  We perform an X-ray spectral analysis of the brightest and cleanest bare AGN
known so far, Ark 120, in order to determine the process(es) at work in the
vicinity of the SMBH. We present spectral analysis of data from an extensive
campaign observing Ark 120 in X-rays with XMM-Newton (4$\times$120 ks, 2014
March 18-24), and NuSTAR (65.5 ks, 2014 March 22). During this very deep X-ray
campaign, the source was caught in a high flux state similar to the earlier
2003 XMM-Newton observation, and about twice as bright as the lower-flux
observation in 2013. The spectral analysis confirms the "softer when brighter"
behaviour of Ark 120. The four XMM-Newton/pn spectra are characterized by the
presence of a prominent soft X-ray excess and a significant FeK$\alpha$
complex. The continuum is very similar above about 3 keV, while significant
variability is present for the soft X-ray excess. We find that relativistic
reflection from a constant-density, flat accretion disk cannot simultaneously
produce the soft excess, broad FeK$\alpha$ complex, and hard X-ray excess.
Instead, Comptonization reproduces the broadband (0.3-79 keV) continuum well,
together with a contribution from a mildly relativistic disk reflection
spectrum. During this 2014 observational campaign, the soft X-ray spectrum of
Ark 120 below $\sim$0.5 keV was found to be dominated by Comptonization of seed
photons from the disk by a warm ($kT_{\rm e}$$\sim$0.5 keV), optically-thick
corona ($\tau$$\sim$9). Above this energy, the X-ray spectrum becomes dominated
by Comptonization from electrons in a hot optically thin corona, while the
broad FeK$\alpha$ line and the mild Compton hump result from reflection off the
disk at several tens of gravitational radii.
