arXiv subjects

Heikki Mäntysaari

Publications and source records attributed to Heikki Mäntysaari.

At least 55 records · Page 3Linked to original sources

arXiv2024

Inclusive and diffractive neutrino-nucleus scattering at high energy

We calculate the energy dependence of inclusive and diffractive neutrino-nucleus deep-inelastic scattering cross sections within the dipole picture, focusing on the ultra-high-energy regime. We predict an up to $\sim 10\%$ nuclear suppression in the inclusive neutrino-Oxygen scattering originating from the non-linear QCD dynamics in the small-$x$ Balitsky-Kovchegov evolution. Diffraction is found to be a small $1\dots 4\%$ contribution to the total cross section across a wide range of neutrino energies relevant for current and near-future experiments. The diffractive cross section is calculated separately for the coherent and incoherent channels that are found to be of equal importance. Additionally, we include the dominant contribution from the $|q\bar q g\rangle$ Fock state of the $W^\pm$ and $Z$ bosons in the high-$Q^2$ limit, along with the lowest-order $|q\bar q\rangle$ contribution. The $|q\bar{q}g\rangle$ contribution is found to be numerically significant, reaching up to 40\% of the diffractive cross section.

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arXiv2024

Inclusive $\mathrm{J}/ψ$ production in forward proton-proton and proton-lead collisions at high energy

We calculate the cross section for forward $\mathrm{J}/ψ$ production in proton-proton and minimum bias proton-lead collisions using the Color Glass Condensate (CGC) and Non-Relativistic QCD (NRQCD) formalism consistently with Deep Inelastic Scattering data. The cross section for color singlet states is sensitive to a 4-point correlator of Wilson lines for which we describe in the Gaussian approximation in the large-$N_c$ limit. Furthermore, we quantify the importance of finite-$N_c$ corrections to have a small $\sim 12\%$ effect. In contrast with the generic NRQCD expectation, we show that the color singlet contribution is only $15\%$ to the total cross section. We also compare our predictions for $\mathrm{J}/ψ$ production as well as for the nuclear modification ratio $R_{pPb}$ to LHCb and ALICE data. We find a good agreement at forward rapidities, except at low transverse momenta where the cross sections are overestimated.

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arXiv2024

Evolution of structure functions at NLO without PDFs

We formulate the Dokshitzer-Gribov-Lipatov-Altarelli-Parisi (DGLAP) evolution of the Deep Inelastic Scattering (DIS) structure functions $F_2$ and $F_{\rm L}$ at next to leading order in $α_s$ (NLO) directly in terms of the structure functions rather than parton distributions (PDFs). We call this the physical basis approach. In practice, we first express the NLO quark singlet and gluon PDFs in terms of the structure functions $F_2$ and $F_{\rm L}$ in momentum space. Employing these expressions in the DGLAP evolution, we arrive at the evolution equations for $F_2$ and $F_{\rm L}$ in the physical basis. We demonstrate how one is free from defining a factorization scale and scheme when using the physical basis evolution equations. We also discuss the process of applying the NLO physical basis to global analysis of LHC cross sections.

hep-ph↗

arXiv2024

Bayesian approach to determine the initial condition for the Balitsky-Kovchegov equation

We present posterior distributions of parameters that characterize the nonperturbative initial input for the Balitsky-Kovchegov evolution equation. The BK equation evolves an initial dipole-target scattering amplitude at moderate $x_{\mathrm{Bj}}$ values toward smaller values. We use Bayesian inference to constrain the model parameters against the precise combined reduced cross section data from HERA, and obtain probability distributions for the free parameters. Our results show the data's preference for the anomalous dimension to be $γ\sim 1$. The distributions provide a rigorous method for propagating uncertainties of the BK initial condition for other CGC calculations. We demonstrate this for inclusive quark production in proton-proton collisions and nuclear modification factor for the total deep inelastic scattering cross section to be measured at the EIC.

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arXiv2024

Probing gluon saturation and nuclear structure in photon-nucleus collisions

We calculate exclusive vector meson photoproduction within the Color Glass Condensate framework in high-energy photon-nucleus scattering probed experimentally in ultra peripheral heavy ion collisions at RHIC and at the LHC. When the free parameters are constrained by the $γ+p$ data from HERA, we predict significant nuclear suppression for both the coherent and incoherent photoproduction cross section in the TeV range. Our results indicate that the LHC data prefers even stronger saturation effects at the highest collision energies. Furthermore, we demonstrate how the linear polarization of photons in ulra peripheral collisions generates azimuthal modulations in the decay products of the exclusively produced vector meson. We show how these measurements can probe details of the nuclear geometry, specifically the deformed structure of the uranium nuclei.

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arXiv2024

Polarized Dipole Scattering Amplitudes meet the Valence Quark Model

The recently revised small-$x$ helicity evolution, resumming the double-logarithmic factor, $α_s\ln^2(1/x)$, allows for the study of helicity distributions of quarks and gluons at small Bjorken $x$, corresponding to high center-of-mass energy. In this work, we calculate the moderate-$x$ initial conditions in the regime, $α_s \ln^2(1/x)\sim 1$, for the small-$x$ helicity evolution using a light-front valence quark model of the proton, which provides additional physical information about the target. The perturbative emission and absorption of a gluon by the valence quarks are also included. The results, given in Eqs. (35), provide a new set of initial conditions with a significantly reduced number of free parameters than conventional models. Consequently, the predictive power of small-$x$ helicity evolution is expected to improve once the initial conditions from this work are incorporated.

