Measurement of the lensing B-mode power spectrum, using cross-correlation with estimates of the lensing potential as discussed in Sect. 3.2. The theoretical lensing B-mode power spectrum, for the parameters of the fiducial cosmological model of Sect. 2, is plotted as dashed black. Green squares and blue triangles are results using the TT and MV φ reconstructions, respectively, to construct the lens-induced B-mode template, while red circles use the CIB (from the Planck545 GHz channel) to construct a proxy for φ. Lensing B-mode power is detected with the expected scale dependence and amplitude at a significance level of approximately 10σ.