# Phenomenology of elementary particles

Louvain-La-Neuve

The phenomenology of the fundamental interactions encopasses a wide range of research activities, whose main characteristic is to sit at the boundary between theory and experiment. Day-to-day interactions and collaborations between theorists and the experimentalists at the Centre foster new ideas in different ways.

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:

1. Collider phenomenology
2. Flavour physics
3. Precision EW and QCD calculations
4. BSM : model building and alternative EWSB mechanims
5. Computational tools for HEP

### Projects

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)

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).

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

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).

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.

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

External collaborators: Cen Zhang, Celine Degrande.

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.

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

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

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-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).

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

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,...

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.

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).

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.

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 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).

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).

### Recent publications

#### 2018

Long-Lived Particles at the Energy Frontier: The MATHUSLA Physics Case
Curtin, David and others
[Abstract] [PDF]
21st June.
Constraining anomalous gluon self-interactions at the LHC: a reappraisal
Valentin Hirschi, Fabio Maltoni, Ioannis Tsinikos, Eleni Vryonidou
12th June.
Leptogenesis and the Dirac Phase
Marco Drewes
[Journal]
Contribution to proceedings. 11th June.
Perspectives to find heavy neutrinos with NA62
Drewes, Marco and Hajer, Jan and Klaric, Juraj and Lanfranchi, Gaia
[Abstract] [PDF]
Contribution to proceedings. 11th June.
BSM Hadronic Matrix Elements for epsilon'/epsilon and K->PiPi Decays in the Dual QCD Approach
Jason Aebischer, Andrzej J. Buras and Jean-Marc Gérard
25th May.
MoMEMta, a modular toolkit for the Matrix Element Method at the LHC
Brochet, Sébastien and Delaere, Christophe and François, Brieuc and Lemaître, Vincent and Mertens, Alexandre and Saggio, Alessia and Vidal Marono, Miguel and Wertz, Sébastien
[Abstract] [PDF]
23rd May.
Impact of cosmological and astrophysical constraints on dark matter simplified models
Chiara Arina
[Abstract] [PDF]
Refereed paper. 11th May.
Probe Higgs-gluon coupling via jet energy profile at e + e − colliders
Gexing Li, Zhao Li, Yandong Liu, Yan Wang, and Xiaoran Zhao
Refereed paper. 10th May.
Automated computation of one-loop amplitudes
C. Degrande, V. Hirschi, O. Mattelaer
9th May.
MadDM v.3.0: a Comprehensive Tool for Dark Matter Studies
F. Ambrogi, C. Arina, M. Backovic, J. Heisig, F. Maltoni, L. Mantani, O. Mattelaer, G. Mohlabeng
[Abstract] [PDF]
Refereed paper. 30th March.
Dual QCD Insight into BSM Hadronic Matrix Elements for K0−K¯0 Mixing from Lattice QCD
Buras, Andrzej J. and Gerard, Jean-Marc
[Abstract] [PDF]
29th March.
Leptogenesis, dark matter and neutrino masses
$K\to\pi\pi$ and $K-\pi$ Matrix Elements of the Chromomagnetic Operators from Dual QCD