  Weak lensing source galaxy catalogs used in estimating the masses of galaxy
clusters can be heavily contaminated by cluster members, prohibiting accurate
mass calibration. In this study we test the performance of an estimator for the
extent of cluster member contamination based on decomposing the photometric
redshift $P(z)$ of source galaxies into contaminating and background
components. We perform a full scale mock analysis on a simulated sky survey
approximately mirroring the observational properties of the Dark Energy Survey
Year One observations (DES Y1), and find excellent agreement between the true
number profile of contaminating cluster member galaxies in the simulation and
the estimated one. We further apply the method to estimate the cluster member
contamination for the DES Y1 redMaPPer cluster mass calibration analysis, and
compare the results to an alternative approach based on the angular correlation
of weak lensing source galaxies. We find indications that the correlation based
estimates are biased by the selection of the weak lensing sources in the
cluster vicinity, which does not strongly impact the $P(z)$ decomposition
method. Collectively, these benchmarks demonstrate the strength of the $P(z)$
decomposition method in alleviating membership contamination and enabling
highly accurate cluster weak lensing studies without broad exclusion of source
galaxies, thereby improving the total constraining power of cluster mass
calibration via weak lensing.
