### Conveners

#### Hadron Spectroscopy and Interactions

- Sinead Ryan (Trinity College Dublin)
- Maxwell Hansen (The University of Edinburgh (GB))

#### Hadron Spectroscopy and Interactions

- Hartmut Wittig (Johannes Gutenberg Universitaet Mainz (DE))

#### Hadron Spectroscopy and Interactions

- Robert Edwards (Thomas Jefferson National Accelerator Facility)

#### Hadron Spectroscopy and Interactions

- Daniel Mohler (GSI Helmholtzzentrum fuer Schwerionenforschung)
- Marc Wagner

#### Hadron Spectroscopy and Interactions

- Gunnar Bali (Universität Regensburg)

#### Hadron Spectroscopy and Interactions

- Ross Young

#### Hadron Spectroscopy and Interactions

- John Bulava (DESY-Zeuthen)
- Agostino Patella (Humboldt-Universität zu Berlin)

#### Hadron Spectroscopy and Interactions

- Raul Briceno (Thomas Jefferson National Accelerator Facillity)

#### Hadron Spectroscopy and Interactions

- Nilmani Mathur

#### Hadron Spectroscopy and Interactions

- Akaki Rusetsky (Univerity of Bonn)
- Christopher Thomas (University of Cambridge)

We present a lattice QCD calculation of the energy eigenvalues of the dibaryon system using the gauge ensembles generated with the domain wall fermion action. Using the sparsening field method, multiple dibaryon interpolating operators are used to reduce the contamination from excited states. Some relevant results for the weak transition matrix elements of the dibaryon system are also shown.

In this work we study the large $N_c$ scaling of pion-pion scattering lengths for $N_f=4$ degenerate quark flavours. We focus on the standard isospin-2 channel and the adjoint-antisymmmetric representation, which is unique for $N_f \geq 4$. We compare the results obtained for two regularisations (Wilson and Twisted-Mass) and three values of the lattice spacing, and observe significant...

Finite-volume scattering at physical pion mass is still an exploratory field in lattice QCD. This generally involves the extraction of excited states through multi-particle correlators on systems with resonances. In that context, distillation has demonstrated to be effective both as a smearing kernel and a computational tool. Motivated by the study of the smearing profile of the distillation...

The scattering length is an important quantity that describes scattering at low energies. We will present our evaluation of the $K\pi$ scattering length in the isospin $I=\frac12$ and $I=\frac32$ channels. The computation uses the RBC-UKQCD 2+1-flavour ensembles with Domain Wall Fermions at near-physical quark masses. With the help of all-to-all methods, we construct the correlation functions,...

We present a finite volume spectroscopy calculation of I=1 pi-pi scattering utilizing the (stochastic) distillation framework on close to physical and physical point N_f = $2+1$ CLS ensembles. Using the finite volume energy levels, we discuss the long-distance behavior of the vector correlator, which is dominated by the two-pion channel. This part can be accurately constrained using the...

We numerically investigate different techniques to extract scattering amplitudes from a Euclidean Lattice $\phi^4$ theory with two fields having different masses. We present an exploratory study of a recently proposed method by Bruno and Hansen for extracting the scattering length from a four-point function (cf. arXiv:2012.11488) and a study of the two and three particle quantization condition.

We present a lattice QCD study of $\pi-N$ scattering in the iso-spin $I=3/2$ channel.

The calculation is performed using $N_f=2+1+1$ flavors of twisted mass fermions including an ensemble with

physical pion mass. We compute energy levels for all the moving frames with total momentum up to $\vec{P}=2\pi L(1,1,1)$,

and for all the relevant irreducible representation of the lattice symmetry...

In their seminal publication of 1990, Maiani and Testa showed that physical amplitudes away from threshold cannot be directly extracted (i.e. without analytically continuing or solving an inverse problem), from infinite-volume Euclidean correlators. As a result, in realistic lattice calculations, the limited knowledge of correlation functions on finite subsets of points allows only for the...

The quantization of the energy levels of interacting two-particle system in a finite volume has been well considered in which the exponential suppressed finite volume effect was usually omitted. The partial waving mixing effect in the finite volume is also an obstacle to extracting the interacting information in the infinite volume. In this work, we propose a framework to calculate the energy...

We investigate the two-flavour Schwinger model in the canonical formulation with fixed fermion number. We use Wilson fermions on the lattice and present a formalism which describes the Dirac operator with dimensionally reduced canonical operators. These reduced operators allow the direct examination of arbitrary meson sectors and the determination of the energy spectrum in each of the sectors....

