arXiv subjects

Zhun Lu

Publications and source records attributed to Zhun Lu.

At least 91 records · Page 5Linked to original sources

arXiv2012

T-odd quark-gluon-quark correlation function in the diquark model

We study the transverse momentum dependent quark-gluon-quark correlation function. Using a spectator diquark model, we calculate the eight time-reversal-odd interaction-dependent twist-3 quark distributions appearing in the decomposition of the transverse momentum dependent quark-gluon-quark correlator. In order to obtain finite results, we assume a dipole form factor for the nucleon-quark-diquark coupling, instead of a point-like coupling. The results are compared with the time-reversal-odd interaction-independent twist-3 TMDs calculated in the same model.

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arXiv2011

Transverse momentum dependent twist-three result for polarized Drell-Yan processes

We study the polarized Drell-Yan processes from the collision of two spin-1/2 hadrons at order 1/Q based on the framework of transverse momentum dependent factorization.We give the complete twist-three results of total sixteen independent structure functions in terms of twist-two and twist-three transverse momentum dependent distribution functions.

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arXiv2011

The $\cos2ϕ$ azimuthal asymmetry of unpolarized dilepton production at the $Z$-pole

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, and therefore it is measurable. The experimental confirmation of this sign change of the asymmetry from the low $Q^2$ region to the $Z$-pole provides direct evidence of the chiral odd structure of quarks inside an unpolarized nucleon.

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arXiv2011

Azimuthal asymmetries in single polarized proton-proton Drell-Yan processes

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 provide valuable information of the chiral-odd structure of the nucleon both in the valence and sea regions.

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arXiv2011

The $\sin2ϕ$ azimuthal asymmetry in single longitudinally polarized $πN$ Drell-Yan process

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 only give the information on the new 3-dimensional parton distribution functions in momentum space, but also shed light on the chiral-odd structure of the longitudinally polarized nucleon.

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arXiv2011

Single spin asymmetry in $πp$ Drell-Yan process

We study the single spin asymmetries for the $πp^\uparrow\rightarrowμ^+μ^-X$ process. We consider the asymmetries contributed by the coupling of the Boer-Mulders function with the transversity distribution and the pretzelosity distribution, characterized by the $\sin(ϕ+ϕ_S)$ and $\sin(3ϕ-ϕ_S)$ azimuthal angular dependence, respectively. We estimate the magnitude of these asymmetries at COMPASS by using proper weighting functions. We find that the $\sin(ϕ+ϕ_S)$ asymmetry is of the size of a few percent and can be measured through the experiment. The $\sin(3ϕ-ϕ_S)$ asymmetry is smaller than the $\sin(ϕ+ϕ_S)$ asymmetry. After a cut on $q_T$, we succeed in enhancing the asymmetry.

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arXiv2010

Orbital structure of quarks inside the nucleon in the light-cone diquark model

We study the orbital angular momentum structure of the quarks inside the proton. By employing the light-cone diquark model and the overlap representation formalism, we calculate the chiral-even generalized parton distribution functions (GPDs) $H_q(x,ξ,Δ^2)$, $\widetilde{H}_q(x,ξ,Δ^2)$ and $E_q(x,ξ,Δ^2)$ at zero skewedness for $q=u$ and $d$ quarks. In our model $E_u$ and $E_d$ have opposite sign with similar size. Those GPDs are applied to calculate the orbital angular momentum (OAM) distributions, showing that $L_u(x)$ is positive, while $L_d(x)$ is consistent with zero compared with $L_u(x)$. We introduce the impact parameter dependence of the quark OAM distribution. It describes the position space distribution of the quark orbital angular momentum at given $x$. We found that the impact parameter dependence of the quark OAM distribution is axially symmetric in the light-cone diquark model.

