Speaker
Description
We present a first calculation of the $K\gamma \to K\pi$ transition amplitude in the presence of a resonant $K^*$ from lattice quantum chromodynamics. In this process, the kaon interacts with a photon and scatters strongly to a $K\pi$ in the final state. The $K\pi$ state is in a lowest relative $S$ $\&$ $P$-wave, with the $K^*$ resonance appearing in the $P$-wave.
The matrix elements for the $K\gamma \to K\pi$ transition are calculated in finite-volume lattice QCD. To map these matrix elements to the infinite volume transition amplitudes which are measured in experiments, we apply the Lellouch-Lüscher formalism. We determine the transition amplitude for different $K\pi$ energies and photon virtualities to observe an enhancement due to the $K^*$ resonance. From the energy dependence, we extract the $Kγ \to Kπ$ transition form factor for the unstable $K^*$ by analytically continuing into the complex energy plane and calculating the residue at the $K^*$ pole.
| speaker affiliation | William & Mary / Tata Institute of Fundamental Research |
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