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Improving the kinematics for high-energy QCD evolution equations in coordinate space

ECT* Seminar

Guillaume Clement Beuf

25 Nov 2015 - 11:15
Villa Tambosi 2nd Floor, Seminar Room

For Deep inelastic scattering or pp or pA collisions in the high energy limit, large logs typically appears in perturbative expansions. For inclusive enough observables, evolution equations such as BFKL (in the dilute-dilute case) or BK (in the dilute-dense case)are supposed to resum the high-energy leading logarithms.  However, typical derivations of these evolution equations require to take the high-energy limit in a very strict manner, with drastic approximations on the kinematics. For that reason, it is not fully consistent to apply these equations to scattering processes at finite energy, not matter how large it is. At leading log accuracy, this issue leads to an overestimate of the speed of the high-energy evolution of the observables. And at next-to-leading logarithmic accuracy, it leads to a collapse of the standard high-energy formalisms due to the appearance of spurious large logarithms, giving unphysical predictions such as negative and/or oscillating cross-sections.  I will explain how these issues are resolved by a more careful treatment of the kinematics in the derivation of the BK or BFKL equations, leading modified evolution equations with a reduced phase-space for gluon emission.   Ref:G. Beuf, Phys.Rev. D89 (2014) 7, 074039, arXiv:1401.0313