arXiv subjects

Pier Francesco Monni

Publications and source records attributed to Pier Francesco Monni.

At least 37 records · Page 2Linked to original sources

arXiv2024

A collinear shower algorithm for NSL non-singlet fragmentation

We formulate a collinear partonic shower algorithm that achieves next-to-single-logarithmic (NSL, $α_s^n L^{n-1}$) accuracy for collinear-sensitive non-singlet fragmentation observables. This entails the development of an algorithm for nesting triple-collinear splitting functions. It also involves the inclusion of the one-loop double-collinear corrections, through a $z$-dependent NLO-accurate effective $1\to 2$ branching probability, using a formula that can be applied more generally also to future full showers with $1\to3$ splitting kernels. The specific NLO branching probability is calculated in two ways, one based on slicing, the other using a subtraction approach based on recent analytical calculations. We close with demonstrations of the shower's accuracy for non-singlet partonic fragmentation functions and the energy spectrum of small-$R$ quark jets. This work represents an important conceptual step towards general NNLL accuracy in parton showers.

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arXiv2024

Exploring high-purity multi-parton scattering at hadron colliders

Multi-parton interactions are a fascinating phenomenon that occur in almost every high-energy hadron--hadron collision, yet are remarkably difficult to study quantitatively. In this letter we present a strategy to optimally disentangle multi-parton interactions from the primary scattering in a collision. That strategy enables probes of multi-parton interactions that are significantly beyond the state of the art, including their characteristic momentum scale, the interconnection between primary and secondary scatters, and the pattern of three and potentially even more simultaneous hard scatterings. This opens a path to powerful new constraints on multi-parton interactions for LHC phenomenology and to the investigation of their rich field-theoretical structure.

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arXiv2024

Collinear fragmentation at NNLL: generating functionals, groomed correlators and angularities

Jet calculus offers a unique mathematical technique to bridge the area of QCD resummation with Monte Carlo parton showers. With the ultimate goal of constructing next-to-next-to-leading logarithmic (NNLL) parton showers we study, using the language of generating functionals, the collinear fragmentation of final-state partons. In particular, we focus on the definition and calculation of the Sudakov form factor, which physically describes the no-emission probability in an ordered branching process. We review recent results for quark jets and compute the Sudakov form factor for the collinear fragmentation of gluon jets at NNLL. The NNLL corrections are encoded in a $z$ dependent two-loop anomalous dimension $B_2(z)$, with $z$ being a suitably defined longitudinal momentum fraction. This is obtained from the integration of the relevant $1\to 3$ collinear splitting kernels combined with the one-loop corrections to the $1\to 2$ counterpart. This work provides the missing ingredients to extend the methods of jet calculus in the collinear limit to NNLL and gives an important element of the next generation of NNLL parton shower algorithms. As an application we derive new NNLL results for both the fractional moments of energy-energy correlation $FC_x$ and the angularities $λ_x$ measured on mMDT/Soft-Drop ($β=0$) groomed jets.

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arXiv2023

Introduction to the PanScales framework, version 0.1

In this article, we document version 0.1 of the PanScales code for parton shower simulations. With the help of a few examples, we discuss basic usage of the code, including tests of logarithmic accuracy of parton showers. We expose some of the numerical techniques underlying the logarithmic tests and include a description of how users can implement their own showers within the framework. Some of the simpler logarithmic tests can be performed in a few minutes on a modern laptop. As an early step towards phenomenology, we also outline some aspects of a preliminary interface to Pythia, for access to its hard matrix elements and its hadronisation modules.

