arXiv subjects

M. Siddikov

Publications and source records attributed to M. Siddikov.

At least 19 recordsLinked to original sources

arXiv2025

The exclusive photoproduction of $\chi_{c}\gamma$ pairs in the small-$x$ kinematics

In this manuscript we analyze the exclusive photoproduction of the $\chi_{c}\gamma$ pairs. We focus on the small-$x$ kinematics and evaluate the cross-sections in the Color Glass Condensate framework. We found that in the leading order in the strong coupling $\alpha_{s}$, this process is sensitive only to the forward color dipole scattering amplitude. We estimated numerically the cross-sections for different polarizations of $\chi_{c}$ mesons in the kinematics of the ultraperipheral collisions at LHC and the future Electron Ion Collider. We also analyzed the role of this process as a potential background to exclusive $\chi_{c}$ photoproduction, which has been recently suggested as an alternative channel for studies of odderons. According to our estimates, the cross-section of $\chi_{c}\gamma$ with undetected photons is comparable to that of odderons at small momentum transfer $|t|\lesssim1$ GeV$^{2}$, but becomes less relevant at larger $|t|$. We also found that a dominant background to odderon-mediated production of $\chi_{c}$ comes from the radiative decays of $\psi(2S)$ mesons, which potentially can present a challenge for odderon studies via $\chi_{c}$ photoproduction.

hep-ph↗

arXiv2025

Inclusive hadroproduction of charmonia-bottomonia pairs in the CGC framework

In this preprint we analyze the inclusive hadroproduction of heavy charmonia-bottomonia pairs in the Color Glass Condensate framework in the dilute-dense approximation. The production mechanisms can be classified by number of gluons emitted from projectile as Single- and Double Parton Scattering. We analyzed separately both types of contributions and evaluated the corresponding impact factors in the leading order in strong coupling $\alpha_{s}$. For the Double Parton Scattering the impact factors factorize into a product of impact factors of single charmonia and bottomonia production cross-sections, and the cross-section in the large-$N_{c}$ limit reduces to the well-known pocket formula. For the Single Parton Scattering we found that the cross-section of the process is sensitive to dipole, quadrupole, sextupole and octupole scattering amplitudes (correlators of Wilson lines), thus opening possibility to study phenomenologically these novel objects. We also made phenomenological estimates of the cross-sections in the dilute approximation and found that the suggested approach provides a fair qualitative description of the LHCb data for $J/\psi+\Upsilon(1S)$ production.

hep-ph↗

arXiv2024

Photoproduction of $\eta_{c}\gamma$ pairs in CGC framework

In this paper we analyzed the exclusive photoproduction of $\eta_{c}\gamma$ pairs in the Color Glass Condensate framework. We found that the cross-section of this process is sensitive only to the forward dipole scattering amplitude, and thus could be used as a new tool for analysis of this fundamental nonperturbative object. Using the phenomenological parametrizations of this object, we estimated numerically the production cross-section and counting rates in the kinematics of the ongoing and forthcoming experiments at LHC and future Electron Ion Collider. We found that the cross-section is sufficiently large for dedicated experimental study. We also estimated the role of this process as a potential background to $\eta_{c}$ photoproduction, which is conventionally considered as a gateway for studies of odderons. We found that the contribution of $\eta_{c}\gamma$ (with undetected photon) is on par with expected contributions of odderons in the kinematics of small momentum transfer $|t|\lesssim1$ GeV$^{2}$, though decreases rapidly at larger $|t|$. Finally, we also calculated the feed-down contribution (from radiative decays of other charmonia) and found that a sizable correction comes from $J/\psi\to\eta_{c}\gamma$ decays. This contribution remains pronounced even at relatively large $|t|$ and potentially can impose constraint on detectability of odderons via $\eta_{c}$ photoproduction.

