Madweight is a algorithm to automatically reweight experimental events with the squared matrix element, and therefore provides the required computation techniques for a practical application of the matrix element method. We also study the usefullness of MadWeight to estimate differential cross-section via the marginal distributions of the the experimental weights .
External collaborators: Pierre Artoisenet (Ohio state university).
The top quark is the heaviest elementary particle discovered so far, and many properties related to this quark are still to be understood. Its observation and mass measurement at Tevatron highlighted the uncommon nature of this quark. The fact that its electroweak decay is faster than the hadronization time scale implies that the top quark exists only as a free quark, so that the effects from new physics should show up very clearly by comparing measurements with the precise Standard Model preditions. Its "re-discovery" at LHC will be a major milestone for the experiments, since the complexity of the final state demands a fairly good knowledge of the experimental apparatus and a certain degree of control of the backgrounds. Its expected large coupling to Higgs bosons will also be relevaant for the searches for higgs sectors beyond the Standard Model.
External collaborators: CMS collaboration.
At LHC, the Z boson can be produced in association with one or two b-quarks, which is here refereed as b(b)Z production. This process has been seen for the first time at LHC, and measurement of it is an important test of QCD calculations. For the first time, we observed the Z+b final state and measured of the Z+b/Z+j cross-section ratio in 35.9/pb of pp collisions at 7 TeV, using particle flow jets and simple secondary vertex b-tagging algorithm in the definition of the signal.Emphasis is put on kinematic properties of the jets. With more luminosity, we are working on the measurement of the cross-section for the b(b)Z process, with the identification of one or two b-jets.
External collaborators: Anne-Marie Magnan (IC London), Alexandre Nikitenko (IC London), Natalie Heracleous (Aachen-I), Adrian Perieanu (Aachen-I).
Search for Higgs boson(s) within the Standard Model and beyond and also withing a minimal extension of the scalar sector (2HDM). The final state under study is a Z decaying into a lepton pair associated with two b-jets. This topology is sensitive to a light SM Higgs via the associate ZH production, as well as a middle mass range SM Higgs boson via the inclusive Higgs production followed by its decay into ZZ with one Z decaying into a lepton pair and the other into bbar. It is also very sensitive to the production of a non standard heavy Higgs boson decaying into Z plus A (pseudo scalar Higgs boson).
External collaborators: Nick van Remortel (Belgium, UA), Barbara Clerbaux (Belgium, ULB), and CMS collaboration.
Development of silicon sensors (strixels) for CMS tracker upgrade for very high luminosity at LHC. This activity is making usr of the cyclotron of UCL, the probe stations and the SYCOC set-up: SYCOC stands for "SYstem de mesure de COllection de Charge". This system is intended to measure charge collection efficiency of semiconductor detectors with both a laser and radiactive sources. This installation is used in the characterization of semiconductor detectors in order to study its radiation hardness. This project is done in collaboration with RD50 team at CERN.
External collaborators: CRC, Frank Hartman (Karlsruhe) and RD50 and CMS collaboration.
The matrix element reweighting method attempts to compute the full likelihood of an observed event given a theoretical model. The method therefore measures the degree of compatibility of the event with the given model using as much information as available. MadWeight is a tool that fully automatize the computation of the event likelihood for any model implemented in MadGraph, by performing phase-space integration and providing a framework for taking into account the experimental resolution on the observed final state objects. This project aims at validating the matrix element reweighting technique implemented in MadWeight on a number of benchmark searches. In some cases, the final goal is the efficient identification of background events. The final states that are being considered are: Zbb, single top, ttbar resonances and dimuon resonances.
