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Z. G. Xiao

Publications and source records attributed to Z. G. Xiao.

32 records · Page 2Linked to original sources
arXiv2014

Influence of $ϕ$ mesons on negative kaons in Ni+Ni collisions at 1.91A GeV beam energy

$ϕ$ and K$^-$ mesons from Ni+Ni collisions at the beam energy of 1.91A GeV have been measured by the FOPI spectrometer, with a trigger selecting central and semi-central events amounting to 51% of the total cross section. The phase space distributions, and the total yield of K$^-$, as well as the kinetic energy distribution and the total yield of $ϕ$ mesons are presented. The $ϕ$\K$^-$ ratio is found to be $0.44 \pm 0.07(\text{stat}) ^{+0.18}_{-0.12} (\text{syst})$, meaning that about 22% of K$^-$ mesons originate from the decays of $ϕ$ mesons, occurring mostly in vacuum. The inverse slopes of direct kaons are up to about 15 MeV larger than the ones extracted within the one-source model, signalling that a considerable share of gap between the slopes of K$^+$ and K$^-$ could be explained by the contribution of $ϕ$ mesons to negative kaons.

nucl-ex↗
arXiv2014

Azimuthal Emission Patterns of $K^{+}$ and of $ K^{-} $ Mesons in Ni + Ni Collisions near the Strangeness Production Threshold

Azimuthal emission patterns of $K^\pm$ mesons have been measured in Ni + Ni collisions with the FOPI spectrometer at a beam kinetic energy of 1.91 A GeV. The transverse momentum $p_{T}$ integrated directed and elliptic flow of $K^{+}$ and $K^{-}$ mesons as well as the centrality dependence of $p_{T}$ - differential directed flow of $K^{+}$ mesons are compared to the predictions of HSD and IQMD transport models. The data exhibits different propagation patterns of $K^{+}$ and $K^{-}$ mesons in the compressed and heated nuclear medium and favor the existence of a kaon-nucleon in-medium potential, repulsive for $K^{+}$ mesons and attractive for $K^{-}$ mesons.

nucl-ex↗
arXiv2011

Systematics of azimuthal asymmetries in heavy ion collisions in the 1 A GeV regime

Using the large acceptance apparatus FOPI, we study central and semi-central collisions in the reactions (energies in A GeV are given in parentheses): 40Ca+40Ca (0.4, 0.6, 0.8, 1.0, 1.5, 1.93), 58Ni+58Ni (0.15, 0.25, 0.4), 96Ru+96Ru (0.4, 1.0, 1.5), 96Zr+96Zr (0.4, 1.0, 1.5), 129Xe+CsI (0.15, 0.25, 0.4), 197Au+197Au (0.09, 0.12, 0.15, 0.25, 0.4, 0.6, 0.8, 1.0, 1.2, 1.5). The observables include directed and elliptic flow. The data are compared to earlier data where possible and to transport model simulations. A stiff nuclear equation of state is found to be incompatible with the data. Evidence for extra-repulsion of neutrons in compressed asymmetric matter is found.

nucl-ex↗
arXiv2011

Transverse Spin Structure of the Nucleon through Target Single Spin Asymmetry in Semi-Inclusive Deep-Inelastic $(e,e^\prime π^\pm)$ Reaction at Jefferson Lab

Jefferson Lab (JLab) 12 GeV energy upgrade provides a golden opportunity to perform precision studies of the transverse spin and transverse-momentum-dependent structure in the valence quark region for both the proton and the neutron. In this paper, we focus our discussion on a recently approved experiment on the neutron as an example of the precision studies planned at JLab. The new experiment will perform precision measurements of target Single Spin Asymmetries (SSA) from semi-inclusive electro-production of charged pions from a 40-cm long transversely polarized $^3$He target in Deep-Inelastic-Scattering kinematics using 11 and 8.8 GeV electron beams. This new coincidence experiment in Hall A will employ a newly proposed solenoid spectrometer (SoLID). The large acceptance spectrometer and the high polarized luminosity will provide precise 4-D ($x$, $z$, $P_T$ and $Q^2$) data on the Collins, Sivers, and pretzelocity asymmetries for the neutron through the azimuthal angular dependence. The full 2$π$ azimuthal angular coverage in the lab is essential in controlling the systematic uncertainties. The results from this experiment, when combined with the proton Collins asymmetry measurement and the Collins fragmentation function determined from the e$^+$e$^-$ collision data, will allow for a quark flavor separation in order to achieve a determination of the tensor charge of the d quark to a 10% accuracy. The extracted Sivers and pretzelocity asymmetries will provide important information to understand the correlations between the quark orbital angular momentum and the nucleon spin and between the quark spin and nucleon spin.

hep-ph↗
arXiv2010

Systematics of central heavy ion collisions in the 1A GeV regime

Using the large acceptance apparatus FOPI, we study central collisions in the reactions (energies in A GeV are given in parentheses): 40Ca+40Ca (0.4, 0.6, 0.8, 1.0, 1.5, 1.93), 58Ni+58Ni (0.15, 0.25, 0.4), 96Ru+96Ru (0.4, 1.0, 1.5), 96Zr+96Zr (0.4, 1.0, 1.5), 129Xe+CsI (0.15, 0.25, 0.4), 197Au+197Au (0.09, 0.12, 0.15, 0.25, 0.4, 0.6, 0.8, 1.0, 1.2, 1.5). The observables include cluster multiplicities, longitudinal and transverse rapidity distributions and stopping, and radial flow. The data are compared to earlier data where possible and to transport model simulations.

