### Conveners

#### Small-x, Diffraction and Vector Mesons: Parallel Sessions 1

- Tolga Altinoluk (National Centre for Nuclear Research)

#### Small-x, Diffraction and Vector Mesons

- Tolga Altinoluk (National Centre for Nuclear Research)

#### Small-x, Diffraction and Vector Mesons: Parallel Sessions 3

- Tolga Altinoluk (National Centre for Nuclear Research)

#### Small-x, Diffraction and Vector Mesons: Parallel Sessions 3

- Daniel Tapia Takaki (University of Kansas)

#### Small-x, Diffraction and Vector Mesons: Parallel Sessions 4

- Marta Luszczak (University of Rzeszow)

#### Small-x, Diffraction and Vector Mesons: Parallel Sessions 5

- Daniel Tapia Takaki (University of Kansas)

#### Small-x, Diffraction and Vector Mesons: Parallel Sessions 5

- Marta Luszczak (University of Rzeszow)

#### Small-x, Diffraction and Vector Mesons

- Marta Luszczak (University of Rzeszow)

LHCb is a fully instrumented spectrometer covering the forward rapidity region at the LHC, and provides unique access to the small x region inside the nucleus. This talk will present a selection of recent results from the LHCb heavy ion program, including data on charged hadrons, open charm and charmonia production in pPb collisions, and J/psi production in peripheral PbPb collisions....

In this talk we present the analysis of prompt photon production at the LHC with the kT-factorization approach. We consider two leading partonic channels, qg*->q\gamma and g*g*->q\bar{q}\gamma and three theoretical schemes known under the acronyms KMR, GBW, CCFM. We find sensitivity of the calculated prompt photon transverse momentum distribution to the gluon transverse momentum distribution....

We present, the results of a phenomenology analysis at Next-to-Leading accuracy for the Mueller-Tang jet process, where two jets separated by a large rapidity interval and no other radiation are observed. This process is of high interest, as one might be able to investigate Balitsky-Fadin-Kuraev-Lipatov (BFKL) dynamics which emerges in the high-energy limit of quantum chromodynamics...

This paper presents an experimental study of proton-proton collision events where the two leading jets are separated by a large pseudorapidity interval devoid of particle activity, referred to as jet-gap-jet events. The pseudorapidity gap is expected from hard color-singlet exchange. The analysis is based on data collected by the CMS and TOTEM experiments during a low luminosity,...

Inclusive measurements of forward back-to-back dijets/dihadrons in deeply inelastic scattering (DIS) present a promising channel to access signatures of gluon saturation inside nuclear matter at the future Electron-Ion Collider (EIC). Most phenomenological studies employ the transverse momentum dependent (TMD) factorization framework; however, there are important kinematic (perturbative power)...

We study production of two jets in DIS for EIC kinematics using the small-x improved TMD factoriztion (ITMD) framework. The ITMD can be derived within the Color Glass Condensate (CGC) as an adequate limit when the hard scale is considerably higher than the saturation scale, but being still in the nonlinear domain. Production of two tagged colored partons in photon-nucleus collisions is the...

A framework to study gluon saturation in QCD using trijet processes is presented.

The so-called small-x Improved Transverse Momentum Dependent factorization (ITMD) was originally formulated for the dijet final states in hadron collisions. I present results for a multiparton extension, in particular for trijets both for proton-proton and proton-lead collisions at center of mass energy 5.02...

One of the key components to solving the proton spin problem is understanding the small-x asymptotics of the helicity parton distribution functions (hPDFs). Several years ago, novel, small-x evolution equations were derived using the shock-wave/Wilson line formalism, designed for calculating the x-dependence of the quark and gluon hPDFs and the proton g1 structure function. These equations can...

We apply the formalism developed earlier $[1,2]$ for studying the small-$x$ asymptotics of transverse momentum dependent parton distribution functions (TMDs) to construct the small-$x$ asymptotics of the quark Sivers function. We explicitly construct the transversely polarized, fundamental "Wilson line" operator to sub-sub-eikonal order. We then express the Sivers function in terms of dipole...

