arXiv subjects

Thomas Teubner

Publications and source records attributed to Thomas Teubner.

At least 19 recordsLinked to original sources

arXiv2026

Muon lifetime and Fermi constant: an update

We present an updated prediction for the lifetime of the muon including a detailed analysis of all relevant uncertainties. Our prediction includes QED corrections up to order $\alpha^3$ and state-of-the-art hadronic contributions based on dispersive methods. Radiative corrections and finite-electron-mass effects are parametrized by the correction factor $\Delta q$ in $\tau_\mu^{-1}=G_F^2m_\mu^5(1+\Delta q)/(192\pi^3)$, for which we obtain $\Delta q=(-4\, 384\, 678 \pm 34)\times 10^{-9}$. This reduces the uncertainty associated with $\Delta q$ by an order of magnitude compared to the previous prediction at order $\alpha^2$. We use our results to provide an updated value of the Fermi coupling constant, $G_F=1.166\,378\, 59 \, (59) \times 10^{-5} \, \mathrm{GeV}^{-2}$. Further improvements will require better measurements of the muon lifetime and mass.

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arXiv2026

Muon $g$$-$2: correlation-induced uncertainties in precision data combinations

We present a general and systematic framework to quantify uncertainties arising from imperfectly known systematic correlations in data combinations. Formulated at the level of the combined data, the method enables controlled variation of the correlation structure, leading to the construction of covariance matrices directly on the resulting combination and thus providing a robust and systematic estimate of correlation-induced uncertainties. We apply the method to $e^+e^- \to \mathrm{hadrons}$ cross section data, with the resulting covariance matrices propagated to derived observables, including dispersive determinations of the hadronic vacuum polarization (HVP) contribution to the muon anomalous magnetic moment, $a_\mu^\mathrm{HVP}$. We find that uncertainties from systematic correlation assumptions are generally subdominant but non-negligible, and do not fully account for differences between existing $e^+e^- \to \mathrm{hadrons}$ data combinations. The framework is broadly applicable to correlated data combinations in precision measurements and constitutes a new component of the upcoming KNTW data combination for $a_\mu^\mathrm{HVP}$.

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arXiv2024

Radiative corrections and Monte Carlo tools for low-energy hadronic cross sections in $e^+ e^-$ collisions

We present the results of Phase I of an ongoing review of Monte Carlo tools relevant for low-energy hadronic cross sections. This includes a detailed comparison of Monte Carlo codes for electron-positron scattering into a muon pair, pion pair, and electron pair, for scan and radiative-return experiments. After discussing the various approaches that are used and effects that are included, we show differential cross sections obtained with AfkQed, BabaYaga@NLO, KKMC, MCGPJ, McMule, Phokhara, and Sherpa, for scenarios that are inspired by experiments providing input for the dispersive evaluation of the hadronic vacuum polarisation.

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arXiv2024

Muon $g$$-$$2$: blinding for data-driven hadronic vacuum polarization

The KNT(W) data-driven determinations of the hadronic vacuum polarization (HVP) are crucial inputs to previous and future Standard Model (SM) predictions of the muon's anomalous magnetic moment, $a_\mu$. With the muon $g$$-$$2$'s new physics case uncertain due to disagreeing HVP evaluations, new SM predictions and experimental measurements of $a_\mu$ expected soon, and a complete revamp of the KNTW analysis framework underway, this letter motivates and describes a blinding scheme for data-driven HVP determinations that has been implemented for future KNTW analyses.

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arXiv2023

An alternative evaluation of the leading-order hadronic contribution to the muon g-2 with MUonE

We propose an alternative method to extract the leading-order hadronic contribution to the muon g-2, $a_{\mu}^\text{HLO}$, with the MUonE experiment. In contrast to the traditional method based on the integral of the hadronic contribution to the running of the effective fine-structure constant $\Delta\alpha_{had}$ in the space-like region, our approach relies on the computation of the derivatives of $\Delta\alpha_{had}(t)$ at zero squared momentum transfer $t$. We show that this approach allows to extract $\sim 99\%$ of the total value of $a_{\mu}^\text{HLO}$ from the MUonE data, while the remaining $\sim 1\%$ can be computed combining perturbative QCD and data on $e^+e^-$ annihilation to hadrons. This leads to a competitive evaluation of $a_{\mu}^\text{HLO}$ which is robust against the parameterization used to model $\Delta\alpha_{had}(t)$ in the MUonE kinematic region, thanks to the analyticity properties of $\Delta\alpha_{had}(t)$, which can be expanded as a polynomial at $t\sim 0$.

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arXiv2022

Implications of exclusive $J/\psi$ photoproduction in a tamed collinear factorisation approach to NLO

We discuss exclusive $J/\psi$ photoproduction, initially in conventional collinear factorisation at NLO and then subsequently in a refined approach with a programme of low $x$ resummation and implementation of a crucial low $Q_0$ subtraction included. We compare and contrast predictions in both frameworks and remark about the possibility to constrain and ultimately determine the low $x$ and low scale gluon PDF, emphasising the significance of this for future global PDF analyses.

