A tmQCD mixed-action approach to flavour physics

We discuss a mixed-action approach in which sea quarks are regularised using non-perturbatively ${\rm O}(a)$ improved Wilson fermions, while a fully-twisted tmQCD action is used for valence quarks. In this setup, automatic ${\rm O}(a)$ improvement is preserved for valence observables, apart from small residual ${\rm O}(a)$ effects from the sea. A strategy for matching sea and valence is set up, and carried out for $N_\mathrm{f}=2+1$ CLS ensembles with open boundary conditions at several simulation points. The scaling of basic light-quark observables such as the pseudoscalar meson decay constant is studied, as well as the isospin splitting of pseudoscalar meson masses.Comment: 11 pages, 5 figures, Proceedings of the 35th International Symposium on Lattice Field Theory (Lattice 2017), 18-24 June 2017, Granada, Spai

Towards precision charm physics with a mixed action

39th International Symposium on Lattice Field Theory, LATTICE 2022 Bonn 8 August 2022 through 13 August 2022 Code 187776We report on our first set of results for charm physics, using a mixed-action setup with maximally twisted valence fermions on CLS Nf = 2+1 ensembles. This setup avoids the need of improvement coefficients to subtract O (amc) effects. The charm quark mass, D and Ds decay constants are computed on a subset of CLS ensembles, which allows to take the continuum limit and extrapolate to the physical pion mass, and assess the scaling properties. Special attention is paid to the implementation of techniques to deal with systematic uncertainties. Our results show excellent prospects for high-precision computations on the full set of ensemblesWe acknowledge PRACE and RES for giving us access to computational resources at MareNostrum (BSC). We thank CESGA for granting access to Finis Terrae II. This work is supported by the European Union’s Horizon 2020 research and innovation programme under grant agreement No 813942 and by the Spanish MINECO through project PGC2018-094857-B-I00, the Centro de Excelencia Severo Ochoa Programme through SEV-2016-0597 and the Ramón y Cajal Programme RYC-2012-024

Hadronic physics from a Wilson fermion mixed-action approach: Charm quark mass and D(s)D_{(s)} meson decay constants

We present our first set of results for charm physics, using the mixed-action setup introduced in a companion paper. Maximally twisted Wilson valence fermions are used on a sea of non-perturbatively $O(a)$-improved Wilson fermions, made up by CLS $N_{\mathrm{\scriptstyle f}}=2+1$ ensembles. Our charm-sector observables are free from $O(am_c)$ discretisation effects, without need of tuning any improvement coefficient, and show continuum-limit scaling properties consistent with leading cutoff effects of $O(a^2)$. We consider a subset of CLS ensembles -- including four values of the lattice spacing and pion masses down to 200 MeV -- allowing to take the continuum limit and extrapolate to the physical pion mass. A number of techniques are incorporated in the analysis in order to estimate the systematic uncertainties of our results for the charm quark mass and the $D_{(s)}$-meson decay constants. This first study of observables in the charm sector, where the emphasis has been on the control of the methodology, demonstrates the potential of our setup to achieve high-precision results.Comment: 44 pages, 21 figure

