scholarly journals Grooming at the cusp: all-orders predictions for the transition region of jet groomers

2021 ◽  
Vol 2021 (11) ◽  
Author(s):  
Kees Benkendorfer ◽  
Andrew J. Larkoski
Keyword(s):  
Phase Space ◽  
Transition Region ◽  
Mass Distribution ◽  
Hard Core ◽  
Factorization Theorem ◽  
Cusp Region ◽  
Fixed Order ◽  
Logarithmic Accuracy

Abstract Jet grooming has emerged as a necessary and vital tool for mitigating contamination radiation in jets. The additional restrictions on emissions imposed by the groomer can result in non-smooth behavior of resulting fixed-order distributions of observables measured on groomed jets. As a concrete example, we study the cusp in the hemisphere mass distribution of e+e−→ hadrons events groomed with soft drop. We identify the leading emissions that contribute in the region about the cusp and formulate an all-orders factorization theorem that describes how the cusp is resolved through arbitrary strongly-ordered soft and collinear emissions. The factorization theorem exhibits numerous novel features such as contributions from collinear modes that can cross hemisphere boundaries as well as requiring explicit subtraction of the limit in which resolved emissions become collinear to the hard core. We present resummation of the cusp region through next-to-leading logarithmic accuracy and describe how it can be matched with established factorization theorems that describe other groomed phase space regions.

scholarly journals Combined subleading high-energy logarithms and NLO accuracy for W production in association with multiple jets

2021 ◽  
Vol 2021 (4) ◽  
Author(s):  
Jeppe R. Andersen ◽  
James A. Black ◽  
Helen M. Brooks ◽  
Emmet P. Byrne ◽  
Andreas Maier ◽  
...  
Keyword(s):  
Phase Space ◽  
Hadron Collider ◽  
High Energy ◽  
Logarithmic Order ◽  
Order Accuracy ◽  
Logarithmic Corrections ◽  
Multiple Jets ◽  
Fixed Order ◽  
Two Jets ◽  
Logarithmic Accuracy

Abstract Large logarithmic corrections in $$ \hat{s}/{p}_t^2 $$ s ̂ / p t 2 lead to substantial variations in the perturbative predictions for inclusive W-plus-dijet processes at the Large Hadron Collider. This instability can be cured by summing the leading-logarithmic contributions in $$ \hat{s}/{p}_t^2 $$ s ̂ / p t 2 to all orders in αs. As expected though, leading logarithmic accuracy is insufficient to guarantee a suitable description in regions of phase space away from the high energy limit.We present (i) the first calculation of all partonic channels contributing at next-to-leading logarithmic order in W-boson production in association with at least two jets, and (ii) bin-by-bin matching to next-to-leading fixed-order accuracy. This new perturbative input is implemented in High Energy Jets, and systematically improves the description of available experimental data in regions of phase space which are formally subleading with respect to $$ \hat{s}/{p}_t^2 $$ s ̂ / p t 2 .

scholarly journals QED corrections in $$ \overline{B}\to \overline{K}{\mathrm{\ell}}^{+}{\mathrm{\ell}}^{-} $$ at the double-differential level

2020 ◽  
Vol 2020 (12) ◽  
Author(s):  
Gino Isidori ◽  
Saad Nabeebaccus ◽  
Roman Zwicky
Keyword(s):  
Phase Space ◽  
Detailed Analysis ◽  
Invariant Mass ◽  
Mass Distribution ◽  
Invariant Mass Distribution ◽  
Semileptonic Decays ◽  
Lepton Pair ◽  
Specific Choice ◽  
Slicing Method

Abstract We present a detailed analysis of QED corrections to $$ \overline{B}\to \overline{K}{\mathrm{\ell}}^{+}{\mathrm{\ell}}^{-} $$ B ¯ → K ¯ ℓ + ℓ − decays at the double-differential level. Cancellations of soft and collinear divergences are demonstrated analytically using the phase space slicing method. Whereas soft divergences are found to cancel at the differential level, the cancellation of the hard-collinear logs ln mℓ require, besides photon-inclusiveness, a specific choice of kinematic variables. In particular, hard-collinear logs in the lepton-pair invariant mass distribution (q2), are sizeable and need to be treated with care when comparing with experiment. Virtual and real amplitudes are evaluated using an effective mesonic Lagrangian. Crucially, we show that going beyond this approximation does not introduce any further infrared sensitive terms. All analytic computations are performed for generic charges and are therefore adaptable to semileptonic decays such as $$ \overline{B}\to D\mathrm{\ell}\overline{\nu } $$ B ¯ → D ℓ ν ¯ .

