arXiv subjects

N. Ya. Ivanov

Publications and source records attributed to N. Ya. Ivanov.

At least 19 recordsLinked to original sources

arXiv2022

Conceptual design of the Spin Physics Detector

The Spin Physics Detector, a universal facility for studying the nucleon spin structure and other spin-related phenomena with polarized proton and deuteron beams, is proposed to be placed in one of the two interaction points of the NICA collider that is under construction at the Joint Institute for Nuclear Research (Dubna, Russia). At the heart of the project there is huge experience with polarized beams at JINR. The main objective of the proposed experiment is the comprehensive study of the unpolarized and polarized gluon content of the nucleon. Spin measurements at the Spin Physics Detector at the NICA collider have bright perspectives to make a unique contribution and challenge our understanding of the spin structure of the nucleon. In this document the Conceptual Design of the Spin Physics Detector is presented.

hep-ex↗

arXiv2021

On the physics potential to study the gluon content of proton and deuteron at NICA SPD

The Spin Physics Detector (SPD) is a future multipurpose experiment foreseen to run at the NICA collider, which is currently under construction at the Joint Institute for Nuclear Research (JINR, Dubna, Russia). The physics program of the experiment is based on collisions of longitudinally and transversely polarized protons and deuterons at $\sqrt{s}$ up to 27 GeV and luminosity up to 10$^{32}$ cm$^{-2}$ s$^{-1}$. The SPD will operate as a universal facility for comprehensive study of unpolarized and polarized gluon content of the nucleon, using different complementary probes such as: charmonia, open charm, and prompt photon production processes. The aim of this work is to make a thorough review of the physics objectives that can potentially be addressed at the SPD, underlining related theoretical aspects and discussing relevant experimental results when available. Among different pertinent phenomena particular attention is drawn to the study of the gluon helicity, gluon Sivers and Boer-Mulders functions in the nucleon, as well as the gluon transversity distribution in the deuteron, via the measurement of specific single and double spin asymmetries.

hep-ex↗

arXiv2019

Probing the linearly polarized gluons in unpolarized proton with heavy-quark pair production

We consider the azimuthal $\cos φ$ and $\cos 2φ$ distributions and the Callan-Gross ratio $R={\rm d}σ_L/{\rm d}σ_T$ in heavy-quark pair electroproduction, $lN\rightarrow l^{\prime}Q\bar{Q}X$, as probes of linearly polarized gluons in unpolarized nucleons. Our analysis shows that the azimuthal asymmetries and Callan-Gross ratio are predicted to be large and very sensitive to the contribution of the gluonic counterpart of the Boer-Mulders function, $h_{1}^{\perp g}$, describing the linear polarization of gluons inside unpolarized nucleon. In particular, the maximum values of the azimuthal distributions vary from 0 to 1 depending on $h_{1}^{\perp g}$. We conclude that future measurements of these quantities at the proposed EIC and LHeC colliders could clarify in details the proton spin decomposition puzzle.

hep-ph↗

arXiv2018

How to measure the linear polarization of gluons in unpolarized proton using the heavy-quark pair production

In recent papers [1,2], two new ways have been proposed to probe the linear polarization of gluons in unpolarized proton: using the azimuthal asymmetries and Callan-Gross ratio in heavy-quark pair leptoproduction, $lN\rightarrow l^{\prime}Q\bar{Q}X$. In this talk, we discuss in details the sensitivity of the QCD predictions for the azimuthal $\cos φ$ and $\cos 2φ$ asymmetries to the contribution of linearly polarized gluons inside unpolarized proton, where the azimuth $φ$ is the angle between the lepton scattering plane $(l,l^{\prime})$ and the heavy quark production plane $(N,Q)$. Our analysis shows that the azimuthal distributions under consideration vary from 0 to 1 depending on the transverse-momentum dependent gluonic counterpart of the Boer-Mulders function, $h_{1}^{\perp g}$. We conclude that the $\cos φ$ and $\cos 2φ$ asymmetries in heavy-quark pair production in DIS processes are predicted to be large in wide kinematic ranges and sensitive to the contribution of linearly polarized gluons.

