List of previous students

Nicola Orlando
Faten 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

Devdatta Majumder is a PhD student from Tata Institute of Fundamental Research, Mumbai, India working on CMS, on a three-month MCnet studentship in Lund.

The study of inclusive Wγ production with W decaying to leptons, in p-p collisions at the LHC, will be an interesting validation of the electroweak gauge structure of Standard Model as well as for searches of physics beyond the Standard Model. In the Wγ events, the most interesting parameter is the transverse momentum of the photon, which is sensitive to deviations from the Standard Model value of the coupling of the WWγ vertex.

As a preparation for the analysis of data from the LHC, one needs to use monte carlo simulation to assess the signal and background expected from the detectors and to tune our analysis strategy accordingly. This calls for a proper choice on an event generator which can correctly simulate the Wγ production in proton-proton collision at the LHC.

I applied for Marie Curie Research Training Network for Monte Carlo generators with the aim to understand Monte Carlo generators and the theory behind them. This was outside the usual course of my study where we are mostly the end users of well-tuned monte carlo generators. The goal of this studentship was, in a period of three months, to make a comparative study of event generators for simulating my signal sample (the Wγ) and to choose the proper Monte Carlo generator. I was particularly interested in Baur WGAMMA which is a next to leading order matrix element generator for inclusive Wγ events which full QCD corrections up to order αS.

As mentioned previously, the study of photons are the most important part of the analysis as discovery of new features beyond the Standard Model could most likely show up in the photon's transverse momentum distribution. Photons can originate from the WWγ vertex or from one of the incoming quarks or from the charged lepton from W-decay. We therefore deem it important to study the various origins of the photon and understand each of their contribution.

In the tenure of the MCnet studentship, I compared Pythia with the Baur WGAMMA generator. Interference between photons coming from the WWγ vertex and those from ISR (initial-state radiation) from the incoming quarks as well as the interplay between the photon and gluon radiation (which may fake photon showers in the detector) were studied.

Baur WGAMMA being an NLO matrix element generator which generates only the hard part of the scattering, one needs to match it appropriately to a showering and hadronization generator (SHG) for simulating the entire proton-proton collision event. As our usual workhorse, the general purpose generator Pythia is chosen as the showering and hadronization generator. We devise a matching strategy for integrating Baur events to Pythia with the QCD jet from Baur NLO correction properly matched.

The present Pythia 8 will become one of the standard MC generators at future experiments, replacing the recent Pythia 6. A comparison is made between Pythia 6 results with those from Pythia 8 as a validation process for this new generator. Besides, some new features of Pythia 8 like multiple hard interactions is explored as well, in the context of studying photons from hard scattering processes and underlying events.