of perturbative QCD with gluon saturation mechanism and hydrodynamics. We observe that the EKRT model underestimates the experimental data upto top RHIC energy but seems to explain the data at LHC energies.

Figure 11 represents the variations of the product of Bjorken energy density ($\epsilon_{Bj}$) and formation time ($\tau$) with respect to $\sqrt{s_{NN}}$ from AGS to LHC energies. Furthermore, our model explains the experimental data [@Sahoo:2014aca; @Adam:2016thv; @Adler:2004zn] very well upto RHIC energies while it fails to explain the data at LHC energies. We also show the results obtained after incorporating collective flow in our model and found a very good agreement with experimental data including that at LHC. We also fit the experimental data using the logarithmic function $\displaystyle A + B\;ln(\sqrt{s_{NN}})$, where A = - 2.32 $\pm$ 0.51 and B=1.46 $\pm$ 0.12 are fit parameters. We notice that this function fits the data only upto RHIC energies and fails at LHC energies which suggests that logarithmic behaviour is not valid at LHC energies in this case. This could be an indication of a different particle production mechanism playing a role at LHC energies, which needs further investigations.

![Transverse energy per charged particle ($E_{T}/N_{ch}$) as a function of collision 