### Conveners

#### Small-x, Diffraction and Vector Mesons: Day2-morning-1

- Robert Ciesielski ()
- Daniel Tapia Takaki (University of Kansas)

#### Small-x, Diffraction and Vector Mesons: Day2-morning-2

- Daniel Tapia Takaki (University of Kansas)

#### Small-x, Diffraction and Vector Mesons: Day2-afternoon-2

- There are no conveners in this block

#### Small-x, Diffraction and Vector Mesons: Day2-morning-1

- There are no conveners in this block

#### Small-x, Diffraction and Vector Mesons: Day3-morning-2

- There are no conveners in this block

#### Small-x, Diffraction and Vector Mesons: Day3-afternoon-1

- There are no conveners in this block

#### Small-x, Diffraction and Vector Mesons: Day3-afternoon-2

- There are no conveners in this block

#### Small-x, Diffraction and Vector Mesons: Day4-morning-1

- There are no conveners in this block

Observables sensitive to saturation in DIS will be reviewed. Particular triggers on final state particles in DIS make unitarity limits and saturation prominent. Perhaps surprisingly, it appears that one can even trigger on events where unitarity limits are visible for quark-antiquark dipoles, due to gluon saturation, but where quark occupancies are below saturation.

I will present the most recent developments on the reformulation of small x physics in terms of TMD distributions, and how it allows to study spin physics without going beyond the eikonal approximation.

Color charge correlations in the proton at moderately small $x \sim 0.1$

are extracted from its light-cone wave function. The charge

fluctuations are far from Gaussian. Correlators are described by

n-body GPDs which exhibit interesting dependence on impact parameter

as well as on the relative transverse momentum (or distance) of the

gluon probes.

Furthermore, this analysis provides...

Calculations at small $x$ are usually made in the eikonal approximation. This is the case in the Color Glass Condensate (CGC) effective theory where the propagation of high energy partons in the intense colour field of a hadron or nucleus, approximated by a shockwave, is described by Wilson lines. In this talk we will review attempts to go beyond the eikonal approximation in the CGC framework,...

Inclusive single diffractive dissociation (pp->pX) is studied using data collected by the ATLAS experiment at the LHC. The intact proton is reconstructed and measured in the ALFA forward spectrometer, while charged particles from the dissociative system (X) are reconstructed and measured using the ATLAS inner tracking detector and calorimeters. Differential cross sections are presented as a...

We present the first measurements of diffraction in $\sqrt{s_{NN}}=8.16$ TeV proton-lead collisions within CMS. The very large angular coverage of CMS is used to tag rapidity gaps on both the proton-going and lead-going sides and to identify both pomeron-lead and pomeron-proton topologies. Since the previous highest energy measurement of these processes was at $\sqrt{s_{NN}}=30$ GeV, the...

The CMS Precision Proton Spectrometer consists of tracking and timing detectors placed close to the beam at about 200m from the interaction point. The goal of PPS is to measure the kinematic parameters of the protons scattered in interactions where at least one of them emerges intact. Silicon tracking detectors measure the momentum lost by the proton and diamond timing detectors measure its...

In the Ingelman-Schlein approach for hard diffraction the cross sections can be factorized into diffractive PDFs and perturbatively calculable partonic coefficient functions. The diffractive PDFs can be determined in a global QCD analysis using data for diffractive processes in DIS in a similar manner as for inclusive PDFs. However, it has been observed that this factorization breaks down in...

Diffractive Deep Inelastic Scattering – defined by a colorless exchange between the target nucleus and the incoming electron – is sensitive to the geometric structure of hadrons, and hence can be used as a probe for exploring the mystery of confinement and saturation. Experimentally, this process manifests itself by a rapidity gap in the detector between the outgoing nucleus/remnants and the...

We present our recent analysis on the nucleon and pion gluon distribution functions in the framework of holographic QCD, focusing on the small Bjorken $x$ region. Based on an approximate relation, the gluon distributions are extracted from structure functions of the unpolarized deep inelastic scattering which can be calculated with a holographic QCD model, assuming the Pomeron exchange in the...

