2021/12/02 by R. Frezzotti, Frezzotti, R., G. Gagliardi +9
Physics and Astronomy · #FOS: Physical sciences #High Energy Physics - Lattice (hep-lat) #High Energy Physics - Phenomenology (hep-ph) #hep-lat #hep-ph
paper · pdf · doi:10.48550/arxiv.2112.01066
12 pages, 6 figures. Talk presented at the 38th International Symposium on Lattice Field Theory (Lattice 2021), 26-30 July, 2021, Zoom/Gather@Massachusetts Institute of Technology
arxiv created 2021/12/02 · arxiv updated 2021/12/03
We present our preliminary results concerning the charged/neutral pion mass difference Mπ+ - Mπ0 at order O(αem) in the QED interactions, and for Mπ+ - Mπ0 at order O( (md-mu)2) in the strong isospin-breaking term. The latter contribution provides a determination of the \rmSU(2) chiral perturbation theory low-energy constant ℓ7, whose present estimate is affected by a rather large uncertainty. The disconnected contributions appearing in the diagrammatic expansion of Mπ+ - Mπ0, being very noisy, are notoriously difficult to evaluate and have been neglected in our previous calculations. By making use of twisted mass Lattice QCD simulations and adopting the RM123 method, we will show that taking profit from our recently proposed rotated twisted-mass (RTM) scheme, tailored to improve the signal on these kinds of observables, it is possible to evaluate the disconnected diagrams with good precision. For the QED induced pion mass difference, we obtain, after performing the extrapolation towards the continuum and thermodynamic limit and at the physical point, the preliminary value Mπ+-Mπ0 = 4.622~(95)~\rm MeV, that is in good agreement with the experimental result. For the determination of the low-energy constant ℓ7, our result ℓ7 = 2.5~(1.4)× 10-3, which is limited so far to a single lattice spacing, is in agreement and improves phenomenological estimates.