### Conveners

#### Hadron Spectroscopy and Interactions: Hadron Spectroscopy and Interactions I

- William Detmold (MIT)

#### Hadron Spectroscopy and Interactions: Hadron Spectroscopy and Interactions II

- Stephen Sharpe (University of Washington)

#### Hadron Spectroscopy and Interactions: Hadron Spectroscopy and Interactions III

- Sara Collins (University of Regensburg)

#### Hadron Spectroscopy and Interactions: Hadron Spectroscopy and Interactions IV

- Padmanath Madanagopalan (Helmholtz Institut Mainz)

#### Hadron Spectroscopy and Interactions: Hadron Spectroscopy and Interactions V

- Daniel Mohler (TU Darmstadt)

#### Hadron Spectroscopy and Interactions: Hadron Spectroscopy and Interactions VI

- Amy Nicholson (UNC Chapel Hill)

#### Hadron Spectroscopy and Interactions: Hadron Spectroscopy and Interactions VII

- Maxim Mai (uni-bonn)

#### Hadron Spectroscopy and Interactions: Hadron Spectroscopy and Interactions VIII

- Max Hansen (University of Edinburgh)

We present results for the energy levels for two pions and a kaon, and two kaons and a pion, all at maximal isospin, on CLS ensembles D200 and N203, with pion/kaon masses of

200/480 MeV and 340/440 MeV, respectively. We use multiple frames, and have determined many energy levels on each ensemble. We fit these levels, together with those for $2\pi^+$, $2K^+$ and $\pi^+ K^+$, to the predictions...

The quest of unraveling the nature of excited hadrons necessarily involves determination of universal (reaction independent) parameters of these states. Such determinations require input, either from experiment or theory.

Lattice gauge theory is the only tool available to us to tackle the non-perturbative dynamics of QCD encoded in the determined finite-volume interaction spectra. Many...

We study a three-particle resonance in Euclidean Lattice $\phi^4$ theory with two fields, having different masses and an interaction that makes the heavy field decay into three light. We observe the avoided-level crossings characteristic of a resonance and analyse the data with two formalisms FVU and RFT with an aim to determine the mass and the width of the resonance.

Recent years have witnessed a rapid growth of interest to the three-body

problem on the lattice. In this connection, the derivation of a relativistic-

invariant three-particle quantization condition, which relates the finite-volume

lattice spectrum to the infinite-volume observables in the three-particle sec-

tor, has become a major challenge. First and foremost, providing a...

In this talk, I will present our recent results on two- and three-particle scattering in the O(3) non-linear sigma model in 1+1 dimensions. We focus on the isospin-1 and 2 channels for the two-particle case, and the isospin-2 and 3 channels for three particles. We perform numerical simulations at four values of the physical volume and three lattice spacings, using a three-cluster...

We investigate the energy levels corresponding to the Roper resonance based on a two-flavor chiral effective Lagrangian at leading one-loop order. We show that the Roper mass can be extracted from these levels for not too large lattice volumes.

Further, to include three body dynamics, such as $N \pi \pi$, we introduce a non-relativistic effective field theory for the Roper resonance within a...

Finite-volume pionless effective field theory is an efficient framework with which to perform the extrapolation of finite-volume lattice QCD calculations of multi-nucleon spectra and matrix elements to infinite volume and to nuclei with larger atomic number. In this contribution, a new implementation of this framework based on correlated Gaussian wavefunctions optimized using differentiable...

This talk presents a new method for computing correlators for systems of many identical mesons. The method allows the computation of every meson correlator up to N mesons from propagators using only a single N by N eigendecomposition. This pushes the frontier of many-meson calculations from dozens to thousands, and as a demonstration I will present the computation of the maximal-isospin pion...

The formalism for relating finite-volume energies and matrix elements to scattering and decay amplitudes has been established for three-pion states with all possible isospins in the so called RFT (relativistic field theory) method. This necessarily leads to coupled-channel systems. The three-pion I=1 channel, for example, includes all two-pion isospins as sub-channels. In this talk I describe...

