Observation of the hindered electromagnetic Dalitz decay psi(3686) -> e(+) e(-)eta(c)

• Using a data sample of (448.1 +/- 2.9) x 10(6) psi(3686) decays collected at an e(+)e(& minus;) center-of-mass energy of 3.686 GeV by the BESIII detector at Beijing Electron Positron Collider II, we report an observation of the hindered electromagnetic Dalitz decay psi(3686) -> e(+)e(& minus;)eta(c) with a significance of 7.9 sigma. The branching fraction is determined to be B(psi(3686) -> e(+)e(& minus;)eta(c)) = (3.77 +/- 0.40(stat) +/- 0.18(syst)) x 10(& minus;5), agreeing well with the prediction of the vector meson dominance model. This is the first measurement of the electromagnetic Dalitz transition between the psi(3686) and the eta(c), which provides new insight into the electromagnetic properties of this decay, and offers new opportunities to measure the absolute branching fractions of eta(c) decays.

Subject headings

NATURVETENSKAP  -- Fysik -- Subatomär fysik (hsv//swe)

NATURAL SCIENCES  -- Physical Sciences -- Subatomic Physics (hsv//eng)

NATURVETENSKAP  -- Fysik -- Astronomi, astrofysik och kosmologi (hsv//swe)

NATURAL SCIENCES  -- Physical Sciences -- Astronomy, Astrophysics and Cosmology (hsv//eng)

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