Searcharxiv⌕ Search

arXiv subjects

M. C. Gonzalez-Garcia

Publications and source records attributed to M. C. Gonzalez-Garcia.

At least 127 records · Page 7Linked to original sources
arXiv2006

Extraction of the atmospheric neutrino fluxes from experimental event rate data

The precise knowledge of the atmospheric neutrino fluxes is a key ingredient in the interpretation of the results from any atmospheric neutrino experiment. In the standard atmospheric neutrino data analysis, these fluxes are theoretical inputs obtained from sophisticated numerical calculations. In this contribution we present an alternative approach to the determination of the atmospheric neutrino fluxes based on the direct extraction from the experimental data on neutrino event rates. The extraction is achieved by means of a combination of artificial neural networks as interpolants and Monte Carlo methods.

hep-ph↗
arXiv2006

Determination of the atmospheric neutrino fluxes from experimental data

The precise knowledge of the atmospheric neutrino fluxes is a key ingredient in the interpretation of the results from any atmospheric neutrino experiment. In the standard atmospheric neutrino data analysis, these fluxes are theoretical inputs obtained from sophisticated numerical calculations. In this contribution we present an alternative approach to the determination of the atmospheric neutrino fluxes based on the direct extraction from the experimental data on neutrino event rates.

astro-ph↗
arXiv2006

p p -> j j e+/- mu+/- nu nu and j j e+/- mu-/+ nu nu at O(α_{em}^6) and O(α_{em}^4 α_s^2) for the Study of the Quartic Electroweak Gauge Boson Vertex at LHC

We analyze the potential of the CERN Large Hadron Collider (LHC) to study the structure of quartic vector-boson interactions through the pair production of electroweak gauge bosons via weak boson fusion q q -> q q W W. In order to study these couplings we have performed a partonic level calculation of all processes p p -> j j e+/- mu+/- nu nu and pp -> j j e+/- mu-/+ nu nu at the LHC using the exact matrix elements at O(α_{em}^6) and O(α_{em}^4 α_s^2) as well as a full simulation of the t tbar plus 0 to 2 jets backgrounds. A complete calculation of the scattering amplitudes is necessary not only for a correct description of the process but also to preserve all correlations between the final state particles which can be used to enhance the signal. Our analyses indicate that the LHC can improve by more than one order of magnitude the bounds arising at present from indirect measurements.

hep-ph↗
arXiv2006

Effects of Environment Dependence of Neutrino Mass versus Solar and Reactor Neutrino Data

In this work we study the phenomenological consequences of the environment dependence of neutrino mass on solar and reactor neutrino phenomenology. Such dependence can be induced, for example, by Yukawa interactions with a light scalar particle which couples to neutrinos and matter and it is expected, among others, in mass varying neutrino scenarios. Under the assumption of one mass scale dominance, we perform a global analysis of solar and KamLAND neutrino data which depends on 4 parameters: the two standard oscillation parameters, Delta m^2 and tan^2(theta), and two new coefficients, which parameterize the environment dependence of the neutrino mass. We find that, generically, the inclusion of the environment dependent terms does not lead to a very statistically significant improvement on the description of the data in the most favoured MSW LMA (or LMA-I) region. It does, however, substantially improve the fit in the high-Delta m^2 LMA (or LMA-II) region which can be allowed at 98.9% CL. Conversely the analysis allow us to place stringent constraints on the size of the environment dependence terms, which can be translated on a bound on the product of the effective neutrino-scalar (lambda^ν) and matter-scalar (lambda^N) Yukawa couplings, as a function of the scalar field mass (m_S) in these models.

hep-ph↗
arXiv2005

Mass Varying Neutrinos in the Sun

In this work we study the phenomenological consequences of the dependence of mass varying neutrinos on the neutrino density in the Sun, which we precisely compute in each point along the neutrino trajectory. We find that a generic characteristic of these scenarios is that they establish a connection between the effective Delta m^2 in the Sun and the absolute neutrino mass scale. This does not lead to any new allowed region in the oscillation parameter space. On the contrary, due to this effect, the description of solar neutrino data worsens for large absolute mass. As a consequence a lower bound on the level of degeneracy can be derived from the combined analysis of the solar and KamLAND data. In particular this implies that the analysis favours normal over inverted mass orderings. These results, in combination with a positive independent determination of the absolute neutrino mass, can be used as a test of these scenarios together with a precise determination of the energy dependence of the survival probability of solar neutrinos, in particular for low energies.