hep-ph↗

arXiv2024

Exclusive photoproduction of $\eta_{c}\gamma$ pairs with large invariant mass

In this preprint we analyzed the exclusive photoproduction of $\eta_{c}\gamma$ pairs in the collinear factorization framework and evaluated its cross-section in leading order in the strong coupling $\alpha_{s}$. We found that this process is mostly sensitive to the behavior of the unpolarized gluon GPD $H_{g}$ in the Efremov-Radyushkin-Brodsky-Lepage kinematics. We estimated numerically the cross-section and the expected counting rates in the kinematics of middle-energy photoproduction experiments which can be realized at the future Electron-Ion Collider and in the kinematics of ultraperipheral collisions at LHC. We found that the cross-section is sufficiently large for dedicated experimental study.

hep-ph↗

arXiv2017

Suppression vs enhancement of heavy quarkonia in pA collisions

We describe production of heavy quarkonia in pA collisions within the dipole approach, assuming dominance of the perturbative color-singlet mechanism (CSM) in the $p_T$-integrated cross section. Although accounting for a nonzero heavy $Q$-$\bar Q$ separation is a higher twist correction, usually neglected, we found it to be the dominant source of nuclear effects, significantly exceeding the effects of leading twist gluon shadowing and energy loss. Moreover, this contribution turns out to be the most reliably predicted, relying on the precise measurements of the dipole cross section at HERA. The nuclear suppression of quarkonia has been anticipated to become stronger with energy, because the dipole cross section steeply rises. However, the measured nuclear effects remain essentially unchanged within the energy range from RHIC to the LHC. A novel production mechanism is proposed, which enhances the charmonium yield. Nuclear effects for the production of $J/ψ$, $ψ(2S)$, $Υ(1S)$ and $Υ(2S)$ are calculated, in agreement with data from RHIC and LHC. The dipole description offers a unique explanation for the observed significant nuclear suppression of $ψ(2S)$ to $J/ψ$ ratio, related to the nontrivial features of the $ψ(2S)$ wave function.

hep-ph↗

arXiv2016

Production of pentaquarks in $pA$-collisions

We argue that a hidden-charm pentaquark recently observed in weak decays of $Λ_{b}$ can be produced in proton-nucleus collisions without electroweak intermediaries. We analyze the production cross-section for several scenarios of internal structure and find that a cross-section is sizable. This process can be studied both in collider as well as in fixed-target experiments. In the former case, the pentaquarks are produced at very forward rapidities, whereas in the latter case, pentaquarks are produced with relatively small rapidities and can be easily detected via invariant mass distribution of a forward $J/ψ$ and a comoving proton. Additionally, the suggested process allows to check the existence of a neutral pentaquark $P_{c}^{0}$ (an isospin partner of $P_{c}^{+}$) predicted in several models. The rapidity and transverse momentum distributions of pentaquarks could provide comprehensive information about the $\bar{c}c$ component of this exotic baryon.

hep-ph↗

arXiv2015

Semiclassical solution to the BFKL equation with massive gluons

In this paper we proceed to study the high energy behavior of a scattering amplitudes in the Yang-Mills theory with the Higgs mechanism for the gauge boson mass. The spectrum of the $j$-plane singularities of the $t$-channel partial waves, and corresponding eigenfunctions of the BFKL equation in leading log approximation (LLA), were previously calculated by us numerically in arXiv:1401.4671 . Here we develop a semiclassical approach and investigate the influence of the impact parameter exponential decrease, existing in this model, on the high energy asymptotic behaviour of the scattering amplitude. This approach is much simpler than the numerical calculations, and reproduces our earlier numerical results. The analytical (semianalytical) solutions which have been found in this paper, can be used to incorporate correctly the large impact parameter behavior in the framework of CGC/saturation approach. This behaviour is interesting as provides the high energy amplitude for the electroweak theory, which can be measured experimentally.

hep-ph↗

arXiv2015

Nuclear effects in neutrinoproduction of pions

In this paper we study nuclear effects in the neutrinoproduction of pions. We found that in a Bjorken kinematics, for moderate $x_{B}$ accessible in ongoing and forthcoming neutrino experiments the cross-section is dominated by the incoherent contribution; the coherent contribution becomes visible only for small $|t|\lesssim1/R_{A}^{2}$, which requires $x_{B}\lesssim0.1$. Our results could be relevant to the kinematics of the ongoing MINERvA experiment in ME configuration. We provide a code which could be used for evaluation of the $ν$DVMP observables using different parametrizations of GPDs and different models of nuclear structure.

