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Sanjin Benić

Publications and source records attributed to Sanjin Benić.

18 recordsLinked to original sources
arXiv2026

The eikonal spin-dependent Odderon and gluon Sivers function of a proton, and its small-$x$ evolution

The matrix element in the proton of the eikonal Odderon operator, with a helicity flip, has been shown to correspond to the dipole gluon Sivers function. We employ a three quark light-front model of the proton to determine the Sivers function at moderately small $x_0 \sim 0.1$ and transverse momentum $k_\perp \lesssim 1$~GeV. The model light-cone (LC) wave function predicts the properties of $x f_{1T}^{\perp g}(x,k_\perp)$ such as its overall magnitude, the position of its peak in $k_\perp$, and its behavior at small $k_\perp$. We then compute numerically the BFKL anomalous dimension characterizing the power-law tail at $k_\perp \gtrsim 1.5$~GeV of the gluon Sivers function at small (but pre-asymptotic) LC momentum fractions, $α_s \log x_0/x = 1$: $x f_{1T}^{\perp g}(x,k_\perp) \sim k_\perp^{-3.3}$.

hep-ph↗
arXiv2026

Generalized transverse momentum distributions at small-$x$

We compute the complete set of the leading-twist gluon and sea-quark generalized transverse momentum distributions (GTMDs) in the small-$x$, or eikonal, approximation at vanishing skewness $ξ= 0$. All the gluon GTMDs become expressed in terms of the basic gluon dipole operator featuring also proton helicity-flips. Consequently, we establish universal relations between otherwise distinct GTMDs that hold in the small-$x$ limit. The obtained results are systematically projected onto the transverse momentum dependent distributions (TMD) and the generalized parton distribution (GPD) cases, recovering known results where available. In case of sea-quarks all the GTMDs are given in terms of the gluon dipole convoluted with a hard kernel. We generalize the unpolarized sea-quark GTMD to non-zero momentum transfers and find new results for the proton helicity-flip distributions. We pay special attention to their perturbative, high transverse momentum, tails to confirm that it becomes governed by the small-$x$ gluon GPDs. The obtained results provide guidance to the phenomenological modeling of the GTMDs but also allow for their explicit computations.

hep-ph↗
arXiv2025

Off forward non-SCHC contributions to exclusive vector quarkonium production from the "spin dependent BFKL Pomeron"

A novel contribution to off-forward, exclusive vector quarkonium production, $γ^{(*)}+p \to V+p$, at high energy is derived which corresponds to a $t$-channel exchange of a BFKL hard Pomeron, with a helicity flip of the proton. This ``spin-dependent BFKL Pomeron" is required in a consistent expansion in powers of the momentum transfer $ t \approx -Δ_\perp^2$ beyond first order. The spin-dependent Pomeron violates $s$-channel helicity conservation (SCHC) at ${\cal O}(Δ_\perp^2)$, and beyond. Expanding to leading twist only, it corresponds to GPD $E_g(x,t)$ for vanishing skewness. We derive explicit expressions for the eikonal BFKL amplitudes, to all orders in dipole size times momentum transfer, for all helicity configurations of the particles in the initial and final states. We also provide numerical estimates of the helicity flip two gluon exchange amplitude at moderate $x$ from a light-cone quark model of the proton. The spin dependent BFKL Pomeron could, in principle, be discovered via double spin asymmetries in $e+p \to e+p+J/ψ$ with transversely polarized proton and longitudinally polarized electron in the initial state.

hep-ph↗
arXiv2025

Single spin asymmetry in forward $pA$ collisions from Pomeron-Odderon interference

Working in the hybrid framework of the high energy $pA$ collisions we identify a new contribution to transverse single spin asymmetry (SSA). The phase necessary for the SSA is provided by the Pomeron-Odderon interference in the dense nuclear target. The complete formula for the $pA \to h X$ polarized cross section also contains the transversity distribution for the polarized projectile as well as the real part of the twist-3 fragmentation function. We numerically estimate the asymmetry $A_N$ and its nuclear dependence. Based on a model computation we find that $A_N$ can be a percent level in the forward and low-$P_{h\perp}$ region. For large nuclei we find significant suppression, with $A_N \propto A^{-7/6}$ parametrically. As a notable feature we find a node of $A_N$ as a function of the $P_{h\perp}$ around the values of the initial saturation scale that could be used to test this mechanism experimentally.

