arXiv subjects

Heikki Mäntysaari

Publications and source records attributed to Heikki Mäntysaari.

At least 37 records · Page 2Linked to original sources

arXiv2025

Nuclear Suppression in Diffractive Vector Meson Production within the Color Glass Condensate Framework

We extend a recent global Bayesian analysis of diffractive $\mathrm{J}/ψ$ production in $γ+p$ and $γ+\mathrm{Pb}$ collisions within the color glass condensate (CGC) framework to investigate potential modifications of the nucleon structure inside nuclei. To this end, we perform fits that allow the effective nucleon structure parameters in Pb nuclei to differ from those of free protons. This approach directly addresses the question of whether the proton's spatial gluon distribution at intermediate to large $x$ is modified in the nuclear environment. We compare results obtained with shared and independent nucleon structure parameters and assess the impact on the simultaneous description of $γ+p$ data from HERA and the LHC, as well as $γ+\mathrm{Pb}$ data from the LHC. Our findings show that there is no hint of difference in the nucleon structure beyond those already present in the CGC when embedding nucleons inside a nuclear environment.

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arXiv2025

Exclusive $\mathrm{J}/ψ$ production off a dilute proton within a refined hotspot description

We revisit the calculation of exclusive $\mathrm{J}/ψ$ production in electron-proton scattering within the QCD dipole model, employing a refined description of the proton in terms of gluonic hot spots in the dilute regime. In contrast to earlier studies, we incorporate key missing elements: the event-by-event fluctuations in both the number of hot spots and their local saturation scales, as well as the first relativistic corrections to the $\mathrm{J}/ψ$ wave function. We perform a Bayesian analysis to constrain the model parameters using HERA data. These enhancements significantly improve the agreement with HERA data. Saturation scale fluctuations are found to be more important than fluctuations in the number of hot spots. Including the first relativistic correction is found to be important, especially in order to describe the observed power-law behavior in the incoherent cross section at large $t$.

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arXiv2025

Next-to-leading order evolution of structure functions without PDFs

We formulate and numerically solve the Dokshitzer-Gribov-Lipatov-Altarelli-Parisi~(DGLAP) evolution equations at next-to-leading order in perturbation theory directly for a basis of 6 physical, observable structure functions in deeply inelastic scattering. By expressing the evolution in the physical basis one evades the factorization scale and scheme dependence. Working in terms of observable quantities, rather than parametrizing and fitting unobservable parton distribution functions (PDFs), provides an unambiguous way to confront predictions of perturbative Quantum Chromodynamics with experimental measurements. We compare numerical results for the DGLAP evolution for structure functions in the physical basis to the conventional evolution with PDFs.

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arXiv2025

Nuclear suppression in diffractive vector meson production within the color glass condensate framework

We perform a global Bayesian analysis of diffractive $\mathrm{J}/ψ$ production in $γ+p$ and $γ+\mathrm{Pb}$ collisions within a Color Glass Condensate based framework. Using data from HERA and the LHC, we find that a simultaneous description of $γ+p$ and $γ+\mathrm{Pb}$ observables is challenging. Introducing a global $K$-factor to account for theoretical uncertainties improves the agreement with data and enhances the framework's predictive power. We present predictions for integrated $\mathrm{J}/ψ$ cross sections at different photon-nucleus energies and study their $A$-dependence relative to a no-saturation baseline, quantifying nuclear suppression and providing insights into the onset of saturation effects.

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arXiv2025

Perturbative high-energy evolution in the IP-Glasma initial state

We include the perturbative JIMWLK energy evolution into the IP-Glasma initial state description used to simulate the early-time dynamics in heavy ion collisions. By numerically solving the JIMWLK equation on an event-by-event basis, we obtain the energy (Bjorken-$x$) dependent structure of the colliding nuclei. Combining the initial state with hydrodynamic simulations, this enables us to predict how observables evolve when moving from RHIC to LHC energies.

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arXiv2025

Initial condition for the Balitsky-Kovchegov equation at next-to-leading order

We determine the initial condition of the Balitsky-Kovchegov evolution equation at next-to-leading order (NLO) accuracy using HERA deep inelastic scattering data. Posterior distributions characterizing the initial condition are extracted using Bayesian inference. The total cross section and charm quark production data from HERA are found to provide stringent constraints on the posterior. These distributions quantify the uncertainty in the initial condition and serve as necessary input for propagating uncertainties to all NLO calculations within the Color Glass Condensate framework.