hep-ph↗
arXiv2005

Probing Planck scale physics with IceCube

Neutrino oscillations can be affected by decoherence induced e.g. by Planck scale suppressed interactions with the space-time foam predicted in some approaches to quantum gravity. We study the prospects for observing such effects at IceCube, using the likely flux of TeV antineutrinos from the Cygnus spiral arm. We formulate the statistical analysis for evaluating the sensitivity to quantum decoherence in the presence of the background from atmospheric neutrinos, as well as from plausible cosmic neutrino sources. We demonstrate that IceCube will improve the sensitivity to decoherence effects of ${\cal O}(E^2/M_{\rm Pl})$ by 17 orders of magnitude over present limits and, moreover, that it can probe decoherence effects of ${\cal O}(E^3/M_{\rm Pl}^2)$ which are well beyond the reach of other experiments.

hep-ph↗
arXiv2005

Physics Reach of High-Energy and High-Statistics IceCube Atmospheric Neutrino Data

This paper investigates the physics reach of the IceCube neutrino detector when it will have collected a data set of order one million atmospheric neutrinos with energies in the 0.1 \sim 10^4 TeV range. The paper consists of three parts. We first demonstrate how to simulate the detector performance using relatively simple analytic methods. Because of the high energies of the neutrinos, their oscillations, propagation in the Earth and regeneration due to τdecay must be treated in a coherent way. We set up the formalism to do this and discuss the implications. In a final section we apply the methods developed to evaluate the potential of IceCube to study new physics beyond neutrino oscillations. Not surprisingly, because of the increased energy and statistics over present experiments, existing bounds on violations of the equivalence principle and of Lorentz invariance can be improved by over two orders of magnitude. The methods developed can be readily applied to other non-conventional physics associated with neutrinos.

hep-ph↗
arXiv2004

Global Analysis of Neutrino Data

In this talk I review the present status of neutrino masses and mixing and some of their implications for particle physics phenomenology. I first discuss the minimum extension of the Standard Model of particle physics required to accommodate neutrino masses and introduce the new parameters present in the model and in particular the possibility of leptonic mixing. I then describe the phenomenology of neutrino masses and mixing leading to flavour oscillations and present the existing evidence from solar, reactor, atmospheric and long-baseline neutrinos as well as the results from laboratory searches at short distances. I derive the allowed ranges for the mass and mixing parameters when the bulk of data is consistently analyzed in the framework of mixing between the three active neutrinos and obtain as a result the most up-to-date determination of the leptonic mixing matrix. Then I briefly summarize the status of some proposed phenomenological explanations to accommodate the LSND results: the role of sterile neutrinos and the violation of CPT. Finally I comment how within the present experimental precision it is possible to use the observation of oscillation patterns to impose severe constraints on the possible violation of fundamental symmetries in particle physics such as Lorentz invariance or the weak equivalence principle.