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arXiv2022

Exclusive $J/\psi$ and $\Upsilon$ production in high energy $pp$ and $p$Pb collisions

We present a formalism for determining the cross section for exclusive heavy vector meson production ($J/\psi, \Upsilon$) as a function of rapidity, in both high energy proton-proton and proton-heavy ion collisions, at next-to-leading order in QCD. We compare and contrast the production in $pp$ and $p$Pb collisions and show how data for these processes can give information on the low $x$ gluon distribution of the proton and heavy ions at a range of different scales.

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arXiv2021

Mixed leptonic and hadronic corrections to the anomalous magnetic moment of the muon

Higher-order hadronic corrections to the anomalous magnetic moment of the muon have been evaluated including next-to-next-to-leading-order insertions of hadronic vacuum polarization and next-to-leading-order corrections to hadronic light-by-light scattering. This leaves a set of mixed leptonic and hadronic corrections in the form of double-bubble topologies as the only remaining hadronic effect at ${\mathcal O}(\alpha^4)$. Here, we estimate these contributions by analyzing the respective cuts of the diagrams, suggesting that the impact is limited to $\lesssim 1\times 10^{-11}$ and thus negligible at the level of the final precision of the Fermilab $g-2$ experiment.

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arXiv2021

Predictions of exclusive $\Upsilon$ photoproduction at the LHC and future colliders

The cross section for exclusive $\Upsilon$ ultraperipheral photoproduction at present and future colliders is determined using the low $x$ gluon PDF extracted from an analysis of exclusive $J/\psi$ measurements performed at HERA and the LHC. Predictions are given at next-to-leading order in collinear factorisation over a wide $\gamma p$ centre-of-mass energy range, calculated assuming the non-relativistic approximation for the $\Upsilon$ wave function, and with skewing corrections incorporated.

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arXiv2021

Exclusive heavy vector meson electroproduction to NLO in collinear factorisation

We compute the exclusive electroproduction, $\gamma^* p \rightarrow V p$, of heavy quarkonia $V$ to NLO in the collinear factorisation scheme, which has been formally proven for this process. The inclusion of an off-shell virtuality $Q^2$ carried by the photon extends the photoproduction phase space of the exclusive heavy quarkonia observable to electroproduction kinematics. This process is relevant for diffractive scattering at HERA and the upcoming EIC, as well as at the proposed LHeC and FCC.

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arXiv2020

Very low $x$ gluon density determined by LHCb exclusive $J/\psi$ data

The low $x$ behaviour of the gluon density $xg(x,\mu^2)$ at scale $\mu^2=2.4$ GeV$^2$ is determined using exclusive $J/\psi$ production data from HERA and LHCb within the framework of collinear factorisation at next-to-leading order (NLO). It is shown that in the interval $3\times 10^{-6} < x <10^{-3}$ the gluon distribution function grows as $xg(x,\mu^2)\propto x^{-\lambda}$ with $\lambda=0.135\pm 0.006 $. The impact this experimental data will have for the global parton distribution function (PDF) analyses in this low $x$ domain is quantified. No indication in favour of parton density saturation is observed.

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arXiv2020

The $g-2$ of charged leptons, $α(M_Z^2)$ and the hyperfine splitting of muonium

Following updates in the compilation of $e^+e^-\rightarrow{\rm hadrons}$ data, this work presents re-evaluations of the hadronic vacuum polarisation contributions to the anomalous magnetic moment of the electron ($a_e$), muon ($a_μ$) and tau lepton ($a_τ$), to the ground-state hyperfine splitting of muonium and also updates the hadronic contributions to the running of the QED coupling at the mass scale of the $Z$ boson, $α(M_Z^2)$. Combining the results for the hadronic vacuum polarisation contributions with recent updates for the hadronic light-by-light corrections, the electromagnetic and the weak contributions, the deviation between the measured value of $a_μ$ and its Standard Model prediction amounts to $Δa_μ = (28.02 \pm 7.37) \times 10^{-10}$, corresponding to a muon $g-2$ discrepancy of $3.8σ$.

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arXiv2019

How to include exclusive $J/\psi$ production data in global PDF analyses

We compare the cross section for exclusive $J/\psi$ photoproduction calculated at NLO in the collinear factorization approach with HERA and LHCb data. Using the optimum scale formalism together with the subtraction of the low $k_t<Q_0$ contribution from the NLO coefficient function to avoid double counting we show that the existing global parton distribution functions (PDFs) are consistent with the data within their uncertainties. However, at low $x$ the uncertainties of the present global PDFs are large. On the other hand, the accuracy of the LHCb data are rather good. Therefore, these data provide the possibility to directly measure the gluon PDF over the very large interval of $x$, $10^{-6}<x<10^{-2}$, at a fixed low scale.

