Measurements of branching ratios for η decays into charged particles

Abstract

The WASA-at-COSY experiment has collected 3 × 10 7 events with η mesons produced via the reaction pd → 3 He η at T = 1.0 GeV. Using this data set, we evaluate the branching ratios of the decays η → π + π − γ ,

A data-driven approach to ${{\rm{\pi }}}^{0},{\rm{\eta }}$ and ${{\rm{\eta }}}^{\prime}$ single and double Dalitz decays

“…2, for the factorisation approach, and from the uncertainty associated with the slope, b η , for the description using CAs. Comparing with present experimental status, our prediction for η → e + e − e + e − is compatible at less than 1σ with the KLOE measurement [11], as well as with the recent measurement value of the WASA@COSY collaboration [6], while our estimate for η → µ + µ − µ + µ − respects the current upper bound of Ref. [5].…”

“…The branching ratio for the decay η → e + e − γ has recently been measured by the A2 Collaboration at MAMI [3], (6.6±0.4±0.4)×10 −3 (see also the most recent result in Ref. [4]), and the CEL-SIUS/WASA Collaboration [5], (7.8 ± 0.5 ± 0.8) × 10 −3 , whilst the PDG quoted value is (6.9 ± 0.4) × 10 −3 [1], in accordance with the result, (6.72 ± 0.07 ± 0.31) × 10 −3 , from the WASA@COSY Collaboration [6]. The decay η → µ + µ − γ has been studied by the NA60 Collaboration at CERN SPS [7], though they do not provide a value for the branching ratio.…”

“…Regarding the double Dalitz decays, the KTeV Collaboration measured the branching ratio of the decay π 0 → e + e − e + e − , (3.46 ± 0.19) × 10 −5 [10], thus averaging the PDG result to (3.38 ± 0.16) × 10 −5 [1]. The KLOE Collaboration reported the first experimental measurement of η → e + e − e + e − [11], (2.4 ± 0.2 ± 0.1) × 10 −5 , which is in agreement with the result, (3.2±0.9±0.5)×10 −5 , provided by the WASA@COSY Collaboration [6]. In Ref.…”

Experimental input for the HLbL contribution to themuon(g−2)

“…To extend the predictions to other kinematic regions of the η and η TFFs, the data for other processes are needed e.g. e + e − → η ( ) π + π − (recent measurements from SND [59] and BaBar [60]) or decays η ( ) → π + π − e + e − (recent study of the η decay at WASA-at-COSY [61]).…”

Spin Dependence of η Meson Production in Proton-Proton Collisions Close to Threshold

“…In particular, the η → γγ and η → 3π 0 → 6γ decay channels with the highest branching ratios (altogether over 71% [30]) were used in the presented analysis. A detailed description of the WASA-at-COSY experiment, as well as methods and results of the monitoring of the interaction region, was given in the dedicated articles [31][32][33][34].…”