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At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Measurements of Born cross sections for e + e − → Λ c + Λ ¯ c ( 2595 ) − + c . c . and e + e − → Λ c + Λ ¯ c ( 2625 ) − + c . c . at s = 4918.0 and 4950.9 MeV

Using e + e − collision data collected with the BESIII detector operating at the BEPCII collider, the Born cross sections of e + e − → Λ c + Λ ¯ c ( 2595 ) − + c . c . and e + e − → Λ c + Λ ¯ c ( 2625 ) − + c . c . are measured for the first time at center-of-mass energies of s = 4918.0 and 4950.9 MeV. Nonzero cross sections are observed very close to the production threshold. The measured Born cross sections of e + e − → Λ c + Λ ¯ c ( 2625 ) − + c . c . are about 2–3 times greater than those of e + e − → Λ c + Λ ¯ c ( 2595 ) − + c . c . , providing the similar behavior as semileptonic decays of Λ b 0 , but different behavior from that in the hadronic decays of Λ b 0 . The Born cross sections are 15.6 ± 3.1 ± 0.9 pb and 29.4 ± 3.7 ± 2.7 pb for e + e − → Λ c + Λ ¯ c ( 2595 ) − + c . c . , and are 43.4 ± 4.0 ± 4.1 pb and 76.8 ± 6.5 ± 4.2 pb for e + e − → Λ c + Λ ¯ c ( 2625 ) − + c . c . at s = 4918.0 and 4950.9 MeV, respectively. Based on the polar angle distributions of the Λ ¯ c ( 2625 ) − and Λ c ( 2625 ) + , the form-factor ratios | G E | 2 + 3 | G M | 2 / | G C | are determined for e + e − → Λ c + Λ ¯ c ( 2625 ) − + c . c . for the first time, which are 5.95 ± 4.07 ± 0.15 and 0.94 ± 0.32 ± 0.02 at s = 4918.0 and 4950.9 MeV, respectively. All of these first uncertainties are statistical and second systematic. Published by the American Physical Society 2024

Astronomy & Astrophysics↗
DOE OSTI2018

A combined crossed molecular beams and computational study on the formation of distinct resonantly stabilized C 5 H 3 radicals via chemically activated C 5 H 4 and C 6 H 6 intermediates

The crossed molecular beams technique was utilized to investigate the formation of three isomers of resonantly stabilized (C 5 H 3 ) radicals along with their d 2 -substituted counterparts via the bimolecular reactions of singlet/triplet dicarbon [C 2 (X 1 Σ + g /a 3 Π u )] with methylacetylene [CH 3 CCH(X 1 A 1 )], d 3 -methylacetylene [CD 3 CCH(X 1 A 1 )], and 1-butyne [C 2 H 5 CCH(X 1 A')] at collision energies up to 26 kJ mol -1 via chemically activated singlet/triplet C 5 H 4 /C 5 D 3 H and C 6 H 6 intermediates. These studies exploit a newly developed supersonic dicarbon [C 2 (X 1 Σ + g /a 3 Π u )] beam generated via photolysis of tetrachloroethylene [C 2 Cl 4 (X 1 A g )] by excluding interference from carbon atoms, which represent the dominating (interfering) species in ablation-based dicarbon sources. We assessed the performance of the dicarbon [C 2 (X 1 Σ + g /a 3 Π u )] beam in reactions with methylacetylene [CH 3 CCH(X 1 A 1 )] and d 3 -methylacetylene [CD 3 CCH(X 1 A 1 )]; the investigations demonstrate that the reaction dynamics match previous studies in our laboratory utilizing ablation-based dicarbon sources involving the synthesis of 1,4-pentadiynyl-3 [HCCCHCCH(X 2 B 1 )] and 2,4-pentadiynyl-1 [H 2 CCCCCH(X 2 B 1 )] radicals via hydrogen (deuterium) atom elimination. Considering the C 2 (X 1 Σ + g /a 3 Π u )–1-butyne [C 2 H 5 CCH(X 1 A')] reaction, the hitherto elusive methyl-loss pathway was detected. This channel forms the previously unknown resonantly stabilized penta-1-yn-3,4-dienyl-1 [H 2 CCCHCC(X 2 A)] radical along with the methyl radical [CH 3 (X 2 A 2 ")] and is open exclusively on the triplet surface with an overall reaction energy of -86 ± 10 kJ mol -1 . The preferred reaction pathways proceed first by barrierless addition of triplet dicarbon to the π-electronic system of 1-butyne, either to both acetylenic carbon atoms or to the sterically more accessible carbon atom, to form the methyl-bearing triplet C 6 H 6 intermediates [ i4 1b ] and [ i8 1b ], respectively, with the latter decomposing via a tight exit transition state to penta-1-yn-3,4-dienyl-1 [(H 2 CCCHCC(X 2 A)] plus the methyl radical [CH 3 (X 2 A 2 ")]. The successful unraveling of this methyl-loss channel – through collaborative experimental and computational efforts – underscores the viability of the photolytically generated dicarbon beam as an unprecedented tool to access reaction dynamics underlying the formation of resonantly stabilized free radicals (RSFR) that are vital to molecular mass growth processes that ultimately lead to polycyclic aromatic hydrocarbons (PAHs)

