High Energy QCD at NLO: from light-cone wave function to JIMWLK evolution

Soft components of the light cone wave-function of a fast moving projectile hadron is computed in perturbation theory to third order in QCD coupling constant. At this order, the Fock space of the soft modes consists of one-gluon, two-gluon, and a quark-antiquark states. The hard component of the wave-function acts as a non-Abelian background field for the soft modes and is represented by a valence charge distribution that accounts for non-linear density effects in the projectile. When scattered off a dense target, the diagonal element of the S-matrix reveals the Hamiltonian of high energy evolution, the JIMWLK Hamiltonian. This way we provide a new direct derivation of the JIMWLK Hamiltonian at the Next-to-Leading Order.Comment: 83 pages, 15 figures; explanatory comments added, published versio

Conformal symmetry of JIMWLK Evolution at NLO

We construct the Next to Leading Order JIMWLK Hamiltonian for high energy evolution in ${\cal N}=4$ SUSY theory, and show that it possesses conformal invariance, even though it is derived using sharp cutoff on rapidity variable. The conformal transformation properties of Wilson lines are not quite the naive ones, but at NLO acquire an additional anomalous piece. We construct explicitly the inversion symmetry generator. We also show how to construct for every operator $O$, including the Hamiltonian itself, its "conformal extension" $\cal O$, such that it transforms under the inversion in the naive way.Comment: 20 page

Dihadron production in DIS at NLO: the real corrections

By using the formalism of the light-cone wave function along with the colour glass condensate effective theory, we consider next-to-leading order (NLO) corrections to the production of a pair of hadrons in electron-proton, or electron-nucleus, collisions at small Bjorken $x$. To the order of interest, the process involves the fluctuation of a virtual photon into a quark-antiquark pair, followed by the emission of a gluon from either the quark, or the antiquark. For the case of a virtual photon with transverse polarization, we compute the real NLO corrections, where the emitted gluon is present in the final state. We first compute the tree-level cross-section for the production of the quark-antiquark-gluon system and then deduce the real NLO corrections to dihadron production by integrating out the kinematics of the gluon. We verify in detail that, in the limit where the gluon is soft, our calculation reproduces the (real piece of the) B-JIMWLK evolution of the leading-order cross-section for quark-antiquark production. Similarly, in the limit where the gluon is collinear with its emitter, we recover the real terms in the DGLAP evolution of the fragmentation function. The virtual NLO corrections to dihadron production will be presented by one of us in a subsequent publication.Comment: 43 pages, 13 figure

Multi-particle Production in Proton-Nucleus Collisions at High Energy

International audienceUsing the formalism of the light-cone wave function in perturbative QCD together with the hybrid factorization, we compute the cross section for three particle production at forward rapidities in proton–nucleus collisions. In this picture, the three produced partons — a quark accompanied by a gluon pair, or two quarks plus one antiquark — are all generated via one or two successive splittings of a quark from the incoming proton, that was originally collinear with the latter. The three partons are put on-shell by their scattering off the nuclear target, described as the Lorentzcontracted shockwave. We explicitly compute the three-parton Fock space components of the light-cone wave function of the incoming quark and its outgoing state, which encodes the information both on the evolution in time as well as the scattering process. This outgoing state is also an ingredient for other interesting calculations, like the next-to-leading order correction to the cross section for the production of a pair of jets

Forward trijet production in proton-nucleus collisions

International audienceUsing the formalism of the light-cone wave function in perturbative QCD together with the hybrid factorization, we compute the cross-section for three particle production at forward rapidities in proton-nucleus collisions. In this picture, the three produced partons --- a quark accompanied by a gluon pair, or two quarks plus one antiquark --- are all generated via one or two successive splittings of a quark from the incoming proton, that was originally collinear with the latter. The three partons are put on-shell by their scattering off the nuclear target, described as Lorentz-contracted shockwave.We explicitly compute the three-parton Fock space components of the light-cone wave function of the incoming quark and its outgoing state, which encodes the information both on the evolution in time as well as the scattering process. This outgoing state is also an ingredient for other interesting calculations, like the next-to-leading order correction to the cross-section for the production of a pair of jets