In the Color Glass Condensate effective theory framework, the evolution of high energy scattering amplitudes with collision energy is given by thy Balitsky-Kovchegov (BK) equation. It is usually derived from the JIMWLK hierarchy in the in the large-Nc limit. The next-to-leading order evolution equation for the 2-point correlator, related to the total deep inelastic scattering cross section,...

We present the first computation of the next-to-leading order (NLO) photon+dijet impact factor in e+A DIS at small $x$ in the framework of the Color Glass Condensate (CGC) effective field theory. When combined with the recent derivation of JIMWLK small $x$ evolution to next-to-leading logarithm (in $x$) accuracy, this result provides us with a prediction of the photon+dijet cross-section in...

Deep Inelastic Scattering (DIS) is the cleanest tool available to probe the content of a fast proton or nucleus. In the regime of low Bjorken x, one enters in the nonlinear regime of gluon saturation, where the gluons are better described within the framework of Color Glass Condensate (CGC) and the dipole factorization. This framework allows to resum coherent multiple scattering on the target,...

The agreement between calculations inspired by the resummation of energy logarithms, known as BFKL approach, and experimental data in the semi-hard sector of QCD has become manifest after a wealthy series of phenomenological analyses. However, the contingency that the same data could be concurrently portrayed at the hand of fixed-order, DGLAP-based calculations, has been pointed out recently,...

We perform analysis of the pole structure of the BFKL eigenvalues in Mellin space with different forms of the kinematical constraint imposed on the low x evolution. We find that all of them generate the same leading anti-collinear poles which agree with BFKL up to NLL order and up to NNLL in N=4 sYM. The coefficients of subleading poles vanish up to NNLL order for all constraints and we prove...

Deep inelastic scattering (DIS) total cross section data at small-x as measured by the HERA experiments is well described by Balitsky-Kovchegov (BK) evolution in the leading order dipole picture [1-3]. Recently the full Next-to-Leading Order (NLO) dipole picture total cross sections have become available for DIS [4-6], and a working factorization scheme has been deviced which substracts the...

Using the formalism of the light-cone wave function in pQCD together with the hybrid factorization, we compute the cross-section for two and three particle production at forward rapidities in proton-nucleus collisions. We focus on the quark channel, in which the three produced partons -- a quark accompanied by a gluon pair, or two quarks plus one antiquark -- are all generated via two...

We present the computation of exclusive and inclusive dijet production in electron-proton and electron-nucleus collisions at small-x within the Color Glass Condensate effective field theory. We compute the cross-sections differentially in mean dijet momentum and momentum imbalance, as well as its corresponding elliptic anisotropy. For exclusive dijet production, we employ a dipole model with...

In the search for a clear signal of underlining BFKL dynamics in high-energy diffractive processes the Mueller-Tang jet observables have been proven to be a particularly fortunate choice.

Despite unavoidable unperturbative effects that can affect the rapidity gap signature good agreement was found between the BFKL predictions and the Tevatron data.

The extent of the agreement was partially...

A study of events where the two leading jets are separated by a large pseudorapidity interval void of particle activity, known as jet-gap-jet events, is presented. The jets have transverse momentum pT, jet > 40 GeV and pseudorapidity 1.4 < | ηjet | < 4.7, and opposite-signed pseudorapidities ηjet1 · ηjet2 < 0. The analysis is based on an inclusive dijet data sample collected by the CMS...

The central issue of the presentation will be theoretical study of four charged pion photoproduction that come from ultraperipheral heavy-ion collision. I take into account the single photoproduction of the radial excitations of the $\rho^0$ vector meson. The analysis includes a contribution from the incoherent sum of the $\rho'(1450)$ and $\rho''(1700)$ vs single $\rho(1570)$ vector mesons. I...

