arXiv subjects

V. Guzey

Publications and source records attributed to V. Guzey.

At least 19 recordsLinked to original sources

arXiv2025

Partonic structure of nuclei from UPCs

We present an overview of theoretical and phenomenological studies on the partonic structure of nuclei and small-$x$ QCD dynamics using photon-nucleus $(\gamma A$) scattering in heavy ion ultraperipheral collisions (UPCs). Focusing on nuclear shadowing, we review implications of coherent charmonium and inclusive dijet production in Pb-Pb UPCs at the LHC and discuss the potential of inelastic $\gamma A$ scattering accompanied by forward neutrons in a zero degree calorimeter (ZDC).

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arXiv2025

Probing fluctuating protons using forward neutrons in soft and hard inelastic proton-nucleus scattering

We present a model for the distribution of the number of forward neutrons emitted in soft (minimum bias) and hard inelastic proton-nucleus ($pA$) scattering at the LHC. It is based on the Gribov-Glauber model for the distribution over the number of inelastic collisions (wounded nucleons) combined with a parametrization of cross section (color) fluctuations in the projectile proton, which depend on the parton momentum fraction $x_p$, and the assumption of independent neutron emissions. We observe that while the effect of soft color fluctuations is modest, a reduction of the interaction strength with increasing $x_p$ provides the dominant effect. It allows us to qualitatively describe the trend of the ATLAS data on the ZDC energy spectra of forward neutrons emitted in dijet production in inelastic $pA$ scattering at $\sqrt{s_{NN}}=8.16$ TeV.

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arXiv2024

Suppression of diffraction in DIS on nuclei and dynamical mechanism of leading twist nuclear shadowing

Using the leading twist approach (LTA) to nuclear shadowing (NS), we calculate the ratio of the diffractive-to-total DIS cross sections $R_{\rm diff/tot}$ for a heavy nucleus and proton and confirm that $R_{\rm diff/tot} \approx 0.5-1$ in contrast with $R_{\rm diff/tot} \approx 1.5-2$ in the dipole model. We show that the magnitude of $R_{\rm diff/tot}$ is controlled by an effective dipole cross section so that $R_{\rm diff/tot} \to 1$ in the black disk limit. We also argue that strong leading twist NS as well as the dilute nuclear density deplete nuclear enhancement of the saturation scale leading to $Q_{sA}^2(b=0)/Q_{sp}^2(b=0) \sim 1$.

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arXiv2024

Suppression of diffraction in deep-inelastic scattering on nuclei and dynamical mechanism of leading twist nuclear shadowing

Using the leading twist approach (LTA) to nuclear shadowing, we calculate the ratios of diffractive and usual parton distributions for a heavy nucleus (Pb) and the proton, $R_{A/p}=(f_{i/A}^{D(3)}/f_{i/A})/(f_{i/p}^{D(3)}/f_{i/p})$, for coherent and summed (coherent plus quasi-elastic) nuclear deep-inelastic scattering. We find that $R_{A/p} \approx 0.5-1$ for quarks as well as for the ratio of the diffractive and total cross sections $[(dσ_{\rm diff}/dM_X^2)/σ_{\rm tot}]_{eA}/[(dσ_{\rm diff}/dM_X^2)/σ_{\rm tot}]_{ep}$ and $R_{A/p} \approx 0.5-1.3$ for gluons in a broad range of $x$, including the kinematics of the Electron-Ion Collider, which reaffirms the difference from the nuclear enhancement of $R_{A/p}$ predicted in the gluon saturation framework. We demonstrate that the magnitude of $R_{A/p}$ is controlled by the cross section of the interaction of hadronic fluctuations of the virtual photon with target nucleons, which explains an enhancement of $R_{A/p}$ in the color dipole model and its suppression in LTA. We argue that the black disk limit corresponds to $R_{A/p}=1$ and $R^{\rm coh}_{A/p}=0.86$ for the summed and coherent scattering, respectively. Relying on an intuitive definition of the saturation scale, we show that the ratio of the saturation scales of a heavy nucleus and proton $Q_{sA}^2(b)/Q_{sp}^2(b) \approx 1$ at small impact parameters $b$ due to the strong leading twist nuclear shadowing and diluteness of the nuclear density.

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arXiv2024

Slicing Pomerons in ultraperipheral collisions using forward neutrons from nuclear breakup

We argue that measurements of forward neutrons from nuclear breakup in inclusive high energy photon-nucleus ($γA$) scattering provide a novel way to study small-$x$ dynamics of QCD in heavy-ion ultraperipheral collisions (UPCs). Using models for hadronic fluctuations of the real photon and neutron emission in nuclear fragmentation, we calculate the distribution over the number of evaporation neutrons produced in $γPb$ collisions at the LHC. We show that it is correlated with the number of wounded nucleons (inelastic collisions) and, hence, can constrain the mechanism of nuclear shadowing and its $x$ dependence.

