arXiv subjects

Xiaozhi Bai

Publications and source records attributed to Xiaozhi Bai.

5 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↗

arXiv2025

ALICE highlights

The recent ALICE results on hard probes, focusing on open heavy flavor, quarkonia, and jet measurements in pp and Pb--Pb collisions are presented. During the LHC Run 3, the continuous readout of the upgraded Time Projection Chamber (TPC) with GEM technology, along with improved tracking from ITS2 and the newly installed Muon Forward Tracker (MFT), have enabled high-precision studies of quarkonia and heavy flavour production, and jet modification in the quark-gluon plasma (QGP). These new measurements provide crucial constraints on parton energy loss mechanisms and heavy-quark dynamics in hot QCD matter. Future upgrades planned for Run 4, as well as the long-term ALICE 3 with an all-silicon tracking system, will further enhance the ability to study the properties of QGP with unprecedented accuracy.

nucl-ex↗

arXiv2024

Flavor Physics at the CEPC: a General Perspective

We discuss the landscape of flavor physics at the Circular Electron-Positron Collider (CEPC), based on the nominal luminosity outlined in its Technical Design Report. The CEPC is designed to operate in multiple modes to address a variety of tasks. At the $Z$ pole, the expected production of 4 Tera $Z$ bosons will provide unique and highly precise measurements of $Z$ boson couplings, while the substantial number of boosted heavy-flavored quarks and leptons produced in clean $Z$ decays will facilitate investigations into their flavor physics with unprecedented precision. We investigate the prospects of measuring various physics benchmarks and discuss their implications for particle theories and phenomenological models. Our studies indicate that, with its highlighted advantages and anticipated excellent detector performance, the CEPC can explore beauty and $\tau$ physics in ways that are superior to or complementary with the Belle II and Large-Hadron-Collider-beauty experiments, potentially enabling the detection of new physics at energy scales of 10 TeV and above. This potential also extends to the observation of yet-to-be-discovered rare and exotic processes, as well as testing fundamental principles such as lepton flavor universality, lepton and baryon number conservation, etc., making the CEPC a vibrant platform for flavor physics research. The $WW$ threshold scan, Higgs-factory operation and top-pair productions of the CEPC further enhance its merits in this regard, especially for measuring the Cabibbo-Kobayashi-Maskawa matrix elements, and Flavor-Changing-Neutral-Current physics of Higgs boson and top quarks. We outline the requirements for detector performance and considerations for future development to achieve the anticipated scientific goals.

hep-ex↗

arXiv2024

Data-driven analysis of the beauty hadron production in p+p collisions at the LHC with Bayesian unfolding

Heavy flavour production in proton-proton (pp) collisions provides insights into the fundamental properties of Quantum Chromodynamics (QCD). Beauty hadron production measurements are widely performed through indirect approaches based on their inclusive decay modes. A Bayesian unfolding data-driven analysis of the ALICE and LHCb data was performed in this study, which recovers the full kinematic information of the beauty hadrons via different inclusive decay channels. The corresponding beauty hadron production cross sections obtained after the Bayesian unfolding are found to be consistent within their uncertainties. The weighted average open beauty production cross sections are presented as a function of the transverse momentum and rapidity in pp collisions at $\sqrt{s}$ = 5.02 TeV and $\sqrt{s}$ = 13 TeV, respectively. The $p_T$-integrated open beauty production $\mathrm{d}\sigma/\mathrm{d}y$ and the total $\mathrm{b}\rm\overline{b}$ cross section $\sigma_{\rm \mathrm{b}\rm\overline{b}}$ are also reported. The precision of these results significantly improves upon worldwide measurements, providing valuable validation and constraints on mechanisms of heavy flavour production in pp collisions at the LHC energies.

nucl-ex↗

arXiv2020

Quarkonium measurements in nucleus-nucleus collisions with ALICE

Heavy quarks are produced in the early stages of nucleus-nucleus collisions and can therefore provide important insight into the Quark-Gluon Plasma (QGP). Quarkonia are proposed as crucial probes to study the QGP. The extent of the medium modification for heavy-quark quarkonium production in heavy-ion collisions is measured in terms of a nuclear modification factor $R_{\rm AA}$, defined as the quarkonium yield in heavy-ion collisions divided by the relative quarkonium cross section in pp collisions scaled by the nuclear overlap function. A possible path-length dependent quarkonium dissociation, as well as a contribution of (re-)generation of quarkonia from heavy quarks in the medium, would lead to an azimuthal anisotropy of quarkonium production relative to the reaction plane. In this contribution, the recent ALICE measurements of quarkonium in Pb-Pb collisions at $\sqrt{s_{\rm NN}}$ = 5.02 TeV will be discussed for both mid- and forward rapidity. The dependence of $R_{\rm AA}$ on centrality and $p_{\rm T}$ for J/$\psi$, $\Upsilon$(1S), $\Upsilon$(2S), as well as the J/$\psi$ elliptic flow $v_{2}$ will be shown. The experimental data and the current theoretical model calculations will be also discussed.

hep-ex↗