The XMM Cluster Survey: The Halo Occupation Number of BOSS galaxies in
  X-ray clusters
  We present a direct measurement of the mean halo occupation distribution
(HOD) of galaxies taken from the eleventh data release (DR11) of the Sloan
Digital Sky Survey-III Baryon Oscillation Spectroscopic Survey (BOSS). The HOD
of BOSS low-redshift (LOWZ: $0.2 < z < 0.4$) and Constant-Mass (CMASS: $0.43 <z
<0.7$) galaxies is inferred via their association with the dark-matter halos of
174 X-ray-selected galaxy clusters drawn from the XMM Cluster Survey (XCS).
Halo masses are determined for each galaxy cluster based on X-ray temperature
measurements, and range between ${\rm log_{10}} (M_{180}/M_{\odot}) = 13-15$.
Our directly measured HODs are consistent with the HOD-model fits inferred via
the galaxy-clustering analyses of Parejko et al. for the BOSS LOWZ sample and
White et al. for the BOSS CMASS sample. Under the simplifying assumption that
the other parameters that describe the HOD hold the values measured by these
authors, we have determined a best-fit alpha-index of 0.91$\pm$0.08 and
$1.27^{+0.03}_{-0.04}$ for the CMASS and LOWZ HOD, respectively. These
alpha-index values are consistent with those measured by White et al. and
Parejko et al. In summary, our study provides independent support for the HOD
models assumed during the development of the BOSS mock-galaxy catalogues that
have subsequently been used to derive BOSS cosmological constraints.
