2024 has come to an end, and we take this opportunity to look back and highlight the remarkable milestones achieved by the LPHE research teams throughout the year.
Physics Results
The LPHE researchers have actively contributed to several significant physics results released during the year, including:
Lepton flavour universality under test
The LHCb experiment at CERN has performed the first measurement to test lepton flavour universality between muons and electrons using B+→ K⁺π+π–l+l– decays. Moreover, the collaboration reported also the first observation of the B+→ K⁺π+π– e+e– decay. The measured ratio of branching fractions RKππ-1 = 1.31+0.18-0.17 (stat) +0.12-0.09 (syst) is compatible with Standard Model prediction at 1.7σ, setting constraints on possible lepton flavour universality violating extesions of the Standard Model.
For more details, see the paper here.
Observation of the K+ → π+νν̅
The NA62 experiment at CERN has achieved a groundbreaking measurement of the ultra-rare K⁺ → π⁺νν̅ decay, based on data collected from 2016 to 2022. The branching ratio was determined to be (13.0+3.3−3.0 )×10−11, the smallest ever measured with a significance above 5σ. This result marks a major milestone in precision tests of the Standard Model.
For more details, see the paper here.
Neutrino Tagging
The NA62 experiment at CERN has achieved the first-ever detection of a tagged neutrino candidate. This milestone was based on data from 2022, where a K⁺ → μ⁺νμ decay was reconstructed, and the neutrino was identified through its charged-current interaction in the liquid krypton calorimeter.
See the paper here.
Study of the rare decay J/ψ → μ⁺μ⁻μ⁺μ⁻
The LHCb experiment at CERN has observed the rare electromagnetic decay J/ψ → μ⁺μ⁻μ⁺μ⁻ with a significance well above the discovery threshold. Based on data collected between 2016 and 2018, the branching fraction of this decay is determined to be (1.13 ± 0.10 ± 0.05 ± 0.01) × 10⁻⁶, providing new insights into quantum electrodynamics and the properties of the J/ψ particle.
See the publication:
Review of HNL searches in CMS
The CMS collaboration has published a review of searches for vector-like quarks, vector-like leptons and heavy neutral leptons in p-p collisions. These new particles appear in many possible extensions of the standard model and are well motivated theoretically, explaining the appearance of three generations of leptons and quarks, the mass hierarchy across these generations and the nonzero neutrino masses. The results provided by our lab, specifically in the HNL searches at the CMS experiment, are an important contribution to publication in the field of beyond Standard Model physics.
The review can be read here.
Microlens-enhanced SiPMs
In the context of the LHCb Upgrade II, our lab is working on a novel concept for Silicon PhotoMultipliers coating to enhance the photon detection efficiency of these photodetectors. Results after placing spherical cap microlenses on top of the SiPM pixels show an important improvement in SiPM characteristics, such as an increase in light collection efficiency, a reduction in noise and an overall better time performance.
See the publication on Arxiv.
In other news
- In June, Elisabeth Maria Niel, a postdoc at LPHE at the time, was awarded the LHCb Early-Career Scientist award for her outstanding contributions to the commissioning and operation of the SciFi detector.
- Still in June, Sara Celani, former LPHE PhD student, has been awarded with the LHCb Thesis Award 2024 for her thesis “Testing lepton flavour universality in B+→ K⁺π+π–l+l– decays with LHCb”
- In August, Prof. Fred Blanc became the Physics Coordinator of the LHCb experiment for 2024-2026 period.
- In November, two SNSF Starting Grants were awarded: Chiara Perrina (LPHE) with the project title “SPACER – Redefining the Cosmic-Ray and Gamma-Ray Physics Frontier in Space with DAMPE and HERD“; and Laurent Dufour (CERN) with the project title “Connecting searches for New Physics in Charm decays (CONNECT)“.
- We had one PhD student graduating from our group: Sebastian Schulte. He is now working at the Swiss Post Headquarters in Bern.
- This year we had an outstanding amount of 13 master students completing their master projects under the responsibility of LPHE.