Wen-Chen Chang, Dipangkar Dutta
The Drell-Yan process is an invaluable tool for probing the structure of hadrons, and the pion-induced Drell-Yan process is unique in its sensitivity to several subtleties of the partonic structure. This is a brief review of the pionic Drell-Yan process with particular emphasis on the dilepton angular distributions and nuclear modification of the parton distributions (the EMC effect).
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To investigate the high mass dilepton production cross section produced due to the Drell-Yan process in hadronic collisions such as nucleon- nucleus, the valence and sea quarks distribution functions inside nucleus is used. In this study, in the framework of the shell and Fermi gas models, by adding quarks distribution functions of pions inside nucleus besides the quarks distribution functions of bound nucleons, the changes in the dilepton production cross section were investigated. For this reason, pionic contribution in the structure function of 63Cunucleus and its EMC ratio was first studie…
Pion-induced Drell-Yan processes are proposed as a potential tool to measure the flavor dependence of the EMC effect, that is, the flavor-dependent modification of quark distributions in the nuclear medium. Existing pionic Drell-Yan data are compared with calculations using a recent model for nuclear quark distributions that incorporates flavor-dependent nuclear effects. While no firm conclusions can yet be drawn, we demonstrate that existing Drell-Yan data seem to imply a flavor dependence of the EMC effect. We highlight how pion-induced Drell-Yan experiments on nuclear targets can access imp…
The Drell-Yan massive lepton-pair production in hadronic collisions provides a unique tool complementary to the Deep-Inelastic Scattering for probing the partonic substructures in hadrons. We review key concepts, approximations, and progress for QCD factorization of the Drell-Yan process in terms of collinear or transverse momentum dependent (TMD) parton distribution functions. We present experimental results from recent fixed-target Drell-Yan as well as $W$ and $Z$ boson production at colliders, focussing on the topics of flavor structure of the nucleon sea as well as the extraction of novel …
We study the Drell-Yan production cross section and structure functions in proton (deuteron)-nucleus collisions using the Color Glass Condensate formalism. The nucleus is treated in the Color Glass Condensate framework which includes both higher twist effects due to the inclusion of multiple scatterings and leading twist pQCD shadowing due to the small x resummation, while the proton (or deuteron) is treated within the DGLAP improved parton model. In particular, the Drell-Yan structure functions are used in order to investigate the Lam-Tung relation at small x, which is known to be identically…
We calculate nuclear effect in Drell-Yan massive lepton-pair production in terms of parton multiple scattering in Quantum Chromodynamics (QCD). We present the nuclear modification to inclusive Drell-Yan cross section $dσ/dQ^2$ in terms of multiparton correlation functions. By extracting the size of the correlation functions from measured Drell-Yan transverse momentum broadening in nuclear medium, we determine the nuclear modification at $O(α_s/Q^2)$. We find that the nuclear modification strongly enhances the inclusive Drell-Yan cross section in the intermediate mass region (IMR): $1.5 < Q < 2…
We study the azimuthal asymmetries in proton-proton Drell-Yan processes with one incident proton being transversely or longitudinally polarized. We consider particularly the asymmetries contributed by the leading-twist chiral-odd quark distributions. We analyze the asymmetries with $\sin(2ϕ+ϕ_S)$ and $\sin(2ϕ-ϕ_S)$ modulations in transverse single polarized $p^\uparrow p$ Drell-Yan and $\sin2ϕ$ asymmetries in longitudinal single polarized $p^\rightarrow p$ Drell-Yan at RHIC, J-PARC, E906 (Fermi Lab) and NICA (JINR). We show that the measurements of the asymmetries in those facilities can provi…
We study the $\sin2ϕ$ azimuthal asymmetry in the $πN$ Drell-Yan process, when the nucleon is longitudinally polarized. The asymmetry is contributed by the combination of the Boer-Mulders function and the longitudinal transversity distribution function. We consider the Drell-Yan processes by $π^\pm$ beams colliding on the proton and deuteron targets, respectively. We calculate the $\sin2ϕ$ azimuthal asymmetries in these processes using the Boer-Mulders function and the longitudinal transversity from spectator models. We show that the study on single polarized $πN$ Drell-Yan processes can not on…
We predict the triple differential cross section of the unpolarized Drell-Yan process at sqrt(S)=6 GeV. The model incorporates primordial parton transverse momentum and quark off-shellness effects caused by the initial state interaction.
We propose a flavor asymmetry in the light quark sea of $Σ^{\pm}$, which can be measured in Drell-Yan experiments using charged hyperon beams on proton and deuteron targets. Such a measurement would help to reinforce the presence of pseudoscalar mesons in a quark model of baryons.
