118481454
Electromagnetic matrix elements for negative parity nucleons
Here we present preliminary results for the evaluation of the electromagnetic form factors for the lowest-lying negative-parity, spin-$\frac{1}{2}$ nucleons, namely the $S_{11}(1535)$ and $S_{11}(1650)$, through the use of the variational method. We find that the characteristics of the electric form factor, $G_{E}$, are similar between these states, however significant differences are observed between the quark-sector contributions to the magnetic form factor, $G_{M}$. Within simple constituent quark models, these states are understood to be admixtures of $s=\frac{1}{2}$ and $s=\frac{3}{2}$ states coupled to orbital angular momentum $\ell = 1$. Our results reveal a qualitative difference in the manner in which the singly-represented quark sector contributes to these baryon magnetic form factors.
123843313
Correlation Matrix Techniques at Non-Zero Momentum
In recent years, the use of variational analysis techniques in lattice QCD has been demonstrated to be remarkably succes sful in the investigation of the rest-mass spectrum of many hadrons. Ho wever, due to parity-mixing, more care must be taken for inve stigations of boosted states to ensure that the projected correlation f unctions provided by the variational analysis correspond t the same states at zero momentum. In this Letter we demonstrate a novel metho d for ensuring the successful and consistent isolation of bo sted states by expanding the operator basis used to construct the orrelation matrix to include operators of the opposite par ity.
58907444
Light Meson Transition Form Factors on the Lattice
Here we present exploratory calculations of the light meson radiative transition moment r → gp from lattice QCD. We observe interesting chiral curvature in the form factor and a definite environment sensitivity in the quark sector contributions. Results are compared with the simple quark model and experiment.
54043832
Electromagnetic Form Factors of the Lambda(1405) in (2+1)-flavour Lattice QCD
The Λ(1405) is unusual in that it lies surprisingly low in mass. At 1405.1MeV, it lies lower than the lowest-lying odd-parity state of the nucleon, even though it contains a valence strange quark. We build on our recent success in isolating this otherwise elusive state in lattice QCD using correlation matrix techniques coupled with source and sink smearing, and present first results from our world-first calculation of the electromagnetic form factors of this unusual state. We use the PACS-CS (2+1)-flavour full-QCD ensembles, available through the ILDG.
118559096
Lattice baryon spectroscopy with multiparticle interpolators
In 2 + 1 flavour lattice QCD the spectrum of the nucleon is presented for both parities using local meson-baryon type interpolating fields in addition to the standard three-quark nucleon interpolators. The role of local five-quark operators in extracting the nucleon excited state spectrum via correlation matrix techniques is explored on dynamical gauge fields with $m_\pi$ = 293 MeV, leading to the observation of a state consistent with the S-wave $N\pi$ scattering threshold in the negative-parity sector. Furthermore, the robustness of the variational technique is examined by studying the spectrum on a variety of operator bases. Fitting a single-state ansatz to the eigenstate-projected correlators provides robust energies for the low-lying spectrum that are essentially invariant despite being extracted from qualitatively different bases.
119108531
Finite-volume corrections to charge radii
Abstract The finite-volume nature of lattice QCD entails a variety of effects that must be handled in the process of performing chiral extrapolations. Since the pion cloud that surrounds hadrons becomes distorted in a finite volume, hadronic observables must be corrected before one can compare with the experimental values. The electric charge radius of the nucleon is of particular interest when considering the implementation of finite-volume corrections. It is common practice in the literature to transform electric form factors from the lattice into charge radii prior to analysis. However, there is a fundamental difficulty with using these charge radii in a finite-volume extrapolation. The subtleties are a consequence of the absence of a continuous derivative on the lattice. A procedure is outlined for handling such finite-volume corrections, which must be applied directly to the electric form factors themselves rather than to the charge radii.
118508940
Implementation of the frequency-modulated sideband search method for gravitational waves from low mass x-ray binaries
We describe the practical implementation of the sideband search, a search for periodic gravitational waves from neutron stars in binary systems. The orbital motion of the source in its binary system causes frequency modulation in the combination of matched filters known as the $\mathcal{F}$-statistic. The sideband search is based on the incoherent summation of these frequency-modulated $\mathcal{F}$-statistic sidebands. It provides a new detection statistic for sources in binary systems, called the $\mathcal{C}$-statistic. The search is well suited to low-mass x-ray binaries, the brightest of which, called Sco X-1, is an ideal target candidate. For sources like Sco X-1, with well-constrained orbital parameters, a slight variation on the search is possible. The extra orbital information can be used to approximately demodulate the data from the binary orbital motion in the coherent stage, before incoherently summing the now reduced number of sidebands. We investigate this approach and show that it improves the sensitivity of the standard Sco X-1 directed sideband search. Prior information on the neutron star inclination and gravitational wave polarization can also be used to improve upper limit sensitivity. We estimate the sensitivity of a Sco X-1 directed sideband search on ten days of LIGO data and show that it can beat previous upper limits in current LIGO data, with a possibility of constraining theoretical upper limits using future advanced instruments.