Física del charm con una acción mixta de QCD en la red

Tesis Doctoral inédita leída en la Universidad Autónoma de Madrid, Facultad de Ciencias, Departamento de Física Teórica. Fecha de Lectura: 027-05-2022In this thesis we study a mixed-action Lattice QCD setup, which combines Nf = 2 + 1 O(a)-improved Wilson fermions and Nf = 2 + 1 + 1 Wilson twisted mass (Wtm) fermions at maximal twist in the valence. We take advantage of automatic O(a) improvement in the valence sector to extract charm physics results without improvement coefficients. Our results include the determination of the charm quark mass, as well as of the decay constants of the D and Ds mesons, relevant for electroweak leptonic decays. Quarkonium states are also studied. We carry out an analysis that focuses on controlling the statistical and systematic errors. Systematic effects are considered in the framework of Bayesian statistics. Different model parameterizations are taken into consideration to perform a model average. Our final results are among the most precise in the literature for computations employing Wilson-like fermions and will contribute significantly to the current world averagesEn esta tesis estudiamos una configuración de acción mixta, que combina Nf = 2+1 fermiones Wilson mejorados a O(a) y Nf = 2+1+1 fermiones Wilson twisted mass (Wtm) a twist máximo. Aprovechamos el mejorado a O(a) automático en el sector de valencia para extraer resultados de física de charm sin coeficientes de mejora. Nuestros resultados incluyen la determinación de la masa del quark charm, así como también las constantes de desintegración de los mesones D y Ds, relevantes para las desintegraciones electrodébiles leptónicas. También estudiamos estados de quarkonio. Consideramos efectos sistemáticos en un contexto de estadística Bayesiana. Se consideran diferentes parametrizaciones para efectuar una media de modelos. Nuestro resultados finales están entre los resultados más precisos de la literatura con cálculos que emplean fermiones Wilson-like y contribuirán significativamente a las medias mundiales actuale

A tmQCD mixed-action approach to flavour physics

We discuss a mixed-action approach in which sea quarks are regularised using non-perturbatively O(a) improved Wilson fermions, while a fully-twisted tmQCD action is used for valence quarks. In this setup, automatic O(a) improvement is preserved for valence observables, apart from small residual O(a) effects from the sea. A strategy for matching sea and valence is set up, and carried out for Nf = 2 + 1 CLS ensembles with open boundary conditions at several simulation points. The scaling of basic light-quark observables such as the pseudoscalar meson decay constant is studied, as well as the isospin splitting of pseudoscalar meson masses

Scale Setting from a Mixed Action with Twisted Mass Valence Quarks

We present preliminary results for a scale setting procedure based on a mixed action strategy consisting of Wilson twisted mass valence fermions at maximal twist on CLS ensembles with $N_f=2+1$ flavours of O($a$)-improved Wilson sea quarks. Once the matching of valence and sea quark masses is performed, universality tests are carried out by comparing the continuum-limit results of the mixed action setup to those of the regularisation based solely on O($a$)-improved Wilson fermions. The scale setting uses the pion and kaon decay constants, in units of the gradient flow scale $t_0$, obtained from combining computations with the unitary Wilson action and the mixed action. The proper isolation of ground states as well as the continuum-chiral extrapolations are evaluated through model variation techniques. An update on the determination of $t_0$ will be presented

Hadronic physics from a Wilson fermion mixed-action approach: charm quark mass and D(s)D_{(s)} D ( s ) meson decay constants

Abstract We present our first set of results for charm physics, using the mixed-action setup introduced in a companion paper [1]. Maximally twisted Wilson valence fermions are used on a sea of non-perturbatively O(a)-improved Wilson fermions, made up by CLS $$N_\mathrm {\scriptstyle f}=2+1$$ N f = 2 + 1 ensembles. Our charm-sector observables are free from $$O(am_c)$$ O ( a m c ) discretisation effects, without need of tuning any improvement coefficient, and show continuum-limit scaling properties consistent with leading cutoff effects of $$O(a^2)$$ O ( a 2 ) . We consider a subset of CLS ensembles – including four values of the lattice spacing and pion masses down to 200 MeV – allowing to take the continuum limit and extrapolate to the physical pion mass. A number of techniques are incorporated in the analysis in order to estimate the systematic uncertainties of our results for the charm quark mass and the $$D_{(s)}$$ D ( s ) -meson decay constants. This first study of observables in the charm sector, where the emphasis has been on the control of the methodology, demonstrates the potential of our setup to achieve high-precision results

Light meson physics and scale setting from a mixed action with Wilson twisted mass valence quarks

We consider a mixed action approach where valence Wilson twisted mass (Wtm) fermions at maximal twist are combined with CLS ensembles consisting of $N_f$=2+1 flavours of O($a$)-improved Wilson sea quarks. We present an update of the results of the matching of valence and sea quarks, and of the subsequent continuum-limit scaling studies of light-quark observables. A scale setting procedure combining the results from the O($a$)-improved Wilson setup to the ones from the valence Wtm regularisation is discussed