arXiv subjects
Publications and source records attributed to Ian M. Nugent.
In the Quantum Electrodynamics process $e^{+}e^{-}\to l^{+}l^{-}(nγ)$, there are two well known angular asymmetries in the $cos(θ)$ and the $cos(θ^{*})$ distributions. In this paper, the QED angular asymmetry related to the $cos(θ^{*})$ distribution is investigated in terms of the Dirac propagator and the associated boundary conditions from which the Dirac propagator is constructed and the potential implications are examined.
The Flux-Tube Breaking Model in ee$\in$MC is expanded to include the residual QCD potential between the Final-State mesons, within the non-relativistic limit. These residual QCD potentials have been predicted in the context of the Flux-Tube Breaking Models to generate meson-meson molecular states for the $f_{0}(500)$, $f_{0}(980)$, $a_{0}(980)$, through the colour hyper-fine spin-spin interaction. These residual potentials are also found to have an important impact on the $S_{1}$ decay of the $a_{1}$ and $K_{1}$ axial-vector mesons due to the colour hyper-fine spin-spin interaction. It is found that in the low mass regions, the $ρ(770)$ and $K^{*}(892)$ are sensitive to the linear-confining potential and colour-Coulomb potential suggesting that with the high statistics at the B-Factories, it may be possible to probe the linear-confining potential and colour-Coulomb potential through a model dependent description of the resonance shape or by exploiting multiple production process.
The ee$\in$MC generator package is extended to include $e^{+}e^{-} \to Hadrons (nγ)$ events where the photons can be generated in either the initial-state or final-state production. In particular, the $e^{+}e^{-} \to π^{+}π^{-} (nγ)$, $e^{+}e^{-} \to Υ(4s) (mγ) \to B^{+}B^{-} (nγ)$ and $e^{+}e^{-} \to Υ(4s) (mγ) \to B^{0}\bar{B}^{-} (nγ)$ decay channels have been implemented in the generator. The B-mesons are not decayed in ee$\in$MC, but are left for other generators that specialized in B-mesons. Both the initial-state-radiation and final-state-radiation are simulated using the Yennie-Frautschi-Suura Exponentiation procedure \cite{Yennie:1961}, where several effective models are implemented to investigate the assumption of the radiative structure of the final-state vertex. The impact of these radiative models on the $e^{+}e^{-} \to Υ(4s) (mγ) \to B^{+}B^{-} (nγ)$ and $e^{+}e^{-} \to Υ(4s) (mγ) \to B^{0}\bar{B}^{-} (nγ)$ processes, excludes some models, particularly, in regards to the Coulomb potential. This has an important impact for meson and baryon systems near threshold.
The radiative emissions in the ee$\in$MC generator are extended to include the Initial/Final-State radiative diagrams, with Initial-State/Final-State interference, for the NLO and NNLO calculations and the Initial-State radiative diagrams associated with the NNNLO calculation for $e^{+}e^{-} \to μ^{+}μ^{-} (nγ)$ and $e^{+}e^{-} \to τ^{+}τ^{-} (nγ)$ Events. The NNNLO Initial-State radiative diagrams represent the largest contribution to the perturbative Feynman series in the emission of 4 hard-photons. From the convergence of the total cross-section for $e^{+}e^{-} \to μ^{+}μ^{-} (nγ)$ and $e^{+}e^{-} \to τ^{+}τ^{-} (nγ)$, we estimate an uncertainty on the theoretical error corresponding to the truncation of the perturbative Feynman series as a function of the soft-photon cut-off applied in the exponentiation using the technique described in [1]. We discuss how this estimation procedure of the theoretical error associated with the truncation of the perturbative Feynman series can be extended to most experimentally measurable physical observables and the potential pitfalls of this strategy.
We present a modified spin algorithm, including spin correlations, which has been implemented in {\tt ee$\in$MC} for the simulation of $e^{+}e^{-} \to τ^{+}τ^{-} (γ)$ events with an arbitrary initial spin configuration. This algorithm is suitable for the proposed BELLE-II polarization upgrade to SuperKEKB, both for the ideal case and for the case where there are misalignments, radiative effects and allows for changing polarization conditions. The spin $1/2$ states of the polarized beams are constructed in terms of a super-positioning of the helicity states corresponding to the polarimetric-vector describing the overall beam polarization and implemented both through a modification of the initial state in the modified Altrelli-Parsis Density Function as well as a change of basis of the helicity states.
We present a new Monte-Carlo generator, {\tt ee$\in$MC}, for the simulation of $e^{+}e^{-} \to μ^{+} μ^{-} (γ) $, $e^{+}e^{-} \to τ^{+}τ^{-} (γ) $ and $τ$ lepton decays which is suitable for $e^{+}e^{-}$ colliders from threshold up to energy of $\sim 10.58GeV$. The $e^{+}e^{-} \to μ^{+} μ^{-}(γ) $, $e^{+}e^{-} \to τ^{+}τ^{-}(γ)$ interactions are computed up to the exact LO matrix element where the running of $α_{QED}$ includes both the LO leptonic and hadronic vacuum polarization. Infra-red divergences are investigated within the Yennie-Frautschi-Suura Exponentiation formalism, where several well-known approximations and a formulation based on the exact LO contribution to the soft and virtual photons are applied. The simulation of the $τ$ lepton consists of the leptonic decay modes at Born level and theoretical models based on Flux-Tube Breaking Models and Chiral Resonance Lagrangian Models as well as experimental models for the majority of semi-leptonic decay modes. This includes hadronic models for investigating the origin of low mass scalar sector recently observed in decays of the $τ$ lepton and their association with the origin of the constituent-quark mass through Chiral-symmetry Breaking.
Using 342$fb^{-1}$ of $e^{+}e^{-}$ annihilation data collected with the BABAR detector at the SLAC PEP-II electron-positron asymmetric energy collider operating at a center-of-mass energies near 10.58GeV, we present the preliminary measurements of the invariant mass distributions of $τ^{-} \rightarrow π^{-}π^{-}π^{+}ν$, $τ^{-} \rightarrow K^{-}π^{-}π^{+}ν$, $τ^{-} \rightarrow K^{-}π^{-}K^{+}ν$ and $τ^{-} \rightarrow K^{-}K^{-}K^{+}ν$, where events with $K_{S}^{0}\rightarrow π^{-}π^{+}$ decays are excluded.
The weak interaction between the first and second generation of quarks, the Cabibbo-Kobayashi-Maskawa matrix (CKM) element |Vus|, can be probed using hadronic tau decays. In this paper, we present the recent measurements of hadronic tau decays from BELLE and BABAR and the improvements in the determination of |Vus| from tau decays.