A Monte-Carlo simulation of double parton scattering

Abstract

In this work, a new Monte-Carlo simulation of double parton scattering (DPS) at parton level is presented. The simulation is based on the QCD framework developed recently by M. Diehl, J. R. Gaunt and K. Schönwald. With this framework, the dynamics of the 1 → 2 perturbative splittings is consistently included inside the simulation, with the impact-parameter dependence taken into account. The simulation evolves simultaneously two hard systems from a common hard scale down to the hadronic scale. The evolution is performed using an angular-ordered parton shower which is combined with a set of double parton distributions that depend explicitly on the inter-parton distance. An illustrative study is performed in the context of same-sign WW production at the LHC, with the quark content of the proton being limited to three flavours. In several distributions we see differences compared to DPS models in Herwig, Pythia, and the DPS "pocket formula". 6 Summary 39 A Evolution equations for valence and sea components 41 B Initial conditions and number sum rules 42 C Validation plots and scale variations 43

Sum rule improved double parton distributions in position space

“…On the other hand, there are sum rules [77,78], which involve DPDs integrated over y (or evaluated at Δ = 0) and express the conservation of momentum and quark number. So far, only a small number of studies [2,77,[79][80][81] have used these sum rule to constrain DPDs, and it is the goal of the present paper to continue this line of work. Whereas the DPD models in [2,77,79,80] are formulated for DPDs at Δ = 0, we work with DPDs in y space, because these are the quantities required for computing DPS cross sections in the formalism of [45].…”

Combining single and double parton scatterings in a parton shower

“…In addition to this, there can be non-perturbative correlations between the parton momentum fractions and y in the dPDFs, and correlations in spin, colour and flavour between partons [5,73] (for a review, see [74]). All of these types of effects can lead to differences in the DPS rate and/or DPS shapes (for examples of these, see [8,70,[75][76][77][78][79][80][81][82]), where effects on the DPS shapes are particularly important with regards to the correct experimental extraction of DPS contributions.…”

“…We refer to this algorithm as dShower. In a previous work [79] we developed a parton-shower description of the DPS term, with proper account of the y dependence and 1 → 2 splitting effects, and a cut-off on the y integral ∼ 1/ν ∼ 1/Q h . That is, we recast the first core aspect of the DGS framework into a parton-shower description.…”

“…The paper is organised as follows. In section 2 we present a brief review of the DGS framework, along with an overview of the key features of the DPS shower that we developed in [79]. Section 3 describes in detail our implementation of the DGS subtraction scheme at the differential level in the parton shower.…”

Heavy meson hadroproduction:open issues

“…A retuning of the hadronization/FF parameters would have consequences even over the MPI parameters. The simplest case of MPI is Dual Parton Scattering, and considerable theoretical efforts have been performed to develop rigorous descriptions of the latter [15,16], beyond the phenomenological pocket formula often used; it might be interesting to bridge the gap by applying more rigorous procedures to estimate the DPS contribution in the phenomenological analyses of heavy-flavour hadroproduction. Third, it is useful including higher-order corrections: the uncertainty band related to (µ R , µ F ) scale variation, not shown in Fig.…”