arXiv subjects

Zhun Lu

Publications and source records attributed to Zhun Lu.

At least 73 records · Page 4Linked to original sources

arXiv2017

Transverse polarization of the $Λ$ hyperon from unpolarized quark fragmentation in the diquark model

We investigate the spin-dependent (naive) T-odd fragmentation function $D^\perp_{1T}$, which can provide an explanation on the transverse polarization of the $Λ^0$ hyperon produced in an unpolarized process. We calculate $D^\perp_{1T}$ for light flavors in the spectator diquark model, with a Gaussian form factor at the hyperon-quark-diquark vertex. We include in the calculation both the scalar diquark and axial-vector diquark spectators. We determine the values of the model parameters by fitting the unpolarized fragmentation function $D^Λ_1$ to the DSV parametrization for $D^Λ_1$. In addition, we compute the longitudinal polarization fragmentation function $G^Λ_1$ and compare it with the known parametrization of $G^Λ_1$. We also estimate the transverse polarizations of $Λ$ production, in both semi-inclusive deep inelastic scattering and single inclusive $e^+e^-$ annihilation.

hep-ph↗

arXiv2017

Boer-Mulders function of pion meson and $q_T$-weighted $\cos2ϕ$ asymmetry in the unpolarized $π^- p$ Drell-Yan at COMPASS

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 measured at COMPASS in the near future.

hep-ph↗

arXiv2017

Polarized Lambda hyperon production in Semi-inclusive deep inelastic scattering off an unpolarized nulceon target

We study the production of polarized $Λ$ hyperon in semi-inclusive deep inelastic scattering off an unpolarized target. We include the cases in which the $Λ$ hyperon is longitudinally polarized or transversely polarized, and in which the lepton beam is unpolarized or longitudinally polarized. Within the framework of the transverse momentum dependent factorization, we take into account the complete decomposition of the parton correlator for fragmentation up to twist-3. We present the cross section of the process to order $1/Q$. The expressions of the polarized structure functions, which may give rise to various spin asymmetries, are also given.

hep-ph↗

arXiv2016

Gluon Sivers function in a light-cone spectator model

We calculate the gluon Sivers function of the proton in the valence-$x$ region using a light-cone spectator model with the presence of the gluon degree of freedom. We obtain the values of the parameters by fitting the model resulting gluon density distribution to the known parametrization. We find that our results agree with the recent phenomenological extraction of the gluon Sivers function after considering the evolution effect. We also estimate the mean transverse momentum of the gluon in a transversely polarized proton and find that it is within the range implied by the Burkardt sum rule.

hep-ph↗

arXiv2016

Double-spin asymmetry $A^{\cosϕ_S}_{LT}$ in semi-inclusive DIS at CLAS12 and EIC within the collinear framework

We study the longitudinal-transverse double-spin asymmetry with a $\cosϕ_S$ modulation in semi-inclusive deep inelastic scattering for charged and neutral pions production. We consider the particular case in which the transverse momentum of the final state hadron is integrated out. The corresponding asymmetry may be contributed by two parts: one is the convolution of the twist-3 distribution function $g_{T}(x)$ and the unpolarized fragmentation function $D_1(z)$, the other is related to the coupling of the transversity distribution function $h_1(x)$ and the collinear twist-3 fragmentation function $\tilde{E}(z)$. We take into account both contributions to predict the $\cosϕ_S$ asymmetry at the kinematics of CLAS12 and a future Electron Ion Collider. We find that the asymmetry of pion production at CLAS12 is sizable, and $\tilde{E}(z)$ can play an important role in the asymmetry in the large-$z$ region.

hep-ph↗

arXiv2016

Twist-3 T-odd fragmentation functions $G^\perp$ and $\tilde{G}^\perp$ in a spectator model

We present a calculation of the twist-3 T-odd chiral-even fragmentation functions $G^{\perp}$ and $\tilde{G}^{\perp}$ using a spectator model. We consider the effect gluon exchange to calculate all necessary one-loop diagrams for the quark-quark and quark-gluon-quark correlation functions. We find that the gluon loops corrections generate non-zero contribution to these two fragmentation function. We numerically calculate their half-$k_T$ moments by integrating over the transverse momentum and also verify the equation of motion relation among $G^{\perp}$, $\tilde{G}^{\perp}$ and the Collins function.

