arXiv subjects

Florian Herren

Publications and source records attributed to Florian Herren.

At least 19 recordsLinked to original sources

arXiv2026

Closing the knowledge gap in semileptonic $B\rightarrow X_c\ellν$ decays

In this work we summarize the current status of measured exclusive semileptonic branching fractions containing charm mesons. We use the available experimental data to evaluate the difference between the sum of exclusive measurements and the inclusive determination. By including experimental results of branching fractions relative to semi-inclusive $B\rightarrow D X\ellν$ decays, we demonstrate that the unmeasured components of the total branching fraction are dominated by final states devoid of $D$ mesons, hinting towards sizeable contributions from baryonic final states and $D_s$ mesons. Based on the obtained fractions, we discuss candidates that could potentially close the remaining difference and propose searches for promising final states. Furthermore, we provide simplified models for S-wave $B\rightarrow Dη\ellν$ and $B\rightarrow D_s K\ellν$ decays that contribute marginally to the unmeasured components of the total inclusive rate.

hep-ph↗

arXiv2026

On the simulated kinematic distributions of heavy meson decays

Modern measurements in flavour physics rely on accurate simulations of signal and background processes, provided by a wide range of general-purpose and specialised Monte-Carlo event generators. Due to the inclusion of a larger amount of specialised decays of heavy hadrons, EvtGen is often the tool of choice for many scenarios. We investigate the phase-space sampling algorithm of EvtGen and demonstrate that it generates unphysical features in kinematic distributions of semileptonic $B$ decays involving resonances, originating from neglected phase-space factors. We provide a short-term solution to correct the affected simulated samples through reweighting of the hadronic invariant mass distribution.

hep-ph↗

arXiv2026

Advanced parametrisations for hadronic form factors

The rich analytic structure of hadronic form factors makes a theoretically consistent yet easily applicable parametrisation cumbersome. Consequently, most parametrisations are limited to reproducing the simplest analytic features sufficient to describe form factors on their first Riemann sheet. Here, we introduce two novel form factor parametrisations that allow resonance poles and left-hand cuts on the second Riemann sheet to be studied, while also making the connection to partial-wave amplitudes manifest.

hep-ph↗

arXiv2025

A model-independent parameterization of $B\rightarrowππ\ellν$ decays

We introduce a novel parameterization of $B\rightarrowππ\ellν$ form factors relying on partial-wave decompositions and series expansions in suitable variables. We bound the expansion coefficients through unitarity and include left-hand cut contributions using established dispersive methods. The two-hadron lineshapes are treated in a model-independent manner using Omnès functions, thus allowing for a data-driven determination of the expansion parameters. We study the underlying composition of the di-pion system in $B\rightarrowππ\ellν$ decays through fits to differential spectra of $B^{+} \rightarrow π^{+}π^{-} \ell^+ ν$ measured by the Belle experiment. In contrast to previous works, we are able to study the full phase-space and are not limited to certain kinematic regions. As a consequence, we extract branching fractions for the different partial waves of the di-pion system. We find: \begin{align*} \mathcal{B}(B^+\rightarrow (π^+ π^-)_S \ell^+ ν) &= 2.2^{+1.4}_{-1.0}\times 10^{-5}\,,\\ \mathcal{B}(B^+\rightarrow (π^+ π^-)_P \ell^+ν) &= 19.6^{+2.8}_{-2.7}\times 10^{-5}\,,\\ \mathcal{B}(B^+\rightarrow (π^+ π^-)_D \ell^+ ν) &= 3.5^{+1.3}_{-1.1}\times 10^{-5}\,.\\ \end{align*} In addition, we derive predictions for the thus far unobserved $B^+\rightarrow π^0π^0\ell^+ν$ decay and obtain a sizeable branching fraction of $\mathcal{B}(B^+\rightarrow π^0π^0\ell^+ν) = 2.9^{+0.9}_{-0.7}\times 10^{-5}$.

hep-ph↗

arXiv2024

A model independent description of $B\rightarrow D π\ell ν$ decays

We introduce a new parameterization of $B\rightarrow D π\ell ν$ form factors using a partial-wave expansion and derive bounds on the series coefficients using analyticity and unitarity. This is the first generalization of the model-independent formalism developed by Boyd, Grinstein, and Lebed for $B \to D \ell ν$ to semileptonic decays with multi-hadron final states, and enables data-driven form factor determinations with robust, systematically-improvable uncertainties. Using this formalism, we extract the form-factor parameters for $B \to D_2^\ast(\to Dπ) \ell ν$ decays in a model-independent way from fits of data from the Belle Experiment, and, for the first time, study the two-pole structure in the $Dπ$ S-wave in semileptonic decays employing lineshapes from unitarized chiral perturbation theory.

