The clustering of the SDSS-IV extended Baryon Oscillation Spectroscopic
  Survey DR14 quasar sample: structure growth rate measurement from the
  anisotropic quasar power spectrum in the redshift range $0.8<z<2.2$
  We analyse the clustering of the Sloan Digital Sky Survey IV extended Baryon
Oscillation Spectroscopic Survey Data Release 14 quasar sample (DR14Q). We
measure the redshift space distortions using the power spectrum monopole,
quadrupole and hexadecapole inferred from 148,659 quasars between redshifts 0.8
and 2.2 covering a total sky footprint of 2112.9 deg$^2$. We constrain the
logarithmic growth of structure times the amplitude of dark matter density
fluctuations, $f\sigma_8$, and the Alcock-Paczynski dilation scales which allow
constraints to be placed on the angular diameter distance $D_A(z)$ and the
Hubble $H(z)$ parameter. At the effective redshift of $z_{\rm eff}=1.52$,
$f\sigma_8(z_{\rm eff})=0.420\pm0.076$, $H(z_{\rm eff})=[162\pm 12]\, (r_s^{\rm
fid}/r_s)\,{\rm km\, s}^{-1}{\rm Mpc}^{-1}$, and $D_A(z_{\rm eff})=[1.85\pm
0.11]\times10^3\,(r_s/r_s^{\rm fid})\,{\rm Mpc}$, where $r_s$ is the comoving
sound horizon at the baryon drag epoch and the superscript `fid' stands for its
fiducial value. The errors take into account the full error budget, including
systematics and statistical contributions. These results are in full agreement
with the current $\Lambda$-Cold Dark Matter ($\Lambda$CDM) cosmological model
inferred from Planck measurements.
  Finally, we compare our measurements with other eBOSS companion papers and
find excellent agreement, demonstrating the consistency and complementarity of
the different methods used for analysing the data.
