Energy Correlators within Jets in Transversely Polarized Proton-Proton Collisions at βs =200 GeV
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73 NUCLEAR PHYSICS AND RADIATION PHYSICSβ
Engineering topics
Gu, A.
Publications and source records attributed to Gu, A..
Tracking the baryon number with nuclear collisions
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73 NUCLEAR PHYSICS AND RADIATION PHYSICSβ
First Observation of Deuteron-Ξ Correlations at RHIC
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73 NUCLEAR PHYSICS AND RADIATION PHYSICSβ
Measurement of inclusive $J/Ο$ production in Au+Au collisions at $\sqrt{s_{\textrm{NN}}}$ = 54.4 GeV at STAR
This article presents measurements of inclusive J/Ο production at midrapidity (|y| < 1.0) in Au+Au collisions at $\sqrt{s_{\textrm{NN}}}$ = 54.4 GeV with the STAR detector at the Relativistic Heavy Ion Collider. A suppression of the J/Ο yield, quantified using the nuclear modification factors (R AA , R CP ), is observed with respect to the scaled production p + p in collisions. The dependence of R AA on collision centrality and J/Ο transverse momentum is measured with improved precision compared to previous measurements at 39 and 62.4 GeV, while the centrality dependence of R CP is measured and compared to the same results at 39, 62.4, and 200 GeV. In central collisions, no significant collision energy dependence of R AA is found within uncertainties for collision energies between 17.3 and 200 GeV. Two transport model calculations that include dissociation and regeneration contributions are consistent with the experimental results within uncertainties. Although no significant collision energy dependence of the J/Ο suppression in high energy heavy-ion collisions up to $\sqrt{s_{\textrm{NN}}}$ = 200 GeV is observed within uncertainties, the newly measured results at 54.4 GeV Au+Au collisions provide additional constraints on theoretical calculations of the hot medium evolution and cold nuclear matter effects.
73 NUCLEAR PHYSICS AND RADIATION PHYSICSβ
Probing late-stage hadronic interactions at high baryon density via $K^{β0}$ production in the RHIC beam energy scan program
A precision measurement of the $K^{β0}$ meson yield is reported in Au+Au collisions at $\sqrt{s_{NN}}$ = 7.7, 11.5, 14.6, 19.6, and 27 GeV using the high-statistics data sample collected by the STAR experiment during the Beam Energy Scan II (BES-II) program at RHIC. The transeverse momentum (p T )-integrated yield ratios $\large{(}K^{β0} + \overline{K^{β0}}\large{)}/(K^+ + K^{-})$ in central collisions show a suppression relative to peripheral collisions at the (1.7β3.6) Ο level, while a thermal model without final-stage rescattering overpredicts this ratio with a deviation of (6.9β8.2) Ο. These results indicate a loss of the measured $K^{β0}$ signal in central collisions due to re-scattering of its hadronic decay products in the hadronic phase. The p T -integrated yield of charged kaons exhibits an approximate scaling with charged-particle multiplicity, independent of collision energy and system size. A similar trend is observed for the short-lived $K^{β0}$ resonance, although significant deviations emerge at lower energies. At BES energies, the $K^{β0}/K$ ratio shows stronger suppression than at the highest RHIC and LHC energies within a given multiplicity bin, particularly in central and mid-central collisions. This behavior is consistent with changes in the effective hadronic interaction cross section and is supported by transport model calculations, which indicate dominant mesonβbaryon interactions at lower energies and mesonβmeson interactions at higher energies.