The Hadron Spectrum Collaboration (HSC) presented new results on

two of their ensembles for s-wave scattering phase shifts

in the open-charm sector of QCD. For such ensembles we have made

predictions that are based on the chiral Lagrangian that were published two years ago. In this talk

we confront our phase shifts with those of HSC. A remarkably

consistent picture emerges. In...

We present continuum limit results of the quark mass dependence of octet and decuplet baryon masses obtained from Lattice QCD simulations. This is part of our large-scale programme connected to CLS of simulating $N_f=2+1$ flavours of non-perturbatively improved Wilson fermions where ensembles with large volumes together with a wide range of quark masses, including the physical point, are used....

In this talk I will discuss several new results from the NPLQCD Collaboration that combine lattice QCD results on (hyper)nuclear systems at unphysical pion masses together with nuclear effective field theories. Two-baryon channels with strangeness $0$ to $-4$ are analized, with findings that point to interesting symmetries observed in hypernuclear forces as predicted in the limit of QCD with a...

A calculation of baryon-baryon scattering via finite-volume spectroscopy using distillation will be reported. Ensembles with SU(3) flavor symmetry and a pion/kaon/eta mass of roughly 420 MeV, covering a wide range of lattice spacings, are employed. For the first time, we take the continuum limit, finding large discretization effects. In the singlet sector, we obtain a weakly bound H dibaryon.

We present the current status of our ongoing efforts in search of the H-dibaryon on $N_f=2+1$ CLS ensembles away from the SU(3) flavor symmetric point. Utilizing the distillation framework (also known as LapH) in its exact and stochastic forms, we calculate two-point correlation matrices using large bases of bi-local two-baryon interpolators to reliably determine the low energy spectra. We...

Multi-baryon systems are challenging to study with lattice QCD in particular because of small gaps between the ground state and excited states for large lattice volumes. Variational methods have long been known to be useful for disentangling closely spaced energy levels but require approximations to all-to-all quark propagators that are computationally prohibitive to compute exactly. In this...

Lattice QCD calculations of two-nucleon interactions have been underway for about a decade, but still haven't reached the pion mass regime necessary for matching onto effective field theories and extrapolating to the physical point. Furthermore, results from different methods, including the use of the Luscher formalism with different types of operators, as well as the HALQCD potential method,...

The relationship between finite volume multi-hadron energy levels and matrix elements and two particle scattering phase shifts and decays is well known, but the inclusion of long range interactions such as QED is non-trivial. Inclusion of QED is an important systematic error correction to K->\pi\pi decays. In this talk, we present a method of including a truncated, finite-range Coulomb...

L\"{u} scher method for two-particle scattering is a critical tool for

connecting finite-volume spectrum to infinite-volume scattering phaseshifts.

We numerically validate the quantization conditions up to partial waves l=4.

Various setups used in practice are considered: cubic or elongated lattices, rest or moving frames, unequal or equal masses, and integer or half-integer total...

We discuss developments in calculating multi-hadron form-factors and transition processes via lattice QCD. Our primary tools are finite-volume scaling relations, which map spectra and matrix elements to the corresponding multi-hadron infinite-volume amplitudes. We focus on two hadron processes probed by an external current, and provide various checks on the finite-volume formalism in the...

We summarize the results of the recent work of calculating the $\pi\pi$ scattering phase shifts for both the s-wave I=0 and I=2 channels at 4 different energies around the kaon mass with physical quark mass and focus on three new topics presented in that work. (i) A determinant test that can be applied to multi-operator data at a single time separation to detect excited state contamination. ...

A variety of phenomena in the Standard Model and its extensions manifest in long-range processes involving on-shell multi-hadron intermediate states. Given recent algorithmic and conceptual progress, such processes are now realistic targets for lattice QCD. In this talk, I present a recently developed formalism that makes possible the determination of reactions of the form...

There are a number of tetraquark channels for which some phenomenological models -- already constrained by the ordinary meson and baryon spectrum -- predict deep binding. We present results from our lattice calculations of doubly-charmed and bottom-charm channels where such predictions exist. Finding no evidence of deep binding, we can rule out those models, although this does not preclude the...