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arXiv2024

Nuclear suppression of coherent $J/\psi$ photoproduction in heavy-ion UPCs and leading twist nuclear shadowing

We determine the nuclear suppression factor $S_{Pb}(x)$, where $x=M_{J/\psi}^2/W_{\gamma p}^2$ with $M_{J/\psi}$ the $J/\psi$ mass and $W_{\gamma p}$ the photon-nucleon energy, for the cross section of coherent $J/\psi$ photoproduction in heavy-ion ultraperipheral collisions (UPCs) at the Large Hadron Collider (LHC) and Relativistic Heavy Ion Collider (RHIC) by performing the $\chi^2$ fit to all available data on the cross section $d\sigma^{AA \to J/\psi AA}/dy$ as a function of the $J/\psi$ rapidity $y$ and the photoproduction cross section $\sigma^{\gamma A \to J/\psi A}(W_{\gamma p})$ as a function of $W_{\gamma p}$. We find that while the $d\sigma^{AA \to J/\psi AA}/dy$ data alone constrain $S_{Pb}(x)$ for $x \geq 10^{-3}$, the combined $d\sigma^{AA \to J/\psi AA}/dy$ and $\sigma^{\gamma A \to J/\psi A}(W_{\gamma p})$ data allow us to determine $S_{Pb}(x)$ in the wide interval $10^{-5} < x < 0.05$. In particular, the data favor $S_{Pb}(x)$, which decreases with a decrease of $x$ in the $10^{-4} < x < 0.01$ interval, and can be both decreasing or constant for $x< 10^{-4}$. Identifying $S_{Pb}(x)$ with the ratio of the gluon distributions in Pb and the proton $R_g(x,Q_0^2)=g_A(x,Q_0^2)/[A g_p(x,Q_0^2)]$, we demonstrate that the leading twist approximation (LTA) for nuclear shadowing provides a good description of all the data on $d\sigma^{AA \to J/\psi AA}/dy$ and $\sigma^{\gamma A \to J/\psi A}(W_{\gamma p})$ as well as on the experimental values for $S_{Pb}(x)$ derived from $\sigma^{\gamma A \to J/\psi A}(W_{\gamma p})$. We also show that modern nuclear PDFs reasonably reproduce $S_{Pb}(x)$ as well.

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arXiv2024

Inclusive and diffractive dijet photoproduction in ultraperipheral Pb-Pb collisions at the LHC

In this contribution, we summarize NLO pQCD predictions for inclusive and diffractive dijet photoproduction in Pb-Pb UPCs at the LHC. We demonstrate that the theory describes well the preliminary ATLAS data on the inclusive cross section, which probes nuclear parton distributions (PDFs) down to $x_A \approx 0.005$ and which can reduce current uncertainties of the small-$x$ nuclear gluon distribution by approximately a factor of 2. Employing predictions of the leading twist approach to nuclear shadowing for nuclear diffractive PDFs, we calculate the cross section of diffractive dijet photoproduction and show that its $x_γ$ dependence is sensitive to the effect of nuclear shadowing and the mechanism of QCD factorization breaking in hard diffraction. We also find that due to large leading twist nuclear shadowing and restricted kinematics, the diffractive contribution to the inclusive cross section of dijet photoproduction does not exceed $5-10$%, which helps with an ambiguous interpretation of the ATLAS data.

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arXiv2023

UPCs as probes of partonic structure -- exclusive and inclusive processes

Ultraperipheral collisions (UPCs) at the LHC and RHIC provide important new information on the partonic structure of the proton and nuclei and small-$x$ dynamics in QCD. We review phenomenological applications of the collinear factorization at leading and next-to-leading orders of perturbative QCD and the dipole model to coherent and incoherent $J/ψ$ photoproduction in Pb-Pb UPCs at the LHC emphasizing the strong leading twist gluon nuclear shadowing, the role of quark-antiquark-gluon dipoles, and a possible onset the gluon saturation in nuclei. We also discuss inclusive and diffractive dijet photoproduction in UPCs, which give complementary constraints on nuclear parton distributions and the pattern of factorization breaking in diffraction.

