Conventional versus single-ladder-splitting contributions to double parton scattering production of two quarkonia, two Higgs bosons, andcc¯cc¯

Abstract

The double parton distributions (dPDF), both conventional and those corresponding to parton splitting, are calculated and compared for different two-parton combinations. The conventional and splitting dPDFs have very similar shape in x 1 and x 2 . We make a first quantitative evaluation of the single-ladder-splitting contribution to double parton scattering (DPS) production of two S-or Pwave quarkonia, two Higgs bosons and cccc. The ratio of the single-ladder-splitting to conventional contributions is discussed as a function of centre-of-mass energy, mass of the produced system and other kinematical variables. Using a simple model for the dependence of the conventional twoparton distribution on transverse parton separation (Gaussian and independent of x i and scales), we find that the 2v1 contribution is as big as the 2v2 contribution discussed in recent years in the literature. This means that the phenomenological analyses of σ ef f including only the conventional DPS mechanism have to be revised including explicitly the single-ladder-splitting contributions discussed here. The differential distributions in rapidity and transverse momenta calculated for conventional and single-ladder-splitting DPS processes are however very similar which causes their experimental separation to be rather difficult, if not impossible. The direct consequence of the existence of the two components (conventional and splitting) is the energy and process dependence of the empirical parameter σ ef f . This is illustrated in our paper for the considered processes.

Correlations in double parton distributions: perturbative and non-perturbative effects

“…[40], only the homogeneus part of dPDFs evolution is implemented, for the moment being, in our scheme. According to some studies, the inhomogeneus part could play some role in this phenomenology [35,43]; its analysis is beyond the scope of the present paper.…”

Dynamical approach to MPI four-jet production in Pythia

“…The Pythia regularization formula in this case can be viewed as an ansatz for twist expansion, which may include part of the MPI. Note that the ladder splitting scale is much smaller than the scales of hard dijets created by partons that evolve after the splitting [25,26]. So the effective ladder splitting is partly taken into account for UE by a high p 0 T value.…”

Open charm production in double parton scattering processes in the forward kinematics

“…2. We calculate R by solving by iterations the evolution equation for 2 G P D [8,11,12]. The cross section due to the 1 ⊗ 2 mechanism is calculated as [8] …”

“…It was pointed out starting with [5,33,34] that the rate of DPS calculated under assumption that partons in nucleons are uncorrelated (and using information as regards the gluon GPDs available from the analysis [33,34] of the HERA data) is too low to explain the data. It was pointed out in [11,12,16,17,35] that correlations generated in the course of the DGLAP evolution-the 1 ⊗ 2 mechanism-explain the DPS rates in the central rapidity region [11,12,16,17,35] provided the starting scale for the QCD evolution-Q 2 0 = 0.5 ÷ 1GeV 2 is chosen. The remaining problem seems to be a strong enhancement of the processes involving J/ pro-duction [36,37] at √ s = 2TeV, which does not show up in the LHCb data.…”