  In this paper, new upper limits on the parameters of the Continuous
Spontaneous Localization (CSL) collapse model are extracted. To this end, the
X-ray emission data collected by the IGEX collaboration are analyzed and
compared with the spectrum of the spontaneous photon emission process predicted
by collapse models.
  This study allows the obtainment of the most stringent limits within a
relevant range of the CSL model parameters, with respect to any other method.
The collapse rate $\lambda$ and the correlation length $r_C$ are mapped, thus
allowing the exclusion of a broad range of the parameter space.
