Pinning down |Delta c|=|Delta u|=1 couplings with rare charm baryon decays

Abstract

We study the full angular distribution of semileptonic rare charm baryon decays in which the secondary baryon undergoes weak decay with sizable polarization parameter, Xi _c^+rightarrow Sigma ^+,(rightarrow ppi ^0)ell ^+ell ^-, Xi _c^0rightarrow Lambda ^0,(rightarrow p pi ^-)ell ^+ell ^- and Omega _c^0rightarrow Xi ^0,(rightarrow Lambda ^{0} pi ^0)ell ^+ell ^-. Such self-analyzing decay chains allow for seven additional observables compared to three-body decays such as Lambda _c rightarrow p ell ^+ ell ^-, with different sensitivities to the |Delta c|=|Delta u|=1 weak couplings. Opportunities to test the standard model in c rightarrow u transitions with standard model null tests and other angular observables are worked out. We show that a joint model-independent analysis of the leptonic A_{text {FB}}^ell , hadronic A_{text {FB}}^{text {H}}, and combined forward–backward asymmetry A_{text {FB}}^{ell text {H}} together with the fraction of longitudinally produced leptons, F_L, is able to pin down the dipole couplings C_{7},C^prime _{7} and the semileptonic (axial-) vector ones C_{10},C^prime _{9},C^prime _{10}. A_{text {FB}}^{text {H}} is also accessible with dineutrino c rightarrow u nu {bar{nu }} modes and probes right-handed currents.