Search

The GlueX experiment at Jefferson Lab (Newport News, VA USA) is designed to explore the spectrum of mesons up to about 3 GeV. We present results on the production of light-quark resonances with linearly polarized photons. These results enhance our understanding of photoproduction mechanisms, which is valuable in subsequent searches for exotic hybrid mesons. Measurements of the J/ψ photoproduction cross section at threshold are also presented. [ABSTRACT FROM AUTHOR]

In this talk I reviewed the present status and recent progress on lightmeson scattering analyses, by means of dispersive or analytic methods. The recent application of these model independent techniques have settled the controversy about the existence and parameters of long debated light meson resonances. I will thus discuss here the state of the art and recent changes on our knowledge about the spectroscopy of light scalar mesons when observed from such scattering processes. [ABSTRACT FROM AUTHOR]

We discuss how holographic models of QCD are used to study the the hadronic light-by-light (HLbL) scattering amplitude contribution to the muon anomalous magnetic moment. After a brief description of the various models, we focus on a particular one, introduced by Hirn and Sanz, emphasizing the role it assigns to the pion, and the vector and-axial vector resonances. We review how the parameters of the model are fixed by imposing condition on the low energy and the deep Euclidean limit of two-point correlators of QCD vector and axial vector currents. We then focus on the evaluation of the three-point axial-vector-vector current correlator and the pion anomalous transition form factor to be used in the one-pion exchange HLbL diagram and study its asymptotic properties. Finally, we present preliminary results on the four vector current correlator that defines the Hadronic Light-by-Light tensor. We find that axial-vector resonances play an important rule in recovering the correct asymptotic behaviour predicted by QCD at large Euclidean momenta. [ABSTRACT FROM AUTHOR]

I provide updates for the theoretical predictions of the muon and electron anomalous magnetic moments, for the shift in the fine structure constant α(MZ)and for the weak mixing parameter sin 2 Θ w (M Z) $ \mathop {\sin }\nolimits^2 \mathop \Theta \nolimits_w (\mathop M\nolimits_Z) $. Phenomenological results for Euclidean time correlators, the key objects in the lattice QCD approach to hadronic vacuum polarization, are briefly considered. Furthermore,I present a list of isospin breaking and electromagnetic corrections for the lepton moments, which may be used to supplement lattice QCD results obtained in the isospin limit and without the e.m. corrections. [ABSTRACT FROM AUTHOR]

We study the relation between two order parameters for deconfinement, normally employed in the literature: the continuum threshold s0, in the context of QCD Sum Rules, and the trace of the Polyakov loop Φ in the framework of a nonlocal SU(2) chiral quark model. We establish a bridge between both order parameters at finite temperature T and baryonic chemical potential µ. In our analysis, we also include the the chiral quark condensate, the order parameter for the chiral symmetry restoration. We found that s0 and Φ provide us with the same information for the deconfinement transition, both for the zero and finite chemical potential cases. At zero density, the critical temperatures for both quantities coincide exactly. This part of the analysis has been reinforced by the discussion of the corresponding susceptibilities and the static quark entropy behavior. At finite µ both order parameters provide evidence for the appearance of a quarkyonic phase. [ABSTRACT FROM AUTHOR]

We present results on several new search channels and strategies for heavy vector-like quark partners or vector resonances at the LHC run-II. Run-II has sensitivity to single- and pair-produced quark partners with masses beyond 1 TeV, and for even higher masses for vector resonances. Decays of such heavy particles yield highly boosted tops, Higgses, and weak gauge bosons. At high boost, the Standard Model background of hadronic final states can be substantially suppressed when applying jet-substructure techniques. We present several case studies where the identification of hadronically decaying tops, Higgses, and/or electroweak gauge bosons allow to make new search channels competitive at run-II. [ABSTRACT FROM AUTHOR]

If an excess potentially heralding new physics is noticed in collider data, it would be useful to be able to compare the data with entire classes of models at once. This talk discusses a method that applies when the new physics corresponds to the production and decay of a single, relatively narrow, s-channel resonance. A simplifed model of the resonance allows us to convert an estimated signal cross section into model-independent bounds on the product of the branching ratios corresponding to production and decay. This quickly reveals whether a given class of models could possibly produce a signal of the observed size. We will describe how to apply our analysis framework to cases of current experimental interest, including resonances decaying to dibosons, diphotons, dileptons, or dijets. [ABSTRACT FROM AUTHOR]