nucl-ex↗
arXiv2009

Measurement of the in-medium K0 inclusive cross section in pi- -induced reactions at 1.15 GeV/c

The K0 meson production by pi- mesons of 1.15 GeV/c momentum on C, Al, Cu, Sn and Pb nuclear targets was measured with the FOPI spectrometer at the SIS accelerator of GSI. Inclusive production cross-sections and the momentum distributions of K0 mesons are compared to scaled elementary production cross-sections and to predictions of theoretical models describing the in-medium production of kaons. The data represent a new reference for those models, which are widely used for interpretation of the strangeness-production in heavy-ion collisions. The presented results demonstrate the sensitivity of the kaon production to the reaction amplitudes inside nuclei and point to the existence of a repulsive KN-potential of 20+-5 MeV at normal nuclear matter density.

nucl-ex↗
arXiv2005

Model dependent analyses on the $N_c$ dependence of the $σ$ pole trajectory

We explore the nature of the$σ$ or $f_0(600)$ meson using large $N_c$ technique, assuming that the $σ$ pole dominates low energy physics in the IJ=00 channel. We trace the $N_c$ dependence of the $σ$ pole position using [1,1] Padé approximation of SU(3) chiral amplitude, [1,2] Padé approximation of SU(2) chiral amplitudes, and the PKU parametrization form. We find that in all 3 cases the $σ$ pole moves to the real axis of the complex $s$-plane. Finally we construct a pedagogical example using the SU(2) Padé amplitude to show that when the analyticity property of the scattering amplitude is violated, it is possible that the $σ$ pole resides on the complex $s$ plane when $N_c$ is large.

hep-ph↗
arXiv2005

Analyticity and the $N_c$ counting rule of $S$ matrix poles

By studying $ππ$ scattering amplitudes in the large $N_c$ limit, we clarify the $N_c$ dependence of the $S$ matrix pole position. It is demonstrated that analyticity and the $N_c$ counting rule exclude the existence of $S$ matrix poles with ${\cal M}, Γ\sim O(1)$. Especially the properties of $σ$ and $f_0(980)$ with respect to the $1/N_c$ expansion are discussed. We point out that in general tetra-quark resonances do not exist.

hep-ph↗
arXiv2005

The pole structure of the unitary, crossing symmetric low energy $ππ$ scattering amplitudes

The pole structure of the low energy $ππ$ scattering amplitudes is studied using a proper chiral unitarization method combined with crossing symmetry and the low energy phase shift data. It is found that the $σ$ pole position is at $M_σ=470\pm 50MeV$, $Γ_σ=570\pm 50MeV$. The existence of the virtual state pole in the IJ=20 channel is reconfirmed. Various threshold parameters are estimated and are found in general in good agreement with the results obtained from the Roy equation analyses.

hep-ph↗
arXiv2004

On the nature of the lightest scalar resonances

We briefly review the recent progresses in the new unitarization approach being developed by us. Especially we discuss the large $N_c$ $ππ$ scatterings by making use of the partial wave $S$ matrix parametrization form. We find that the $σ$ pole may move to the negative real axis on the second sheet of the complex $s$ plane, therefore it raises the interesting question that this `$σ$' pole may be related to the $σ$ in the linear $σ$ model.

hep-ph↗
arXiv2003

The $κ$ resonance in s wave $πK$ scatterings

A new unitarization approach incorporated with chiral symmetry is established and applied to study the $πK$ elastic scatterings. We demonstrate that the $κ$ resonance exists, if the scattering length parameter in the I=1/2, J=0 channel does not deviate much from its value predicted by chiral perturbation theory. The mass and width of the $κ$ resonance is found to be $M_κ=594\pm 79MeV$, $Γ_κ=724\pm 332MeV$, obtained by fitting the LASS data up to 1430MeV. Better determination to the pole parameters is possible if the chiral predictions on scattering lengths are taken into account.

hep-ph↗
arXiv2003

The properties of the $σ$ and $κ$ resonances in a new unitarization approach

A new unitarization approach is discussed and applied to study the elastic $πK$ scattering process. The existence of the light $κ$ resonance is firmly established if the scattering length in the I=1/2 channel does not deviate too much from its value obtained from chiral perturbation theory, and a precise determination to the mass and width of the $κ$ resonance requires a precise determination of the scattering length parameter.

hep-ph↗
arXiv2002

The Constraints of Unitary on $ππ$ Scattering Dispersion Relations

A new dispersion relation for the partial wave $ππ$ scattering $S$ matrix is set up. Using the dispersion relation we generalize the single channel unitarity condition, $SS^+=1$, to the entire complex $s$ plane, which is equivalent to the generalized unitarity condition in quantum mechanics. The pole positions of the $σ$ resonance and the $f_0(980)$ resonance are estimated based on the theoretical relations we obtained. The central value of the $σ$ pole position is $M_σ\simeq 410$MeV, $Γ_σ\simeq 550$MeV, obtained after including the the constraint of the Adler zero condition.

hep-ph↗