We present the first calculation within lattice QCD of excited light meson resonances with $J^{PC} = 1^{--}$, $2^{--}$ and $3^{--}$. Working with an exact SU(3) flavor symmetry, for the singlet representation of pseudoscalar-vector scattering, we find two $1^{--}$ resonances, a lighter broad state and a heavier narrow state, a broad $2^{--}$ resonance decaying in both $P$-- and $F$--waves, and...

The two-photon decay process ηc→2γ can provide an ideal testing ground for the understanding of nonperturbative nature of QCD. In this study, we propose a direct method to calculate the matrix element of a hadron decaying to two-photon. Various systematic effects are examined in this work. The method developed here can also be applied for other processes which involve the leptonic or radiative...

WE perform an exploratory study of glueballs on a RBC/UKQCD gauge ensembles with a large

lattice size and with the $N_f = 2 + 1$ dynamical quark masses being tuned at the physical point. The

noises of glueball correlation functions are considerably reduced through the cluster-decomposition-

error-reduction scheme. The Bethe-Salpeter wave functions are obtained for the salar, the tensor

and...

Removing ultraviolet noise from the gauge fields is necessary for glueball spectroscopy in lattice QCD. It is known that the Yang-Mills gradient flow method is an alternative approach instead of smearing or fuzzing of the links in various aspects. In this talk, we study the application of the gradient flow technique to the construction of the extended glueball operators. We find that a simple...

In recent years many candidates for states beyond the most simple realization of the quark model were found in various experiments around the world. However, so far no consensus exists on their structure, although there is strong evidence that at least some of those are dynamically generated from meson-meson interactions.

We provide an important missing piece from the theoretical side to...

The lightest scalar charm-light $D_0^\star$ and charm-strange $D_{s0}^\star$ mesons have been puzzling in that experiments have found them at approximately the same mass. This is in contrast with the quark-model prediction. For the first time, we map out the energy dependence of the elastic Isospin-1/2 $D\pi$ scattering amplitude and find a complex $D_0^\star$ resonance pole, using Lattice QCD...

We compare two frequently discussed competing structures for a stable $\bar{b} \bar{b} u d$ tetraquark with quantum numbers $I(J^P) = 0(1^+)$ by considering meson-meson as well as diquark-antidiquark creation operators. We treat the heavy antiquarks as static with fixed positions and find diquark-antidiquark dominance for $\bar{b} \bar{b}$ separations $r < 0.25 \, \text{fm}$, while for $r >...

We study $I = 0$ quarkonium resonances decaying into pairs of heavy-light mesons using static-static-light-light potentials from lattice QCD. To this end, we solve a coupled channel Schrödinger equation with a confined quarkonium channel and channels with a heavy-light meson pair to compute phase shifts and t-matrix poles for the lightest decay channel. Additionally, we study the quark...

I will discuss some recent lattice QCD calculations of $DK$ and $D\bar{K}$ scattering, relevant for the enigmatic $D^\ast_{s0}(2317)$, with light-quark masses corresponding to $m_\pi = 239$ MeV and $m_\pi = 391$ MeV. The S-waves contain interesting features including a near-threshold $J^P = 0^+$ bound state in isospin-0 $DK$, corresponding to the $D^\ast_{s0}(2317)$, with an effect that is...

We study the charmonium spectrum on an ensemble with two heavy dynamical quarks with a mass at half the physical charm quark mass. Operators for different quantum numbers are used in the framework of distillation with different smearing profiles to increase the overlap with ground and excited states. The use of exact distillation, large statistics and the absence of light quarks gives robust...

We investigate doubly heavy tetraquarks with quark structure $ \bar{Q}\bar{Q}'qq'$ in full lattice QCD using the NRQCD formalism for bottom quarks. We focus mainly on bound states in systems with two heavy antiquarks $ \bar{b}\bar{b} $ and $ \bar{b}\bar{c} $ in the present of light quarks $q \in \{u,d,s\} $.

There are several unexplained resonances in the charmonium sector. To this end we present a study of the masses and decay constants of the lightest multiplet of charmonium-like hybrid mesons. We obtain precise measurements through the use of a variational basis and a large number of configurations at three lattice spacings. We use staggered fermion operators and our configurations are...

In 2011, Belle discovered two $Z_b^+$ hadrons with quark content $\bar{b}b\bar{d}u$. Lattice study of hadrons with this quark content is challenging because they can decay to two $B$-mesons and also to a bottomonium and a light meson, leading to a large number of decay channels. We present a lattice study of the $\bar{b}b\bar{d}u$ system with the static bottom quarks. Only the channel that...

