Higher-order multipole amplitude measurement in ${\ensuremath{\psi}}^{\ensuremath{'}}\ensuremath{\rightarrow}\ensuremath{\gamma}{\ensuremath{\chi}}_{c2}$

Higher-order multipole amplitude measurement in $ψ^{'} \to γ χ_{c 2}$

M. Ablikim et al. (BESIII Collaboration)

Phys. Rev. D 84, 092006 – Published 22 November 2011

Abstract

Using $106 \times 10^{6}$ $ψ^{'}$ events collected with the BESIII detector at the BEPCII storage ring, the higher-order multipole amplitudes in the radiative transition $ψ^{'} \to γ χ_{c 2} \to γ π^{+} π^{-} / γ K^{+} K^{-}$ are measured. A fit to the $χ_{c 2}$ production and decay angular distributions yields $M 2 = 0.046 \pm 0.010 \pm 0.013$ and $E 3 = 0.015 \pm 0.008 \pm 0.018$ , where the first errors are statistical and the second systematic. Here M2 denotes the normalized magnetic quadrupole amplitude and E3 the normalized electric octupole amplitude. This measurement shows evidence for the existence of the M2 signal with $4.4 σ$ statistical significance and is consistent with the charm quark having no anomalous magnetic moment.