Topic of Research Seminar: An Overview of Flavor Physics

Abstract: An overview of Flavor Physics in the quark sector of particle physics is presented, concentrating on some selected topics. The principal focus of this talk is on the precision measurements undertaken at a number of high energy physics laboratories, in particular, the B-factories and the LHC. On the theoretical side, great progress has been made with the help of QCD, the theory of strong interactions. The low energy effective theory of the charged weak currents is characterized by the universal couplings to the fermions, and the main parameters are the Fermi coupling constant and the Cabibbo-Kobayashi-Maskawa (CKM) matrix elements. At higher energies, the Fermi coupling constant is replaced by the charged weak boson mass. Their current precise determinations are reviewed. The next topic is the physics of rare $B$-meson decays, induced by weak neutral currents. They are absent in the standard model Lagrangian, and arise through virtual loops, in which the heavy quarks top and charm play a dominant role. Precise theoretical calculations for these processes are undertaken in the framework of an effective Hamiltonian, which is used to incorporate the strong interaction effects, carried out in perturbative QCD, involving higher orders in the QCD coupling constant, and non-perturbative quantities, such as the hadronic matrix elements and form factors. The experimental era of rare $B$-decays started with the measurement of the decay $B \to K^* \gamma$ by CLEO in 1993, followed two years later by the measurement of the inclusive decay $B \to X_s \gamma$, which serves as the standard candle in this field. The frontier has broadened and moved in the meanwhile to the experiments at the LHC, with the decay $B^0 \to \mu^+ \mu^-$ at about 1 part in $10^{10}$ being the smallest branching fraction measured so far. Experimental precision achieved in this area has put the standard model to unprecedented stringent tests, and more are in the offing in the near future. The high-luminosity LHC and Belle II experiment at the Japanese KEK laboratory are expected to contribute greatly in this endeavor.

Name of Speaker: Prof. Ahmed Ali

Professorial Rank of Speaker: Professor

Affiliation of Speaker: Yaroslavl State University, Russia

Date and Venue: (Wednesday) 04 February, 2026, 12:00 PM, Seminar Hall, School of Mechanical and Manufacturing Engineering (SMME), NUST Islamabad