Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “CaIn”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Exclusive J / ψ , ψ ( 2 s ) , and e + e - pair production in Au + Au ultraperipheral collisions at the BNL Relativistic Heavy Ion Collider

Measurements of exclusive J/ψ, ψ(2⁢s), and electron-positron (e + ⁢e - ) pair photoproduction in Au+Au ultraperipheral collisions are reported by the STAR experiment at $\sqrt{s_{NN}}$ = 200GeV. Here, we report several first measurements at the BNL Relativistic Heavy Ion Collider, which are (i) J/ψ photoproduction with large momentum transfer up to 2.2⁢(GeV/c) 2 , (ii) coherent J/ψ photoproduction associated with neutron emissions from nuclear breakup, (iii) the rapidity dependence of incoherent J/ψ photoproduction, (iv) the ψ⁡(2⁢s) photoproduction cross section at midrapidity, and (v) e + ⁢e - pair photoproduction up to high invariant mass of 6GeV/c 2 . For measurement (ii), the coherent J/ψ total cross section of γ + Au → J/ψ + Au as a function of the center-of-mass energy W γN 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/ψ 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.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2024

Correlations of event activity with hard and soft processes in p + Au collisions at $\sqrt{s_{NN}}$ = 200 GeV at the RHIC STAR experiment

With the STAR experiment at the BNL Relativistic Heavy Ion Collider, we characterize $\sqrt{s_{NN}}$ = 200GeV p + Au collisions by event activity (EA) measured within the pseudorapidity range η ϵ[–5,–3.4] in the Au-going direction and report correlations between this EA and hard- and soft-scale particle production at midrapidity (η ϵ[–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. Furthermore, 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 + Au collisions at $\sqrt{s_{NN}}$ = 200GeV.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2024

Production of protons and light nuclei in Au +Au collisions at $\sqrt{s_{NN}}$ = 3 GeV with the STAR detector

We report the systematic measurement of protons and light nuclei production in Au +Au collisions at $\sqrt{s_{NN}}$ = 3 GeV by the STAR experiment at the Relativistic Heavy Ion Collider (RHIC). The transverse momentum (𝑝 𝑇 ) spectra of protons (𝑝) , deuterons (𝑑) , tritons (𝑡) , 3 He , and 4 He have been measured from midrapidity to target rapidity for different collision centralities. We present the rapidity and centrality dependence of particle yields (𝑑⁢𝑁/𝑑⁢𝑦), average transverse momentum (⟨𝑝 𝑇 ⟩), yield ratios (𝑑/𝑝, 𝑡/𝑝, 3 He/𝑝, 4 He/𝑝), as well as the coalescence parameters (𝐵 2 ,𝐵 3 ). The 4⁢𝜋 yields for various particles are determined by utilizing the measured rapidity distributions, 𝑑⁢𝑁/𝑑⁢𝑦. Furthermore, we present the energy, centrality, and rapidity dependence of the compound yield ratios (𝑁 𝑝 ×𝑁 𝑡 /𝑁$^{2}_{d}$) and compare them with various model calculations. Furthermore, the physics implications of these results on the production mechanism of light nuclei and the QCD phase structure are discussed.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2024

Measurement of flow coefficients in high-multiplicity 𝑝 + Au, 𝑑 + Au, and 3 He + Au collisions at $\sqrt{s_{NN}}$ = 200 GeV

Flow coefficients (𝑣 2 and 𝑣 3 ) are measured in high-multiplicity 𝑝 + Au, 𝑑 + Au, and 3 He + Au collisions at a center-of-mass energy of $\sqrt{s_{NN}}$ = 200 GeV using the STAR detector. The measurements utilize two-particle correlations with a pseudorapidity requirement of |𝜂| < 0.9 and a pair gap of |Δ⁢𝜂| > 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. 𝑣 𝑛 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. As a result, the prospects for future measurements to improve our understanding of flow decorrelation and subnucleonic fluctuations are also discussed.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2025

Measurement of directed flow in Au + Au collisions at $\sqrt{s{NN}}$ = 19.6 and 27 GeV with the STAR event plane detector

In heavy-ion collision experiments, the global collectivity of final-state particles can be quantified by anisotropic flow coefficients (𝑣 𝑛 ) . The first-order flow coefficient, also referred to as the directed flow (𝑣 1 ), describes the collective sideward motion of produced particles and nuclear fragments in heavy-ion collisions. It carries information on the very early stage of the collision, especially at large pseudorapidity (𝜂), where it is believed to be generated during the nuclear passage time. Directed flow therefore probes the onset of bulk collective dynamics during thermalization, providing valuable experimental guidance to models of the pre-equilibrium stage. In 2018, the Event Plane Detector (EPD) was installed in STAR and used for the Beam Energy Scan phase-II (BES-II) data taking. The combination of EPD (2.1 < |𝜂| < 5.1) and high-statistics BES-II data enables us to extend the 𝑣 1 measurement to the forward and backward 𝜂 regions. In this paper, we present the measurement of 𝑣 1 over a wide 𝜂 range in Au + Au collisions at $\sqrt{s_{NN}}$ = 19.6 and 27 GeV using the STAR EPD. The results of the analysis at $\sqrt{s_{NN}}$ = 19.6 GeV exhibit excellent consistency with the previous PHOBOS measurement, while elevating the precision of the overall measurement. The increased precision of the measurement also revealed finer structures in heavy-ion collisions, including a potential observation of the first-order event-plane decorrelation. Multiple physics models were compared to the experimental results. Only a transport model and a three-fluid hybrid model can reproduce a sizable 𝑣 1 at large 𝜂 as was observed experimentally. The model comparison also indicates 𝑣 1 at large 𝜂 might be sensitive to the QGP phase transition.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2025

