Interplay between IR-improved DGLAP-CS theory and the precision of an NLO ME matched parton shower MC in relation to LHCb data

We use comparison with recent LHCb data on single Z/gamma* production and decay to lepton pairs as a vehicle to study the current status of the application of our approach of exact amplitude-based resummation in quantum field theory to precision quantum chromodynamics (QCD) calculations, by realistic MC event generator methods, as needed for precision large hadron collider (LHC) physics. This represents an extension of the phase space of our previous studies based on comparison with CMS and ATLAS data, as the pseudo-rapidity range measured by the LHCb for leptons in the data we study is 2.0 < eta < 4.5 to be compared with vertical bar eta vertical bar < 4.6(2.4) in our previous CMS(ATLAS) data comparison for the same processes. To be precise, for mu(+)mu(-) decays, the CMS data (h)ad vertical bar eta vertical bar < 2.1 while, for e(+)e(-) decays, the CMS data had vertical bar eta vertical bar < 2.1 for both leptons for the Z gamma* p(T) spectrum and had one lepton with vertical bar eta vertical bar < 2.5 and one with vertical bar eta vertical bar < 4.6 for the Z/gamma* rapidity spectrum. The analyses we present here with the LHCb data thus represent an important addition to our previous results, as it is essential that theoretical predictions be able to control all of the measured phase space at LHC. The level of agreement between the new theory and the data continues to be a reason for optimism.