We develop a framework for the formation of exotic muonic kaon atoms (μK) in semileptonic D^0 decays, using the effective weak Hamiltonian, a helicity-based treatment of the leptonic current, and a nonrelativistic bound-state projection. The resulting branching ratio, BR(D^0→(μK)ν_μ)=2.29×10^-10, is implemented in a ROOT-based code to estimate yields at RHIC, LHC, and STCF. We show quantitatively that μK atoms – also produced through coalescence in the quark-gluon plasma (QGP) – provide a sensitive probe of low-momentum primordial muons and early-time electromagnetic radiation, offering complementary constraints in an otherwise unexplored phase space for thermal dilepton and photon emission. Newly estimated dissociation cross sections in detector material indicate that secondary-vertex reconstruction should be experimentally feasible, allowing clean experimental identification of the atoms. Projected yields from QGP coalescence in LHC and RHIC heavy-ion collisions, and from D^0 decays in LHC high-luminosity p+p collisions indicate that the first observation of μK atoms is within reach.

In this paper, we review recent highlights in heavy-ion collisions and proton-proton collisions at top energies from STAR experiment at the Relativistic Heavy Ion Collider (RHIC) with key contributions from Chinese groups, including the Quark-Gluon Plasma (QGP) bulk properties, electromagnetic probes, heavy flavor and jets, antimatter hyper-nucleus, nuclear structure, global polarization, and nucleon spin structure. These data serve as important ingredients in the physics of Quantum Chromodynamics (QCD).

Electron–positron colliders operating in the GeV center-of-mass range, or tau-charm energy region, have been proved to enable competitive frontier research due to several unique features. With the progress of high-energy physics in the last two decades, a new-generation Tau-Charm factory, called the Super Tau-Charm Facility (STCF), has been actively promoted by the particle physics community in China. STCF has the potential to address fundamental questions such as the essence of color confinement and the matter–antimatter asymmetry within the next decades. The main design goals of the STCF are a center-of-mass energy ranging from 2 to 7 GeV and a luminosity surpassing 5 × 1034 cm−2 s−1 that is optimized at a center-of-mass energy of 4 GeV, which is approximately 50 times that of the currently operating Tau-Charm factory—BEPCII. The STCF accelerator has two main parts: a double-ring collider with a crab-waist collision scheme and an injector that provides top-up injections for both electron and positron beams. As a typical third-generation electron–positron circular collider, the STCF accelerator faces many challenges in both accelerator physics and technology. In this paper, the conceptual design of the STCF accelerator complex is presented, including the ongoing efforts and plans for technological research and development, as well as the required infrastructure. The STCF project aims to secure support from the Chinese central government for its construction during the 15th Five-Year Plan (2026–2030).

We report the collision energy dependence of the cross section of dielectrons from the Breit-Wheeler process in heavy-ion collisions computed by the lowest-order QED. It has been demonstrated that the experimental measurements of the Breit-Wheeler process in ultra-relativistic heavy-ion collisions can be used to quantitatively constrain the nuclear charge radius.

In the paper, we discuss the development of the multi-gap resistive plate chamber Time-of-Flight (TOF) technology and the production of the STAR TOF detector in China at the beginning of the 21st century. Then we review recent experimental results from the first beam energy scan program (BES-I) at the Relativistic Heavy Ion Collider (RHIC). Topics cover measurements of collectivity, chirality, criticality, global polarization, strangeness, heavy-flavor, di-lepton and light nuclei productions.