The first lattice study of coupled-channel $D\bar D$ and $D_s\bar D_s$ scattering is presented. The partial waves $l=0,2$ are investigated on CLS ensembles. The resulting scattering matrix suggests the existence of three charmonium-like states with $J^{PC}=0^{++}$ in addition to $\chi_{c0}(1P)$: a $D\bar D$ bound state just below threshold, a broader resonance likely related to ...

Preliminary results for the spectra of excited and exotic $B$, $B_s$ and $B_c$ mesons are presented. The calculation on a dynamical anisotropic lattice employs distillation, enabling a large basis of interpolating operators including those proportional to the gluonic field strength which are relevant for hybrid states. A comparison with a similar calculation of $D$ and $D_s$ mesons is made.

The current precision reached by lattice QCD calculations

of low-energy hadronic observables, requires not only the introduction

of electromagnetic corrections, but also a control over all the potential

systematic uncertainties introduced by the lattice version of QED.

Introducing a massive photon as an infrared regulator in lattice QED, provides a

well defined theory, dubbed...

In recent years many QCD observables have reached (sub-)percent level precision. At this level strong ($m_u \neq m_d$) and weak (charges of up, down and strange) isospin breaking effects have to be accounted for. Different methods exist to include QED into lattice QCD simulations. In massive QED (QEDm) the photon is given a mass $m_\gamma$, allowing for a local formulation of QED on the...

In this contribution we announce the formation of a new initiative to study Stabilised Wilson Fermions (SWF). They are an interesting new avenue for QCD calculations with Wilson fermions and we report results on our continued study of this framework: Tuning the clover improvement coefficient we extend the reach of lattice spacings to $a=0.055,~0.064,~0.080,~0.094,~0.12\,$fm. We further tune...

We present preliminary results of lattice QCD simulations with dynamical light and strange quarks, all flavors defined using Stabilised Wilson Fermions (SWF). The ensembles are tuned, see the preceding talk by A. Francis, at the flavor symmetric point $m_\pi=m_K=412$ MeV and the physical point is reached keeping fixed the trace of the quark mass matrix. We show a first determination of the...

We extend our study of the static potential in $N_f$=2+1 QCD to determine its quark mass dependence. We use a set of CLS (Coordinated Lattice Simulations) ensembles at a lattice spacing a=0.064 fm along a chiral trajectory of constant sum of the bare quark masses. The pion masses range from $m_\pi$=420 MeV at the symmetric point down to $m_\pi$=200 MeV. We use a model to parametrize the lowest...

We compute hybrid static potentials in SU(3) Yang-Mills theory at short quark-antiquark separations using four different small lattice spacings as small as 0.04 fm. The resulting static potentials are important e.g. when computing masses of heavy hybrid mesons in the Born-Oppenheimer approximation. We also discuss and exclude possible systematic errors from topological freezing, the finite...

Flux tube spectra are expected to have full towers of levels due to the quantization of the string vibrations. We study a spectrum of flux tubes with static quark and antiquark sources with pure gauge SU(3) lattice QCD in 3+1 dimensions up to a significant number of excitations. To go high in the spectrum, we specialize in the most symmetric case $\Sigma_g^+$, use a large set of operators,...

A high-statistics computation of meson-baryon scattering amplitudes is presented on a single ensemble from the Coordinated Lattice Simulations (CLS) consortium with $m_{\pi}=200{\rm MeV}$ and $N_{\rm f} = 2+1$ dynamical fermions. The finite-volume approach is employed to determine the lowest few partial waves from ground and excited state energies computed by solving the Generalized Eigenvalue...

We use the Infinite Volume Reconstruction Method to calculate the charged/neutral pion mass difference. The hadronic tensor is calculated on lattice QCD and then combined with an analytic photon propagator, and the mass shift is calculated with exponentially-suppressed finite volume errors. In this talk we discuss the Feynman diagrams relevant to the pion mass difference and we recapitulate...

Hyperon physics is expected to play a role in neutron stars, where the extreme neutron degeneracy pressure could push neutrons into hyperons; indeed, the composition of neutron stars contributes to the "softness" or "stiffness" of the equation of state, therefore setting limits on the possible sizes and masses of neutron stars. In this talk, I will present calculations of hyperonic...

