Experimental Particle and Astro-Particle Physics Seminar

3 October

Precision Tests in the High Energy Era

With increasing integrated luminosity, precision tests of the SM are gaining importance as New Physics search tools at the LHC. I focus on precision studies of SM processes at high-energy and on the challenges that this program faces from a BSM perspective. In particular I discuss the implications of interesting BSM-SM non-interference rules and describe broad scenarios of vector/fermion/scalar compositeness that constitute the primary target for this type of searches.

Signatures of Earth-Shadowing in the Direct Detection of Dark Matter
Direct detection experiments aim to detect the interaction of Galactic Dark Matter (DM) particles with terrestrial nuclei. But many of these DM particles will pass through the Earth before reaching the detector. During this transit, they may interact and scatter, altering their distribution at the Earth's surface and therefore the expected signal at direct detection experiments. Even with current stringent constraints, there remain interesting regions of the DM parameter space where this scattering can be significant. I will therefore sketch the first fully self-consistent calculation of the resulting ‘Earth-Shadowing’ effect, taking into account DM particle deflection and assuming the most general DM-nucleon interactions. Remarkably, in some scenarios, Earth-Shadowing can actually increase the DM flux, while in others the flux is depleted. This results in distinctive daily modulation signatures in direct detection experiments which may be used to confirm the DM origin of a signal or even help distinguish between different DM-nucleon interactions in the future.

D. Buttazzo

Search for CP violation in baryon decays in LHCb

The phenomenon of CP violation has been observed in the K- and B-meson systems, but not yet in the decay of any baryonic particle. Decays of beauty baryons to final states consisting of hadrons with no charm quarks are predicted to have non-negligible CP asymmetries in the SM, as large as 20% for certain three-body decay modes. The LHCb experiment is collecting unprecedented statistics of beauty baryons allowing for the first time to study CP violation in these decays. A systematic study of CP violation in beauty baryon decays can test the validity of the CKM mechanism in the baryon sector, for example by comparing asymmetries with B meson decays with identical underlying quark transitions.

We report on searches for CP violation in baryon decays at LHCb using Run I data. We find evidence for CP violation in Lambdab -> p pi- pi+ pi- decays with a statistical significance corresponding to 3.3 standard deviations, including systematic uncertainties, which might bring to the discovery of CP violation in the baryon sector with additional statistics. An overview of recent LHCb searches for CP violation in baryon decays will be presented, and also prospects for the future.

AEGIS: An experiment to measure the gravitational interaction of antimatter

Two decades after the first production of (relativistic) antihydrogen atoms, and a good decade after the first production of “cold” antihydrogen, first measurements of the properties of antihydrogen have recently begun. Together with the start-up of an additional dedicated low energy antiproton decelerator (ELENA), and the development of a wide range of techniques that permit precise atomic measurements, the study of antihydrogen atoms is set to start in earnest. This presentation will provide an overview of the present status and outlook for fundamental physics with antihydrogen atoms. A special focus will be put on the AEGIS experiment, which in a first step aims to reach a 1% precision on the gravitational interaction of antihydrogen by measuring its free fall over its parabolic trajectory, as well as on the technological developments from a variety of fields on which it relies.

5 December

Top quark physics at 13 TeV with the CMS experiment

The top quark is the most massive elementary particle known. Due to this, it has unique properties. The top quark is deeply related to the Higgs boson and it is expected to play a role in many models of physics beyond the standard model. The measurement of its properties is a test of the standard model consistency.

During the Run-1 of the LHC top physics at the LHC started pushing the high precision regime, especially in top mass. Two months into Run-2, the first measurements of inclusive cross sections of top quark production were made public, establishing top as a standard model model candle at the LHC. With already more than 30 million of top quark pairs produced in collisions at 13TeV at the CMS experiment so far, the Run-2 of the LHC has unlimited potential to explore the top sector. During this talk, top physics at the LHC will be discussed and motivated, and the latest Run-2 results will be presented. We are now in an era of differential measurements, key to understand and improve the modelling of top quark processes, but also potentially sensitive to new physics phenomena. The CMS experiment starts to be sensitive to low cross section processes, such as tt produced with vector bosons or Higgs bosons. In the next months, the first properties at a new center of mass energy will be measured. By the end of this Run, we expect advances in all fronts in top quark physics, potentially shedding light on long standing questions in particle physics.

Vidyo/Talk

F. Canelli