arXiv subjects

Benoît Blossier

Publications and source records attributed to Benoît Blossier.

At least 19 recordsLinked to original sources

arXiv2026

Event-Chain Monte Carlo for Yang-Mills SU(N) lattice field theory I : Design and proof of concept

We develop two implementations of the Event-Chain Monte Carlo (ECMC) algorithm for Yang-Mills $\mathrm{SU}(N)$ lattice gauge theories with the Wilson action. These algorithms consist in a succession of local ballistic updates intersped with stochastic events, resulting in an irreversible and rejection-free Markov process. The resulting dynamics satisfy global balance, ensuring the correct equilibrium distribution. The algorithms are formulated for general $\mathrm{SU}(N)$ Yang-Mills theories with Wilson action and implemented for the case $N=3$. Numerical tests on four-dimensional lattices show that standard gauge observables, such as the mean plaquette, agree with results obtained using conventional Monte Carlo algorithms. These results provide a first validation of ECMC as a viable sampling scheme for Yang-Mills lattice gauge theories.

hep-lat↗

arXiv2025

Hadronic decay of vector charmonium from the lattice

Estimating decay parameters in lattice simulations is a computationally demanding problem, requiring several volumes and momenta. We explore an alternative approach, where the transition amplitude can be extracted from the spectral decomposition of particular ratios built from correlation functions. This so-called ratio method has the advantage of not needing various irreducible representations or volumes, and it allows us to predict the decay width $Γ$ and the energy shift $ε$ of the spectrum directly. In this work, we apply this method to study the hadronic decay $ψ(3770)\to \bar{D}D$ on two CLS $N_\text{f}=2$ ensembles. This approach requires close to on-shell kinematics to work, and we employ twisted boundary conditions to precisely tune the on-shell point. Although our study is yet to approach the continuum limit, we find a value of $Γ$ fully compatible to the physical result, and $ε$ informs us by how much our spectrum would shift in a fully dynamical simulation. Besides lattice calculations, many analytical tools have been proposed to understand decay processes. A relatively simple, early example is the ${}^3P_0$ quark model, which provides a physical insight of the decay process.

hep-lat↗

arXiv2024

The hadronic decay of vector charmonium

The extraction of decay parameters using lattice techniques is a computationally expensive task, requiring several volumes and group irreps to relate the spectrum on a lattice simulation to the infinite volume scattering. In this project we employ an alternative method based on a narrow-width approximation to extract the hadronic mixing $<\bar{D}D|ψ(3770)>$, which is needed to compute the decay $Γ(ψ(3770)\to\bar{D}D)$ between the second excited state of vector charmonium and a pair of $D$-mesons in a $p$-wave. We carry out our lattice simulations on two CLS ensembles at $m_π\sim 440~\text{MeV}$ and $a\sim 0.066~\text{fm}$ and obtain results compatible with experiment. Furthermore, we interpret our results analytically using the ${}^3P_0$ quark model.

hep-lat↗

arXiv2024

The distribution amplitude of the $η_c$-meson at leading twist from Lattice QCD

Distribution amplitudes are functions of non-perturbative matrix elements describing the hadronization of quarks and gluons. Thanks to factorization theorems, they can be used to compute the scattering amplitude of high-energy processes. Recently, new ideas have allowed their computation using lattice QCD, which should provide us with a general, fully relativistic determination. We present the first lattice calculation of the $η_c$-meson distribution amplitude at leading twist. Starting from the relevant matrix element in discrete Euclidean space on a set of $N_f=2$ CLS ensembles, we explain the method to connect to continuum Minkowski spacetime. After addressing several sources of systematic uncertainty, we compare to Dyson-Schwinger and non-relativistic QCD determinations of this quantity. We find significant deviations between the latter and our result even at small Ioffe times.

hep-lat↗

arXiv2024

The $η_c$-meson leading-twist distribution amplitude

In this project, we employ the short-distance factorization to compute the distribution amplitude of the $η_c$-meson from Lattice QCD at leading twist. We employ a set of CLS $N_f=2$ ensembles at three lattice spacings and various quark masses to extrapolate the pseudo distribution to the physical point in the isospin limit. We solve the inverse problem modeling the distribution amplitude, and we match our results to the light-cone in the $\overline{\text{MS}}$-scheme. We include a complete error budget, and we compare to two alternative approaches: non-relativistic QCD and Dyson-Schwinger equations, finding good agreement with the latter but not with the former.

hep-lat↗

arXiv2024

The distribution amplitude of the $η_c$-meson

In this proceeding we determine the distribution amplitude of the $η_c$-meson from first principles. This quantity appears as a consequence of factorization theorems, and it is necessary to compute the amplitude of multiple exclusive processes. Since it is defined along a light-cone, its calculation via lattice QCD was impossible until recently, when a generalization to Euclidean metric was proposed, and a connection to the physical limit was established. We briefly explain the method of short distance factorization, which allows us to compute the distribution amplitude, and our lattice setup. After summarizing the steps for the continuum and chiral extrapolation, we present our results and compare them to two alternative determinations, one using non-relativistic QCD and another solving the Dyson-Schwinger equations; we find a large discrepancy with the former.

