Next-to-leading order Balitsky-Kovchegov equation with resummation

Apr 12, 2016, 9:40 AM
15m
SR4b (DESY Hamburg)

SR4b

DESY Hamburg

Small-x, Diffraction and Vector Mesons WG5 Small-x and Diffraction

Speaker

Dr Heikki Mäntysaari (Brookhaven National Laboratory)

Description

The Color Glass Condensate framework has been successfully applied to many high-energy scattering processes, and it has also been seen as a powerful tool to describe initial state of heavy ion collisions. An important next step for the CGC phenomenology is to perform these calculations at next-to-leading order accuracy, which would allow a qualitative test of the saturation picture. A necessary ingredient in these calculations is the solution to the CGC evolution equation, the Balitsky-Kovchegov (BK) equation, at NLO accuracy. In our previous work [1] it was shown that the NLO BK equation is unstable and results in an unintegrated gluon distribution to decrease as momentum fraction x decreases. It could also drive the dipole amplitude to become negative even with physically relevant initial conditions. We show that when large single and double logarithmic corrections [2,3] are resumed in the equation, the evolution becomes stable and a physical solution is obtained. We determine the optimal way to include a maximal amount of full NLO result in the resummation by fixing the constant under the resummed large transverse logarithm. By direct numerical solution we show that the as^2 terms that are not enhanced by large logarithms can be neglected at large saturation scales (late in the evolution). However, these numerically demanding terms have a significant effect close to phenomenologically relevant initial conditions. The NLO evolution obtained in this work should be suitable for phenomenological calculations with NLO cross sections. The work presented in this talk is published in [4]. References [1] T. Lappi and H. Mäntysaari, Direct numerical solution of the coordinate space Balitsky-Kovchegov equation at next to leading order, Phys. Rev. D91 (2015) [arXiv:1502.02400 [hep-ph]] [2] E. Iancu, J. D. Madrigal, A. H. Mueller, G. Soyez and D. N. Triantafyllopoulos, Resumming double logarithms in the QCD evolution of color dipoles, Phys. Lett. B744 (2015) 293 [arXiv:1502.05642 [hep-ph]]. [3] E. Iancu, J. D. Madrigal, A. H. Mueller, G. Soyez and D. N. Triantafyllopoulos, Collinearly-improved BK evolution meets the HERA data, arXiv:1507.03651 [hep-ph]. [4] T. Lappi, H. Mäntysaari, Next-to-leading order Balitsky-Kovchegov equation with resummation. arXiv:1601.06598

Primary author

Dr Heikki Mäntysaari (Brookhaven National Laboratory)

Co-author

Dr Tuomas Lappi (University of Jyväskylä)

Presentation materials