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arXiv2010

Updating Boer-Mulders functions from unpolarized pd and pp Drell-Yan data

We extract the Boer-Mulders functions for the proton by combining the unpolarized pd and pp Drell-Yan data measured by the E866/NuSea Collaboration by the assumption that the $\cos 2ϕ$ asymmetry is from the Boer-Mulders function. Using the extracted Boer-Mulders functions, we present the predictions for the $\cos 2 ϕ$ asymmetries in future pp experiments at J-PARC and $p \bar{p}$ experiments at PANDA and PAX.

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arXiv2009

Comparing AdS/CFT Calculations to HERA F_2 Data

We show that HERA data for the inclusive structure function F_2(x,Q^2) at small Bjorken-x and Q^2 can be reasonably well described by a color-dipole model with an AdS/CFT-inspired dipole-proton cross section. The model contains only three free parameters fitted to data. In our AdS/CFT-based parameterization the saturation scale varies in the range of 1-3 GeV becoming independent of energy/Bjorken-x at very small x. This leads to the prediction of x-independence of the F_2 and F_L structure functions at very small x. We provide predictions for F_2 and F_L in the kinematic regions of future experiments. We discuss the limitations of our approach and its applicability region, and argue that our AdS/CFT-based model of non-perturbative physics could be viewed as complimentary to the perturbative description of data based on saturation/Color Glass Condensate physics.

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arXiv2009

Lepton Number Violating Processes Mediated by Majorana Neutrinos at Hadron Colliders

We study the Lepton number violating like-sign dilepton processes $h_1 h_2 \to l^\pm l^{\prime \pm} jj X$ and $h_1 h_2 \to l^\pm l^{\prime \pm} W^\pm X$, mediated by heavy GeV scale Majorana neutrinos. We focus on the resonantly enhanced contributions with a nearly on-mass-shell Majorana neutrino in the s-channel. We study the constraints on like-sign dilepton production at the Tevatron and the LHC on the basis of the existing experimental limits on the masses of heavy neutrinos and their mixings $U_{αN}$ with $α= ν_{e}, ν_μ, ν_τ$. Special attention is paid to the constraints from neutrinoless double beta decay. We note that searches for like-sign $e^{\pm} e^{\pm}$ events at Tevatron and LHC may shed light on CP-violation in neutrino sector. We also discuss the conditions under which it is possible to extract individual constraints on the mixing matrix elements in a model independent way.

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arXiv2009

Cronin effect for protons and pions in pA collisions

Pions and protons production cross-sections are analyzed in proton-proton and proton-nucleus collisions at the RHIC energy at midrapidity. We employ the pQCD factorization scheme supplemented with the color-dipole formalism to investigate the Cronin effect. We calculate the broadening in the color-dipole approach for different centralities. Our main goal is to investigate, in a parameter-free manner within a unified framework, how much of the cronin effect for both pions and baryons comes from the transverse momentum broadening due to initial partons multi-scatterings. We conclude that final-state effects in pA collisions are important. Uncertainties in nuclear shadowing of various parton distributions and parton fragmentation functions are also discussed.

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arXiv2008

Azimuthal angle dependence of di-jet production in unpolarized hadron scattering

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 is a color factor enhancement in the gluonic cross-section, compared with the result from the standard generalized parton model. We estimate the $\cos δϕ$ asymmetry of di-jet production at RHIC, showing that the color factor enhancement in the angular dependent of $J_q+J_q$ production will reverse the sign of the asymmetry.

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arXiv2008

$\cos 2 ϕ$ asymmetries in unpolarized semi-inclusive DIS

We use the Boer-Mulders functions parameterized from unpolarized $p+D$ Drell-Yan data by the FNAL E866/NuSea Collaboration combined with recently extracted Collins functions to calculate the $\cos 2 ϕ$ asymmetries in unpolarized semi-inclusive deeply inelastic scattering (SIDIS) processes both for ZEUS at Hadron Electron Ring Accelerator (HERA) and Jefferson Lab experiments (JLab), and to compare our results with their data. We also give predictions for the $\cos 2 ϕ$ asymmetries of SIDIS in the kinematical regime of HERMES Collaboration, and the forthcoming JLab experiments. We predict that the $\cos 2 ϕ$ asymmetries of semi-inclusive $π^-$ production are somewhat larger than that of $π^+$ production. We suggest to measure these two processes separately, which will provide more detail information on the Boer-Mulders functions as well as on the Collins functions.

