The NRQCD $\Upsilon$ spectrum at non-zero temperature using Backus-Gilbert regularisations

TL;DR

This paper investigates the temperature-dependent properties of bottomonium mesons in quark-gluon plasma using lattice NRQCD and regularisation techniques to extract spectral functions from Euclidean correlators.

Contribution

It introduces a novel application of Backus-Gilbert regularisation to lattice NRQCD data for bottomonium spectral functions at finite temperature.

Findings

Successful extraction of bottomonium spectral functions at various temperatures.

Comparison of Backus-Gilbert and HLT regularisation methods.

Insights into meson mass shifts and decay widths with temperature.

Abstract

Understanding how the properties of heavy mesons change as temperature increases is crucial for gaining valuable insights into the quark-gluon plasma. Information about meson masses and decay widths is encoded in the meson spectral function, which, in principle, can be extracted from Euclidean correlation functions via generalised Laplace transformations. However, this inverse problem is ill-posed for lattice correlation functions and requires regularisation. In this work, we present the latest results for bottomonium spectral functions obtained within the lattice NRQCD framework using the Backus-Gilbert regularisation, along with two other variants, one of which is commonly referred to as the HLT method. Our analysis employs Generation 2L anisotropic lattice configurations produced by the \textsc{Fastsum} collaboration.