arXiv subjects

Sinead M. Ryan

Publications and source records attributed to Sinead M. Ryan.

At least 19 recordsLinked to original sources

arXiv2021

Spectral reconstruction in NRQCD via the Backus-Gilbert method

We present progress results from the FASTSUM collaboration's programme to determine the spectrum of the bottomonium system as a function of temperature using a variety of approaches. In this contribution, the Backus Gilbert method is used to reconstruct spectral functions from NRQCD meson correlator data from FASTSUM's anisotropic ensembles at nonzero temperature. We focus in particular on the resolving power of the method, providing a demonstration of how the underlying resolution functions can be probed by exploiting the Laplacian nature of the NRQCD kernel. We conclude with estimates of the bottomonium ground state mass and widths at nonzero temperature.

hep-lat↗

arXiv2021

A comparison of spectral reconstruction methods applied to non-zero temperature NRQCD meson correlation functions

We present results from the fastsum collaboration's programme to determine the spectrum of the bottomonium system as a function of temperature. Three different methods of extracting spectral information are discussed: a Maximum Likelihood approach using a Gaussian spectral function for the ground state, the Backus Gilbert method, and the Kernel Ridge Regression machine learning procedure. We employ the fastsum anisotropic lattices with 2+1 dynamical quark flavours, with temperatures ranging from 47 to 375 MeV.

hep-lat↗

arXiv2021

Reconstruction of bottomonium spectral functions in thermal QCD using Kernel Ridge Regression

We discuss results for bottomonium at nonzero temperature obtained using NRQCD on Fastsum Generation 2L ensembles, as part of the Fastsum collaboration's programme to determine the spectrum of the bottomonium system as a function of temperature using a variety of approaches. Here we give an update on results for spectral functions obtained using Kernel Ridge Regression. We pay in particular attention to the generation of training data and introduce the notion of using lattice QCD ensembles to learn how to improve the generation of training data. A practical implementation is given.

hep-lat↗

arXiv2019

News from bottomonium spectral functions in thermal QCD

New results on bottomonium at nonzero temperature are presented, using the FASTSUM Generation 2L ensembles. Preliminary results for spectral function reconstruction using Kernel Ridge Regression, a machine learning technique, are shown as well and compared to results from the Maximum Entropy Method.

hep-lat↗

arXiv2019

Spectral quantities in thermal QCD: a progress report from the FASTSUM collaboration

In order to study spectral quantities in thermal QCD, the FASTSUM collaboration employs anisotropic lattice simulations with N_f=2+1 flavours of Wilson fermions. Here we discuss our Generation 2 and Generation 2L ensembles, which differ in the pion mass. The focus is on observables related to the light quarks and chiral symmetry restoration.

hep-lat↗

arXiv2014

2+1 flavour thermal studies on an anisotropic lattice

The FASTSUM collaboration has initiated a detailed study of thermal QCD using 2+1 flavours of improved Wilson quarks on anisotropic lattices. Spatial volumes of (3fm)^3 and (4fm)^3 are used at fixed cut-off with temperatures ranging from 40 to 350 MeV (corresponding to temporal lattice extents of 128 to 16 lattice units). Results presented here include the deconfinement temperature and a study of the restoration of chiral symmetry, together with a brief summary of our collaboration's other results from these ensembles.

hep-lat↗

arXiv2013

Excited spectroscopy of mesons containing charm quarks from lattice QCD

We present highly excited spectra of charmonium, charm-light and charm-strange mesons using the dynamical anisotropic lattices of the Hadron Spectrum Collaboration. The use of novel techniques has allowed us to extract these spectra with a high degree of statistical precision, while also enabling us to observe states as high as spin-4, states with exotic quantum numbers and candidate gluonic excitations. We discuss the phenomenology of these spectra, and also present preliminary results of Dπ scattering considering only the lowest partial wave in the isospin-3/2 channel.

hep-lat↗

arXiv2013

P wave bottomonium spectral functions in the QGP from lattice NRQCD

We present an overview of bottomonium spectral functions in the quark-gluon plasma, obtained by the FASTSUM collaboration, using lattice QCD simulations with two light quark flavours on anisotropic lattices. The bottom quark is treated nonrelativistically. While we find that the S wave ground states survive up to the highest temperature we consider, we have strong indications that P wave states melt immediately above Tc.

hep-lat↗

arXiv2013

Excited spectroscopy of charmed mesons from lattice QCD

We present spectra of highly excited D and Ds mesons up to around 3.8 GeV determined using dynamical lattice QCD. We employ novel computational techniques and the variational method with a large basis of carefully constructed operators in order to extract and reliably identify the continuum spin of an extensive set of excited states. These include states with high spin and states identified as having an explicit gluonic contribution. Calculations were performed on two volumes, both with a pion mass of approximately 400 MeV, achieving a high statistical precision for both ground and excited states. We discuss our results in light of experimental observations, comment on the phenomenological implications and identify the lightest `supermultiplet' of hybrid mesons in each sector.