hep-ph↗

arXiv2024

ALARIC: A NLL accurate Parton Shower algorithm

In this contribution, we summarize the key concepts behind the next-to-leading-logarithm accurate parton shower algorithm ALARIC. We discuss tests of the logarithmic accuracy and present comparisons to LEP data.

hep-ph↗

arXiv2024

Model-independent description of $B\rightarrow D π\ell ν$ decays

In this contribution we present a novel, model-independent description of semileptonic $B\rightarrow D π\ell ν$ decays. In addition, we discuss recent developments in the understanding of coupled-channel $D π$-$D η$-$D_s K$ S-wave scattering and, for the first time, apply them to semileptonic decays. We not only obtain model-independent predictions for kinematic distributions in $B\rightarrow D π\ell ν$ decays, but also rule out the hypothesis that the gap between the inclusive $B\rightarrow X\ellν$ branching fraction and the sum over exclusive channels is made up predominantly by $B\rightarrow D^{(\ast)} η\ell ν$ decays.

hep-ph↗

arXiv2024

NNLO QCD corrections to the $q^2$ spectrum of inclusive semileptonic $B$-meson decays

We calculate the next-to-next-to-leading order QCD corrections to the leptonic invariant mass ($q^2$) spectrum of semileptonic $b \to c$ inclusive decays, taking into account the mass of the charm quark and the charged lepton in the final state. We obtain analytic results in terms of generalized polylogarithms and present numerical studies of the $\mathcal{O}(α_s^2)$ corrections to the $q^2$ spectrum of $b \to c \ell \bar ν_\ell$ decays, for $\ell =e, μ$ and $τ$, in the kinetic scheme. Our computation can be used to incorporate the recent measurements of $q^2$ moments by Belle and Belle II into global fits of inclusive semileptonic $B$-decays.

hep-ph↗

arXiv2023

Simulating $\mathbb{Z}_2$ lattice gauge theory on a quantum computer

The utility of quantum computers for simulating lattice gauge theories is currently limited by the noisiness of the physical hardware. Various quantum error mitigation strategies exist to reduce the statistical and systematic uncertainties in quantum simulations via improved algorithms and analysis strategies. We perform quantum simulations of $1+1d$ $\mathbb{Z}_2$ gauge theory with matter to study the efficacy and interplay of different error mitigation methods: readout error mitigation, randomized compiling, rescaling, and dynamical decoupling. We compute Minkowski correlation functions in this confining gauge theory and extract the mass of the lightest spin-1 state from fits to their time dependence. Quantum error mitigation extends the range of times over which our correlation function calculations are accurate by a factor of six and is therefore essential for obtaining reliable masses.

hep-lat↗

arXiv2023

A new approach to color-coherent parton evolution

We present a simple parton-shower model that replaces the explicit angular ordering of the coherent branching formalism with a differentially accurate simulation of soft-gluon radiation by means of a non-trivial dependence on azimuthal angles. We introduce a global kinematics mapping and provide an analytic proof that it satisfies the criteria for next-to leading logarithmic accuracy. In the new algorithm, initial and final state evolution are treated on the same footing. We provide an implementation for final-state evolution in the numerical code Alaric and present a first comparison to experimental data.

hep-ph↗

arXiv2023

Efficient phase-space generation for hadron collider event simulation

We present a simple yet efficient algorithm for phase-space integration at hadron colliders. Individual mappings consist of a single t-channel combined with any number of s-channel decays, and are constructed using diagrammatic information. The factorial growth in the number of channels is tamed by providing an option to limit the number of s-channel topologies. We provide a publicly available, parallelized code in C++ and test its performance in typical LHC scenarios.

hep-ph↗

arXiv2022

$\texttt{tapir}$: A tool for topologies, amplitudes, partial fraction decomposition and input for reductions

The demand for precision predictions in the field of high energy physics has dramatically increased over recent years. Experiments conducted at the LHC, as well as precision measurements at the intensity frontier such as Belle II require equally precise theoretical predictions to make full use of the acquired data. To match the experimental precision, two-, three- and, for certain quantities, even higher-loop calculations are required. To facilitate such calculations, computer software automating as many steps as possible is required. Yet, each calculation poses different challenges and thus, a high level of configurability is required. In this context we present $\texttt{tapir}$: a tool for identification, manipulation and minimization of Feynman integral families. It is designed to integrate in $\texttt{FORM}$-based toolchains which is common practice in the field. $\texttt{tapir}$ can be used to reduce the complexity of multi-loop problems with cut-filters, topology mapping, partial fraction decomposition and alike.

