arXiv subjects

Pengzhong Lu

Publications and source records attributed to Pengzhong Lu.

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 $Λ$ polarization puzzle, in which $Λ$ 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↗

arXiv2025

Quantification of the low-$p_{\rm T}$ pion excess in heavy-ion collisions at the LHC and top RHIC energy

While the abundances of the final state hadrons in relativistic heavy-ion collisions are rather well described by the thermal particle production, the shape of the transverse momentum, $p_{\rm T}$, distribution below $p_{\rm T}\approx500$ MeV$/c$, is still poorly understood. We propose a procedure to quantify the model-to-data differences using Bayesian inference techniques, which allows for consistent treatment of the experimental uncertainties and tests the completeness of the available hydrodynamic frameworks. Using relativistic fluid framework Fluid${\it u}$M with PCE coupled to \trento initial state and FastReso decays, we analyse \pt distribution of identified charged hadrons measured in heavy-ion collisions at top RHIC and the LHC energies, and identify an excess of pions produced below $p_{\rm T}\approx500$ MeV$/c$. Our results provide new input for the interpretation of the pion excess as either missing components in the thermal particle yield description or as an evidence for a different particle production mechanism.

hep-ph↗

arXiv2025

Probing Gluon Shadowing in Heavy Nuclei through Bayesian Reweighting of J/$ψ$ Photoproduction in Ultra-Peripheral Collisions

The gluon distribution in nuclei plays a pivotal role in understanding quantum chromodynamics (QCD) under extreme nuclear environments, yet remains poorly constrained compared to quark distributions. Coherent \jpsi photoproduction in ultra-peripheral heavy-ion collisions ($γ+ A \rightarrow \mathrm{J}/ψ+ A$) provides a unique solution to this challenge, serving as a sensitive probe of nuclear gluon densities. In this study, we perform Bayesian reweighting on the EPPS21 and nCTEQ15 sets of nuclear parton distribution functions (nPDF) by incorporating coherent \jpsi photoproduction measurements from both RHIC and LHC. The Bayesian-reweighted gluon modification factors $\mathrm{R_g^{A}}(x, Q^2 = 2.4\ \mathrm{GeV}^2)$ reveal pronounced nuclear shadowing in the Pb nuclei, with $\mathrm{R_g^{\mathrm{Pb}}} \approx 0.60$ at $x = 10^{-4}$, while simultaneously achieving a great reduction of the uncertainties in the density of the gluon across the critical Bjorken-$x$ range $10^{-5} < x < 10^{-3}$ compared to initial predictions of the nPDF. This work establishes coherent \jpsi photoproduction as a precision tool for gluon nPDF extraction, overcoming traditional deep-inelastic scattering limitations through perturbative QCD-calibrated probes. The constrained nPDFs demonstrate improved consistency with the experimental data across collider energies, particularly in the shadowing-dominated regime.

hep-ph↗

arXiv2021

Qualification tests of 997 8-inch photomultiplier tubes for the water Cherenkov detector array of the LHAASO experiment

The Large High-Altitude Air Shower Observatory (LHAASO) is being built at Haizi Mountain, Sichuan province of China at an altitude of 4410 meters. One of its main goals is to survey the northern sky for very-high-energy gamma ray sources via its ground-based water Cherenkov detector array (WCDA). 900 8-inch photomultiplier tubes (PMTs) CR365-02-1 from Beijing Hamamatsu Photon Techniques INC. (BHP) are installed in the WCDA, collecting Cherenkov photons produced by air shower particles crossing water. The design of the PMT base with a high dynamic range for CR365-02-1, the PMT batch test system, and the test results of 997 PMTs are presented in this paper.

physics.ins-det↗