hep-ph↗
arXiv2025

Directed flow from parton spin-orbit coupling in $pp$ and $pA$ collisions

We point out a novel mechanism to generate $\cos ϕ$ two-particle azimuthal correlation (`directed flow') in unpolarized proton-proton and proton-nucleus collisions in the forward rapidity region of the projectile proton. This is a direct consequence of the recently discovered strong spin-orbit coupling in gluons at small-$x$. The observable simultaneously serves as a unique probe into the double helicity parton distribution functions of the proton.

hep-ph↗
arXiv2024

Photon-Odderon interference in exclusive $χ_{c}$ charmonium production at the Electron-Ion Collider

Exclusive $C=+1$ scalar, axial-vector, and tensor quarkonium production in high-energy electron-proton scattering requires a $C$-odd $t$-channel exchange of a photon or a three gluon ladder. We derive the expressions for the corresponding amplitudes. The relative phase of the photon vs. three gluon exchange amplitudes is determined by the sign of the light-front matrix element of the eikonal color current operator $d^{abc}J^{+a}J^{+b}J^{+c}$ at moderate $x$, and is not affected by small-$x$ QCD evolution. Model calculations predict constructive interference, which is particularly strong for momentum transfer $|t|\sim 1$~GeV$^2$ where the cross section for $χ_{cJ}$ production exceeds that for pure photon exchange by up to a factor of 4. We find that exclusive $χ_{cJ}$ electroproduction at the Electron-Ion Collider should occur with well measurable rates and measurements of these processes should allow to find an evidence of the perturbative Odderon exchange. We also compute the total electroproduction cross section as a function of energy and provide first estimates of the number of $χ_{cJ}$ events per month at the Electron-Ion Collider design luminosity.

hep-ph↗
arXiv2024

Perturbative QCD contribution to transverse single spin asymmetries in Drell-Yan and SIDIS

In a previous publication [Beni\' c et al., Phys. Rev. D104 (2021) 094027], we have computed the perturbative QCD contribution to transverse single spin asymmetries (SSAs) in semi-inclusive Deep Inelastic Scattering (SIDIS) involving the $g_T(x)$ distribution. In this paper, we first present a more efficient derivation of the asymmetries which is applicable to both transverse and longitudinal SSAs, and correct some inconsistencies in our previous calculation. We then adapt the method to compute transverse SSAs in Drell-Yan proportional to $g_T(x)$ and its gluonic counterpart, and discuss the crossing symmetry between the results for SIDIS and Drell-Yan. Finally, we present numerical results for various asymmetries measurable at the EIC, RHIC, COMPASS and Fermilab (SpinQuest), including also part of the genuine twist-three corrections to $g_T(x)$ from a recent global analysis. We find that the asymmetries can reach percent-level magnitude, if the kinematics predominantly probes the large-$x$ (valence) region of the polarized proton, but remain at sub-percent levels otherwise.

hep-ph↗
arXiv2023

Exclusive $η_c$ production from small-$x$ evolved Odderon at a electron-ion collider

We compute exclusive $η_c$ production in high energy electron-nucleon and electron-nucleus collisions that is sensitive to the Odderon. In perturbative QCD the Odderon is a $C$-odd color singlet consisting of at least three $t$-channel gluons exchanged with the target. By using the Color Glass Condensate effective theory our result describes the Odderon exchange at the high collision energies that would be reached at a future electron-ion collider. The Odderon distribution is evolved to small-$x$ using the Balitsky-Kovchegov evolution equation with running coupling corrections. We find that while at low momentum transfers $t$ the cross section off a proton is dominated by the Primakoff process, the Odderon becomes relevant at larger momentum transfers of $|t|\geq1.5$ GeV$^2$. We point that the Odderon could also be extracted at low-$t$ using neutron targets since the Primakoff component is strongly suppressed. In the case of nuclear targets, the Odderon cross section becomes enhanced thanks to the mass number of the nuclear target. The gluon saturation effect induces a shift in the diffractive pattern with respect to the Primakoff process that could be used as a signal for the Odderon.