hep-ph↗

arXiv2016

Predicting the $\sinϕ_S$ Transverse Single-spin Asymmetry of Pion Production at an Electron Ion Collider

We study the transverse single-spin asymmetry with a $\sinϕ_S$ modulation in semi-inclusive deep inelastic scattering. Particularly, we consider the case in which the transverse momentum of the final state hadron is integrated out. Thus, the asymmetry is merely contributed by the coupling of the transversity distribution function $h_1(x)$ and the twist-3 collinear fragmentation function $\tilde{H}(z)$. Using the available parametrization of $h_1(x)$ from SIDIS data and the recent extracted result for $\tilde{H}(z)$, we predict the $\sinϕ_S$ asymmetry for charged and neutral pion production at an Electron Ion Collider. We find that the asymmetry is sizable and could be measured. We also study the impact of the leading-order QCD evolution effect and find that it affects the $\sinϕ_S$ asymmetry at EIC considerably.

hep-ph↗

arXiv2016

Twist-3 fragmentation functions in a spectator model with gluon rescattering

We study the twist-3 fragmentation functions $H$ and $\tilde{H}$, by applying a spectator model. In the calculation we consider the effect of the gluon rescattering at one loop level. We find that in this case the hard-vertex diagram, which gives zero contribution to the Collins function, does contribute to the fragmentation function $H$. The calculation shows that the twist-3 T-odd fragmentation functions are free of light-cone divergences. The parameters of the model are fitted from the known parametrization of the unpolarized fragmentation $D_1$ and the Collins function $H_1^\perp$. We find our result for the favored fragmentation function is consistent with the recent extraction on $H$ and $\tilde{H}$ from pp data. We also check numerically the equation of motion relation for $H$, $\tilde{H}$ and find that relation holds fairly well in the spectator model.

hep-ph↗

arXiv2015

Double Spin Asymmetries $A_{LT}^{\cosϕ_S}$ and $A_{LT}^{\cos(2ϕ_h -ϕ_S)}$ in semi-inclusive DIS

We investigate the double spin asymmetries of pion production in semi-inclusive deep inelastic scattering with a longitudinal polarized beam off a transversely polarized proton target. Particularly, we consider the $\cosϕ_S$ and $\cos(2ϕ_h -ϕ_S)$ modulations, which can be interpreted by the convolution of the twist-3 transverse momentum dependent distributions and twist-2 fragmentation functions. Three different origins are taken into account simultaneously for each asymmetry: the $g_T D_1$ term, the $e_T H_1^\perp$ term, and the $e_T^\perp H_1^\perp$ term in the $\cosϕ_S$ asymmetry; and the $g_T^\perp D_1$ term, the $e_T H_1^\perp$ term, and the $e_T^\perp H_1^\perp$ term in the $\cos(2ϕ_h -ϕ_S)$ asymmetry. We calculate the four twist-3 distributions $g_T(x,\boldsymbol{k}_T^2)$, $g_T^\perp(x,\boldsymbol{k}_T^2)$, $e_T(x,\boldsymbol{k}_T^2)$, and $e_T^\perp(x,\boldsymbol{k}_T^2)$ in a spectator-diquark model including vector diquarks. Then we predict the two corresponding asymmetries for charged and neutral pions at the kinematics of HERMES, JLab, and COMPASS for the first time. The numerical estimates indicate that the two different angular-dependence asymmetries are sizable by several percent at HERMES and JLab, and the $\cosϕ_S$ asymmetry has a strong dependence on the Bjorken $x$. Our predictions also show that the dominant contribution to the $\cosϕ_S$ asymmetry comes from the $g_T D_1$ term, while the $g_T^\perp D_1$ term gives the main contribution to the $\cos(2ϕ_h -ϕ_S)$ asymmetry; the other two $T$-odd terms almost give negligible contributions. In particular, the $\cos(2ϕ_h -ϕ_S)$ asymmetry provides a unique opportunity to probe the distribution $g_T^\perp$.