73 NUCLEAR PHYSICS AND RADIATION PHYSICSβ
Measurement of kaon directed flow in Au+Au collisions in the high baryon density region
Rapidity-odd directed flow v 1 measurements are presented for $K^Β±$ and $K^0_S$ in Au + Au collisions for $\sqrt{s_{NN}}$ from 3.0 to 3.9 GeV with the STAR experiment. For comparison, v 1 of Ο Β± , protons, and Ξ from the same collisions are also discussed. The mid-rapidity v 1 slope dv 1 /dy| y=0 for protons and Ξ is positive in these collisions. On the other hand, v 1 slope of kaons exhibits a strong dependence: negative at p T < 0.6 GeV/c and positive at higher p T . A similar p T dependence is also evident for the v 1 slope of charged pions. Compared to the spectator-removed calculations in Au+Au collisions at $\sqrt{s_{NN}}$ = 3.0β3.9 GeV, the JAM model demonstrates a pronounced shift of the v 1 slopes of mesons towards the negative direction. It suggests that the shadowing effect of the spectators plays an important role in the observed kaon anti-flow at low p T in the high baryon density region of non-central collisions.
73 NUCLEAR PHYSICS AND RADIATION PHYSICSβ
Measuring spin correlation between quarks during QCD confinement
The vacuum is now understood to have a rich and complex structure, characterized by fluctuating energy fields and a condensate of virtual quarkβantiquark pairs. The spontaneous breaking of the approximate chiral symmetry, signalled by the nonvanishing quark condensate $\langle$$q\bar{q}$$\rangle$, is dynamically generated through topologically nontrivial gauge configurations such as instantons. The precise mechanism linking the chiral symmetry breaking to the mass generation associated with quark confinement remains a profound open question in quantum chromodynamics (QCD)βthe fundamental theory of strong interaction. High-energy protonβproton collisions could liberate virtual quarkβantiquark pairs from the vacuum that subsequently undergo confinement to form hadrons, whose properties could serve as probes into QCD confinement and the quark condensate. Here we report evidence of spin correlations in $Ξ\bar{Ξ}$ hyperon pairs inherited from spin-correlated strange quarkβantiquark virtual pairs. Measurements by the STAR experiment at the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory reveal a relative polarization signal of (18 Β± 4)% that links the virtual spin-correlated quark pairs from the QCD vacuum to their final-state hadron counterparts. Crucially, this correlation vanishes when the hyperon pairs are widely separated in angle, consistent with the decoherence of the quantum system. Our findings provide a new experimental model for exploring the dynamics and interplay of quark confinement and entanglement.
73 NUCLEAR PHYSICS AND RADIATION PHYSICSβ
Temperature measurement of Quark-Gluon plasma at different stages
In a Quark-Gluon Plasma (QGP), the fundamental building blocks of matter, quarks and gluons, are under extreme conditions of temperature and density. A QGP could exist in the early stages of the Universe, and in various objects and events in the cosmos. The thermodynamic and hydrodynamic properties of the QGP are described by Quantum Chromodynamics (QCD) and can be studied in heavy-ion collisions. Despite being a key thermodynamic parameter, the QGP temperature is still poorly known. Thermal lepton pairs (e + e β and ΞΌ + ΞΌ β ) are ideal penetrating probes of the true temperature of the emitting source, since their invariant-mass spectra suffer neither from strong final-state interactions nor from blue-shift effects due to rapid expansion. Here we measure the QGP temperature using thermal e+eβ production at the Relativistic Heavy Ion Collider (RHIC). The average temperature from the low-mass region (in-medium Ο 0 vector-meson dominant) is (2.01 Β± 0.23) Γ 10 12 K, consistent with the chemical freeze-out temperature from statistical models and the phase transition temperature from Lattice QCD. The average temperature from the intermediate mass region (above the Ο0 mass, QGP dominant) is significantly higher at (3.25 Β± 0.60) Γ 10 12 K. This work provides essential experimental thermodynamic measurements to map out the QCD phase diagram and understand the properties of matter under extreme conditions.