hep-ph↗
arXiv2022

On the odderon mechanism for transverse single spin asymmetry in the Wandzura-Wilczek approximation

We compute the transverse single spin asymmetry in forward $p^\uparrow p \to hX$ and $p^\uparrow A \to hX$ collisions from the odderon mechanism originally suggested by Kovchegov and Sievert [1]. Working in the hybrid approach of the Color Glass Condensate effective theory we firstly identify the relevant collinear parton distribution function (PDF) of the transversely polarized proton $p^\uparrow$ as the intrinsic twist-3 $g_T(x)$ distribution. We further argue that the complete polarized cross section also contains contributions from the kinematical and the dynamical twist-3 PDFs, in addition to the intrinsic twist-3 PDF. By restricting to the Wandzura-Wilczek approximation, where the dynamical twist-3 PDFs are dropped, we find that the odderon contribution to the polarized cross section for inclusive hadron production is exactly zero at the next-to-leading order in the strong coupling.

hep-ph↗
arXiv2022

Isolated photon-hadron production in high energy $pp$ and $pA$ collisions at RHIC and LHC

We compute the isolated photon production in association with a charged hadron at mid rapidity in $pp$ and $pA$ based on the Color Glass Condensate (CGC) framework of high energy QCD where, for the first time, we incorporate the Sudakov effect of soft gluon emissions. Our results are based on the leading order $q g \to q γ$ channel in the CGC framework and confronted with the recent data from RHIC and LHC concerning the angular distributions and out-of-plane transverse momentum distributions. We find that, while the CGC computation alone results in too narrow distributions, with the help of the Sudakov effect, we can get a satisfactory description of the data. With this as a benchmark, we provide predictions for the magnitude of the nuclear effect brought by the phenomena of gluon saturation in the CGC.

hep-ph↗
arXiv2021

The $g_T(x)$ contribution to single spin asymmetries in SIDIS

Motivated by a novel origin of transverse single spin asymmetry (SSA) in semi-inclusive Deep Inelastic Scattering (SIDIS) uncovered by some of us, we quantitatively investigate its impact on the theoretical understanding of the mechanism responsible for SSA. This new contribution from the quark-initiated channel first appears in two-loop perturbation theory and involves the $g_T(x)$ distribution. We point out another entirely analogous piece from the gluon-initiated channel proportional to the gluon helicity distribution $ΔG(x)$. Both contributions are solely expressed in terms of twist-two polarized parton distribution functions and twist-two fragmentation functions in the Wandzura-Wilczek approximation, such that they can be unambiguously evaluated without introducing free parameters. We make predictions for measurements of the asymmetries $A_{UT}$ at the future Electron-Ion Collider (EIC), and find that $A_{UT}$ associated with the $\sin (ϕ_h-ϕ_S)$, $\sin ϕ_S$ and $\sin (2ϕ_h-ϕ_S)$ harmonics can reach up to 1-2\% even at the top EIC energy.

hep-ph↗
arXiv2019

Single spin asymmetry in forward $pA$ collisions: Phenomenology at RHIC

We confront the theoretical result of single spin asymmetry (SSA) $A_N$ in forward $pA$ collisions $p^\uparrow A \to hX$ including the gluon saturation effect with the recent preliminary experimental data from the PHENIX and STAR collaborations at RHIC. While we find overall reasonable agreement with the STAR data, our results indicate that the strong nuclear suppression of the asymmetry $A_N\sim A^{-1/3}$ observed by the PHENIX collaboration cannot be explained within the present understanding of this problem.

hep-ph↗
arXiv2019

Constraining unintegrated gluon distributions from inclusive photon production in proton-proton collisions at the LHC

