Lattice study of two-photon decay widths for scalar and pseudo-scalar charmonium *

Abstract

This exploratory study computes two-photon decay widths of pseudo-scalar ( ) and scalar ( ) charmonium using two ensembles of twisted mass lattice QCD gauge configurations. The simulation is performed using two lattice ensembles with lattice spacings fm with size and fm with size . The decay widths for the two charmonia are obtained within the expected ballpark, but are however smaller than the experimental ones. Possible reasons for these discrepancies are discussed.

Lattice calculation of $χ_{c0} \rightarrow 2γ$ decay width

“…In this paper, we study the two-photon decay width of χ c0 , which has been extensively studied from both experimental and theoretical sides. On the experimental side, using the decay of ψ(3686) → γχ c0 , χ c0 → γγ, both CLEO-c and BESIII collaborations reported results of the two-photon decay width Γ γγ (χ c0 ) [3,4]: (35) stat (22) syst keV Γ BESIII γγ (χ c0 ) = 2.03 (8) stat (14) syst keV Γ P DG γγ (χ c0 ) = 2.20 (22)keV (1) where the first line from CLEO-c, the second from BE-SIII and the last line being the PDG quoted value with combined errors. It is expected that more accurate results for these decay width will become available in the near future.…”

Opportunities for studying C+ resonances at 3--12 GeV photon collider

“…Within this formalism, physical quantities are encoded in various Euclidean correlation functions, which in turn can be measured by performing Monte Carlo simulations. Two-photon decay widths for scalar and pseudoscalar charmonium are recently estimated to be about 1 keV [28] that is smaller than experimental values.…”

“…Another way to study non-perturbative QCD is the lattice QCD [25][26][27][28][29], which is a quantum field theory defined on the discrete Euclidean space-time. Within this formalism, physical quantities are encoded in various Euclidean correlation functions, which in turn can be measured by performing Monte Carlo simulations.…”

Two-photon transitions of charmonia on the light front

“…A DSE/BSE result is included for comparison [16]. Two recent Lattice calculations are less successful due to the difficulty to represent the photon with large virtuality [12,13]. More recent Lattice calculations instead focus on the on-shell amplitude.…”

“…Lattice computation of the two-photon transition with off-shell photons is particularly challenging, as demonstrated by the large discrepancy between theoretical predictions and the PDG value, since the energetic virtual photon is not an eigenstate of the QCD Hamiltonian [11]. Nevertheless, strides have been made to access the twophoton width [10,[12][13][14][15], and transition form factors [10,12]. Calculations from other relativistic approaches, notably DSE/BSE, have also been reported in the literature and appear successful [16].…”