Angular distributions of charged particles relative to jet axes are studied in v sNN = 200 GeV Au+Au collisions as a function of the jet orientation with respect to the event plane. This differential study tests the expected path-length dependence of energy loss experienced by a hard-scattered parton as it traverses the hot and dense medium formed in heavy-ion collisions. A second-order event plane is used in the analysis as an experimental estimate of the reaction plane formed by the collision impact parameter and the beam direction. Charged-particle jets with 15 < p(T, jet) < 20 and 20 < p(T, jet) < 40 GeV/c were reconstructed with the anti-k(T) algorithm with radius parameter setting of R = 0.4 in the 20-50% centrality bin to maximize the initial-state eccentricity of the interaction region. The reaction plane fit method is implemented to remove the flow-modulated background with better precision than prior methods. Yields and widths of jet-associated charged-hadron distributions are extracted in three angular bins between the jet axis and the event plane. The event-plane (EP) dependence is further quantified by ratios of the associated yields in different EP bins. No dependence on orientation of the jet axis with respect to the event plane is seen within the uncertainties in the kinematic regime studied. This finding is consistent with a similar experimental observation by ALICE in root sNN = 2.76 TeV Pb-Pb collision data.

A study of prompt Xi(+)(c) production in proton-lead collisions is performed with the LHCb experiment at a centerof-mass energy per nucleon pair of 8.16 TeV in 2016 in pPb and Pbp collisions with an estimated integrated luminosity of approximately 12.5 and 17.4 nb(-1), respectively. The Xi(+)(c) roduction cross section, as well as the Xi(+)(c) to Lambda(+)(c) production cross-section ratio, are measured as a function of the transverse momentum and rapidity and compared to the latest theory predictions. The forward-backward asymmetry is also measured as a function of the Xi(+)(c) ransverse momentum. The results provide strong constraints on theoretical calculation and are a unique input for hadronization studies in different collision systems.

The longitudinal and transverse spin transfers to Lambda (Lambda) hyperons in polarized proton-proton collisions are expected to be sensitive to the helicity and transversity distributions, respectively, of (anti)strange quarks in the proton, and to the corresponding polarized fragmentation functions. We report improved measurements of the longitudinal spin transfer coefficient, D-LL, and the transverse spin transfer coefficient, D-TT,D- to Lambda and Lambda in polarized proton-proton collisions at root s=200 GeV by the STAR experiment at RHIC. The dataset includes longitudinally polarized proton-proton collisions with an integrated luminosity of 52 pb(-1), and transversely polarized proton-proton collisions with a similar integrated luminosity. Both datasets have about twice the statistics of previous results and cover a kinematic range of |eta(Lambda (Lambda))|<1.2 and transverse momentum p(T,Lambda( (Lambda)) up to 8 GeV/c. We also report the first measurements of the hyperon spin transfer coefficients D-LL and D-TT as a function of the fractional jet momentum z carried by the hyperon, which can provide more direct constraints on the polarized fragmentation functions.

We report the first measurements of cumulants, up to 4th order, of deuteron number distributions and proton-deuteron correlations in Au+Au collisions recorded by the STAR experiment in phase-I of Beam Energy Scan (BES) program at the Relativistic Heavy Ion Collider. Deuteron cumulants, their ratios, and proton-deuteron mixed cumulants are presented for different collision centralities covering a range of center-of-mass energy per nucleon pair root s(NN) = 7.7 to 200 GeV. It is found that the cumulant ratios at lower collision energies favor a canonical ensemble over a grand canonical ensemble in thermal models. An anti-correlation between proton and deuteron multiplicity is observed across all collision energies and centralities, consistent with the expectation from global baryon number conservation. The UrQMD model coupled with a phase-space coalescence mechanism qualitatively reproduces the collision-energy dependence of cumulant ratios and proton-deuteron correlations.

