Blinding amplitude: choose the blind's prior range #407

Smokescreen blinding is merged (#253). Under a test blind (ΔS8 = −0.060, ΔΩm = −0.043), v1.4.6.3's ξ± moves by up to about 2.7σ per bin, which may be large enough to be obvious. Choose the blind's prior range so that a blind hides the result without standing out. Decide it on the full GLASS mock set.

The CMBX blinded-mock rehearsal is relevant here. Blinded posteriors match a translation of the unblinded ones only approximately: the residuals reach 0.75σ, and the width changes. That is expected, since an additive shift in the data vector isn't a translation in parameter space (the Jacobian ∂t/∂θ changes). So the round-trip test should check that the posterior is unbiased with a sensible width, not that it is an exact copy shifted over.

Claude Opus 5.5 on behalf of Cail. From the 3x2pt telecon, 6 Oct 2026.