The Lüscher scattering formalism, the standard approach for relating the discrete finite-volume energy spectrum to two-to-two scattering amplitudes, fails when analytically continued so far below the infinite-volume two-particle threshold that one encounters the t-channel cut. This is relevant, especially in baryon-baryon scattering applications, as finite-volume energies can be observed in...

The γ⋆γ⋆ → ππ scattering amplitude can help constrain hadronic contributions to the anomalous magnetic moment of the muon, as well as structural information of glueball and tetraquark candidates. To leading order in QED, this amplitude can be accessed from matrix elements from non-local products of electromagnetic currents evaluated in an infinitely large Minkowski spacetime. In this talk, we...

Determining the internal structure of hadrons is a necessary step to advance our understanding of the dynamics of confined partons. Extracting form factors of resonances directly from lattice QCD requires a formal connection between the finite volume Euclidean correlation functions and the infinite volume Minkowski amplitudes. In this talk we describe a novel procedure to extract transitions...

Recently, a doubly charmed tetraquark $T_{cc}$ with flavor $cc\bar u\bar d$ just $0.36(4)~$MeV below $D^0D^{*+}$ threshold was discovered by the LHCb collaboration. We present the first lattice study of $DD^*$ scattering in this channel, involving rigorous determination of pole singularities in the related scattering amplitudes that point to the existence of $T_{cc}$. Working with a heavier...

The doubly charm tetraquark with exotic quark composition $cc\bar u \bar d$ is the longest-lived exotic hadron discovered in the experiment. Our lattice simulation establishes a virtual bound state pole in DD* scattering at $m_\pi\simeq 280$ MeV, which is likely related to this state. We discuss the expected dependence of this hadron on the light and heavy quark masses, and compare it to the...

We study a doubly-bottomed tetra-quark state $(bb\bar{u}\bar{d})$ with quantum number $I(J^P)=0(1^+)$, denoted by $T_{bb}$, in lattice QCD with the NRQCD quark action for $b$ quarks.

Employing $(2+1)$-flavor gauge configurations at $a \approx 0.09$ {fm} on $32^3\times 64$ lattices, we have extracted the coupled channel HAL QCD potential between $\bar{B}\bar{B}^*$ and $\bar{B}^* \bar{B}^*$,...

We report progress on finite-volume determinations of heavylight-meson -- Goldstone boson scattering phase shifts using the Luescher method on CLS 2+1 flavor gauge field ensembles. In a first iteration we will focus on D-meson -- pion scattering in the elastic scattering region at various pion masses using ensembles with three lattice spacings. We employ ensembles on the CLS quark-mass...

We present an investigation of the spectrum of exotic charmonium-like mesons using lattice QCD. The focus is on $\bar cc \bar qq$ $J^{PC}=1^{+\pm}$ states with isospin 1. Many mesons with properties incompatible with a $\bar cc$ structure have already been discovered, e. g. the $Z_c$ mesons with isospin 1. A lattice study of a four-quark system with two different total momenta and on two...

Optimized meson operators in the distillation framework are used to study the charmonium spectrum in two ensembles with two heavy dynamical quarks at half the physical charm quark mass but different lattice spacings. The use of optimal meson distillation profiles is shown to increase the overlap with the ground state significantly, as well as grant access to excited states, for multiple...

We determine the gradient flow scale $t_0$ at the physical point with an overall uncertainty of around $0.5\%$ using the $\Xi$ baryon mass as input. We utilise 47 CLS ensembles generated with $N_f=2+1$ non-perturbatively $O(a)$ improved Wilson dynamical fermions comprising six lattice spacings in the range $a=0.04-0.1$ fm, spatial volumes with $LM_\pi>4$ and pion masses ranging from around 420...

The OpenLat initiative presents its results of lattice QCD simulations using Stabilized Wilson Fermions (SWF) using 2+1 quark flavors. Focusing on the $SU(3)$ flavor symmetric point $m_\pi=m_K=412$ MeV, four different lattice spacings ($a = 0.064,0.077,0.094,0.12$ fm) are used to perform the continuum limit to study the cutoff effects.

We present the results of basic gauge observables and...

