Measurement of $J/ψ\toγη_{\rm c}$ decay rate and $η_{\rm c}$ parameters at KEDR

Abstract

Using the inclusive photon spectrum based on a data sample collected at the J/ψ peak with the KEDR detector at the VEPP-4M e + e − collider, we measured the rate of the radiative decay J/ψ → γη c as well as η c mass and width. Taking into account an asymmetric photon lineshape we obtained Γ 0 γη c = 2.98 ± 0.18 +0.15 −0.33 keV, M η c = 2983.5 ± 1.4 +1.6 −3.6 MeV/c 2 , Γ η c = 27.2 ± 3.1 +5.4 −2.6 MeV.

Study of the radiative decay $J/ψ\rightarrowη_{c}+γ$ in light cone sum rules

“…We hope more efforts on the experimental field will be made to clarify the inconsistencies among various experiments. The second column is the results of lattice QCD [12][13][14][15][16][17], which are totally independent of the mass of c quark, and the lattice QCD results 2.4 − 2.9 keV keep good consistent with current experimental value [3]. The third column is the outcomes from the non-relativistic effective field theories of QCD [10,11], with Ref.…”

“…In this section we focus on the numerical study of the form factor and decay width for J/ψ → η c + γ. For this purpose, we first take several parameters as m η c = 2.9835 GeV, m J/ψ = 3.0969 GeV and f η c / f J/ψ = 0.54 [3,24,25].…”

“…Table I presents a comparison of our decay width with those from experiments and other theoretical models for this process. The first column shows the experimental values of decay width from Crystal Ball [1], CLEO Collaboration [2] and KEDR [3]. It can be seen that the experimental results in different periods of time are inconsistent, and the values are gradually increasing.…”

“…Comparing the experimental and theoretical rates of radiative transition offers a guidance to enhance our understanding of the internal structure of charmonium. Over years, some radiative transition experiments involving J/ψ → η c + γ decay have been measured [1][2][3], and comprehensive theoretical studies have been carried out. The method of dispersion sum rules [4] for J/ψ → η c +γ decay was used on the basis of local duality hypothesis in early papers, however, the local duality hypothesis for the lowest state is not merely a consequence of general principles, because if it is true, one should be proved on the basis of specific dynamics of the process considered.…”

What can we learn about light-meson interactions at electron–positron colliders?

“…The special cases are those of η and η decays, which only involve the pseudoscalar nonet. In the case of the η c , the large decay width 32.0(7) MeV presents certain challenges for amplitude analyses: depending on the decay mode there may be significant contributions from interference with the nonresonant J/ψ → γX decays to the identical final states [530][531][532]. Therefore a viable alternative, where the η c is produced in two-photon processes, is discussed in this section.…”