We compute the leading order (LO) $qg\to q γ$ and next-to-leading order (NLO) $gg\to q{\bar q} γ$ contributions to inclusive photon production in proton-proton (p+p) collisions at the LHC. These channels provide the dominant contribution at LO and NLO for photon transverse momenta $k_{γ\perp}$ corresponding to momentum fractions of $x\leq 0.01$ in the colliding protons. Our computations, performed in the dilute-dense framework of the Color Glass Condensate effective field theory (CGC EFT), show that the NLO contribution dominates at small-$x$ because it is sensitive to $k_\perp$-dependent unintegrated gluon distributions in both of the protons. We predict a maximal $10\%$ modification of the cross section at low $k_{γ\perp}$ as a direct consequence of the violation of $k_\perp$-factorization. The coherence effects responsible for this modification are enhanced in nuclei and can be identified from inclusive photon measurements in proton-nucleus collisions. We provide numerical results for the isolated inclusive photon cross section for $k_{γ\perp}\leq 20$ GeV in p+p collisions that can be tested in the future at the LHC.

hep-ph↗
arXiv2018

Single spin asymmetries in ultra-peripheral $p^\uparrow A$ collisions

We suggest inclusive hadron production in ultra-peripheral proton-nucleus collisions (UPCs) $p^\uparrow A \to h AX$ as a new channel to investigate single spin asymmetries (SSAs), in particular, to test the assumed dominance of the contribution from twist-three fragmentation functions. The UPC cross sections are obtained by considering the photoproduction limit of semi-inclusive deep inelastic scattering (SIDIS). In particular, we find simple formulas for the polarized UPC cross sections in the collinear twist-three framework. We then numerically calculate the fragmentation contribution to SSA in $p^\uparrow A \to πA X$ at $\sqrt{s} = 200$ GeV and find a few percent asymmetry in the forward region.

hep-ph↗
arXiv2017

Prompt photon - jet angular correlations at central rapidities in p+A collisions

Photon-jet azimuthal correlations in proton-nucleus collisions are a promising tool for gaining information on the gluon distribution of the nucleus in the regime of non-linear color fields. We compute such correlations from the process $g+A\to q \bar{q} γ$ in the rapidity regime where both the projectile and target light-cone momentum fractions are small. By integrating over the phase space of the quark which emits the photon, subject to the restriction that the photon picks up most of the transverse momentum (to pass an isolation cut), we effectively obtain a $g+A\to q γ$ process. For nearly back-to-back photon-jet configurations we find that it dominates over the leading order process $q+A\to q γ$ by two less powers of $Q_\perp / Q_S$, where $\boldsymbol{Q}_\perp$ and $Q_S$ denote the net photon-jet pair momentum and the saturation scale of the nucleus, respectively. We determine the transverse momentum dependent gluon distributions involved in $g+A\to q γ$ and the scale where they are evaluated. Finally, we provide analytic expressions for $\langle\cos nϕ\rangle$ moments, where $ϕ$ is the angle between $\boldsymbol{Q}_\perp$ and the average photon-jet transverse momentum $\tilde{\boldsymbol{P}}_\perp$, and first qualitative estimates of their transverse momentum dependence.

hep-ph↗
arXiv2015

Multiquark interactions and heavy hybrid stars

We introduce a two flavor Nambu--Jona-Lasinio (NJL) model with 8-quark interactions in the scalar and the vector channel. With the lower density region described by the density-dependent relativistic mean field model we construct a hybrid equation of state. We especially focus on the 4-quark vector couplings and the 8-quark vector NJL couplings and allocate a region in this parameter subspace where hybrid stars with masses larger than $2M_\odot$ exist.

nucl-th↗
arXiv2012

Thermodynamic instabilities in dynamical quark models with complex conjugate mass poles

We show that the CJT thermodynamic potential of dynamical quark models with a quark propagator represented by complex conjugate mass poles inevitably exhibits thermodynamic instabilities. We find that the minimal coupling of the quark sector to a Polyakov loop potential can strongly suppress but not completely remove such instabilities. This general effect is explicitly demonstrated in the framework of a covariant, chirally symmetric, effective quark model.

hep-ph↗