hep-ph↗

arXiv2015

On relation between rest frame and light-front descriptions of quarkonium

In this paper we study the relation between the light-front (infinite momentum) and rest-frame descriptions of quarkonia. While the former is more convenient for high-energy production, the latter is usually used for the evaluation of charmonium properties. In particular, we discuss the dynamics of a relativistically moving system with nonrelativistic internal motion and give relations between rest frame and light-front potentials used for the description of quarkonium states. We consider two approximations, first the small coupling regime, and next the nonperturbative small binding energy approximation. In both cases we get consistent results. Our results could be relevant for the description of final state interactions in a wide class of processes, including quarkonium production on nuclei and plasma. Moreover, they can be extended to the description of final state interactions in the production of weakly bound systems, such as for example the deuteron.

hep-ph↗

arXiv2014

Survival of charmonia in a hot environment

A colorless c-cbar dipole emerging from a heavy ion collision and developing the charmonium wave function can be broken-up by final state interactions (FSI) propagating through the hot medium created in the collision. We single out two mechanisms of charmonium attenuation: (i) Debye color screening, called melting; and (ii) color-exchange interaction with the medium, called absorption. The former problem has been treated so far only for charmonia at rest embedded in the medium, while in practice their transverse momenta at the LHC are quite high, =7-10 GeV^2. We demonstrate that a c-cbar dipole may have a large survival probability even at infinitely high temperature. We develop a procedure of Lorentz boosting of the Schroedinger equation to a moving reference frame and perform the first realistic calculations of the charmonium survival probability employing the path-integral technique, incorporating both melting and absorption. These effects are found to have comparable magnitudes. We also calculated the FSI suppression factor for the radial excitation psi(2S) and found it to be stronger than for J/psi, except large p_T, where psi(2S) is relatively enhanced. The azimuthal asymmetry parameter v_2 is also calculated.

hep-ph↗

arXiv2014

Charmonium in a hot medium: melting vs absorption

A charmonium produced in heavy ion collisions at RHIC and LHC propagates through a dense co-moving matter with a rather high relative momentum, =4-10GeV^2. In spite of Debye screening of the binding potential, the charmonium survives with a substantial probability, even if the c-cbar potential is completely screened in the hot environment. In addition, the color-exchange interaction with the medium is another important source of charmonium suppression. Attenuation in a hot medium caused by both effects is evaluated by means of the path integral technique, which requires ability of boosting the binding potential to a moving reference frame. This problem is solved in the approximation of small intrinsic velocities of the charmed quarks.

nucl-th↗

arXiv2014

Generalized parton distributions from neutrino experiments: twist-three effects

We study the twist-3 corrections to the neutrino induced deeply virtual meson production due to the chiral odd transversity Generalized Parton Distribution (GPD). We found that in contrast to pion electroproduction, in neutrino-induced processes these corrections are small. This occurs due to large contribution of unpolarized GPDs $H,\, E$ to the twist-2 amplitude in neutrinoproduction. Our results are important for analyses of the pion and kaon production in the Minerva experiment at FERMILAB.

hep-ph↗

arXiv2014

Higher-twist contributions to neutrino-production of pions

In this paper we estimate the size of twist-3 corrections to the deeply virtual meson production in neutrino interactions due to the chiral odd transversity Generalized Parton Distribution (GPD). We conclude that in contrast to pion electroproduction, in neutrino-induced reactions these corrections are small. This happens due to large contribution of unpolarized GPDs H, E to the leading-twist amplitude in neutrinoproduction. We provide a computational code, which can be used for evaluation of the cross-sections accounting for these twist-3 corrections with various GPD models. Our results are particularly relevant for analyses of the pion and kaon production in the Minerva experiment at FERMILAB.

