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Disparity in Λ decay that reveals ΔI =1/2 rule

2024-03-08 Author:
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The BESIII collaboration recently reported “Investigation of the ΔI = 1/2 rule and test of CP symmetry through the measurement of decay asymmetry parameters in Ξ- decays”, which has been published in Physical Review Letters on 06 March 2024 [Phys. Rev. Lett. 132, 101801 (2024)].

The disparity between decay asymmetry parameters for different decay modes signifies the existence of the Isospin ΔI = 3/2 transition in hyperon decays. The values for the final states in P-wave are measured for the first time and are found to be different from that in S-wave.

The ΔI =1/2 rule is one of the long-standing puzzles that the weak transitions changing isospin by 1/2 (ΔI =1/2) are enhanced over the ΔI =3/2 transitions by a factor of 22.4 in kaon decay. The ΔI =1/2 rule is also applicable in the decay of spin 1/2 hyperons, where can be in addition studied by the decay asymmetry parameters. The decay asymmetry parameters are also more sensitive to the direct CP symmetry violation than a difference between signal yields for particle and antiparticle decays and therefore a good platform for CP symmetry test.

In this study, numerous decay asymmetry parameters are simultaneously determined from the sequential decay of double-strange baryon based on 10 billion J/psi events collected with the BESIII detector.  CP violation and the ΔI = 1/2 rule are studied from the measurements. The ratio of ΔI = 1/2 to ΔI = 3/2 transitions in S-wave is consistent with that in kaon decay, while the ratio in P-wave is measured for the first time and found different from that in S-wave. The complementary measurement provides an indispensable constraint for lattice QCD and dual QCD approach to understand the ΔI = 1/2 rule.

DOI: 10.1103/PhysRevLett.132.101801