Null Tests and Lepton Universality in $\Xi_{cc}$ Baryon Decays

We develop a precision framework for doubly charmed baryon decays based on symmetry-protected observables and effective-field-theory diagnostics. In nonleptonic $\Xi_{cc}$ decays, we construct a null combination of widths that vanishes in the heavy-diquark factorization limit, providing a direct probe of nonfactorizable QCD dynamics. For semileptonic decays, we identify the light-lepton universality ratio $R_{\Xi_c}^{\mu e}$ as an observable in which leading hadronic normalization cancels at the amplitude level, yielding direct sensitivity to short-distance charged-current interactions. Percent-level precision probes $|C_{V_L}^{\mu}|\sim \mathcal{O}(10^{-2})$, whereas $\mathcal{O}(10^{-1})$ deformations induce order-one deviations. Scalar contributions remain parametrically suppressed. Combining baryonic and mesonic inputs, we show that $\Xi_{cc}$ decays constrain the same short-distance interaction with complementary scaling, lifting degeneracies inherent to meson-only analyses. Mapping to a charged-vector benchmark demonstrates sensitivity to multi-TeVnew-physics scales. These results establish doubly charmed baryons as an independent probe of charged-current interactions beyond the Standard Model.