arXiv subjects

Timothy J. Burns

Publications and source records attributed to Timothy J. Burns.

14 recordsLinked to original sources

arXiv2026

Predictions for the scalar partner of the LHC tetraquark $X(6600)$

We consider how the recent CMS measurements of the masses and quantum numbers of $X(6600)$, $X(6900)$ and $X(7100)$ can help to reveal the internal structure of these apparent $cc\bar{c}\bar{c}$ tetraquark states. The measured $J^{PC} = 2^{++}$ quantum numbers of $X(6600)$ are consistent with our previous prediction, and imply the existence of lighter $0^{++}$ partner $X(6400)$ which also decays to $J/ψJ/ψ$. There may already be indications for this scalar partner in the recent CMS data fits, which include a Breit-Wigner peak with mass around 6400~MeV. We give predictions for the masses and decay properties of the scalar and other partner states, which are key experimental tests to discriminate between quark and diquark models. We urge closer experimental scrutiny in this mass region, to establish an S-wave multiplet of $cc \bar c \bar c$ states (the first of its kind), leading to a breakthrough in exotic hadron research and our understanding of exclusively heavy quark exotics.

hep-ph↗

arXiv2026

Heavy quark thermodynamics with anisotropic lattices

We present recent results from the FASTSUM collaboration, using anisotropic lattice QCD to study spectral properties of heavy quarkonia and open heavy flavour systems at high temperature. For heavy quarkonium, our results using a number of different methods suggest a small but significant and robust negative mass shift as well as an increasing thermal width. We present the first lattice results for masses and spectral functions of B mesons at high temperature, and preliminary results for a high-precision calculation of the static quark potential.

hep-lat↗

arXiv2025

Finite temperature hadronic spectral properties

The FASTSUM collaboration has a long-standing project examining hadronic properties using anisotropic lattice QCD. We determine the spectral properties of bottomonia at finite temperature using lattice NRQCD and describe how our newer simulations improve our control over systematic errors. Motivated by these efforts, the temperature dependence of charm hadron masses is determined where it is found that temperature effects can extend into the confining phase and that some species remain stable deep past the pseudo-critical temperature.

hep-lat↗

arXiv2025

Spectral properties of bottomonium at high temperature: a systematic investigation

We investigate spectral features of bottomonium at high temperature, in particular the thermal mass shift and width of ground state S-wave and P-wave state. We employ and compare a range of methods for determining these features from lattice NRQCD correlators, including direct correlator analyses (multi-exponential fits and moments of spectral functions), linear methods (Backus-Gilbert, Tikhonov and HLT methods), and Bayesian methods for spectral function reconstruction (MEM and BR). We comment on the reliability and limitations of the various methods.

hep-lat↗

arXiv2025

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

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.

hep-lat↗

arXiv2025

Anisotropic excited bottomonia from a basis of smeared operators

Bottomonia play a crucial role in our understanding of the quark gluon plasma. We present lattice non-relativistic QCD calculations of bottomonia at temperatures in the range $T \in [47, 380]$ MeV using the Fastsum Generation 2L anisotropic $N_f = 2 + 1$ ensembles. The use of a basis of smeared operators allows the extraction of excited-state masses at zero temperature and an investigation of their thermal properties at non-zero temperature. We find that the ground state signal is substantially improved by this variational approach at finite temperature. We also apply the time-derivative moments approach to the projected or optimal correlation functions at finite temperature.

hep-lat↗

arXiv2024

Thermal lattice QCD results from the FASTSUM collaboration

The FASTSUM Collaboration has developed a comprehensive research programme in thermal lattice QCD using 2+1 flavour ensembles. We review our recent hadron spectrum analyses of open charm mesons and charm baryons at non-zero temperature. We also detail our determination of the interquark potential in the bottomonium system using NRQCD quarks. All of our work uses anisotropic lattices where the temporal lattice spacing is considerably finer than the spatial one allowing better resolution of temporal correlation functions.

hep-lat↗

arXiv2024

Non-zero temperature study of spin 1/2 charmed baryons using lattice gauge theory

We study the behaviour of spin $1/2$ charmed baryons as the temperature increases. We make use of anisotropic lattice QCD simulations with $N_f = 2 + 1$ dynamical flavours. After determining the positive and negative parity ground state masses at the lowest temperature, we investigate the effect of rising temperature using ratios of thermal lattice correlators with both so-called reconstructed correlators and with simple model correlators. This avoids difficulties associated with non-zero temperature fitting or spectral reconstruction. We find that temperature effects are prominent throughout the hadronic phase for all negative parity channels considered and for some positive parity channels. Subsequently and where possible, we determine the masses of the ground states as a function of temperature. Finally we consider the effect of chiral symmetry restoration and extract an estimate of the pseudocritical temperature from singly charmed baryonic correlators.

