Planck 2015 results. XV. Gravitational lensing
  We present the most significant measurement of the cosmic microwave
background (CMB) lensing potential to date (at a level of 40 sigma), using
temperature and polarization data from the Planck 2015 full-mission release.
Using a polarization-only estimator we detect lensing at a significance of 5
sigma. We cross-check the accuracy of our measurement using the wide frequency
coverage and complementarity of the temperature and polarization measurements.
Public products based on this measurement include an estimate of the lensing
potential over approximately 70% of the sky, an estimate of the lensing
potential power spectrum in bandpowers for the multipole range 40<L<400 and an
associated likelihood for cosmological parameter constraints. We find good
agreement between our measurement of the lensing potential power spectrum and
that found in the best-fitting LCDM model based on the Planck temperature and
polarization power spectra. Using the lensing likelihood alone we obtain a
percent-level measurement of the parameter combination $\sigma_8
\Omega_m^{0.25} = 0.591\pm 0.021$. We combine our determination of the lensing
potential with the E-mode polarization also measured by Planck to generate an
estimate of the lensing B-mode. We show that this lensing B-mode estimate is
correlated with the B-modes observed directly by Planck at the expected level
and with a statistical significance of 10 sigma, confirming Planck's
sensitivity to this known sky signal. We also correlate our lensing potential
estimate with the large-scale temperature anisotropies, detecting a
cross-correlation at the 3 sigma level, as expected due to dark energy in the
concordance LCDM model.
