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List of previous students

Nicola OrlandoFaten Hariri

Emma Kuwertz

Spyridon Argyropoulo

Sabrina Sacerdoti

Simone Amoroso

Jesper Roy Christiansen

Nathan Hartland

Christian Roehr

Benjamin Watt

Philip Ilten

Nishita Desai

Sercan Sen

Miroslav Myska

Sudha Ahuja

Holger Schulz

Avi Gershan

Aleksander Kusina

Magdalena Slawinska

Flavia Dias

Kenneth Wraight

Irais Bautista Guzman

Sparsh Navin

Paolo Francavilla

Riccardo Di Sipio

Seyi Latunde-Dada

Devdatta Majumder

Martijn Gosselink

Christopher Bignamini

Marek Schönherr

Michal Deak

Noam Hod

Florian Bechtel

Jonathan Ferland

Manuel Bähr

Alexander Flossdorf

Piergiulio Lenzi

Modified CKKW-L merging for HEJ plus Pythia

HEJ is a parton-level Monte Carlo generator designed to calculate cross sections for multi-jet processes at the LHC in the limit where the jets are widely separated in rapidity. The HEJ formalism provides an all-order description of wide angle radiation, which becomes logarithmically enhanced in this limit. In the HEJ treatment, the jets which arise will only contain a small number partons, that is, they will be largely unpopulated. This is not necessarily a problem if the observables of interest are sufficiently inclusive, however, studies of jet vetoes and gap fractions for example (which are of relevance to Higgs couplings measurements) are known to be sensitive to both wide angle radiation described by HEJ, and the soft-collinear radiation described by the parton shower.

It is not sufficient to simply shower the final state from HEJ however, because soft singularities are already included in HEJ to all orders, thus doing so would be to double count an infinite tower of terms. Instead it is necessary to modify the splitting kernel of the parton shower. Furthermore, as the parton shower is ordered, certain states produced by HEJ have a configuration which would unphysically restrict the parton shower evolution. This may be amended by reweighting on an event to event basis with Sudakov factors, or the probability the shower would have produced that event, in a similar way to the treatment in the CKKW-L merging algorithm. These elements form the core of a new merging algorithm which was implemented for Pythia as part of a short-term (3 month) studentship at Lund.