Four-jet production at LHC and Tevatron in QCD

Abstract

We demonstrate that in the back-to-back kinematics the production of four jets in the collision of two partons is suppressed in the leading log approximation of pQCD, compared to the hard processes involving the collision of four partons. We derive the basic equation for four-jet production in QCD in terms of the convolution of generalized two-parton distributions of colliding hadrons in the momentum space representation. Our derivation leads to geometrical approach in the impact parameter space close to that suggested within the parton model and used before to describe the four-jet production. We develop the independent parton approximation to the light-cone wave function of the proton. Comparison with the CDF and D0 data shows that the independent parton approximation to the light-cone wave function of the proton is insufficient to explain the data. We argue that the data indicate the presence of significant multiparton correlations in the light-cone wave functions of colliding protons.

Perturbative and nonperturbative correlations in double parton distributions

“…The measurements covering a larger range of the resolution scale variation might reveal the evolution effects more distinctly in accordance with the numerical estimations in Ref. [50] and the asymptotic QCD behavior considered above.…”

“…Unlike naively accepted expectations, the QCD dynamical correlations imply the dependence [38,50,68,69] of the experimentally extracted effective cross section of DPS on the resolution scale. The measurements covering a larger range of the resolution scale variation might reveal the evolution effects more distinctly in accordance with the numerical estimations in Ref.…”

“…Note that the particular solutions (10) of nonhomogeneous equations contribute to the inclusive cross section of DPS with a larger weight (different effective cross section) [38,39,41,42,50,57] as compared to the solutions (9) of homogeneous equations. The latter solutions are usually approximated by a factorized form if the initial nonperturbative correlations are absent.…”

“…Such estimates for the contribution of single perturbative splitting graphs to the DPS cross section were recently done in Ref. [50] (the three-parton interactions in the authors' terminology), and it was pointed out that the relative contribution of the evolution effects increases with increasing hard scales and may resolve the long standing puzzle: why the observed effective DPS cross section is underestimated by a factor of two in the independent parton approximation (with regard to the "traditional" factorization component only)?…”

Angular correlations in the double Drell-Yan process

“…A mini-review on earlier developments of the subject is given in [31], and an overview of current developments can be found in the conference proceedings [35,36]. Recently there has been renewed interest in understanding the theoretical foundations of multiple hard scattering [37][38][39][40][41][42][43][44][45][46][47], with many issues remaining to be clarified or worked out.…”