hep-ph↗

arXiv2013

S wave bottomonium states moving in a quark-gluon plasma from lattice NRQCD

We extend our study of bottomonium spectral functions in the quark-gluon plasma to nonzero momentum. We use lattice QCD simulations with two flavours of light quark on highly anisotropic lattices and treat the bottom quark with nonrelativistic QCD (NRQCD). We focus on S wave (Upsilon and eta_b) channels and consider nonrelativistic velocities, v/c < 0.2. A comparison with predictions from effective field theory is made.

hep-lat↗

arXiv2013

Excited $D$ and $D_{s}$ meson spectroscopy from lattice QCD

We present highly excited spectra of charm-light and charm-strange mesons from dynamical lattice QCD. Our calculations are performed on anisotropic $N_{f} = 2+1$ dynamical ensembles generated by the Hadron Spectrum Collaboration. The use of novel techniques and a large basis of interpolating operators have allowed us to extract these spectra to a high degree of statistical precision, extract states of high spin and observe candidate hybrid mesons. We interpret and discuss our results in light of the current experimental situation.

hep-lat↗

arXiv2012

Two topics from lattice NRQCD at non-zero temperature: heavy quark mass dependence and S-wave bottomonium states moving in a thermal bath

Using Non-Relativistic QCD (NRQCD), we study heavy quark mass dependence of S-wave and P-wave bottomonium correlators for 0.42Tc <= T <= 2.09Tc and study spectral functions of S-wave bottomonium states moving in a thermal bath at these temperatures using Maximum Entropy Method with NRQCD kernel. For the studied momentum range, the energy of moving states shows quadratic momentum-dependence and the width of moving states does not show significant changes as the momentum of bottomonium is increased. Also, we find that in correlator ratios, the temperature effect is larger than the effect caused by 20% change in the bottom quark mass.

hep-lat↗

arXiv2011

Charmonium spectroscopy from an anisotropic lattice study

We present a progress report on our study of the charmonium spectrum in full QCD on anisotropic lattices generated by the Hadron Spectrum Collaboration. We adopt a large basis of interpolating operators to extract the excited charmonium states using the variational method. A detailed spectrum of excited charmonium mesons in many $J^{PC}$ channels is obtained. Hybrid states with exotic and non-exotic quantum numbers are determined and preliminary results from a study of disconnected contributions to the $η_c$ are presented.

hep-lat↗

arXiv2011

What happens to the Upsilon and eta_b in the quark-gluon plasma? Bottomonium spectral functions from lattice QCD

We study bottomonium spectral functions in the quark-gluon plasma in the Upsilon and eta_b channels, using lattice QCD simulations with two flavours of light quark on highly anisotropic lattices. The bottom quark is treated with nonrelativistic QCD (NRQCD). In the temperature range we consider, 0.42 < T/T_c < 2.09, we find that the ground states survive, whereas the excited states are suppressed as the temperature is increased. The position and width of the ground states are compared to analytical effective field theory (EFT) predictions. Systematic uncertainties of the maximum entropy method (MEM), used to construct the spectral functions, are discussed in some detail.

hep-lat↗

arXiv2011

Bottomonium at Non-zero Temperature from Lattice Non-relativistic QCD

The temperature dependence of bottomonium states at temperatures above and below $T_c$ is presented, using non-relativistic dynamics for the bottom quark and full relativistic lattice QCD simulations for two light flavors on a highly anisotropic lattice. We find that the S-waves ($Υ$ and $η_b$) show little temperature dependence in this range while the P wave propagators show a crossover from the exponential decay characterizing the hadronic phase to a power-law behavior consistent with nearly-free dynamics at approximately twice the critical temperature.

hep-ph↗

arXiv2009

Excited-Nucleon Spectroscopy with 2+1 Fermion Flavors

We present progress made by the Hadron Spectrum Collaboration (HSC) in determining the tower of excited nucleon states using 2+1-flavor anisotropic clover lattices. The HSC has been investigating interpolating operators projected into irreducible representations of the cubic group in order to better calculate two-point correlators for nucleon spectroscopy; results are published for quenched and 2-flavor anisotropic Wilson lattices. In this work, we present the latest results using a new technique, distillation, which allows us to reach higher statistics than before. Future directions will be outlined at the end.

hep-lat↗

arXiv2007

Radial and orbital excitations of static-light mesons

We present results for the spectrum of static-light mesons from Nf=2 lattice QCD. These results were obtained using all-to-all light quark propagators on an anisotropic lattice, yielding an improved signal resolution when compared to more conventional lattice techniques. With a light quark mass close to the strange quark, we have measured the splittings between the ground-state S-wave static-light meson and higher excitations. We attempt to identify the quantum numbers of the excited states in the context of the reduced spatial symmetries of the lattice.

hep-lat↗

arXiv2006

Dynamical QCD simulations on anisotropic lattices

The simulation of QCD on dynamical (Nf=2) anisotropic lattices is described. A method for nonperturbative renormalisation of the parameters in the anisotropic gauge and quark actions is presented. The precision with which this tuning can be carried out is determined in dynamical simulations on 8^3x48 and 8^3x80 lattices.

hep-lat↗