Conveners
WG2: Small-x, Diffraction and Vector Mesons: Session 1
- Rafał Staszewski (IFJ PAN Cracow (PL))
- Daria Sokhan (CEA Saclay / Glasgow U.)
- Guillaume Beuf
WG2: Small-x, Diffraction and Vector Mesons: Session 2
- Rafał Staszewski (IFJ PAN Cracow (PL))
- Guillaume Beuf
- Daria Sokhan (CEA Saclay / Glasgow U.)
WG2: Small-x, Diffraction and Vector Mesons: Session 3
- Guillaume Beuf
- Rafał Staszewski (IFJ PAN Cracow (PL))
- Daria Sokhan (CEA Saclay / Glasgow U.)
To calculate the PDFs from first principles in Lattice gauge theories
it is convenient to consider the Ioffe-time distribution defined through gauge-invariant bi-local operators with spacelike separation.
Lattice calculations provide values for a limited range of the distance separating the bi-local operators. In order to perform the Fourier transform and obtain the pseudo- and the...
We perform the fit to the structure function F2 data from HERA including terms due to the resummation at small x. The equation for the unintegrated gluon density is solved, previously established within the renormalization group improved small x framework. We find very good description of the structure function F2 and its charm component Fc2. The resulting unintegrated gluon density is found...
We present our theoretical results of the next-to-leading order approach (NLO) of [Eur. Phys. J. C 80, 1029 (2020)] in contrast with the experimental HERA data. This approach includes the re-summed NLO corrections to the kernel of the evolution equation, the correct asymptotic behavior in the NLO at $\tau = r^{2}Q_{S}^{2} \gg 1$; the impact parameter dependence of the saturation scale in...
A central ingredient in calculations of scattering processes in the high energy saturation regime of QCD is the light cone wavefunction. It is a universal QCD quantity encoding the light cone gauge partonic structure of a high energy projectile, and a necessary ingredient in cross section calculations for different scattering processes. This talk will report on the recent calculation of the...
We investigate the proposal by Kharzeev and Levin of a maximally entangled proton wave function in Deep Inelastic Scattering at low x and the proposed relation between parton number and final state hadron multiplicity. Contrary to the original formulation we determine partonic entropy from the sum of gluon and quark distribution functions at low x, which we obtain from an unintegrated gluon...
Possibilities for the measurement of the longitudinal structure function in diffraction FDL at the future US Electron Ion Collider are investigated. The sensitivity to FDL arises from the variation of the reduced diffractive cross section with centre-of-mass energy. Simulations are performed with various sets of beam energy combinations and for different assumptions on the precision of the...
The study of the dense gluonic matter emerging in QCD at high energies represents one of the main goals of the experimental program at the future Electron-Ion Collider. We demonstrate that dijet production via inelastic diffraction is a promising channel for probing gluon saturation, including in the hard regime at high photon virtuality, where the collinear factorisation applies. By...
The search for gluon saturation is one of the main pillars for the scientific program of the future Electron-Ion Collider (EIC). In recent years, significant progress has been made in advancing saturation physics to a precision science as we prepare for the EIC era. We contribute to these efforts by performing the first complete next-to-leading order (NLO) computation of inclusive dijet...
Using the spinor helicity formalism we calculate the one-loop corrections to inclusive di-hadron production in DIS at small $x$ using the Color Glass Condensate description of the target proton or nucleus. It is shown that all divergences either cancel or can be absorbed into evolution of hadron fragmentation functions. We discuss phenomenological applications of our results to EIC and...
We revisit inclusive $J/\psi$ and $\Upsilon$ photoproduction at lepton-hadron colliders, namely in the limit when the exchanged photon is quasi real. Our computation includes the next-to-leading-order (NLO) $\alpha_s$ corrections to the leading-order contributions in $v^2$.
We consider first large-$P_T$ inclusive photoproduction of $J/\psi$ at HERA and provide NLO predictions for the EIC...
We investigate the Feynman-$x$ spectra of the neutrons produced in the very forward direction in $ep$ collisions using the impact-parameter dependent color dipole model with and without saturation. Our analysis demonstrates that the W and $Q^2$ dependence of the cross-section are independent of the presence of a forward neutron, as predicted by Feynman-scaling. The models prediction are...
New measurements of impact parameter dependence of photon-photon interactions in ultraperipheral PbPb collisions (UPC) are presented, using data collected by the CMS detector during the LHC Run 2. The “UPC centrality” is classified based on the number of neutrons (including 0, 1, or at least two) detected in the very forward pseudorapidity to control the impact parameter of UPCs. The...