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Measurements of branching fractions of Λ$^{+}_{c}$ → Σ + ⁢η and Λ$^{+}_{c}$ → Σ + ⁢η' and asymmetry parameters of Λ$^{+}_{c}$ → Σ + ⁢π 0 , Λ$^{+}_{c}$ → Σ + ⁢η, and Λ$^{+}_{c}$ → Σ + ⁢η'

We report a study of Λ c + → Σ + π 0 , Λ c + → Σ + η , and Λ c + → Σ + η ' using the data sample corresponding to an integrated luminosity of 980 fb - 1 collected with the Belle detector at the KEKB asymmetric-energy e + e - collider. The branching fractions relative to Λ c + → Σ + π 0 are measured as B Λ c + → Σ + η / B Λ c + → Σ + π 0 = 0.25 ± 0.03 ± 0.01 and B Λ c + → Σ + η ' / B Λ c + → Σ + π 0 = 0.33 ± 0.06 ± 0.02 . Using B Λ c + → Σ + π 0 = ( 1.25 ± 0.10 ) % , we obtain B Λ c + → Σ + η = ( 3.14 ± 0.35 ± 0.17 ± 0.25 ) × 10 - 3 and B Λ c + → Σ + η ' = ( 4.16 ± 0.75 ± 0.25 ± 0.33 ) × 10 - 3 . Here the uncertainties are statistical, systematic, and from B Λ c + → Σ + π 0 , respectively. The ratio of the branching fraction of Λ c + → Σ + η ' with respect to that of Λ c + → Σ + η is measured to be B Λ c + → Σ + η ' / B Λ c + → Σ + η = 1.34 ± 0.28 ± 0.08 . We update the asymmetry parameter of Λ c + → Σ + π 0 , α Σ + π 0 = - 0.48 ± 0.02 ± 0.02 , with a considerably improved precision. The asymmetry parameters of Λ c + → Σ + η and Λ c + → Σ + η ' are measured to be α Σ + η = - 0.99 ± 0.03 ± 0.05 and α Σ + η ' = - 0.46 ± 0.06 ± 0.03 for the first time.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2024

Search for charmed baryons in the Λ c + η system and measurement of the branching fractions of Λ c ( 2880 ) + and Λ c ( 2940 ) + decaying to Λ c + η and p D 0 relative to Σ c ( 2455 ) π

We search for excited charmed baryons in the Λ c + η system using a data sample corresponding to an integrated luminosity of 980 fb − 1 . The data were collected by the Belle detector at the KEKB e + e − asymmetric-energy collider. No significant signals are found in the Λ c + η mass spectrum, including the known Λ c ( 2880 ) + and Λ c ( 2940 ) + . Clear Λ c ( 2880 ) + and Λ c ( 2940 ) + signals are observed in the p D 0 mass spectrum. We set upper limits at 90% credibility level on ratios of branching fractions of Λ c ( 2880 ) + and Λ c ( 2940 ) + decaying to Λ c + η relative to Σ c ( 2455 ) π of < 0.13 for the Λ c ( 2880 ) + and < 1.11 for the Λ c ( 2940 ) + . We measure ratios of branching fractions of Λ c ( 2880 ) + and Λ c ( 2940 ) + decaying to p D 0 relative to Σ c ( 2455 ) π of 0.75 ± 0.03 ( stat ) ± 0.07 ( syst ) for the Λ c ( 2880 ) + and 3.59 ± 0.21 ( stat ) ± 0.56 ( syst ) for the Λ c ( 2940 ) + . Published by the American Physical Society 2024

Astronomy & Astrophysics↗
DOE OSTI2023

Measurement of the mass and width of the Λ c ⁢(2625) + charmed baryon and the branching ratios of Λ c ⁢(2625) + → Σ$^{0}_{c}$π + and Λ c ⁢(2625) + → Σ$^{++}_{c}$π -

