arXiv subjects

Sandro Mächler

Publications and source records attributed to Sandro Mächler.

9 recordsLinked to original sources

arXiv2026

New Physics in inclusive $\bar{B} \to X_c \ell \barν$ decays

We present the first global phenomenological fit of inclusive $\bar B\to X_c\ell\barν$ observables to all available experimental data allowing for generic dimension-six New Physics interactions in the Weak Effective Theory. The fit includes both New Physics Wilson coefficients and non-perturbative QCD parameters. New Physics contributions are calculated including power corrections up to $\mathcal O(Λ_{\rm QCD}^3/m_b^3)$ and perturbative QCD corrections up to $\mathcal O(α_s)$. We find no significant preference for New Physics and obtain bounds on the size of the relevant Wilson Coefficients competitive with those coming from exclusive modes.

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arXiv2025

New Physics in inclusive semileptonic $B$ decays

We study inclusive semileptonic $\bar{B}\to X_c \ell \barν$ decays ($\ell = e,μ$) in the presence of generic physics Beyond the Standard Model (BSM) that is heavy compared to the $b$-quark mass. Its effect is encoded in the Wilson coefficients of dimension-six operators of the Weak Effective Theory (WET). We compute the resulting BSM contributions to the experimentally measured kinematic moments and the total decay rate through order $\mathcal{O}(Λ_{\rm QCD}^3/m_b^3)$ in the Heavy Quark Expansion, as well as the $\mathcal{O}(α_s)$ corrections for the right-handed vector current. We then perform fits to the full set of available inclusive measurements in several single-mediator scenarios and in the full WET basis. We find qualitatively new bounds in several of these scenarios, complementary to and competitive with constraints from exclusive decays.

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arXiv2024

Short- vs. long-distance physics in $B\to K^{(*)} \ell^+\ell^-$: a data-driven analysis

We analyze data on $B\to Kμ^+μ^-$ and $B\to K^*μ^+μ^-$ decays in the whole dilepton invariant mass spectrum with the aim of disentangling short- vs. long-distance contributions. The sizable long-distance amplitudes from $c \bar{c}$ narrow resonances are taken into account by employing a dispersive approach. For each available $q^2=m_{μμ}^2$ bin and each helicity amplitude an independent determination of the Wilson coefficient $C_9$, describing $b\to s\ell^+\ell^-$ transitions at short distances, is obtained. The consistency of the $C_9$ values thus obtained provides an a posteriori check of the absence of additional, sizable, long-distance contributions. The systematic difference of these values from the Standard Model expectation supports the hypothesis of a non-standard $b\to s μ^+μ^-$ amplitude of short-distance origin.

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arXiv2023

On the study of inclusive semileptonic decays of $B_s$-meson from lattice QCD

In this contribution we describe a recent study focused on the lattice calculation of inclusive decay rates of heavy mesons. We show how the inclusive calculation can be achieved starting from four-point lattice correlation functions normalised appropriately. The correlators used in this project come from gauge ensembles provided by the JLQCD and ETM collaborations. An essential point of this method is the extraction of spectral densities from lattice correlators which is obtained using two of the most recent approaches in the literature. Our results are in remarkable agreement with analytical predictions from the operator-product expansion. This study represents the first step towards a full lattice QCD study of heavy mesons inclusive semileptonic decays.

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arXiv2023

Finite $W$ mass corrections to inclusive $B$ decays

We compute the effects of a finite $W$ boson mass on the inclusive $b\rightarrow c \ell ν$ decay rate and the semileptonic moments. To this end we keep terms of $\mathcal{O}\left(q^2/m_W^2 \right)$ when integrating out the $W$ boson in the Weak Effective Theory. In the third hadronic invariant mass moment such corrections reach the $0.5\%$ level but they are smaller than the present-day experimental uncertainties in all observables.

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arXiv2022

Inclusive semileptonic $B$-decays from lattice QCD

We present the lattice QCD calculation of inclusive semileptonic $B_s$-meson decays. We follow a recently proposed method, which is based on the extraction of smeared spectral densities from Euclidean correlation functions and on the numerical reconstruction of the integration kernel relevant for the inclusive decay rate calculation. We compute four-point Euclidean correlation functions using JLQCD and ETM gauge ensembles with unphysically light $b$-quark masses, and apply two different methods for the integration kernel reconstruction. Finally, we show that the lattice results obtained in this work are in good agreement with the analytic predictions of the operator-product-expansion. This opens the path for a future full lattice QCD calculation to be used as theoretical input for the determination of the magnitude of the CKM element $V_{cb}$.

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arXiv2022

Towards the computation of inclusive decay rates using lattice QCD

We present a non-perturbative computation of inclusive rates of semileptonic decays of heavy mesons from lattice QCD simulations. The calculation is based on the extraction of smeared spectral functions obtained from four-point Euclidean correlation functions computed on configuration ensembles of the JLQCD and ETM collaborations. We compare our results for the inclusive decay rates with analytical predictions from the operator-product expansion, finding a good agreement for the calculation of the inclusive decay rate. This opens the path to the theoretical determination of the magnitude of the Cabibbo-Kobayashi-Maskawa matrix element $V_{cb}$ to a level of precision competitive with the present experimental uncertainty.

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arXiv2022

Lattice QCD study of inclusive semileptonic decays of heavy mesons

We present an ab initio study of inclusive semileptonic decays of heavy mesons from lattice QCD. Our approach is based on a recently proposed method, that allows one to address the study of these decays from the analysis of smeared spectral functions extracted from four-point correlators on the lattice, where the smearing is defined in terms of the phase-space integration relevant to the inclusive decays. We present results obtained from gauge-field ensembles from the JLQCD and ETM collaborations, and discuss their relation with theoretical predictions from the operator-product expansion.

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arXiv2021

Comparison of lattice QCD results for inclusive semi-leptonic decays of $B$ mesons with the OPE

A recently proposed approach to compute the inclusive semi-leptonic decay rate on the lattice allows for the calculation of various quantities (differential distributions and moments) in different subchannels. We systematically compare the lattice QCD results for an unphysically light bottom quark with OPE-based predictions, including leading order perturbative and $\mathcal{O}\left(1/m^3 \right)$ power corrections, and explore possible strategies to decrease the systematic uncertainty.

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