5 derniers séminaires
In the Standard Model, Yukawa-like interactions are short-range interactions between the fermions and the Higgs boson. Even though these interactions have important macroscopic consequences, only a subset of them could be observed directly and their origin remains unclear. At the LHC, the top and the b-quark are very sensitive probes for particles with Yukawa-like interactions, due to their large mass. This includes Higgs bosons, but also new scalar particles predicted by theories beyond the standard model and connected to the dark sector. By virtue of the t→bW branching ratio being close to 100%, both b- and top quarks are inferred by the presence of hadronic jets initiated by b-quarks, called b-jets, in the final state. I will introduce b-jet identification at the LHC and demonstrate its crucial role to study the coupling of the Higgs boson to third-generation fermions and probe the dark sector. I will highlight the importance of b-jet identification for the future steps of the LHC physics program and discuss the main experimental challenges.
Plan A: Vidyo
Charged-lepton magnetic moments play a special role in probing the standard model (SM) of particle physics, which is complementary to direct searches for new physics at the energy frontier. In particular, the experimental value of the anomalous contribution to the muon magnetic moment, $a_\mu=(g_\mu-2)/2$, has exhibited a persistent discrepancy of over 3 standard deviations with the SM prediction, ever since the very precise measurement made at Brookhaven National Lab in the early 2000s. This is particularly enticing, because it could indicate the presence new, fundamental physics. At present, theoretical and experimental uncertainties are comparable in size. However, a new experiment underway at Fermilab, and another one planned at J-PARC, are aiming to reduce the error on the measurement of $a_\mu$ by a factor of 4. To fully leverage these future measurements, and possibly claim the presence of new fundamental physics, it is imperative to check the SM prediction with independent methods and to reduce its uncertainties. After an introduction and a discussion of the current experimental and theoretical status of $a_\mu$, I will present a new lattice QCD calculation of the contribution to this quantity that most limits the precision of its SM prediction. Surprisingly, our result eliminates the need to invoke new physics to explain the current measurement of $a_\mu$.
France +33 1 7037 2246
France +33 1 7037 9729
France +33 7 5678 4048
Plan B: Vidyo
Two thirds of the surface of our planet are covered by water and are still poorly instrumented, which has prevented the earth science community from addressing numerous key scientific questions. The strategy explored here is to leverage the network of fiber optic seafloor telecom cables already in place and that criss-cross the oceans. This is made possible by the metrological approach called Distributed Acoustic Sensing (DAS) which analyze the properties of the light back-propagated to infer strain variations of the fiber. I will present results of measurements performed on the 41.5 km-long MEUST-NUMerEnv telecom cable deployed offshore Toulon, France. Our observations demonstrate the capability of the approach to turn the cable into a dense network of seismo-acoustic sensors; here we recorded at 2kHz over more than 6500 sensors. With these sensors we can monitor with unprecedented details the ocean-solid earth interactions from the coast to the abyssal plain, the propagation of waves generated by regional micro-earthquakes or simply track passing boats. The ability of DAS to provide a dense sampling of the seismo-acoustic wavefield over large distances is unique and paves the way to many more applications and new discoveries.
Anthony Sladen: https://asladen.github.io
The Belle II international collaboration has published its first results in a paper selected as an Editors’ Suggestion in Physical Review Letters. The paper reports the first search for a new type of elementary particle that may act as a “portal” between ordinary matter and dark matter, which is understood to make up some 85% of the matter in the universe. Cosmological observations in recent years provide strong evidence that only 15% of the mass of the matter of the universe is known to us, while the remaining 85% is composed of some still undetected and mysterious particles known as dark matter. A great deal of effort in the international particle physics community, including the Belle II experiment, is now focused on finding evidence of dark matter particles.
The Belle II experiment, which operates at the SuperKEKB electron-positron collider in Tsukuba, Japan, searched for a hypothetical new particle called the Z’ that may act as a “portal” between ordinary matter and dark matter. Belle II data collected in 2018 shows no evidence of the Z’, setting new limits on the properties of such a particle.
Plan A: Vidyo