hep-ph↗

arXiv2013

Bethe-Heitler type radiative corrections to deeply virtual neutrinoproduction of mesons

We study the electromagnetic Bethe-Heitler type contribution to neutrino-induced deeply virtual meson production (\nuDVMP). Such O(α_{em})-corrections decrease with Q^{2} in the Bjorken regime less steeply than the standard \nuDVMP handbag contribution. Therefore, they are relatively enhanced at high Q^{2}. The Bethe-Heitler terms give rise to an angular correlation between the lepton and hadron scattering planes with harmonics sensitive to the real and imaginary parts of the DVMP amplitude. These corrections constitute a few percent effect in the kinematics of the forthcoming Minerva experiment at Fermilab and should be taken into account in precision tests of GPD parametrizations. For virtualities Q^{2}~100 GeV^{2} these corrections become on a par with DVMP handbag contributions. A computational code, which can be used for the evaluation of these corrections employing various GPD models is provided.

hep-ph↗

arXiv2012

Flavor structure of generalized parton distributions from neutrino experiments

The analysis of deeply virtual meson production is extended to neutrino-production of the pseudo-Goldstone mesons (pions, kaons, eta-mesons) on nucleons, with the flavor content of the recoil baryon either remaining intact, or changing to a hyperon from the SU(3) octet. We rely on the SU(3) relations and express all the cross-sections in terms of the proton generalized parton distributions (GPDs). The corresponding amplitudes are calculated at the leading twist level and in the leading order in α_{s}, using a phenomenological parametrization of GPDs. We provide a computational code, which can be used for evaluation of the cross-sections employing various GPD parametrizations. We conclude that these processes can be studied in the experiment Minerva at FERMILAB, which could supplement the measurements at JLAB and help to extract the GPD flavor structure from data.

hep-ph↗

arXiv2012

Nonperturbative features of the axial current

We study the nonperturbative structure of the axial current and evaluate the two-point light-cone distribution amplitudes (DA) associated with the correlator \int dξexp(-iqξ)<0|\barψ(x)Γψ(y)J_μ^{5}(ξ)|0> within the instanton vacuum model in the leading order in O(1/N_c). Due to the built-in chiral symmetry, four of eight axial DAs are related to that for pions. Knowledge of these nonperturbative objects is important for phenomenological study of high-energy neutrino interactions and semileptonic decays of heavy quarks. We provide a code for evaluation of these DAs and an interpolation formula valid in the region Q^2 < 1 GeV^2.

hep-ph↗

arXiv2012

Incurable Adler relation for soft neutrino interactions

The Adler relation (AR), which bridges soft interactions of neutrinos and pions, might look as a manifestation of pion dominance. However neutrino cannot fluctuate to a pion because of lepton current conservation, instead it interacts via much heavier hadronic components. This fact leads to nontrivial relations between interaction amplitudes of different hadronic species, in particular, it links diagonal and off-diagonal diffractive interactions of pions. Absorptive corrections break these relations making the AR impossible to hold universally, i.e. for any target and at any energy. We predict a dramatic breakdown of the AR for coherent neutrino-production of pions on nuclei at all energies.

hep-ph↗

arXiv2012

Diffractive neutrino-production of pions on nuclei: Adler relation within the color-dipole description

Effects of coherence in neutrino-production of pions off nuclei are studied employing the color dipole representation and path integral technique. If the nucleus remains intact, the process is controlled by the interplay of two length scales. One is related to the pion mass and is quite long (at low Q^2), while the other, associated with heavy axial-vector states, is much shorter. The Adler relation is found to be broken at all energies, but especially strongly at ν> 10 GeV, where the cross section is suppressed by a factor ~A^{-1/3}. On the contrary, in a process where the recoil nucleus breaks up into fragments, the Adler relation turns out to be strongly broken at low energies, where the cross section is enhanced by a factor ~A^{1/3}, but has a reasonable accuracy at higher energies, where all the coherence length scales become long.

hep-ph↗