The relevance of subnucleonic degrees of freedom and their fluctuations in the description of multiple experimental observations in small collision systems (flow harmonics, diffractive phenomena, hollowness effect...) has been recently established.
A representative example is the first measurement of symmetric cumulants, SC(n,m), performed by the CMS Collaboration in the three collision systems available at the LHC (p+p,p+Pb,Pb+Pb) . In particular, SC(2,3), that provides a direct access to initial state fluctuations, shows a sign change with increasing centrality in p+p resembling the behavior of p+Pb and Pb+Pb interactions. This fact constitutes a powerful and stringent constraint on any realistic initial state model. We present a systematic study on the influence of spatial correlations between the proton constituents, in our case gluonic hot spots, their size and their number on SC(2,3) within a Monte Carlo Glauber framework . When modeling the proton as composed by 3 gluonic hot spots, the most common assumption in the literature, we find that the inclusion of spatial correlations is indispensable to reproduce the negative sign of SC(2,3) in the highest centrality bins as dictated by data. Further, the subtle interplay between the different scales of the problem is discussed. To conclude, the possibility of feeding a 2+1D viscous hydrodynamic simulation with our entropy profiles and the theoretical uncertainties associated to this procedure are exposed.
 arXiv:1707.05592 (under review in PLB)
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