The electromagnetic field of a fast charged particle can be described as a flux of quasi-real photons whose intensity is proportional to the square of the electric charge of the particle. In the case of lead ions circulating in the LHC there are copious photonuclear interactions. If the impact parameter of the colliding lead ions is larger than the sum of their radii, photon-induced processes...

In recent years the STAR Collaboration collected a large sample

of ultra-peripheral heavy-ion collisions. The photoproduction of

J/Psi vector mesons is sensitive to the gluon content of the target

nucleon or nucleus. We will present results from a statistically

large sample of J/Psi production in Au+Au collisions. A significant

result comes from the study of the pT distributions, which...

The high flux of quasi-real photons from fast moving lead ions at the LHC allows us to study photon-induced reactions in ultra-peripheral collisions (UPC) of Pb-Pb nuclei in a new kinematic regime. In addition, this flux makes it possible to study J/$\Psi$ exclusive photoproduction off protons in p-Pb collisions at the LHC. Measuring the scattering angle of the produced vector meson one can...

We investigate saturation e?ffects in ep scattering as well as in ultraperipheral pA and AA collisions at small x with four variants of the impact parameter dependent color dipole model: with and without gluon saturation and with and without a novel mechanism that suppresses unphysical dipole radii above the confinement scale.

We show that ep scattering at HERA can be very well described by...

We present a model with which we predict the cross sections for exclusive and dissociative photo and electroproduction of light and heavy vector mesons off protons; the model describes correctly available experimental data. The model is based on the color-dipole approach and incorporates geometric fluctuations of the target-proton partonic structure in the impact-parameter plane. The number of...

We show how exclusive vector meson production off light ions can be used to probe the spatial distribution of small-𝑥 gluons in the deuteron and 3He wave functions. In particular, we demonstrate how short range repulsive nucleon-nucleon interactions affect the predicted coherent J/Psi production spectra. Fluctuations of the nucleon substructure are shown to have a significant effect on the...

We study exclusive quarkonium production in the dipole picture at next-to-leading order (NLO) accuracy, using the non-relativistic expansion for the quarkonium wavefunction. This process offers one of the best ways to obtain information about gluon distributions at small $x$, in ultraperipheral heavy ion collisions and in deep inelastic scattering. The quarkonium light cone wave functions...

We start with an overview of the recent results on charmonia and bottomonia production in electro- and photoproduction processes. An emphasis will be given to the careful treatment of light-front wavefunctions of heavy quarkonia in the potential approach formulated in the color dipole picture. A significant role of spin effects and the D-wave component is found and quantified. Our light-front...

Fully instrumented in the forward acceptance, LHCb provides the unique capabilities to study nuclear environment using open and hidden heavy flavor production in the forward region. In this talk, we present the recent LHCb measurements of open charm hadron production in pPb collisions at sqrt(s_NN)=8.16 TeV, event-activity dependent chic1(3872) production in pp collisions at sqrt(s)=8TeV, and...

We report on the measurement of the Central Exclusive

Production of charged particle pairs $h^{+}h^{-}$ ($h = \pi, K, p$)

with the STAR detector at RHIC in proton-proton collisions at

$\sqrt{s} = 200$ GeV. The charged particle pairs produced in the

reaction $p+p \rightarrow p^\prime+h^{+}h^{-}+p^\prime$ are reconstructed from

the tracks in the central detector and identified using the...

Central exclusive production at hadron colliders results in a hadronic state at or close to midrapidity, and forward scattered protons. The rapidity range between the midrapidity tracks and the forward scattered system is void of particles, thereby yielding a double gap topology which can be identified experimentally. At the high energies of the LHC, pomeron-pomeron fusion dominates the...

In this talk, we will present recent results on ultra-peripheral heavy-ion collisions with the CMS detector. This will include measurements on vector meson photoproduction in ultra-peripheral pPb and PbPb collisions, as well as light-by-light scattering measurements, and new studies of exclusive processes in photon-induced interactions to study low-x QCD dynamics. In addition, recent results...

