Precise Measurements of Decay Parameters and CP Asymmetry with Entangled Λ−Λ¯

Study of the processes χcJ → Ξ−$$ \overline{\Xi} $$ + and Ξ0 $$ \overline{\Xi} $$0

“…All the Ξ − parameters other than α J/ψ are consistent with the neutral Ξ ones; these results will provide important information on the decay dynamics. The parameter α Λ is found to be in excellent agreement with the determinations from J/ψ → Λ Λ and J/ψ → Ξ − Ξ+ samples [13,15], but in 3.5σ tension with the CLAS result, 0.721 ± 0.006 stat ± 0.005 syst [40]. With the properties of quantum-entangled baryon-antibaryon, the proposed future super tau-charm factories [41,42] have more potential to discover CP V in the baryon sector.…”

“…In the fit, the events from the data side-band regions and the Σ 0 (1385) MC sample are included with a negative weight to subtract the background effects, where the likelihood function of background events is the same as the signal events. The results are summarized in Table I, together with previous measurements [13,18,34].…”

“…The advent of high-intensity facilities producing baryons and antibaryons in abundance, opens up a new possibility: the search for CP V in baryon decays [8][9][10][11]. This has been demonstrated in several measurements by the BESIII collaboration, where analyses of polarized and entangled pairs of single-strange Λ [12,13] and Σ + [14] baryons resulted in the most precise CP tests so far for baryons. Sequential decays of double-strange Ξ baryons allow the separation of strong and weak phase differences, as demonstrated by the measurements of Ξ − [15,16].…”

“…A 9-dimensional maximum likelihood fit is performed on the joint angular distribution from data to determine the eight ω parameters, similar to that in Ref. [13]. In the fit, the events from the data side-band regions and the Σ 0 (1385) MC sample are included with a negative weight to subtract the background effects, where the likelihood function of background events is the same as the signal events.…”

First Simultaneous Measurement of $Ξ^0$ and $\barΞ^0$ Asymmetry Parameters in $ψ(3686)$ Decay

“…Therefore, a test of CPV in hyperon decays is sensitive to the sources of CPV from physics beyond the SM [10,11]. At present, BESIII has performed CPV tests in the decays of Λ [12][13][14], Σ + [15], and Ξ − [16,17] hyperons, where for Ξ − hyperons, the most precise asymmetry parameter measurement was reported in J/ψ decay. BESIII has also performed the first determination of the weak phase in the Ξ − hyperon using entangled Ξ − Ξ+ pairs [16].…”