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arXiv2024

Gluon imaging using azimuthal correlations in diffractive scattering at the Electron-Ion Collider

We study coherent diffractive photon and vector meson production in electron-proton and electron-nucleus collisions within the Color Glass Condensate effective field theory. We show that electron-photon and electron-vector meson azimuthal angle correlations are sensitive to non-trivial spatial correlations in the gluon distribution of the target, and perform explicit calculations using spatially dependent McLerran-Venugopalan initial color charge configurations coupled to the numerical solution of small $x$ JIMWLK evolution equations. We compute the cross-section differentially in $Q^2$ and $|t|$ and find sizeable anisotropies in the electron-photon and electron-$\mathrm{J}/ψ$ azimuthal correlations ($v_{1,2} \approx 2 - 10 \%$) in electron-proton collisions for the kinematics of the future Electron-Ion Collider. In electron-gold collisions these modulations are found to be significantly smaller ($v_{1,2} <0.1 \%$). We also compute incoherent diffractive production where we find that the azimuthal correlations are sensitive to fluctuations of the gluon distribution in the target.

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arXiv2024

Cubic color charge correlator in a proton made of three quarks and a gluon

The three point correlation function of color charge densities is evaluated explicitly in light cone gauge for a proton on the light cone. This includes both $C$-conjugation even and odd contributions. We account for perturbative corrections to the three-quark light cone wave function due to the emission of an internal gluon which is not required to be soft. We verify the Ward identity as well as the cancellation of UV divergences in the sum of all diagrams so that the correlator is independent of the renormalization scale. It does, however, exhibit the well known soft and collinear singularities. The expressions derived here provide the $C$-odd contribution to the initial conditions for high-energy evolution of the dipole scattering amplitude to small $x$. Finally, we also present a numerical model estimate of the impact parameter dependence of quantum color charge three-point correlations in the proton at moderately small $x$.

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arXiv2024

Vector meson production in ultraperipheral heavy ion collisions

We review model calculations of exclusive vector meson production in ultraperipheral heavy ion collisions. We highlight differences and similarities between different dipole models and leading twist shadowing calculations. Recent color glass condensate calculations are presented with focus on effects from nuclear structure and azimuthal anisotropies driven by interference effects.

nucl-th↗

arXiv2024

Energy dependent nuclear suppression from gluon saturation in exclusive vector meson production

We calculate the exclusive $\mathrm{J}/ψ$ photoproduction cross section at high energies from the Color Glass Condensate approach. The results are compared to the center-of-mass energy dependent $γ+A\to\mathrm{J}/ψ+A$ cross sections extracted from measurements in ultra peripheral heavy ion collisions at RHIC and LHC. We predict strong saturation-driven nuclear suppression at high energies, while LHC data prefers even stronger suppression. We explore the effect of nucleon shape fluctuations on the nuclear suppression in the coherent and incoherent cross sections, and show that the most recent measurement of the $|t|$-differential incoherent $\mathrm{J}/ψ$ cross section prefers large event-by-event fluctuations of the nucleon substructure in heavy nuclei, comparable to that found for a free proton.

hep-ph↗

arXiv2024

Inferring the initial condition for the Balitsky-Kovchegov equation

We apply Bayesian inference to determine the posterior likelihood distribution for the parameters describing the initial condition of the small-$x$ Balitsky-Kovchegov evolution equation at leading logarithmic accuracy. The HERA structure function data is found to constrain most of the model parameters well. In particular, we find that the HERA data prefers an anomalous dimension $γ\approx 1$ unlike in previous fits where $γ>1$ which led to e.g. the unintegrated gluon distribution and the quark-target cross sections not being positive definite. The determined posterior distribution can be used to propagate the uncertainties in the non-perturbative initial condition when calculating any other observable in the Color Glass Condensate framework. We demonstrate this explicitly for the inclusive quark production cross section in proton-proton collisions and by calculating predictions for the nuclear modification factor for the $F_2$ structure function in the EIC and LHeC/FCC-he kinematics.

