La physique des particules explore les briques élémentaires de la matière et leurs interactions, qui déterminent la structure et les propriétés de la matière dans l'univers. Le portail web rend ces recherches fascinantes compréhensibles pour un public intéressé.en plus

Image : ESO, R. Fosburyen plus

Precision with a Broad Benefit

Marco Valente is a PhD student, born in Ticino and is currently working at the University of Geneva. He is evaluating the performance of a method from which it is expected to improve important measurements of the ATLAS experiment at CERN. For his current studies, the 23 years old researcher has just been awarded with a poster prize given by the Swiss Physical Society (SPS).

Marco Valente with the poster awarded on the occasion of the CHIPP/SPS annual meeting 2016 in Lugano.
Image : B. Vogel

In towns like Basel, Bern, Geneva, Lausanne or Zurich particle physics has a strong basis in academic institutions active in research and teaching in theoretical and experimental particle physics. Even though Ticino has its own university, there is no academic institution dedicated to particle physics in southern Switzerland. High school students who intend to study particle physics after their graduation subsequently have to look for a university on the northern side of the Alps.

From LHCb to ATLAS

Marco Valente, born in Mendrisio as the son of an architect and a saleswoman, moved to Lausanne and joined EPFL for his undergraduate studies. In March 2016 he finished his physics studies with a Master's thesis on mixing and CP violation in charmed meson systems that he elaborated within the LHCb group of Prof. Olivier Schneider at EPFL. Subsequently, Marco obtained a PhD research position under the supervision of Prof. Anna Sfyrla, a particle physicist at the University of Geneva working on ATLAS, one of the large experiments at the CERN Large Hadron Collider (LHC).

Junior researchers newly joining the ATLAS team are expected to perform a 'qualification task' during their first year of membership. This is a research activity providing the new members of the ATLAS collaboration an insight into the working of the ATLAS experiment but also resulting in a benefit to the whole collaboration. The qualification task of Marco Valente concerns the so-called 'missing transverse momentum', usually referred as MET. In a very general way, MET is a physical quantity measured by the LHC particle detectors after the collision of two protons. The principle underlying this measurement is a very basic law of physics, which states that the total transverse momentum of a high-energy collision has to be conserved (for two LHC protons the total transverse momentum is initially null). Supposing that all the particles resulting from the proton-proton collision would be perfectly reconstructed by the ATLAS detector, this law would immediately imply a null missing transverse momentum (MET= 0). However, the presence of particles escaping the detection would produce an imbalance of the total transverse momentum and a non-zero MET value. Within the Standard Model of particle physics, neutrinos are generally the source of non-zero values of MET at the LHC. Nevertheless, in many of the modern theoretical physics models, this feature is also a hint for the existence of hitherto unknown forms of matter, e.g. dark matter or supersymmetric particles.

A basis for further research activities

The measurement of MET with maximal precision represents a fundamental asset for the searches conducted by the ATLAS experiment. Marco Valente: "Actually, a team of about 10 physicists is trying to commission a reconstruction technique on ATLAS called ‘Particle Flow’, aiming to improve the object reconstruction of the ATLAS detector. During my first half year at the ATLAS experiment I have tried to apply this reconstruction method to the measurement of MET and I have provided a preliminary performance assessment using various simulated event samples. From my actual studies, it seems that Particle Flow is successfully improving the precision of the MET measurement at the ATLAS detector. If this outcome will be confirmed by the upcoming validation it will serve in future as a basis for different ATLAS working groups dealing with the search for dark matter, supersymmetric particles, sterile neutrinos and studies of the recently discovered Higgs boson."

Marco Valente has showcased his provisional findings at the poster session of the annual meeting of the SPS taking place on 23–25 August 2016 at the Università della Svizzera italiana (USI) in Lugano. For this outstanding contribution to the ATLAS collaboration he received one of three Poster Prizes awarded in Lugano. This work is also expected to be for Marco Valente the first step towards the intended PhD thesis on supersymmetric particle searches. This investigation is dedicated to the general goal confirming the idea of theoretical physicists that every of the 18 known elementary particles has a supersymmetric partner. „We hope to be able to detect supersymmetric particles with the current LHC run at an energy of 13 TeV“, says Valente. Fantastic perspectives!

Author: Benedikt Vogel


  • Particules élémentaires
  • Physique des particules élémentaires