From 1310.6×106 J/ψ and 448.1×106 ψ(3686) events collected with the BESIII experiment, we report the first observation of ς+ and ς¯-spin polarization in e+e-→J/ψ[ψ(3686)]→ς+ς¯-decays. The relative phases of the form factors Δφ have been measured to be (-15.5±0.7±0.5)° and (21.7±4.0±0.8)° with J/ψ and ψ(3686) data, respectively. The nonzero value of Δφ allows for a direct and simultaneous measurement of the decay asymmetry parameters of ς+→pπ0(α0=-0.998±0.037±0.009) and ς¯-→p¯π0(α¯0=0.990±0.037±0.011), the latter value being determined for the first time. The average decay asymmetry, (α0-α¯0)/2, is calculated to be-0.994±0.004±0.002. The CP asymmetry ACP,ς=(α0+α¯0)/(α0-α¯0)=-0.004±0.037±0.010 is extracted for the first time, and is found to be consistent with CP conservation.
Bibliographical noteFunding Information:
The BESIII collaboration thanks the staff of BEPCII and the IHEP computing center for their strong support. This work is supported in part by National Key Basic Research Program of China under Contract No. 2015CB856700; National Natural Science Foundation of China (NSFC) under Contracts No. 11625523, No. 11635010, No. 11735014, No. 11805037, No. 11822506, No. 11835012, No. 11935015, No. 11935016, No. 11935018, and No. 11961141012; the Chinese Academy of Sciences (CAS) Large-Scale Scientific Facility Program; Joint Large-Scale Scientific Facility Funds of the NSFC and CAS under Contracts No. U1732102, No. U1732263, No. U1832103, No. U1832121, and No. U1832207; CAS Key Research Program of Frontier Sciences under Contracts No. QYZDJ-SSW-SLH003 and No. QYZDJ-SSW-SLH040; 100 Talents Program of CAS; INPAC and Shanghai Key Laboratory for Particle Physics and Cosmology; ERC under Contract No. 758462; German Research Foundation DFG under Contracts No. Collaborative Research Center CRC 1044 and No. FOR 2359; Instituto Nazionale di Fisica Nucleare, Italy; Ministry of Development of Turkey under Contract No. DPT2006K-120470; National Science and Technology fund; STFC (United Kingdom); The Knut and Alice Wallenberg Foundation (Sweden) under Contract No. 2016.0157; The Royal Society, U.K. under Contracts No. DH140054 and No. DH160214; The Swedish Research Council; Olle Engkvist Foundation under Contract No. 200-0605; U.S. Department of Energy under Contracts No. DE-FG02-05ER41374 and No. DE-SC-0012069.
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