CP violation with beautiful baryons

Abstract

CP violation can be studied in modes of charmed or bottom baryons when a decay process is compared with its charge-conjugated partner. It can show up as a rate asymmetry and in a study of other decay parameters. Neither tagging nor time-dependences are required to observeCP violation with modes of baryons, in contrast to the conventionalB ⁰ modes. Numerous modes of bottom baryons have the potential to show largeCP-violating effects within the Standard Model. Those effects can be substantial for modes with aD ⁰, which is seen in a final state that can also be fed from a$\bar D^0$. For instance, a comparison of theΛ _b→Λ ⁰_CP with the$\bar \Lambda _b \to \bar \Lambda D_{CP}^0$ process can show sizeableCP violation. HereD ^o_CP denotesCP eigenstates ofD ⁰, which occur at a few percent. Six related processes, such asΛ _b→ΛD ⁰,$\Lambda _b \to \Lambda \bar D^0$,Λ _b→Λ ⁰_CP , and their charge-conjugated counterparts, can extract ϕ, which is the most problematic angle of the unitarity triangle and which is conventionally probed with theB _s→ρ⁰ K _S asymmetry. HereD ⁰ andD ⁻⁰ are identified by their charged kaon or lepton. We predictB(Λ _b→ΛD ⁰)∼10⁻⁵, thusB(Λ _b→Λ ⁰_CP )∼10⁻⁷. Under favourable circumstances,CP violation can occur at the few tens of percent level. Thus 10²–10³ Λ _b→Λ ⁰_CP decays start probing ϕ. Tables list many additional modes with typical branching ratios at the 10⁻⁵–10⁻⁶ level, with large detection efficiencies (in contrast to theD ⁰_CP ), and with potentially largeCP-violating effects, such as Ξ ⁰_b →ΛΨ, Λϕ, ΛK^*0; Ξ ⁻_b →ΛK^(*)−, Ξ⁻K_s, Ξ⁻K^*0, Ω ⁻_b →Ξ⁻φ, Ξ⁻ρ⁰, ΛK^(*)−, ΩK_s, Ω⁻K^*0.