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arXiv2022

Momentum-space resummation for transverse observables and the Higgs $p_\perp$ at N$^3$LL+NNLO

We present an approach to the momentum-space resummation of global, recursive infrared and collinear safe observables featuring kinematic zeros away from the Sudakov limit. In the hadro-production of a generic colour singlet, we consider the family of inclusive observables which do not depend on the rapidity of the radiation, prime examples being the transverse momentum of the singlet, and $ϕ^*$ in Drell-Yan pair production. We derive a resummation formula valid up to next-to-next-to-next-to-leading-logaritmic accuracy for the considered observables. This formula reduces exactly to the customary resummation performed in impact-parameter space in the known cases, and it also predicts the correct power-behaved scaling of the cross section in the limit of small value of the observable. We show how this formalism is efficiently implemented by means of Monte Carlo techniques in a fully exclusive generator that allows one to apply arbitrary cuts on the Born variables for any colour singlet, as well as to automatically match the resummed results to fixed-order calculations. As a phenomenological application, we present state-of-the-art predictions for the Higgs-boson transverse-momentum spectrum at the LHC at next-to-next-to-next-to-leading-logarithmic accuracy matched to fixed next-to-next-to-leading order.

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arXiv2022

Theory uncertainties in the fiducial Drell-Yan cross section and distributions

In these proceedings we study various sources of theoretical uncertainty in the Drell-Yan $p_T^{\ell\ell}$ spectrum focussing on the $p_T^{\ell\ell} \lesssim 100\, {\rm GeV}$ region. We consider several perturbative aspects related to the choice of the scale setting adopted in resummed calculations, and we assess their impact on the theoretical prediction both for the differential $p_T^{\ell\ell}$ spectrum and for the $\rm{N}^3\rm{LO}$ fiducial cross section. For both quantities, we find the results obtained with the different setups to be compatible with each other within the quoted uncertainty, highlighting the robustness of the theoretical prediction. In all cases, the experimental LHC data for the $p_T^{\ell\ell}$ spectrum is well described by our calculation.

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arXiv2022

The analytic two-loop soft function for leading-jet $p_T$

We present the calculation of the two-loop soft function for the transverse momentum distribution of the leading jet produced in association with any colour-singlet system (e.g.~a Higgs or a $Z$ boson). This constitutes a central ingredient for the resummation of the above distribution as well as the jet-vetoed cross section at the next-to-next-to-next-to-leading logarithmic order, both of which play an important role in the precision physics programme at the Large Hadron Collider. The calculation is performed in soft-collinear effective theory with an appropriate regularisation of the rapidity divergences that occur in the phase-space integrals. We obtain analytic results by employing an exponential regulator and by taking a Laurent expansion in the jet radius $R$. All expressions are presented as ancillary files with this article.

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arXiv2022

NNLO+PS with MiNNLO$_{\rm PS}$: status and prospects

We summarize the current status and near future prospects for next-to-next-to-leading order calculations matched to parton shower based on the MiNNLO$_{\rm PS}$ method. We give a theoretical overview, illustrate selected results for $ZZ\to 4\ell$ and top-pair production processes at the LHC, and provide an outlook of the future challenges.

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arXiv2022

Leveraging universality of jet taggers through transfer learning

A significant challenge in the tagging of boosted objects via machine-learning technology is the prohibitive computational cost associated with training sophisticated models. Nevertheless, the universality of QCD suggests that a large amount of the information learnt in the training is common to different physical signals and experimental setups. In this article, we explore the use of transfer learning techniques to develop fast and data-efficient jet taggers that leverage such universality. We consider the graph neural networks LundNet and ParticleNet, and introduce two prescriptions to transfer an existing tagger into a new signal based either on fine-tuning all the weights of a model or alternatively on freezing a fraction of them. In the case of $W$-boson and top-quark tagging, we find that one can obtain reliable taggers using an order of magnitude less data with a corresponding speed-up of the training process. Moreover, while keeping the size of the training data set fixed, we observe a speed-up of the training by up to a factor of three. This offers a promising avenue to facilitate the use of such tools in collider physics experiments.

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arXiv2022

Next-to-next-to-leading order event generation for top-quark pair production

The production of top-quark pairs in hadronic collisions is among the most important reactions in modern particle physics phenomenology and constitutes an instrumental avenue to study the properties of the heaviest quark observed in nature. The analysis of this process at the Large Hadron Collider relies heavily on Monte Carlo simulations of the final state events, whose accuracy is challenged by the outstanding precision of experimental measurements. In this letter we present the first matched computation of top-quark pair production at next-to-next-to-leading order in QCD with all-order radiative corrections as implemented via parton-shower simulations. Besides its intrinsic relevance for LHC phenomenology, this work also establishes an important step towards the simulation of other hadronic processes with colour charges in the final state.