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arXiv2025

Inclusive $\mathrm{D}^0$ photoproduction in ultraperipheral collisions

We compute the differential cross section for inclusive $\mathrm{D}^0$ production in ultraperipheral collisions within the Color Glass Condensate framework. Our predictions are found to be in relatively good agreement with the CMS data at small transverse momentum, which is the region of validity of our approach. Furthermore, we quantify saturation effects by a nuclear modification ratio $R_{pA}$ for $\mathrm{D}^0$ photoproduction and examine both analytically and numerically the collinear factorization limit of the $\mathrm{D}^0$ differential photoproduction cross section.

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arXiv2025

The impact of glasma on heavy flavor azimuthal correlations and spectra

We study the phenomenological impact of the pre-equilibrium glasma initial stage of heavy-ion collisions on heavy quark azimuthal correlations and spectra. Using our numerical solver, we simulate the transport of heavy quark test particles in an SU(3) glasma background field. The glasma field equations are formulated using classical real-time lattice gauge theory, and the heavy quark dynamics are described by classical transport equations numerically solved using the colored particle-in-cell method. For the first time, the effect of the glasma stage on the azimuthal correlations of $c\overline{c}$ and $b\overline{b}$ pairs is studied. The resulting azimuthal width $σ_{Δϕ}$ exhibits a large and quick decorrelation due to the strong glasma fields. Further, we evaluate how the $p_T$-broadening in the glasma affects heavy quark $p_T$-spectra, which are initialized according to the Fixed-Order Next-to-Leading Logarithm (FONLL) heavy quark production calculation. The nuclear modification factor $R_{AA}$ is extracted for $c$ and $b$ quarks in the glasma and additional nuclear PDF effects accounting for gluon shadowing are included.

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arXiv2025

Heavy flavor angular correlations as a direct probe of the glasma

We use classical equations of motion for heavy quarks to show that the pre-equilibrium glasma phase of a heavy ion collision has an extremely strong effect on heavy quark angular correlations. At the same time, the effect on the single inclusive spectrum is much more moderate. This suggests that $D\overline{D}$ meson angular correlations in future LHC measurements could provide direct experimental access to the physics of the pre-equilibrium stage.

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arXiv2025

The impact of glasma on heavy quark spectra and correlations

We investigate the effect of the glasma classical color fields, produced in the very early stage of heavy-ion collisions, on the transport of heavy quarks. The glasma fields evolve according to the classical Yang-Mills equations, while the dynamics of heavy quarks is described by Wong's equations. We numerically solve these equations and compute the transport coefficient $κ$, which is anisotropic and initially very large. Further, we extract observables sensitive to the initial glasma stage. The heavy quark nuclear modification factor $R_{AA}$ is affected by the glasma but the effect is moderate compared to the nPDF contribution. Our main finding is that the glasma has a large impact on the azimuthal correlation between $Q\overline{Q}$ pairs, initially produced back-to-back.

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arXiv2025

Finite-size effects on small-$x$ evolution and saturation in proton and nuclear targets

Within the Color Glass Condensate effective field theory, we assess the importance of including a finite size for the target on observables sensitive to small-$x$ evolution. To this end, we study the Balitsky-Kovchegov (BK) equation with impact-parameter dependence in the initial condition. We demonstrate that neglecting the dependence on the impact parameter can result in overestimated saturation effects for protons, while it has little effect for heavy nuclei at the energies available at current experiments. When fixing the nonperturbative parameters to the energy dependence of the exclusive $J/ψ$ photoproduction cross section with proton targets, predictions for lead targets are not sensitive to the applied running-coupling prescription, the scheme chosen to resum large transverse logarithms in the BK equation, or the infrared regulator in the evolution.

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arXiv2025

Nucleon Energy Correlators for the Odderon

We investigate the T-odd nucleon energy correlator (NEC) at small $x$ and establish its connection with the spin-dependent odderon. Probing the T-odd NEC involves measuring a single transverse spin asymmetry (SSA) for the energy pattern in the target fragmentation region in deep inelastic scattering. We find that while the inclusive energy pattern results in a vanishing SSA, a nonzero SSA emerges when restricting the measurement to charged hadrons, which are directly measured in tracking detectors. To describe this effect, we introduce the track-based NEC and evaluate its small-$x$ limit from fracture functions using the energy sum rule. The resulting SSA exhibits an opposite sign between positively and negatively charged hadrons, providing a clear experimental signature of the odderon. Furthermore, by incorporating charge weighting into the NEC, we construct a C-odd tag in the final state, eliminating potential contamination from C-even gluonic contributions. Our results demonstrate that these track-based energy-pattern observables offer a clean and sensitive probe for unveiling odderon dynamics at the future electron-ion collider.

