arXiv subjects

Marcel Wald

Publications and source records attributed to Marcel Wald.

8 recordsLinked to original sources

arXiv2024

NNLO beam functions for angularity distributions

The popular class of angularity event shapes provides a wealth of information on the hadronic final-state distribution in collider events. While initially proposed for $e^+ e^-$ collisions, angularities have more recently attracted considerable interest as a jet substructure observable at hadron colliders. Moreover, angularities can be measured as a global event shape in deep inelastic electron-nucleon scattering (DIS), and the respective factorisation theorem contains a beam function that parametrises the collinear initial-state radiation. In the present work, we compute the quark and gluon beam functions for seven different angularities to next-to-next-to-leading order (NNLO) in the strong-coupling expansion. Our calculation is based on an automated framework that was previously developed for SCET-2 observables, and which we transfer in the current work to the generic SCET-1 case. Our results are relevant for resumming DIS angularity distributions at NNLL$'$ accuracy.

hep-ph↗

arXiv2024

The NNLO gluon beam function for jet-veto resummation

We compute the gluon beam function for jet-veto resummation to next-to-next-to-leading order (NNLO) in the strong-coupling expansion. Our calculation is based on an automated framework that was previously used for the computation of the respective quark beam function, and which we significantly extended for the present calculation. In particular, the perturbative matching kernels are directly calculated in momentum space, without the need to perform an additional Mellin transform. We present results for both gluon and quark-initiated processes, which we cross-checked with an independent semi-analytical method that exploits the similarity of the beam functions to the more familiar case of transverse-momentum resummation. Our computation is relevant for jet-veto resummations at NNLL$'$ accuracy.

hep-ph↗

arXiv2023

Higher twist corrections to $B$-meson decays into a proton and dark antibaryon from QCD light-cone sum rules

The $B$-Mesogenesis framework anticipates decays of $B$ mesons into a dark antibaryon $\Psi$ and various Standard Model baryons. Here, we focus on the exclusive decay process $B\to p \Psi$ observed as a proton and missing energy in the final state and determine the decay width by employing the QCD light-cone sum rule framework. We include all contributions up to twist six to the nucleon distribution amplitudes in order to parameterize the non-perturbative effects in the operator product expansion. We obtain the decay width and branching fraction with respect to the mass $m_{\Psi}$ of the dark antibaryon $\Psi$, normalized to the model-dependent effective four-fermion coupling.

hep-ph↗

arXiv2022

Automated Calculation of Beam Functions at NNLO

We present an automated framework for the calculation of beam functions that describe collinear initial-state radiation at hadron colliders at next-to-next-to leading order (NNLO) in perturbation theory. By exploiting the infrared behaviour of the collinear matrix elements, we factorise the phase-space singularities with suitable observable-independent parametrisations. Our numerical approach applies to a large class of collider observables, and as a check of its validity, we compute the quark beam functions for transverse-momentum resummation and N-jettiness, which are known analytically at this order, finding excellent agreement.

hep-ph↗

arXiv2022

The NNLO quark beam function for jet-veto resummation

We consider the quark beam function that describes collinear initial-state radiation that is constrained by a veto on reconstructed jets. As the veto is imposed on the transverse momenta of the jets, the beam function is subject to rapidity divergences, and we use the collinear-anomaly framework to extract the perturbative matching kernels to next-to-next-to-leading order (NNLO) in the strong-coupling expansion. Our calculation is based on a novel framework that automates the computation of beam functions in Mellin space and it provides the ingredients to extend jet-veto resummations for quark-initiated processes to NNLL$'$ accuracy.

hep-ph↗

arXiv2022

$B$-meson decay into a proton and dark antibaryon from QCD light-cone sum rules

The recently developed $B$-Mesogenesis scenario predicts decays of $B$ mesons into a baryon and hypothetical dark antibaryon $\Psi$. We suggest a method to calculate the amplitude of the simplest exclusive decay mode $B^+\to p \Psi$. Considering two models of $B$-Mesogenesis, we obtain the $B\to p$ hadronic matrix elements by applying QCD light-cone sum rules with the proton light-cone distribution amplitudes. We estimate the $B^+\to p \Psi$ decay width as a function of the mass and effective coupling of the dark antibaryon.

hep-ph↗

arXiv2021

Automation of Beam and Jet functions at NNLO

We present a novel framework to streamline the calculation of jet and beam functions to next-to-next-to-leading order (NNLO) in perturbation theory. By exploiting the infrared behaviour of the collinear splitting functions, we factorise the singularities with suitable phase-space parametrisations and perform the observable-dependent integrations numerically. We have implemented our approach in the publicly available code {\tt pySecDec} and present first results for sample jet and beam functions.

hep-ph↗

arXiv2021

QCD sum rules for parameters of the $B$-meson distribution amplitudes

We obtain new estimates for the parameters $λ_{E}^2$, $λ_H^2$ and their ratio $\mathcal{R} = λ_{E}^2/λ_H^2$, which appear in the second moments of the $B$-meson light-cone distribution amplitudes defined in the heavy-quark effective field theory. The computation is based on two-point QCD sum rules for the diagonal correlation function and includes all contributions up to mass dimension seven in the operator-product expansion. For the ratio we get $\mathcal{R} = (0.1 \pm 0.1)$ with $λ_H^2 = (0.15 \pm 0.05) \, \text{GeV}^2$ and $λ_E^2 = (0.01 \pm 0.01) \, \text{GeV}^2$.

hep-ph↗