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Guo, T.

Publications and source records attributed to Guo, T..

At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Nonprompt direct-photon production in Au + Au collisions at $\sqrt{s_{NN}}$ = 200 GeV

The measurement of the direct-photon spectrum from Au + Au collisions at $\sqrt{s_{NN}}$ = 200 GeV is presented by the PHENIX Collaboration using the external-photon-conversion technique for 0%–93% central collisions in a transverse-momentum (𝑝 𝑇 ) range of 0.8–10 GeV/𝑐. An excess of direct photons, above prompt-photon production from hard-scattering processes, is observed for 𝑝 𝑇 < 6 GeV/𝑐. Nonprompt direct photons are measured by subtracting the prompt component, which is estimated as 𝑁 coll -scaled direct photons from 𝑝 + 𝑝 collisions at 200 GeV, from the direct-photon spectrum. Results are obtained for 0.8 < 𝑝 𝑇 < 6.0 GeV/𝑐 and suggest that the spectrum has an increasing inverse slope from ≈0.2 to 0.4 GeV/𝑐 with increasing 𝑝 𝑇 , which indicates a possible sensitivity of the measurement to photons from earlier stages of the evolution of the collision. In addition, like the direct-photon production, the 𝑝 𝑇 -integrated nonprompt direct-photon yields also follow a power-law scaling behavior as a function of collision-system size. Finally, the exponent, 𝛼, for the nonprompt component is found to be consistent with 1.1 with no apparent 𝑝 𝑇 dependence.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2014

Evolution of silver nanoparticles in the rat lung investigated by X-ray absorption spectroscopy

Following a 6-h inhalation exposure to aerosolized 20 and 110 nm diameter silver nanoparticles, lung tissues from rats were investigated with X-ray absorption spectroscopy, which can identify the chemical state of silver species. Lung tissues were processed immediately after sacrifice of the animals at 0, 1, 3, and 7 days post exposure and the samples were stored in an inert and low-temperature environment until measured. We found that it is critical to follow a proper processing, storage and measurement protocol; otherwise only silver oxides are detected after inhalation even for the larger nanoparticles. The results of X-ray absorption spectroscopy measurements taken in air at 85 K suggest that the dominating silver species in all the postexposure lung tissues were metallic silver, not silver oxide, or solvated silver cations. The results further indicate that the silver nanoparticles in the tissues were transformed from the original nanoparticles to other forms of metallic silver nanomaterials and the rate of this transformation depended on the size of the original nanoparticles. Furthermore, we found that 20 nm diameter silver nanoparticles were significantly modified after aerosolization and 6-h inhalation/deposition, whereas larger, 110 nm diameter nanoparticles were largely unchanged. Over the seven-day postexposure period the smaller 20 nm silver nanoparticles underwent less change in the lung tissue than the larger 110 nm silver nanoparticles. In contrast, silica-coated gold nanoparticles did not undergo any modification processes and remained as the initial nanoparticles throughout the 7-day study period.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Study of e + e - → p p ¯ π 0 in the vicinity of the ψ ( 3770 )

The process e + e - →pp¯π 0 has been studied by analyzing data collected at √s=3.773 GeV, at s√=3.650 GeV, and during a ψ(3770) line shape scan with the BESIII detector at the BEPCII collider. The Born cross section of pp¯π 0 in the vicinity of the ψ(3770) is measured, and the Born cross section of ψ(3770)→pp¯π 0 is extracted considering interference between resonant and continuum production amplitudes. Two solutions with the same probability and a significance of 1.5σ are found. The solutions for the Born cross section of ψ(3770)→pp¯π 0 are 33.8±1.8±2.1 pb and 0.06 +0.10 -0.04 +0.01 -0.01 pb (<0.22 pb at a 90% confidence level). Using the estimated cross section and a constant decay amplitude approximation, the cross section σ(pp¯→ψ(3770)π 0 ) is calculated for the kinematic situation of the planned P¯ANDA experiment. The maximum cross section corresponding to the two solutions is expected to be less than 0.79 nb at 90% confidence level and 122±10 nb at a center-of-mass energy of 5.26 GeV.

Ablikim, M.↗