scholarly journals Improving the understanding of jet grooming in perturbation theory

2020 ◽  
Vol 2020 (9) ◽  
Author(s):  
Andrew J. Larkoski
Keyword(s):  
Perturbation Theory ◽  
Phase Space ◽  
Cross Section ◽  
Power Counting ◽  
Numerical Results ◽  
Factorization Theorem ◽  
Jet Physics ◽  
Leading Order ◽  
Physics Program ◽  
Jet Observables

Abstract Jet grooming has emerged as a necessary and powerful tool in a precision jet physics program. In this paper, we present three results on jet grooming in perturbation theory, focusing on heavy jet mass in e+e−→ hadrons collisions, groomed with the modified mass drop tagger. First, we calculate the analytic cross section at leading-order. Second, using the leading-order result and numerical results through next-to-next-to-leading order, we show that cusps in the distribution on the interior of phase space at leading-order are softened at higher orders. Finally, using analytic and numerical results, we show that terms that violate the assumptions of the factorization theorem for groomed jet mass are numerically much smaller than expected from power counting. These results provide important information regarding the convergence of perturbation theory for groomed jet observables and reliable estimates for residual uncertainties in a precision calculation.

scholarly journals Groomed jet mass as a direct probe of collinear parton dynamics

2020 ◽  
Vol 80 (9) ◽  
Author(s):  
Daniele Anderle ◽  
Mrinal Dasgupta ◽  
Basem Kamal El-Menoufi ◽  
Marco Guzzi ◽  
Jack Helliwell
Keyword(s):  
Mass Distribution ◽  
Leading Order ◽  
Order Calculation ◽  
Fixed Order ◽  
Collinear Limit

AbstractWe study the link between parton dynamics in the collinear limit and the logarithmically enhanced terms of the groomed jet mass distribution, for jets groomed with the modified mass-drop tagger (mMDT). While the leading-logarithmic (LL) result is linked to collinear evolution with leading-order splitting kernels, here we derive the NLL structure directly from triple-collinear splitting kernels. The calculation we present is a fixed-order calculation in the triple-collinear limit, independent of resummation ingredients and methods. It therefore constitutes a powerful cross-check of the NLL results previously derived using the SCET formalism and provides much of the insight needed for resummation within the traditional QCD approach.

Measuring Two Angularities on a Single Jet

2015 ◽  
Vol 37 ◽  
pp. 1560046
Author(s):  
Andrew Larkoski ◽  
Ian Moult ◽  
Duff Neill
Keyword(s):  
Phase Space ◽  
Cross Sections ◽  
Effective Field Theory ◽  
Evolution Equations ◽  
Effective Field ◽  
Jet Physics ◽  
Multiple Measurements ◽  
Single Jet ◽  
Jet Structure ◽  
Logarithmic Accuracy

We present an analysis of the complete singular phase space of a jet when multiple measurements have been made about the jet structure. Using Soft-Collinear Effective Field Theory, strict factorization theorems are found only for the boundaries of physical phase space in these multi-differential cross-sections. These theorems have incompatible evolution equations, but nonetheless, a resummation ansazt can be found that interpolates between the boundaries. While logarithmic accuracy cannot be guaranteed in the bulk of phase space, the ansazt reproduces the correct resummation exactly at any boundary. Aside from jet physics, applications to more exclusive PDF's and Drell-Yan event shapes are indicated.

scholarly journals Extraction of partonic transverse momentum distributions from semi-inclusive deep-inelastic scattering, Drell-Yan and Z-boson production

2017 ◽  
Vol 2017 (6) ◽  
Author(s):  
Alessandro Bacchetta ◽  
Filippo Delcarro ◽  
Cristian Pisano ◽  
Marco Radici ◽  
Andrea Signori
Keyword(s):  
Transverse Momentum ◽  
Inelastic Scattering ◽  
Deep Inelastic Scattering ◽  
Z Boson ◽  
Boson Production ◽  
High Transverse Momentum ◽  
Momentum Distributions ◽  
Fixed Order ◽  
Global Fit ◽  
Logarithmic Accuracy

Abstract We present an extraction of unpolarized partonic transverse momentum distributions (TMDs) from a simultaneous fit of available data measured in semi-inclusive deep-inelastic scattering, Drell-Yan and Z boson production. To connect data at different scales, we use TMD evolution at next-to-leading logarithmic accuracy. The analysis is restricted to the low-transverse-momentum region, with no matching to fixed-order calculations at high transverse momentum. We introduce specific choices to deal with TMD evolution at low scales, of the order of 1 GeV2. This could be considered as a first attempt at a global fit of TMDs.

