2024/10/31 by Brian Colquhoun, Colquhoun, Brian, C. T. H. Davies +3
Physics and Astronomy · #FOS: Physical sciences #High Energy Physics - Lattice (hep-lat) #High Energy Physics - Phenomenology (hep-ph) #High-Energy Particle Collisions Research #Particle physics theoretical and experimental studies #Quantum Chromodynamics and Particle Interactions
paper · pdf · doi:10.48550/arxiv.2410.24041
openalex publication_date 2024/10/31 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/31
We calculate the decay rate for ηb → γγ in lattice QCD for the first time, providing a precise prediction for the Belle II experiment. Our calculation includes u, d, s and c quarks in the sea, using gluon field configurations generated by the MILC collaboration, at three values of the lattice spacing from 0.06 fm to 0.03 fm. All quarks are treated in the Highly Improved Staggered Quark formalism, which enables us to reach the b quark mass for our valence quarks on these fine lattices. We calculate quark-line connected correlation functions only. By working at additional heavy quark masses between those of c and b we map out the behaviour of the ratio fηh/(Mηh2Fηh(0,0)), where f is the decay constant, M, the mass and F(0,0), the form factor for decay to two on-shell photons for the pseudoscalar heavyonium meson, ηh. This ratio takes the approximate value 0.5 in leading-order non-relativistic QCD (NRQCD) but we are able to give a much more accurate analysis than this. Focussing on the b quark mass, we find a ratio of 0.467(11), giving Γ(ηb → γγ) = 0.559(32)fit(1)syst keV. Combined with a value for the branching fraction from NRQCD, our result can be used to determine the total width of the ηb with a 6% uncertainty.