### Conveners

#### WG4: Small-x and Diffraction

- Deniz Sunar Cerci (Adiyaman University)
- Martin Hentschinski (Universidad de las Americas Puebla)

#### WG4: Small-x and Diffraction

- Martin Hentschinski (Universidad de las Americas Puebla)
- Deniz Sunar Cerci (Adiyaman University)

#### WG4: Small-x and Diffraction

- Martin Hentschinski (Universidad de las Americas Puebla)
- Deniz Sunar Cerci (Adiyaman University)

#### WG4: Small-x and Diffraction

- Deniz Sunar Cerci (Adiyaman University)
- Martin Hentschinski (Universidad de las Americas Puebla)

The studies as a function of the charged-particle multiplicity allowed the discovery of heavy-ion-like effects in pp collisions. However, to some degree, the multiplicity classifiers used so far bias the sample towards hard processes like multi-jet final states. This limitation of the existing event classifiers makes it difficult to perform, for example, jet-quenching searches in...

We study the proposal by Kharzeev-Levin to determine entanglement entropy in Deep Inelastic Scattering (DIS) from parton distribution functions (PDFs) and relates the former to the entropy of final state hadrons. We find several uncertainties in the current comparison to data, in particular uncertainties related to the overall normalization, the relation between charged versus total hadron...

In this talk, we review some recent advances in understanding the interplay between transverse momentum dependent gluon distributions on the one hand, and the saturation phenomenon at low $x$ on the other hand. Using the example of forward heavy-quark pair hadro- or leptoproduction, we argue that saturation corrections are needed to properly take the gauge-dependence and polarisation...

The two-scale evolution of Collins-Soper-Sterman-type for the unintegrated PDF in the regime qT << mu is derived from the BFKL evolution in physical rapidity with longitudinal momentum conservation constraint in coordinate space form. Comparisons of analytic results with Monte-Carlo implementation of the evolution are also done. This work is a continuation of the calculation done in Phys. Rev....

Strong electromagnetic fields of accelerated heavy ions at the LHC can be used to probe photon-photon and photon-hadron interactions in a new kinematic regime. ALICE has extensively studied these processes in ultra-peripheral collisions (UPC) characterized by impact parameters larger than the sum of nuclear radii. In recent years, photon-induced processes have been also observed in heavy ion...

In this contribution we analyze the double vector meson production in photon–hadron interactions at the LHC and present predictions for the $\rho \rho$, $\phi \phi$, $J/\Psi J/\Psi$, $\rho J/\Psi$ and $\phi J/\Psi$ production considering the double scattering mechanism. We estimate the total cross sections and rapidity distributions at LHC energies and compare our results with the...

It is explained that the Good – Walker model of diffraction is viable only for small t which are parametrically smaller than the inverse square of the nucleon radius. Example of J/\psi production in inelastic rapidity gap kinematics is considered and it is argues that the knockout mechanism becomes important/ dominates already at -t ~ 0.5 GeV^2. Restrictions on the distribution of gluons in...

On behalf of the ZEUS Collaboration.

The exclusive photoproduction reactions γp → J/ψ(1S)p and γp → ψ(2S)p have

been measured at an ep centre-of-mass energy of 318 GeV with the ZEUS detector

at HERA using an integrated luminosity of 373 pb−1. The measurement was made

in the kinematic range 30 < W < 180 GeV, Q2 < 1 GeV2 and |t| < 1 GeV2, where

W is the photon–proton centre-of-mass energy, Q2...

The back-to-back di-$\pi^{0}$ correlation functions in forward directions have been observed to be suppressed in $p(d)+$A collisions relative to $p$$+$$p$ collisions. The nonlinear gluon dynamics in nuclei is one of the possible mechanisms responsible for the suppression. In addition, theorists pointed out that the double-parton scattering (DPS) can be an alternative explanation of the...

The three point light-cone correlation function of color charge densities is evaluated in light-cone gauge. The proton is approximated as a non-perturbative 3-quark state plus perturbative corrections due to the emission of a gluon which is not required to be soft. The resulting expressions provide the C-odd contribution to the initial conditions for high-energy evolution of the dipole...

We study, to all orders in perturbative QCD, the universal behavior of the saturation momentum $Q_s(L)$ controlling the transverse momentum distribution of a fast parton propagating through a dense QCD medium with large size $L$. Due to the double logarithmic nature of the quantum evolution of the saturation momentum, its large $L$ asymptotics is obtained by slightly departing from the double...

The elastic scattering of protons at 13 TeV is measured in the range of protons??? transverse momenta allowing the access to the Coulomb-Nuclear-Interference region. The data were collected thanks to dedicated special LHC beta* = 2.5km optics. The total cross section as well as rho-parameter, the ratio of the real to imaginary part of the forward elastic scattering amplitude, are measured and...

CMS results on diffraction and low x

We present a phenomenological analysis of events with two high transverse momentum (pT_{T}T) jets separated by a large (pseudo-)rapidity interval void of particle activity, also known as jet-gap-jet events. In the limit where the collision energy $\sqrt{s}$ is much larger than any other momentum scale, the jet-gap-jet process is described in terms of perturbative pomeron exchange between...

We study inclusive dijet production in deep inelastic scattering at NLO within the Color Glass Condensate effective field theory. We begin by considering this process in general small-$x$ kinematics. We first show that the differential cross-section is infrared and collinear safe. We demonstrate the factorization of large rapidity logarithms that can then be resummed via JIMWLK...

We study dijet production within the small-x improved TMD factorization, which is a formalism based on the Color Class Condensate suitable to study relatively hard jet production processes and to take into account gluon saturation. The formalism also allows to perform the Sudakov resummation as well as implements the power corrections that are necessary to access the dijet decorrelation...