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Marcus Petschlies

Publications and source records attributed to Marcus Petschlies.

At least 19 recordsLinked to original sources
arXiv2026

Higher Mellin Moments of the Unpolarized PDF of the Pion and the Kaon from Lattice QCD

We present results on the Mellin moments of the unpolarized parton distribution function (PDF) of the pion and kaon up to the fourth order. The computation is done using one $N_f=2+1+1$ gauge ensemble of twisted mass fermions with quark masses tuned to approximately their physical values. We reconstruct the valence pion and kaon PDFs using the connected contributions to the three Mellin moments. We compare our results on the Mellin moments and the reconstructed PDFs with other lattice QCD and phenomenological determinations.

hep-lat↗
arXiv2025

$\eta$, $\eta^\prime$ mesons from lattice QCD in fully physical conditions

We determine masses and mixing parameters of the $\eta$ and $M_{\eta^\prime}$ meson in lattice QCD. The calculations are carried out on a set of 13 ETMC gauge ensembles with $N_f=2+1+1$ (maximally) twisted-mass Clover-improved quarks. These ensemble cover four values of the lattice spacing $a=0.057\mathrm{fm},...,0.092\mathrm{fm}$ and pion masses from $140\mathrm{MeV}$ to $360\mathrm{MeV}$, including three ensembles at physical quark masses and six ensembles with $M_\pi<200\mathrm{MeV}$. The strange-quark contribution is treated in a mixed-action approach using Osterwalder-Seiler fermions to avoid complications due to flavor mixing in the heavy quark sector and to enable the use of the one-end trick in the computation of strange quark-disconnected diagrams. With the strange-quark mass tuned to its physical value and several ensembles having close-to-physical light-quark mass, uncertainties related to the chiral extrapolations are reduced significantly compared to earlier studies. Physical results are computed with fully controlled systematics from a combined chiral, continuum and infinite-volume extrapolation, and a full error budget is obtained from model averages over of various fit ans\"atze and data cuts. Our results for the masses are given by $M_\eta=551(16)\mathrm{MeV}$ and $M_{\eta^\prime}=972(20)\mathrm{MeV}$, respectively, where statistical and systematic errors have been added in quadrature. For the mixing angle and decay-constant parameters the Feldmann-Kroll-Stech scheme is employed to compute them from pseudoscalar matrix elements in the quark-flavor basis. For the mixing angle we obtain $\phi^\mathrm{phys}=39.3(2.0)^\circ$ and our results for the decay-constant parameters are given by $f_l^\mathrm{phys}=138.6(4.4)\mathrm{MeV}$ and $f_s^\mathrm{phys}=170.7(3.3)\mathrm{MeV}$.

hep-lat↗
arXiv2025

Quark and gluon momentum fractions in the pion and in the kaon

We present results on the momentum fraction carried by quarks and gluons in the pion and the kaon. We employ three gauge ensembles generated with $N_f=2+1+1$ Wilson twisted-mass clover-improved fermions with physical quark masses. We perform, for the first time, a continuum extrapolation directly at the physical pion. We find that the total momentum fraction carried by quarks is $\langle x \rangle_{q, R}^{\pi}= 0.575(79)$ and $\langle x \rangle_{q,R}^{K} = 0.683(50)$ and by gluons $\langle x \rangle_{g, R}^{\pi}=0.402(53)$ and $\langle x \rangle_{g, R}^{K}=0.422(67)$ in the pion and in the kaon, respectively, in the $\overline{\mathrm{MS}}$ scheme and at the renormalization scale of 2 GeV. Having computed both the quark and gluon contributions in the continuum limit, we verify the momentum sum, finding 0.984(89) for the pion and 1.13(11) for the kaon.

hep-lat↗
arXiv2025

$B \to \rho \ell \bar{\nu}$ resonance form factors from $B \to \pi\pi \ell \bar{\nu}$ in lattice QCD

