We report the results of a joint analysis of data from BICEP2/ Keck Array and Planck .
BICEP2 and Keck Array have observed the same approximately 400 deg ^ { 2 } patch of sky centered on RA 0h , Dec . -57.5 ^ { \circ } .
The combined maps reach a depth of 57 nK deg in Stokes Q and U in a band centered at 150 GHz . Planck has observed the full sky in polarization at seven frequencies from 30 to 353 GHz , but much less deeply in any given region ( 1.2 \mu K deg in Q and U at 143 GHz ) .
We detect 150 \times 353 cross-correlation in B -modes at high significance .
We fit the single- and cross-frequency power spectra at frequencies \geq 150 GHz to a lensed- \Lambda CDM model that includes dust and a possible contribution from inflationary gravitational waves ( as parameterized by the tensor-to-scalar ratio r ) , using a prior on the frequency spectral behavior of polarized dust emission from previous Planck analysis of other regions of the sky .
We find strong evidence for dust and no statistically significant evidence for tensor modes .
We probe various model variations and extensions , including adding a synchrotron component in combination with lower frequency data , and find that these make little difference to the r constraint .
Finally we present an alternative analysis which is similar to a map-based cleaning of the dust contribution , and show that this gives similar constraints .
The final result is expressed as a likelihood curve for r , and yields an upper limit r _ { 0.05 } < 0.12 at 95 % confidence .
Marginalizing over dust and r , lensing B -modes are detected at 7.0 \sigma significance .