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arXiv2023

Exclusive heavy vector meson photoproduction on nuclei in NLO perturbative QCD

We make predictions for the cross section of coherent $J/ψ$ photoproduction in Pb-Pb and O-O ultraperipheral collisions (UPCs) at the LHC as a function of the $J/ψ$ rapidity $y$ in the framework of collinear factorization and next-to-leading order (NLO) perturbative QCD. We quantify the strong scale dependence and significant uncertainties due to nuclear PDFs and show that our approach provides a reasonable description of the LHC data on coherent $J/ψ$ photoproduction in Pb-Pb UPCs. We demonstrate that these uncertainties are reduced by approximately a factor of 10 in the scaled ratio of the O-O and Pb-Pb UPC cross sections. Our analysis indicates the dominance of the quark contribution to the UPC cross section at central rapidities, which affects the interpretation of the UPC data.

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arXiv2023

Inclusive and diffractive dijet photoproduction at the Electron-Ion Collider in NLO QCD

In the framework of collinear factorization and next-to-leading order (NLO) perturbative QCD, we make predictions for inclusive and diffractive dijet photoproduction in electron-proton and electron-nucleus scattering in the EIC kinematics. We establish kinematic ranges in the ${\bar p}_T$, ${\bar η}$, $x_A^{\rm obs}$ and $x_γ^{\rm obs}$ variables, quantify sensitivity to small-$x$ nuclear PDFs, and analyze various scenarios of factorization breaking in the case of diffractive scattering.

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arXiv2023

Numerical evaluation of the nonlinear Gribov-Levin-Ryskin-Mueller-Qiu evolution equations for nuclear parton distribution functions

We numerically study for the first time the nonlinear GLR-MQ evolution equations for nuclear parton distribution function (nPDFs) to next-to-leading order accuracy and quantify the impact of gluon recombination at small $x$. Using the nCTEQ15 nPDFs as input, we confirm the importance of the nonlinear corrections for small $x \lesssim 10^{-3}$, whose magnitude increases with a decrease of $x$ and an increase of the atomic number $A$. We find that at $x=10^{-5}$ and for heavy nuclei, after the upward evolution from $Q_0=2$ GeV to $Q=10$ GeV, the quark singlet $Ω(x,Q^2)$ and the gluon $G(x,Q^2)$ distributions become reduced by $9-15$%, respectively. The relative effect is much stronger for the downward evolution from $Q_0=10$ GeV to $Q=2$ GeV, where we find that $Ω(x,Q^2)$ is suppressed by 40%, while $G(x, Q^2)$ is enhanced by 140%. These trends propagate into the $F_2^A(x,Q^2)$ nuclear structure function and the $F_L^A(x,Q^2)$ longitudinal structure function, which after the downward evolution become reduced by 45% and enhanced by 80%, respectively. Our analysis indicates that the nonlinear effects are most pronounced in $F_L^A(x,Q^2)$ and are already quite sizable at $x \sim 10^{-3}$ for heavy nuclei. We have checked that our conclusions very weakly depend on the choice of input nPDFs. In particular, using the EPPS21 nPDFs as input, we obtain quantitatively similar results.

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arXiv2022

Photoproduction of $J/ψ$ in d+Au ultraperipheral collisions at the BNL Relativistic Heavy Ion Collider

We argue that the STAR data on $J/ψ$ photoproduction in $d+Au$ ultraperipheral collisions (UPCs) at the momentum transfer $t \neq 0$ primarily probes elastic and possibly nucleon-dissociative $J/ψ$ photoproduction on quasi-free nucleons, while being essentially insensitive to expectedly weak nuclear modifications of the gluon distribution in the deuteron. Analyzing the STAR detector capabilities for selection of UPC events, we explore the possibility that the contribution of nucleon-dissociative $J/ψ$ photoproduction is negligibly small and obtain a very good description of the $t$ dependence of the STAR total cross section.

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arXiv2022

Coherent $J/ ψ$ electroproduction on $^4$He and $^3$He at the Electron-Ion Collider: probing nuclear shadowing one nucleon at a time

While the phenomenon of gluon nuclear shadowing at small $x$ has been getting confirmation in QCD analyses of various LHC measurements involving heavy nuclei, it has not been possible so far to establish experimentally the number of target nucleons responsible for nuclear shadowing in a given process. To address this issue, we study coherent $J / ψ$ electroproduction on $^4$He and $^3$He in the kinematics of a future electron-ion collider and show that this process has the power to disentangle the contributions of the interaction with a specific number of nucleons $k$, in particular, with two nucleons at the momentum transfer $t \neq 0$. We predict a dramatic shift of the $t$-dependence of the differential cross section toward smaller values of $|t|$ due to a non-trivial correlation between $x$ and $k$. This calculation, which makes use for the first time of realistic wave functions, provides a stringent test of models of nuclear shadowing and a novel probe of the 3D imaging of gluons in light nuclei. In addition, thanks to this analysis, unique information on the real part of the corresponding scattering amplitude could be accessed.

