Lattice QCD determination of the normalization of the leading-twist photon distribution amplitude and susceptibility of the quark condensate

Le résumé fourni par la source

The normalization of the leading-twist photon distribution amplitude (DA), f γ ⊥ , is an important ingredient in the study of exclusive processes involving the photon emission by means of QCD sum-rules. In this paper we determine the up-, down- and strange-quark contribution to f γ ⊥ by exploiting its relation to the zero-momentum two-point correlation function of the electromagnetic current J em μ and the electric component of the tensor current T μ ν . To that end we employ the gauge ensembles obtained by using N f = 2 + 1 + 1 Wilson-Clover twisted-mass quark flavors, generated by the Extended Twisted Mass (ETM) Collaboration, and after adding all sources of systematic uncertainties, we obtain a total error of 1.5% and 3.5%, respectively, for the light- ( u and d ) and strange-quark contribution to f γ ⊥ ( 2 GeV ) in the MS ¯ scheme, thus improving their accuracy by a factor of 2.3 and 2.8, respectively. For the strange-quark contribution f γ , s ⊥ ( 2 GeV ) , we observe a discrepancy with respect to previous lattice calculations. By combining our result with the world average lattice value of the chiral condensate, we obtain for the susceptibility of the quark condensate χ d MS ¯ ( 2 GeV ) ≃ χ u MS ¯ ( 2 GeV ) = 2.17 ( 12 ) GeV − 2 . Published by the American Physical Society 2024

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