Measurements of exclusive $J/\ensuremath{\psi}, \ensuremath{\psi}(2s)$, and electron-positron (${e}^{+}{e}^{\ensuremath{-}}$) pair photoproduction in $\mathrm{Au}+\mathrm{Au}$ ultraperipheral collisions are reported by the STAR experiment at $\sqrt{{s}_{{}_{\mathrm{NN}}}}=200\phantom{\rule{4pt}{0ex}}\mathrm{GeV}$. We report several first measurements at the BNL Relativistic Heavy Ion Collider, which are (i) $J/\ensuremath{\psi}$ photoproduction with large momentum transfer up to ${2.2\phantom{\rule{4pt}{0ex}}(\mathrm{GeV}/c)}^{2}$, (ii) coherent $J/\ensuremath{\psi}$ photoproduction associated with neutron emissions from nuclear breakup, (iii) the rapidity dependence of incoherent $J/\ensuremath{\psi}$ photoproduction, (iv) the $\ensuremath{\psi}(2s)$ photoproduction cross section at midrapidity, and (v) ${e}^{+}{e}^{\ensuremath{-}}$ pair photoproduction up to high invariant mass of $6\phantom{\rule{4pt}{0ex}}\mathrm{GeV}/{c}^{2}$. For measurement (ii), the coherent $J/\ensuremath{\psi}$ total cross section of $\ensuremath{\gamma}+\mathrm{Au}\ensuremath{\rightarrow}\mathrm{J}/\ensuremath{\psi}+\mathrm{Au}$ as a function of the center-of-mass energy ${W}_{\ensuremath{\gamma}N}$ has been obtained without photon energy ambiguities. The data are quantitatively compared with the Monte Carlo models STARlight, Sartre, BeAGLE, and theoretical calculations of gluon saturation with color glass condensate, nuclear shadowing with leading twist approximation, quantum electrodynamics, and the next-to-leading-order perturbative QCD. At the photon-nucleon center-of-mass energy of 25.0 GeV, the coherent and incoherent $J/\ensuremath{\psi}$ cross sections of Au nuclei are found to be $71%\ifmmode\pm\else\textpm\fi{}10%$ and $36%\ifmmode\pm\else\textpm\fi{}7%$, respectively, of that of free protons. These data provide an important experimental constraint for nuclear parton distribution functions and a unique opportunity to advance the understanding of the nuclear modification effect at the top RHIC energy.

The CMS detector, including its muon system, has been operating at the CERN LHC in increasingly challenging conditions for about 15 years. The muon detector was designed to provide excellent triggering and track reconstruction for muons produced in proton–proton collisons at an instantaneous luminosity ( ℒ ) of 1 × 10^34 cm ^-2 s ^-1 . During the Run 2 data-taking period (2015–2018), the LHC achieved an instantaneous luminosity of twice its design value, resulting in larger background rates and making the efficient detection of muons more difficult. While some backgrounds result from natural radioactivity, cosmic rays, and interactions of the circulating protons with residual gas in the beam pipe, the dominant source of background hits in the muon system arises from proton–proton interactions themselves. Charged hadrons leaving the calorimeters produce energy deposits in the muon chambers. In addition, high-energy particles interacting in the hadron calorimeter and forward shielding elements generate thermal neutrons, which leak out of the calorimeter and shielding structures, filling the CMS cavern. We describe the method used to measure the background rates in the various muon subsystems. These rates, in conjunction with simulations, can be used to estimate the expected backgrounds in the High-Luminosity LHC. This machine will run for at least 10 years starting in 2029 reaching an instantaneous luminosity of ℒ = 5 ×10^34 cm^-2 s^-1 and increasing ultimately to ℒ = 7.5 ×10^34 cm^-2 s^-1 . These background estimates have been a key ingredient for the planning and design of the muon detector upgrade.

