The kagome material CsTi$_3$Bi$_5$, which is isostructural to the extensively studied charge density wave (CDW) compound CsV$_3$Sb$_5$, exhibits intriguing electronic features within its two-dimensional kagome lattices of titanium atoms. Here, we perform optical spectroscopic measurements together with the first-principles calculations on single-crystalline CsTi$_3$Bi$_5$ to investigate its electronic properties comprehensively. It is found that the overall optical spectra are very similar to those of CsV$_3$Sb$_5$, but the existence of CDW instability is ruled out in CsTi$_3$Bi$_5$. Via careful comparison to the optical responses of CsV$_3$Sb$_5$, we attribute this difference to a significant reduction in the itinerant carrier density of CsTi$_3$Bi$_5$, which is associated with the absence of van Hove singularity near the Fermi level at $M$ point. This result supports the scenario that the CDW in CsV$_3$Sb$_5$ is driven by the nesting of van Hove singularity. Additionally, we unveil some exotic low-lying absorption features, which provide clear evidence of flat bands in CsTi$_3$Bi$_5$. Our findings contribute to a deeper understanding of exotic phenomena in CsTi$_3$Bi$_5$ and provide valuable insights into the role of van Hove singularity in CsV$_3$Sb$_5$.

The chiral magnetic effect (CME) is a phenomenon that arises from the QCD anomaly in the presence of an external magnetic field. The experimental search for its evidence has been one of the key goals of the physics program of the Relativistic Heavy-Ion Collider. The STAR Collaboration has previously presented the results of a blind analysis of isobar collisions (Ru4496+Ru4496, Zr4096+Zr4096) in the search for the CME. The isobar ratio (Y) of CME-sensitive observable, charge separation scaled by elliptic anisotropy, is close to but systematically larger than the inverse multiplicity ratio, the naive background baseline. This indicates the potential existence of a CME signal and the presence of remaining nonflow background due to two- and three-particle correlations, which are different between the isobars. In this postblind analysis, we estimate the contributions from those nonflow correlations as a background baseline to Y, utilizing the isobar data as well as Heavy Ion Jet Interaction Generator simulations. This baseline is found consistent with the isobar ratio measurement, and an upper limit of 10% at 95% confidence level is extracted for the CME fraction in the charge separation measurement in isobar collisions at sNN=200 GeV. Published by the American Physical Society 2024

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.

The full data set of the Daya Bay reactor neutrino experiment is used to probe the effect of the charged current non-standard interactions (CC-NSI) on neutrino oscillation experiments. Two different approaches are applied and constraints on the corresponding CC-NSI parameters are obtained with the neutrino flux taken from the Huber-Mueller model with a $5\%$ uncertainty. For the quantum mechanics-based approach (QM-NSI), the constraints on the CC-NSI parameters $\epsilon_{e\alpha}$ and $\epsilon_{e\alpha}^{s}$ are extracted with and without the assumption that the effects of the new physics are the same in the production and detection processes, respectively. The approach based on the weak effective field theory (WEFT-NSI) deals with four types of CC-NSI represented by the parameters $[\varepsilon_{X}]_{e\alpha}$. For both approaches, the results for the CC-NSI parameters are shown for cases with various fixed values of the CC-NSI and the Dirac CP-violating phases, and when they are allowed to vary freely. We find that constraints on the QM-NSI parameters $\epsilon_{e\alpha}$ and $\epsilon_{e\alpha}^{s}$ from the Daya Bay experiment alone can reach the order $\mathcal{O}(0.01)$ for the former and $\mathcal{O}(0.1)$ for the latter, while for WEFT-NSI parameters $[\varepsilon_{X}]_{e\alpha}$, we obtain $\mathcal{O}(0.1)$ for both cases.

Measurements of exclusive J/psi, psi(2s), and electron-positron (e(+) e(-)) pair photoproduction in Au + Au ultraperipheral collisions are reported by the STAR experiment at root s(NN) = 200 GeV. We report several first measurements at the BNL Relativistic Heavy Ion Collider, which are (i) J/psi photoproduction with large momentum transfer up to 2.2 (GeV/c)(2), (ii) coherent J/psi photoproduction associated with neutron emissions from nuclear breakup, (iii) the rapidity dependence of incoherent J/psi photoproduction, (iv) the psi(2s) photoproduction cross section at midrapidity, and (v) e(+) e(-) pair photoproduction up to high invariant mass of 6 GeV/c(2). For measurement (ii), the coherent J/psi total cross section of gamma + Au -> J/psi + Au as a function of the center-of-mass energy W-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/psi cross sections of Au nuclei are found to be 71% +/- 10% and 36% +/- 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 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.