We compute the static energy of a quark-antiquark pair in lattice QCD using a method which is not based on Wilson loops, but where the trial states are formed by eigenvector components of the covariant lattice Laplace operator. The computational effort of this method is significantly lower than the standard Wilson loop calculation, when computing the static potential not only for on-axis, but...

We present SU(3) lattice Yang-Mills data for hybrid static potentials from five ensembles with different small lattice spacings and the corresponding parametrizations for quark-antiquark separations $0.08 \text{ fm} \le r \le 1.12 \text{ fm}$. We remove lattice discretization errors at tree level of perturbation theory and at leading order in $a^2$ as well as the $a$-dependent self-energy. In...

We study four-quark systems using lattice QCD, which consist of two heavy antiquarks (either $ \bar{b}\bar{b} $ or $\bar{b}\bar{c}$) and two light quarks (either $ ud $ or $ us $) and search for bound states in these channels. In addition to commonly used local interpolating operators we also employ scattering interpolating operators, which seem to be very important for an accurate extraction...

We present the leading order mixed-action effect $\Delta_{\rm mix}\equiv m_{\pi,{\rm vs}}^2-\frac{m_{\pi,{\rm vv}}^2+m_{\pi,{\rm ss}}^2}{2}$ using HISQ,

clover or overlap valence fermion actions on the gauge ensembles with kinds of

sea fermion actions among a widely used lattice spacing range $a\in [0.04,0.19]$~fm. The results suggest that $\Delta_{\rm mix}$ decreases on the forth order

of...

We investigate the glueball spectrum for $N_f=4$ fermions corresponding to low pion masses of $m_\pi \sim 260$MeV. We do so by making use of configurations produced with maximally twisted fermions within the framework of the Extended Twisted Mass Collaboration (ETMC). We extract states that belong to irreducible representations of the octagonal group of rotations $R$ in combination with the...

It is a fundamental question: what is the origin of the glueball masses? In the pure Yang-Mills theory, there is no mass scale in the classical level, while the breaking of scale invariance is induced by quantum effects. This is regarded as the trace anomaly, which is associated with the non-vanishing trace of the energy-momentum tensor (EMT) operator. In this context, the origin of the...

Lattice simulations of QED in 2+1 dimensions are done both in the Lagrangian and Hamiltonian formalism. Though equivalent in the continuum limit, at finite lattice spacing there is no trivial correspondence among the physical parameters, and a matching is required. This can be done non-perturbatively, finding the Hamiltonian parameters that reproduce the $a_t \to 0$ limit of asymmetric lattice...

The RBC and UKQCD Collaborations continue to generate 2+1 flavor

domain wall fermion ensembles to support a variety of physics goals.

With the current set of ensembles, which includes one with physical

quark masses and an inverse lattice spacing of 2.7 GeV, we can

revisit the scale setting approach we have previously used in Phys.

Rev. D 93 (2016) 7, 074505. This global-fit approach...

We present first results from our effort to incorporate isospin-breaking effects stemming from the non-degeneracy of the light quark masses and electromagnetic interactions into the determination of the lattice scale. To this end we compute the masses of octet and decuplet baryons on isospin-symmetric ensembles generated by the CLS effort for $N_f=2+1$ flavours and include...

We present results for the static energy in ($2+1+1$)-flavor QCD over a wide range of lattice spacings and several quark masses, including the physical quark mass, with ensembles of lattice-gauge-field configurations made available by the MILC Collaboration. We obtain results for the static energy out to distances of nearly $1$ fm, allowing us to perform a simultaneous determination of the...

Variational methods can be used to provide robust upper bounds on the energy spectra of hadrons and nuclei, but the presence of small energy gaps for multi-hadron states makes it difficult to ensure that the ground- and lowest-energy excited-states have been identified. I will discuss recent calculations of two-baryon systems using large and varied sets of interpolating operators, including...

Substantial progress has been made recently in the generation of master-field ensembles.

This has to be paired with efficient techniques to compute observables on gauge field configurations with a large volume.

