Recent progress in QCD at the LHC

Perturbative Quantum Chromodynamics has experienced an impressive progress in the last few years, boosted by the requirements of the LHC experimental program. In this contribution, I briefly review a selection of recent results in QCD and LHC phenomenology, covering progress in parton distribution functions, automation of NLO calculations, merging and matching at NLO, new calculations at NNLO accuracy and their matching to parton showers, and new developments and techniques in jet physics and jet substructure tools.Comment: 10 pages, 3 figures, to appear in the proceedings of the "Rencontres de physique de la Vallee d'Aoste 2014" Conference, La Thuile, Italy, February 201

Progress in jet reconstruction and heavy ion collisions

We review recent developments related to jet clustering algorithms and jet reconstruction, with particular emphasis on their implications in heavy ion collisions. These developments include fast implementations of sequential recombination algorithms, new IRC safe algorithms, quantitative determination of jet areas and quality measures for jet finding, among many others. We also show how jet reconstruction provides a useful tool to probe the characteristics of the hot and dense medium created in heavy ion collisions, which allows one to distinguish between different models of parton-medium interaction.Comment: 7 pages, 4 figures, to appear in the proceedings of the 13th International Conference on Elastic & Diffractive Scattering, CERN, 29th June - 3rd July 200

Machine Learning tools for global PDF fits

The use of machine learning algorithms in theoretical and experimental high-energy physics has experienced an impressive progress in recent years, with applications from trigger selection to jet substructure classification and detector simulation among many others. In this contribution, we review the machine learning tools used in the NNPDF family of global QCD analyses. These include multi-layer feed-forward neural networks for the model-independent parametrisation of parton distributions and fragmentation functions, genetic and covariance matrix adaptation algorithms for training and optimisation, and closure testing for the systematic validation of the fitting methodology.Comment: 12 pages, 9 figures, to appear in the proceedings of the XXIIIth Quark Confinement and the Hadron Spectrum conference, 1-6 August 2018, University of Maynooth, Irelan

Review on recent developments in jet finding

We review recent developments related to jet clustering algorithms and jet finding. These include fast implementations of sequential recombination algorithms, new IRC safe algorithms, quantitative determination of jet areas and quality measures for jet finding, among many others. We also briefly discuss the status of jet finding in heavy ion collisions, where full QCD jets have been measured for the first time at RHIC.Comment: 5 pages, 5 figures, proceedings of the International Symposium on Multiparticle Dynamics 08, 15-20 september 2008, DES

Brief history of the Lehmann Symposia: Origins, goals and motivation

The idea of the Lehmann Symposia as platforms to encourage a revival of interest in fundamental questions in theoretical statistics, while keeping in focus issues that arise in contemporary interdisciplinary cutting-edge scientific problems, developed during a conversation that I had with Victor Perez Abreu during one of my visits to Centro de Investigaci\'{o}n en Matem\'{a}ticas (CIMAT) in Guanajuato, Mexico. Our goal was and has been to showcase relevant theoretical work to encourage young researchers and students to engage in such work. The First Lehmann Symposium on Optimality took place in May of 2002 at Centro de Investigaci\'{o}n en Matem\'{a}ticas in Guanajuato, Mexico. A brief account of the Symposium has appeared in Vol. 44 of the Institute of Mathematical Statistics series of Lecture Notes and Monographs. The volume also contains several works presented during the First Lehmann Symposium. All papers were refereed. The program and a picture of the participants can be found on-line at the website http://www.stat.rice.edu/lehmann/lst-Lehmann.html.Comment: Published at http://dx.doi.org/10.1214/074921706000000347 in the IMS Lecture Notes--Monograph Series (http://www.imstat.org/publications/lecnotes.htm) by the Institute of Mathematical Statistics (http://www.imstat.org

Progress in the NNPDF global analysis and the impact of the legacy HERA combination

The H1 and ZEUS collaborations have recently presented their final results for the combination of inclusive cross-section measurements taken during Run I and Run II at the HERA collider. In this contribution, following an overview of recent progress in the NNPDF framework, we quantify the impact of the legacy HERA dataset on the NNPDF3.0 analysis, finding that it has a very moderate effect in the global fit. On the other hand, we also find that a HERA-only fit using the legacy dataset leads to a rather more accurate determination of PDFs as compared to a fit including only the HERA-I data. We also explore the sensitivity of the fit with respect to kinematical cuts in the small-x and small-Q region, finding hints of a possible tension between data and theory.Comment: 9 pages, 8 figures, to appear in the proceedings of the European Physical Society Conference on High Energy Physics 2015 (EPS-HEP 2015), Vienna, Austria, 22nd to 29th of July 201

Parton Distributions in the Higgs Boson Era

Parton distributions are an essential ingredient of the LHC program. PDFs are relevant for precision Standard Model measurements, for Higgs boson characterization as well as for New Physics searches. In this contribution I review recent progress in the determination of the parton distributions of the proton during the last year. Important developments include the impact of new LHC measurements to pin down poorly known PDFs, studies of theoretical uncertainties, higher order calculations for processes relevant for PDF determinations, PDF benchmarking exercises with LHC data, as well as methodological and statistical improvements in the global analysis framework. I conclude with some speculative considerations about future directions in PDF determinations from the theory point of view.Comment: 11 pages, 5 figures, write-up of the plenary talk at the XXI International Workshop on Deep-Inelastic Scattering and Related Subjects (DIS2013), Marseille, 22-26 April 201

Improving quark flavor separation with forward W and Z production at LHCb

We quantify the constraints on the flavour separation between the quarks and antiquarks in the proton provided by the recent forward weak gauge boson production data from the LHCb experiment at $\sqrt{s}=7$ and 8 TeV. Performed in the framework of the NNPDF3.1 global analysis, this study highlights the key role that the LHCb W and Z data have in achieving a robust quark flavour separation in the large-x region, including the strange and charm quarks. We demonstrate how the LHCb measurements lead to improved determinations of the the up and down quark PDFs in the region $x\ge 0.1$, with an uncertainty reduction that can be as large as a factor 2. We also show how the LHCb forward measurements severely restrict the size of the fitted charm PDF at large x, imposing stringent constraints on non-perturbative models for the charm content of the nucleon.Comment: 5 pages, 5 figures, to appear in the proceedings of the XXV International Workshop on Deep-Inelastic Scattering and Related Subjects, 3-7 April 2017, University of Birmingham, U