## Phenomenology of elementary particles

Sometimes a top-down approach is followed : New theoretical models and mechanisms are proposed and possible measurements at colliders or in other experiments are suggested. Search for Higgs scalars, supersymmetry or gravitational effects at the TeV scale are examples of such activities.

Alternatively, a bottom-up approach can be employed where new experimental possibilities are suggested or experimental data are scrutinized that call for a deeper understanding of standard model physics and/or (hopefully!) for new physics effects.

The research activities in this area cover several fields of investigation that can broadly associated to following categories:

- Collider phenomenology

- Flavour physics

- Precision EW and QCD calculations

- BSM : model building and alternative EWSB mechanims

- Computational tools for HEP

### Members

#### Professors

##### Chiara Arina

Christophe Delaere

Claude Duhr

Jean-Marc Gérard

Andrea Giammanco

Vincent Lemaitre

Fabio Maltoni

Krzysztof Piotrzkowski

#### Research scientists

##### Jérôme de Favereau

Pavel Demin

### Projects

#### a C++ software package to compute Matrix Element weights: MoMEMta

MoMEMta is a C++ software package to compute Matrix Element weights. Designed in a modular way, it covers the needs of experimental analysis workflows at the LHC. MoMEMta provides working examples for the most common final states (, WW, ...). If you are an expert user, be prepared to feel the freedom of configuring your MEM computation at all levels.

MoMEMta is based on:

- C++, ROOT, Lua scripting language

- Cuba (Monte-Carlo integration library)

- External PDFs (LHAPDF by default)

- External Matrix Elements (currently provided by our MadGraph C++ exporter plugin)

#### Complementarity of dark matter searches in simplified models

Study of the complementarity between dark matter relic abundance, direct detection, indirect detection and collider searches applied to the dark matter simplified models. These models consider a dark matter candidate communicating to the quark (especially top) sector of the standard model via a bosonic or vectorial mediator.

External collaborators: Eric Conte (GPRHE), Benjamin Fuks (LPTHE), Jun Guo (Chinese Academy of Science), Jan Heisig (RWTH), Kentarou Mawatari (LPSC Grenoble), Michael Kraemer (RWTH), Mathieu Pellen (University of Wuerzburg).

#### CP and chiral symmetry in K physics.

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

#### Dark matter and neutrino masses in SUSY models

We study supersymmetric models in which modifications of the neutrino sector, to include a mass term, are connected to the dark matter sector. We analyse if the dark matter particles can be good dark matter candidates by considering cosmological and astrophysical constraints, as well as if the new neutrino sector can accommodate neutrino data.

External collaborators: Suchitat Kulkarni (OAW Wien).

#### Development of a framework for fast simulation of a generic collider experiment: Delphes

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.

#### EFT@NLO

Implementation of the SMEFT at NLO in QCD in the Feynrules MadGraph5_aMC@NLO chain and phenomenological studies

External collaborators: Cen Zhang, Celine Degrande.

#### Electroweak corrections

Automation of the calculation of NLO Electroweak corrections and phenomenological studies of their impact on Standard-Model and Beyond-the-Standard-Model processes at colliders.

#### FeynRules

An automated framework for BSM phenomenology that allows one to compute Feynman rules from a Lagrangian.

External collaborators: Céline Degrande (CERN) Benjamin Fuks (Jussieu).

#### Higgs phenomenology at the LHC

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.

#### High energy photon induced interactions at the LHC

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, we performed using the CMS data first measurement of two-photon muon pair production as well as first ever observation of W boson pairs produced by photon fusion. Now our group is leading unique investigations of quartic couplings between photons and W and Z bosons.

External collaborators: CMS FSQ analysis group and the group of A. Szczurek (Krakow).

#### Loop-induced processes in the SM and Beyond

Automation within MadGraph5_aMC@NLO and phenomenological studies of loop-induced processes for the LHC

#### MadGraph5_aMC@NLO

Monte Carlo development.

External collaborators: Benjamin Fuks, Kentarou Mawatari, Kaoru Hagiwara, Tim Stelzer, Stefano Frixione, Marco Zaro, Rikkert Frederix, Valentin Hirschi, Paolo Torrielli, Johan Alwall, Hua-Sheng Shao, Mihailo Backovic,...

#### On the unification of gauge coupling constants

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.

#### Precision Phenomenology at the LHC

Higher order corrections to key processes at the LHC (Higgs,...) are computed to higher orders in perturbation theory.

External collaborators: Babis Anastasiou (ETH Zurich) Vittorio Del Duca (ETH Zurich & INFN Frascati) Falko Dulat (SLAC) Elisabetta Furlan (ETH Zurich) Thomas Gehrmann (Universität Zurich) Franz Herzog (Nikhef) Achilleas Lazopoulos (ETH Zurich) Bernhard Mistlberger (CERN).

#### Search for nonresonant Higgs boson pair production in the llbb+MET final state

The discovery of a Higgs boson (H) by the ATLAS and CMS experiments fixes the value of the self-coupling λ in the scalar potential whose form is determined by the symmetries of the Standard Model and the requirement of renormalisability. Higgs boson pair production is sensitive to the self-coupling and will play a major role in investigating the scalar potential structure.

This project consists in a search for nonresonant Higgs boson pair production via gluon fusion in the final state with two leptons, two b jets and missing transvere energy – gg → H(bb) H(WW) asking for the leptonic decay of the W's. The analysis is conducted in close collaboration with phenomenologists to ensure the approach is theoretically sound and future-proof.

#### Study of processes with heavy quarks in the initial state

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.

#### SUSY phenomenology at LHC

Study of the supersymmetric phenomenology at LHC connected to the leptonic experimental searches to go beyond the simplified model spectra approach.

External collaborators: Michael Chala (Desy), Victor Martin Lozano (IFT Madrid), Germano Nardini (ITP Bern).

#### Tensions in flavor physics and two Higgs doublet models

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).

Show past projects.

### Publications

#### 2017

*Brivio, I. and Gavela, M. B. and Merlo, L. and Mimasu, K. and No, J. M. and del Rey, R. and Sanz, V.*

[Abstract] [PDF]

Refereed paper. 22nd January.

*Celine Bœhm,Celine Degrande Olivier Mattelaer, Aaron C. Vincent*

Refereed paper. 9th January.

#### 2016

*R. Frederix, S. Frixione, V. Hirschi, D. Pagani, H.-S. Shao, M. Zaro*

[Abstract] [PDF]

Refereed paper. 10th December.