IR-Improved DGLAP-CS QCD Parton Showers in Pythia8

We introduce the recently developed IR-improved DGLAP-CS theory into the showers in Pythia8, as this Monte Carlo event generator is in wide use at LHC. We show that, just as it was true in the IR-improved shower Monte Carlo Herwiri, which realizes the IR-improved DGLAP-CS theory in the Herwig6.5 environment, the soft limit in processes such as single heavy gauge boson production is now more physical in the IR-improved DGLAP-CS theory version of Pythia8. This opens the way to one's getting a comparison between the actual detector simulations for some of the LHC experiments between IR-improved and unimproved showers as Pythia8 is used in detector simulations at LHC whereas Herwig6.5, the environment of the only other IR-improved DGLAP-CS QCD MC in the literature, Herwiri1.031, is not any longer so used. Our achieving the availability of the IR-improved DGLAP-CS Pythia8 then is an important step in the further development of the LHC precision theory program under development by the author and his collaborators.Comment: 6 pages, 1 figur

Interplay of IR-Improved DGLAP-CS Theory and NLO Parton Shower MC Precision

We present the interplay between the new IR-improved DGLAP-CS theory and the precision of NLO parton shower/ME matched MC`s as it is realized by the new MC Herwiri1.031 in interface to MC@NLO. We discuss phenomenological implications using comparisons with recent LHC data on single heavy gauge boson production.Comment: 8 pages, 4 figures; presented by BFLW at ICHEP 201

QCD for the LHC

We discuss the new era of precision QCD as it relates to the physics requirements of the LHC for both the signal and background type processes. Some attention is paid to the issue of the theoretical error associated with any given theoretical prediction. In the cases considered, we present where the theory precision is at this writing and where it needs to go in order that it not impede the discovery potential of the LHC physics program. To complete the discussion, we also discuss possible paradigms the latter program may help us understand and some new developments that may play a role in achieving that respective understanding.Comment: 15 pages, 5 figures. Invited talk presented at 2011 Epiphany Conference, Krakow, Poland, Jan., 2011; improved references; added Baylor preprint numbe

Phenomenology of the Interplay between IR-Improved DGLAP-CS Theory and NLO ME Matched Parton Shower MC Precision

We present the current status of the application of our approach of {\it exact} amplitude-based resummation in quantum field theory to precision QCD calculations, by realistic MC event generator methods, as needed for precision LHC physics.In this ongoing program of research, we discuss recent results as they relate to the interplay of the attendant IR-Improved DGLAP-CS theory of one of us and the precision of exact NLO matrix element matched parton shower MC's in the Herwig6.5 environment in relation to recent LHC experimental observations. There continues to be reason for optimism in the attendant comparison of theory and experiment.Comment: 11 pages, 3 figures; now 12 pages, 4 figures -- explanatory material added and title changed for publication in Phys. Lett.

Hadronic Jets: flavour and substructure

Hadronic jets, collimated sprays of particles produced in high-energy particle collisions, play a crucial role in the study of particle physics. In this PhD thesis, the focus is on two aspects of hadronic jets: flavour and substructure. The flavour of a jet refers to the identity of the initiating quark or gluon, and can provide information about the underlying physics processes that produced the jet. The substructure of a jet refers to its internal structure and is sensitive to the properties of the partons within the jet. The thesis presents a comprehensive study of the flavour and substructure of hadronic jets, including the development of new analysis techniques. Additionally, this thesis discusses the advancement of existing techniques for performing high-accuracy calculations for jet substructure observables, critical for comparing theoretical predictions with experimental measurements. Recently, there has been a growing interest in machine learning and quantum computing techniques applied to jet physics or other close-related subjects. Machine learning algorithms are increasingly being used to identify and classify jets, while quantum computers have the potential to revolutionize high-precision calculations in jet physics. This thesis discusses a novel method to calculate the gradient of a function on quantum computers, further advancing the use of quantum computing in jet physics. The results of this study are ready for further phenomenological applications, contributing to a better understanding of the properties of hadronic jets and the physics of high-energy particle collisions

Factorization and Resummation for Groomed Multi-Prong Jet Shapes

Observables which distinguish boosted topologies from QCD jets are playing an increasingly important role at the Large Hadron Collider (LHC). These observables are often used in conjunction with jet grooming algorithms, which reduce contamination from both theoretical and experimental sources. In this paper we derive factorization formulae for groomed multi-prong substructure observables, focusing in particular on the groomed $D_2$ observable, which is used to identify boosted hadronic decays of electroweak bosons at the LHC. Our factorization formulae allow systematically improvable calculations of the perturbative $D_2$ distribution and the resummation of logarithmically enhanced terms in all regions of phase space using renormalization group evolution. They include a novel factorization for the production of a soft subjet in the presence of a grooming algorithm, in which clustering effects enter directly into the hard matching. We use these factorization formulae to draw robust conclusions of experimental relevance regarding the universality of the $D_2$ distribution in both $e^+e^-$ and $pp$ collisions. In particular, we show that the only process dependence is carried by the relative quark vs. gluon jet fraction in the sample, no non-global logarithms from event-wide correlations are present in the distribution, hadronization corrections are controlled by the perturbative mass of the jet, and all global color correlations are completely removed by grooming, making groomed $D_2$ a theoretically clean QCD observable even in the LHC environment. We compute all ingredients to one-loop accuracy, and present numerical results at next-to-leading logarithmic accuracy for $e^+e^-$ collisions, comparing with parton shower Monte Carlo simulations. Results for $pp$ collisions, as relevant for phenomenology at the LHC, are presented in a companion paper.Comment: 66 pages, 18 figure