Monte Carlo study of double logarithms in the smallxregion

Abstract

We investigate the effect of the resummation of collinear double logarithms in the BFKL gluon Green function using the Monte Carlo event generator BFKLex. The resummed collinear terms in transverse momentum space were calculated in Ref.[1] and correspond to the addition to the NLO BFKL kernel of a Bessel function of the first kind whose argument contains the strong coupling and a double logarithm of the ratio of the squared transverse momenta of the reggeized gluons. We discuss how these additional terms improve the collinear convergence of the whole approach and reduce the asymptotic growth with energy of cross sections. Taking advantage of the Monte Carlo implementation, we show how the new results reduce the diffusion of the gluon ladder into infrared and ultraviolet transverse momentum scales, while strongly affecting final state configurations by reducing the mini-jet multiplicity.

The high-energy radiation pattern from BFKLex with double-log collinear contributions

“…This feature is clearly seen at LO and gets reduced in higher-order calculations. This reduction is related of the shrinkage of the diffusion picture at LO+Double Logs shown in our previous work in [1]. The areas under the different distributions are much larger at LO for any Y due to the strong suppression of the Pomeron intercept when going beyond LO.…”

“…In a recent work [1] we have shown how to implement this collinear resummation in the BFKLex Monte Carlo event generator and investigated what is its effect in the behavior of the gluon Green function. It is the target of this letter to extend that discussion to investigate the structure of the final state radiation, or, in other words, to which extend this collinear resummation affects the exclusive production of jets as obtained from the BFKL approach.…”

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Abstract: We study high-energy jet production in the multi-Regge limit making use of the Monte Carlo event generator BFKLex which includes collinear improvements in the form of double-log contributions as presented in [1]. Making use of the anti-k t jet algorithm in the FastJet implementation, we present results for the average transverse momentum and azimuthal angle of the produced jets when two tagged forward/backward jets are present in the final state.

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Single bottom quark production in k ⊥-factorisation

“…It also shows, that our initial assumption, that the unintegrated gluon density from HERA would not fail at the LHC, was justified. We plan to JHEP09(2015)123 extend our study toward obtaining more exclusive information with regard to the final state by using the BFKL Monte Carlo code BFKLex [67,68]. The code is an implementation of an iterative solution to the NLx BFKL equation and has already been used in a number of projects [69][70][71].…”

Pomeron Physics at the LHC

“…In addition to multiplicity, other observables were recently proposed [21,22] using this mini-jet radiation…”