arXiv subjects

An Gu

Publications and source records attributed to An Gu.

4 recordsLinked to original sources

arXiv2026

Hyperon-Nucleon Spectrometer

Chirality lies at the heart of low-energy QCD, governing the symmetry structure that shapes hadron masses and strong interaction dynamics. Among the most compelling open questions tied to chiral dynamics and spontaneous chiral symmetry breaking is the longstanding $\Lambda$ polarization puzzle, in which $\Lambda$ hyperons produced in unpolarized hadronic collisions exhibit a surprisingly large transverse polarization that remains theoretically unexplained. This whitepaper presents the proposal for the Hyperon-Nucleon Spectrometer (H-NS) at the High-Intensity heavy-ion Accelerator Facility (HIAF). Leveraging the high energy and high intensity of HIAF's proton and heavy-ion beams, the H-NS experiment will perform systematic studies of hyperon polarization phenomena and their underlying mechanisms in proton-proton ($pp$), proton-nucleus ($pA$), and nucleus-nucleus ($AA$) collisions in the fixed target mode. A wide-range beam energy scan, including proton beams from 3 GeV up to 9.3 GeV (HIAF) and up to 32 GeV (upgraded HIAF), will be conducted to examine the dependence of polarization on collision energy. The spectrometer is designed with specialized detectors capable of high-precision reconstruction of final-state baryon polarizations. Among its many interesting and important measurements, H-NS will simultaneously measure hyperon and proton spin observables to explore the polarization mechanism in hadronic interactions and the spin structure of baryons. Furthermore, the use of $pA$ and $AA$ collisions will enable detailed investigations of cold and hot nuclear matter effects on spin polarization. Its physics program and detector development will significantly benefit the future Electron-ion Collider in China.

physics.ins-det↗

arXiv2023

Acceptance effect on the $N_{\rm t} N_{\rm p}/N_{\rm d}^2$ ratio of light nuclei coalescence yields as a probe of nucleon density fluctuations

We employ a coalescence model to form deuterons ($\rm d$), tritons (${\rm t}$) and helium-3 ($^3{\rm He}$) nuclei from a uniformly distributed volume of protons ({\rm p}) and neutrons ({\rm n}). We study the ratio $N_{\rm t} N_{\rm p}/N_{\rm d}^2$ of light nuclei yields as a function of the neutron density fluctuations. We investigate the effect of finite transverse momentum ($p_{\rm T}$) acceptance on the ratio, in particular, the "extrapolation factor" ($f$) for the ratio as functions of the $p_{\rm T}$ spectral shape and the magnitude of neutron density fluctuations. It is found that $f$ is monotonic in $p_{\rm T}$ spectra "temperature" parameter and neutron density fluctuation magnitude; variations in the latter are relatively small. We also examine $f$ in realistic simulations using kinematic distributions of protons measured in heavy ion collision data. It is found that $f$ is smooth and monotonic as a function of beam energy. We conclude that extrapolation from limited $p_{\rm T}$ ranges would not create, enhance, or reduce a local peak of the $N_{\rm t} N_{\rm p}/N_{\rm d}^2$ ratio in beam energy. Our study provides a necessary benchmark for light nuclei ratios as a probe of nucleon density fluctuations, an important observable in the search for the critical point of nuclear matter.

nucl-th↗

arXiv2023

Transverse momentum spectra of $f_0(980)$ from coalescence model

We use a coalescence model to generate $f_{0}$(980) particles for four configurations: ${s\bar{s}}$ meson, ${u\bar{u}s\bar{s}}$ tetraquark, ${K^{+}K^{-}}$ molecule and $u\bar{u}$ p-wave state. The phase-space information of the coalescing constituents is taken from a multi-phase transport (AMPT) simulation of proton-proton and proton-lead collisions at the LHC. It is shown that the transverse momentum spectra and production yields of $f_0(980)$ differ significantly among the configurations. It is suggested that the $p_T$ spectra of the $f_0(980)$ compared to those of other hadrons (such as pion) and the ratio of the $f_0(980)$ $p_T$ spectra in pPb over pp can be exploited to tell the configuration of the $f_0(980)$.

hep-ph↗

arXiv2019

Elliptical flow coalescence to identify the $f_{0}$(980) content

We use a simple coalescence model to generate $f_{0}$(980) particles for three configurations: a ${s\bar{s}}$ meson, a ${u\bar{u}s\bar{s}}$ tetraquark, and a ${K^{+}K^{-}}$ molecule. The phase-space information of the coalescing constituents is taken from a multi-phase transport (AMPT) simulation of heavy-ion collisions. It is shown that the number of constituent quarks scaling of the elliptic flow anisotropy can be used to discern ${s\bar{s}}$ from ${u\bar{u}s\bar{s}}$ and ${K^{+}K^{-}}$ configurations.

nucl-ex↗