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Tolga Altinoluk

Publications and source records attributed to Tolga Altinoluk.

At least 37 records · Page 2Linked to original sources
arXiv2024

On running coupling in the JIMWLK evolution and its Langevin formulation

Various conventional running coupling prescriptions reproducing $β_ 0$-dependent terms of NLO JIMWLK are reviewed and found to be theoretically inconsistent: the JIMWLK evolution Hamiltonian with running coupling violates the requirement of positive semidefiniteness. This requirement appears to be tightly related to the possibility of having a Langevin formulation for the evolution. We also review the scheme that attributes a part of $β_0$-dependent terms to the DGLAP evolution of the projectile. The remaining $β_0$-dependent contributions sum up into so-called the ``daughter dipole'' prescription, which leads to a manifestly positive semidefinite Hamiltonian.

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arXiv2024

Next-to-eikonal corrections to dijet production in Deep Inelastic Scattering in the dilute limit of the Color Glass Condensate

We analyze the effects of next-to-eikonal corrections on dijet production in Deep Inelastic Scattering off nuclear targets in the framework of the Color Glass Condensate. They require the knowledge of correlators of fields in the target beyond those computed in the standard McLerran-Venugopalan model, specifically those between transverse and boost-enhanced components, and of the recoil of the fields. We neglect the latter, while for the former we develop a linear model valid for large nuclei. We considered the unpolarized cross sections for dijet production in the approximation of a homogenous dilute nucleus, obtaining simple analytic expressions for the cross sections at nex-to-eikonal accuracy, valid in the limit of total dijet momentum and dijet momentum imbalance larger than the saturation scale of the nucleus. We perform a numerical study of the results at energies of the Electron Ion Collider, finding $\mathcal{O}(10\%)$ effects in the cross sections at large total momentum. We also analyze the azimuthal asymmetries between total momentum and imbalance, finding that non-eikonal corrections induce odd azimuthal harmonics for the situation of jets with equal momentum fractions from the virtual photon, where they are absent in the eikonal approximation. Finally, in the eikonal approximation we have compared the results of our analytic expansion valid in the dilute limit of the target, and the full Color Glass Condensate results in the McLerran-Venugopalan model and their correlation limit. Our analytic expressions match the correlation limit ones in the region where both should be simultaneously valid and reproduce very well the full Color Glass Condensate results in its validity region.

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arXiv2023

Probing quark transverse momentum distributions in the Color Glass Condensate: quark-gluon dijets in Deep Inelastic Scattering at next-to-eikonal accuracy

We study the production, in Deep Inelastic Scattering at high energy, of a quark-gluon dijet induced by $t$-channel quark exchange with the target, which goes beyond the eikonal approximation. Throughout this study we follow the Color Glass Condensate approach, keep full dependence on the quark mass and consider the target to be unpolarized. We focus on the correlation limit in which the produced jets fly almost back-to-back and find a factorized expression for the cross section, for both longitudinal and transverse photons, involving the unpolarized quark transverse momentum dependent distribution. Quark-gluon dijets can be distinguished from other types of dijets at least in the heavy quark case, thanks to heavy flavor tagging. In that case, the dominant background is expected to come from the eikonal production of a quark-antiquark-gluon system. We propose experimental cuts to suppress that background contribution, making the process of quark-gluon dijet production in Deep Inelastic Scattering a new method to probe the quark transverse momentum dependent distribution at the Electron Ion Collider.

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arXiv2023

DIS dijet production at next-to-eikonal accuracy in the CGC

We compute dijet production in Deep Inelastic Scattering at low $x$ in the dipole formalism at next-to-eikonal accuracy. We calculate the contributions induced by single photon exchange of either longitudinal or transverse polarization. We include all types of corrections to the eikonal approximation in the gluon background field: (i) finite longitudinal width of the target, (ii) interaction of the quark-antiquark pair with the subleading (transverse) component of the background field and (iii) dynamics of the target which is encoded in the $z^-$-coordinate dependence of the background field. The final expressions for the dijet cross section are written as sum of a "generalized eikonal" contribution (where longitudinal momentum $p^+$ exchange between the target and the incoming quark-antiquark pair is allowed since the average $z^-$ dependence of the background field is kept) and explicit next-to-eikonal corrections that involve decorated dipole and quadrupole operators.

