  We present high-precision photometry and polarimetry for the protoplanetary
disk around HD142527, with a focus on determining the light scattering
parameters of the dust. We re-reduced polarimetric differential imaging data of
HD142527 in the VBB (735 nm) and H-band (1625 nm) from the ZIMPOL and IRDIS
subinstruments of SPHERE/VLT. With polarimetry and photometry based on
reference star differential imaging, we were able to measure the linearly
polarized intensity and the total intensity of the light scattered by the
circumstellar disk with high precision. We used simple Monte Carlo simulations
of multiple light scattering by the disk surface to derive constraints for
three scattering parameters of the dust: the maximum polarization of $P_{\rm
max}$, the asymmetry parameter $g$, and the single-scattering albedo $\omega$.
We measure a reflected total intensity of $51.4\pm1.5$ mJy and $206\pm12$ mJy
and a polarized intensity of $11.3\pm0.3$ mJy and $55.1\pm3.3$ mJy in the VBB
and H-band, respectively. We also find in the visual range a degree of
polarization that varies between $28\%$ on the far side of the disk and $17\%$
on the near side. The disk shows a red color for the scattered light intensity
and the polarized intensity, which are about twice as high in the near-infrared
when compared to the visual. We determine with model calculations the
scattering properties of the dust particles and find evidence for strong
forward scattering ($g\approx 0.5-0.75$), relatively low single-scattering
albedo ($\omega \approx 0.2-0.5$), and high maximum polarization ($P_{\rm max}
\approx 0.5-0.75$) at the surface on the far side of the disk for both observed
wavelengths. The optical parameters indicate the presence of large aggregate
dust particles, which are necessary to explain the high maximum polarization,
the strong forward-scattering nature of the dust, and the observed red disk
color.