Recent lattice QCD results for the first two low-lying odd-parity excitations of the nucleon have revealed that they have magnetic moments consistent with constituent-quark-model expectations. Thus, in constructing a basis of states to describe scattering in this channel, one should not represent both odd-parity excitations by a single three-quark basis state. Two single-particle basis...

We present the results of a lattice calculation of tetraquark states with quark contents $\bar{b}\bar{c}\,q_1q_2, \, q_1,q_2 \subset u,d,s$ in both spin zero ($J=0$) and spin one ($J=1$) sectors. For the spin one states, when the light quark ($q_1, q_2$) masses are lighter, we find at least one energy level below the possible thresholds energy levels. These calculations are performed on three...

We present a Lattice calculation of the mass difference between neutron and proton, obtained at 1st order in the $QED$ coupling $\alpha_{EM}$ and in the mass difference between $u$ and $d$ quarks $\frac{m_d-m_u}{\Lambda_{QCD}}$. We adopt a purely hadronic scheme to renormalize the theory and to separate the $QED$ and strong $IB$ contributions.

The simulation is carried out using the ETMC...

We will present the pion mass and decay constant using the overlap fermion valence on DW fermion sea at several lattice lattice spacings. The mixed action effect in the lattice calculation is also studied, and the result suggests that the mixed action effect with overlap valence on DW sea would be proportional to the fourth power of the lattice spacing. The preliminary determination of the...

The first lattice QCD study of the mixing of $\eta_c$ and the pseudoscalar glueball is performed. We generate a large gauge configuration ensemble with $N_f=2$ degenerate charm quarks on an isotropic lattice. The correlation functions of the charm quark bilinear operators, both connected part and disconnected part, are computed via the distillation method. And the correlation functions of...

We present the first lattice analysis of the pseudoscalar mesons with consideration for the mixing between the flavour-singlet states $\pi^0$, $\eta$ and $\eta'$. We extract the masses and flavour compositions of the pseudoscalar meson nonet in nf = 1 + 1 + 1 lattice QCD+QED around an SU(3)-flavour symmetric point, and observe interesting features of the extracted data, along with preliminary...

We determine, with Twisted Mass Lattice QCD simulations and adopting the RM123 method, the charged/neutral pion mass difference $M_{\pi_{+}} - M_{\pi_{0}}$ at order $\mathcal{O}(\alpha_{em})$ in the QED interactions and present preliminary results for $M_{\pi_{+}} - M_{\pi_{0}}$ at order $\mathcal{O}\left( (m_{d}-m_{u})^{2}\right)$ in the strong isospin-breaking term. The latter contribution...

This talk is an update on the ongoing effort of the RC$^\star$ collaboration to generate fully dynamical QCD+QED configurations. We present the results of several ensembles with C$^\star$ boundary conditions that were generated using the openQ$^\star$D code. The simulations were tuned to the U-symmetric point ($m_d=m_s$) with pions at $m_{\pi^{\pm}} \approx 400$ MeV and a splitting of...

In this talk we present preliminary results for the masses of the proton, neutron and Omega- baryons obtained from $n_f$=1+2+1 QCD+QED lattice simulations performed using C$^*$ boundary conditions. Spin-1/2 and spin-3/2 baryon two-point correlators are extracted from full QCD+QED lattice simulations through an extension to the OpenQ$^*$D publicly available code. The correlators are computed by...

We present work designed to compute baryon masses on $N_f=2+1$ CLS ensembles including isospin breaking effects due to non-degenerate light quark masses and electromagnetic interactions. These effects are determined at leading order via a perturbative expansion around the iso-symmetric theory. We furthermore apply a group theoretical operator construction for the various interpolators...

Experiments show that the flavor-singlet pseudoscalars usually have large production ratios in the radiative decays of $J/\psi$.

In this work we perform the first lattice investigation on this topic based on a gauge ensemble generated on an anisotropic lattice with two degenerate light dynamical quarks. The mass parameter of the light quarks is tuned to give a pion mass around 300 MeV. The...

We investigate the parity odd $\Delta I = 1$ pion-nucleon coupling $h^1_\pi$ from lattice QCD. With the PCAC-based use of a parity-conserving effective Hamiltonian, we extract the coupling by determining the nucleon mass splitting arising from effective 4-quark interactions using the Feynman-Hellmann theorem. We present preliminary results of the mass shift for a $32^3 \times 64$ ensemble...

The last years have seen significant developments in methods relating two- and three-particle finite-volume energies to scattering observables. These relations holds for both weakly and strongly interacting systems, and studying their predictions in limiting cases can provide important cross checks as well as giving useful insights to the general formulae. In this talk, I present analytic...