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arXiv2024

Complete Next-to-Leading Order Calculation of Single Inclusive $π^0$ Production in Forward Proton-Nucleus Collisions

We present the first fully consistent calculation of inclusive $π^0$ production at forward rapidities at next-to-leading order (NLO) accuracy in proton-lead collisions at $\sqrt{s}=8.16$ TeV within the Color Glass Condensate approach. The center-of-mass energy dependence is determined by the Balitsky-Kovchegov equation with the initial condition constrained at NLO accuracy by the proton structure function measurements. We find that the LHCb data further constrain this non-perturbative input, and that both the NLO corrections to the evolution equation and to the impact factor have significant effects on the nuclear modification factor $R_{p\mathrm{Pb}}$. The complete NLO calculation is shown to be in qualitative agreement with the LHCb data, and the predictions are found to be sensitive to the details of the applied deep inelastic scattering (DIS) fit. These results demonstrate the need to perform global analyses of DIS and LHC data in order to probe gluon saturation phenomena at precision level at very small momentum fraction $x$.

hep-ph↗

arXiv2024

Diffractive deep inelastic scattering at NLO in the dipole picture

We compute the transverse and longitudinal diffractive structure functions to full next-to-leading order accuracy in the dipole picture of deep inelastic scattering. Our calculation uses the standard light-cone perturbation theory method for the partonic content of the virtual photon, together with the Color Glass Condensate description of the target color field. Our result includes as a subset the $q\bar{q}g$ contribution calculated earlier. We show that there is a rapidity divergence that can be factorized into the BK/JIMWLK evolution of the target Wilson lines, and that all other divergences cancel.

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arXiv2023

Probing nuclear structure at the Electron-Ion Collider and in ultra-peripheral nuclear collisions

Within the Color Glass Condensate framework, we demonstrate that exclusive vector meson production at high energy is sensitive to the geometric deformation of the target nucleus and subnucleon scale fluctuations. Deformation of the nucleus enhances the incoherent cross section in the small $|t|$ region. Subnucleon scale fluctuations increase the incoherent cross section in the large $|t|$ region. In ultra-peripheral collisions (UPCs), larger deformation leads to a wider distribution of the minimal impact parameter $B_{min}$ required to produce a UPC. This, together with larger incoherent cross sections for larger deformation, results in smaller extracted radii. Our results demonstrate great potential for future studies of nuclear structure in UPCs and electron-ion collisions.

nucl-th↗

arXiv2023

Theoretical developments on the initial state in relativistic particle collisions

We discuss recent progress towards developing accurate initial state descriptions for heavy ion collisions focusing on weak coupling based approaches, that enable one to constrain the high-energy structure of nuclei from deep inelastic scattering or proton-nucleus collisions. We review recent developments to determine the event-by-event fluctuating nuclear geometry, to describe gluon saturation phenomena at next-to-leading order accuracy, and to include longitudinal dynamics to the initial state descriptions.

nucl-th↗

arXiv2023

Effects of nuclear structure and quantum interference on diffractive vector meson production in ultra-peripheral nuclear collisions

We study diffractive vector meson production in ultra-peripheral collisions (UPCs) of heavy nuclei, utilizing a theoretical framework based on the Color Glass Condensate (CGC) formalism. We focus on Au+Au, U+U, Ru+Ru, Zr+Zr, and Pb+Pb collisions, examining the transverse momentum dependence of vector meson production cross-sections and ${\rm cos(2ΔΦ)}$ asymmetries in the decay product distributions to explore the role of nuclear geometry. The angular modulation is due to the linear polarization of the incoming photons and quantum interference effects. We extract nuclear radii and find them to be consistent with experimental data from the STAR collaboration. The amplitudes of the ${\rm cos(2ΔΦ)}$ modulation in the cross-section and the extracted radii depend on the nuclear geometry. This dependence is dominated by the geometry-dependent variation of the minimum impact parameter required for ultra-peripheral collisions.

nucl-th↗

arXiv2023

Coherently diffractive dissociation in electron-hadron collisions: from HERA to the future EIC

We present numerical results on diffractive dissociation with large invariant mass diffractive final states in the scattering of an electron off a hadron. The diffractive large-mass resummation is performed using the nonlinear Kovchegov-Levin equation, taking into account running coupling corrections. For the scattering off the proton, a (modified) McLerran-Venugopalan amplitude is used as the initial condition for the nonlinear evolution, with free parameters being constrained by the HERA inclusive data. The results show a reasonable description of the HERA diffractive structure function data at moderately large diffractive mass when the impact parameter profile is constrained by the low-mass diffractive cross section data. The calculation is extended to nuclear scattering, where the initial condition is generalized from the proton case employing the optical Glauber model. The nonlinear large-mass resummation predicts a strong nuclear modification in diffractive scattering off a nuclear target in kinematics accessible at the future Electron-Ion collider.

hep-ph↗

arXiv2023

Rapidity gap distribution of diffractive small-$x_{I\hspace{-0.3em}P}$ events at HERA and at the EIC

We use the Kovchegov-Levin equation to resum contributions of large invariant mass diffractive final states to diffractive structure functions in the dipole picture of deep inelastic scattering. For protons we use a (modified) McLerran-Venugopalan model as the initial condition for the evolution, with free parameters obtained from fits to the HERA inclusive data. We obtain an adequate agreement to the HERA diffractive data in the moderately high-mass regimes when the proton density profile is fitted to the diffractive structure function data in the low-mass region. The HERA data is found to prefer a proton shape that is steeper than a Gaussian. The initial conditions are generalized to the nuclear case using the optical Glauber model. Strong nuclear modification effects are predicted in diffractive scattering off a nuclear target in kinematics accessible at the future Electron-Ion collider. In particular, the Kovchegov-Levin evolution has a strong effect on the Q 2 -dependence of the diffractive cross section.

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