In terms of multiple scattering picture, I compute the nuclear dependence in Drell-Yan transverse momentum distribution, $dσ/ dQ^2 dq_T^2$, in hadron-nucleus collisions. I present the results for large $q_T$ region and discuss the possible suppression in small $q_T$ region.
The effects of parton energy loss in nuclear matter on the Drell-Yan process in pA and $π$A collisions at fixed-target energies are investigated. Calculations are based on the Baier-Dokshitzer-Mueller-Peigné-Schiff (BDMPS) framework embedded in a next-to-leading order calculation, using the transport coefficient extracted from $J/ψ$ measurements. Model calculations prove in good agreement with preliminary measurements by the E906 experiment, despite a slightly different magnitude, supporting a consistent picture between Drell-Yan and $J/ψ$ data. Predictions for the COMPASS future measurements …
We investigate how Drell-Yan processes can be used to measure the magnitude of flavor symmetry violation in the proton sea. We examine the utility of the following beams: protons, charged pions, and charged kaons. In each case we present an approximate expression for the Drell-Yan asymmetry. Using currently available parton distributions, we locate those kinematic regions which provide the greatest information on the quantity $\bar{d}^p(x) - \bar{u}^p(x)$. If sufficiently intense $K^+$ beams were available, they could provide an efficient measurement of this quantity. Finally we present and di…
We calculate the Drell-Yan cross section, resolving the full kinematics of the lepton pair, at high transverse momentum for hadron nucleus collisions. We use the general framework of Luo, Qiu and Sterman to calculate double scattering contributions that are of twist-4 and demonstrate their nuclear enhancement. By comparing single and double scattering at RHIC energies we find that double scattering gives contributions of comparable size. We also show that the angular dependence of the Drell-Yan pair discriminates between the various double scattering contributions.
We show that the polarized proton-antiproton Drell-Yan process is ideal to probe the pretzelosity distribution ($h_{1T}^\perp$), which is one of the new transverse-momentum-dependent parton distributions of the nucleon. We present predictions of the $\cos(2ϕ+ ϕ_a - ϕ_b)$ asymmetry in the transversely polarized proton-antiproton Drell-Yan process at PAX kinematics and find that the results are significantly larger compared with those of the $\sin(3ϕ_h - ϕ_S)$ asymmetry in the semi-inclusive deep inelastic scattering process at HERMES, COMPASS, and JLab kinematics. We conclude that the $\cos(2ϕ+…
Test for universality of short-range correlations in pion-induced Drell-Yan Process
针对π介子诱导Drell-Yan过程，研究采用核与π介子部分子分布函数计算核-自由核子微分截面比，提出普适修正函数以检验短程关联普适性，深化对核结构与强相互作用的理解。
By measuring Drell-Yan massive lepton-pair's angular distributions, we can identify the polarization of the virtual photon of invariant mass $Q$ which decays immediately into the lepton-pair. In terms of a modified QCD factorization formula for Drell-Yan process, which is valid even if $Q_T\gg Q$, we calculate the massive lepton-pair's angular distributions at large $Q_T$. We find that the virtual photons produced at high $Q_T$ are more likely to be transversely polarized. We discuss the implications of this finding to the J/$ψ$ mesons' polarization measured recently at Fermilab.
We analyze $x_F$ dependence of Drell-Yan transverse momentum broadening in hadron-nucleus collisions. In terms of generalized factorization theorem, we show that the $x_F$ dependence of transverse momentum broadening, $ Δ< q_T^2 > (x_F) $, can be calculated in perturbative QCD. We demonstrate that $Δ< q_T^2 > (x_F)$ is a good observable for studying the effects of initial-state multiple scattering and extracting quark-gluon correlation functions.
Partonic interpretation of high-energy reactions is known to depend on a reference frame. Particularly, in the rest frame of the target Drell-Yan process looks like freeing of the projectile lepton-antilepton fluctuation, rather than q+qbar -> l+lbar annihilation. The light-cone representation for Drell-Yan reaction is very similar to that in DIS and exposes a substantial contamination of soft interactions, which turn out to be dominant in diffractive production of lepton pairs and in nuclear shadowing. We estimate the fraction of diffractive events in the total Drell-Yan cross section, which …
We calculate the nuclear enhancement in Drell-Yan transverse momentum distribution in hadron-nucleus collisions. In terms of multiple scattering picture, we compute the contributions from double scattering. Applying the generalized factorization theorem, we express the nuclear enhancement in terms of twist-4 nuclear parton correlation functions. We demonstrate that these twist-4 nuclear parton correlation functions are universal, and are the same as those used to explain the nuclear dependence in di-jet momentum imbalance and in direct photon production. Using the known information on the twis…
The Chiral Quark-Soliton model of the nucleon contains a mechanism for an attractive interaction between nucleons. This, along with the exchange of vector mesons between nucleons, is used to compute the saturation properties of infinite nuclear matter. This provides a new way to asses the effects of the nuclear medium on a nucleon that includes valence and sea quarks. We show that the model simultaneously describes the nuclear EMC effect and the related Drell-Yan experiments.