Within the Color Glass Condensate effective theory or other related frameworks, the theoretical description of low-x (or high-energy) QCD processes sensitive to the nonlinear gluon saturation physics relies on two main pillars.

The first one is the semiclassical approach: due to the high density of low x gluons in an incoming proton or nucleus target, scattering processes off that target...

We calculate the inclusive quark-photon production in high energy proton-nucleus collisions using a new formalism which includes the dynamics of gluon saturation at small $x$ as well as large x gluons of the target. We show how this unified formalism can be applied to di-jet production in DIS at all Bjorken x.

Quasi parton distribution functions (PDFs) are related to the matrix elements of bilocal operators with space-like separation. The possibility to calculate these objects on the lattice has attracted much attention in the QCD community. I will present the behavior of quark and gluon quasi-PDFs at low-x.

Understanding the relation between QCD evolution in the Bjorken limit and the Regge limit is crucial to achieve a complete and smooth picture of proton and nuclear structure. The hope in the small x regime (where gluon density is expected to reach saturation and the naif partonic breaks down), was that by computing higher order corrections to small x evolution (BK equations) one would capture...

Two-particle azimuthal correlation has been proposed to be one of the most direct and sensitive channels to access the nonlinear gluon dynamics in nuclei. In hadron collisions at RHIC, forward particle production probes gluons at small momentum fraction where the gluon density rises sharply. During the 2015 RHIC run, STAR collected data for measuring azimuthal correlations of neutral pions...

We present an update of the measurements of the azimuthal decorrelation angle between the leading jet and scattered lepton in deep inelastic scattering, with the ZEUS detector at HERA. The studied data was collected 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...

Two-particle azimuthal correlations have been measured in neutral current deep inelastic ep scattering with virtuality $Q^2> 5$ GeV$^2$ at a centre-of-mass energy $\sqrt{𝑠}= 318$ GeV recorded with the ZEUS detector at HERA. The correlations of charged particles have been measured in the range of laboratory pseudorapidity $−1.5 < \eta < 2.0$ and transverse momentum $0.1 < p_T< 5.0$ GeV and...

The ridge phenomenon found in high multiplicity pp and pPb collisions is one of the most important observations at the LHC. In such small systems, final state explanations become challenging. We study particle correlations in the Color Glass Condensate, which offers a weak coupling but non perturbative framework to study how correlations in the wave function of the incoming hadrons reflect on...

The finding of long rapidity range azimuthal correlations in small collision systems, pp and pA, at the LHC poses a crucial challenge for our understanding of hadronic and nuclear collisions at the highest available energies. In such small collisions systems the final state explanations standardly accepted in heavy ion collisions face conceptual problems and initial state alternatives have...

Color charge correlations in the proton at moderately small x are

extracted from its light-cone wave function. ${\cal O}(g^2)$ corrections to the

leading order correlations due to perturbative emission of a gluon,

which is not required to be soft, have been accounted for. This

analysis provides initial conditions for Balitsky-Kovchegov

high-energy evolution of the dipole scattering...

The Precision Proton Spectrometer (PPS) started operating in 2016 and has collected more than 110 fb−1 of data over the course of the LHC Run 2, now fully available for physics analysis. The talk will discuss the key features of PPS alignment and optics calibrations developed from scratch. The reconstructed proton distributions, performance of the PPS simulation and finally validation of the...

We present the forward rapidity gap spectra from proton-lead (pPb) collisions for both pomeron-Pb and pomeron-p topologies measured at CMS. The analysis is performed over 10.4 units of pseudorapidity at a center-of-mass energy of 8.16 TeV, almost 300 times higher than previous measurements of diffractive production in proton-nucleus collisions. For the pomeron-Pb topology, the cross-section...

Possibilities for inclusive diffraction in electron-proton/nucleus collider, EIC in the US are analyzed. We find that thanks to the excellent forward proton tagging, the EIC will be able to access the wider kinematical range of longitudinal momentum fraction and momentum transfer of the leading proton than at HERA. This opens up the possibilities of measurement of subleading diffractive...

We show that the cross section for the diffractive dissociation of a small onium off a large nucleus conditioned to a minimum rapidity gap can be identified to a simple classical observable on the stochastic process representing the quantum evolution of the onium in the QCD dipole model. This holds true in the parametric limit defining the geometric scaling region. Such an identification...