We provide the generalization of the formalism needed to relate the three-particle

finite-volume spectrum to infinite-volume scattering amplitudes for the case of three nondegenerate scalar particles with arbitrary masses. The results can be expressed in a form similar to those for identical particles, except for the addition of an extra flavor index. We do so using a simplified method in...

The past several years have seen significant progress in the theoretical developments for interpreting three-particle finite-volume energies. The successful application of these frameworks using lattice data for three-pion and three-kaon systems with maximal isospin has been demonstrated from several groups using a modest set of energies to constrain the three-particle interactions. Here we...

We present the first determination of the universal parameters of the a1(1260) from QCD. This consists of three steps presented in the talk:

(1) Lattice QCD calculation including three-meson operators; (2) Generalization of three-body quantization condition including sub-systems with spin and coupled channels; (3) Analytic continuation of the infinite-volume amplitude and determination of the...

Much of the resonant spectrum of QCD consists of states which decay strongly into two- and three-body final states. Lattice QCD calculations have matured to the stage where these states can be reliably resolved in first principles numerical calculations. While connecting these finite-volume results to infinite-volume scattering is now commonplace in the two-body sector, three-body physics...

We consider three-particle systems consisting of two identical particles and a third that is different, with all being spinless, e.g. $\pi^+ \pi^+ K^+$. We generalize the formalism necessary to extract two- and three-particle infinite-volume scattering amplitudes from the spectrum of such systems in finite volume. We use a relativistic formalism based on an all-orders diagrammatic analysis in...

Strong interactions produce a rich spectrum of resonances which decay into three or more hadrons. Understanding their phenomenology requires a theoretical framework to extract parameters from experimental data and lattice QCD simulations of hadron scattering. Two classes of relativistic three-body approaches are currently being pursued: the EFT-based and unitarity-based one. We consider a...

We study decuplet baryons from meson-baryon interactions. We report the analysis of the P-wave $\pi N$ interaction with isospin $I=3/2$ and the $\bar{K}\Xi$ interaction with $I=0$, which have channels to a $\Delta$ and $\Omega$ baryon, respectively. The interaction potentials are calculated in the HAL QCD method using 3-quark-type source operators at $m_{\pi} \approx 410~\text{MeV}$. We use...

The hyperon-nucleon interaction with the strangeness $S=-1$ region is complicated and difficult to investigate because its flavor sector involves all the irreducible representation except the flavor singlet and has the worst signal-to-noise ratio among the Strangeness regions [1-2]. Some efforts to overcome such difficulties will be discussed.

References:

[1] H. Nemura et al., AIP...

The baryon-baryon interaction in the strangeness =-1 channel was recently analysed by using the lattice QCD data near the physical point combined with the HAL QCD method [1]. In the present contribution, we show our first attempt to extract the coupled-channel NΛ-NΣ potential from thesame data by using the Misner's method which is known to be a reliable way to perform the partial wave...

We study the systematic error associated with the truncation of the derivative expansion for the potential in HAL QCD method. We introduce the Hamiltonian with the leading-order potential determined in the HAL QCD method and study the corresponding eigenmodes in a finite volume. We show that a temporal correlation function of a designated energy eigenstate can be obtained using the...

The Laplacian Heaviside (LapH) smearing technique is proved to be useful in precision determination of multi-hadron spectrum. We apply the LapH source smearing to the nuclear force calculation by the HAL QCD method, finding that the 1S0 and 3S1-3D1 potentials are obtained with good precision. The parity-odd sector, including the LS force, are also discussed.

In this talk, we report the rho resonance study using the HAL QCD method. We calculate the $I=1$ $\pi \pi$ potential at $m_{\pi} \approx 410$ MeV by a combination of the one-end trick, sequential propagator and covariant approximation averaging (CAA). Thanks to those techniques, we determine the non-local $I=1$ $\pi\pi$ potential at the next-to-next-to-leading order (N$^2$LO) of the derivative...

We propose a method to extract the HAL QCD potential from correlation functions with non-zero total momentum (boosted system). After brief explanation of the formulation with non-zero total momentum ($P$), we apply it to the $I=2$ $\pi\pi$ system. Using 2+1 flavor PACS-CS configurations at $m_\pi=700$ MeV and $a=0.09$ fm on $32^3x64$ lattice, we calculate the $I=2$ $\pi\pi$ potential with...

