Precision measurements of branching fractions forψ′→π0J/ψandηJ/ψ

Abstract

We present a precision study of the ψ ′ → π 0 J/ψ and ηJ/ψ decay modes. The measurements are obtained using 106 × 10 6 ψ ′ events accumulated with the BESIII detector at the BEPCII e + e − collider operating at a center-of-mass energy corresponding to the ψ ′ mass. We obtain B(ψ ′ → π 0 J/ψ) = (1.26 ± 0.02 (stat.) ± 0.03 (syst.)) × 10 −3 and B(ψ ′ → ηJ/ψ) = (33.75 ± 0.17 (stat.) ± 0.86 (syst.)) × 10 −3 . The branching fraction ratio R = B(ψ ′ →π 0 J/ψ) B(ψ ′ →ηJ/ψ) is determined to be (3.74±0.06 (stat.)±0.04 (syst.))×10 −2 . The precision of these measurements of B(ψ ′ → π 0 J/ψ) and R represent a significant improvement over previously published values.

Search for hc→π+π−J/ψ<

“…In order to validate the event selection criteria, we calculate the branching fraction Bðψð3686Þ → ηJ=ψÞ and compare it with a previous BESIII measurement [24], where η is reconstructed via two photons and only the first set of the data sample of ð107.0 AE 0.8Þ million ψð3686Þ taken in 2009 [14] was used. In our calculation, the yield of ψð3686Þ → ηJ=ψ; η → π 0 π þ π − is obtained by counting events in the η signal region and subtracting the events in the η sideband region.…”

Isospin violations at BESIII

“…Thereby, the decay amplitudes reflect the flavor symmetry breaking, and it is the mass differences within the multiplet that generates the isospin or the SU(3) breaking [26]. The ratio R π 0 /η was found to be (3.74 ± 0.06 ± 0.04)% by BESIII, with unprecedented high precision [27]. Another isospin-violating transition ψ ′ → π 0 h c was observed to be B(ψ ′ → π 0 h c ) = (8.4 ± 1.3 ± 1.0) × 10 −4 by the BESIII Collaboration [28].…”

Searches for isospin-violating transitions $χ_{c0,2} \rightarrow π^{0} η_{c}$

“…The maximum value of χ 2 4C is determined by optimizing the statistical significance S/ √ S + B in the η c signal region, where S (B) is the number of signal (background) events obtained from the signal (inclusive) MC samples. For the estimate of S, the branching fractions of χ c0,2 → π 0 η c are assumed to be 10 −3 in analogy with the isospin-violating process ψ(3686) → π 0 J/ψ [1]. The signal region is defined as 2.90 < M K 0 S K ± π ∓ /(GeV/c 2 ) < 3.05.…”

“…± 0.03(syst.)) × 10 −3 [1], whereas for other hadronic transitions such as ψ(3686) → π + π − J/ψ, the branching fraction is (34.45 ± 0.30) × 10 −2 [2] and thus significantly stronger.…”

“…An example observable that has been proposed to obtain the quark mass ratio, m u /m d , is a measurement of the ratio between the branching fractions of the transitions ψ(3686) → π 0 J/ψ and ψ(3686) → ηJ/ψ. Based on a leading-order QCD multipole expansion [12] and the BESIII measurement of this ratio [1], the up-down quark mass ratio is extracted to be m u /m d = 0.407 ± 0.006. This result is smaller than the result, m u /m d = 0.56, obtained using the Goldstone boson masses from a leading-order chiralperturbation theory [13].…”