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By using the cubic spline interpolation method, we reconstruct the shape ofthe primordial scalar and tensor power spectra from the recently released {\itPlanck} temperature and BICEP2 polarization cosmic microwave background data.We find that the vanishing scalar index running ($\dd n_s/\dd\ln k$) model isstrongly disfavored at more than $3\sigma$ confidence level on the $k=0.0002$Mpc$^{-1}$ scale. Furthermore, the power-law parameterization gives a blue-tilttensor spectrum, no matter using only the first 5 bandpowers $n_t =1.20^{+0.56}_{-0.64} (95% {\rm CL})$ or the full 9 bandpowers $n_t =1.24^{+0.51}_{-0.58} (95% {\rm CL})$ of BICEP2 data sets. Unlike the largetensor-to-scalar ratio value ($r\sim0.20$) under the scale-invariant tensorspectrum assumption, our interpolation approach gives $r_{0.002} < 0.060 (95%{\rm CL})$ by using the first 5 bandpowers of BICEP2 data. After comparing theresults with/without BICEP2 data, we find that {\it Planck} temperature withsmall tensor amplitude signals and BICEP2 polarization data with large tensoramplitude signals dominate the tensor spectrum reconstruction on the large andsmall scales, respectively. Hence, the resulting blue tensor tilt actuallyreflects the tension between {\it Planck} and BICEP2 data.

Reconstruction of the primordial power spectra with Planck and BICEP2