hep-lat↗

arXiv2023

The distribution amplitude of the $η_c$ meson

We report on the first lattice determination of the pseudoscalar meson $η_c$ light-cone distribution amplitude, using a set of three CLS $N_f=2$ ensembles at a pion mass $m_π \sim 270~\text{MeV}$ and lattice spacings $a \sim 0.076~\text{fm}$, $0.066~\text{fm}$ and $0.049~\text{fm}$. Employing Short Distance Factorization, we extract the pseudo-DA on the lattice for Ioffe times $ν\leq 4.5$, and the various lattice spacings allow us to take the continuum limit. We employ a basis of Jacobi polynomials to parametrize the distribution amplitude, which allows to express the matching to the pseudo distribution in closed form, and we observe a strong effect which we attribute to the heavy charm-quark mass.

hep-lat↗

arXiv2022

Direct access to hadronic decay parameters with twisted boundary conditions

Our exploratory study looks for direct access to the resonant hadronic transition amplitude without resorting to the Lüscher formalism. We study the decay $Ψ(3770)\to\bar{D}D$ by applying partially twisted boundary conditions to the quenched charm quark, circumventing possible problems with final state interactions. If successful, we could compute the dependence of the transition amplitude on the charm-quark mass and test the predictions made by phenomenological quark-pair-creation models. Finally, we study if and to what extent an extraction of the excited state $Ψ(3770)$ is necessary for this analysis.

hep-lat↗

arXiv2022

Extraction of $B_s \to D^{(*)}_s$ form factors from ${ N_f}=2$ lattice QCD

We report on a two-flavour lattice QCD study of the $B_s \to D_s$ and $B_s \to D^*_s$ transitions parameterized, in the heavy quark limit, by the form factors ${\cal G}$, and $h_{A_1}$, $h_{A_2}$ and $h_{A_3}$, respectively. In the search for New Physics through tests of lepton flavour universality, $B_s$ decay channels are complementary to the $B$ decays widely studied at $B$ factories and LHCb, while on the theory side they can be better controlled than the $B_c$ and $Λ_b$ decays. The purpose of this exploratory two-flavour study is, in preparation for future analyses of lattice QCD simulations with ${N_f>2}$ and physical quark-masses, to gain experience on a suitable method for a lattice extraction of form factors associated with $b \to c$ currents that may yield tighter control over systematic effects like contamination from excited states and cut-off effects. We obtain the zero-recoil values ${\cal G}^{B_s \to D_s}(1)=1.03(14)$ and $h^{B_s \to D^*_s}(1)=0.85(16)$.

hep-lat↗

arXiv2021

$B_s \to D^{(*)}_s$ form factors from lattice QCD with ${ N_f}=2$ Wilson-clover quarks

We report on a two-flavour lattice QCD determination of the $B_s\to D_s$ and $B_s\to D_s^*$ transitions, which in the heavy quark limit can be parameterised by the form factors $\mathcal{G}$, and $h_{\text A_1}$, $h_{\text A_2}$ and $h_{\text A_3}$. In the search of New Physics through tests of lepton-flavour universality, $B_s$ decay channels are complementary to $B$ decays and widely studied at $B$ factories and LHCb. The purpose of our study is to explore a suitable method to extract form factors associated with $b\to c$ currents from lattice QCD. In particular, we present numerical results for $\mathcal{G}$ and $h_{\text A_1}$.

hep-lat↗

arXiv2020

Decay constant of $B_s$ and $B^*_s$ mesons from ${\rm N_f}=2$ lattice QCD}

We report on a two-flavor lattice QCD estimate of the $B_s$ and $B^*_s$ leptonic decays parameterized by the decay constants $f_{B_s}$ and $f_{B^*_s}$. In addition to their relevance for phenomenology, their extraction has allowed us to investigate whether the "step scaling in mass" strategy is suitable with Wlilson-Clover fermions to smoothly extrapolate quantities of the heavy-strange sector up to the bottom scale. From the central value of $f_{D_s}$ quoted by FLAG at $N_f=2$ and our ratio $\frac{f_{B_s}}{f_{D_s}}$, we obtain $f_{B_s}=215(10)(2)(^{+2}_{-5})$ MeV and $f_{B^*_s}/f_{B_s}=1.02(2)(^{+2}_{-0})$.

hep-lat↗

arXiv2018

Some hadronic parameters of charmonia in $\boldsymbol{N_{\text{f}}=2}$ lattice QCD

The phenomenology of leptonic decays of quarkonia holds many interesting features: for instance, it can establish constraints on scenarios beyond the Standard Model with the Higgs sector enriched by a light CP-odd state. In the following paper, we report on a two-flavor lattice QCD study of the $η_c$ and $J/ψ$ decay constants, $f_{η_c}$ and $f_{Jψ}$. We also examine some properties of the first radial excitation $η_c(2S)$ and $ψ(2S)$.