I discuss some recent progress in studying the spectra of mesons using firstprinciples lattice QCD calculations. In particular, I highlight some new results on resonances, near-threshold states and related scattering phenomena - this is an area which is very interesting experimentally and theoretically and where we have made significant advances in the last few years. I conclude with an outlook on future prospects. [ABSTRACT FROM AUTHOR]

The theoretical aspects of the various hadronic contributions to the anomalous magnetic moment of the muon are reviewed, as well as perspectives of their future evolution. [ABSTRACT FROM AUTHOR]

In this talk we discuss how holographic models of QCD have been applied to the study of the light-by-light contribution to the muon anomalous magnetic moment. After a review of the holographic procedure, we discuss the approach we followed in a previous work, in which, using a certain set of holographic model as a "Theory Space", we gave our estimate for the π0 exchange diagram. Our result depended also on the value of the quark magnetic susceptibility. Thus, in the last part of the talk, we concentrate on the attempts which have been done in the literature to apply holographic methods to the evaluation of this important order parameter of QCD. [ABSTRACT FROM AUTHOR]

I describe how hadron-hadron scattering amplitudes are related to the eigenstates of QCD in a finite cubic volume. The discrete spectrum of such eigenstates can be determined from correlation functions computed using lattice QCD, and the corresponding scattering amplitudes extracted. I review results from the Hadron Spectrum Collaboration who have used these finite volume methods to study ππ elastic scattering, including the ρ resonance, as well as coupled-channel πK, ηK scattering. The very recent extension to the case where an external current acts is also presented, considering the reaction πγ*→ππ, from which the unstable ρ →π transition form factor is extracted. Ongoing calculations are advertised and the outlook for finite volume approaches is presented. [ABSTRACT FROM AUTHOR]

The dynamics of strange vector meson resonances (K* and ...) is investigated within the Parton-Hadron-String Dynamics (PHSD) transport approach. We present the time evolution of the production of K*- resonances from the QGP phase by quark fusion as well as from hadronic sources. We also give a brief overview of the modification of the K* through Kπ decay and K* N interaction in a hot and dense nuclear medium. [ABSTRACT FROM AUTHOR]

In this note we present a new parametrization of the hadronic current for the decay τ → πππvτ derived from the chiral lagrangian with explicit inclusion of resonances. We have included both scalar, vector and axial-vector resonances. For the first time, the lowest tensor resonance (f2(1270)) is included as well. Both single and double-resonance contributions to the hadronic form factors are taken into account. To satisfy the correct high energy behaviour of the hadronic form factors, constraints on numerical values of the vertex constants are obtained. [ABSTRACT FROM AUTHOR]

The hadronic current for the τ- → π-π+π-vτ decay calculated in the framework of the Resonance Chiral Theory with an additional modification to include the σ meson is described. Implementation into the Monte Carlo generator Tauola and fitting strategy to get the model parameters using the one-dimensional distributions are discussed. The results of the fit to one-dimensional mass invariant spectrum of the BaBar data are presented. This paper is based on [1]. [ABSTRACT FROM AUTHOR]

Considering the one-loop calculation of the oblique S and T parameters, we have presented a study of the viability of strongly-coupled scenarios of electroweak symmetry breaking with a light Higgs-like boson. The calculation has been done by using an effective Lagrangian, being short-distance constraints and dispersive relations the main ingredients of the estimation. Contrary to a widely spread believe, we have demonstrated that strongly coupled electroweak models with massive resonances are not in conflict with experimental constraints on these parameters and the recently observed Higgs-like resonance. So there is room for these models, but they are stringently constrained. The vector and axial-vector states should be heavy enough (with masses above the TeV scale), the mass splitting between them is highly preferred to be small and the Higgs-like scalar should have a WW coupling close to the Standard Model one. It is important to stress that these conclusions do not depend critically on the inclusion of the second Weinberg sum rule. [ABSTRACT FROM AUTHOR]

The present knowledge on the Higgs-like boson discovered at the LHC is summarized. The data accumulated so far are consistent with the Standard Model predictions and put interesting constraints on alternative scenarios of electroweak symmetry breaking. The measured couplings to gauge bosons and third-generation fermions indicate that a Higgs particle has indeed been found. More precise data are needed to clarify whether it is the unique Higgs boson of the Standard Model or the first member of a new variety of dynamical (either elementary or composite) fields. [ABSTRACT FROM AUTHOR]