The decay $B \to \rho \ell \bar{\nu}$ is an attractive process for determining the magnitude of the smallest CKM matrix element, $|V_{ub}|$, and can provide new insights into the origin of the long-standing exclusive-inclusive discrepancy in determinations of this Standard-Model parameter. This requires a nonperturbative QCD calculation of the $B \to \rho$ form factors $V$, $A_0$, $A_1$, and $A_{12}$. The unstable nature of the $\rho$ resonance has prevented precise lattice QCD calculations of these form factors to date. Here, we present the first lattice QCD calculation of the $B \to \rho$ form factors in which the $\rho$ is treated properly as a resonance in $P$-wave $\pi \pi$ scattering. To this end, we use the Lellouch-L\"uscher finite-volume formalism to compute the $B \to \pi \pi$ form factors as a function of both momentum transfer and $\pi \pi$ invariant mass, and then analytically continue to the $\rho$ resonance pole. This calculation is performed with $2+1$ dynamical quark flavors at a pion mass of approximately 320 MeV, and demonstrates a clear path toward results at the physical point.

hep-lat↗
arXiv2024

Investigation of $\pi N$ contributions to nucleon matrix elements

We investigate an improved method to extract nucleon matrix elements from lattice 3-point functions using a generalized eigenvalue problem (GEVP) with nucleon and pion-nucleon interpolating fields. Our method avoids the computation of the costly three-point functions that have pion-nucleon interpolators at both source and sink. We demonstrate that excited state contamination from $N\pi$ is minimized in nucleon matrix elements of the scalar, vector, pseudoscalar, axial, and tensor currents and discuss our results based on a physical-point ensemble with a pion mass value of 131 MeV. We find that the GEVP is most significant for the isovector pseudoscalar and axial currents.

hep-lat↗
arXiv2024

Investigation of pion-nucleon contributions to nucleon matrix elements

We investigate contributions of excited states to nucleon matrix elements computed in lattice QCD by employing, in addition to the standard nucleon interpolating operator, pion-nucleon ($\pi$-$N$) operators. We solve a generalized eigenvalue problem (GEVP) to obtain an optimal interpolating operator that minimizes overlap with the $\pi$-$N$ states. We derive a variant of the standard application of the GEVP method, which allows for constructing 3-point correlation functions using the optimized interpolating operator without requiring the computationally demanding combination that includes $\pi$-$N$ operators in both sink and source. We extract nucleon matrix elements using two twisted mass fermion ensembles, one ensemble generated using pion mass of 346 MeV and one ensemble tuned to reproduce the physical value of the pion mass. Especially, we determine the isoscalar and isovector scalar, pseudoscalar, vector, axial, and tensor matrix elements. We include results obtained using a range of kinematic setups, including momentum in the sink. Our results using this variational approach are compared with previous results obtained using the same ensembles and multi-state fits without GEVP improvement. We find that for the physical mass point ensemble, the improvement, in terms of suppression of excited states using this method, is most significant for the case of the matrix elements of the isovector axial and pseudoscalar currents.

hep-lat↗
arXiv2024

Quark and gluon momentum fractions in the pion and in the kaon

We present the full decomposition of the momentum fraction carried by quarks and gluons in the pion and the kaon. We employ three gauge ensembles generated with $N_f=2+1+1$ Wilson twisted-mass clover-improved fermions at the physical quark masses. For both mesons we perform a continuum extrapolation directly at the physical pion mass, which allows us to determine for the first time the momentum decomposition at the physical point. We find that the total momentum fraction carried by quarks is 0.532(56) and 0.618(32) and by gluons 0.388(49) and 0.408(61) in the pion and in the kaon, respectively, in the $\overline{\mathrm{MS}}$ scheme and at the renormalization scale of 2 GeV. Having computed both the quark and gluon contributions in the continuum limit, we find that the momentum sum is 0.926(68) for the pion and 1.046(90) for the kaon, verifying the momentum sum rule.

hep-lat↗
arXiv2024

Lattice outlook on $B\to\rho\ell\bar{\nu}$ and $B\to K^\star \ell \ell$

Lattice Quantum Chromodynamics (QCD) has significantly contributed to our understanding of the CKM matrix through precise determinations of hadronic matrix elements. With advancements in theoretical methodologies and computational resources, investigations can now extend to processes involving QCD-unstable hadrons such as the $\rho$ and $K^\star(892)$. These resonances play vital roles in processes such as weak decays of $B$ mesons, opening new avenues for exploration. Finite-volume lattice QCD techniques involving complex computational methods are used to determine the transition amplitudes. Here, we present preliminary results for $B\to\rho\ell\bar{\nu}$.

