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Register a new userImproved quark coalescence model for spin alignments of vector mesons
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Xin-Li Sheng
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We propose an improved quark coalescence model for spin alignment of vector mesons by spin density matrix with phase space dependence. Within this model we propose an understanding of spin alignments of vector mesons $phi$ and $K^{*0}$ in the static limit: a large positive deviation of $rho_{00}$ for $phi$ mesons from $1/3$ may come from the electric part of the vector $phi$ field, while a negative deviation of $rho_{00}$ for $K^{*0}$ mesons may come from the electric part of vorticity fields. In the low-$p_T$ region, $rho_{00}$ for $K^{*0}$ mesons is proportional to $p_T^2$, which is qualitatively agree with experimental results.
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The string melting version of a multi-phase transport model is often applied to high-energy heavy-ion collisions since the dense matter thus formed is expected to be in parton degrees of freedom. In this work we improve its quark coalescence component, which describes the hadronization of the partonic matter to a hadronic matter. We removed the previous constraint that forced the numbers of mesons, baryons, and antibaryons in an event to be separately conserved through the quark coalescence process. A quark now could form either a meson or a baryon depending on the distance to its coalescence partner(s). We then compare results from the improved model with the experimental data on hadron $dN/dy$, $p_{_{rm T}}$ spectra, and $v_2$ in heavy-ion collisions from $sqrt{s_{_{rm NN}}}=62.4$ GeV to $5.02$ TeV. We show that, besides being able to describe these observables for low-$p_{_{rm T}}$ pions and kaons, the improved model also better describes the low-$p_{_{rm T}}$ baryon observables in general, especially the baryon $p_{_{rm T}}$ spectra and antibaryon-to-baryon ratios for multistrange baryons.
We propose an improved quark coalescence model for spin alignment of vector mesons and polarization of baryons by spin density matrix with phase space dependence. The spin density matrix is defined through Wigner functions. Within the model we propose an understanding of spin alignments of vector mesons $phi$ and $K^{*0}$ (including $bar{K}^{*0}$) in the static limit: a large positive deviation of $rho_{00}$ for $phi$ mesons from 1/3 may come from the electric part of the vector $phi$ field, while a negative deviation of $rho_{00}$ for $K^{*0}$ may come from the electric part of vorticity tensor fields. Such a negative contribution to $rho_{00}$ for $K^{*0}$ mesons, in comparison with the same contribution to $rho_{00}$ for $phi$ mesons which is less important, is amplified by a factor of the mass ratio of strange to light quark times the ratio of $leftlangle mathbf{p}_{b}^{2}rightrangle $ on the wave function of $K^{*0}$ to $phi$ ($mathbf{p}_{b}$ is the relative momentum of two constituent quarks of $K^{*0}$ and $phi$). These results should be tested by a detailed and comprehensive simulation of vorticity tensor fields and vector meson fields in heavy ion collisions.
We discuss the phenomenology of the axial-vector mesons within a three-flavour Linear Sigma Model containing scalar, pseudoscalar, vector and axial-vector degrees of freedom.
In this work the neutral meson properties have been investigated in the presence of thermo-magnetic background using two-flavor Nambu--Jona-Lasinio model. Mass, spectral function and dispersion relations are obtained in the scalar ($sigma$) and pseudo-scalar ($pi^0$) channels as well as in the vector ($rho^0$) and axial vector ($a^0_1$) channels. The general Lorentz structures for the vector and axial-vector meson polarization functions have been considered in detail. The ultra-violet divergences appearing in this work have been regularized using a mixed regularization technique where the gamma functions arising in dimensional regularization are replaced with incomplete gamma functions as usually done in the proper time regularization procedure. The meson spectral functions obtained in the presence of a magnetic field possess nontrivial oscillatory structure. Similar to the scalar and pseudo-scalar channel, the spectral functions for each of the modes of $rho^0$ are observed to overlap with the corresponding modes of its chiral partner $a_1^0$ mesons in the chiral symmetry restored phase. We observe discontinuities in the masses of all the mesonic excitations for a non-zero external magnetic field.
The measured electromagnetic form factors of $Lambda$ hyperon in the time-like region are significantly deviated from pQCD prediction. We attribute the non-vanishing cross section near threshold to be the contribution of below-threshold $phi$(2170) state, supporting its exotic structure. Above the threshold, we find significant role of a wide vector meson with the mass of around 2.34 GeV, which would be the same state present in $pbar{p}$ annihilation reactions. As a result, we give a satisfactory description of the behavior of existing data without modifying pQCD expectation.
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