This report documents the verification of the RESRAD-BUILD code, Version 4.0, which was released on December 22, 2022. Two earlier reports verifying Versions 3.0 and 3.1, respectively, were published in 2001 (Kamboj, et al. 2001) and 2003 (Tetra Tech NUS 2003). Version 4.0 of the RESRAD-BUILD code has many new features and modeling enhancements over the earlier versions, including the previously released Version 3.5. Chapter 2 of this report focuses on verifying the external dose and risk modeling for point, line, area, and volume sources, as well as for floor deposition. Besides verification, the external radiation doses calculated by RESRAD-BUILD were also benchmarked with those calculated by the MCNP code (Briemeister 1993). Section J.3 of the RESRAD-BUILD User's Manual Vol. 1 (Yu et al. 2022) documents the results of that benchmarking effort. Chapter 3 of this report focuses on verifying the ventilation modeling, from checking the remaining source inventory, releases of radionuclides to the air, air concentrations and deposited floor concentrations over time, to the radiation dose and risk associated with inhalation, ingestion, and air submersion, with and without vacuuming. The verification efforts involve designing spreadsheets to perform calculations the same as or like those performed by the RESRAD-BUILD code and then comparing the spreadsheet results with those produced by the code. When the results agree or the differences are within acceptable range, the accuracy of model implementation in the code is verified. In addition to model implementation, the implementation of key functions and features that facilitate the modeling or the use of the code were also verified during the release testing of the code. Appendix A presents the test cases developed for these verification testing, and Appendix B presents the testing results that verify proper implementation of key functions and features.

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.

Daya Bay presents the first measurement of cosmogenic He-8 isotope production in liquid scintillator, using an innovative method for identifying cascade decays of He-8 and its child isotope, Li-8. We also measure the production yield of Li-9 isotopes using well-established methodology. The results, in units of 10(-8)mu-1g(-1) cm(2), are 0.307 +/- 0.042, 0.341 +/- 0.040, and 0.546 +/- 0.076 for He-8, and 6.73 +/- 0.73, 6.75 +/- 0.70, and 13.74 +/- 0.82 for 9Li at average muon energies of 63.9 GeV, 64.7 GeV, and 143.0 GeV, respectively. The measured production rate of He-8 isotopes is more than an order of magnitude lower than any other measurement of cosmogenic isotope production. It replaces the results of previous attempts to determine the ratio of He-8 to Li-9 production that yielded a wide range of limits from 0% to 30%. The results provide future liquid-scintillator-based experiments with improved ability to predict cosmogenic backgrounds.

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.

This Letter reports the first measurement of the oscillation amplitude and frequency of reactor antineutrinos at Daya Bay via neutron capture on hydrogen using 1958 days of data. With over 3.6 million signal candidates, an optimized candidate selection, improved treatment of backgrounds and efficiencies, refined energy calibration, and an energy response model for the capture-on-hydrogen sensitive region, the relative ν[over ¯]_{e} rates and energy spectra variation among the near and far detectors gives sin^{2}2θ_{13}=0.0759_{-0.0049}^{+0.0050} and Δm_{32}^{2}=(2.72_{-0.15}^{+0.14})×10^{-3}  eV^{2} assuming the normal neutrino mass ordering, and Δm_{32}^{2}=(-2.83_{-0.14}^{+0.15})×10^{-3}  eV^{2} for the inverted neutrino mass ordering. This estimate of sin^{2}2θ_{13} is consistent with and essentially independent from the one obtained using the capture-on-gadolinium sample at Daya Bay. The combination of these two results yields sin^{2}2θ_{13}=0.0833±0.0022, which represents an 8% relative improvement in precision regarding the Daya Bay full 3158-day capture-on-gadolinium result.