hep-ph↗

arXiv2008

Extracting Boer-Mulders functions from $p+D$ Drell-Yan processes

We extract the Boer-Mulders functions of valence and sea quarks in the proton from unpolarized $p+D$ Drell-Yan data measured by the FNAL E866 Collaboration. Using these Boer-Mulders functions, we calculate the $\cos 2 ϕ$ asymmetries in unpolarized $pp$ Drell-Yan processes, both for the FNAL E866/NuSea and the BNL Relativistic Heavy Ion Collider (RHIC) experiments. We also estimate the $\cos 2 ϕ$ asymmetries in the unpolarized $p\bar{p}$ Drell-Yan processes at GSI.

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arXiv2007

Double transverse spin asymmetry in the $p^\uparrow\bar{p}^\uparrow$ Drell-Yan process from Sivers functions

We show that the transverse double spin asymmetry (DSA) in the Drell-Yan process contributed only from the Sivers functions can be picked out by the weighting function $\frac{Q_T}{M^2}(\cos(ϕ-ϕ_{S_1})\cos(ϕ-ϕ_{S_2})+3\sin(ϕ-ϕ_{S_1})\sin(ϕ-ϕ_{S_2}))$. The asymmetry is proportional to the product of two Sivers functions from each hadron $f_{1T}^{\perp(1)}\times f_{1T}^{\perp (1)}$. Using two sets of Sivers functions extracted from the semi-inclusive deeply elastic scattering data at HERMES, we estimate this asymmetry in the $p^\uparrow\bar{p}^\uparrow$ Drell-Yan process which is possible to be performed in HESR at GSI. The prediction of DSA in the Drell-Yan process contributed by the function $g_{1T}(x,\Vec k_T^2)$, which can be extracted by the weighting function $\frac{Q_T}{M^2}(3\cos(ϕ-ϕ_{S_1})\cos(ϕ-ϕ_{S_2})+\sin(ϕ-ϕ_{S_1})\sin(ϕ-ϕ_{S_2}))$, is also given at GSI.

hep-ph↗

arXiv2007

Flavor separation of the Boer-Mulders function from unpolarized $π^- p$ and $π^- D$ Drell-Yan processes

We show that measuring the $\cos 2ϕ$ angular dependence in unpolarized Drell-Yan processes with $π^-$ beams colliding on proton and deuteron targets can determine the ratio of the Boer-Mulders functions for $d$ and $u$ quarks inside the proton $h_1^{\perp,d}/h_1^{\perp,u}$, which is still lack of theoretical constraint. The comparison of the $\cos 2 ϕ$ asymmetries measured in unpolarized $π^- p$ and $π^- D$ Drell-Yan processes, which are accessible at CERN by the COMPASS collaboration, can help to discriminate whether $h_1^\perp$ effects or QCD vacuum effects are preferred by data.

hep-ph↗

arXiv2007

Transverse spin effects of sea quarks in unpolarized nucleons

We calculate the non-zero Boer-Mulders functions of sea quarks inside the proton in a meson-baryon fluctuation model. The results show that the transverse spin effects of sea quarks in an unpolarized nucleon are sizable. Using the obtained antiquark Boer-Mulders functions, we estimate the $\cos 2 ϕ$ asymmetries in the unpolarized $pp$ and $p D$ Drell-Yan processes at FNAL E866/NuSea experiments. The prediction for the $\cos 2 ϕ$ asymmetries in the unpolarized $pp$ Drell-Yan process at the BNL Relativistic Heavy Ion Collider (RHIC) is also given.

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arXiv2006

The cos 2 phi asymmetry of Drell-Yan and J/psi production in unpolarized ppbar scattering

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 processes may offer an experimentally viable access to the Boer-Mulders function in the early unpolarized stage of GSI experiments.

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