hep-ph↗
arXiv2004

Solar Neutrinos Before and After Neutrino 2004

We compare, using a three neutrino analysis, the allowed neutrino oscillation parameters and solar neutrino fluxes determined by the experimental data available Before and After Neutrino 2004. New data available after Neutrino2004 include refined KamLAND and gallium measurements. We use six different approaches to analyzing the KamLAND data. We present detailed results using all the available neutrino and anti-neutrino data for Delta m^2_{12}, tan^2 theta_{12}, sin^2 theta_{13}, and sin^2 eta (sterile fraction). Using the same complete data sets, we also present Before and After determinations of all the solar neutrino fluxes, which are treated as free parameters, an upper limit to the luminosity fraction associated with CNO neutrinos, and the predicted rate for a 7Be solar neutrino experiment. The 1 sigma (3 sigma) allowed range of Delta m^2_{21} = (8.2 +- 0.3) (^+1.0_-0.8)times 10^{-5} eV^2 is decreased by a factor of 1.7 (5), but the allowed ranges of all other neutrino oscillation parameters and neutrino fluxes are not significantly changed. Maximal mixing is disfavored at 5.8 sigma and the bound on the mixing angle theta_{13} is slightly improved to sin^2 theta_{13}<0.048 at 3 sigma. The predicted rate in a 7Be neutrino-electron scattering experiment is (0.665 +-0.015) of the rate implied by the BP04 solar model in the absence of neutrino oscillations. The corresponding predictions for p-p and pep experiments are, respectively, 0.707 {+0.011}{-0.013} and 0.644 {+0.011}{-0.013}. We derive upper limits to CPT violation in the weak sector by comparing reactor anti-neutrino oscillation parameters with neutrino oscillation parameters. We also show that the recent data disfavor at 91 % CL a proposed non-standard interaction description of solar neutrino oscillations.

hep-ph↗
arXiv2004

Measuring the deviation of the 2-3 lepton mixing from maximal with atmospheric neutrinos

The measurement of the deviation of the 2-3 leptonic mixing from maximal, D_23 = 1/2 - sin^2(theta_23), is one of the key issues for understanding the origin of the neutrino masses and mixing. In the three-neutrino context we study the dependence of various observables in the atmospheric neutrinos on D_23. We perform a global three-neutrino analysis of the atmospheric and reactor neutrino data taking into account the effects of both the oscillations driven by the "solar" parameters (Delta_m_21^2 and theta_12) and the 1-3 mixing. The departure from the one-dominant mass scale approximation results into the shift of the 2-3 mixing from maximal by Delta_sin^2(theta_23) ~ 0.04, so that D_23 ~ 0.04 +- 0.07 (1 sigma). Though value of the shift is not statistically significant, the tendency is robust. The shift is induced by the excess of the e-like events in the sub-GeV sample. We show that future large scale water Cherenkov detectors can determine D_23 with accuracy of a few percent, comparable with the sensitivity of future long baseline experiments. Moreover, the atmospheric neutrinos will provide unique information on the sign of the deviation (octant of theta_23).

hep-ph↗
arXiv2004

Probing Trilinear Gauge Boson Interactions via Single Electroweak Gauge Boson Production at the LHC

We analyze the potential of the CERN Large Hadron Collider (LHC) to study anomalous trilinear vector-boson interactions W^+ W^- γand W^+ W^- Z through the single production of electroweak gauge bosons via the weak boson fusion processes q q -> q q W (-> \ell^\pm ν) and q q -> q q Z(-> \ell^+ \ell^-) with \ell = e or μ. After a careful study of the standard model backgrounds, we show that the single production of electroweak bosons at the LHC can provide stringent tests on deviations of these vertices from the standard model prediction. In particular, we show that single gauge boson production exhibits a sensitivity to the couplings Δκ_{Z,γ} similar to that attainable from the analysis of electroweak boson pair production.

hep-ph↗
arXiv2004

Atmospheric Neutrino Oscillations and New Physics

We study the robustness of the determination of the neutrino masses and mixing from the analysis of atmospheric and K2K data under the presence of different forms of phenomenologically allowed new physics in the nu_mu--nu_tau sector. We focus on vector and tensor-like new physics interactions which allow us to treat, in a model independent way, effects due to the violation of the equivalence principle, violations of the Lorentz invariance both CPT conserving and CPT violating, non-universal couplings to a torsion field and non-standard neutrino interactions with matter. We perform a global analysis of the full atmospheric data from SKI together with long baseline K2K data in the presence of nu_mu -> nu_tau transitions driven by neutrino masses and mixing together with sub-dominant effects due to these forms of new physics. We show that within the present degree of experimental precision, the extracted values of masses and mixing are robust under those effects and we derive the upper bounds on the possible strength of these new interactions in the nu_mu--nu_tau sector.

