Abstract
A new calculation using off-shell matrix elements with TMD parton densities supplemented with a newly developed initial state TMD parton shower is described. The calculation is based on the KaTie package for an automated calculation of the partonic process in high-energy factorization, making use of TMD parton densities implemented in TMDlib. The partonic events are stored in an LHE file, similar to the conventional LHE files, but now containing the transverse momenta of the initial partons. The LHE files are read in by the Cascade package for the full TMD parton shower, final state shower and hadronization from Pythia where events in HEPMC format are produced. We have determined a full set of TMD parton densities and developed an initial state TMD parton shower, including all flavors following the TMD distribution. As an example of application we have calculated the azimuthal de-correlation of high p_t dijets as measured at the LHC and found very good agreement with the measurement when including initial state TMD parton showers together with conventional final state parton showers and hadronization.
Highlights
Measurements in today’s high-energy experiments have reached a new level of precision of a few percent in experimental uncertainty
The great advantage of using transverse momentum dependent (TMD) parton densities is that a parton shower will not change the kinematics of the matrix element process, in contrast to the conventional approach of collinear hard process calculations supplemented with parton showers, and that the main parameters of the TMD parton shower are fixed with the determination of the TMD
We show predictions obtained with off-shell matrix elements of 2 → 2 quantum chromodynamics (QCD) processes using the TMDs obtained in Sect
Summary
Measurements in today’s high-energy experiments have reached a new level of precision of a few percent in experimental uncertainty. In order to fully account for the potential of a TMD parton shower, the initial state kinematics for the hard process calculation should include the transverse momenta. With the development of an automated calculation of multi-leg matrix elements with off-shell initial states [23] the full potential of TMD parton densities and parton showers can be explored. In this article we will describe how the TMD parton densities can be obtained from the KMRW approach [22] and how they can be used in calculations using off-shell matrix elements obtained from KaTie [23], which is based on highenergy factorization [24,25,26]. We illustrate the advantage of using TMD densities with off-shell matrix element calculations in an application to azimuthal de-correlations of high pt dijet measurements at the LHC.
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