arXiv subjects
Publications and source records attributed to R. D. Moise.
The performance of the ring-imaging Cherenkov detectors at the LHCb experiment is determined during the LHC Run 2 period between 2015 and 2018. The stability of the Cherenkov angle resolution and number of detected photons with time and running conditions is measured. The particle identification performance is evaluated with data and found to satisfy the requirements of the physics programme.
The crown jewel of particle physics, the Standard Model (SM), has withstood numerous experimental trials. However, there are still some observations it cannot explain. Examples such as dark matter and the matter-antimatter imbalance in the Universe come to mind. The SM may be extended, by including additional particles and interactions, so as to explain such phenomena. These new particles and interactions are collectively referred to as "new physics" (NP), and the results covered by this article provide a promising lead for their discovery.
The Standard Model of particle physics predicts that charged leptons have the same electroweak interaction strength. This symmetry, called lepton flavour universality, was found to hold in a wide range of particle decays. One observable that is sensitive to lepton flavour universality is the ratio of branching fractions $R_K=\mathcal B(B^+\to K^+μ^+μ^-)$ $/$ $\mathcal B(B^+\to K^+e^+e^-)$. This quantity is measured using $9$ fb$^{-1}$ of proton-proton collision data recorded by the LHCb experiment at CERN's Large Hadron Collider. For the dilepton invariant mass squared range $q^2\in(1.1$ $\text{Ge}\kern -0.1em \text V^2,$ $6.0$ $\text{Ge}\kern -0.1em \text V^2)$, the result is $R_K=0.846^{+0.042}_{-0.039}{}^{+0.013}_{-0.012}$, where the first uncertainty is statistical and the second systematic. The measured value is in tension with the Standard Model prediction at the level of $3.1$ $σ$, thus providing evidence for the violation of lepton flavour universality in $B^+\to K^+\ell^+\ell^-$ decays.