hep-ph↗

arXiv2015

A phenomenological study on the $\cosϕ_h$ azimuthal asymmetry in double longitudinally Polarized SIDIS

We study the $\cos{ϕ_h}$ azimuthal asymmetry in double polarized semi-inclusive pion production by considering dynamical twist-3 effects. In particular, we evaluate the role of the transverse momentum dependent distributions $e_L(x, k_T^2)$ and $g_L^\perp(x, k_T^2)$ on the asymmetry. Using two different sets of spectator model results for these distributions, we predict the $\cos{ϕ_h}$ asymmetry of $π^+$, $π^-$, and $π^0$ at the kinematic configuration available at CLAS, HERMES and COMPASS. Our estimates show that the asymmetries are positive for all the pions and could be accessed by CLAS and HERMES. We also find that $g_L^\perp$ gives the dominant contribution to the $\cosϕ_h$ asymmetry, while the contribution of $e_L$ is almost negligible.

hep-ph↗

arXiv2014

Transverse single-spin asymmetries of pion production in semi-inclusive DIS at subleading twist

We study the single-spin asymmetries with the $\sinϕ_S$ and $\sin(2ϕ_h -ϕ_S)$ angular dependences for charged and neutral pions produced in semi-inclusive deep inelastic scattering on the transversely polarized proton target. The theoretical interpretations of the two asymmetries are presented in terms of the convolution of the twist-3 quark transverse momentum dependent distributions and twist-2 fragmentation functions. Specifically, we investigate the role of the distributions $f_T$, $h_T$ and $h_T^\perp$ in the $\sinϕ_S$ asymmetry, as well as the role of the distributions $f_T^\perp$, $h_T$ and $h_T^\perp$ in the $\sin(2ϕ_h -ϕ_S)$ asymmetry. We calculate these distributions in a spectator-diquark model and predict the corresponding asymmetries for the first time, considering the kinematics at HERMES, JLab and COMPASS. The numerical estimates show that the asymmetries are sizable, and the dominant contribution to the $\sinϕ_S$ asymmetry comes from the T-odd distribution $f_T$, while $f_T^\perp$ gives the main contribution to the $\sin(2ϕ_h -ϕ_S)$ asymmetry. The future measurements on these asymmetries can shed light on the information of twist-3 transverse momentum dependent distributions.

hep-ph↗

arXiv2014

Single-spin asymmetries in electroproduction of pions on the longitudinally polarized nucleon targets

We study the single-spin asymmetries of pions produced in semi-inclusive deep-inelastic scattering on the longitudinally polarized nucleon targets. We particularly consider the effects of the twist-3 transverse-momentum dependent distribution functions $f_L^\perp$ and $h_L$ to the asymmetry. We calculate the asymmetric moment $A_{UL}^{\sinϕ_h}$ for $π^+$, $π^-$ and $π^0$ produced off the proton target at HERMES and compare the results with the HERMES data. We also present the prediction of the same asymmetries for different pions at the kinematics of CLAS 5.5 GeV on a proton target, as well as at COMPASS on a deuteron target.

hep-ph↗

arXiv2014

On the beam spin asymmetries of electroproduction of charged hadrons off the nucleon targets

We study the beam single-spin asymmetries $A_{LU}^{\sinϕ_h}$ for charged hadrons produced in semi-inclusive deep inelastic scattering process, by considering the $e H_1^\perp$ term and the $g^\perp D_1$ term simultaneously. Besides the asymmetries for charged pions, for the first time we present the analysis on the asymmetries in the production of charged kaons, protons and antiprotons by longitudinally polarized leptons scattered off unpolarized proton and deuteron targets. In our calculation we use two sets of transverse momentum dependent distributions $g^\perp(x,\bm k_T^2)$ and $e(x,\bm k_T^2)$ calculated from two different spectator models, and compare the numerical results with the preliminary data recently obtained by the HERMES Collaboration. We also predict the beam spin asymmetries for $π^\pm$, $K^\pm$, $p/\bar{p}$ electroproduction in semi-inclusive deep-inelastic scattering of 12 GeV polarized electrons from unpolarized proton and deuteron targets.

