Study of CP violation in hyperon decays at Super Charm-Tau Factories with a polarized electron beam

Abstract

Non-leptonic two-body weak decays of baryons are an important tool to probe the combined charge-conjugation-parity symmetry (CP) violation. We explain why the decays of strange baryons provide complementary information to the decays of kaons. A model-independent parameterization of the non-leptonic decays of the Λ-and Ξ-baryons is reviewed, and the amplitudes are updated according to the latest experimental input. We demonstrate the potential of performing precision tests in strange baryon decays at the next generation electron-positron J/ψ factories with luminosity of 10 35 cm −2 s −1 . The copious production of spin-entangled hyperon-antihyperon pairs via the J/ψ resonance allows for a direct comparison of the baryon and antibaryon decay properties. Using analytic approximations and numerical calculations, we study the quantitative impact of spin correlations and polarization in such CP tests. We show that by using a longitudinally-polarized electron beam, the statistical precision of the CP tests can be significantly improved compared to the experiments without polarized beams. Furthermore, we map out further directions for possible improvements, like analysis of incompletely reconstructed events or a combination of the isospin related processes. Altogether, these methods are promising for the observation of a statistically significant CP-violation signal with a strength corresponding to the standard model predictions.Our conclusions should encourage more detailed feasibility studies, including optimisation of the measurement methods and studies of systematic effects. Finally, our results call for an update of the theory predictions with increased precision.

Probing hyperon CP violation from charmed baryon decays

“…There are also large data samples at LHCb since the production cross sections of charmed baryons are much larger at the hadron collisions [44], even though the detection effeciencies of hyperons are suppressed due to their longer lifetimes. Besides, the super tau-charm facility also has a possibility to measure the proposed hyperon CPV in charmed baryon decays [45]. It can be expected that the near-future experiments of Belle II and LHCb could provide the most precise measurements on the CPV of individual process of hyperon decays, considering that the current BESIII experiment could not collect more data.…”

New Window on Matter-Antimatter Differences

“…In inclusive (so-called "singletag") measurements, where the decay angles of only the Ξ or only the Ξ are considered, the effects of the C ij terms average out to zero and only the P y terms survive. 23 In contrast, in exclusive ("double-tag") measurements, where the decay angles of both the Ξ and the Ξ and their correlations, are considered event-by-event, the non-zero C ij terms have the effect of increasing the effective polarization and thereby enhance the experimental sensitivity. This is a big effect.…”

“…In the BESIII measurement, these correlations enhance the statistical sensitivity of the ∆ Ξ CP measurement over that for polarized, but unentangled, Ξ-Ξ pairs, by a factor of ∼ 2.5; this is equivalent to a six-fold increase in the number of events. 23 This is the huge benefit of having quantum entangled Ξ Ξ pairs. The fourth big advantage of this reaction is that the Λ and Λ polarizations are determined event-by-event and, thus, φ Ξ and φΞ can be measured.…”