The deconfined quark-gluon plasma (QGP) created in relativistic heavy-ion collisions enables the exploration of the fundamental properties of matter under extreme conditions. Noncentral collisions can produce strong magnetic fields on the order of 1018 G, which offers a probe into the electrical conductivity of the QGP. In particular, quarks and antiquarks carry opposite charges and receive contrary electromagnetic forces that alter their momenta. This phenomenon can be manifested in the collective motion of final -state particles, specifically in the rapidity-odd directed flow, denoted as v1oy thorn . Here, we present the charge-dependent measurements of dv1=dy near midrapidities for pi ⠂, K ⠂, and pop over bar thorn in Au thorn Au and isobar (96 44Ru thorn 9644Ru and 9640Zr thorn 96 40Zr) collisions at ffiffiffiffiffiffiffi p 1/4 200 GeV, and in Au thorn Au collisions at sNN 27 GeV, recorded by the STAR detector at the Relativistic Heavy Ion Collider. The combined dependence of the v1 signal on collision system, particle species, and collision centrality can be qualitatively and semiquantitatively understood as several effects on constituent quarks. While the results in central events can be explained by the u and d quarks transported from initial -state nuclei, those in peripheral events reveal the impacts of the electromagnetic field on the QGP. Our data put valuable constraints on the electrical conductivity of the QGP in theoretical calculations.

An amplitude analysis of the $B^{0}\to K^{*0}\mu^+\mu^-$ decay is presented using a dataset corresponding to an integrated luminosity of $4.7$ fb$^{-1}$ of $pp$ collision data collected with the LHCb experiment. For the first time, the coefficients associated to short-distance physics effects, sensitive to processes beyond the Standard Model, are extracted directly from the data through a $q^2$-unbinned amplitude analysis, where $q^2$ is the $\mu^+\mu^-$ invariant mass squared. Long-distance contributions, which originate from non-factorisable QCD processes, are systematically investigated and the most accurate assessment to date of their impact on the physical observables is obtained. The pattern of measured corrections to the short-distance couplings is found to be consistent with previous analyses of $b$- to $s$-quark transitions, with the largest discrepancy from the Standard Model predictions found to be at the level of 1.8 standard deviations. The global significance of the observed differences in the decay is 1.4 standard deviations.

The differential cross section for Z(0) production, measured as a function of the boson's transverse momentum (p(T)), provides important constraints on the evolution of the transverse momentum dependent parton distribution functions (TMDs). The transverse single spin asymmetry (TSSA) of the Z(0) is sensitive to one of the polarized TMDs, the Sivers function, which is predicted to have the opposite sign in p + p -> W/Z + X from that which enters in semi-inclusive deep inelastic scattering. In this Letter, the STAR Collaboration reports the first measurement of the Z(0)/gamma* differential cross section as a function of its p(T) in p + p collisions at a center-of-mass energy of 510 GeV, together with the Z(0)/gamma* total cross section. We also report the measurement of Z(0)/gamma* TSSA in transversely polarized p + p collisions at 510 GeV.

The nearby radio galaxy M87 is a very high-energy (VHE) gamma-ray emitter established by observations with ground-based gamma-ray detectors. Here we report the long-term monitoring of M87 from 2021 to 2024 with the Large High Altitude Air Shower Observatory (LHAASO). M87 has been detected by LHAASO with a statistical significance similar to 9 sigma. The observed energy spectrum extends to 20 TeV, with a possible hardening at similar to 20 TeV and then a clear softening at higher energies. Assuming that the intrinsic spectrum is described by a single power law up to 20 TeV, a tight upper bound on the extragalactic background light intensity is obtained. A strong VHE flare lasting 8 days, with a rise time of tau(rise)(r) = 1.05 +/- 0.49 days and decay time of tau(decay)(d) = 2.17 +/- 0.58 days, was found in early 2022. A possible GeV flare is seen also in Fermi Large Area Telescope data during the VHE flare period. The variability time as short as 1 day seen in the LHAASO data suggests a compact emission region with a size of similar to 3 x 10(15) delta cm (delta being the Doppler factor of the emitting region), corresponding to a few Schwarzschild radii of the central supermassive black hole in M87. The continuous monitoring of the source reveals a duty cycle of similar to 1% for VHE flares with a flux above 10(-11) erg cm(-2) s(-1).

