A
bstract
We report a new measurement of the production of electrons from open heavy-flavor hadron decays (HFEs) at mid-rapidity (|
y
|
<
0.7) in Au+Au collisions at
$$ \sqrt{s_{\textrm{NN}}} $$
s
NN
...= 200 GeV. Invariant yields of HFEs are measured for the transverse momentum range of 3
.
5
< p
T
<
9 GeV/
c
in various configurations of the collision geometry. The HFE yields in head-on Au+Au collisions are suppressed by approximately a factor of 2 compared to that in
p
+
p
collisions scaled by the average number of binary collisions, indicating strong interactions between heavy quarks and the hot and dense medium created in heavy-ion collisions. Comparison of these results with models provides additional tests of theoretical calculations of heavy quark energy loss in the quark-gluon plasma.
Cyclopentadienone iron dicarbonyl complexes were applied in the alkylation of ketones with various aliphatic and aromatic ketones and alcohols via the borrowing hydrogen strategy in mild reaction ...conditions. DFT calculations and experimental works highlight the role of the transition metal Lewis pairs and the base. These iron complexes demonstrated a broad applicability in mild conditions and extended the scope of substrates.
Borrow hydrogen for iron complexes: A cyclopentadienone iron dicarbonyl complex is applied in the alkylation of ketones with various aliphatic and aromatic ketones and alcohols through the borrowing hydrogen strategy in mild reaction conditions. DFT calculations and experimental works highlight the role of this transition metal Lewis pair and the base.
In this study, synthesis of thiol-functionalized silica/PVDF-HFP poly(vinylidene fluoride-hexafluoropropylene) nanocomposite materials was carried out by reactive extrusion through in situ sol–gel ...reactions of an alkoxysilane inorganic precursor solution composed of polydimethoxysiloxane (PDMOS) and mercaptopropyltriethoxysilane (MPTES). Successful introduction of the functional MPTES and structural PDMOS alkoxysilanes, and subsequent condensation reactions in the PVDF-HFP, were obtained through pre-hydrolysis reactions of the precursors. 29Si-Nuclear magnetic resonance was used to assess the hydrolysis level of the inorganic precursor solution and condensation state in the resulting PVDF-HFP/functionalized silica nanocomposites, while the morphology was observed using scanning electron microscopy (SEM). The hydrolysis-condensation reactions resulting in the inorganic phase were optimized by setting an appropriate R0 molar ratio (H2O/alkoxy function), R1 molar ratio (MPTES/PDMOS) and pH of the solution. Increasing the R0 ratio barely affected the hydrolysis kinetics. However, a higher R1 ratio led to a decrease in the inorganic precursors condensation state and consequently to an increase in the reaction time in the extruder to reach the subsequent condensation state. Hence the morphology of the obtained nanocomposites was finer for the highest R1 ratio and in agreement with the evolution of the solubility parameters. Promising ionic exchange capacity (IEC) and conductivity values were obtained for these innovative nanocomposite materials thanks to a controlled oxidation reaction of the thiol groups into sulfonic acid functions. This original approach demonstrated the possibility of incorporating in situ functionalized silica into a molten fluorinated polymer matrix in a unique reactive extrusion procedure.
•Thiol-functionalized silica/PVDF-HFP nanocomposite synthesis by sol–gel and extrusion.•Promising IEC (0.7 meq g−1) and conductivity (9.6 mS cm−1) values were measured.•Mercaptopropyltriethoxysilane acts as the functional precursor and compatibilizer.
Here, we report a measurement of cumulants and correlation functions of event-by-event proton multiplicity distributions from fixed-target Au+Au collisions at $\sqrt{s_\text{NN}}$ = 3 GeV measured by ...the STAR experiment. Protons are identified within the rapidity (y) and transverse momentum ($p_T$) region –0:9 < $\textit{y}$ < 0 and 0:4 < pT < 2:0 GeV/c in the center-of-mass frame. A systematic analysis of the proton cumulants and correlation functions up to sixth-order as well as the corresponding ratios as a function of the collision centrality, $p_T$, and $\textit{y}$ are presented. The effect of pileup and initial volume fluctuations on these observables and the respective corrections are discussed in detail. The results are compared to calculations from the hadronic transport UrQMD model as well as a hydrodynamic model. In the most central 5% collisions, the value of proton cumulant ratio $C_4 = C_2$ is negative, drastically different from the values observed in Au+Au collisions at higher energies. Compared to model calculations including Lattice QCD, a hadronic transport model, and a hydrodynamic model, the strong suppression in the ratio of $C_4/C_2$ at 3 GeV Au+Au collisions indicates an energy regime dominated by hadronic interactions.