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arXiv2022

MiNNLO$_{\text{PS}}$: A new method to match NNLO QCD to parton showers

We present a novel method to combine QCD calculations at next-to-next-to-leading order (NNLO) with parton shower (PS) simulations, that can be applied to the production of heavy systems in hadronic collisions, such as colour singlets or a $t\bar{t}$ pair. The NNLO corrections are included by connecting the MiNLO$^\prime$ method with transverse-momentum resummation, and they are calculated at generation time without any additional reweighting, making the algorithm considerably efficient. Moreover, the combination of different jet multiplicities does not require any unphysical merging scale, and the matching preserves the structure of the leading logarithmic corrections of the Monte Carlo simulation for parton showers ordered in transverse momentum. We present proof-of-concept applications to hadronic Higgs production and the Drell-Yan process at the LHC.

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arXiv2021

Top-pair production at the LHC with MiNNLO$_{\rm PS}$

We consider the production of a pair of heavy quarks and illustrate the derivation of the MiNNLO method to match next-to-next-to-leading order calculations with parton showers (NNLO+PS) for this class of processes. As a first application, we construct an event generator for the fully differential simulation of hadronic top-quark pair production at NNLO+PS and discuss all details of its implementation in a parton shower Monte Carlo framework. We present new phenomenological results for the Large Hadron Collider obtained by including the tree-level decays of the top quarks, while accounting for spin-correlation effects. A comprehensive comparison to LHC measurements shows an excellent description of experimental data across multiple hadronic and leptonic particle-level observables. The computer code is available for download within the POWHEG-BOX.

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arXiv2021

Higher-order non-global logarithms from jet calculus

Non-global QCD observables are characterised by a sensitivity to the full angular distribution of soft radiation emitted coherently in hard scattering processes. This complexity poses a challenge to their all-order resummation, that was formulated at the leading-logarithmic order about two decades ago. In this article we present a solution to the long-standing problem of their resummation beyond this order, and carry out the first complete next-to-leading logarithmic calculation for non-global observables. This is achieved by solving numerically the recently derived set of non-linear differential equations which describe the evolution of soft radiation in the planar, large-$N_c$ limit. As a case study we address the calculation of the transverse energy distribution in the interjet rapidity region in $e^+e^-\to$ dijet production. The calculation is performed by means of an algorithm that we formulate in the language of jet-calculus generating functionals, which also makes the resummation technique applicable to more general non-global problems, such as those that arise in hadronic collisions. We find that NLL corrections are substantial and their inclusion leads to a significant reduction of the perturbative scale uncertainties for these observables. The computer code used in the calculations is made publicly available.

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arXiv2021

Next-to-leading non-global logarithms in QCD

Non-global logarithms arise from the sensitivity of collider observables to soft radiation in limited angular regions of phase space. Their resummation to next-to-leading logarithmic (NLL) order has been a long standing problem and its solution is relevant in the context of precision all-order calculations in a wide variety of collider processes and observables. In this article, we consider observables sensitive only to soft radiation, characterised by the absence of Sudakov double logarithms, and we derive a set of integro-differential equations that describes the resummation of NLL soft corrections in the planar, large-$N_c$ limit. The resulting set of evolution equations is derived in dimensional regularisation and we additionally provide a formulation that is manifestly finite in four space-time dimensions. The latter is suitable for a numerical integration and can be generalised to treat other infrared-safe observables sensitive solely to soft wide-angle radiation. We use the developed formalism to carry out a fixed-order calculation to ${\cal O}(α_s^2)$ in full colour for both the transverse energy and energy distribution in the interjet region between two cone jets in $e^+e^-$ collisions. We find that the expansion of the resummed cross section correctly reproduces the logarithmic structure of the full QCD result.