Wve report results on an elastic cross section measurement in proton-proton collisions at a center-of-mass energy root s = 510 GeV, obtained with the Roman Pot setup of the STAR experiment at the Relativistic Heavy Ion Collider (RHIC). The elastic differential cross section is measured in the four-momentum transfer squared range 0.23 <= -t <= 0.67 GeV2. This is the only measurement of the proton-proton elastic cross section in this t range for collision energies above the Intersecting Storage Rings (ISR) and below the Large Hadron Collider (LHC) colliders. We find that a constant slope B does not fit the data in the aforementioned t range, and we obtain a much better fit using a second-order polynomial for B(t). This is the first measurement below the LHC energies for which the non-constant behavior B(t) is observed. The t dependence of B is also determined using six subintervals of t in the STAR measured t range, and is in good agreement with the phenomenological models. The measured elastic differential cross section d sigma/dt agrees well with the results obtained at root s = 540 GeV for proton-antiproton collisions by the UA4 experiment. We also determine that the integrated elastic cross section within the STAR t-range is sigma(fid) (el) = 462.1 +/- 0.9(stat.) +/- 1.1(syst.) +/- 11.6(scale) mu b.

In high-energy nucleus-nucleus collisions, highly charged heavy ions moving close to the speed of light generate extremely strong electromagnetic fields, inducing photoproduction processes involving photon-photon and photon-nuclear interactions. These photoproduction processes yield various states, including dilepton pairs and vector mesons. In recent years, several experimental results from ultraperipheral and peripheral heavy-ion collisions have provided excellent conditions and unique opportunities for studying nuclear structures and nucleon distributions through mutual promotion and cross-checking between precise experimental measurements and sophisticated theoretical calculations. This paper briefly introduces recent research achievements on nuclear charge distributions, gluon distributions, neutron skins, etc. based on the data collected from ultraperipheral and peripheral heavy-ion collisions at the Relativistic Heavy Ion Collider and the Large Hadron Collider.

We perform for the first time an amplitude analysis of the decay $D^{+}\to K_{S}^{0}\pi^+\eta$ and report the observation of the decay $D^{+}\to K_{S}^{0}a_{0}(980)^{+}$ using 2.93 fb$^{-1}$ of $e^+e^-$ collision data taken at a center-of-mass energy of 3.773 GeV with the BESIII detector. As the only W-annihilation free decay among $D$ to $a_{0}(980)$-pseudoscalar, $D^{+}\to K_{S}^{0}a_{0}(980)^{+}$ is the ideal decay to extract the contributions of the external and internal $W$-emission amplitudes involving $a_{0}(980)$ and study the final-state interactions. The absolute branching fraction of $D^{+}\to K_{S}^{0}\pi^+\eta$ is measured to be $(1.27\pm0.04_{\rm stat.}\pm0.03_{\rm syst.})\%$. The product branching fractions of $D^{+}\to K_{S}^{0}a_{0}(980)^{+}$ with $a_{0}(980)^{+}\to \pi^+\eta$ and $D^{+}\to \pi^+ K_0^*(1430)^0$ with $K_0^*(1430)^0\to K_{S}^{0}\eta$ are measured to be $(1.33\pm0.05_{\rm stat.}\pm0.04_{\rm syst.})\%$ and $(0.14\pm0.03_{\rm stat.}\pm0.01_{\rm syst.})\%$, respectively.

We report multi-differential measurements of strange hadron production ranging from mid- to target-rapidity in Au+Au collisions at a center-of-momentum energy per nucleon pair of √(s_NN) = 3 GeV with the STAR experiment at RHIC. K_S^0 meson and Λ hyperon yields are measured via their weak decay channels. Collision centrality and rapidity dependences of the transverse momentum spectra and particle ratios are presented. Particle mass and centrality dependence of the average transverse momenta of Λ and K_S^0 are compared with other strange particles, providing evidence of the development of hadronic rescattering in such collisions. The 4π yields of each of these strange hadrons show a consistent centrality dependence. Discussions on radial flow, the strange hadron production mechanism, and properties of the medium created in such collisions are presented together with results from hadronic transport and thermal model calculations.