Azimuthal anisotropy of produced particles is one of the most important observables used to access the collective properties of the expanding medium created in relativistic heavy-ion collisions. ...Here, in this paper, we present second (v2) and third (v3) order azimuthal anisotropies of $K_{S}^{0}$, Φ, Λ, Ξ, and Ω at midrapidity (|y| < 1) in Au+Au collisions at $\sqrt{s_{NN}}$= 54.4 GeV measured by the STAR detector. The v2 and v3 are measured as a function of transverse momentum and centrality. Their energy dependence is also studied. v3 is found to be more sensitive to the change in the center-of-mass energy than v2. Scaling by constituent quark number is found to hold for v2 within 10%. This observation could be evidence for the development of partonic collectivity in 54.4 GeV Au+Au collisions. Differences in v2 and v3 between baryons and antibaryons are presented, and ratios of v3/v$^{3/2}_{2}$ are studied and motivated by hydrodynamical calculations. The ratio of v2 of Φ mesons to that of antiprotons v2(Φ)/v2($\overline{p}$) shows centrality dependence at low transverse momentum, presumably resulting from the larger effects from hadronic interactions on antiproton v2.
In relativistic heavy-ion collisions, a global spin polarization, PH, of Λ and Λ¯¯ hyperons along the direction of the system angular momentum was discovered and measured across a broad range of ...collision energies and demonstrated a trend of increasing PH with decreasing $\sqrt{s{NN}}$. A splitting between Λ and Λ¯¯ polarization may be possible due to their different magnetic moments in a late-stage magnetic field sustained by the quark-gluon plasma which is formed in the collision. The results presented in this study find no significant splitting at the collision energies of $\sqrt{s{NN}}$ = 19.6 and 27 GeV in the BNL Relativistic Heavy Ion Collisions Beam Energy Scan Phase II using the STAR detector, with an upper limit of PΛ¯¯ – PΛ < 0.24 % and PΛ¯¯ – PΛ < 0.35 %, respectively, at a 95% confidence level. We derive an upper limit on the naive extraction of the late-stage magnetic field of B < 9.4 × 1012 T and B < 1.4 × 1013 T at $\sqrt{s{NN}}$ = 19.6 and 27 GeV, respectively, although more thorough derivations are needed. Differential measurements of PH were performed with respect to collision centrality, transverse momentum, and rapidity. With our current acceptance of |y| < 1 and uncertainties, we observe no dependence on transverse momentum and rapidity in this analysis. These results challenge multiple existing model calculations following a variety of different assumptions which have each predicted a strong dependence on rapidity in this collision-energy range.
We report systematic measurements of dielectron (e+e–) invariant-mass Mee spectra at midrapidity in Au + Au collisions at sNN=27 = 27, 39, and 62.4 GeV taken with the STAR detector at the ...Relativistic Heavy Ion Collider. For all energies studied, a significant excess yield of dielectrons is observed in the low-mass region ( 0.40 < Mee < 0.75 MeV / c2) compared to hadronic cocktail simulations at freeze-out. Models that include an in-medium broadening of the ρ -meson spectral function consistently describe the observed excess. In addition, we report acceptance-corrected dielectron-excess spectra for Au + Au collisions at midrapidity ( |yee| < 1) in the 0–80% centrality bin for each collision energy. The integrated excess yields for 0.4 < Mee < 0.75 GeV / c2, normalized by the charged particle multiplicity at midrapidity, are compared with previously published measurements for Au + Au at sNN=27 = 19.6 and 200 GeV. Models that include an in-medium broadening of the ρ -meson spectral function consistently describe the observed excess. Furthermore, the normalized excess yields in the low-mass region show no significant collision energy dependence. The data, however, are consistent with model calculations that demonstrate a modest energy dependence.
The differential cross section for Z0 production, measured as a function of the boson’s transverse momentum (pT), provides important constraints on the evolution of the transverse momentum dependent ...parton distribution functions (TMDs). The transverse single spin asymmetry (TSSA) of the Z0 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 Z0/γ* differential cross section as a function of its pT in p+p collisions at a center-of-mass energy of 510 GeV, together with the Z0/γ* total cross section. We also report the measurement of Z0/γ* TSSA in transversely polarized p+p collisions at 510 GeV.
Angular distributions of charged particles relative to jet axes are studied in $\sqrt{^SNN}$ = 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 < $p_{\text {T,jet}}$ < 20 and 20 < $p_{\text {T,jet}}$ < 40 GeV / $c$ were reconstructed with the anti-$k_{\text {T}}$ 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. Finally, this finding is consistent with a similar experimental observation by ALICE in $\sqrt{^SNN}$ = 2.76 TeV Pb-Pb collision data.
