SDSS-III Baryon Oscillation Spectroscopic Survey: Analysis of Potential
  Systematics in Fitting of Baryon Acoustic Feature
  Extraction of the Baryon Acoustic Oscillations (BAO) to percent level
accuracy is challenging and demands an understanding of many potential
systematic to an accuracy well below 1 per cent, in order ensure that they do
not combine significantly when compared to statistical error of the BAO
measurement. Sloan Digital Sky Survey (SDSS)-III Baryon Oscillation
Spectroscopic Survey (BOSS) SDSS Data Release Eleven (DR11) reaches a distance
measurement with $\sim 1\%$ statistical error and this prompts an extensive
search for all possible sub-percent level systematic errors which could be
safely ignored previously. In this paper, we analyze the potential systematics
in BAO fitting methodology using mocks and data from BOSS DR10 and DR11. We
demonstrate the robustness of the fiducial multipole fitting methodology to be
at $0.1\%-0.2\%$ level with a wide range of tests in mock galaxy catalogs pre-
and post-reconstruction. We also find the DR10 and DR11 data from BOSS to be
robust against changes in methodology at similar level. This systematic error
budget is incorporated into the the error budget of Baryon Oscillation
Spectroscopic Survey (BOSS) DR10 and DR11 BAO measurements. Of the wide range
of changes we have investigated, we find that when fitting pre-reconstructed
data or mocks, the following changes have the largest effect on the best fit
values of distance measurements both parallel and perpendicular to the line of
sight: (a) Changes in non-linear correlation function template; (b) Changes in
fitting range of the correlation function; (c) Changes to the non-linear
damping model parameters. The priors applied do not matter in the estimates of
the fitted errors as long as we restrict ourselves to physically meaningful
fitting regions.[abridged]