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arXiv2025

Stronger $C$-odd color charge correlations in the proton at higher energy

The non-forward eikonal scattering matrix for dipole-proton scattering at high energy obtains an imaginary part due to a $C$-odd three gluon exchange. We present numerical estimates for the perturbative Odderon amplitude as a function of dipole size, impact parameter, their relative azimuthal angle, and light-cone momentum cutoff $x$. The proton is approximated as $ψ_\mathrm{qqq}|qqq\rangle + ψ_\mathrm{qqqg}|qqqg\rangle$, where $ψ_\mathrm{qqq}$ is a non-perturbative three quark model wave function while the gluon emission is computed in light-cone perturbation theory. We find that the Odderon amplitude increases as $x$ decreases from 0.1 to 0.01. At yet lower $x$, the reversal of this energy dependence would reflect the onset of universal small-$x$ renormalization group evolution.

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arXiv2025

Collision energy dependence in heavy ion collisions from nonlinear QCD evolution

We explore the effects of including the energy dependence determined from evolution equations within the color glass condensate framework on observables in ultra-relativistic heavy-ion collisions. This amounts to integrating the JIMWLK evolution equations into the IP-Glasma model, which is then coupled to viscous relativistic hydrodynamics. This methodology allows for a systematic representation of nuclei at specific Bjorken-$x$ values, which are probed at different center-of-mass energies of the collision and rapidities of final state particles. Comparing to the conventional IP-Glasma model, we find significant effects on multiplicity distributions and particle spectra, especially in smaller collision systems at the highest center of mass energies. Our results highlight the importance of incorporating nonlinear QCD evolution in the description of heavy ion collisions at varying center of mass energies, as the precise extraction of transport coefficients will be affected. This work establishes a robust framework for understanding the quark gluon plasma and nuclear structure at high energy, integrating small-$x$ physics into the initial conditions of heavy-ion collisions.

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arXiv2025

Evolution of structure functions in momentum space

We formulate the momentum-space Dokshitzer-Gribov-Lipatov-Altarelli-Parisi (DGLAP) evolution equations for structure functions measurable in deeply inelastic scattering. We construct a six-dimensional basis of structure functions that allows for a full three flavor structure and thereby provides a way to calculate perturbative predictions for physical cross sections directly without unobservable parton distribution functions (PDFs) and without the associated scheme dependence. We derive the DGLAP equations to first non-zero order in strong coupling $α_s$, but the approach can be pursued to arbitrary order in perturbation theory. We also numerically check our equations against the conventional PDF formulation.

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arXiv2025

Relativistic corrections to the vector meson light front wave function

We compute a light front wave function for heavy vector mesons based on long distance matrix elements constrained by decay width analyses in the Non Relativistic QCD framework. Our approach provides a systematic expansion of the wave function in quark velocity. The first relativistic correction included in our calculation is found to be significant, and crucial for a good description of the HERA exclusive $\mathrm{J}/ψ$ production data. When looking at cross section ratios between nuclear and proton targets, the wave function dependence does not cancel out exactly. In particular the fully non-relativistic limit is found not to be a reliable approximation even in this ratio. The important role of the Melosh rotation to express the rest frame wave function on the light front is illustrated.

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arXiv2024

Energy dependence of the deformed nuclear structure at small-$x$

We quantify the effect of high-energy JIMWLK evolution on the deformed structure or heavy (Uranium) and intermediate (Ruthenium) nuclei. The soft gluon emissions in the high-energy evolution are found to drive the initially deformed nuclei towards a more spherical shape, although the evolution is slow ,especially for the longest distance-scale quadrupole deformation. We confirm a linear relationship between the squared eccentricity $\varepsilon_n^2$ and the deformation parameter $β_n^2$ in central collisions across the energy range covered by the RHIC and LHC measurements. The applied JIMWLK evolution is found to leave visible signatures in the eccentricity evolution that can be observed if the same nuclei can be collided at RHIC and at the LHC, or in rapidity-dependent flow measurements. Our results demonstrate the importance of including the Bjorken-$x$ dependent nuclear geometry when comparing simulations of the Quark Gluon Plasma evolution with precise flow measurements at high collision energies.

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arXiv2024

Probing Nuclear Structure of Heavy Ions at the Large Hadron Collider

We perform high-statistics simulations to study the impacts of nuclear structure on the ratios of anisotropic flow observables in $^{208}$Pb+$^{208}$Pb and $^{129}$Xe+$^{129}$Xe collisions at the Large Hadron Collider. Even with $40\%$ difference in atomic numbers between $^{208}$Pb and $^{129}$Xe nuclei, the ratios of anisotropic flow in the same centrality class between the two collision systems are strongly affected by the nuclear structure inputs in the initial state. The ratios of $v_2\{4\}/v_2\{2\}$ in these collisions are sensitive to the nuclear skin thickness of the colliding nuclei, providing indirect constraints on the nuclei's neutron skin. Our model predictions serve as a benchmark to compare with experimental measurements.

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