Measurement of jet-medium interactions via direct photon-hadron correlations in Au + Au and d + Au collisions at s N N = 200 GeV
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73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
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Low-$p_T$ direct-photon production in Au + Au collisions at $\sqrt{s_{NN}}$ = 39 and 62.4 GeV
Here, the measurement of direct photons from Au + Au collisions at $\sqrt{s_{NN}}$ = 39 and 62.4 GeV in the transverse-momentum range 0.4 < $p_T$ < 3 Gev/c is presented by the PHENIX collaboration at the BNLRelativistic Heavy Ion Collider. A significant direct-photon yield is observed in both collision systems. A universal scaling is observed when the direct-photon $p_T$ spectra for different center-of-mass energies and for different centrality selections at $\sqrt{s_{NN}}$ = 62.4 GeV is scaled with $(dN_{\text{ch}}/dη)^α$ for α = 1.21 ± 0.04. This scaling also holds true for direct-photon spectra from Au + Au collisions at $\sqrt{s_{NN}}$ = 200 GeV measured earlier by PHENIX, as well as the spectra from Pb + Pb at $\sqrt{s_{NN}}$ = 2760 GeV published by ALICE. The scaling power α seems to be independent of $p_T$, center of mass energy, and collision centrality. The spectra from different collision energies have a similar shape up to $p_T$ of 2 Gev/c. The spectra have a local inverse slope $T_{\text{eff}}$ increasing with $p_T$ of 0.174 ± 0.018 Gev/c in the range 0.4 < $p_T$ < 1.3 Gev/c and increasing to 0.289 ± 0.024 Gev/c for 0.9 < $p_T$ < 2.1 Gev/c. The observed similarity of low-$p_T$ direct-photon production from $\sqrt{s_{NN}}$ = 39 to 2760 GeV suggests a common source of direct photons for the different collision energies and event centrality selections, and suggests a comparable space-time evolution of direct-photon emission.
73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
Erratum: Lévy-stable two-pion Bose-Einstein correlations in s N N = 200 GeV Au + Au collisions [Phys. Rev. C 97 , 064911 (2018)]
We previously published in 2018 a detailed measurement recorded in 2010 for Au+Au collisions at $\sqrt{^SNN}$ = 200 GeV of charged two-pion correlation functions in 0%-30% centrality. We found the data to be well described by Bose-Einstein correlation functions stemming from L$\acute{e}$vy-stable source distributions. Using a fine transverse momentum binning, we extracted the correlation strength parameter λ, the L$\acute{e}$vy index of stability α and the L$\acute{e}$vy length scale parameter R as a function of average transverse mass of the pair m T .
73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
Centrality dependence of Lévy-stable two-pion Bose-Einstein correlations in $\sqrt{𝑠{𝑁𝑁}}$ = 200 GeV Au + Au collisions
The PHENIX experiment measured the centrality dependence of two-pion Bose-Einstein correlation functions in $\sqrt{𝑠{𝑁𝑁}}$ = 200 GeV Au + Au collisions at the Relativistic Heavy Ion Collider at Brookhaven National Laboratory. The data are well represented by Lévy-stable source distributions. The extracted source parameters are the correlation-strength parameter 𝜆, the Lévy index of stability 𝛼, and the Lévy-scale parameter 𝑅 as a function of transverse mass 𝑚 𝑇 and centrality. The 𝜆(𝑚 𝑇 ) parameter is constant at larger values of 𝑚 𝑇 , but decreases as 𝑚 𝑇 decreases. The Lévy-scale parameter 𝑅(𝑚 𝑇 ) decreases with 𝑚 𝑇 and exhibits proportionality to the length scale of the nuclear overlap region. The Lévy exponent 𝛼(𝑚 𝑇 ) is independent of 𝑚 𝑇 within uncertainties in each investigated centrality bin, but shows a clear centrality dependence. At all centralities, the Lévy exponent 𝛼 is significantly different from that of Gaussian (𝛼 = 2) or Cauchy (𝛼 = 1) source distributions. Comparisons to the predictions of Monte-Carlo simulations of resonance-decay chains show that, in all but the most peripheral centrality class (50%–60%), the obtained results are inconsistent with the measurements, unless a significant reduction of the in-medium mass of the 𝜂′ meson is included. Finally, in each centrality class, the best value of the in-medium 𝜂′ mass is compared to the mass of the 𝜂 meson, as well as to several theoretical predictions that consider restoration of U 𝐴 (1) symmetry in hot hadronic matter.
