423 research outputs found
Bayesian View Of Solar Neutrino Oscillations
We present the results of a Bayesian analysis of solar neutrino data in terms
of nu_e->nu_{mu,tau} and nu_e->nu_s oscillations, where nu_s is a sterile
neutrino. We perform a Rates Analysis of the rates of solar neutrino
experiments, including the first SNO CC result, and spectral data of the CHOOZ
experiment, and a Global Analysis that takes into account also the
Super-Kamiokande day and night electron energy spectra. We show that the
Bayesian analysis does not suffer any problem from the inclusion of the
numerous bins of the CHOOZ and Super-Kamiokande energy spectra and allows to
reach the same conclusions on the favored type of neutrino transitions and on
the determination of the most favored values of the oscillation parameters in
both the Rates and Global Analysis. Our Bayesian analysis shows that nu_e->nu_s
transitions are strongly disfavored with respect to nu_e->nu_{mu,tau}
transitions. In the case of nu_e->nu_{mu,tau} oscillations, the LMA region is
favored by the data (86% probability), the LOW region has some small chance
(13% probability), the VO region is almost excluded (1% probability) and the
SMA region is practically excluded (0.01% probability). We calculate also the
marginal posterior probability distributions for tan^2 theta and Delta m^2 and
we show that the data imply large mixing almost with certainty and large values
of Delta m^2 are favored. We present also the results of a standard
least-squares analysis and we show that the standard goodness of fit test is
not able to rejects pure nu_e->nu_s transitions. The likelihood ratio test
allows to reject pure nu_e->nu_s transitions in favor of nu_e->nu_{mu,tau}
transitions only in the Global Analysis.Comment: 31 pages, 8 figures. Final version to be published in JHE
Statistical Analysis of Solar Neutrino Data
We calculate with Monte Carlo the goodness of fit and the confidence level of
the standard allowed regions for the neutrino oscillation parameters obtained
from the fit of the total rates measured in solar neutrino experiments. We show
that they are significantly overestimated in the standard method. We also
calculate exact allowed regions with correct frequentist coverage. We show that
the exact VO, LMA and LOW regions are much larger than the standard ones and
merge together giving an allowed band at large mixing angles for all Delta m^2
> 10^{-10} eV^2.Comment: 4 pages. Talk presented by C. Giunti at NOW 2000, Conca Specchiulla
(Otranto, Italy), 9-16 Sep. 200
Assessing the role of nuclear effects in the interpretation of the MiniBooNE low-energy anomaly
We study the impact of the effect of multinucleon interactions in the
reconstruction of the neutrino energy on the fit of the MiniBooNE data in terms
of neutrino oscillations. We obtain some improvement of the fit of the
MiniBooNE low-energy excess in the framework of two-neutrino oscillations and a
shift of the allowed region in the -- plane
towards smaller values of and larger values of
. However this effect is not enough to solve the problem of the
appearance-disappearance tension in the global fit of short-baseline neutrino
oscillation data.Comment: 14 pages; to be published in PR
Top-antitop pair hadroproduction in association with a heavy boson at the NLO QCD accuracy + Parton Shower
The PowHel framework allows to make predictions of total and differential
cross-sections of multiparticle hadroproduction processes at both NLO QCD
accuracy and NLO QCD matched to Parton Shower, on the basis of the interface
between the POWHEG-BOX and HELAC-NLO codes. It has already been applied to
study several processes involving a top-antitop pair in association with a
third particle or hadronic jet. Our most recent predictions concern
top-antitop-V hadroproduction (with V = W or Z), at both parton and hadron
level, by considering different decay channels (hadronic and leptonic) of the
heavy particles. In particular, we show the results of our phenomenological
analyses under the same system of cuts also recently adopted by the CMS
collaboration at LHC.Comment: 4 pages, 2 figures, Proceedings of TOP 2012 - 5th International
Workshop on Top Quark Physics, September 16 - 21 2012, Winchester, U
t tbar W and t tbar Z Hadroproduction at NLO accuracy in QCD with Parton Shower and Hadronization effects
We present theoretical predictions for the hadroproduction of t tbar W+, t
tbar W- and t tbar Z at LHC as obtained by matching numerical computations at
NLO accuracy in QCD with Shower Monte Carlo programs. The calculation is
performed by PowHel, relying on the POWHEG-BOX framework, that allows for the
matching between the fixed order computation, with input of matrix elements
produced by the HELAC-NLO collection of event generators, and the Parton Shower
evolution, followed by hadronization and hadron decays as described by PYTHIA
and HERWIG. We focus on the dilepton and trilepton decay channels, studied
recently by the CMS Collaboration.Comment: 21 pages 12 figure
Z0 - boson production in association with a top anti-top pair at NLO accuracy with parton shower effects
We present predictions for the production cross section of a Standard Model
Z0-boson in association with a top-antitop pair at the next-to-leading order
accuracy in QCD, matched with shower Monte Carlo programs to evolve the system
down to the hadronization energy scale. We adopt a framework based on three
well established numerical codes, namely the POWHEG-BOX, used for computing the
cross section, HELAC-NLO, which generates all necessary input matrix elements,
and finally a parton shower program, such as PYTHIA or HERWIG, which allows for
including t-quark and Z0-boson decays at the leading order accuracy and
generates shower emissions, hadronization and hadron decays.Comment: 10 pages, 5 figures; found and corrected a bug in the
phenomenological analysis, just affecting Fig.4 - 5 that turn out to change
slightly with respect to our previous version and the cross-section values
after all cuts. Conclusions qualitatively unchange
Helac-nlo
Based on the OPP technique and the HELAC framework, HELAC-1LOOP is a program
that is capable of numerically evaluating QCD virtual corrections to scattering
amplitudes. A detailed presentation of the algorithm is given, along with
instructions to run the code and benchmark results. The program is part of the
HELAC-NLO framework that allows for a complete evaluation of QCD NLO
corrections.Comment: minor text revisions, version to appear in Comput.Phys.Commu
Statistical treatment of detection cross-section uncertainties in the analysis of solar neutrino data
We propose a modification to the standard statistical treatment of the
detection cross-section uncertainties in the analysis of solar neutrino data.
We argue that the uncertainties of the energy-averaged cross sections of the
different neutrino fluxes in the same experiment should be treated as
correlated. We show that the resulting allowed regions for the neutrino
oscillation parameters are significantly larger than the ones obtained with
uncorrelated uncertainties.Comment: 12 pages. Corrected Figures 4 and 5 (vacuum oscillations
A frequentist analysis of solar neutrino data
We calculate with Monte Carlo the goodness of fit and the confidence level of
the standard allowed regions for the neutrino oscillation parameters obtained
from the fit of solar neutrino data. We show that the values of the goodness of
fit and of the confidence level of the allowed regions are significantly
smaller than the standard ones. Using Neyman's method, we also calculate exact
allowed regions with correct frequentist coverage. We show that the standard
allowed region around the global minimum of the least-squares function is a
reasonable approximation of the exact one, whereas the size of the other
regions is dramatically underestimated in the standard method.Comment: 19 page
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