  High field Q-slope (HFQS) seriously limits the high gradient performance of
the buffered chemically polished (BCP) superconducting radio frequency (SRF)
niobium cavities. The direct cause or mechanism is not yet fully understood. In
our recent extensive data analysis, we concluded that the potential root cause
could be nitrogen contamination on the surface. The nitric contamination could
be created by nitric acid during BCP which uses the mixture of hydrofluoric
acid, nitric acid, and phosphoric acid. Based on this thought, we started to
develop a new chemical polishing acid that replaces the nitric acid by hydrogen
peroxide. We have discovered that this new acid cannot provide smooth surface
finishing, however adding copper catalyst allows this acid to provide a smooth
surface similar to or even better than that from the conventional BCP. This
paper first shows the significance of resolving HFQS, then summarizes our
extensive data analysis results, and finally describes our discovery of the
copper catalyst.