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arXiv2019

Towards a determination of the low $x$ gluon via exclusive $J/ψ$ production

We discuss how the stability of the theoretical prediction for exclusive $J/ψ$ photoproduction has been improved through a systematic taming of the known $\overline{\text{MS}}$ coefficient functions by accounting for a formally power suppressed, but numerically significant, correction encoded within a $Q_0$ cut. The phenomenological implications of this will be emphasised meaning, ultimately, the possibility to include the exclusive data into a global fitter framework to provide constraints on the small $x$ gluon.

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arXiv2018

Exclusive Top Threshold Matching at Lepton Colliders

The threshold scan at future lepton colliders is the most precise known method to determine the top quark mass (well below 100 MeV), a fundamental parameter of the Standard Model that co-determines the stability properties of the electroweak vacuum. We present a new method to match the continuum next-to-leading order QCD corrections with the next-to-leading logarithmic resummation of the Coulomb singularities of the quasi-toponium bound state at threshold where fixed-order perturbation theory is invalid. This matching is performed at the level of the fully exclusive $W^+bW^-\bar{b}$ final state. It allows to study all kinds of differential distributions at or close to threshold. The top mass dependence of these distributions opens up new possibilities for the top mass determination that might be competitive with the inclusive threshold scan.

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arXiv2018

The strong coupling from $e^+e^-\to$ hadrons

We use a new compilation of the hadronic $R$-ratio from available data for the process $e^+e^-\to$ hadrons below the charm mass to determine the strong coupling $α_s$, using finite-energy sum rules. Quoting our results at the $τ$ mass to facilitate comparison to the results obtained from similar analyses of hadronic $τ$-decay data, we find $α_s(m_τ^2)=0.298\pm 0.016\pm 0.006$ in fixed-order perturbation theory, and $α_s(m_τ^2)=0.304\pm 0.018\pm 0.006$ in contour-improved perturbation theory, where the first error is statistical, and the second error combines various systematic effects. These values are in good agreement with a recent determination from the OPAL and ALEPH data for hadronic $τ$ decays. We briefly compare the $R(s)$-based analysis with the $τ$-based analysis.

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arXiv2018

The muon $g-2$ and $α(M_Z^2)$: a new data-based analysis

This work presents a complete re-evaluation of the hadronic vacuum polarisation contributions to the anomalous magnetic moment of the muon, $a_μ^{\rm had, \, VP}$ and the hadronic contributions to the effective QED coupling at the mass of the $Z$ boson, $Δα_{\rm had}(M_Z^2)$, from the combination of $e^+e^-\rightarrow {\rm hadrons}$ cross section data. Focus has been placed on the development of a new data combination method, which fully incorporates all correlated statistical and systematic uncertainties in a bias free approach. All available $e^+e^-\rightarrow {\rm hadrons}$ cross section data have been analysed and included, where the new data compilation has yielded the full hadronic $R$-ratio and its covariance matrix in the energy range $m_π\leq\sqrt{s}\leq 11.2$ GeV. Using these combined data and pQCD above that range results in estimates of the hadronic vacuum polarisation contributions to $g-2$ of the muon of $a_μ^{\rm had, \, LO \, VP} = (693.27 \pm 2.46)\times 10^{-10}$ and $a_μ^{\rm had, \, NLO \, VP} = (-9.82 \pm 0.04)\times 10^{-10}$. The new estimate for the Standard Model prediction is found to be $a_μ^{\rm SM} = (11\ 659 \ 182.05 \pm 3.56) \times 10^{-10}$, which is $3.7σ$ below the current experimental measurement. The prediction for the five-flavour hadronic contribution to the QED coupling at the $Z$ boson mass is $Δα_{\rm had}^{(5)}(M_Z^2)= (276.11 \pm 1.11)\times 10^{-4}$, resulting in $α^{-1}(M_Z^2) = 128.946 \pm 0.015$. Detailed comparisons with results from similar related works are given.

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arXiv2018

The strong coupling from $e^+e^-\to$ hadrons below charm

We use a new compilation of the hadronic $R$-ratio from available data for the process $e^+e^-\to\mbox{hadrons}$ to determine the strong coupling, $α_s$. We make use of all data for the $R$-ratio from threshold to a center-of-mass energy of 2 GeV by employing finite-energy sum rules. Data above 2 GeV, for which at present far fewer high-precision experimental data are available, do not provide much additional constraint but are fully consistent with the values for $α_s$ we obtain. Quoting our results at the $τ$ mass to facilitate comparison to the results obtained from analogous analyses of hadronic $τ$-decay data, we find $α_s(m_τ^2)=0.298\pm 0.016\pm 0.006$ in fixed-order perturbation theory, and $α_s(m_τ^2)=0.304\pm 0.018\pm 0.006$ in contour-improved perturbation theory, where the first error is statistical, and the second error reflects our estimate of various systematic effects. These values are in good agreement with a recent determination from the OPAL and ALEPH data for hadronic $τ$ decays.

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