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arXiv2018

The ratio $R={\rm d}σ_L/{\rm d}σ_T$ in heavy-quark pair leptoproduction as a probe of linearly polarized gluons in unpolarized proton

We study the Callan-Gross ratio $R={\rm d}σ_L/{\rm d}σ_T$ in heavy-quark pair leptoproduction, $lN\rightarrow l^{\prime}Q\bar{Q}X$, as a probe of linearly polarized gluons inside unpolarized proton, where ${\rm d}σ_T$ (${\rm d}σ_L$) is the differential cross section of the $γ^*N\rightarrow Q\bar{Q}X$ process initiated by a transverse (longitudinal) virtual photon. Note first that the maximal value for the quantity $R$ allowed by the photon-gluon fusion with unpolarized gluons is large, about 2. We calculate the contribution of the transverse-momentum dependent gluonic counterpart of the Boer-Mulders function, $h_{1}^{\perp g}$, describing the linear polarization of gluons inside unpolarized proton. Our analysis shows that the maximum value of the ratio $R$ depends strongly on the gluon polarization; it varies from 0 to $\frac{Q^2}{4m^2}$ depending on $h_{1}^{\perp g}$. We conclude that the Callan-Gross ratio in heavy-quark pair leptoproduction is predicted to be large and very sensitive to the contribution of linearly polarized gluons. For this reason, future measurements of the longitudinal and transverse components of the charm and bottom production cross sections at the proposed EIC and LHeC colliders seem to be very promising for determination of the linear polarization of gluons inside unpolarized proton.

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arXiv2018

How to measure the linear polarization of gluons in unpolarized proton using the heavy-quark pair leptoproduction

We study the azimuthal $\cos φ$ and $\cos 2φ$ asymmetries in heavy-quark pair leptoproduction, $lN\rightarrow l^{\prime}Q\bar{Q}X$, as probes of linearly polarized gluons inside unpolarized proton, where the azimuth $φ$ is the angle between the lepton scattering plane $(l,l^{\prime})$ and the heavy quark production plane $(N,Q)$. First, we determine the maximal values for the $\cos φ$ and $\cos 2φ$ asymmetries allowed by the photon-gluon fusion with unpolarized gluons; these predictions are large, $(\sqrt{3}-1)/2$ and $1/3$, respectively. Then we calculate the contribution of the transverse-momentum dependent gluonic counterpart of the Boer-Mulders function, $h_{1}^{\perp g}$, describing the linear polarization of gluons inside unpolarized proton. Our analysis shows that the maximum values of the azimuthal distributions depend strongly on the gluon polarization; they vary from 0 to 1 depending on $h_{1}^{\perp g}$. We conclude that the azimuthal $\cos φ$ and $\cos 2φ$ asymmetries in heavy-quark pair leptoproduction are predicted to be large and very sensitive to the contribution of linearly polarized gluons. For this reason, future measurements of the azimuthal distributions in charm and bottom production at the proposed EIC and LHeC colliders seem to be very promising for determination of the linear polarization of gluons inside unpolarized proton.

hep-ph↗

arXiv2017

QCD predictions for the azimuthal asymmetry in charm leptoproduction for the COMPASS kinematics

We present the QCD predictions for the azimuthal $\cos 2φ$ asymmetry in charm leptoproduction for the kinematics of the COMPASS experiment at CERN. The asymmetry is predicted to be large, about 15%. The radiative corrections to the QCD predictions for the $\cos 2φ$ distribution are estimated to be small, less than 10%. Our calculations show that the azimuthal asymmetry in charm production is well defined in pQCD: it is stable both perturbatively and parametrically, and practically insensitive to theoretical uncertainties in the input parameters. We analyze the nonperturbative contributions to the $\cos 2φ$ distribution due to the gluon transverse motion in the target and the $c$-quark fragmentation. Because of the $c$-quark low mass, the nonperturbative contributions are expected to be sizable, about (30--40)%. We conclude that extraction of the azimuthal asymmetries from available COMPASS data will provide valuable information about the transverse momentum dependent distribution of the gluon in the proton and the $c$-quark hadronization mechanism. Finally, we discuss the $\cos 2φ$ asymmetry as a probe of the gluonic analogue of the Boer-Mulders function, $h_{1}^{\perp g}$, describing the linear polarization of gluons inside unpolarized proton.