For the search of the chiral magnetic effect (CME), STAR previously presented the results from isobar collisions (Ru-96(44) + Ru-96(44), Zr-96(40) + Zr-96(40)) obtained through a blind analysis. The ratio of results in Ru + Ru to Zr + Zr collisions for the CME-sensitive charge-dependent azimuthal correlator (Delta gamma), normalized by elliptic anisotropy (v(2)), was observed to be close to but systematically larger than the inverse multiplicity ratio. The background baseline for the isobar ratio, Y = (Delta gamma/v(2))(Ru)/(Delta gamma/v(2))(Zr), is naively expected to be (1/N)(Ru)/(1/N)(Zr); however, genuine two- and three-particle correlations are expected to alter it. We estimate the contributions to Y from those correlations, utilizing both the isobar data and HIJING simulations. After including those contributions, we arrive at a final background baseline for Y, which is consistent with the isobar data. We extract an upper limit for the CME fraction in the Delta gamma measurement of approximately 10% at a 95% confidence level on in isobar collisions at root S-NN = 200 GeV, with an expected 15% difference in their squared magnetic fields.

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.

Surface events that exhibit incomplete charge collection are an essential background source in the light dark matter detection experiments with p-type point-contact germanium detectors. We propose a machine learning-based algorithm to identify bulk and surface events according to their pulse shape features. We construct the training and test set with part of the γ-source calibration data and use the rising edge of the waveform as the model input. This method is verified with the test set and another part of the γ-source calibration data. Results show that this method performs well on both datasets, and presents robustness against the bulk events’ proportion and the dataset size. Compared with the previous approach, the uncertainty is reduced by 16% near the energy threshold on the physics data of CDEX-1B. In addition, the key pattern identified in the waveform is verified to be consistent with its physical nature by digging into this algorithm.

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.

Abstract 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 $$ \sqrt{s_{\textrm{NN}}} $$ = 3 GeV with the STAR experiment at RHIC. K S 0 $$ {K}_S^0 $$ 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 $$ {K}_S^0 $$ 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.

With the STAR experiment at the BNL Relativistic Heavy Ion Collider, we characterize root s(NN) = 200 GeV p + Au collisions by event activity (EA) measured within the pseudorapidity range eta is an element of [-5,-3.4] in the Au-going direction and report correlations between this EA and hard- and soft-scale particle production at midrapidity (eta is an element of [-1, 1]). At the soft scale, charged particle production in low-EA p + Au collisions is comparable to that in p + p collisions and increases monotonically with increasing EA. At the hard scale, we report measurements of high transverse momentum (p(T)) jets in events of different EAs. In contrast with the soft particle production, high-p(T) particle production and EA are found to be inversely related. To investigate whether this is a signal of jet quenching in high-EA events, we also report ratios of p(T) imbalance and azimuthal separation of dijets in high- and low-EA events. Within our measurement precision, no significant differences are observed, disfavoring the presence of jet quenching in the highest 30% EA p + v Au collisions at root s(NN) = 200 GeV.

We measure triangular flow relative to the reaction plane at 3 GeV center-of-mass energy in Au+Au collisions at the BNL Relativistic Heavy Ion Collider. A significant v_3 signal for protons is observed, which increases for higher rapidity, higher transverse momentum, and more peripheral collisions. The triangular flow is essentially rapidity-odd with a slope at mid-rapidity, dv_3/dy|_(y=0), opposite in sign compared to the slope for directed flow. No significant v_3 signal is observed for charged pions and kaons. Comparisons with models suggest that a mean field potential is required to describe these results, and that the triangular shape of the participant nucleons is the result of stopping and nuclear geometry.

Flow coefficients (v(2) and v(3)) are measured in high-multiplicity p + Au, d + Au, and He-3+ Au collisions at a center-of-mass energy of root s(NN) = 200 GeV using the STAR detector. The measurements utilize two-particle correlations with a pseudorapidity requirement of |eta| < 0.9 and a pair gap of |Delta eta| > 1.0. The primary focus is on analysis methods, particularly the subtraction of nonflow contributions. Four established nonflow subtraction methods are applied to determine v(n), validated using the HIJING event generator. vn values are compared across the three collision systems at similar multiplicities; this comparison cancels the final-state effects and isolates the impact of initial geometry. While v(2) values show differences among these collision systems, v(3) values are largely similar, consistent with expectations of subnucleon fluctuations in the initial geometry. The ordering of v(n) differs quantitatively from previous measurements using two-particle correlations with a larger rapidity gap, which, according to model calculations, can be partially attributed to the effects of longitudinal flow decorrelations. The prospects for future measurements to improve our understanding of flow decorrelation and subnucleonic fluctuations are also discussed.