arXiv subjects

Bijun Fan

Publications and source records attributed to Bijun Fan.

4 recordsLinked to original sources

arXiv2026

Effects of femtoscopic correlations on spin-spin correlation measurements

Hyperon spin correlations serve as sensitive probes of spin dynamics in high-energy collisions, yet their extraction from weak-decay angular distributions can be contaminated by femtoscopic effects due to quantum statistics and final-state interactions. In this work, we quantitatively assess this contamination for $\Lambda\Lambda$ and $\Lambda\bar{\Lambda}$ pairs using the AMPT model combined with spin-dependent weights from the Lednick\'y--Lyuboshits formalism. Because the singlet and triplet spin configurations contribute differently to the decay-angle distribution, femtoscopic weighting induces an apparent angular modulation, creating a fake correlation signal even when no intrinsic spin correlation is present. We find that the induced bias can become substantial in the low-$q_{\mathrm{inv}}$ region, where the combined femtoscopic effect reaches a magnitude comparable to that of the preliminary CMS measurements. Our results establish a framework for evaluating such systematics, highlighting that femtoscopic corrections must be carefully considered in future differential analyses that emphasize the low-relative-momentum region.

nucl-th↗

arXiv2026

Improved Pion-Kaon Identification in Heavy-Ion Collisions with a Two-Dimensional Transformation

Accurate identification of charged pions and kaons is essential for precision measurements in relativistic heavy-ion collisions, but becomes increasingly challenging at intermediate and high transverse momentum due to the overlap between time-of-flight mass-square ($m^{2}$) and ionization energy loss ($n\sigma$) distributions. In this work, we present a two-dimensional shift and rotation method that exploits the correlated information between $m^{2}$ and $n\sigma$ to enhance particle identification performance. The method is validated using Au+Au collision events generated with the AMPT model, where detector response effects are incorporated through a data-driven smearing procedure tuned to reproduce the particle identification performance of the STAR experiment. The reconstructed pion and kaon transverse momentum distributions show excellent agreement with the AMPT input, maintaining a purity exceeding 98\% at high $p_T$ and extend the reliable identification range up to $p_T \approx$ 3 GeV/$c$. The extracted elliptic flow $v_2$ remains consistent with the input over the extended $p_T$ range, demonstrating that the proposed method provides a robust framework for high precision identified hadron measurements.

physics.ins-det↗

arXiv2026

Open charm production and $\Lambda_{c}^{+}/D^{0}$ ratio in pp and Au+Au collisions at the RHIC

We study open charm hadrons production in pp and Au+Au collisions at $\sqrt{s_{\mathrm{NN}}} = 200$~GeV using an improved a multi-phase transport (AMPT) model. Specifically, we show the transverse-momentum spectra and nuclear modification factors $R_{\mathrm{AA}}$ of $D^{0}$ mesons and $\Lambda_{c}^{+}$ baryons, as well as the $\Lambda_{c}^{+}/D^{0}$ ratio in pp and Au+Au collisions. The results obtained from the AMPT model simulations are compared with the STAR experimental data and found to be consistent. We further investigate the $\Lambda_{c}^{+}/D^{0}$ ratio by evaluating contributions from coalescence, fragmentation, and the combined coalescence+fragmentation mechanisms, and we find that fragmentation alone underestimates the pronounced enhancement in Au+Au relative to pp at low and intermediate $p_{\mathrm{T}}$, whereas the coalescence+fragmentation mechanism reproduces the observed trend significantly better. These results indicate that coalescence plays a key role in charm baryon productions and helps constrain the relative importance of different hadronization mechanisms in the ultra-relativistic nuclear collisions.

hep-ph↗

arXiv2026

Measurements of Kaon Femtoscopy in Au+Au Collisions at $\sqrt{s_{NN}}$ = 3.0-4.5 GeV by the STAR Experiment

In these proceedings, we present the measurements of charged $K^{+} - K^{+}$ and neutral $K_{s}^{0} - K_{s}^{0}$ correlation functions from Au+Au fixed-target collisions at $\sqrt{s_{NN}}$ = 3.0, 3.2, 3.5, 3.9 and 4.5 GeV at STAR. This is the first such systematic measurement of correlation functions involving strangeness in the high baryon density region. The source size values do not exhibit a clear energy dependence, and the transverse mass dependence of source size for kaons does not align with the trend observed for pions. Parameters extracted from UrQMD transport model calculations qualitatively capture the measured values.

nucl-ex↗