Energy dependence of polarized 𝛾⁢𝛾 → 𝑒 + ⁢ 𝑒− in peripheral Au+Au collisions at $\sqrt{s_{NN}}$ = 54.4 and 200 GeV with the STAR experiment at RHIC

We report the differential yields at mid-rapidity of the Breit-Wheeler process (𝛾⁢𝛾 → 𝑒 + ⁢𝑒 − ) in peripheral Au+Aucollisions at $\sqrt{s_{NN}}$ = 54.4 and 200 GeV with the STAR experiment at the Relativistic Heavy Ion Collider (RHIC), as a function of energy $\sqrt{s_{NN}}$, 𝑒 + ⁢𝑒 − transverse momentum 𝑝 T , 𝑝$^{2}_{T}$, invariant mass 𝑀 𝑒⁢𝑒 , and azimuthal angle. In the invariant mass range of 0.4 < 𝑀 𝑒⁢𝑒 < 2.6GeV/𝑐 2 at low transverse momentum (𝑝 T < 0.15GeV/𝑐), the yields increase while the pair √⟨𝑝$^{2}_{T}$⟩ decreases with increasing $\sqrt{s_{NN}}$, a feature that is correctly predicted by the QED calculation. Here, the energy dependencies of the measured quantities are sensitive to the nuclear form factor, infrared divergence and photon polarization. The data are compiled and used to extract the charge radius of the Au nucleus.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2020

Underlying event measurements in p + p collisions at s = 200 GeV at RHIC

In this work, particle production sensitive to non-factorizable and non-perturbative processes that contribute to the underlying event associated with a high transverse momentum (p T ) jet in proton+proton collisions at p √s=200 GeV is studied with the STAR detector. Each event is divided into three regions based on the azimuthal angle with respect to the highest-p T jet direction: in the leading jet direction ("Toward"), opposite to the leading jet ("Away"), and perpendicular to the leading jet 3 ("Transverse"). In the Transverse region, the average charged particle density is found to be between 0.4 and 0.6 and the mean transverse momentum,$\langle$p T $\rangle$, between 0.5-0.7 GeV/c for particles with p T >0.2 GeV/c at mid-pseudorapidity (|η|<1) and jet p T >15 GeV/c. Both average particle density and $\langle$p T $\rangle$ depend weakly on the leading jet p T . Closer inspection of the Transverse region hints that contributions to the underlying event from initial- and final-state radiation are significantly smaller in these collisions than at the higher energies, up to 13 TeV, recorded at the LHC. Underlying event measurements associated with a high-p T jet will contribute to our understanding of QCD processes at hard and soft scales at RHIC energies, as well as provide constraints to modeling of underlying event dynamics.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2021

Comparison of transverse single-spin asymmetries for forward π 0 production in polarized pp , p Al and p Au collisions at nucleon pair c.m. energy √sNN=200 GeV

The STAR collaboration reports a measurement of the transverse single-spin asymmetries, A N , for neutral pions produced in polarized proton collisions with protons ( p p ), with aluminum nuclei ( p Al ) and with gold nuclei ( p Au ) at a nucleon-nucleon center-of-mass energy of 200 GeV. Neutral pions are observed in the forward direction relative to the transversely polarized proton beam, in the pseudorapidity region 2.7 < η < 3.8 . Results are presented for π 0 s observed in the STAR forward meson spectrometer electromagnetic calorimeter in narrow Feynman x ( x F ) and transverse momentum ( p T ) bins, spanning the range 0.17 < x F < 0.81 and 1.7 < p T < 6.0 GeV / c . For fixed x F < 0.47 , the asymmetries are found to rise with increasing transverse momentum. For larger x F , the asymmetry flattens or falls as p T increases. Parametrizing the ratio r ( A ) ≡ A N ( p A ) / A N ( p p ) = A P over the kinematic range, the ratio r ( A ) is found to depend only weakly on A , with ( P ) = - 0.027 ± 0.005 . No significant difference in P is observed between the low- p T region, p T < 2.5 GeV / c , where gluon saturation effects may play a role, and the high- p T region, p T > 2.5 GeV / c . It is further observed that the value of A N is significantly larger for events with a large- p T isolated π 0 than for events with a nonisolated π 0 accompanied by additional jetlike fragments. The nuclear dependence r ( A ) is similar for isolated and nonisolated π 0 events.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2022

Measurement of inclusive electrons from open heavy-flavor hadron decays in p + p collisions at s = 200 GeV with the STAR detector

We report a new measurement of the production cross section for inclusive electrons from open heavy-flavor hadron decays as a function of transverse momentum (p T ) at midrapidity (|y| < 0.7) in p + p collisions at √s = 200 GeV. Overall, the result is presented for 2.5 < P T < 10 GeV/c with an improved precision above 6 GeV/c with respect to the previous measurements, providing more constraints on perturbative QCD calculations. Moreover, this measurement also provides a high-precision reference for measurements of nuclear modification factors for inclusive electrons from open-charm and -bottom hadron decays in heavy-ion collisions.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2024

Longitudinal and transverse spin transfer to $Λ$ and $\overline{Λ}$ hyperons in polarized $p$ + $p$ collisions at √s = 200 GeV

The longitudinal and transverse spin transfers to Λ ($\overline{Λ}$) 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 , to Λ and $\overline{Λ}$ in polarized proton-proton collisions at √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 |η Λ ($\overline{Λ}$) | < 1.2 and transverse momentum p T , Λ($\overline{Λ}$) up to 8GeV/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

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