Gluon saturation and initial conditions for relativistic heavy ion collisions

Abstract

We present an overview of theoretical aspects of the phenomenon of gluon saturation in high energy scattering in Quantum Chromo Dynamics. Then we review the state-of-theart of saturation-based phenomenological approaches to the study and characterisation of the initial state of ultra-relativistic heavy ion collisions performed at RHIC and the LHC. Our review focuses mostly in the Color Glass Condensate effective theory, although we shall also discuss other approaches in parallel.

Improved TMD factorization for forward dijet production in dilute-dense hadronic collisions

“…As shown in eq. (4.35), the expressions for H (3) gg→gg , H (4) gg→gg , H (5) gg→gg and H (6) gg→gg differ only by numerical factors. On top of that, when examining further eqs.…”

“…As a result, the cross section involves multipoint correlators of Wilson lines. In particular, the amplitude from figure 2, after squaring, has four terms: a correlator of four Wilson lines, S (4) , corresponding to interactions happening after the emission of the gluon, both in the amplitude and the complex conjugate, then a correlator of two Wilson lines, S (2) , representing the case when interactions with the target take place before the radiation of the gluon in both amplitude and complex conjugate, and two correlators of three Wilson lines, S (3) , for the interference terms. In all the cases the splitting function is the same, and is given by the product of the quark wave functions:…”

“…In addition to the two gluon distributions, F (1) gg and F (2) gg , used in ref. [13], the result to all orders in N c involves a third distribution [12,44], F (3) gg (also sometimes denoted x 2 G (1) and called the Weizsacker-Williams gluon distribution), and the differential cross section reads 14) with the three gluon TMDs defined as…”

“…In terms of diagrams, we always obtain D 1 + D 2 + 2D 3 + D 4 + 2D 5 + 2D 6 , meaning that we recover the collinear matrix elements. Indeed we have (noting that H (3) gg→gg + H (4) gg→gg + H (5) gg→gg = 0):…”

Leptons from heavy-quark semileptonic decay in pA collisions within the CGC framework

“…This equation resums quantum corrections of orders (α s Y ) n in the linear regime, while by unitarity it tames the growth of the transition amplitude in the nonlinear regime. Phenomenological analyses with the rcBK equation have been successful in describing HERA-DIS data as well as LHC hadron production data [34,35].…”