hep-lat↗

arXiv2023

Reconstructed (charm) baryon methods at finite temperature on anisotropic lattices

Reconstructed-correlator methods have been used to investigate thermal effects in mesonic correlation functions in a fit-independent manner. This technique has recently been extended to the baryonic sector. In this work different ways of implementing this approach for baryon correlators are examined. Using both real and synthetic data it is found that for heavy baryons, such as the $Ξ_{cc}(ccu)$ baryon, different choices are equivalent and that for the lighter nucleon the effect of different implementations is minimal. Further comparison to the so-called "double ratio" using the FASTSUM Generation 2L thermal ensembles shows that reconstructed-correlator ratios and double ratios contain nearly identical quantitative information.

hep-lat↗

arXiv2023

Tetraquark mass relations in quark and diquark models

We present new linear relations among the masses of S-wave tetraquarks with either one flavour ($QQ \bar Q \bar Q$) or two ($QQ\bar q \bar q$). Because the relations are sensitive to the hidden-colour, spin, and spatial degrees of freedom, comparison to experimental data can help to reveal the internal structure of tetraquarks, and discriminate among different theoretical models. Depending on the model, the relations are either exact, or valid in perturbation theory, and a thorough comparison with existing literature confirms their validity at the MeV level. Additionally, we explore the connections among tetraquark models, and show how those with effective (quark or diquark) masses are related to dynamical potential models. We also show how the spectrum of diquark models is effectively a limiting case of (more general) quark models, and in particular, that the diquark concept is most relevant in the particular combination $QQ\bar q \bar q$, where $Q$ is much heavier than $\bar q$.

hep-ph↗

arXiv2023

Structure of $cc \bar c \bar c$ tetraquarks and interpretation of LHC states

Motivated by recent experimental evidence for apparent $cc\bar c \bar c$ states at LHCb, CMS and ATLAS, we consider how the mass spectrum and decays of such states can be used to discriminate among their possible theoretical interpretations, with a particular focus on identifying whether quarks or diquarks are the most relevant degrees of freedom. Our preferred scenario is that $X(6600)$ and its apparent partner state $X(6400)$ are the tensor $(2^{++})$ and scalar $(0^{++})$ states of an S-wave multiplet of $cc\bar c \bar c$ states. Using tetraquark mass relations which are independent of (or only weakly dependent on) model parameters, we give predictions for the masses of additional partner states with axial and scalar quantum numbers. Additionally, we give predictions for relations among decay branching fractions to $J/ψJ/ψ$, $J/ψη_c$, $η_cη_c$ and $D^{(*)} \bar{D}^{(*)}$ channels. The scenario we consider is consistent with existing experimental data on $J/ψJ/ψ$, and our predictions for partner states and their decays can be confronted with future experimental data, to discriminate between quark and diquark models.

hep-ph↗

arXiv2022

Charm baryons at finite temperature on anisotropic lattices

Singly, doubly and triply charmed baryons are investigated at multiple temperatures using the anisotropic FASTSUM 'Generation 2L' ensembles. We discuss the temperature dependence of these baryons' spectra in both parity channels with a focus on the confining phase. To further qualify the behaviour of these states around the pseudocritical temperature, we investigate the effect of chiral symmetry restoration for light quarks. We find that an estimate of the pseudocritical temperature can still be found from positive and negative-parity charmed baryon correlators, even when parity doubling itself is not very evident (as expected).

hep-lat↗

arXiv2022

Open charm mesons at nonzero temperature: results in the hadronic phase from lattice QCD

We study what happens to D and D_s mesons as the temperature increases, using lattice QCD simulations with N_f=2+1 dynamical flavours on anistropic lattices. We have access to five temperatures in the hadronic phase. Using the determined groundstate mass at the lowest temperature, we investigate the effect of rising temperature by analysing ratios of mesonic correlators, without the need for further fitting or spectral reconstruction. In the pseudoscalar and vector channels, we demonstrate that temperature effects are at the percent level and can be captured by a reduction of the groundstate mass as the thermal crossover is approached. In the axial-vector and scalar channels on the other hand, temperature effects are prominent throughout the hadronic phase.

hep-lat↗

arXiv2018

Closed-Form Projection Method for Regularizing a Function Defined by a Discrete Set of Noisy Data and for Estimating its Derivative and Fractional Derivative

We present a closed-form finite-dimensional projection method for regularizing a function defined by a discrete set of measurement data, which have been contaminated by random, zero mean errors, and for estimating the derivative and fractional derivative of this function by linear combinations of a few low degree trigonometric or Jacobi polynomials. Our method takes advantage of the fact that there are known infinite-dimensional singular value decompositions of the operators of integration and fractional integration.

math.NA↗