In the spirit of performing a complete phenomenological investigation of the merits of Kimber–Martin–Ryskin(KMR) and Martin–Ryskin–Watt(MRW) unintegratedparton distribution functions (UPDF), we have computed the longitudinal structure function of the proton, FL(x, Q2), from the so-called dipole ap-proximation, using the LO and the NLO-UPDF, prepared in the respective frameworks. The preparation process utilizes the PDFof Martinet al., MSTW2008-LOand MSTW2008-NLO, as the inputs. After-wards, the numerical results are undergone a series of comparisons against the exact kt-factorization and the kt-approximate results, derived from the work of Golec-Biernatand Stasto, against each other and the experimental data from ZEUS and H1 Collaborationsat HERA. Interestingly, our results show a much better agreement with the exact kt-factorization, compared to the kt-approximate outcome. In addition, our results are completely consistent with those prepared from embedding the KMRand MRWUPDFdirectly into the kt-factorization framework. One may point out that the FL, prepared fromthe KMRUPDFshows a better agreement with the exact kt-factorization. This is despite the fact that the MRWformalism employs a bet-ter theoretical description of the DGLAPevolution equation and has anNLOexpansion. Such unexpected consequence appears, due to the different implementation of the angular ordering constraint in the KMRapproach, whichautomatically includes the resummationof ln(1/x), BFKLlogarithms, in the LO-DGLAPevolution equation.
