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The Soft Component of Underlying Events

Student: 
Manuel Bähr
Date: 
February, 2008 to May, 2008
For my Ph.D., I am working on a description of the so-called underlying event for the Event Generator Herwig++. From the experimental point of view, the underlying event contains all activity in a hadronic collision that is not related to the signal particles from the hard process, e.g. leptons or missing transverse energy. The additional particles may result from the initial- or final-state radiation of coloured particles or from multiple semi-hard or soft interactions. The perturbative, i.e. semi-hard part has been implemented into Herwig++ before my short-term studentship.

Building a New Exotic MC Tool

Student: 
Noam Hod
Date: 
April, 2008 to August, 2008
Gathering large set of processes under the umbrella of one simulation code is an ambitious task, where the theoretical studies required make it even harder. We offer to build a modular tool written in a modern object-oriented style, using C++ and separating the MC core from the specific physics processes to enable maximum modularity and flexibility.

Z/W + jets production at the LHC: a comparison among different Monte Carlo generators

Student: 
Pergiulio Lenzi
Date: 
January, 2008 to April, 2008
One of the goals of the first LHC physics will be to measure the Z/W + jets production rates and the characterization of this kind of events. In the early phase of the detector operation these processes will be very useful for calibration purposes: in particular they will be very useful for the determination of the calorimeter system energy scale and for the calibration of the detectors in events in which undetectable particles need to be identified through missing transverse energy (missing Et) signatures.

QCD background to ttbar events

Student: 
Riccardo Di Sipio
Date: 
January, 2009 to May, 2009
The goal of my PhD thesis is the measurement of top-antitop pairs production cross-section in the semileptonic decay channel with the Atlas detector. Events in which top-quark pairs are produced will be extremely important at the LHC, as they will provide a special environment to study physics within the Standard Model and beyond, such as its supersymmetric extension, and to calibrate the detector using leptons, particle jets and evaluation of missing transverse energy.

LO vs NLO comparisons for Z + jets: MC as a tool for background determination for new physics searches at LHC

Student: 
Flavia Dias
Date: 
February, 2010 to June, 2010
The leptonic decays of the heavy gauge bosons W and/or Z provide a clear experimental signature at hadron colliders. The production of accompanying jets is an excellent signal to probe QCD, while also being the main background to many searches for new physics. Describing the complex final state of W or Z + jets is a theoretical challenge with most existing calculations combining matrix elements for high energy jet production with a parton shower for lower energy jet production.

Implementation of novel BSM processes in Pythia

Student: 
Avi Gershan
Date: 
June, 2010 to September, 2010
This studentship involved the implementation, within the Pythia generator, of a class of novel BSM processes which allow flavour changing neutral currents, specifically resulting in ttbar production in the final state. This property arises from the emergence of the effective couplings to proposed new resonant states within the model. Because of the existence of the non relativistic top in the final state, this will involve the full implementation of the spin structure of the interaction which is not, so far, implemented within Pythia.

Monte-Carlo study of pile-up effects in Higgs/subjet analyses

Student: 
Christian Roehr
Date: 
October, 2010 to December, 2010
During his short-term studentship from October to December 2010 at UCL in London, Christian Röhr examined the Higgs/subjet analysis technique for the Higgs search at the LHC. First, general properties of the subjet technique were studied in Monte-Carlo analyses. The second and main part of the work focussed on studying the impact of pile-up on subjet analyses, i.e. of additional radiation due to secondary simultaneous proton-proton interactions. During the studentship a program for simulating pile-up events at event-generator level was written.

Soft Diffraction Dissociation and Underlying Events

Student: 
Sercan Sen
Date: 
August, 2010 to December, 2010
Forward and diffractive physics is part of the LHC program and it covers a wide range of physics subjects, including low-x QCD, diffraction dissociation, underlying event and multiple interactions characteristics. The new experimental opportunities and large rapidity coverage of the detectors in the forward region allow these measurements to be made in as yet unexplored regions. In particular, the soft diffractive processes at the LHC, are important for understanding non-perturbative QCD effects and they also constitute a significant fraction of the total pp cross-section.

Modelling and tuning of Z+b(b) Production

Student: 
Nicola Orlando
Date: 
June, 2014 to September, 2014
One of the main open questions about the newly discovered Higgs boson is to determine if it decays to b-quarks at the expected rate, or if there is some deviation which would hint at new physics. Although the H->bb branching fraction is around 56%, this channel as never been observed, due to experimental challenges in measuring b-jets, and significant and complex backgrounds covering the signal. One of these main backgrounds is associated Z+bb production, with the b-quarks produced by QCD processes.