73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
Cross sections of 𝜂 mesons in 𝑝 +𝑝 collisions at forward rapidity at $\sqrt{𝑠}$ = 500 GeV and central rapidity at $\sqrt{𝑠}$ = 510 GeV
We present the first measurements of the forward and midrapidity 𝜂-meson cross sections from 𝑝 + 𝑝 collisions at $\sqrt{𝑠}$ = 500 and 510 GeV, respectively. We also report the midrapidity 𝜂/𝜋 0 ratio at 510 GeV. The forward cross section is measured differentially in 𝜂-meson transverse momentum (𝑝 𝑇 ) from 1.0 to 6.5 GeV/𝑐 for pseudorapidity 3.0 < |𝜂| < 3.8. The midrapidity cross section is measured from 3.5 to 44 GeV/𝑐 for pseudorapidity |𝜂| < 0.35. Both cross sections serve as critical inputs to an updated global analysis of the 𝜂-meson fragmentation functions.
73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
Materials Data on Ta2Al by Materials Project
Ta2Al is beta Plutonium-derived structured and crystallizes in the tetragonal P4_2/mnm space group. The structure is three-dimensional. there are three inequivalent Ta sites. In the first Ta site, Ta is bonded in a 11-coordinate geometry to nine Ta and five Al atoms. There are a spread of Ta–Ta bond distances ranging from 2.69–3.30 Å. There are a spread of Ta–Al bond distances ranging from 2.97–3.13 Å. In the second Ta site, Ta is bonded in a 12-coordinate geometry to seven Ta and five Al atoms. There are one shorter (2.82 Å) and two longer (3.19 Å) Ta–Ta bond lengths. There are a spread of Ta–Al bond distances ranging from 2.68–2.90 Å. In the third Ta site, Ta is bonded in a 2-coordinate geometry to eleven Ta and four Al atoms. The Ta–Ta bond length is 2.72 Å. There are two shorter (2.72 Å) and two longer (3.03 Å) Ta–Al bond lengths. There are two inequivalent Al sites. In the first Al site, Al is bonded in a 10-coordinate geometry to nine Ta and one Al atom. The Al–Al bond length is 2.79 Å. In the second Al site, Al is bonded to twelve Ta atoms to form edge-sharing AlTa12 cuboctahedra.
36 MATERIALS SCIENCE↗
Materials Data on TaAl3 by Materials Project
Al3Ta is beta Cu3Ti-like structured and crystallizes in the tetragonal I4/mmm space group. The structure is three-dimensional. Ta is bonded to twelve Al atoms to form TaAl12 cuboctahedra that share corners with four equivalent TaAl12 cuboctahedra, corners with eight equivalent AlTa4Al8 cuboctahedra, edges with eight equivalent TaAl12 cuboctahedra, edges with sixteen equivalent AlTa4Al8 cuboctahedra, faces with four equivalent TaAl12 cuboctahedra, and faces with fourteen AlTa4Al8 cuboctahedra. There are four shorter (2.73 Å) and eight longer (2.88 Å) Ta–Al bond lengths. There are two inequivalent Al sites. In the first Al site, Al is bonded to four equivalent Ta and eight equivalent Al atoms to form distorted AlTa4Al8 cuboctahedra that share corners with four equivalent AlTa4Al8 cuboctahedra, corners with eight equivalent TaAl12 cuboctahedra, edges with twenty-four AlTa4Al8 cuboctahedra, faces with six equivalent TaAl12 cuboctahedra, and faces with twelve AlTa4Al8 cuboctahedra. All Al–Al bond lengths are 2.88 Å. In the second Al site, Al is bonded to four equivalent Ta and eight Al atoms to form AlTa4Al8 cuboctahedra that share corners with twelve equivalent AlTa4Al8 cuboctahedra, edges with eight equivalent TaAl12 cuboctahedra, edges with sixteen AlTa4Al8 cuboctahedra, faces with four equivalent TaAl12 cuboctahedra, and faces with fourteen AlTa4Al8 cuboctahedra. All Al–Al bond lengths are 2.73 Å.
36 MATERIALS SCIENCE↗