scholarly journals Next-to-leading power two-loop soft functions for the Drell-Yan process at threshold

2021 ◽  
Vol 2021 (10) ◽  
Author(s):  
Alessandro Broggio ◽  
Sebastian Jaskiewicz ◽  
Leonardo Vernazza
Keyword(s):  
Differential Equations ◽  
Cross Section ◽  
Factorization Theorem ◽  
Dimensional Dependence ◽  
Convolution Integrals ◽  
Fixed Order ◽  
The Cross ◽  
Matter Fields ◽  
Section Level

Abstract We calculate the generalized soft functions at $$ \mathcal{O} $$ O ($$ {\alpha}_s^2 $$ α s 2 ) at next-to-leading power accuracy for the Drell-Yan process at threshold. The operator definitions of these objects contain explicit insertions of soft gauge and matter fields, giving rise to a dependence on additional convolution variables with respect to the leading power result. These soft functions constitute the last missing ingredient for the validation of the bare factorization theorem to NNLO accuracy. We carry out the calculations by reducing the soft squared amplitudes into a set of canonical master integrals and we employ the method of differential equations to evaluate them. We retain the exact d-dimensional dependence of the convolution variables at the integration boundaries in order to regulate the fixed-order convolution integrals. After combining the soft functions with the relevant collinear functions, we perform checks of the results at the cross-section level against the literature and expansion-by-regions calculations, at NNLO and partly at N3LO, finding agreement.

scholarly journals On factorisation schemes for the electron parton distribution functions in QED

2021 ◽  
Vol 2021 (7) ◽  
Author(s):  
S. Frixione
Keyword(s):  
Analytical Solutions ◽  
Parton Distribution ◽  
Distribution Functions ◽  
Parton Distribution Functions ◽  
Electron Positron ◽  
Functional Forms ◽  
Fixed Order ◽  
Logarithmic Accuracy

Abstract The electron, positron, and photon Parton Distribution Functions (PDFs) of the unpolarised electron have recently been computed at the next-to-leading logarithmic accuracy in QED, by adopting the $$ \overline{\mathrm{MS}} $$ MS ¯ factorisation scheme. We present here analogous results, obtained by working in a different framework that is inspired by the so-called DIS scheme. We derive analytical solutions relevant to the large-z region, where we show that the behaviour of the PDFs depends in a dramatic way on whether running-α effects are included to all orders, as opposed to being truncated to some fixed order. By means of suitable initial and evolution conditions, next-to-leading logarithmic accurate PDFs are obtained whose large-z functional forms are identical to those of their leading logarithmic counterparts.

scholarly journals Erratum to: Logarithmic accuracy of parton showers: a fixed-order study

2020 ◽  
Vol 2020 (3) ◽  
Author(s):  
Mrinal Dasgupta ◽  
Frédéric A. Dreyer ◽  
Keith Hamilton ◽  
Pier Francesco Monni ◽  
Gavin P. Salam
Keyword(s):  
Fixed Order ◽  
Logarithmic Accuracy

scholarly journals Jet angularities in Z+jet production at the LHC

2021 ◽  
Vol 2021 (7) ◽  
Author(s):  
Simone Caletti ◽  
Oleh Fedkevych ◽  
Simone Marzani ◽  
Daniel Reichelt ◽  
Steffen Schumann ◽  
...  
Keyword(s):  
Monte Carlo ◽  
Transverse Momentum ◽  
Parton Shower ◽  
Phenomenological Study ◽  
State Of The Art ◽  
Leading Order ◽  
Associate Production ◽  
Fixed Order ◽  
The Impact ◽  
Logarithmic Accuracy

Abstract We present a phenomenological study of angularities measured on the highest transverse-momentum jet in LHC events that feature the associate production of a Z boson and one or more jets. In particular, we study angularity distributions that are measured on jets with and without the SoftDrop grooming procedure. We begin our analysis exploiting state-of-the-art Monte Carlo parton shower simulations and we quantitatively assess the impact of next-to-leading order (NLO) matching and merging procedures. We then move to analytic resummation and arrive at an all-order expression that features the resummation of large logarithms at next-to-leading logarithmic accuracy (NLL) and is matched to the exact NLO result. Our predictions include the effect of soft emissions at large angles, treated as a power expansion in the jet radius, and non-global logarithms. Furthermore, matching to fixed-order is performed in such a way to ensure what is usually referred to as NLL′ accuracy. Our results account for realistic experimental cuts and can be easily compared to upcoming measurements of jet angularities from the LHC collaborations.

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