Study of Dalitz plot

Measurement of the matrix elements for the decays η′→ηπ+π− an

“…central value in Ref [8] fit uncertainty in Ref [8] phase uncertainty in Ref [8] (b) Both the general and the linear representations are used to determine the Dalitz plot parameters, and the corresponding results are summarized in Table II including the systematic uncertainties. The Dalitz plot parameters for both decays are in reasonable agreement and more precise than the previous measurements [9][10][11][12]. The results for η 0 → ηπ þ π − supersede the previous BESIII measurement [11], which used a subsample of the present data.…”

“…As reported in Ref. [11], the discrepancy of the parameter a for η 0 → ηπ þ π − with respect to the VES value [10] is evident, which, at present, stands at about 3.8 standard deviations. The values of the parameter c in η 0 → ηπ þ π − are all consistent with zero within one standard deviation in both representations, in agreement with the charge conjugation conservation in the strong interaction.…”

“…However, a small discrepancy, observed in previous measurements [9][10][11][12][13], is expected due to the mass difference between the charged and neutral pion or due to radiative corrections for the η 0 → ηπ þ π − mode [6]. A second parametrization for the decay amplitude squared used by previous experiments assumes a linear amplitude in Y and keeps the polynomial expansion in X, [10] and BESIII [11] Collaborations. The most recent measurement of η 0 → ηπ 0 π 0 is from the GAMS-4π experiment [12], complementing older results reported by the GAMS-2000 Collaboration [13].…”

Studies of Light Pseudoscalar Mesons at BESIII

“…With 44000 η → π + π − η events in the Dalitz plot, the Dalitz plot parameters have been determined with a new level of precision in a generalized and a linear representation. The results are found to be in agreement with previous measurements [9]. However, the statistical errors are still to large to allow for compelling tests of theory predictions.…”

Cusps in $\eta\prime\rightarrow \eta \pi \pi$ decays

“…Due to the smallness of the πη P-waveā 1 we neglect its contribution. We will use the central values (without errors) of the most recent determinations of the η ′ → ηππ Dalitz plot by the VES collaboration for the charged channel [9], which, adjusting the normalization to the neutral decay, read a = −0.133, b = −0.116, d = −0.094. The charged and the neutral decay amplitude are related by isospin symmetry in the tree-level couplings.…”