73 NUCLEAR PHYSICS AND RADIATION PHYSICSβ
Hyperon global polarization in isobar Ru+Ru and Zr+Zr collisions at $\sqrt{s_{NN}}$ = 200Ge V
The polarization of Ξ, $\overline{Ξ}$, $Ξ$ β , and $\overline{Ξ}$ + hyperons along the angular momentum of the system has been measured in isobar collisions of Ru+Ru and Zr+Zr at $\sqrt{s_{NN}}$ = 200 GeV with the STAR detector at RHIC. The polarization dependence on collision centrality exhibits an increasing trend in more peripheral collisions. Ξ and $\overline{Ξ}$ polarization dependence on the transverse momentum and pseudorapidity have been investigated, but no significant dependence was observed. The polarizations of Ξ and $\overline{Ξ}$ are found to be consistent with each other, indicating little contribution of the spin-magnetic coupling to the measured polarization. Comparison to previously measured polarization in Au+Au collisions show no obvious system size dependence. The results are qualitatively consistent with hydrodynamic calculations including contributions from shear-induced polarization and thermal vorticity. For the first time in heavy-ion collisions, the dependence of the global polarization on the hyperonβs emission azimuthal angle relative to the second-order event plane has been measured, indicating stronger polarization for the in-plane emitted hyperons at the level of 2.4 Ο significance in 20β50 % centrality. The $Ξ$ hyperon polarization measurements via polarization transfer analysis yield finite positive values with 2.9 Ο significance in 20β50 % centrality, slightly larger compared to the inclusive Ξ polarization.
73 NUCLEAR PHYSICS AND RADIATION PHYSICSβ
Semi-inclusive direct photon + jet and π 0 + jet correlations measured in π + π and central Au + Au collisions at $\sqrt{s_{NN}}$ = 200GeV
The STAR experiment at RHIC reports new measurements of jet quenching based on the semi- inclusive distribution of charged-particle jets recoiling from direct photon (Ξ³ dir ) and neutral pion (Ο 0 ) triggers in pp and central Au + Au collisions at $\sqrt{s_{NN}}$ = 200 GeV, for triggers in the range 9 < $E$$^{trig}_{T}$ < 20 GeV. The datasets have integrated luminosities of 3.9nb β1 for Au + Au and 23pb β1 for ππ collisions. Jets are reconstructed using the anti-π π algorithm with resolution parameters π = 0.2 and 0.5. The large uncorrelated jet background in central Au + Au collisions is corrected using a mixed-event approach, which enables precise charged-particle jet measurements at low transverse momentum π$^{ch}_{π,jet}$ and large π . Recoil-jet distributions are reported in the range π$^{ch}_{π,jet}$ < 25 GeV/π. Comparison of the distributions measured in ππ and Au + Au collisions reveals strong medium-induced jet yield suppression for π = 0.2 with markedly less suppression for π = 0.5. Comparison is also made to theoretical models incorporating jet quenching. Furthermore, these data provide new insight into the mechanisms underlying jet quenching and the angular dependence of medium-induced jet-energy transport and provide new constraints on modeling such effects.
73 NUCLEAR PHYSICS AND RADIATION PHYSICSβ
Light nuclei femtoscopy and baryon interactions in 3 GeV Au+Au collisions at RHIC
We report the measurements of proton-deuteron (π-π) and deuteron-deuteron (π-π) correlation functions in Au + Au collisions at $\sqrt{s_{NN}}$ = 3 GeV using fixed-target mode with the STAR experiment at the Relativistic Heavy-Ion Collider (RHIC). For the first time, the source size (π πΊ ), scattering length (π 0 ), and effective range (π 0 ) are extracted from the measured correlation functions with a simultaneous fit. The spin-averaged π 0 for π-π and π-π interactions are determined to be -5.28 Β± 0.11(stat.) Β± 0.82(syst.) fm and -2.62 Β± 0.02(stat.) Β±0.24(syst.) fm, respectively. The measured π-π interaction is consistent with theoretical calculations and low energy scattering experiment results, demonstrating the feasibility of extracting interaction parameters using the femtoscopy technique. The reasonable agreement between the experimental data and the calculations from the transport model indicates that deuteron production in these collisions is primarily governed by nucleon coalescence.