A pair of triply charmed baryons, $\Omega_{ccc}\Omega_{ccc}$, is studied as an ideal dibaryon system by (2+1)-flavor lattice QCD with nearly physical light-quark masses and the relativistic heavy quark action with the physical charm quark mass. The spatial baryon-baryon correlation is related to their scattering parameters on the basis of the HAL QCD method. The $\Omega_{ccc}\Omega_{ccc}$ in...

The estimation of the Källén-Lehmann spectral density from gauge invariant lattice QCD two point correlation functions is proposed, and explored via an inversion strategy based on Tikhonov regularisation. As proof of concept the SU(2) glueball spectrum for the quantum numbers $J^{PC}=0^{++}$ is investigated, for various values of the lattice spacing, using the published data of...

We report on the first master-field simulations of QCD with 2+1 dynamical quark flavours using non-perturbatively improved stabilised Wilson fermions. Our simulations are performed at a lattice spacing of 0.095 fm with 96 and 192 points in each direction. With $Lm_\pi$=12.5 and 25, both lattices feature a pion and kaon mass of about 270 and 450 MeV. This setup is compatible with a chiral...

The master-field approach to lattice QCD envisions performing calculations on a small number of large-volume gauge-field configurations. Substantial progress has been made recently in the generation of such fields, and this must be joined with measurement strategies that take advantage of the large volume.

In this talk, we describe how to compute simple hadronic quantities efficiently and...

Minimally doubled fermions, have been proposed as lattice fermions which preserve chiral symmetry and being strictly local too. In our previous works, we have studied how the broken hypercubic symmetry of Boriçi - Creutz fermions affect the light hadrons spectrum, have proposed a method of how to restore it and also made a simple test on the pion mass using the corrected action. In this work...

We present a determination of the gradient flow scales $w_0$, $\sqrt{t_0}$ and $t_0/w_0$ in isosymmetric QCD, making use of the gauge ensembles produced by the Extended Twisted Mass Collaboration (ETMC) with $N_f=2+1+1$ flavours of Wilson-clover twisted-mass quarks including configurations close to the physical point for all dynamical flavours. The simulations are carried out at three values...

We present a method to improve the lattice effective field theory description of the shape of atomic nuclei by applying unitary transformations to the Hamiltonian. The employed unitary operator is constructed as a reflection transformation from the original and the desired wave function. Similarly to a derivative expansion, it can be improved systematically so that one can tune the $\langle...

Back in 2000, Lellouch and Lüscher derived a formula, relating the

matrix element of the weak $K \rightarrow 2\pi$ decay in a finite

volume to its infinite-volume counterpart.

In contrast, albeit latest theoretical developments enable the

extraction of three-body scattering amplitudes on the lattice,

a three-particle analog of the Lellouch-Lüscher equation has not

been available until...

In this talk, I will review our recent generalization of the Lellouch-Lüscher to study decays to three particles. First, the result in a simplified theory with three identical particles will be presented, and then the generalizations needed to study phenomenologically relevant three-pion decays will be discussed. Specific processes for which this formalism is applicable are the CP-violating $K...

It is common practice to truncate the finite-volume formula for K to pi pi, and other one to two transitions, to only include the lowest partial wave, as in the original derivation by Lellouch and Lüscher. However, as the precision of lattice calculations increases, it may become important to asses the systematic effect of this approximation. With this motivation, we compare the S-wave-only...

Radiative transitions between stable hadrons and hadronic resonances can provide valuable insights into the composition of hadronic resonances. In this talk, we present a toy-model investigation regarding the feasibility of realistic lattice QCD calculations of reactions where a stable hadron undergoes a transition to one of several two-hadron channels. We describe the coupled-channel...

An exotic hybrid meson resonance appearing in $J^{PC}=1^{-+}$ is determined for the first time from lattice QCD. Many finite volume energy levels are computed and used with the coupled-channel extension of the Lüscher formalism to determine the scattering amplitudes in the limit where SU(3) flavour symmetry is exact. The scattering amplitude contains a pole that has a large coupling to an...

We present calculations of form factors and radiative transitions in the low-lying charmonium sector using Lattice QCD. Results for $J/\psi \to \eta_c \gamma$, $\chi_{c0} \to J/\psi \gamma $ partial widths are presented alongside other experimentally unobservable form factors. Comparisons are given to previous results in both lattice and experimental studies. Studying radiative transitions...