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arXiv2022

Snowmass 2021 White Paper: Electron Ion Collider for High Energy Physics

Electron Ion Collider (EIC) is a particle accelerator facility planned for construction at Brookhaven National Laboratory on Long Island, New York by the United States Department of Energy. EIC will provide capabilities of colliding beams of polarized electrons with polarized beams of proton and light ions. EIC will be one of the largest and most sophisticated new accelerator facilities worldwide, and the only new large-scale accelerator facility planned for construction in the United States in the next few decades. The versatility, resolving power and intensity of EIC will present many new opportunities to address some of the crucial and fundamental open scientific questions in particle physics. This document provides an overview of the science case of EIC from the perspective of the high energy physics community.

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arXiv2022

Exclusive $J/ψ$ production in ultraperipheral Pb+Pb collisions to NLO pQCD

We present the first NLO pQCD study of coherent exclusive $J/ψ$ photoproduction in ultraperipheral heavy-ion collisions (UPCs) at the LHC. Taking the generalized parton distributions (GPDs) in their forward limit, as parton distribution functions (PDFs), we quantify the NLO contributions in the rapidity-differential cross section, show that the real part of the amplitude must not be neglected, study the gluon and quark contributions, chart the scale-choice and PDF uncertainties, and compare the NLO results with LHC and HERA data. We show that the scale dependence is significant but a scale choice can be found with which we reproduce the 2.76 and 5.02 TeV UPC data. In particular, we show that the process is clearly more sensitive to the nuclear quark PDFs than thought before.

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arXiv2022

UPC contribution to forward rapidity gap distribution in pPb collisions at the LHC

In this Letter, we consider strong and electromagnetic (ultraperipheral) mechanisms in proton-nucleus coherent diffraction at the CERN Large Hadron Collider. We explicitly demonstrate the dominance of the latter and explain the CMS data on the forward rapidity gap distribution in $pPb$ collisions at $\sqrt{s_{NN}}=8.16$ TeV. In particular, we provide simple estimates, which give a good, semi-quantitative description of both magnitude and shape of the $Δη^F$ distribution in the Pomeron-proton topology. We also make predictions for the proton-oxygen run.

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arXiv2022

Selected topics in diffraction with protons and nuclei: past, present, and future

We review a broad range of phenomena in diffraction in the context of hadron-hadron, hadron-nucleus collisions and deep inelastic lepton-proton/nucleus scattering focusing on the interplay between the perturbative QCD and non-perturbative models. We discuss inclusive diffraction in DIS, phenomenology of dipole models, resummation and parton saturation at low $x$, hard diffractive production of vector mesons, inelastic diffraction in hadron-hadron scattering, formalism of color fluctuations, inclusive coherent and incoherent diffraction as well as soft and hard diffraction phenomena in hadron-hadron/nucleus and photon-nucleus collisions. For each topic we review key results from the past and present experiments including HERA and the LHC. Finally, we identify the remaining open questions, which could be addressed in the continuing experiments, in particular in photon-induced reactions at the LHC and the future Electron-Ion Collider (EIC) in the US, Large Hadron electron Collider (LHeC) and Future Circular Collider (FCC) at CERN.

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arXiv2021

How large is the diffractive contribution to inclusive dijet photoproduction in UPCs at the LHC?

Using next-to-leading order (NLO) perturbative QCD, we calculate the diffractive contribution to inclusive dijet photoproduction in Pb-Pb ultraperipheral collisions (UPCs) at the LHC and find that it does not exceed $5-10$% in small-$x_A$ bins in the ATLAS kinematics at $\sqrt{s_{NN}}=5.02$ TeV. Its smallness is a result of the restricted kinematics ($p_{T1} > 20$ GeV and $x_A > 0.001$), the large nuclear suppression of nuclear diffractive parton distribution functions predicted in the leading twist model of nuclear shadowing, and additional suppression due to QCD factorization breaking in diffraction. At the same time, using looser $p_T$ cuts, e.g., $p_{T1} > 10$ GeV and $p_{T i\neq 1} > 5-7$ GeV, we find that $(dσ_{\rm diff}/dx_A)/(dσ_{\rm inc}/dx_A)$ can reach $10-20$% at $x \approx 5 \times 10^{-4}$. Also, applying our framework to proton-proton UPCs at $\sqrt{s_{NN}}=13$ TeV, we find that the ratio of the diffractive and inclusive cross sections of dijet photoproduction $(dσ_{\rm diff}/dx_p)/(dσ_{\rm inc}/dx_p)$ is as large as $10-15$% for $x_p \sim 5 \times 10^{-4}$. An account of the contribution of Pomeron-Pomeron scattering, which is not included in our analysis, should make this ratio somewhat larger.

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