arXiv subjects

Nelson Pitanga Lachini

Publications and source records attributed to Nelson Pitanga Lachini.

9 recordsLinked to original sources

arXiv2026

$D \to (K π)_{\mathbf{27}}$ at the SU(3)-flavour-symmetric point I: Methodology and strong phase determination

We present part one of an SU(3)-flavour-symmetric lattice QCD calculation of the amplitude for a $D$-meson decaying to a $Kπ$ final state in the 27-dimensional irreducible representation of the flavour symmetry group, denoted $(Kπ)_{\mathbf{27}}$. The Wilson--clover gauge ensembles used in this work, generated by the OpenLat collaboration, are tuned such that $M_π= M_K \approx 410\,\mathrm{MeV}$. Using the distillation framework, we construct a matrix of Euclidean correlation functions from pairs of single-hadron operators projected to definite spatial momentum. Solving a generalised eigenvalue problem yields the finite-volume energy spectrum that is used to determine the scattering phase shift from threshold up to $4 M_π\approx 1640 \,\mathrm{MeV}$, which sits below but plausibly within reach of $M_D^{\rm SU(3)} \simeq 1900\,\mathrm{MeV}$. The calculation is performed across three lattice spacings, and we apply two strategies in which the continuum limit is taken at different stages of the computation: (i) on the extracted scattering parameters and (ii) on the finite-volume energies at fixed physical volume before extracting the scattering parameters. We find consistent results across these methods for the scattering phase shift as a function of the centre-of-mass energy, $δ_{\mathbf{27}}(E_{\sf cm})$. Taking a scattering-length-only parametrisation, we infer a value for the strong phase of the weak decay, $δ_{\mathbf{27}}(M_D^{\rm SU(3)})=-38.4(2.4)^\circ$. We further describe the methodology for using the same operator basis to compute three-point correlation functions to extract $\langle (Kπ)_{\mathbf{27}}| H_W| D\rangle$, for the tree-level effective weak Hamiltonian $H_W$, and for relating such finite-volume matrix elements to the full decay amplitude. The complete analysis leading to the latter will be presented in a forthcoming manuscript.

hep-lat↗

arXiv2026

Resolving the $T_{cc}^+$ with $π$ Exchange from Lattice QCD

We revisit the lattice QCD description of the doubly charmed tetraquark $T_{cc}^+$ using a finite-volume scattering formalism that incorporates one-pion exchange nonperturbatively, thereby making the nearest left-hand cut explicit while respecting unitarity and analyticity. We simultaneously determine the $D D^\star π$ coupling and the isoscalar $DD^\star$ scattering amplitude by reanalyzing the previously computed finite-volume $DD^\star$ spectrum below the $D^\star D^\star$ threshold, on lattices with pion mass $m_π\approx391~{\rm MeV}$. We find that the inclusion of pion exchange changes the $T_{cc}^+$ from a real-valued to a complex-valued pole in the second sheet of the $J^P=1^+$, $DD^\star$ amplitude below threshold. We further predict that the $T_{cc}^+$ pole will move closer to the real-energy axis as the pion mass approaches its physical value.

hep-lat↗

arXiv2026

$K π$ scattering as a step towards $B \to K^* \ell^+ \ell^-$ from Lattice QCD

Rare $b\to s\ell^+\ell^-$ decays provide some of the most sensitive tests of the Standard Model and require precise and systematically improvable hadronic input from lattice QCD. For the phenomenologically important channel $B\to K^*\ell^+\ell^-$ this entails a first-principles treatment of a resonant $Kπ$ final state together with controlled heavy-quark dynamics. We present the status of a new exploratory lattice calculation that combines a variational determination of finite-volume $Kπ$ states with the $1+J\to2$ finite-volume formalism to access the relevant matrix elements. The computation is carried out on an RBC/UKQCD domain-wall fermion ensemble with $a^{-1} \approx 2.7\,\mathrm{GeV}$ and employs a dual heavy-quark strategy, using both a relativistic heavy-quark action tuned to the physical $b$ mass and domain-wall heavy masses extrapolating from charm. All correlation functions are computed using (stochastic) distillation, providing a versatile setup that supports a broad range of heavy-to-light transitions into resonant final states. We show first two-point results for the $K^*\leftrightarrow Kπ$ system and discuss the accessible kinematic region, which allows for a controlled study at high $q^2$. The outlook for extending the calculation to lower $q^2$ and for incorporating effects from charmonium resonances is outlined.

hep-lat↗

arXiv2026

Coupled-channel scattering of $DD, DD^$ and $D^ D^*$ in isospin-$1$ from lattice QCD

