arXiv subjects

Jani Penttala

Publications and source records attributed to Jani Penttala.

30 records · Page 2Linked to original sources

arXiv2025

Transverse Energy--Energy Correlators at Small $x$ for Photon--Hadron Production

We study the transverse energy--energy correlator (TEEC) observable in photon--hadron and photon--jet production in p+p and p+A collisions at small $x$. We derive the relevant expressions in the high-energy limit of the scattering where the dipole picture is applicable and show how the dependence on the fragmentation function of the hadron cancels due to the momentum-sum rule. The nonperturbative scattering with the target nucleus is expressed in terms of the dipole amplitude, which also describes nonlinear gluon saturation effects. The TEEC observable is computed in the RHIC and LHC kinematics, and we show that it can be sensitive to the dipole amplitude, making it a potentially good observable for studying saturation effects.

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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

Determination of the strong coupling constant and the Collins-Soper kernel from the energy-energy correlator in $e^+e^-$ collisions

We have conducted the first simultaneous global fit of the strong coupling constant $α_s$ and the Collins-Soper (CS) kernel using the energy-energy correlators (EEC) of $e^{+} e^{-}$ collisions in the back-to-back limit. This analysis, based on the transverse-momentum-dependent (TMD) factorization of EEC at next-to-next-to-next-to-leading logarithmic ($\rm{N}^{3} \rm{LL}$) accuracy, yields $α_s$ consistent with the world average. We have tested two different parametrizations for the non-perturbative CS kernel and found both to align with results obtained from lattice QCD and fits on semi-inclusive deep inelastic scattering and Drell-Yan process.

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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

Transverse Energy-Energy Correlators in the Color-Glass Condensate at the Electron-Ion Collider

We investigate the transverse energy-energy correlators (TEEC) in the small-$x$ regime at the upcoming Electron-Ion Collider (EIC). Focusing on the back-to-back production of electron-hadron pairs in both $ep$ and $eA$ collisions, we establish a factorization theorem given in terms of the hard function, quark distributions, soft functions, and TEEC jet functions, where the gluon saturation effect is incorporated. Numerical results for TEEC in both $ep$ and $eA$ collisions are presented, together with the nuclear modification factor $R_A$. Our analysis reveals that TEEC observables in deep inelastic scattering provide a valuable approach for probing gluon saturation phenomena. Our findings underscore the significance of measuring TEEC at the EIC, emphasizing its efficacy in advancing our understanding of gluon saturation and nuclear modifications in high-energy collisions.

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arXiv2023

Diffractive Processes at Next-to-Leading Order in the Dipole Picture

In this thesis, we calculate diffractive processes at next-to-leading order (NLO) in the high-energy limit, with an emphasis on exclusive vector meson production and inclusive diffraction in deep inelastic scattering (DIS). Calculations in the high-energy limit can be done using the dipole picture, the basics of which are briefly reviewed. This includes using the color-glass condensate effective field theory to describe the nonperturbative dipole-target scattering amplitude which appears in practically all calculations in the dipole picture. The universality of the dipole-target scattering amplitude at NLO is shown numerically, in the sense that the same dipole-target scattering amplitude can be used to describe the data in both massless and massive quark production in inclusive DIS, and also in diffractive processes where exclusive vector meson production is considered. The analytical NLO calculations of exclusive vector meson production and inclusive diffraction in DIS are also explained. Exclusive vector meson production is calculated in the nonrelativistic limit for heavy mesons and the limit of large photon virtuality for light mesons. Also, the importance of including relativistic corrections to the heavy vector meson wave function in exclusive vector meson production is considered. For inclusive diffraction in DIS, we focus on the NLO corrections to the final state and show how the divergences cancel.

