First observation of the decay φ→η′(958)γ

New measurement of the rare decay φ→η′γ with CMD-2

“…The obtained value of the branching ratio B(φ → η ′ γ) (8.2 +2.1 −1.9 ± 1.1) · 10 −5 . agrees with our previous result based on part of the whole data sample [ 2] (12.0 +7.0 −5.0 ± 1.8) · 10 −5 as well as with the result of the SND group [ 3] (6.7 +3.4 −2.9 ± 1.0) · 10 −5 and is more precise. Within experimental accuracy it is also consistent with the preliminary result of CMD-2 based on other decay modes of the η meson (η → π + π − π 0 , π + π − γ) with four charged pions and two or more photons in the final state [ 6]:…”

“…The results of our analysis have higher statistical significance than before since they are based on a data sample of 21 selected events compared to 6 events in our previous work [ 2] and 5 events observed by SND [ 3]. The obtained value of the branching ratio B(φ → η ′ γ) (8.2 +2.1 −1.9 ± 1.1) · 10 −5 .…”

“…Radiative decays of vector mesons have traditionally been a good laboratory for various tests of the quark model and SU(3) symmetry [ 1]. A recent discovery of the φ → η ′ γ decay by the CMD-2 group [ 2] has been the last link in the otherwise complete picture of radiative magnetic dipole transitions between light vector and pseudoscalar mesons. This observation was later confirmed by the SND group [ 3].…”

Radiative decays of light vector mesons

“…The first observation of this decay was done at VEPP-2M in CMD-2 experiment [8]. The measurement of this decay at SND was performed with η ′ decaying into π + π − η and η into two γ's.…”

Rare Φ Decays and Exotic Hadrons

“…The large number of produced φ mesons at both SND and CMD-2 detectors (N φ ≃ 4.5 · 10 7 ) allows to carry out the search of rare φ decay. The long awaited decay φ → η ′ (958)γ was first observed by CMD-2 [17]. In the decay chain φ → η ′ γ, η ′ → ηπ + π − , η → γγ the branching ratio was (8.2 +2.1 −1.9 ) · 10 −5 .…”