hep-lat↗
arXiv2023

Investigation of two-particle contributions to nucleon matrix elements

We investigate contributions of excited states to nucleon matrix elements by studying the two- and three-point functions using nucleon and pion-nucleon interpolating fields. This study is carried out using twisted mass fermion ensembles with pion masses 346 MeV and 131 MeV. We compare the results obtained using these two ensembles and show preliminary results for nucleon charges.

hep-lat↗
arXiv2023

Exploring a new approach to Hadronic Parity Violation from Lattice QCD

The long-range, parity-odd nucleon interaction generated by single pion exchange is captured in the parity-odd pion-nucleon coupling $h^1_π$. Its calculation in lattice QCD requires the evaluation of 4-quark operator nucleon 3-point functions. We investigate a new numerical approach to compute $h^1_π$ based on nucleon matrix elements of parity-even 4-quark operators and related to the parity-violating electro-weak theory by PCAC and chiral perturbation theory. This study is performed with 2+1+1 dynamical flavors of twisted mass fermions at pion mass $m_π \approx 260\,\text{MeV}$ in a lattice box of $L \approx 3 \,\text{fm} $ and with a lattice spacing of $a \approx 0.091 \,\text{fm}$. From a calculation excluding fermion loop diagrams we find a bare coupling of $h^1_π= 8.08 \,(98) \cdot 10^{-7}$.

hep-lat↗
arXiv2023

Elastic Nucleon-Pion scattering amplitudes in the $\Delta$ channel at physical pion mass from Lattice QCD

We present an investigation of pion-nucleon elastic scattering in the $I\,(J^P) = \frac{3}{2}\,(\frac{3}{2}^+)$ channel using lattice QCD with degenerate up and down, strange and charm quarks with masses tuned to their physical values. We use an ensemble of twisted mass fermions with box size $L = 5.1\,\mathrm{fm}$ and lattice spacing $a = 0.08\,\mathrm{fm}$ and we consider the $\pi N$ system in rest and moving frames up to total momentum $\vec{P}^2 = 3\,(2\pi/L)^2$ = 0.17 GeV$^2$. We take into account the finite volume symmetries and $S$- and $P$-wave mixing, and use the L\"uscher formalism to simultaneously constrain the $J = 1/2,\,\ell = 0$ and $J = 3/2,\,\ell = 1$ scattering amplitudes. We estimate the $\Delta$ resonance pole in the $P$-wave channel as well as the $S$-wave isospin-3/2 scattering length.

hep-lat↗
arXiv2023

Hadronic Parity Violation from Twisted Mass Lattice QCD

We present results for an exploratory lattice calculation of the leading parity-violating pion-nucleon coupling $h_π^1$. 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 4-quark operators. For our study we employ an ensemble of twisted mass fermions with $260$ MeV pion mass. Barring mixing with lower-dimensional operators and renormalization at this stage, we discuss our estimate for $h_π^1$.

hep-lat↗
arXiv2023

Probing the energy-smeared R-ratio on the lattice

We present a first-principles lattice QCD investigation of the $R$-ratio between the $e^+e^-$ cross-section into hadrons and that into muons. By using the method of Ref.[1], that allows to extract smeared spectral densities from Euclidean correlators, we compute the $R$-ratio convoluted with Gaussian smearing kernels of widths of about $600$ MeV and central energies from $220$ MeV up to $2.5$ GeV. Our theoretical results are compared with the corresponding quantities obtained by smearing the KNT19 compilation [2] of $R$-ratio experimental measurements with the same kernels and, by centring the Gaussians in the region around the $ρ$-resonance peak, a tension of about three standard deviations is observed. From the phenomenological perspective, we have not included yet in our calculation QED and strong isospin-breaking corrections and this might affect the observed tension. From the methodological perspective, our calculation demonstrates that it is possible to study the $R$-ratio in Gaussian energy bins on the lattice at the level of accuracy required in order to perform precision tests of the Standard Model.