Ultra-peripheral collisions (UPC) of relativistic heavy-ion beams lead to a diverse set of photon-nucleus interactions. This talk presents two recent ATLAS measurements of photo-nuclear processes in Pb+Pb collisions at 5.02 TeV. The first measurement is that of photon-induced dijet production in UPC events. The clean environment of these events allows for precision measurements in a...
We study correlations originating from the quantum nature of gluons in a hadronic wave function. Bose-Einstein correlation between identical particles lead to the enhancement in the number of pairs of gluons with the same quantum numbers and small relative momentum. We show that these preexisting correlations can be probed in Deep Inelastic Scattering experiments at high energy. Specifically,...
We present our theoretical results for the exclusive photoproduction of heavy quarkonia pairs in the kinematics of the future high-energy colliders, like the future Electron Ion Collider (EIC), the Large Hadron electron Collider (LHeC), and the Future Circular Collider (FCC-he). We found that in the leading order over the strong coupling $\alpha_s$ the produced quarkonia have opposite...
We derive subeikonal corrections to the quark propagator assuming that the quark is propagating through the whole medium in order to study DIS dijet production. We take into account NEik (Next-to-Eikonal) corrections from previous results for splitting before the medium and we calculate a new contribution coming from splitting inside the medium at NEik. This time we include not only...
We apply the formalism developed earlier by Kovchegov, Pitonyak, and Sievert for constructing transverse momentum dependent parton distribution functions (TMDs) at small Bjorken-x to derive the small-x evolution equations for the Boer-Mulders TMD. We construct evolution equations which resum double logarithms $\alpha_s \textrm{ln}^2 (1/x)$, obtaining a closed set of equations in the large $N_c$ limit.
We propose a novel approach to high energy scattering that allows to interpolate between the Bjorken limit and the Regge limit of QCD. It consists in performing a partial twist expansion of cross-sections which allows to resum to all orders higher twists that contribute to gluon saturation at small x. We discuss the case of gluon mediated DIS and DVCS as a first application. In this framework...
We investigate the impact of the Balitsky-Kovchegov (BK) non-linear corrections on the initial conditions and evolution of twist components of the DIS cross-section at small x. The twist decomposition of the BK-driven DIS cross-section is performed in the Mellin space. Three main contributions are found that may be interpreted in the OPE framework as: 1) a modification of the input for DGLAP...
When parton momentum faction $x$ of hadron becomes small, an enhancement from small-$x$ logarithms shows up, and eventually, we enter into a partonic saturation region. A consistent treatment of the small-$x$ logarithms requires an all-order resummation which can be achieved with the BFKL formalism. However, a boundary to delineate the small-$x$ resummation region from saturation one is...
The upcoming Electron Ion Collider (EIC) at Brookhaven National Lab will provide novel opportunities to study the structure of light nuclei. Exclusive reactions in particular, such as Deeply Virtual Compton Scattering (DVCS) and Deeply Virtual Meson Production (DVMP), have clean final states which allow us to effectively extract Generalised Parton Distribution (GPDs). This makes them important...
One of the golden measurements at the Electron-Ion Collider (EIC) is to measure the coherent diffractive Vector Meson (VM) production off heavy nucleus. The measurement is expected to be sensitive to the non-linear gluon dynamics - saturation, and most importantly, it also provides the gluon density distribution of the nucleus. While the measurement was established in the EIC White Paper 10...
We consider the exclusive photo-production of a gamma-meson pair, working in the QCD factorisation framework. Explicitly, we consider a rho meson and a charged pion in the final state. This process has a significant advantage over meson production, since it allows us to probe chiral-odd GPDs, which are not well-known experimentally. The computation is performed at leading order and leading...
STAR’s recent observations of the Breit-Wheeler process and vacuum birefringence have demonstrated that ultra-peripheral heavy-ion collisions provide an abundant source of linearly polarized photons. We utilize such polarized photons in diffractive photo-nuclear vector meson production ($\rho^0 \rightarrow \pi^+ \pi^-$) to observe a novel quantum interference effect between non-identical...
The exclusive photoproduction reactions $\gamma p \to J/\psi(1S) p$ and $\gamma p \to \psi(2S) p$ have been studied 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 has been made in the kinematic range $30 < W < 180$ GeV, $Q^2 < 1$ GeV$^2$, $|t| < 1$ GeV$^2$, where $W$ is the photon--proton...
The exclusive photoproduction of vector mesons provides a unique opportunity to constrain the gluon distribution function within protons and nuclei. Measuring vector mesons of various masses over a wide range of rapidity and as a function of transverse momentum provides important information on the evolution of the gluon distribution within nuclei. A variety of measurements, including the...
