Σ+ and Σ¯− Polarization in the J

Abstract

From 1310.6 × 10 6 J=ψ and 448.1 × 10 6 ψð3686Þ events collected with the BESIII experiment, we report the first observation of Σ þ andΣ − spin polarization in e þ e − → J=ψ½ψð3686Þ → Σ þΣ− decays. The relative phases of the form factors ΔΦ have been measured to be ð−15.5 AE 0.7 AE 0.5Þ°and ð21.7 AE 4.0 AE 0.8Þ°with J=ψ and ψð3686Þ data, respectively. The nonzero value of ΔΦ allows for a direct and simultaneous measurement of the decay asymmetry parameters of Σ þ → pπ 0 ðα 0 ¼ −0.998 AE 0.037 AE 0.009Þ andΣ − →pπ 0 ðᾱ 0 ¼ 0.990 AE 0.037 AE 0.011Þ, the latter value being determined for the first time. The average decay asymmetry, ðα 0 −ᾱ 0 Þ=2, is calculated to be −0.994 AE 0.004 AE 0.002. The CP asymmetry A CP;Σ ¼ ðα 0 þᾱ 0 Þ=ðα 0 −ᾱ 0 Þ ¼ −0.004 AE 0.037 AE 0.010 is extracted for the first time, and is found to be consistent with CP conservation.

Light hyperon physics at BESIII

“…Further, independent measurements are therefore needed to resolve the discrepancy. 5.2 + − → / , → Σ + Σ− BESIII has performed a DT measurement of both / → Σ + Σ− and → Σ + Σ− [21], observing spin polarization of Σ + for the first time in both cases. The value of / is found to be positive while is found to be negative.…”

Measurement of branching fractions of J/ψ and ψ(3686) decays to Σ+ and $$ \overline{\Sigma} $$−

“…The signal MC sample is generated according to a set of decay parameters which have been measured through multi-dimensional fitting of angular distributions, where polarization effects and decay asymmetry have been included [36]. Assuming no CP violation (α 0 = − ᾱ0 ), three decay parameters α Ψ , ∆Φ Ψ and α 0 are used for Ψ decay.…”

Measurement of $Λ$ baryon polarization in $e^+e^-\rightarrowΛ\barΛ$ at $\sqrt{s} = 3.773$ GeV

“…The uncertainty is found to be negligible. The systematic uncertainty due to the kinematic fit is estimated with the same control sample, J/ψ → Λ Λ, with and without a helix correction [22], and it is found to negligible. The uncertainties from the decay parameters of Λ → pπ − , α Λ/ Λ, are estimated by varying the baseline value, obtained from averaging the results in Ref.…”

“…Polarization effects in e + e − collisions were neglected in previous studies [12][13][14][15][16][17][18][19][20]. Recently, the Σ + baryon polarization was studied by the BESIII collaboration in e + e − → J/ψ, ψ(3686) → Σ + Σ− processes [22]. The results do not only reveal a non-zero relative psionic phase, but also that the phase changes sign at the ψ(3686) mass with respect to the value measured at the J/ψ resonance.…”