- Name
- Laurent Forthomme

- Position
- Former member

PhD student in CP3 from September 2010 to April 2016

Current position:**Postdoctoral researcher at the University of Helsinki.**

- My personal homepage

- I am involved in the following research directions:

#### GasToF: ultra fast timing detector

GasToF (Gas Time-of-Flight) detector is a Cherenkov detector developed for very precise (with ~10 ps resolution) flight time measurements of very forward protons at the LHC. Such an excellent time resolution allows, using z-by-timing technique, for precise measurements of the event vertex z-coordinate and the background reduction. This detector is essential for selecting exclusive and semi-exclusive processes at the LHC, and can also be applied for the particle ID at future experiments.

External collaborators: CMS PPS project, M. Albrow (Fermilab), M. Khakzad (Tehran), J. Varela (Lisbon), and E. Schnys (Photonis) and J. Howorth (Photek Ltd).

#### 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).

- Hide past projects.

I am involved in the following research directions:

#### Advanced Techniques for Fast Simulation and Data Analysis in High Energy Physics (ASAP)

The discovery of the 125GeV Higgs boson by the LHC experiments has finally opened a new era in the exploration of the TeV scale. The physics programs of CMS and ATLAS aim far beyond the simple discovery, and vigorously pursue the full characterization of the newly discovered state and the full exploration of the TeV scale in search of new phenomena. A key lesson drawn from first two years of LHC running is that most probably first discoveries and then identification of new states/interactions will not be easy. On the one hand, model-independent searches in simple topologies such as single/multi lepton at high transverse momenta have not shown any hint of new physics so far. On the other, topologies with jets and/or missing transverse energies, much more challenging experimentally, do strongly depend on the underlying theoretical models so that efficiently identifying signal enhanced regions of the phase space is quite involved. In this context, multi-variate techniques have become more and more central in the analysis of data from hadron collider experiments, to maximally exploit the information available on the signal and on the backgrounds. Amongst the most advanced techniques and certainly the most powerful one from the theoretical point of view, the so called matrix element method stands out. The main goal of this proposal is to advance the use and the scope of the matrix-element method so to significantly extend the range of physics applications at the LHC to the search of new physics. First we aim at providing the experimental HEP community with complete and automatic simulation tools, such as MadWeight/MoMEMta and Delphes, that overcome the technical limitations of the method. Second we propose to test and apply the new tools to current analyses in signatures that involve final state leptons and b-jets. Finally, we explore new and original applications of the method to both model-dependent or model-independent searches of new physics at the LHC.

External collaborators: CMS collaboration.

#### Validation of a fully automatic matrix element technique for CMS data analyses

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.

#### 2016

#### 2015

*CMS collaboration*

[Full text]

Public experimental note. 3rd October.

#### 2014

*Gustavo Gil da Silveira, Laurent Forthomme, Krzysztof Piotrzkowski, Wolfgang Sch\"afer, and Antoni Szczurek*

[Abstract] [PDF] [Journal] 26 pages, 40 figures, 2 tables, submitted to JHEP

Refereed paper. 4th September.

#### 2013

*CMS Collaboration*

[Abstract] [PDF] [Journal] [Full text 1] [Full text 2] Published in JHEP 07 (2013) 116 [FSQ-12-010]

Refereed paper. 31st May.