A study of secondary Drell-Yan production in nuclear collisions is presented for SPS energies. In addition to the lepton pairs produced in the initial collisions of the projectile and target nucleons, we consider the potentially high dilepton yield from hard valence antiquarks in produced mesons and antibaryons. We calculate the secondary Drell-Yan contributions taking the collision spectrum of hadrons from the microscopic model URQMD. The contributions from meson-baryon interactions, small in hadron-nucleus interactions, are found to be substantial in nucleus-nucleus collisions at low dilepto…
We have analyzed the data on $J/ψ$-to-Drell-Yan production cross section ratio in proton-nucleus ($p+A$) and nucleus-nucleus ($A+A$) collisions, measured by the NA50 collaboration in the SPS energy domain. Two component QVZ model has been employed to calculate $J/ψ$ production cross sections. For both $J/ψ$ and Drell-Yan production, nuclear modifications to the free nucleon structure functions are taken into account. In heavy-ion collisions, such modifications are assumed to be proportional to the local nuclear density resulting in centrality dependent initial state effects. Differences in qua…
We present a Glauber-based study of J/Psi and Drell-Yan yields in nucleus-nucleus collisions. Using this approach, we have investigated the impact of energy loss by the colliding nuclei on observed yields and transverse momentum spectra of J/Psi and Drell-Yan. These studies permit an assessment of the importance of initial state energy loss in relation to "anomalous" J/Psi suppression.
We discuss the possibility of finding polarized antiquark flavor asymmetry in Drell-Yan processes. We find that the difference between polarized proton-proton and proton-deuteron Drell-Yan cross sections should provide valuable information on the polarized flavor asymmetry. Numerical results indicate that the asymmetry effects are conspicuous especially in the large-x_F region. Our analysis is important for the transversity distributions because the flavor asymmetry cannot be found by inclusive lepton scattering and W-production processes.
Pionic gluons from global QCD analysis of experimental and lattice data
本研究首次结合实验与格点数据开展π介子部分子分布函数全局QCD分析，降低了大x区间胶子分布的不确定性，发现大x下π介子胶子密度高于质子、小x下存在相对压低。
The experimental discovery that the nucleus is approximately transparent to low energy pions is reviewed. The consequences of this for nuclear deep inelastic scattering and Drell-Yan interactions are discussed. I argue that low energy nucleus data imply that there is little nuclear enhancement of the pion cloud of a nucleon, and try to interpret this in terms of nucleon-nucleon correlations.
We study nuclear medium effects in Drell-Yan processes at small target x using quark parton distribution functions and nucleon structure functions for a bound nucleon calculated in a microscopic nuclear model which takes into account the effect of Fermi motion, nuclear binding and nucleon correlations through a relativistic spectral function. The contributions of $π$ and $ρ$ mesons, target mass corrections and nuclear shadowing are also included. The results are compared with the theoretical and experimental results. The model is able to successfully explain the low target x results of E772 an…
Generalizing a recent convolution model of the nucleon which explicitly conserves charge and momentum we reexamine the influence of an enhanced pion field in nuclei on EMC and Drell-Yan ratios. Due to wave function renormalization constants the effect is more than 50% smaller than predicted by the standard pion excess model. In particular there is no discrepancy between the EMC data and our results in the x-region which was expected to be most sensitive to the pion.
SU(3), baryon octets and a meson cloud model are compared for the flavor asymmetry of sea quarks in the $Σ^+$, as an example. Large differences are found, especially between SU(3) and the meson cloud model. We suggest Drell-Yan measurements of $Σ^{+}-p$ and $Σ^{+}- d$ to test the prediction of various models. We use the meson cloud model to predict both valence and sea quark distributions.
We investigate effects of nuclear medium on antiquark distribution in nuclei applying the results of a recently developed relativistically-covariant self-consistent model for the pion and the isobar. We take into account Fermi motion including Pauli blocking and binding effects on the nucleons and medium effects on the isobar and pion leading to modest enhancement of the pion light-cone-momentum distribution in large nuclei. As a consequence the Drell-Yan cross-section ratio with respect to the deuteron exceeds one only for small values of the light-cone momentum.
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