hep-ph↗

arXiv2016

Perturbatively stable observables in heavy-quark leptoproduction

We study the perturbative and parametric stability of the QCD predictions for the Callan-Gross ratio $R(x,Q^2)=F_L/F_T$ and azimuthal $\cos(2φ)$ asymmetry, $A(x,Q^2)$, in heavy-quark leptoproduction. We review the available theoretical results for these quantities and conclude that, contrary to the production cross sections, the ratios $R(x,Q^2)$ and $A(x,Q^2)$ are stable under radiative QCD corrections in wide region of the variables $x$ and $Q^2$. This implies that large radiative contributions to the structure functions cancel each other in the ratios $R(x,Q^2)$ and $A(x,Q^2)$ with good accuracy. Then we consider some experimental and phenomenological applications of the observed perturbative stability. We provide compact analytic predictions for $R(x,Q^2)$ and azimuthal $\cos(2φ)$ asymmetry in the case of low $x\ll 1$. It is demonstrated that our obtained results will be useful in the extraction of the structure functions from measurements of the reduced cross sections. Finally, we analyze the properties of $R(x,Q^2)$ and $A(x,Q^2)$ within the variable-flavor-number scheme (VFNS) of QCD. We conclude that the Callan-Gross ratio and azimuthal asymmetry are perturbatively stable but sensitive to resummation of the mass logarithms of the type $α_{s}\ln\left( Q^{2}/m^{2}\right)$. For this reason, the quantities $R(x,Q^2)$ and $A(x,Q^2)$ will be good probes of the heavy-quark content of the proton.

hep-ph↗

arXiv2016

Azimuthal Asymmetry and Ratio $R= F_L / F_T$ as Probes of the Charm Content of the Proton

We study two experimental ways to measure the heavy-quark content of the proton: using the Callan-Gross ratio $R(x,Q^2)=F_L/F_T$ and/or azimuthal $\cos(2φ)$ asymmetry in deep inelastic lepton-nucleon scattering. Our approach is based on the perturbative stability of the QCD predictions for these two quantities. We resume the mass logarithms of the type $α_{s}\ln\left( Q^{2}/m^{2}\right)$ and conclude that heavy-quark densities in the nucleon can, in principle, be determined from data on the Callan-Gross ratio and/or azimuthal asymmetry. In particular, the charm content of the proton can be measured in future studies at the proposed Large Hadron-Electron (LHeC) and Electron-Ion (EIC) Colliders.

hep-ph↗

arXiv2016

Single Spin Asymmetry in Open Charm Photoproduction and Decay as a Test of pQCD

We analyze the possibility of measuring the single spin asymmetry (SSA) in open charm production by linearly polarized photons in the planned E160/E161 experiments at SLAC using the inclusive spectra of secondary (decay) leptons. In leading order pQCD, the SSA in the azimuthal distribution of the charged decay lepton is predicted to be about 0.2 for SLAC kinematics. Our calculations show that the SSA in the decay lepton distribution is well defined in pQCD: it is stable both perturbatively and parametrically, and practically insensitive to theoretical uncertainties in the charm semileptonic decays. Nonperturbative contributions to the leptonic SSA due to the gluon transverse motion in the target, heavy quark fragmentation and Fermi motion of the $c$-quark inside the $D$-meson are predicted to be about 10%. We conclude that measurements of the azimuthal asymmetry in the secondary lepton distribution would provide a good test of the applicability of pQCD to open charm production at energies of fixed target experiments. Our analysis of the SLAC experimental conditions shows that this SSA can be measured in E160/E161 with an accuracy of about ten percent.

hep-ph↗

arXiv2012

Perturbative stability of the QCD predictions for the ratio $R=F_L/F_T$ and azimuthal asymmetry in heavy-quark leptoproduction

We analyze the perturbative and parametric stability of the QCD predictions for the Callan-Gross ratio $R(x,Q^2)=F_L/F_T$ and azimuthal $\cos(2φ)$ asymmetry in heavy-quark leptoproduction. Our analysis shows that large radiative corrections to the structure functions cancel each other in their ratio $R(x,Q^2)$ and azimuthal asymmetry with good accuracy. As a result, the NLO contributions to the Callan-Gross ratio and $\cos(2φ)$ asymmetry are less than 10% in a wide region of the variables $x$ and $Q^2$. We provide compact analytic predictions for $R(x,Q^2)$ and asymmetry in the case of low $x\ll 1$. Simple formulae connecting the high-energy behavior of the Callan-Gross ratio and azimuthal asymmetry with the low-$x$ asymptotics of the gluon density in the target are derived. It is shown that the obtained hadron-level predictions for $R(x,Q^2)$ and azimuthal asymmetry are stable at $x\ll 1$ under the DGLAP evolution of the gluon distribution function. Concerning the experimental aspects, we propose to exploit the observed perturbative stability of the Callan-Gross ratio and $\cos(2φ)$ asymmetry in the extraction of the structure functions from the corresponding reduced cross sections. In particular, our obtained analytic expressions simplify essentially the determination of $F_2^c(x,Q^2)$ and $F_2^b(x,Q^2)$ from available data of the H1 Collaboration. Our results will also be useful in extraction of the azimuthal asymmetries from the incoming and future data on heavy-quark leptoproduction.

hep-ph↗

arXiv2012

How to measure the charm density in the proton

We study two experimental ways to measure the heavy-quark content of the proton: using the Callan-Gross ratio $R(x,Q^2)=F_L/F_T$ and/or the azimuthal $\cos(2φ)$ asymmetry in DIS. Our approach is based on the following observations. First, the ratio $R(x,Q^2)=F_L/F_T$ and azimuthal $\cos(2φ)$ asymmetry in heavy-quark leptoproduction are stable, both parametrically and perturbatively, within pQCD. Second, both these quantities are sensitive to resummation of the mass logarithms of the type $α_{s}\ln(Q^{2}/m^{2})$. We conclude that the heavy-quark densities in the nucleon can, in principle, be determined from high-$Q^2$ data on the Callan-Gross ratio and/or the azimuthal asymmetry. In particular, the charm content of the proton can be measured in future studies at the proposed Large Hadron-Electron (LHeC) and Electron-Ion (EIC) Colliders.

hep-ph↗

arXiv2010

How to measure the Charm Density in the Proton at EIC

We study two experimental ways to measure the heavy-quark content of the proton: using the Callan-Gross ratio $R(x,Q^2)=F_L/F_T$ and/or the azimuthal $\cos(2ϕ)$ asymmetry in deep inelastic lepton-nucleon scattering. Our approach is based on the following observations. First, unlike the production cross sections, the ratio $R(x,Q^2)=F_L/F_T$ and the azimuthal $\cos(2ϕ)$ asymmetry in heavy-quark leptoproduction are sufficiently stable, both parametricallly and perturbatively, in a wide region of variables $x$ and $Q^2$ within the fixed-flavor-number scheme of QCD. Second, both these quantities, $R(x,Q^2)=F_L/F_T$ and $\cos(2ϕ)$ asymmetry, are sensitive to resummation of the mass logarithms of the type $α_{s}\ln\left(Q^{2}/m^{2}\right)$ within the variable-flavor-number schemes. These two facts together imply that the heavy-quark densities in the nucleon can, in principle, be determined from high-$Q^2$ data on the Callan-Gross ratio and/or the azimuthal asymmetry in heavy-quark leptoproduction. In particular, the charm content of the proton can be measured in future studies at the proposed Large Hadron-Electron (LHeC) and Electron-Ion (EIC) Colliders.

hep-ph↗

arXiv2008

The Ratio $R=F_L/F_T$ in DIS as a Probe of the Charm Content of the Proton

We analyze the Callan-Gross ratio $R(x,Q^2)=F_L/F_T$ in heavy-quark leptoproduction as a probe of the charm content of the proton. To estimate the charm-initiated contributions, we use the ACOT($χ$) variable-flavor-number scheme. Our analysis shows that charm densities of the recent CTEQ sets of parton distributions have sizeable impact on the Callan-Gross ratio in a wide region of $x$ and $Q^2$. In particular, the ACOT($χ$) predictions for the quantity $R(x,Q^2)$ are about half as large as the corresponding expectations of the photon-gluon fusion mechanism for $x\sim 10^{-2}-10^{-1}$ and $Q^2\gg m^2$. This is because the structure functions $F_T (x,Q^2)$ and $F_L (x,Q^2)$ have different dependences on the mass logarithms of the type $α_{s}\ln(Q^{2}/m^{2})$. On the other hand, our recent studies indicate that, contrary to the production cross sections, the Callan-Gross ratio is sufficiently stable under radiative corrections to the photon-gluon fusion component for $x\gtrsim 10^{-4}$. We conclude that the quantity $R(x,Q^2)$ in heavy-quark leptoproduction is perturbatively stable but sensitive to resummation of the mass logarithms. For this reason, in contrast to the structure functions, the ratio $R(x,Q^2)=F_L/F_T$ could be good probe of the charm density in the proton.

hep-ph↗

arXiv2008

On the Perturbative Stability of the QCD Predictions for the Ratio $R=F_L/F_T$ in Heavy-Quark Leptoproduction

