half a single sentence (in sec 4.4) change
Present and Future CP Measurements
We review theoretical and experimental results on CP violation summarizing
the discussions in the working group on CP violation at the UK phenomenology
workshop 2000 in Durham.Comment: 104 pages, Latex, to appear in Journal of Physics
Design and Test of a Forward Neutron Calorimeter for the ZEUS Experiment
A lead scintillator sandwich sampling calorimeter has been installed in the
HERA tunnel 105.6 m from the central ZEUS detector in the proton beam
direction. It is designed to measure the energy and scattering angle of
neutrons produced in charge exchange ep collisions. Before installation the
calorimeter was tested and calibrated in the H6 beam at CERN where 120 GeV
electrons, muons, pions and protons were made incident on the calorimeter. In
addition, the spectrum of fast neutrons from charge exchange proton-lucite
collisions was measured. The design and construction of the calorimeter is
described, and the results of the CERN test reported. Special attention is paid
to the measurement of shower position, shower width, and the separation of
electromagnetic showers from hadronic showers. The overall energy scale as
determined from the energy spectrum of charge exchange neutrons is compared to
that obtained from direct beam hadrons.Comment: 45 pages, 22 Encapsulated Postscript figures, submitted to Nuclear
Instruments and Method
Search for dark Higgsstrahlung in e+ e- -> mu+ mu- and missing energy events with the KLOE experiment
We searched for evidence of a Higgsstrahlung process in a secluded sector,
leading to a final state with a dark photon U and a dark Higgs boson h', with
the KLOE detector at DAFNE. We investigated the case of h' lighter than U, with
U decaying into a muon pair and h' producing a missing energy signature. We
found no evidence of the process and set upper limits to its parameters in the
range 2m_mu<m_U<1000 MeV, m_h'<m_U.Comment: 16 pages, 7 figures, submitted to Physics Letters
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