In this talk we present various measurements sensitive to non-perturbative physics performed using data collected by the ATLAS experiment at the LHC. 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...

We present results on the inclusive and identified (pion, kaon, proton and their antiparticles) charged-particle production in single diffractive dissociation process in proton-proton collisions at $\sqrt{s}= 200$ GeV with the STAR detector at RHIC. The forward-scattered proton is measured in the Roman Pot system, while the charged particle tracks are reconstructed in the STAR Time...

We discuss mechanisms of dilepton production in proton-proton collisions with rapidity gap in the main detector and one forward proton in the forward proton detectors. This is relevant for LHC measurements by ATLAS+ALFA and CMS+TOTEM. The calculations are performed including transverse momenta of the virtual photons and using relevant off-shell matrix elements. Differential distributions in...

We present results on the Central Exclusive Production of charged particle pairs $h^{+}h^{-}$ ($h = \pi, K, p$) obtained in the STAR experiment at RHIC in proton-proton collisions at center-of-mass energy of $\sqrt{s} = 200$ GeV. All final-state particles of the process $pp\to p^\prime+h^{+}h^{-}+p^\prime$ were reconstructed, including forward-scattered protons detected in the Roman Pot...

Exclusive emissions of vector mesons in forward directions of rapidity offer us a faultless chance to probe the proton structure at small-$x$. Here, a high-energy factorization formula is established within the Balitsky-Fadin-Kuraev-Lipatov (BKFL), given as the convolution of a impact factor depicting the forward-meson emission and of an unintegrated gluon distribution (UGD) driving the gluon...

Exclusive photoproduction of $\rho^0(770)$ mesons is studied using the H1 detector at the $ep$ collider HERA. A sample of about 900000 events is used to measure single- and double-differential cross sections for the reaction $\gamma p\to \pi^{+}\pi^{−}Y$. Reactions where the proton stays intact ($m_Y=m_p$) are statistically separated from those where the proton dissociates to a low-mass...

Lead ions circulating in the LHC provide copious photonuclear interactions.

These dominate the interaction rate via ultra-peripheral collisions (UPC),

when the impact parameter of the colliding lead ions is larger than the sum of their radii.

The study of \rho^0 meson photonuclear production is important,

because its cross section in UPC at the LHC is so large that it becomes a proper...

Exclusive scattering processes are especially powerful probes of the proton and nuclear structure at small $x$. In particular, the possibility to measure the total momentum transfer allows for the extraction of the spatial distribution of small-$x$ partons, including their event-by-event fluctuations[1].

More detailed information about the target structure can be obtained by studying more...

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 $p_T$ distributions,...

Ultra-peripheral collisions (UPCs) at the LHC, studied using the ALICE detector, allow us to investigate, using photon-induced interactions, processes sensitive to the low x behaviour of the gluon distribution of the colliding particles and provide important constraints on the initial stages of the collision.

The first measurement of the t-dependence of the coherent $\rm{J/\psi}$...

We investigate the exclusive photoproduction of J/ψ mesons in ultraperipheral heavy-ion collisions in the color dipole approach. We use the color dipole formulation of Glauber-Gribov theory to calculate the diffractive amplitude on the nuclear target. We compare our results to recent published data on exclusive J/ψ production in ultraperipheral lead-lead collisions at √sNN=2.76 and...

We investigate the momentum transfer dependence of differential cross sections $d\sigma/dt$ in diffractive electroproduction of heavy quarkonia.

The calculations have been performed within the light-front QCD dipole formalism using realistic quarkonium wave functions determined from various potential models in the $Q\bar Q$ rest frame.

Model predictions for $d\sigma/dt$ including a...

We study the exclusive production of $J^{PC}=0^{++}$ and $0^{--}$ charmonium states in proton-proton collisions at the LHC energies. The amplitudes for $gg \to \chi_{c0}$ as well as for $gg \to \eta_c$ mechanisms are derived in the $k_{T}$-factorization approach. The $p p \to p p \eta_c$ reaction is discussed for the first time. We have discussed rapidity and transverse momentum...

