Precise determination of the eta_c mass and width in the radiative J/Psi -> eta_c gamma decay

Abstract

We present an effective field theory based extraction of the η c mass and width from a recent measurement by CLEO of the photon line shape in the J/ψ → η c γ decay.

Current Topics in Heavy Quarkonium Physics

“…The quarkonium magnetic moment is explicitly calculated and turns out to be very small in agreement with a recent lattice calculation [40]; the M1 transition of the lowest quarkonium states at relative order v 2 turn out to be completely accessible in perturbation theory [63]. A description of the η c line shape has been given in [58]. and effective field theory calculation of electric dipole transitions is currently in elaboration [49].…”

Review of heavy quarkonium at weak coupling

“…Finally we mention another interesting study done in Ref. [131] concerning the determination of the η c mass and its total decay width. In that work, the photon line shape was considered in the NR limit using the sum of the magnetic (it has been pointed out in Ref.…”

“…(184) and (185) for the theoretical signal together with the two background sources used in CLEO. From Ref [131]…”

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

“…Here ω is a photon energy, α is the fine structure constant, e c and m c are c-quark charge (in electron charge units) and mass, M = η c | j 0 (ωr/2)|J/ψ is the matrix element of the transition (without relativistic corrections), j 0 (x) = sin(x)/x, BW(ω) is a Breit-Wigner function. A typical momentum transfer inside the charmonium bound state is about 700 to 800 MeV [16] (this is of the order of the inverse size of the system), so the matrix element is almost constant (close to one) up to such photon energies. Therefore, in this energy range the decay spectrum dΓ(ω) dω ∼ ω 3 BW(ω).…”