Thu·Feb 11, 2021Thursday·February 11, 2021

1. 01*

   Study of the $\eta$ to ${\pi }^0$ Ratio in Heavy-Ion Collisions

   Yuanjie Ren🇺🇸 · Axel Drees🇺🇸

   We demonstrate that the $p_T$ dependence of the $\eta /{\pi }^0$ ratio is universal within a few percent for high energy $p$+$p$, $p$+A and $d$+A collisions, over a broad range of collision energies. The $\eta /{\pi }^0$ ratio increases with $p_T$ up to 4 to 5 GeV/$c$ where it saturates at a nearly constant value of 0.487$\pm$0.024. Above $p_T=5$ GeV/$c$ the same constant value is also observed in A+A collisions independent of collision system, energy, and centrality. At lower $p_T$, where accurate $\eta /{\pi }^0$ data is absent for A+A collisions, we estimate possible deviations from the universal behavior, which could arise due to the rapid radial hydrodynamic expansion of the A+A collision system. For A+A collisions at RHIC we find that possible deviations are limited to the $p_T$ range from 0.4 to 3 GeV/$c$, and remain less than 20% for the most central collisions.

   nucl-exPRC(2021)·14 citations
2. 02*

   The effect of hadronic scatterings on the measurement of vector meson spin alignments in heavy-ion collisions

   Diyu Shen🇨🇳 · Jinhui Chen🇨🇳 · Zi-Wei Lin🇺🇸

   Spin alignments of vector mesons and hyperons in relativistic heavy-ion collisions have been proposed as signals of the global polarization. The STAR experiment first observed the $\mathrm{\Lambda }$ polarization. Recently, the ALICE collaboration measured the transverse momentum ($p_T$) and the collision centrality dependence of $K^{\ast }$ and $\varphi$ spin alignments in Pb-Pb collisions at $\sqrt{{\mathrm{s}}_{\mathrm{NN}}}$ = 2.76 TeV. A large signal is observed in the low $p_T$ region of mid-central collisions for $K^{\ast }$ while the signal is much smaller for $\varphi$, and these have not been understood yet. Since vector mesons have different lifetimes and their decay products have different scattering cross sections, they suffer from different hadronic effects. In this paper, we study the effect of hadronic interactions on the spin alignment of $K^{\ast }$, $\varphi$ and $\rho$ mesons in relativistic heavy-ion collisions with a multi-phase transport model. We find that hadronic scatterings lead to a deviation of the observed spin alignment matrix element ${\rho }_{00}$ away from the true value for $\rho$ and $K^{\ast }$ mesons (with a bigger effect on $\rho$) while the effect is negligible for the $\varphi$ meson. The effect depends on the kinematic acceptance: the observed ${\rho }_{00}$ value is lower than the true value when the pseudorapidity ($\eta$) coverage is small while there is little effect when the $\eta$ coverage is big. Our study thus provides valuable information to understand the vector meson spin alignment signals observed in the experiments.

   nucl-exnucl-thCPC(2021)·15 citations
3. 03*

   Non-flow effects in correlation between harmonic flow and transverse momentum in nuclear collisions

   Chunjian Zhang🇺🇸 · Arabinda Behera🇺🇸 · Somadutta Bhatta🇺🇸 · Jiangyong Jia🇺🇸

   A large anti-correlation signal between elliptic flow $v_2$ and average transverse momentum $[p_{\mathrm{T}}]$ was recently measured in small collision systems, consistent with a final-state hydrodynamic response to the initial geometry. This negative $v_2$-$[p_{\mathrm{T}}]$ correlation was predicted to change to positive correlation for events with very small charged particle multiplicity $N_{\mathrm{ch}}$ due to initial-state momentum anisotropies of the gluon saturation effects. However, the role of non-flow correlations is expected to be important in these systems, which is not yet studied. We estimate the non-flow effects in $pp$, $p$Pb and peripheral PbPb collisions using {\tt Pythia} and {\tt Hijing} models, and compare them with the experimental data. We show that the non-flow effects are largely suppressed using the rapidity-separated subevent cumulant method (details of the cumulant framework are also provided). The magnitude of the residual non-flow is much less than the experimental observation in the higher $N_{\mathrm{ch}}$ region, supporting the final-state response interpretation. In the very low $N_{\mathrm{ch}}$ region, however, the sign and magnitude of the residual non-flow depend on the model details. Therefore, it is unclear at this moment whether the sign change of $v_2$-$[p_{\mathrm{T}}]$ can serve as evidence for initial state momentum anisotropies predicted by the gluon saturation.

