Saturation effects in SIDIS at very forward rapidities

Abstract

Using the dipole picture for electron-nucleus deep inelastic scattering at small Bjorken x, we study the effects of gluon saturation in the nuclear target on the cross-section for SIDIS (single inclusive hadron, or jet, production). We argue that the sensitivity of this process to gluon saturation can be enhanced by tagging on a hadron (or jet) which carries a large fraction z ≃ 1 of the longitudinal momentum of the virtual photon. This opens the possibility to study gluon saturation in relatively hard processes, where the virtuality Q2 is (much) larger than the target saturation momentum $$ {Q}_s^2 $$ Q s 2 , but such that z(1 − z)Q2 ≲ $$ {Q}_s^2 $$ Q s 2 . Working in the limit z(1 − z)Q2 ≪ $$ {Q}_s^2 $$ Q s 2 , we predict new phenomena which would signal saturation in the SIDIS cross-section. For sufficiently low transverse momenta k⊥ ≪ Qs of the produced particle, the dominant contribution comes from elastic scattering in the black disk limit, which exposes the unintegrated quark distribution in the virtual photon. For larger momenta k⊥ ≳ Qs, inelastic collisions take the leading role. They explore gluon saturation via multiple scattering, leading to a Gaussian distribution in k⊥ centred around Qs. When z(1 − z)Q2 ≪ Q2, this results in a Cronin peak in the nuclear modification factor (the RpA ratio) at moderate values of x. With decreasing x, this peak is washed out by the high-energy evolution and replaced by nuclear suppression (RpA< 1) up to large momenta k⊥ ≫ Qs. Still for z(1 − z)Q2 ≪ $$ {Q}_s^2 $$ Q s 2 , we also compute SIDIS cross-sections integrated over k⊥. We find that both elastic and inelastic scattering are controlled by the black disk limit, so they yield similar contributions, of zeroth order in the QCD coupling.

Dijet impact factor in DIS at next-to-leading order in the Color Glass Condensate

“…Another interesting possibility is to integrate out one of the jets in our differential cross-section, and obtain the NLO impact factor for single inclusive jet production. This computation is very similar to the NLO studies of inclusive forward jet production in proton-nucleus collisions [105].…”

The importance of kinematic twists and genuine saturation effects in dijet production at the Electron-Ion Collider

“…The Color Glass Condensate (CGC) is a semi-classical effective field theory (EFT) for small-x gluons in this regime [12][13][14][15][16][17][18][19][20][21][22]. The CGC has been applied for a variety of processes in proton-nucleus collisions as well as DIS: structure functions (inclusive [23,24] and diffractive [25]), semi-inclusive production (photon [26][27][28][29], inclusive single hadron [30][31][32][33][34], dihadron/dijet [35][36][37][38], quarkonia [39][40][41][42]), and exclusive processes (deeply virtual Compton scattering and vector meson [43][44][45][46][47][48][49][50][51], dijet [52][53][54][55], trijet [56][57][58] production) to name a few (for a recent review see ...…”

Mining for Gluon Saturation at Colliders

“…These measurements are analogous to those at RHIC and the LHC, where the nuclear modification factor R eA develops a Cronin-like peak at mid rapidity which is then suppressed by saturation (See Figure 32). Preliminary studies in [205] show very characteristic features of the transverse momentum distribution when studied at different rapidities and different virtualities and in DIS. The authors propose that this observable can be studied at perturbative virtualities Q 2 1 GeV 2 and that sensitivity to the saturated regime is enhanced for hadrons that carry a large longitudinal momentum fraction z.…”

“…As for other observables that can be measured in DIS, recently, new signatures of gluon saturation have been proposed by studying single inclusive particle production [204,205]. These measurements are analogous to those at RHIC and the LHC, where the nuclear modification factor R eA develops a Cronin-like peak at mid rapidity which is then suppressed by saturation (See Figure 32).…”

“…In this figuresQ 2= z(1 − z)Q 2 ,where z is the longitudinal momentum fraction of the hadron relative to the virtual photon, and is chosen to be close to unity. Figure from the work in[205].…”