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 $\sin^2 2\vartheta$--$\Delta{m}^2$ plane towards smaller values of $\sin^2 2\vartheta$ and larger values of $\Delta{m}^2$. 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