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arXiv2021

$C$-parameter hadronisation in the symmetric 3-jet limit and impact on $α_s$ fits

Hadronisation corrections are crucial in extractions of the strong coupling constant ($α_s$) from event-shape distributions at lepton colliders. Although their dynamics cannot be understood rigorously using perturbative methods, their dominant effect on physical observables can be estimated in singular configurations sensitive to the emission of soft radiation. The differential distributions of some event-shape variables, notably the $C$ parameter, feature two such singular points. We analytically compute the leading non-perturbative correction in the symmetric three-jet limit for the $C$ parameter, and find that it differs by more than a factor of two from the known result in the two-jet limit. We estimate the impact of this result on strong coupling extractions, considering a range of functions to interpolate the hadronisation correction in the region between the 2 and 3-jet limits. Fitting data from ALEPH and JADE, we find that most interpolation choices increase the extracted $α_s$, with effects of up to $4\%$ relative to standard fits. This brings a new perspective on the long-standing discrepancy between certain event-shape $α_s$ fits and the world average.

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arXiv2021

Fiducial distributions in Higgs and Drell-Yan production at N$^3$LL+NNLO

The perturbative description of certain differential distributions across a wide kinematic range requires the matching of fixed-order perturbation theory with resummation of large logarithmic corrections to all orders. We present precise matched predictions for transverse-momentum distributions in Higgs boson (H) and Drell-Yan pair (DY) production as well as for the closely related ${ϕ^{*}_η}$ distribution at the LHC. The calculation is exclusive in the Born kinematics, and allows for arbitrary fiducial selection cuts on the decay products of the colour singlets, which is of primary relevance for experimental analyses. Our predictions feature very small residual scale uncertainties and display a good convergence of the perturbative series. A comparison of the predictions for DY observables to experimental data at 8 TeV shows a very good agreement within the quoted errors.

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arXiv2020

Higgs transverse momentum with a jet veto: a double-differential resummation

We consider the simultaneous measurement of the Higgs ($p_t^{\tiny{\mbox{H}}}$) and the leading jet ($p_t^{\tiny{\mbox{J}}}$) transverse momentum in hadronic Higgs-boson production, and perform the resummation of the large logarithmic corrections that originate in the limit $p_t^{\tiny{\mbox{H}}}\,,p_t^{\tiny{\mbox{J}}} \ll m_{\tiny{\mbox{H}}}$ up to next-to-next-to-leading-logarithmic order. This work constitutes the first simultaneous (double differential) resummation for two kinematic observables of which one involves a jet algorithm in hadronic collisions, and provides an important milestone in the theoretical understanding of joint resummations. As an application, we provide precise predictions for the Higgs transverse-momentum distribution with a veto $p_t^{\tiny{\mbox{J}}} \leq p_{t}^{\tiny{\mbox{J,v}}}$ on the accompanying jets, whose accurate description is relevant to the Higgs precision programme at the Large Hadron Collider.

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arXiv2020

Disentangling observable dependence in SCETI and SCETII anomalous dimensions: angularities at two loops

The resummation of radiative corrections to collider jet observables using soft collinear effective theory is encoded in differential renormalization group equations (RGEs), with anomalous dimensions depending on the observable under consideration. This observable dependence arises from the ultraviolet (UV) singular structure of real phase space integrals in the effective field theory. We show that the observable dependence of anomalous dimensions in SCETI problems can be disentangled by introducing a suitable UV regulator in real radiation integrals. Resummation in the presence of the new regulator can be performed by solving a two-dimensional system of RGEs in the collinear and soft sectors, and resembles many features of resummation in SCETII theories by means of the rapidity renormalization group. We study the properties of SCETI with the additional regulator and explore the connection with the system of RGEs in SCETII theories, highlighting some universal patterns that can be exploited in perturbative calculations. As an application, we compute the two-loop soft and jet anomalous dimensions for a family of recoil-free angularities and give new analytic results. This allows us to study the relations between the SCETI and SCETII limits for these observables. We also discuss how the extra UV regulator can be exploited to calculate anomalous dimensions numerically, and the prospects for numerical resummation.

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