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arXiv2023

Single inclusive particle production at next-to-leading order in proton-nucleus collisions at forward rapidities: hybrid approach meets TMD factorization

We revisit the calculation of the cross section for forward inclusive single hadron production in $pA$ collisions within the hybrid approach. We show that the proper framework to perform this calculation beyond leading order is not the collinear factorization, as has been assumed so far, but the TMD factorized framework. Within the TMD factorized approach we show that all the large transverse logarithms appearing in the fixed order calculation, are resummed into the evolution of the TMD PDFs and TMD FFs with factorization scale. The resulting expressions, when written in terms of TMDs evolved to the appropriate, physically well understood factorization scale, contain no additional large logarithms. The absence of any large logarithms in the resummed result should ensure positivity of the cross section and eradicate the persistent problem that have plagued the previous attempts at calculating this observable in the hybrid approach.

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arXiv2023

DIS dijet production at next-to-eikonal accuracy in the CGC

In this work, we derive the cross-section for inclusive DIS dijet production at full next-to-eikonal order. We include the corrections that stem from taking a finite width of the target, the interaction of the quark with the transverse component of the background field and also the dynamics of the target.

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arXiv2023

The case for an EIC Theory Alliance: Theoretical Challenges of the EIC

We outline the physics opportunities provided by the Electron Ion Collider (EIC). These include the study of the parton structure of the nucleon and nuclei, the onset of gluon saturation, the production of jets and heavy flavor, hadron spectroscopy and tests of fundamental symmetries. We review the present status and future challenges in EIC theory that have to be addressed in order to realize this ambitious and impactful physics program, including how to engage a diverse and inclusive workforce. In order to address these many-fold challenges, we propose a coordinated effort involving theory groups with differing expertise is needed. We discuss the scientific goals and scope of such an EIC Theory Alliance.

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arXiv2022

Finite width effects on the azimuthal asymmetry in proton-nucleus collisions in the Color Glass Condensate

We perform a numerical analysis of the two particle azimuthal correlations at central rapidities generated in $p$A collisions within the framework of the Color Glass Condensate. We extend the standard computations to include the subeikonal corrections which stem from considering the finite longitudinal width of the dense target. For practical reasons, we only consider the next-to-next-to-eikonal corrections instead of using the all-order expressions for the inclusive two gluon production cross section. We show that the subeikonal terms that we account for in the two gluon yields contribute to both even and odd harmonics, the latter being absent in the standard Color Glass Condensate calculations performed at eikonal accuracy. Our analysis confirms the vanishing of the subeikonal effects with increasing collision energy and when going to forward rapidities, as expected.

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arXiv2022

Multi-particle production in proton-nucleus collisions in the Color Glass Condensate

We compute multi-gluon production in the Color Glass Condensate approach in dilute-dense collisions, p$A$, extending previous calculations up to four gluons. We include the contributions that are leading in the overlap area of the collision but keep all orders in the expansion in the number of colors. We develop a diagrammatic technique to write the numerous color contractions and exploit the symmetries to group the diagrams and simplify the expressions. To proceed further, we use the McLerran-Venugopalan and Golec-Biernat-Wüsthoff models for the projectile and target averages, respectively. We use a form of the Lipatov vertices that leads to the Wigner function approach for the projectile previously employed, that we generalise to take into account quantum correlations in the projectile wave function. We provide analytic expressions for integrated and differential two gluon cumulants and show a smooth dependence on the parameters defining the projectile and target Wigner function and dipole, respectively. For four gluon correlations we find that the second order four particle cumulant is negative, so a sensible second Fourier azimuthal coefficient can be defined. The effect of correlations in the projectile on this result results qualitatively and quantitatively large.

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arXiv2022

Multiparticle production in proton-nucleus collisions beyond eikonal accuracy

We study the effects on multigluon production at mid-rapidity in the Color Glass Condensate of the non-eikonal corrections that stem from relaxing the shockwave approximation and giving the target a finite size. We extend previous works performed in the dilute-dilute approximation suitable for proton-proton collisions, to the dilute-dense one applicable to proton-nucleus. We employ the McLerran-Venugopalan model for the projectile averages. For the target averages, we use the Golec-Biernat--Wüsthoff model and restrict to the leading contributions in overlap area that allow a factorization of ensembles of Wilson lines into products of dipoles. We make the connection with the jet quenching formalism and compare with previous results in the literature, providing a parametrization of the so-called decorated dipoles. We show that the non-eikonal effects on single inclusive particle production, contrary to what happens in jet quenching, are only sizable, of a few percent, for modest energies $\sqrt{s_{NN}}\leq 100$ GeV and central rapidities. On the other hand, we find that the effects on double inclusive gluon production are larger for the same kinematics. We show that, as found previously in the dilute-dilute situation, non-eikonal corrections break the accidental symmetry in the CGC, allowing for the existence of non-vanishing odd azimuthal harmonics.