hep-ph↗

arXiv2013

Inflation in the Generalized Inverse Power Law Scenario

We propose a single field inflationary model by generalizing the inverse power law potential from the intermediate model. We study the implication of our model on the primordial anisotropy of cosmological microwave background radiation. Specifically, we apply the slow-roll approximation to calculate the scalar spectral tilt $n_s$ and the tensor-to-scalar ratio $r$. The results are compared with the recent data measured by the Planck satellite. We found that by choosing proper values for the parameters, our model can well describe the Planck data.

hep-th↗

arXiv2013

Beam Spin Asymmetries of Charged and Neutral Pion Productions in Semi-inclusive DIS

We present a study on the beam single spin asymmetries $A_{LU}^{\sinϕ_h}$ of $π^+$, $π^-$ and $π^0$ production in semi-inclusive deep inelastic scattering process, by considering Collins effect and the $g^\perp D_1$ term simultaneously. We calculate the twist-3 distributions $e(x, \bm k_T^2)$ and $g^\perp(x,\bm k_T^2)$ for the valence quarks inside the proton in a spectator model. We consider two different options for the form of diquark propagator, as well as two different choices for the model parameters in the calculation. Using the model results, we estimate the beam spin asymmetries $A_{LU}^{\sinϕ_h}$ for the charged and neutral pions and compare the results with the measurement from the HERMES Collaboration. We also make predictions on the asymmetries at CLAS with a $5.5 \,\textrm{GeV}$ beam using the same model results. It is found that different choices for the diquark propagator will not only lead to different expressions for the distribution functions, but also result in different sizes of the asymmetries. Our study also shows that, although the spectator model calculation can describe the asymmetries for certain pion production in some kinematic regions, it seems difficult to explain the asymmetries of pion production for all three pions in a consistent way from the current versions.

hep-ph↗

arXiv2013

Quark helicity distributions in transverse momentum space and transverse coordinate space

The transverse momentum dependent helicity distributions of valence quarks are calculated in the light-cone diquark model by adopting two different approaches. We use the model results to analyze the $P_{h\perp}$-dependent double spin asymmetries for $π^+$, $π^-$ and $π^0$ productions in semi-inclusive deep inelastic scattering, and find that the asymmetries agree with the CLAS data in one of the approaches. By taking the Fourier transform of the transverse momentum dependent helicity distributions, we obtain the helicity distributions of valence quarks in the transverse coordinate space, and then apply them further to predict the Bessel-weighted double spin asymmetries of $π^+$, $π^-$ and $π^0$ productions in semi-inclusive deep inelastic scattering at CLAS, COMPASS and HERMES for the first time. The shape of the Bessel-weighted double spin asymmetry thereby provides a direct probe on the transverse structure of longitudinally polarized quarks.

hep-ph↗

arXiv2013

Beam single spin asymmetry of neutral pion production in semi-inclusive deep inelastic scattering

We study the beam spin asymmetry $A_{LU}^{\sinϕ_h}$ in semi-inclusive $π^0$ electroproduction contributed by the T-odd twist-3 distribution function $g^\perp(x,k_T^2)$. We calculate this transverse momentum dependent distribution function for the $u$ and $d$ quarks inside the proton in a spectator model including the scalar and the axial-vector diquark components. Using the model results, we estimate the asymmetry $A_{LU}^{\sinϕ_h}$ in the $e p \rightarrow e^\prime π^0 X$ process in which the lepton beam is longitudinally polarized. The model prediction is compared with the data measured by the CLAS and the HERMES Collaborations and it is found that our numerical results agree with experimental data reasonably. Especially, our results can well describe the CLAS data at the region where the Bjorken $x$ and the pion transverse momentum is not large. We also make a prediction on the asymmetry $A_{LU}^{\sinϕ_h}$ in a $π^0$ electroproduction at CLAS12 using the same model calculation.

hep-ph↗

arXiv2012

Boer-Mulders function of the pion in the MIT bag model

We apply the MIT bag model to study the Boer-Mulders function of the pion, a $T$-odd function that describes the transverse polarization distribution of the quark inside the pion. We simulate the effect of the gauge link through the "one-gluon-exchange" approximation. We consider both the quark helicity nonflip and double-flip contributions. The result in the MIT bag model is compared with those in the spectator models.

hep-ph↗