Using the entire data sample of 980 fb -1 collected at or near the Y⁡(4⁢S) resonance with the Belle detector operating at the KEKB asymmetric-energy e + ⁢e - collider, we report the measurement of the mass, width, and the branching ratios of the Λ c (2625) + charmed baryon. The mass difference between Λ c ⁢(2625) + and Λ$^{+}_{c}$ is measured to be M⁡(Λ c ⁢(2625) + )-M⁡(Λ$^{+}_{c}$)=341.518±0.006±0.049 MeV/c 2 . The upper limit on the width is measured to be Γ⁡(Λ c ⁢(2625) + )<0.52 MeV/c 2 at 90% confidence level. Based on a full Dalitz plot fit, branching ratios with respect to the mode Λ c⁢ (2625) + →Λ$^{+}_{c}$π + ⁢π - are measured to be $\frac{\mathscr{B}⁡(Λ_c(2625)^+ → Σ^{0}_{c}π^+)} {\mathscr{B}⁡(Λ_c(2625)^+ → ^{+}_{c}⁢π^+⁢π^-)}$ = (5.19±0.23±0.40)% and $\frac{\mathscr{B}(Λ_c (2625)^+ → Σ{_c^+}^+ π^-)}{\mathscr{B}(Λ_c (2625)^+ → Λ{_c^+} π^+π^-)}$ = (5.13±0.26±0.32)%, where the first and second uncertainties are statistical and systematic, respectively. These measurements can be used to further constrain the parameters of the underlying theoretical models.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2024

Study of h c → 3 ( π + π − ) π 0 , h c → 2 ( π + π − ) ω , h c → 2 ( π + π − ) π 0 η , h c → 2 ( π + π − ) η , and h c → p p ¯

Based on ( 2712.4 ± 14.1 ) × 10 6 ψ ( 3686 ) events collected with the BESIII detector, we study the decays h c → 3 ( π + π − ) π 0 , h c → 2 ( π + π − ) ω , h c → 2 ( π + π − ) π 0 η , h c → 2 ( π + π − ) η , and h c → p p ¯ via ψ ( 3686 ) → π 0 h c . The decay channel h c → 3 ( π + π − ) π 0 is observed for the first time, and its branching fraction is determined to be ( 9.28 ± 1.14 ± 0.77 ) × 10 − 3 , where the first uncertainty is statistical and the second is systematic. In addition, first evidence is found for the modes h c → 2 ( π + π − ) π 0 η and h c → 2 ( π + π − ) ω with significances of 4.8 σ and 4.7 σ , and their branching fractions are determined to be ( 7.55 ± 1.51 ± 0.77 ) × 10 − 3 and ( 4.00 ± 0.86 ± 0.35 ) × 10 − 3 , respectively. No significant signals of h c → 2 ( π + π − ) η and h c → p p ¯ are observed, and the upper limits of the branching fractions of these decays are determined to be < 6.19 × 10 − 4 and < 4.40 × 10 − 5 at the 90% confidence level, respectively. Published by the American Physical Society 2024

Astronomy & Astrophysics↗
DOE OSTI2016

Phase relations of Fe 3 C and Fe 7 C 3 up to 185 GPa and 5200 K: Implication for the stability of iron carbide in the Earth's core

We have investigated phase relations and melting behavior of Fe 3 C and Fe 7 C 3 using X-ray diffraction in a laser-heated diamond cell up to 185 GPa and 5200 K. Our results show that the starting Fe 3 C sample decomposes into a mixture of solid orthorhombic Fe 7 C 3 and hcp-Fe at above 145 GPa upon laser heating and then transforms into Fe-C liquid and solid Fe 7 C 3 at temperatures above 3400 K. Using the intensity of the diffuse scattering as a primary criteria for detecting melting, the experimentally derived liquidus for a bulk composition of Fe 3 C fitted with the Simon-Glatzel equation is T m (K) = 1800 × [1 + (P m -5.7)/15.10 ± 2.55] 1/2.41 ± 0.17 at 24–185 GPa, which is ~500 K higher than the melting curve of iron reported by Anzellini et al. (2013) at Earth's core pressures. The higher melting point and relative stability of Fe 7 C 3 in Fe-rich Fe-C system at Earth's core conditions indicate that Fe 7 C 3 could solidify out of the early Earth's molten core to become a constituent of the innermost inner core.

58 GEOSCIENCES↗
DOE OSTI2016

Expanding the Chemistry of Actinide Metallocene Bromides. Synthesis, Properties and Molecular Structures of the Tetravalent and Trivalent Uranium Bromide Complexes: (C 5 Me 4 R) 2 UBr 2 , (C 5 Me 4 R) 2 U(O-2,6- i Pr 2 C 6 H 3 )(Br), and [K(THF)][(C 5 Me 4 R) 2 UBr 2 ] (R = Me, Et)

The organometallic uranium species (C 5 Me 4 R) 2 UBr 2 (R = Me, Et) were obtained by treating their chloride analogues (C 5 Me 4 R) 2 UCl 2 (R = Me, Et) with Me 3 SiBr. Treatment of (C 5 Me 4 R) 2 UCl 2 and (C 5 Me 4 R) 2 UBr 2 (R = Me, Et) with K(O-2,6- i Pr 2 C 6 H 3 ) afforded the halide aryloxide mixed-ligand complexes (C 5 Me 4 R) 2 U(O-2,6- i Pr 2 C 6 H 3 )(X) (R = Me, Et; X = Cl, Br). