In this paper, we study the azimuthal asymmetry in the $J/ψ$ leptoproduction in unpolarized $ep$ collisions. There are two independent azimuthal asymmetry modulations, namely $\mathrm{cos}(ψ)$ and $\mathrm{cos}(2ψ)$, where $ψ$ is the azimuthal angle of the lepton scattering plane with respect to the hadron-interacting plane. We calculate the two modulations as functions of four kinematic variables, and find that they provide a very good laboratory to distinguish several models describing the heavy quarkonium production, including the color-singlet (CS) model, the nonrelativistic QCD (NRQCD) associated with the $^1S_0^{[8]}$ dominance picture, and the NRQCD in which the values of all the three color-octet (CO) long-distance matrix elements are of the same order. In order to make definite conclusions, we restrict our calculation in a specific kinematic region, where the CS and CO mechanisms can be distinguished by scrutinizing the values of the $\mathrm{cos}(ψ)$ modulation, while the $^1S_0^{[8]}$ dominance picture can be tested by measuring the values of the $\mathrm{cos}(2ψ)$ modulation. Calculating their values and carrying out a meticulous statistical analysis, we find that at an integrated luminosity $\mathcal{L}=1000\mathrm{pb}^{-1}$, the statistical uncertainties of the two quantities are small enough to tell the three models apart. When this experiment is implemented at the future $ep$ colliders such as the EIC, crucial information for the $J/ψ$ production mechanism might be discovered.
By examining the symmetry constraints on the semi-inclusive pseudoscalar particle production in unpolarized inelastic lepton-hadron scattering, we present a complete, exact Lorentz decomposition for the corresponding hadronic tensor. As a result, we find that it contains five independent terms, instead of the four as have been suggested before. The newly identified one is odd under the naive time reversal transformation, and the corresponding structure function is directly related to the single spin asymmetry in the semi-inclusive pseudoscalar meson production by a polarized lepton beam off an…
We consider the leading order result for polarized leptoproduction, putting emphasis on transverse momentum dependent effects appearing in azimuthal asymmetries. Measurements of weighted cross sections enable extraction of the distribution of transversely polarized quarks. We focus on the distribution in a longitudinally polarized hadron and estimate the expected asymmetries in leptoproduction.
We investigate the origin of the cos 2 phi azimuthal asymmetry in unpolarized semiinclusive DIS. The contributions to this asymmetry arising from the intrinsic transverse motion of quarks are explicitly evaluated, and predictions for the HERMES and COMPASS kinematic regimes are presented. We show that the effect of the leading-twist Boer-Mulders function h_1^perp(x, k_T^2), which describes a correlation between the transverse momentum and the transverse spin of quarks, is quite significant and may also account for a part of the cos 2 phi asymmetry measured by ZEUS in the perturbative domain.
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-mo…
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\…
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-M…
We show that the transverse momentum dependent transversity function is proportional to the longitudinal polarization of a quark in a transversely polarized proton. This result suggests an alternative, convenient method for determining transversity, without knowing unusual fragmentation functions. The method consists of measuring the double spin azimuthal asymmetry in semi-inclusive pion leptoproduction by a transversely polarized proton target. The asymmetry, which is twist 3, is estimated to be more than 10% under the most favorable conditions. The experiment we suggest is feasible at facili…
We consider the azimuthal asymmetries in semi-inclusive deep inelastic leptoproduction arising due to both perturbative and nonperturbative effects at HERMES energies and show that the $k_T^2/Q^2$ order corrections to $< \cosϕ>$ and $< \cos2ϕ>$ are significant. We also reconsider the results of perturbative effects for $< \cosϕ>$ at large momentum transfers \cite{A1} using the more recent sets of scale-dependent distribution and fragmentation functions, which bring up to $18{%}$ difference in $< \cosϕ>$. In the same approach we calculate the $< \cos2ϕ>$ as well.
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 th…
We analyze the longitudinal-transverse double-spin asymmetry in lepton-nucleon collisions where a single hadron is detected in the final state, i.e., $\vec{\ell}\,N^\uparrow \rightarrow h\,X$. This is a subleading-twist observable in collinear factorization, and we look at twist-3 effects in both the transversely polarized nucleon and the unpolarized outgoing hadron. Results are anticipated for this asymmetry from both HERMES and Jefferson Lab Hall A, and it could be measured as well at COMPASS and a future Electron-Ion Collider. We also perform a numerical study of the distribution term, whic…
We point out the role of intrinsic transverse momentum of partons in the study of azimuthal asymmetries in deep-inelastic 1-particle inclusive leptoproduction. Leading asymmetries often appear in combination with spin asymmetries. This leads not only to transverse momentum dependence in the parton distribution functions, but also to functions beyond the ones known from inclusive deep-inelastic scattering (DIS). We use Lorentz invariance and the QCD equations of motion to study the evolution of functions that appear at leading (zeroth) order in a 1/Q expansion in azimuthal asymmetries. This inc…
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 …
We estimate the size of the azimuthal asymmetry of the semi-inclusive pion production in the deep-inelastic scattering of a polarized lepton beam off an unpolarized nucleon target for the produced hadron, arising due to both nonperturbative and perturbative effects.
Using a previous extraction of the quark Boer-Mulders distributions from semiinclusive deep inelastic scattering data, we fit the unpolarized Drell-Yan data on the $\cos 2 ϕ$ asymmetry, determining the antiquark Boer-Mulders distributions. A good agreement with the data is found in the region of low $q_T$, where the transverse-momentum factorization approach applies.
We study the Sivers asymmetry in inelastic $J/ψ$ leptoproduction, $ep^\uparrow \to e+ J/ψ+X$, within a transverse momentum dependent scheme, the so-called generalized parton model (GPM). The effects of final-state interactions are properly taken into account by employing the color-gauge invariant GPM (CGI-GPM). For the $J/ψ$ formation the non-relativistic QCD (NRQCD) framework is adopted. Predictions for unpolarized cross sections and maximized Sivers asymmetries at EIC energies are given.
We examined the symmetry aspect of the semi-inclusive one-pion production in the deep inelastic scattering of a lepton beam off an unpolarized nucleon target, with an emphasis on the positivity restrictions on the corresponding structure functions. In combination with the Callan-Gross-type relation between two twist-two structure functions $W_1$ and $W_2$, we derived an upper bound on the Levelt-Mulders asymmetry, which occurs when the lepton beam is longitudinally polarized.
The COMPASS Collaboration is measuring the asymmetries in the azimuthal distributions of positive and negative hadrons produced in Deep Inelastic Scattering (DIS) on unpolarized protons. The data have been collected in 2016 and 2017 with a 160 GeV/$c$ muon beam scattering off a liquid hydrogen target. The amplitudes of three modulations, $A_{UU}^{\cosϕ_h}$, $A_{UU}^{\cos 2ϕ_h}$ and $A_{LU}^{\sinϕ_h}$ are measured as function of the Bjorken variable $x$, of the fraction of virtual photon energy carried by the hadron $z$, and of the hadron transverse momentum with respect to the virtual photon $…
We present the leading order unpolarized and polarized cross sections in electroweak semi-inclusive deep inelastic leptoproduction. The azimuthal dependences in the cross section differential in the transverse momentum of the vector boson arise due to intrinsic transverse momenta of the quarks. However, the presented asymmetries are not suppressed by inverse powers of the hard scale. We discuss the different opportunities to measure specific asymmetries as offered by neutral compared to charged current processes and point out the optimal kinematical regions. The present and (proposed) future H…
The measurement of azimuthal modulations in hadron leptoproduction on unpolarized nucleons allows to get information on the intrinsic transverse momentum $\langle k_T^2 \rangle$ of quarks in a nucleon through both the Cahn effect and the Boer-Mulders function. We have compared the azimuthal asymmetries in the cross section of $160\, \rm{GeV}/c$ muons scattered off an unpolarised deuteron target as measured by COMPASS with a Monte Carlo program, based on the ${}^3P_0$ model of quark anti-quark pair production at string breaking, which accounts for the Cahn effect. Large differences have been ob…
I review the phenomenology of unpolarized cross sections and azimuthal asymmetries in semi-inclusive deeply inelastic scattering (SIDIS). The general theoretical framework is presented and the validity of the Gaussian model is discussed. A brief account of the existing analyses is provided.
Azimuthal correlations in two hadron production in deep inelastic scattering of unpolarized leptons off transversely polarized nucleon are discussed. Specifically, a simple approach for accessing ratios of structure functions corresponding to Sivers effect and transversity induced single spin azimuthal asymmetries to unpolarized structure functions is presented. This approach is then applied to a sample pseudo-data generated by a modified version of the LEPTO Monte Carlo event generator that includes the Sivers effect. Using this data it is shown, that the azimuthal correlations in the Sivers-…
We calculate the $\cos2ϕ$ azimuthal asymmetry of the unpolarized $p\bar{p}$ Drell-Yan dilepton production process in the $Z$-resonance region at the Tevatron kinematic domain. Such an azimuthal asymmetry can provide additional information about a spin-related new parton distribution function, i.e., the Boer-Mulders function of the proton, compared to the $pp$ process. Therefore the available data of unpolarized proton-antiproton collision at Tevatron can contribute to our study on the spin structure of the nucleon.
We study the dihadron azimuthal correlation produced nearly back-to-back in unpolarized hadron collisions, arising from the product of two Collins fragmentation functions. Using the latest Collins fragmentation functions extracted from the global analysis of available experimental data, we make predictions for the azimuthal correlation of two-pion production in $pp$ collisions at RHIC energies. We find that the correlation is sizable in the mid-rapidity region for moderate jet transverse momentum.
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 acc…
We study the azimuthal asymmetry of the unpolarized Drell-Yan in the framework of the T-odd functions. We find, on the basis of quite general arguments, that for |{\bf q}_{\perp}| << Q such an asymmetry decreases as Q^{-2}, where {\bf q}_{\perp} and Q are respectively the transverse momentum and the center-of-mass energy of the muon pair. The experimental results support this conclusion.
We calculate the Boer-Mulders effect contribution to the $\cos2ϕ$ azimuthal asymmetry of unpolarized dilepton production near the $Z$-pole. Based on the tree-level expression in the transverse momentum dependent factorization framework, we show that the corresponding asymmetry near the $Z$-pole is negative, which is opposite to the asymmetry in the low $Q^2$ region, dominated by the production via a virtual photon. We calculate the asymmetry generated by the Boer-Mulders effect near the $Z$-pole at RHIC, with $\sqrt{s}=500$ GeV. We find that the magnitude of the asymmetry is several percent, a…
We present a phenomenological analysis of the cos-phi and cos-2phi asymmetries in unpolarized semi-inclusive deep inelastic scattering, based on the recent multidimensional data released by the COMPASS and HERMES Collaborations. In the TMD framework, valid at relatively low transverse momenta, these asymmetries arise from intrinsic transverse momentum and transverse spin effects, and from their correlations. The role of the Cahn and Boer-Mulders effects in both azimuthal moments is explored up to order 1/Q. As the kinematics of the present experiments is dominated by the low-Q^2 region, higher…
We consider the azimuthal distribution of the final observed hadron in semi-inclusive deep-inelastic scattering and the lepton pair in the Drell-Yan process. In particular, we focus on the $\cos ϕ$ modulation of the unpolarized cross section and on its dependence upon transverse momentum. At low transverse momentum, for these observables we propose a factorized expression based on tree-level approach and conjecture that the same formula is valid in transverse-momentum dependent (TMD) factorization when written in terms of subtracted TMD parton distributions. Our formula correctly matches with …
We study the Sivers azimuthal asymmetry for $J/ψ$ production in semi-inclusive deep inelastic scattering, and the still poorly known gluon Sivers function. We concentrate on the $J/ψ$ low transverse momentum region, employing the transverse-momentum dependent generalised parton model (GPM), and its colour gauge invariant extension (CGI-GPM), which includes final-state interactions at leading order. We adopt the nonrelativistic QCD (NRQCD) framework for the quarkonium formation mechanism, and compare our results for the unpolarised cross section and the Sivers asymmetry with available data, res…
We study the azimuthal angular dependence of back-to-back di-jet production in unpolarized hadron scattering $H_A+H_B \to J_1 + J_2 +X$, arising from the product of two Boer-Mulders functions, which describe the transverse spin distribution of quarks inside an unpolarized hadron. We find that when the di-jet is of two identical quarks ($J_q+J_q$) or a quark-antiquark pair ($J_q+J_{\bar{q}}$), there is a $\cos δϕ$ angular dependence of the di-jet, with $δϕ=ϕ_1-ϕ_2$, and $ϕ_1$ and $ϕ_2$ are the azimuthal angles of the two individual jets. In the case of $J_q+J_q$ production, we find that there i…
Taking into account the effect of final state interaction, we calculate the non-zero (naïve) $T$-odd transverse momentum dependent distribution $h_1^{\perp}(x,\kp^2)$ of the pion in a quark-spectator-antiquark model with effective pion-quark-antiquark coupling as a dipole form factor. Using the model result we estimate the $\cos 2ϕ$ asymmetries in the unpolarized $π^- N$ Drell-Yan process which can be expressed as $h_1^{\perp}\times\bar{h}_1^{\perp}$. We find that the resulting $h_{1π}^\p(x,\kp^2)$ has the advantage to reproduce the asymmetry that agrees with the experimental data measured by …
We show that for Drell-Yan events by unpolarized hadronic projectiles and nuclear targets, azimuthal asymmetries can arise from the nuclear distortion of the hadronic projectile wave function, typically a spin-orbit effect occurring on the nuclear surface. The asymmetry depends on quantities that enter also the spin asymmetry in the corresponding Drell-Yan event on polarized free nucleonic targets. Hence, this study can be of help in exploring the spin structure of the nucleon, in particular the transverse spin distribution of partons inside the proton. All arguments can be extended also to an…
First information on the chirally odd twist-3 proton distribution function e(x) is extracted from the azimuthal asymmetry, A_{LU}, in the electro-production of pions from deeply inelastic scattering of longitudinally polarized electrons off unpolarized protons, which has been recently measured by CLAS collaboration. Furthermore parameter-free predictions are made for azimuthal asymmetries, A_{UL}, from scattering of an unpolarized beam on a polarized proton target for CLAS kinematics.
Semi-inclusive $J/ψ$ production in electron-proton collisions is a promising process to study gluon transverse momentum distributions (TMDs) at the future Electron-Ion Collider. In this article, we improve on previous studies of the $\cos 2 ϕ$ azimuthal asymmetry that arises from the linear polarization of gluons inside unpolarized protons by including TMD evolution. We find that in the TMD regime the asymmetry grows monotonically with increasing transverse momentum of the outgoing $J/ψ$, in contrast to tree level calculations with Gaussian TMDs. Our predictions for the asymmetry at EIC can be…
We consider the leading twist $T$-odd contributions as the dominant source of the $\cos 2ϕ$ azimuthal asymmetry in unpolarized $p\bar{p}\to μμ^+ X$ dilepton production in Drell-Yan Scattering. This asymmetry contains information on the distribution of quark transverse spin in an unpolarized proton. In a parton-spectator framework we estimate these asymmetries at $50 {\rm GeV}$ center of mass energy. This azimuthal asymmetry is interesting in light of proposed experiments at GSI, where an anti-proton beam is ideal for studying the transversity properties of quarks due to the dominance of {\em v…
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 distri…
We analyse the role of partonic transverse motion in unpolarized Semi-Inclusive Deep Inelastic Scattering (SIDIS) processes. Imposing appropriate kinematical conditions, we find some constraints which fix an upper limit to the range of allowed k_perp values. We show that, applying these additional requirements on the partonic kinematics, we obtain different results with respect to the usual phenomenological approach based on the Gaussian smearing with analytical integration over an unlimited range of k_perp values. These variations are particularly interesting for some observables, like the < …
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 analysi…
We calculate the two leading-twist transverse momentum dependent distribution functions of the pion meson, the unpolarized distribution $f_{1π}(x,\bm{k}^2_T)$ and the Boer-Mulders function $h_{1π}^\perp (x,\bm{k}^2_T)$, using the pion wave functions derived from a light-cone approach. The evolution effect of the first $\bm k_T$-moment of the pion Boer-Mulders function is studied by employing an approximate evolution kernel. Using the model resulting distributions, we predict the transverse momentum weighted $\cos2ϕ$ azimuthal asymmetry in the unpolarized $π^- p$ Drell-Yan process which can be …
We consider transverse momentum dependent gluon distributions inside both unpolarized and transversely polarized protons and show how they can be probed by looking at azimuthal modulations in $e \, p \to e \, J/ψ\, \mathrm{jet} \, X$. We find that the contribution due to quark induced subprocesses is always suppressed in the considered kinematic regions, accessible in principle at a future Electron-Ion Collider. Our model-independent estimates of the maximal values of these asymmetries allowed by positivity bounds suggest the feasibility of their measurement. In addition, by adopting the McLer…
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, …
We investigate the theoretical framework of the $\cos 2ϕ$ azimuthal asymmetry contributed by the coupling of two Boer-Mulders functions in the dilepton production unpolarized $πp$ Drell-Yan process by applying the transverse momentum dependent factorization at leading order. We adopt the model calculation results of the unpolarized distribution function $f_1$ and Boer-Mulders function $h_1^\perp$ of pion meson from the light-cone wave functions. We take into account the transverse momentum evolution effects for both the distribution functions of pion and proton by adopting the existed extracti…
The energy loss parameter $\hat q$ is one of the fundamental transport parameters of hadronic matter. Using the twist-4 collinear approach, we show that the $\cos ϕ$ azimuthal asymmetry in unpolarized semi-inclusive deeply inelastic scattering (SIDIS) off a large nucleus at intermediate transverse momentum is a sensitive observable for its determination. The effect is due to the suppression of the azimuthal asymmetry by final-state multiple scattering.
We present a detailed study of vector meson photoproduction in ultraperipheral heavy ion collisions (UPCs). Using the dipole model, we develop a framework for the joint impact parameter and transverse momentum dependent cross sections. We compute the unpolarized cross section and $\cos 2ϕ$ azimuthal angular correlation for $ρ^0$ photoproduction with $ϕ$ defined as the angle between the $ρ^0$'s transverse momentum and its decay product pion meson's transverse momentum. Our result on unpolarized coherent differential cross section gives excellent description to the STAR experimental data. A firs…
We calculate the Sivers and $\cos2ϕ$ azimuthal asymmetries in $J/ψ$ production in polarized and unpolarized semi-inclusive $ep$ collision respectively, using the formalism based on transverse momentum dependent parton distributions (TMDs). Non-relativistic QCD based color octet model is employed for calculating the $J/ψ$ production rate. The Sivers asymmetry in this process directly probes the gluon Sivers function. The estimated Sivers asymmetry at $z=1$ is negative which is in good agreement with COMPASS data. We also investigate the effect of TMD evolution on the Sivers asymmetry. The $\cos…
We investigate the cos 2 phi azimuthal asymmetry in Drell--Yan and J/psi production from unpolarized ppbar scattering at GSI-HESR energies. The contribution to this asymmetry arising from the leading-twist Boer-Mulders function h_1^perp(x, k_T^2), which describes a correlation between the transverse momentum and the transverse spin of quarks in an unpolarized hadron, is explicitly evaluated, and predictions for the GSI-HESR kinematic regime are presented. We show that the cos 2 phi asymmetry is quite sizable both on the J/psi peak and in the Drell-Yan continuum region. Therefore these processe…
Using a generalized parton model approach including spin and intrinsic parton motion effects, and assuming the validity of factorization for large-pT jet production in hadronic collisions, we study the azimuthal distribution around the jet axis of leading unpolarized or (pseudo)scalar hadrons, namely pions, produced in the jet fragmentation process. We identify the observable leading-twist azimuthal asymmetries for the unpolarized and single-polarized case related to quark and gluon-originated jets. We account for all physically allowed combinations of the transverse momentum dependent (TMD) p…
We study the $\cos 2 ϕ$ azimuthal asymmetry in unpolarized semi-inclusive DIS, taking into account both the perturbative contribution (gluon emission and splitting) and the non perturbative effects arising from intrinsic transverse motion and transverse spin of quarks. In particular we explore the possibility to extract from $<\cos 2 ϕ>$ some information about the Boer--Mulders function $h_1^{\perp}$, which represents a transverse--polarization asymmetry of quarks inside an unpolarized hadron. Predictions are presented for the HERMES, COMPASS and JLab kinematics, where $<\cos 2 ϕ>$ is dominate…
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 de…
In the fragmentation of a transversely polarized quark several left-right asymmetries are possible for the hadrons in the jet. When only one unpolarized hadron is selected, it exhibits an azimuthal modulation known as Collins effect. When a pair of oppositely charged hadrons is observed, three asymmetries can be considered, a di-hadron asymmetry and two single hadron asymmetries. In lepton deep inelastic scattering on transversely polarized nucleons all these asymmetries are coupled with the transversity distribution. From the high statistics COMPASS data on oppositely charged hadron-pair prod…
We investigate the inclusive emission in unpolarized proton collisions of a charm-flavored hadron in association with a Higgs boson, featuring large transverse momenta and produced with a large rapidity distance. Taking advantage of a narrow timing coincidence between the ATLAS detector and the future FPF ones, we study the behavior of cross sections and azimuthal correlations for ultraforward rapidities of the detected hadron. We provide evidence that the hybrid high-energy and collinear factorization, encoding the BFKL resummation of large energy logarithms and supplemented by collinear dens…
In this paper, we show how a presence of the exotic scalar, tensor weak interactions in addition to the standard vector-axial (V-A) one may help to distinguish the Dirac from Majorana neutrinos in the elastic scattering of (anti)neutrino beam off the unpolarized electrons in the limit of vanishing (anti)neutrino mass. We assume that the incoming (anti)neutrino beam comes from the polarized muon decay at rest and is the left-right chiral mixture with assigned direction of the transversal spin polarization with respect to the production plane. We display that the azimuthal asymmetry in the angul…
Using a generalized parton model approach including spin and intrinsic parton motion effects, and assuming the validity of factorization for large p_T jet production in hadronic collisions, we study the azimuthal distribution around the jet axis of leading pions, produced in the jet fragmentation process. We identify the observable leading-twist azimuthal asymmetries for the unpolarized and single-polarized case related to both quark and gluon-originated jets. We account for all physically allowed combinations of the transverse momentum dependent (TMD) parton distribution and fragmentation fun…
Using the Coulomb Eikonal Phase associated with a transversely polarized nucleon, we calculate the azimuthal single spin asymmetry of unpolarized electrons elastically scattered from a transversely polarized nucleon target. The azimuthal asymmetry in this case is attributed to the fact that in a transversely polarized nucleon, the transverse charge density is no longer axially symmetric and is distorted due to the transverse spin of the nucleon. This asymmetry in the nucleon charge density causes a left-right asymmetry in the azimuthal distribution of the scattered electrons. In our approach, …
We study the azimuthal asymmetries for quark pair production in proton-nucleus collisions using a hybrid approach in which the nucleus is treated in the Color Glass Condensate (CGC) framework while the Lipatov approximation is applied on the proton side. Our treatment goes beyond the large N_c limit. We particularly focus on the so-called correlation limit where the imbalance of the transverse momentum of the quark pair is much smaller than the out-going individual quark transverse momenta. In this kinematic region, a matching between the hybrid approach and a factorization in terms of transve…