hep-lat↗

arXiv2017

On the $D^*_s$ and charmonia leptonic decays

Among the different scenarios of New Physics, those with an extended Higgs sector are examined with a lot of attention. Recent experimental observations of several anomalies in flavour physics with respect to expectations of the Standard Model further motivate the effort of phenomenologists. First, informations about the $R_{D_s}$ ratio, a test of lepton flavour universality equivalent to $R_D$, already measured, but with the $s$ quark as spectator, are awaited in coming years to constrain the corner of an extended Higgs sector with charged doublets. On another side, leptonic widths of pseudoscalar quarkonia are particularly interesting to test an extended Higgs sector with a light CP-odd Higgs boson singlet, through the study of its mixing with quarkonia states. Hadronic parameters entering those processes have to be determined from lattice QCD with enough confidence on the control of systematic errors. We report on the very first step of a long-term program tackled with ${\rm N_f}=2$ Wilson-Clover fermions to put relevant constraints on extensions of the Higgs sector: extraction of decay constants of $D^*_s$, $η_c$, $η_c(2S)$, $J/ψ$ and $ψ(2S)$ with lattice ensembles provided by the CLS effort, considering 2 lattice spacings and a large range of pion masses to estimate cut-off effects and extrapolate results to the chiral limit.

hep-lat↗

arXiv2016

Density distributions in the $B$ meson

We report on a two-flavor lattice QCD study of the axial, charge and matter distributions of the $B$ meson and its first radial excitation. As our framework is the static limit of Heavy Quark Effective Theory (HQET), taking their Fourier transform gives access to several form factors at the kinematical point $q^2=0$. Moreover they provide some useful information on the nature of an excited state, i.e. a radial excitation of a quark-antiquark bound state or a multihadron state.

hep-lat↗

arXiv2015

B-meson spectroscopy in HQET at order 1/m

We present a study of the B spectrum performed in the framework of Heavy Quark Effective Theory expanded to next-to-leading order in 1/m and non-perturbative in the strong coupling. Our analyses have been performed on Nf=2 lattice gauge field ensembles corresponding to three different lattice spacings and a wide range of pion masses. We obtain the Bs-meson mass and hyperfine splittings of the B- and Bs-mesons that are in good agreement with the experimental values and examine the mass difference m_{Bs}-m_B as a further cross-check of our previous estimate of the b-quark mass. We also report on the mass splitting between the first excited state and the ground state in the B and Bs systems.

hep-lat↗

arXiv2015

Renormalization of quark propagator, vertex functions and twist-2 operators from twisted-mass lattice QCD at $N_f$=4

We present a precise non-perturbative determination of the renormalization constants in the mass independent RI'-MOM scheme. The lattice implementation uses the Iwasaki gauge action and four degenerate dynamical twisted mass fermions. The gauge configurations are provided by the ETM Collaboration. Renormalization constants for scalar, pseudo-scalar, vector and axial operators, as well as the quark propagator renormalization, are computed at three different values of the lattice spacing, two volumes and several twisted mass parameters. The method we developed allows for a precise cross-check of the running, thanks to the particular proper treatment of hypercubic artifacts. Results for the twist-2 operator $O_{44}$ are also presented.

hep-lat↗

arXiv2015

Pion couplings to the scalar B meson

We present two-flavor lattice QCD estimates of the hadronic couplings $g_{B^*_0 B π}$ and $g_{B_1^* B_0^* π}$ that parametrise the non leptonic decays $B^*_0 \to B π$ and $B^*_1 \to B_0^* π$. We use CLS two-flavour gauge ensembles. Our framework is the Heavy Quark Effective Theory (HQET) in the static limit and solving a Generalized Eigenvalue Problem (GEVP) reveals crucial to disentangle the $B^*_0$($B^*_1$) state from the $B π$($B^*π$) state. This work brings us some experience on how to treat the possible contribution from multihadronic states to correlation functions calculated on the lattice, especially when $S$-wave states are involved.

hep-lat↗

arXiv2014

$B \to D^{**}$ -- puzzle 1/2 vs 3/2

Understanding the composition of final states in $B \to X_c l ν$ could help to get a feedback on the persisting disagreement between exclusive and inclusive determinations of $V_{cb}$. In particular the series of orbital excitations $D^{**}$ and radial excitations ($D'$, $D^*\,'$) has received a lot of attention; a misinterpretation as a scalar state of the ($D' \to D π$) spectrum tail could have induced an experimental overestimate of the broad states contribution to the total $B \to X_c l ν$ width with respect to theoretical expectations, all of them made however in the infinite mass limit: it is the so-called 1/2 vs 3/2 puzzle. We describe first attempts to measure on the lattice form factors of $B \to D^{**} l ν$ at realistic quark masses. Cleaner processes, like hadronic decays $B \to D^{**} π$ and semileptonic decays $B_s \to D_s^{**} l ν$ in the strange sector have recently been examined by phenomenologists, putting new interesting ideas on those issues with, again, the need of lattice inputs.

hep-ph↗