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

Abstract

We use comparison with recent LHCb data on single Z/γ * 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 QCD calculations, by realistic MC event generator methods, as needed for precision 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 < η < 4.5 to be compared with |η| < 4.6(2.4) in our previous CMS(ATLAS) data comparison for the same processes. 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.

Role of IR-improvement in Precision LHC/FCC Physics and in Quantum Gravity

“…The infrared functions SUM IR (QCED) and D QCED and the residuals are defined in Ref. [35,36]. In the implementation of parton shower/ME matching, we have the replacements β n,m →β n,m .…”

“…These replacements allow us, via the basic formula 2) to connect with MC@NLO [37,38] as explained in Ref. [35,36].…”

“…In Refs. [35,36,39], two of us (BFLW and SAY) have interfaced the realization of IRimproved DGLAP-CS [40,41,42,43,44,45,46,47,48] theory as realized in Herwiri1.031 [7] with MC@NLO and with MG5_aMC@NLO [49] for precision studies of Z and W+jets production at the LHC. In Refs.…”

IR-improved DGLAP parton shower effects in W+jets in pp collisions at s=7Shakerin1, Ward2 2019Phys. Rev. D4020View full textAdd to dashboardCite

“…One can show that the exact, amplitude-based resummation leads to the IR-improvement of the usual DGLAP-CS theory [10][11][12][13] which results in a new set of kernels, parton distributions and attendant reduced cross sections, so that the QCD perturbative results for the respective hadron-hadron or lepton-hadron cross section are unchanged order-by-order in α s at large squared-momentum transfers. This IR-improved behavior, for example, results in kernels that are integrable in the IR limit and therefore are more amenable to realization by the Monte Carlo (MC) method [14][15][16][17][18][19][20] to arbitrary precision. The advantage of this IR-improved method is better control on the accuracy of a given fixed-order calculation throughout the entire phase space of the respective physical process, especially when the prediction is given by the MC method.…”

“…In this paper, we extend the studies in Refs. [14][15][16][17][18][19][20], which were focused on the single Z/γ * production at FNAL and LHC, to the single W production at the LHC, with the additional change that we look into the properties of jets, produced in association with the W, in relation to the physics of IR-improved DGLAP-CS kernels. We study whether the manifestation of the IR-improved kernels as seen in the decay lepton observables in Refs.…”