Heavy ions accelerated at ultra-relativistic energies generate a strong electromagnetic field, leading to photon-photon and photonuclear interactions during the collision. The photoproduction of the J/$\psi$ vector meson has been widely studied in ultra-peripheral collisions with an impact parameter larger than twice the ion radius, where hadroproduction is negligible. In the last few years,...
We present a new study on helicity amplitudes and cross sections for the exclusive production of $\rho$ mesons at the EIC in high-energy factorization. In this framework the analytic expression of amplitudes takes the form of a convolution between an off-shell impact factor depicting the $\gamma^* \to \rho$ transition and a nonperturbative density, known as Unintegrated Gluon Distribution...
Coherent exclusive $J/\psi$ photoproduction in heavy-ion ultraperipheral collisions (UPCs) at the LHC, Pb+Pb $\rightarrow$ Pb+$J/\psi$+Pb, has traditionally been suggested as an efficient probe of the gluon distributions. We show, by approximating the GPDs involved in this process with collinear PDFs, that this is indeed the case in the leading order pQCD but at NLO the situation changes...
The transverse momentum transfer dependence of differential cross sections for coherent photoproduction of heavy quarkonia on nuclei is studied in the framework of the color dipole model.
In our calculations, the higher-twist nuclear shadowing related to the $\bar QQ$ Fock component of the photon includes the correlation between dipole orientation $\vec r$ and impact parameter of a...
Exclusive vector meson production is a powerful process to probe the small Bjorken-$x$ structure of protons and nuclei, as such processes are especially sensitive to gluonic structure and also provide access to the spatial distribution of small-$x$ gluons in nuclei. A powerful theoretical framework to study vector meson production at high energy, and to describe the initial condition of heavy...
Determining the multi dimensional structure of protons and nuclei at high energy is one central goal of the future Electron-Ion Collider. This fundamental information is a crucial input for models describing the initial state of heavy ion collisions. In particular the event-by-event fluctuating proton geometry should have a strong effect on the flow and multiplicity distribution in high...
The gluon radius of the proton is expected to increase at small gluon momentum fractions x, an effect which has hitherto not been considered in the dipole model framework. We investigate the energy dependence of exclusive J/ψ, φ, and ρ production by introducing three models for x dependence of the gluon thickness function. We allow the transverse width of the proton to increase as x decreases,...
We investigate photo-production of vector mesons $J/\Psi$ and $\Psi(2s)$ and their potential use for finding evidence for the presence of non-linear QCD evolution at the LHC and future collider projects. Our study is based both on unintegrated gluon densities, subject to BK (non-linear) and NLO BFKL (linear) QCD low x evolution, and the study of dipole models. While the energy dependence of...
With a unique geometry covering the forward rapidity region, the LHCb detector provides unprecedented kinematic coverage at low Bjorken-$x$ down to $x \sim 10^{-5}$ or lower. The excellent momentum resolution, vertex reconstruction and particle identification allow precision measurements down to very low hadron transverse momentum. In this contribution we present the latest studies of the...
The STAR collaboration has recently reported on the observation of a significant suppression of forward back-to-back hadron pairs produced in p-Au and p-Al collisions compared to p-p collisions [1]. The A-dependence of this suppression follows the expectations of the color glass condensate effective theory of high-energy QCD, thus giving evidence of the manifestation of gluon saturation at...
The broadening of the away side peak of the photon-hadron cross section has been predicted to be a sensitive probe of non-linear gluon dynamics in high energy pp and especially pA collisions. In this contribution I plan to show explicit results [1] based on our extensive numerical computation of the photon-hadron cross section that has been recently measured by PHENIX [2] at 200 and 510 GeV in...
I discuss C-conjugation odd color charge correlations in the
light-front wave function of the proton at moderately small $x$,
and for perturbative momenta.
The proton is approximated by an effective three-quark Fock
state to which we add the one-gluon emission correction in
light-cone perturbation theory.
The observed non-trivial dependence of the correlations on
impact parameter and on...
My talk is baesed on our work of presenting the first complete next-to-leading-order (NLO) prediction for the single inclusive jet production in pA collisions at forward rapidities within the color glass condensate (CGC) effective theory. Our prediction is fully differential over the final state physical kinematics, which allows the implementation of the full jet clustering algorithm in our...
The energy dependence of the total inclusive hadroproduction cross section of pseudo-scalar quarkonia and photoproduction cross section of vector quarkonia is computed via matching Next-to-Leading Order (NLO) Collinear-Factorisation (CF) results with resummed higher-order corrections, proportional to $\alpha_s^n ln^{n-1} (1/z)$, to the CF hard-scattering coefficient, where $z=M^2/\hat{s}$...