   ↳ nucl-thhep-phnucl-exPLB(2021)·27 citations
4. 04*

   Constraints on the Symmetry Energy from PREX-II in the Multimessenger Era

   Tong-Gang Yue🇨🇳 · Lie-Wen Chen🇨🇳 · Zhen Zhang🇨🇳 · Ying Zhou🇨🇳

   The neutron skin thickness $\Delta r_{\mathrm{np}}$ of heavy nuclei is essentially determined by the symmetry energy density slope $L(\rho )$ at ${\rho }_c=0.11{\mathrm{fm}}^{-3}\approx 2/3{\rho }_0$ (${\rho }_0$ is nuclear saturation density), roughly corresponding to the average density of finite nuclei. The PREX collaboration recently reported a model-independent extraction of $\Delta r_{\mathrm{np}}^{208}=0.283\pm 0.071$ fm for the $\Delta r_{\mathrm{np}}$ of ${}^{208}$Pb, suggesting a rather stiff symmetry energy $E_{\mathrm{sym}}(\rho )$ with $L({\rho }_c)\ge 52$ MeV. We show that the $E_{\mathrm{sym}}(\rho )$ cannot be too stiff and $L({\rho }_c)\le 73$ MeV is necessary to be compatible with (1) the ground-state properties and giant monopole resonances of finite nuclei, (2) the constraints on the equation of state of symmetric nuclear matter at suprasaturation densities from flow data in heavy-ion collisions, (3) the largest neutron star (NS) mass reported so far for PSR J0740+6620, (4) the NS tidal deformability extracted from gravitational wave signal GW170817 and (5) the mass-radius of PSR J0030+045 measured simultaneously by NICER. This allows us to obtain $52\le L({\rho }_c)\le 73$ MeV and $0.212\le \Delta r_{\mathrm{np}}^{208}\le 0.271$ fm, and further $E_{\mathrm{sym}}({\rho }_0)=34.3\pm 1.7$ MeV, $L({\rho }_0)=83.1\pm 24.7$ MeV, and $E_{\mathrm{sym}}(2{\rho }_0)=62.8\pm 15.9$ MeV. A number of critical implications on nuclear physics and astrophysics are discussed.

   ↳ nucl-thastro-ph.HEhep-phnucl-exPRResearch(2022)·75 citations
5. 05*

   Baryonic matter and the medium modification of the baryon masses

   Nam-Yong Ghim🇰🇷 · Ghil-Seok Yang🇰🇷 · Hyun-Chul Kim🇰🇷 · Ulugbek Yakhshiev🇰🇷

   We investigate the properties of baryonic matter within the framework of the in-medium modified chiral soliton model by taking into account the effects of surrounding baryonic environment on the properties of in-medium baryons. The internal parameters of the model are determined based on nuclear phenomenology at nonstrange sector and fitted by reproducing nuclear matter properties near the saturation point. We discuss the equations of state in different nuclear environments such as symmetric nuclear matter, neutron and strange matters. We show that the results for the equations of state are in good agreement with the phenomenology of nuclear matter. We also discuss how the SU(3) baryons masses undergo changes in these various types of nuclear matter.

   ↳ nucl-thastro-ph.HEhep-phnucl-exPRC(2021)·5 citations
6. 06*

   Can the nature of $a_0(980)$ be tested in the $D_s^{+}\to {\pi }^{+}{\pi }^0\eta$ decay?