hep-lat↗
arXiv2023

A lattice QCD study of the $B \to ππ\ell \barν$ transition

$V_{ub}$ is the smallest and least known of all CKM matrix elements; the community currently determines its magnitude primarily through the exclusive process $B\toπ\ell\barν$. Here we present our progress toward a lattice QCD determination of the $V_{ub}$ matrix element from a novel transition -- $B\toππ\ell\barν$ process, where the $ππ$ system is in a $P$ wave and scattering features the $ρ(770)$ resonance as an enhancement. We perform our calculation on $N_f=2+1$ isotropic clover fermions on a lattice of $L\approx 3.6$ fm and a pion mass of $\approx 320$ MeV; for the $b$-quark we use the anisotropic clover action. After a brief overview of the theoretical framework, we will discuss some preliminary results.

hep-lat↗
arXiv2022

Lattice calculation of the R-ratio smeared with Gaussian kernel

The ratio $R(E)$ of the cross-sections for $e^+e^-\to$ hadrons and $e^+e^-\to μ^+μ^-$ is a valuable energy-dependent probe of the hadronic sector of the Standard Model. Moreover, the experimental measurements of $R(E)$ are the inputs of the dispersive calculations of the leading hadronic vacuum polarization contribution to the muon $g-2$ and these are in significant tension with direct lattice calculations and with the muon $g-2$ experiment. In this talk we discuss the results of our first-principles lattice study of $R(E)$. By using a recently proposed method for extracting smeared spectral densities from Euclidean lattice correlators, we have calculated $R(E)$ convoluted with Gaussian kernels of different widths $σ$ and central energies up to $2.5$ GeV. Our theoretical results have been compared with the KNT19 [1] compilation of experimental results smeared with the same Gaussian kernels and a tension (about three standard deviations) has been observed for $σ\sim 600$ MeV and central energies around the $ρ$-resonance peak.

hep-lat↗
arXiv2022

Pseudoscalar-pole contributions to the muon $g-2$ at the physical point

Pseudoscalar-pole diagrams are an important component of estimates of the hadronic light-by-light (HLbL) contribution to the muon $g-2$. We report on our computation of the transition form factors $\mathcal{F}_{P \rightarrow γ^* γ^*}$ for the neutral pseudoscalar mesons $P=π^0$ and $η$. The calculation is performed using twisted-mass lattice QCD with physical quark masses. On the lattice, we have access to a broad range of (space-like) photon four-momenta and therefore produce form factor data complementary to the experimentally accessible single-virtual direction, which directly leads to an estimate of the pion- and $η$-pole components of the muon $g-2$. For the pion, our result for the $g-2$ contribution in the continuum is comparable with previous lattice and data-driven determinations, with combined relative uncertainties below $10\%$. For the $η$ meson, we report on a preliminary determination from a single lattice spacing.

hep-lat↗
arXiv2022

Short \& intermediate distance HVP contributions to muon g-2: SM (lattice) prediction versus $e^+e^-$ annihilation data

We present new lattice results of the ETM Collaboration, obtained from extensive simulations of lattice QCD with dynamical up, down, strange and charm quarks at physical mass values, different volumes and lattice spacings, concerning the SM prediction for the so-called intermediate window (W) and short-distance (SD) contributions to the leading order hadronic vacuum polarization (LO-HVP) term of the muon anomalous magnetic moment, $a_μ$. Results for $a_μ^{\rm LO-HVP,W}$ and $a_μ^{\rm LO-HVP,SD}$, besides representing a step forward to a complete lattice computation of $a_μ^{\rm LO-HVP}$ and a useful benchmark among lattice groups, are compared here with their dispersive counterparts based on experimental data for $e^+e^-$ into hadrons. The comparison confirms the tension in $a_μ^{\rm LO-HVP,W}$, already noted in 2020 by the BMW Collaboration, while showing no tension in $a_μ^{\rm LO-HVP,SD}$.

hep-ph↗