content_image/395459.jpg
Unfortunately, the calculation of correlation contri- bution Δ( t ) to the effective cross section σ exp eff is not yet possible in the framework of some kind of existing event generators. For instance, the double parton scat- terings are implemented in the Monte-Carlo generator PYTHIA [26, 27] taking into account some correlations which, however, are not quite adequate for the case of evolution effects under consideration (unlike the theoret- ical investigations in Ref. [11]). The implementation of the QCD evolution of two-parton distribution functions in some Monte-Carlo generator, as this was done for sin- gle distributions, is not a trivial task. However we can “predict” a functional form of p jet2 T -dependence of σ exp eff : 

inspired by the explicit expression for the correlation term [14] and the evolution variable t . The results from Eq. (11) are also shown in Fig. 1 at k = 0 . 1 (dashed line) and k = 0 . 5 (solid line) to illustrate the two possi- ble slopes of σ exp eff in the observation region: visually im- perceptible (practically constant) and noticeable falling slopes. The normalization point p jet2 T 0 = 22 . 5 GeV with σ 0 eff = 16 . 3 mb is fixed to reproduce the experimental value in the central p jet2 T bin. 

We argue that the QCD dynamical correlations result effectively in the dependence of the experimentally ex- tracted σ exp eff on the resolution scale unlike naive accepted expectations. The measurements covering a larger range of the resolution scale variation with a smaller uncer- 

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<img src='content_image/395459.jpg'>

## IV. CONCLUSIONS 

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In order to investigate the more delicate characteris- tics of double parton scatterings (distributions over var- ious kinematic variables with various kinematic cuts) it is also desirable to implement the QCD evolution of the two-parton distribution functions in some Monte Carlo event generator as this was done for the single distri- butions, for instance, within PYTHIA [26]. It is worth noticing once more that the evolution of the two-parton distribution functions has the same confidence status as the well-established evolution of the single distribution functions in the framework of the leading logarithm ap- proximation of perturbative QCD. Therefore the exper- imental direct or indirect observation of this evolution effect is significant to answer to many challenging ques- tions of yet poorly-understood aspects of QCD. 

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## Acknowledgments 

