Blinding multi-probe cosmological experiments
  The goal of blinding is to hide an experiment's critical results -- here the
inferred cosmological parameters -- until all decisions affecting its analysis
have been finalised. This is especially important in the current era of
precision cosmology, when the results of any new experiment are closely
scrutinised for consistency or tension with previous results. In analyses that
combine multiple observational probes, like the combination of galaxy
clustering and weak lensing in the Dark Energy Survey (DES), it is challenging
to blind the results while retaining the ability to check for (in)consistency
between different parts of the data. We propose a simple new blinding
transformation that works by modifying the summary statistics that are input to
parameter estimation, such as two-point correlation functions. The
transformation shifts the measured statistics to new values that are consistent
with (blindly) shifted cosmological parameters, while preserving internal
(in)consistency. We apply the blinding transformation to simulated data for the
projected DES Year 3 galaxy clustering and weak lensing analysis, demonstrating
that practical blinding is achieved without significant perturbation of
internal-consistency checks, as measured here by degradation of the $\chi^2$
between data and best-fitting model. Our blinding method conserves $\chi^2$
more precisely as experiments evolve to higher precision.
