Cosmology, Particle Physics and Phenomenology - CP3

We study the observation of single top quarks in photoproduction at the LHC as a way of detecting the presence of flavour changing neutral currents, predicted by some theories beyond the standard model.

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).

Study anomalous effect on the energy distribution and try to extract the parameter from experimental data.

We try to lower the bound on the first new physics states in the toy model proposed in arxiv:1009.2477 by adding extra custodial symmetry breaking term that are also require to obtain a realistic mass spectrum. The model is based on custodial and L-R symmetry in order to protect the Zbbar coupling.

Observability of new phenomenological models in High Energy experiments is delicate to evaluate, due to the complexity of the related detectors, DAQ chain and software. Delphes is a new framework for fast simulation of a general purpose experiment. The simulation includes a tracking system, a magnetic field, calorimetry and a muon system, and possible very forward detectors arranged along the beamline. The framework is interfaced to standard file format from event generators and outputs observable analysis data objects. The simulation takes into account the detector resolutions, usual reconstruction algorithms for complex objects (FastJet) and a simplified trigger emulation. Detection of very forward scattered particles relies on the transport in beamlines with the Hector software. Finally, the FROG 2D/3D event display is used for visualisation of the collision final states.

External collaborators: Severine Ovyn, Xavier Rouby from pfease company.

To study graviton production through multi-jet final state processes at hadron colliders taking into account the following models: ADD, RS and a massless graviton model.

External collaborators: Qiang Li (Paul Scherrer Institut - PSI, Switzerland) and prof. Kaoru Hagiwara (KEK Theory Center and Sokendai, Japan).

We study the Vector Boson Fusion production channel for the Higgs boson and other particles at the LHC, mainly focusing on the role of QCD corrections.

Monte Carlo development.

In collaboration with MadGraph and FeynRules teams and many external collaborators

External collaborators: Claude Duhr, Benjamin Fuks, Kentarou Mawatari, Kaoru Hagiwara, Tim Stelzer, Johan Alwall, Stefano Frixione, Roberto Pittau, Valentin Hirshi, Rikkert Frederix.

The goal of this work is to explore the phenomenology of a two Higgs doublet model with a custodial symmetry. It provides topologies that are unusual in the models usually considered in the literature. Notably, it opens the possibility of having an inverted mass spectrum with respect to MSSM with the lightest Higges being a pseudo-scalar and an heavier triplet of charged and neutral higgses.

External collaborators: Simon de Visscher (Zurich university).

In the standard model version of the grand unified theory different gauge couplings intend to, but do not, meet at some higher scale. Here we will look for some better ways for the unification of the gauge coupling constants.

High-energy photon-photon and photon-proton interactions at the LHC offer interesting possibilities for the study of the electroweak sector up to TeV scale and the search for processes beyond the Standard Model. After in-depth exploratory studies, first investigations of anomalous photon interactions in CMS are being performed.

External collaborators: CMS forward physics analysis group, R. Schicker (Heidelberg) and A. Szczurek (Krakow).

The difference between predictions obtained with a massive scheme, where a heavy quark is treated as a finale massive state and the massless scheme, where the heavy quark is viewed as an initial parton may be extremely sizable. The aim of the project is to gain a better understanding of the size of the collinear logarithms arising when a heavy quark is treated as a final massive state and to investigate its kinematical origin.

External collaborators: Maria Ubiali, Giovanni Ridolfi.

Study of the tensions observed between the K and the B meson systems and their implications for scalar-mediated flavor changing currents in the framework of two Higgs doublet models (2HDM).

We study the phenomenology the top quark at colliders as well as at low energy via loops.

External collaborators: Christophe Grojean, Geraldine Servant, Scott Willenbrock, Benjamin Fuks.