We present a new study of the central exclusive diffractive production of $f_{1}(1285)$ and $f_{1}(1420)$ mesons in proton-proton collisions within the tensor-pomeron approach [1], [2]. Two ways to construct the pomeron-pomeron-$f_{1}$ coupling are presented. We adjust the parameters of our model to the WA102 experimental data [3] and compare with predictions of the Sakai-Sugimoto model, where...

High-energy coherent photoproduction can be used to image the transverse position of gluons in heavy nuclei (similar to the Generalized Parton Distribution, but for nuclei). The two-dimensional Fourier transform of dsigma/dt gives the transverse distribution of interaction sites in the nuclei; for photoproduction, this probes the gluon distributions. However, there are many systematic...

Exclusive vector meson production is a powerful process to probe the gluonic structure of protons and nuclei at small Bjorken-$x$, and it also makes it possible to study the geometry of the nuclei in the transverse plane. An accurate description of the process requires us to go beyond the leading order and include corrections of higher orders. These include relativistic corrections to the...

Color Glass Condensate (CGC) effective field theory (EFT) at leading order describes well the Deep Inelastic Scattering (DIS) inclusive cross section data at small-x as measured by the HERA experiments [1-3]. Recently the inclusive DIS impact factors have been calculated in Next-to-Leading Order (NLO) accuracy in CGC EFT [4-6], and the soft gluon divergence present at NLO has been factorized...

We use Lipatov's high energy effective action to determine the next-to-leading order corrections to Higgs production in the forward region. As a new element we provide a proper definition of the desired next-to-leading order coefficient within the high energy effective action framework, extending a previously proposed prescription. We further propose a subtraction mechanism to achieve for...

The Precision Proton Spectrometer (PPS) is a new subdetector of CMS introduced for the LHC Run 2, which provides a powerful tool for advancement of BSM searches.The talk will present the new results on exclusive diphoton, Z+X, and diboson production explored with with PPS, illustrating the unique sensitivity which can be achieved using proton tagging. The upcoming Run 3 will bring new...

We describe an analysis comparing the $p\bar{p}$ elastic cross section as measured by the D0 Collaboration at a center-of-mass energy of 1.96~TeV to that in $pp$ collisions as measured by the TOTEM Collaboration at 2.76, 7, 8, and 13 TeV using a model-independent approach. The TOTEM cross sections extrapolated to a center-of-mass energy of $\sqrt{s} =$ 1.96 TeV are compared with the D0...

Dijet processes can be used in several ways to probe the nuclear initial state. Exclusive dijet photoproduction in ultra-peripheral heavy-ion collisions has recently been suggested as a probe of the gluon Wigner distribution. In particular, the angular correlation of exclusive dijets can assess the azimuthal anisotropy of the gluon distribution in the nuclear target. In this talk, we present...

We present results of our studies of diffractive dijet photoproduction at the recently approved electron-ion collider (EIC) at BNL. Apart from establishing the kinematic reaches for various beam types, energies and kinematic cuts, we make precise predictions at next-to-leading order (NLO) of QCD in the most important kinematic variables. We show that the EIC will provide new and more precise...

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...

We present our recent studies of intranuclear fluctuations in eA collisions using both the saturated and non-saturated dipole models. These have a sizable effect in the large |t|-region of exclusive diffraction. We use a model of geometrical fluctuations, where we extrapolate the fluctuation of nucleon configurations into a model of gluon hotspots within hotspots. As the saturated dipole model...

The LHeC and the FCC-eh will extend the kinematic region presently available in DIS to very small values of $x$ in the perturbative $Q^2$ region. Therefore, they will be able to establish the dynamics of the strong interaction at small $x$ or high energies, and unravel the existence of a new non-linear regime of QCD where parton densities are expected to saturate. In this talk we will review...

A modern renaissance in how to understand and use quantum mechanics has arrived in nuclear and particle physics. Quantum tomography bypasses model-dependent assumptions and unnecessary theoretical superstructure that characterized the old use of quantum mechanics, which as designed for exclusive processes. A modern description of inclusive reactions is closely tied to the correlations of what...