73 NUCLEAR PHYSICS AND RADIATION PHYSICSβ
Electric-charge-dependent directed flow splitting of produced quarks in Au+Au collisions
We report directed flow (v 1 ) of multistrange baryons ($Ξ$ and Ξ©) and improved v 1 data for K β ,$\overline{p}$, $\overline{Ξ}$, and Ο in Au+Au collisions at $\sqrt{s_{NN}}$ = 27 and 200 GeV from the STAR experiment at the Relativistic Heavy Ion Collider (RHIC). We focus on particles whose constituent quarks are not transported from the incoming nuclei but instead are produced in the collisions. At intermediate impact parameters, we examine quark coalescence behavior for particle combinations with identical quark content, and search for any departure from this behavior (βsplittingβ) for combinations having non-identical quark content. Under the assumption of quark coalescence for produced quarks, the splitting strength appears to increase with the electric charge difference of the constituent quarks in the combinations, consistent with electromagnetic effect expectations.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDSβ
New Strong Gravitational Lenses from the DESI Legacy Imaging Surveys Data Release 9
We have conducted a search for strong gravitational lensing systems in the Dark Energy Spectroscopic Instrument (DESI) Legacy Imaging Surveys Data Release 9. This is the third paper in a series. These surveys together cover ~19,000 deg 2 visible from the Northern Hemisphere, reaching a z-band AB magnitude of ~22.5. We use a deep residual neural network, trained on a compilation of known lensing systems and high-grade candidates as well as nonlenses in the same footprint. After applying our trained neural network to the survey data, we visually inspect and rank images with probabilities above a threshold which has been chosen to balance precision and recall. We have found 1895 lens candidates, of which 1512 are identified for the first time. Combining the discoveries from this work with those from Papers I (335) and II (1210), we have discovered a total of 3057 new candidates in the Legacy Surveys.
79 ASTRONOMY AND ASTROPHYSICSβ
Material compatibility evaluation for liquid oxygen turbopump fluid foil bearings
Three series of tests were carried out on three polymer-coated Inconel substrate materials, Teflon S, polyimide bonded graphite fluoride (PBGF), and Teflon, which are considered for use in fluid foil bearings for a liquid oxygen turbopump. All the candidate materials passed the liquid oxygen frictional heating test. During the gaseous oxygen frictional heating test, all coatings wore off before ignition occured. Both Teflon S and PBGF coated foils passed 100 start/stop cycles against chrome-plated Inconel 718 shaft in the direct foil bearing lift-off simulation test in liquid oxygen.
Stoltzfus, J. M.β
Liquid hydrogen turbopump foil bearing
Space transfer vehicles and other power and propulsion systems require long-life turbopumps. Rolling element bearings used in current turbopumps do not have sufficient life for these applications. Process fluid foil bearings have established long life, with exceptional reliability, over a wide range of temperatures and fluids in many high-speed turbomachinery applications. However, liquid hydrogen turbopumps require high-load capacity bearings. An experimental study was conducted to measure foil journal bearing load capacity in liquid hydrogen, using a bearing designed specifically for cryogenic hydrogen turbopump applications. Additional performance parameters such as power loss, stability, cooling flow requirements, and bearing life were measured. These tests showed a load capacity safety factor of approximately 10 for liquid hydrogen turbopump applictions. These tests also demonstrated good rotor stability, low power loss and cooling flow, and long life.
Saville, M.β
Evaluation of a series hybird thrust bearing at DN values to three million. 1: Analysis and design
The analysis and design are presented of a hybrid bearing consisting of a 150-mm ball bearing and a centrifugally actuated, conical, fluid film bearing fitting an envelope with an outer radius of 86.4 mm (3.4 in.) and an inner radius of 71 mm (2.8 in.). The bearing analysis, combined with available torque data on ball bearings, indicates that an effective speed split between the ball and fluid-film bearings of 50 percent may be expected during operation at 20,000 rpm and under an axial load of 17,800 newtons (4000 lbs.). This speed split can result in a ten-fold increase in the life of the ball bearing when compared to a simple ball bearing system operating under similar conditions.
Gu, A.β