   Xi-Zhe Ling🇨🇳 · Ming-Zhu Liu🇨🇳 · Jun-Xu Lu🇨🇳 · Li-Sheng Geng🇨🇳 · Ju-Jun Xie🇨🇳

   From the amplitude analysis of the $D_s^{+}\to {\pi }^{+}{\pi }^0\eta$ decay, the BESIII Collaboration firstly observed the $D_s^{+}\to a_0(980{)}^{+}{\pi }^0$ and $D_s^{+}\to a_0(980{)}^0{\pi }^{+}$ decay modes, which are expected to occur through the pure $W$-annihilation processes. The measured branching fraction $\mathcal{B}[D_s^{+}\to a_0(980{)}^{+(0)}{\pi }^{0(+)},a_0(980{)}^{+(0)}\to {\pi }^{+(0)}\eta ]$ is, however, found to be larger than those of known $W$-annihilation decays by one order of magnitude. This apparent contradiction can be reconciled if the two decays are induced by internal $W$-conversion or external $W$-emission mechanisms instead of $W$-annihilation mechanism. In this work, we propose that the $D_s^{+}$ decay proceeds via both the external and internal $W$-emission instead of $W$-annihilation mechanisms. In such a scenario, we perform a study of the $D_s^{+}\to {\pi }^{+}{\pi }^0\eta$ decay by taking into account the contributions from the tree diagram $D_s^{+}\to {\rho }^{+}\eta \to {\pi }^{+}{\pi }^0\eta$ and the intermediate ${\rho }^{+}\eta$ and $K^{\ast }\bar{K}/K{\bar{K}}^{\ast }$ triangle diagrams. The intermediate $a_0(980)$ state can be dynamically generated from the final state interactions of coupled $K\bar{K}$ and $\pi \eta$ channels, and it is shown that the experimental data can be described fairly well, which supports the interpretation of $a_0(980)$ as a molecular state.

   ↳ hep-phhep-exnucl-exnucl-thPRD(2021)·37 citations
7. 07*

   Transverse $\Lambda$ Polarization in $e^{+}{e}^{-}$ collisions

   Leonard Gamberg🇺🇸 · Zhong-Bo Kang🇺🇸 · Ding Yu Shao🇺🇸 · John Terry🇺🇸 · Fanyi Zhao🇺🇸

   In this paper we study transverse polarization of $\Lambda$ hyperons in single-inclusive leptonic annihilation. We show that when the transverse momentum of the $\Lambda$ baryon is measured with respect to the thrust axis, a transverse momentum dependent (TMD) factorization formalism is required and the polarization is generated by the TMD polarizing fragmentation function (TMD PFF), $D_{1T}^{\perp }$. However, when the transverse momentum of the $\Lambda$ baryon is measured with respect to the momentum of the initial leptons, a collinear twist-3 formalism is required and the polarization is generated by the intrinsic collinear twist-3 fragmentation function $D_T$. Thus while these measurements differ from one another only by a change in the measurement axis, they probe different distribution functions. Recently, Belle measured a significant polarization in single-inclusive $\Lambda$ baryon production as a function of the transverse momentum with respect to the thrust axis. However, this data can in principle be re-analyzed to measure the polarization as a function of the transverse momentum of the $\Lambda$ baryon with respect to the lepton pair. This observable could be the first significant probe of the function, $D_T$. In this paper, we first develop a TMD formalism for $\Lambda$ polarization; we then present a recent twist-3 formalism that was established to describe $\Lambda$ polarization. Using the TMD formalism, we demonstrate that the $\Lambda$ polarization at OPAL and Belle can be described using the twist-2 TMD factorization formalism. Finally, we make a theoretical prediction for this polarization in the collinear twist-3 formalism at Belle.

   ↳ hep-phhep-exnucl-exnucl-thPLB(2021)·31 citations
8. 08*

   Theoretical Study of Isotope Production in The Peripheral Heavy-ion Collision 136Xe + Pb at 1 GeV/nucleon

   H. Imal🇹🇷 · R. Ogul🇹🇷

   We have studied the fragment yields emitted from the fragmentation of excited projectile nuclei in peripheral collisions of 136Xe+Pb at 1 GeV/nucleon, and measured with the high-resolution magnetic spectrometer, the Fragment Separator (FRS) of GSI. The mass, charge and isotope distributions of nuclear fragments formed in the reactions were calculated within a statistical ensemble approach and compared to the experimental data. The ensemble of excited projectilelike source nuclei were created in the framework of a previous analysis of similar reactions performed at 600 MeV/nucleon (ALADIN-experiments, GSI). In addition, the ensemble of the low-excited compound nuclei is involved in the analysis. The overall agreement between theory and experiment was very satisfactory in reproducing the experimental data of isotope yields measured in the heavy-ion collisions. It is confirmed that a broad range of elements can be reproduced within a universal statistical disintegration of the excited projectile residues.

   ↳ nucl-thnucl-exNPA(2021)·5 citations

* Reconstructed cohort: no mailing for this day survives in the archive. Papers are grouped by their submission times and arXiv's announcement cut-off, assuming announcement without delay; positions follow identifier order. Validated at ~91% exact-day agreement against the archived era.