hep-ph↗
arXiv2003

Bosonic Quartic Couplings at LHC

We analyze the potential of the CERN Large Hadron Collider (LHC) to study anomalous quartic vector-boson interactions Z Z gamma gamma, Z Z Z gamma, W+ W- gamma gamma, and W+ W- Z gamma through the weak boson fusion processes q q -> q q gamma gamma and q q -> q q gamma Z(-> l+ l-) with l = electron or muon. After a careful study of the backgrounds and how to extract them from the data, we show that the process p p -> j j gamma l+ l- is potentially the most sensitive to deviations from the Standard Model, improving the sensitivity to anomalous couplings by up to a factor 10^4 (10^2) with respect to the present direct (indirect) limits.

hep-ph↗
arXiv2003

Status of the CPT Violating Interpretations of the LSND Signal

We study the status of the CPT violating neutrino mass spectrum which has been proposed to simultaneously accommodate the oscillation data from LSND, KamLAND, atmospheric and solar neutrino experiments, as well as the non-observation of anti-neutrino disappearance in short-baseline reactor experiments. We perform a three-generation analysis of the global data with the aim of elucidating the viability of this solution. We find no compatibility between the results of the oscillation analysis of LSND and all-but-LSND data sets below 3$σ$ CL. Furthermore, the global data without LSND show no evidence for CPT violation: the best fit point of the all-but-LSND analysis occurs very close to a CPT conserving scenario.

hep-ph↗
arXiv2003

Three-Neutrino Mixing after the First Results from K2K and KamLAND

We analyze the impact of the data on long baseline ν_μdisappearance from the K2K experiment and reactor \barν_e disappearance from the KamLAND experiment on the determination of the leptonic three-generation mixing parameters. Performing an up-to-date global analysis of solar, atmospheric, reactor and long baseline neutrino data in the context of three-neutrino oscillations, we determine the presently allowed ranges of masses and mixing and we consistently derive the allowed magnitude of the elements of the leptonic mixing matrix. We also quantify the maximum allowed contribution of Δm^2_{21} oscillations to CP-odd and CP-even observables at future long baseline experiments.

hep-ph↗
arXiv2003

Solar Neutrinos Before and After KamLAND

We use the recently reported KamLAND measurements on oscillations of reactor anti-neutrinos, together with the data of previously reported solar neutrino experiments, to show that: (1) the total 8B neutrino flux emitted by the Sun is 1.00(1.0 \pm 0.06) of the standard solar model (BP00) predicted flux, (2) the KamLAND measurements reduce the area of the globally allowed oscillation regions that must be explored in model fitting by six orders of magnitude in the Delta m^2-tan^2 theta plane, (3) LMA is now the unique oscillation solution to a CL of 4.7sigma, (4) maximal mixing is disfavored at 3.1 sigma, (5) active-sterile admixtures are constrained to sin^2 eta<0.13 at 1 sigma, (6) the observed ^8B flux that is in the form of sterile neutrinos is 0.00^{+0.09}_{-0.00} (1 sigma), of the standard solar model (BP00) predicted flux, and (7) non-standard solar models that were invented to completely avoid solar neutrino oscillations are excluded by KamLAND plus solar at 7.9 sigma . We also refine quantitative predictions for future 7Be and p-p solar neutrino experiments.

hep-ph↗
arXiv2003

Neutrino Masses and Mixing: Evidence and Implications

Measurements of various features of the fluxes of atmospheric and solar neutrinos have provided evidence for neutrino oscillations and therefore for neutrino masses and mixing. We review the phenomenology of neutrino oscillations in vacuum and in matter. We present the existing evidence from solar and atmospheric neutrinos as well as the results from laboratory searches, including the final status of the LSND experiment. We describe the theoretical inputs that are used to interpret the experimental results in terms of neutrino oscillations. We derive the allowed ranges for the mass and mixing parameters in three frameworks: First, each set of observations is analyzed separately in a two-neutrino framework; Second, the data from solar and atmospheric neutrinos are analyzed in a three active neutrino framework; Third, the LSND results are added, and the status of accommodating all three signals in the framework of three active and one sterile light neutrinos is presented. We review the theoretical implications of these results: the existence of new physics, the estimate of the scale of this new physics and the lessons for grand unified theories, for supersymmetric models with R-parity violation, for models of extra dimensions and singlet fermions in the bulk, and for flavor models.

hep-ph↗