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arXiv2022

Dijet photoproduction at low $x$ at next-to-leading order and its back-to-back limit

We compute the cross section for the inclusive photoproduction of a pair of jets at next-to-leading order accuracy in the Color Glass Condensate (CGC) effective theory. The aim is to study the back-to-back limit, to investigate whether transverse momentum dependent (TMD) factorization can be recovered at this order. In particular, we focus on the large Sudakov double logarithms, which are major ingredients of the TMD evolution. Interestingly, the kinematical improvement of the low-$x$ resummation scheme turns out to be a key ingredient in the analysis.

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arXiv2022

Quark and scalar propagators at next-to-eikonal accuracy in the CGC through a dynamical background gluon field

We revisit the calculation of quark and scalar propagators in a gluon background field at Next-to-Eikonal accuracy, which will provide the first power correction to scattering processes in the high-energy limit, including gluon saturation effects. The two main results of our study are as follows. First, we derive a very general Next-to-Eikonal expansion of the quark propagator in terms of the scalar propagator, which allows us to isolate spinor-specific Next-to-Eikonal corrections from the universal ones. Second, we present a new method allowing, for the first time, a systematic calculation of the Next-to-Eikonal corrections coming from the $x^-$ dependence of the background field. This opens the possibility to study high-energy scattering processes on a target with non-trivial dynamics instead of on a static one, by going beyond infinite Lorentz time dilation of the target.

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arXiv2021

Correlations between azimuthal asymmetries and multiplicity and mean transverse momentum in small collisions systems in the CGC

Considering a dilute-dense situation suitable for pA collisions, we compute in the Color Glass Condensate the correlation between azimuthal asymmetries, specifically the squared second Fourier coefficient $v_2^2$, and the total multiplicity in the event. We also analyse the correlation between $v_2^2$ and the mean squared transverse momentum of particles in the event. In both cases, we find that the correlations are generally very small, consistent with the observations. We also note an interesting sharp change in the value of $v_2^2$ and its correlations as a function of the width of the transverse momentum bin, related with a change of the dominance of Bose and HBT quantum correlations.

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arXiv2021

Low-$x$ improved TMD approach to the lepto- and hadroproduction of a heavy-quark pair

We study lepto- and hadroproduction of a heavy-quark pair in the ITMD factorization framework for dilute-dense collisions. Due to the presence of a nonzero quark mass and/or nonzero photon virtuality, new contributions appear compared to the cases of photo- and hadroproduction of dijets, for which the ITMD framework was originally derived. The extra terms are sensitive to gluons that are not fully linearly polarized. At small $x$ those gluons emerge only when saturation effects are taken into account, and in a proper way. As a result, in linear small-$x$ frameworks where gluon are fully linearly polarized, such contributions are absent. We show however that they are not always negligible, even for large gluon transverse momentum, due to the behavior of the off-shell hard factors.

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arXiv2021

Quarks at next-to-eikonal accuracy in the CGC I: Forward quark-nucleus scattering

We derive Next-to-Eikonal (NEik) corrections to the background quark propagator, which stem from (i) considering a finite longitudinal width target instead of an infinitely thin shockwave and (ii) including the interaction of the quark with the transverse components of the background field. These two different corrections to the eikonal approximation combine together and provides a gauge covariant expression for the quark propagator at NEik accuracy. We then apply our results to quark (or antiquark) scattering on a nucleus at NEik accuracy, considering both unpolarized cross section and helicity asymmetry.

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arXiv2020

Angular correlations in pA collisions from CGC: multiplicity and mean transverse momentum dependence of $v_2$

Within the dense-dilute Color Glass Condensate approach, and using the Golec-Biernat-Wuesthoff model for the dipole scattering amplitude, we calculate $v_2^2$ as well as the correlations between $v_2^2$ and both the total multiplicity and the mean transverse momentum of produced particles. We find that the correlations are generally very small consistent with the observations. We note an interesting sharp change in the value of $v^2_2$ as well as of its correlations as a function of the width of the transverse momentum bin. This crossover is associated with the change from Bose enhancement dominance of the correlation for narrow bin to HBT dominated correlations for larger bin width.

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