hep-ph↗

arXiv2022

The forward-backward asymmetry and differences of partial moments in inclusive semileptonic B decays

Global fits to moments of kinematic distributions measured in inclusive semileptonic $B\rightarrow X_c l ν_l$ enable the determination of the Cabibbo-Kobayashi-Maskawa matrix element $|V_{cb}|$ together with non-perturbative matrix elements of the heavy quark expansion. In current fits, only two distinct kinematic distributions are employed and, as a consequence, higher moments of these distributions need to be taken into account to extract the relevant non-perturbative matrix elements. The moments of a given distribution are highly correlated and experimental uncertainties increase for higher moments. To address these issues, Turczyk suggested the inclusion of the charged lepton forward-backward asymmetry $\mathcal{A}_{FB}$ in global fits, since it provides information on non-perturbative parameters beyond the commonly used moments. It is possible to construct differences of partial moments of kinematic distributions, which can provide additional information on the non-perturbative parameters beyond $\mathcal{A}_{FB}$ and are studied in this work for the first time. Further, experimental cuts on the four-momentum transfer square are studied and are shown to preserve the shape of the angular distribution, in contrast to commonly used cuts on the lepton energy. Finally, the impact of final-state radiation and experimental lepton identification requirements on measurements of $\mathcal{A}_{FB}$ and differences of partial moments are discussed.

hep-ph↗

arXiv2021

Higher-order $β$-functions in the Standard Model and beyond

In this contribution we consider the recent computation of the gauge coupling $β$-function at four loops and the Yukawa matrix $β$-function at three loops in the most general, renormalizable and four-dimensional quantum field theory. Furthermore, we discuss ambiguities and divergences arising in Yukawa matrix $β$-functions.

hep-ph↗

arXiv2021

General Gauge-Yukawa-Quartic $β$-Functions at 4-3-2--Loop Order

We determine the full set of coefficients for the completely general 4-loop gauge and 3-loop Yukawa $ β$-functions for the most general renormalizable four-dimensional theories. Using a complete parametrization of the $ β$-functions, we compare the general form to the specific $ β$-functions of known theories to constrain the unknown coefficients. The Weyl consistency conditions provide additional constraints, completing the determination.

hep-ph↗

arXiv2021

Real corrections to Higgs boson pair production at NNLO in the large top quark mass limit

In this paper we consider the next-to-next-to-leading order total cross section of Higgs boson pair production in the large top quark mass limit and compute four expansion terms in $1/m_t^2$. Good convergence is observed below the top quark threshold, which makes our results a valuable input for approximation methods which aim for next-to-next-to-leading order corrections over the whole kinematic range. We present details on various steps of our calculation; in particular, we provide results for three- and four-particle phase-space master integrals and describe in detail the evaluation of the collinear counterterms.

hep-ph↗

arXiv2021

On Ambiguities and Divergences in Perturbative Renormalization Group Functions

There is an ambiguity in choosing field-strength renormalization factors in the $ \overline{\text{MS}} $ scheme starting from the 3-loop order in perturbation theory. More concerning, trivially choosing Hermitian factors has been shown to produce divergent renormalization group functions, which are commonly understood to be finite quantities. We demonstrate that the divergences of the RG functions are such that they vanish in the RG equation due to the Ward identity associated with the flavor symmetry. It turns out that any such divergences can be removed using the renormalization ambiguity and that the use of the flavor-improved $ β$-function is preferred. We show how our observations resolve the issue of divergences appearing in previous calculations of the 3-loop SM Yukawa $ β$-functions and provide the first calculation of the flavor-improved 3-loop SM $ β$-functions in the gaugeless limit.

hep-th↗

arXiv2021

Higgs boson decay into photons at four loops

Future precision measurements of Higgs boson decays will determine the branching fraction for the decay into two photons with a precision at the one percent level. To fully exploit such measurements, equally precise theoretical predictions need to be available. To this end we compute four-loop QCD corrections in the large top quark mass expansion to the Higgs boson--photon form factor, which enter the two-photon decay width at next-to-next-to-next-to-leading order. Furthermore we obtain corrections to the two-photon decay width stemming from the emission of additional gluons, which contribute for the first time at next-to-next-to-leading order. Finally, we combine our results with other available perturbative corrections and estimate the residual uncertainty due to missing higher-order contributions.

hep-ph↗