Ultra-relativistic heavy ion collisions are expected to produce some of the strongest magnetic fields ($10^{13}-10^{16}$ Tesla) in the Universe[1].

These intense electromagnetic fields have been proposed as a source of linearly-polarized, quasi-real photons[2] that can interact via the Breit-Wheeler process to produce $e^+e^-$ pairs[3]. Demonstration that these photons are linearly polarized...

The azimuthal decorrelation angle between the leading jet and scattered lepton in deep inelastic scattering is studied with the ZEUS detector at HERA. The data was taken in the HERA II data-taking period and corresponds to an integrated luminosity of 330 pb$^{-1}$. Azimuthal angular decorrelation has been proposed to study the $Q^2$ dependence of the evolution of the transverse momentum...

An important phenomenological consequence of the phenomenon of gluon saturation is the suppression of back-to-back hadron and jet pairs produced in the forward region of pA collisions. We present a new calculation of this process within the dilute-dense formalism of the color glass condensate (CGC) effective theory. Following Ref. [1], we collide a large-$x$, dilute probe, described in terms...

The interplay between the small x limit of QCD amplitudes and QCD factorization at moderate x has been studied extensively in recent years. It was finally shown that semiclassical formulations of small x physics can have the form of an infinite twist framework involving Transverse Momentum Dependent (TMD) distributions in the eikonal limit. In this work, we demonstrate that small x...

Scattering amplitudes have always been essential to compute cross sections and production rates at colliders. In the last few years, though, there has been terrific progress in understanding the rich mathematical structure of scattering amplitudes, the more so in specific kinematic regions, like the Regge limit. In this talk, I will outline what we have learnt about the weak-coupling...

We propose an all-loop expression for scattering amplitudes in planar N=4 super Yang-Mills theory in multi-Regge kinematics valid for all multiplicities, all helicity configurations and arbitrary logarithmic accuracy. Our expression is arrived at from comparing explicit perturbative results with general expectations from the integrable structure of a closely related collinear limit. A crucial...

We analyze the possibilities for the study of inclusive diffraction offered by future electron-proton/nucleus colliders in the tera-electron-volt regime, the Large Hadron-electron Collider (LHeC) as an upgrade of the HL-LHC, and the Future Circular Collider in electron-hadron mode. Compared to ep collisions at HERA, we find an extension of the available kinematic range in x by a factor of...

Quantum tomography reconstructs higher dimensional features of quantum mechanical

systems from lower dimensional experimental information. The method is practical and directly processes experimental data while bypassing field-theoretic formalism. Quantum tomography can probe entanglement while avoiding model assumptions such as factorization. We review recent work applying quantum tomography...

The proton as a quantum object is in a pure state and is described by a completely coherent wave function with zero entropy. On the other hand in high energy experiments (DIS) when probed by a small external probe, it behaves like an incoherent ensemble of (quasi-free)

partons.

In this talk, we define the "entropy of ignorance" which quantifies the entropy associated with ability to perform...

We present a holographic analysis of diffractive photoproducton of charmonium J/ψ and upsilonium Υ on a proton, considered as a bulk Dirac fermion, for all ranges of √s, i.e., from near threshold to very high energy. Using the bulk wave functions of the proton and vector mesons, within holographic QCD, and employing Witten diagrams in the bulk, we compute the diffractive photoproduction...

We present a first measurement of two-particle angular correlations for charged hadrons emitted from photon-proton, $\gamma p$, interactions over a wide range of pseudorapidity and full azimuth. The $\gamma p$ events were produced within ultra-peripheral pPb collisions at $\sqrt{s_{NN}}$ = 8.16 TeV and were selected by requiring a large rapidity gap in the lead-going direction and no neutron...

In this talk, we will present recent results on ultra-peripheral heavy-ion collisions with the CMS detector. This will include measurements on vector meson photoproduction in ultra-peripheral pPb and PbPb collisions, as well as light-by-light scattering measurements, and new studies of exclusive processes in photon-induced interactions to study low-x QCD dynamics.