We present a novel study on the inclusive production of a heavy quarkonium (J/Ψ or Υ), in association with a light-flavored jet, as a test field of the high-energy QCD dynamics. The large transverse momenta at which the two final-state objects are detected permits to perform an analysis in the spirit of the variable-flavor number scheme (VFNS), in which the cross section for the...
Factorization formulas for scattering cross sections typically involve a parton-level cross section and PDFs associated with scattering hadrons. In hybrid kT-factorization, one PDF depends on the transverse momentum components of the parton besides the momentum component longitudinal to the hadron momentum. Furthermore, also in the partonic cross section these transverse components are not...
I summarize our attempts to describe HERA experimental data for the F_2 structure function using our implementation of the collinearly improved JIMWLK equation. I briefly describe the numerical framework based on Langevin reformulation of the JIMWLK equation and I illustrate the impact of the improvement on the dipole amplitude. I also comment on the influence of different functional forms of...
Based on the light-cone wave function approach, we derive the the JIMWLK evolution equations with massive quarks. This is a generalization of previous work of NLO JIMWLK with massless quarks. The introduction of quark mass not only complicates relevant integrals due to massive energy denominators (propagators), but also gives rise to some divergences that are not present for cases with...
We consider a derivation of the hierarchy of correlators of ordered exponentials directly from the Lipatov's effective action
formulated in terms of interacting ordered exponentials.
The derivation of the Balitsky equation from the hierarchy is discussed as well as
the way the sub-leading eikonal corrections to the Balitsky equation arise from the transverse field contribution and...
We discuss models with Pomeron interactions in zero transverse dimensions. We show how to construct unitary models that allow for emission of more than one parton in one step of high energy evolution, and study some properties of particle distributions in these models.
We provide the first calculation of two-gluon production at mid-rapidity in ultra-peripheral collisions in the Color Glass Condensate framework. To estimate systematic uncertainty associated with poor understanding of the wave function of the nearly real photon, we consider two diametrically different models: the dilute quark-antiquark dipole approximation and a
vector meson, in which...
We develop a numerical method to nonperturbatively study scattering and gluon emission of a quark from a colored target using a light-front Hamiltonian approach. The target is described as a classical color field, as in the color glass condensate effective theory. The Fock space of the scattering system is restricted to the |𝑞⟩+|𝑞𝑔⟩ sectors, but the time evolution of this truncated system is...
We study the production of $2\pi^+2\pi^-$ in ultra-peripheral heavy-ion collisions at RHIC and LHC energies. The recent H1 preliminary data [1] are utilized to improve the description of the poorly known $\gamma p \to 4\pi^\pm p$ process. Predictions for photon-nucleus interactions were calculated for various excited states of $\rho$ meson. We will present an agreement of theory with the...
The LHCb spectrometer has the unique capability to function as a fixed-target experiment by injecting gas into the LHC beampipe while proton or ion beams are circulating. The resulting beam+gas collisions cover an unexplored energy range that is above previous fixed-target experiments, but below the top RHIC energy for AA collisions. Here we present new results on antiproton and charm...
A phenomenological study of the isolated photon and dilepton production in association with leading hadron in $pp$ and $pA$ collisions at RHIC and LHC energies is performed. Using the color dipole approach we investigate the production cross section differential in the
transverse momentum of the photon (di-lepton pair) considering three different phenomenological models for the universal...
The differential cross section of proton-proton elastic scattering, as a function of the magnitude of the four-momentum transfer squared |t|, evolves in a consistent manner with $\sqrt{s}$ at LHC energies. The "dip" and "bump" structures change their positions in $|t|$ as a function of $\sqrt{s}$ and the slope at low values of $|t|$ and integrated elastic cross section grow with $\sqrt{s}$....
For several years there has been a strong interest in measuring collective effects in small systems such as proton-proton (pp) and proton-lead (pPb). Such measurements give new insights into the nature of QCD and the meaning of collectivity. In the recent years ALEPH, ATLAS, and ZEUS collaborations have extended these studies to electromagnetic interactions such as electron-positron (ee),...
Precise theoretical predictions of physical processes at hadron colliders are a fundamental ingredient of the LHC precision programme. In the production of a heavy quark pair in proton-proton collisions, the final-state invariant mass can be much smaller than the collider energy. Under these conditions, high-energy logarithms may spoil the perturbativity of fixed order perturbation theory....
Transverse momentum broadening (TMB) of energetic partons in QCD matter plays a central role in a variety of processes studied at colliders to probe QCD, ranging from TMD gluon distributions that encode information on the 3D structure of the proton and nuclei in electron-proton or proton-proton collisions to jet suppression in heavy ion collisions.
In this talk, based on [1,2], we study the...