The first coupled-channel determination of two-body $D$ and $D^*$ scattering amplitudes in isospin-$1$ from lattice quantum chromodynamics is presented. Using three lattice volumes at $m_π\approx 391~\mathrm{MeV}$, finite-volume energies relevant for the channels of interest are determined. Through the Lüscher formalism, these energies are used to constrain amplitudes of coupled $J^P=0^+$ $DD - DD^*$, $J^P=1^+$ $DD^*- D^*D^*$ and $J^P=2^+$ $DD - DD^* - D^* D^*$ scattering. All channels feature weakly repulsive interactions in $S$ wave, except for a weak $D^* D^*$ attraction in $J^P=0^+$. No amplitude singularities corresponding to physical states are found. Some of these amplitudes will be a necessary component of future lattice QCD analyses of $DDπ$ and $DD^*$ scattering taking into account three-body and left-hand cut effects.

hep-lat↗

arXiv2025

Physical-mass calculation of $ρ(770)$ and $K^*(892)$ resonance parameters via $ππ$ and $K π$ scattering amplitudes from lattice QCD

We present our study of the $ρ(770)$ and $K^*(892)$ resonances from lattice quantum chromodynamics (QCD) employing domain-wall fermions at physical quark masses. We determine the finite-volume energy spectrum in various momentum frames and obtain phase-shift parameterizations via the Lüscher formalism, and as a final step the complex resonance poles of the $ππ$ and $K π$ elastic scattering amplitudes via an analytical continuation of the models. By sampling a large number of representative sets of underlying energy-level fits, we also assign a systematic uncertainty to our final results. This is a significant extension to data-driven analysis methods that have been used in lattice QCD to date, due to the two-step nature of the formalism. Our final pole positions, $M+iΓ/2$, with all statistical and systematic errors exposed, are $M_{K^{*}} = 893(2)(8)(54)(2)~\mathrm{MeV}$ and $Γ_{K^{*}} = 51(2)(11)(3)(0)~\mathrm{MeV}$ for the $K^*(892)$ resonance and $M_ρ = 796(5)(15)(48)(2)~\mathrm{MeV}$ and $Γ_ρ = 192(10)(28)(12)(0)~\mathrm{MeV}$ for the $ρ(770)$ resonance. The four differently grouped sources of uncertainties are, in the order of occurrence: statistical, data-driven systematic, an estimation of systematic effects beyond our computation (dominated by the fact that we employ a single lattice spacing), and the error from the scale-setting uncertainty on our ensemble.

hep-lat↗

arXiv2025

Light and strange vector resonances from lattice QCD at physical quark masses

We present the first ab initio calculation at physical quark masses of scattering amplitudes describing the lightest pseudoscalar mesons interacting via the strong force in the vector channel. Using lattice quantum chromodynamics, we postdict the defining parameters for two short-lived resonances, the $ρ(770)$ and $K^*(892)$, which manifest as complex energy poles in $ππ$ and $K π$ scattering amplitudes, respectively. The calculation proceeds by first computing the finite-volume energy spectrum of the two-hadron systems, and then determining the amplitudes from the energies using the Lüscher formalism. The error budget includes a data-driven systematic error, obtained by scanning possible fit ranges and fit models to extract the spectrum from Euclidean correlators, as well as the scattering amplitudes from the latter. The final results, obtained by analytically continuing multiple parameterizations into the complex energy plane, are $M_ρ= 796(5)(50)~\mathrm{MeV}$, $Γ_ρ= 192(10)(31)~\mathrm{MeV}$, $M_{K^*} = 893(2)(54)~\mathrm{MeV}$ and $Γ_{K^*} = 51(2)(11)~\mathrm{MeV}$, where the subscript indicates the resonance and $M$ and $Γ$ stand for the mass and width, respectively, and where the first bracket indicates the statistical and the second bracket the systematic uncertainty.

hep-lat↗

arXiv2022

Exploring distillation at the SU(3) flavour symmetric point

In these proceedings 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 a non-perturbative investigation of hadronic D-decays, for which one needs to control the multi-hadron final states. As a first step we study two-to-two s-wave scattering of pseudoscalar mesons. In particular we examine the reliability of the extraction of finite-volume energies as a function of the number of eigenvectors of the gauge-covariant Laplacian entering our distillation setup.

hep-lat↗

arXiv2022

Towards $Kπ$ scattering with domain-wall fermions at the physical point using distillation

Resonances play an important role in Standard Model phenomenology. In particular, hadronic resonances feature in $B$ 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 $Kπ$ and thus the hadronic resonance $K^*$. In this work, we approach $Kπ$ scattering on a domain-wall $N_f = 2+1$ RBC-UKQCD ensemble at a physical pion mass. We use the distillation method within Grid and Hadrons software to compute sets of operator basis. That allows solving an eigenvalue problem to extract the low-energy finite-volume spectra, which are then translated into scattering information. We update the state of the calculation by reviewing the smearing process, outlining the variational analysis and concluding by showing preliminary data.

hep-lat↗

arXiv2021

$K π$ scattering at physical pion mass using distillation

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 been demonstrated to be effective both as a smearing kernel and a computational tool. Motivated by the study of the smearing profile of the distillation operator, we compare stochastic and exact distillation cases for different numbers of Laplacian eigenvectors using an RBC-UKQCD $N_f=2+1$ domain-wall fermion lattice with a physical pion mass.

hep-lat↗