Speaker
Description
Measuring the leptonic CP phase $\delta_{CP}$ and resolving the
$\theta_{23}$ octant are primary objectives of DUNE and T2HK.
We show that two distinct effects can compromise the reliability of
these measurements. First, the poorly constrained $\nu_e$ and
$\bar{\nu}_e$ cross sections allow energy-dependent distortions that
partially mimic the $\delta_{CP}$-dependent spectral modulation,
reducing DUNE's CP-violation sensitivity by up to $\sim\!3\sigma$.
We demonstrate that the proposed $\nu$SCOPE facility at CERN can
recover this loss through percent-level measurements of
$\sigma_{\nu_\mu}$ and the $\sigma_{\nu_e}/\sigma_{\nu_\mu}$ ratio.
Second, complex non-standard interactions (NSI) in propagation ---
motivated by the current $\sim\!2\sigma$ NOvA--T2K tension --- induce
correlated biases in $\delta_{CP}$ and the $\theta_{23}$ octant when
DUNE data are interpreted under the standard three-flavor hypothesis.
Since T2HK is largely insensitive to these propagation effects, a
$\sim\!3\sigma$ discrepancy between the two experiments would
constitute a clear diagnostic of BSM physics. These results highlight
that both external cross-section constraints and baseline
complementarity are essential to ensure a robust and unbiased
determination of the oscillation parameters in the precision era.