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arXiv2023

Proton structure functions in the dipole picture at next-to-leading order

We predict heavy quark production cross sections in Deep Inelastic Scattering at high energy by applying the CGC effective theory. We demonstrate that when the calculation is performed consistently at next-to-leading order accuracy with massive quarks it becomes possible, for the first time in the dipole picture with perturbatively calculated center-of-mass energy evolution, to simultaneously describe both light and heavy quark production data at small $x$. We furthermore show how the heavy quark cross section data provides additional strong constraints on the extracted non-perturbative initial condition for the small-$x$ evolution equations.

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arXiv2023

Proton structure functions at NLO in the dipole picture with massive quarks

We predict heavy quark production cross sections in Deep Inelastic Scattering at high energy by applying the Color Glass Condensate effective theory. We demonstrate that when the calculation is performed consistently at next-to-leading order accuracy with massive quarks it becomes possible, for the first time in the dipole picture with perturbatively calculated center-of-mass energy evolution, to simultaneously describe both light and heavy quark production data at small $x_\mathrm{Bj}$. We furthermore show how the heavy quark cross section data provides additional strong constraints on the extracted non-perturbative initial condition for the small-$x_\mathrm{Bj}$ evolution equations.

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arXiv2022

Exclusive production of light vector mesons at next-to-leading order in the dipole picture

Exclusive production of light vector mesons in deep inelastic scattering is calculated at next-to-leading order in the dipole picture in the limit of high photon virtuality. The resulting expression is free of any divergences and suitable for numerical evaluations. The higher-order corrections are found to be numerically important, but they can be mostly captured by the nonperturbative fit parameters describing the initial condition for the small-$x$ evolution of the dipole scattering amplitude. The vector meson production cross section is shown to depend only weakly on the meson distribution amplitude and the factorization scale. We also present phenomenological comparisons of our result to the existing exclusive $ϕ$ and $ρ$ production data from HERA and find an excellent agreement at high virtualities.

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arXiv2022

Complete calculation of exclusive heavy vector meson production at next-to-leading order in the dipole picture

Exclusive production of transversely polarized heavy vector mesons in deep inelastic scattering at high energy is calculated at next-to-leading order accuracy in the Color Glass Condensate framework. In addition to the first QCD correction proportional to the strong coupling constant $α_s$, we systematically also include the first relativistic correction proportional to the heavy quark velocity squared $v^2$. When combined with our previously published results for longitudinal vector meson production at next-to-leading order accuracy, these results make phenomenological calculations of heavy vector meson production possible at the order $\mathcal{O}(α_s v^0, α_s^0 v^2)$. When applied to $\mathrm{J}/ψ$ and $Υ$ production at HERA and at the LHC, a good agreement between the next-to-leading order calculations and experimental data is found. Additionally, we demonstrate that vector meson production can provide additional constraints compared to structure function analyses when the nonperturbative initial condition for the Balitsky-Kovchegov evolution equation is extracted.

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arXiv2022

Exclusive heavy vector meson production at next-to-leading order in the dipole picture

We calculate exclusive production of a longitudinally polarized heavy vector meson at next-to-leading order in the dipole picture. The large quark mass allows us to separately include both the first QCD correction proportional to the coupling constant $α_s$, and the first relativistic correction suppressed by the quark velocity $v^2$. Both of these corrections are found to be numerically important in $\mathrm{J}/ψ$ production. The results obtained are directly suitable for phenomenological calculations. We also demonstrate how vector meson production provides complementary information to structure function analyses when one extracts the initial condition for the energy evolution of the proton small-$x$ structure.

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arXiv2021

Higher-order corrections to exclusive heavy vector meson production

We present results for higher-order corrections to exclusive $\mathrm{J}/ψ$ production. This includes the first relativistic correction of order $v^2$ in quark velocity, and next-to-leading order corrections in $α_s$ for longitudinally polarized production. The relativistic corrections are found to be important for a good description of the HERA data, especially at small values of the photon virtuality. The next-to-leading order results for longitudinal production are evaluated numerically. We also demonstrate how the vector meson production provides complementary information to the structure functions for extracting the initial condition for the small-$x$ evolution of the dipole-proton scattering amplitude.

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