Here we present the results of the computation of hadronic observables, including hadron masses and meson decay constants, on large-volume and master-field ensembles with physical...

We present a fully non-perturbative determination of a relativistic heavy quark action's parameters on the CLS ensembles using neural networks, with a particular focus on the charm sector. We then further illustrate the applicability of such an approach for lattice NRQCD bottom quarks.

In this talk we present an exact distillation setup with stabilised Wilson fermions at the SU(3) flavour symmetric point utilising the flexibility of the Grid and Hadrons software libraries. This work is a stepping stone towards the non-perturbative investigation of hadronic D-decays where we need to control the multi-hadron final states. As a first step we study two-to-two s-wave scattering...

An understanding of the nearly decades-long controversy between calculations of nucleon-nucleon interactions using the Luscher spectroscopy method and the HALQCD potential method has seen significant advancement in recent years due to the efforts of several groups. In particular, the use of improved operator methods has shed light on possible issues related to excited state contamination,...

Partial quenching can be used to avoid isospin mixing in a theory incorporating a mass twist, but comes at the cost of introducing unitarity violation. This talk will examine pion-pion scattering in partially-quenched twisted-mass lattice QCD using chiral perturbation theory. The specific partially-quenched setup corresponds to that used in numerical lattice QCD calculations of the $I=0$...

Several outstanding puzzles involve electroweak interactions of low-energy nuclear systems. Observables such as long-range matrix elements can be used to study processes such as neutral meson mixing or the substructure of hadrons. Contributions from multi-hadron states to these matrix elements are central to many of these puzzles. In this talk, we present a framework for studying long-range...

We present the finite volume contributions to the long distance behavior of the vector correlator, which is dominated by the two-pion scattering states in the I = 1 channel. The finite volume spectroscopy calculations have been performed using the (stochastic) distillation framework on the physical point Nf = 2 + 1 CLS ensemble. We also compute the timelike pion form factor to reconstruct the...

We calculate the decay rates for $J/\Psi \to \gamma \eta_c$, $J/\Psi \to \eta_c e^+ e^-$ and $\eta_c \to \gamma \gamma$ in lattice QCD with the effect of u, d, s and c quarks in the sea for the first time. Our calculations are carried out on gluon field configurations generated by the MILC collaboration that include 2+1+1 flavours of Highly Improved Staggered sea quarks. Valence $c$ quarks...

We present results for an exploratory lattice calculation of the leading parity-violating pion-nucleon coupling $h^1_\pi$. Based on the PCAC relation we use a parity-conserving Lagrangian and focus on the techniques to determine the nucleon matrix elements of the effective four-quark operators. For our study we employ an ensemble of Twisted Mass fermions with 260 MeV pion mass. Barring mixing...

We give an update on the ongoing effort of the RC$^\star$ collaboration to generate fully dynamical QCD+QED configurations with C$^\star$ boundary conditions using the openQ$^\star$D code. The simulations are tuned to the U-symmetric point ($m_d=m_s$) with pions at $m_{\pi^{\pm}} \approx 400$ MeV. The splitting of the light mesons is used as one of three tuning observables and fixed to...

We determine, from Lattice QCD, the elastic $\pi \pi$ scattering amplitude in the isoscalar $I=0$ channel, and the $\sigma$ resonance. We extract its lineshape for two different quark masses corresponding with $m_\pi \sim 283$ and $330$ MeV; where it is predicted that this state transitions from bound to virtual bound. In order to provide an accurate picture we use a high statistics volume for...

We present our calculations for the I=1/2,3/2 K-pi scattering length, extracted from the interaction energy of Euclidean two-point functions. We use the domain wall fermion action with physical quark masses at a single lattice spacing. We are specifically interested in the systematic effects due to around-the-world terms on the overall determination of the scattering length. We present our...

Resonances play an important role in Standard Model phenomenology. In particular, hadronic resonances are found in flavour-physics processes, such as $B$ and $D$ decays, which can be central for New Physics searches. Lattice QCD simulations combined with the finite-volume method can nowadays be used to reliably study strongly coupled scattering processes such as $K\pi$ and thus the hadronic...