We analyze the perturbative and parametric stability of the QCD predictions for the Callan-Gross ratio $R(x,Q^2)=F_L/F_T$ in heavy-quark leptoproduction. We consider the radiative corrections to the dominant photon-gluon fusion mechanism. In various kinematic regions, the following contributions are investigated: exact NLO results at low and moderate $Q^2\lesssim m^2$, asymptotic NLO predictions at high $Q^2\gg m^2$, and both NLO and NNLO soft-gluon (or threshold) corrections at large Bjorken $x$. Our analysis shows that large radiative corrections to the structure functions $F_T(x,Q^2)$ and $F_L(x,Q^2)$ cancel each other in their ratio $R(x,Q^2)$ with good accuracy. As a result, the NLO contributions to the Callan-Gross ratio are less than 10% in a wide region of the variables $x$ and $Q^2$. We provide compact LO predictions for $R(x,Q^2)$ in the case of low $x\ll 1$. A simple formula connecting the high-energy behavior of the Callan-Gross ratio and low-$x$ asymptotics of the gluon density is derived. It is shown that the obtained hadron-level predictions for $R(x\to 0,Q^2)$ are stable under the DGLAP evolution of the gluon distribution function. Our analytic results simplify the extraction of the structure functions $F_2^c(x,Q^2)$ and $F_2^b(x,Q^2)$ from measurements of the corresponding reduced cross sections, in particular at DESY HERA.

hep-ph↗

arXiv2007

Azimuthal Dependence of the Heavy Quark Initiated Contributions to DIS

We analyze the azimuthal dependence of the heavy-quark-initiated contributions to the lepton-nucleon deep inelastic scattering (DIS). First we derive the relations between the parton level semi-inclusive structure functions and the helicity $γ^{*}Q$ cross sections in the case of arbitrary values of the heavy quark mass. Then the azimuth-dependent ${\cal O}(α_{s})$ lepton-quark DIS is calculated in the helicity basis. Finally, we investigate numerically the properties of the $\cosϕ$ and $\cos2ϕ$ distributions caused by the photon-quark scattering (QS) contribution. It turns out that, contrary to the basic photon-gluon fusion (GF) component, the QS mechanism is practically $\cos2ϕ$-independent. This fact implies that measurements of the azimuthal distributions in charm leptoproduction could directly probe the charm density in the proton.

hep-ph↗

arXiv2007

Azimuthal Asymmetries in DIS as a Probe of Intrinsic Charm Content of the Proton

We calculate the azimuthal dependence of the heavy-quark-initiated ${\cal O}(α_{s})$ contributions to the lepton-nucleon deep inelastic scattering (DIS). It is shown that, contrary to the photon-gluon fusion (GF) component, the photon-quark scattering (QS) mechanism is practically $\cos2ϕ$-independent. We investigate the possibility to discriminate experimentally between the GF and QS contributions using their strongly different azimuthal distributions. Our analysis shows that the GF and QS predictions for the azimuthal $\cos2ϕ$ asymmetry are quantitatively well defined in the fixed flavor number scheme: they are stable, both parametrically and perturbatively. We conclude that measurements of the azimuthal distributions at large Bjorken $x$ could directly probe the intrinsic charm content of the proton. As to the variable flavor number schemes, the charm densities of the recent CTEQ and MRST sets of parton distributions have a dramatic impact on the $\cos2ϕ$ asymmetry in the whole region of $x$ and, for this reason, can easily be measured.

hep-ph↗

arXiv2003

Azimuthal Asymmetries in Heavy Quark Leptoproduction as a Test of pQCD

We analyze the perturbative and parametric stability of the QCD predictions for the azimuthal asymmetries in heavy quark leptoproduction. At leading order, the $\cos ϕ$ asymmetry vanishes whereas the $\cos 2ϕ$ one is of leading twist and predicted to be about 15% at energies sufficiently above the production threshold. We calculate the NLO soft-gluon corrections to $ϕ$-dependent leptoproduction to the next-to-leading logarithmic accuracy. The soft-gluon approximation provides a good description of the available exact NLO results at $Q^{2}\lesssim m^{2}$. Our analysis shows that, contrary to the production cross sections, the $\cos 2ϕ$ asymmetry is practically insensitive to soft radiation for $Q^{2}\lesssim m^{2}$ at energies of the fixed target experiments. We conclude that the $\cos 2ϕ$ asymmetry is well defined in pQCD: it is stable both perturbatively and parametrically, and insensitive (in the case of bottom production) to nonperturbative contributions. Measurements of the azimuthal asymmetries would provide an excellent test of pQCD applicability to heavy flavor production.

hep-ph↗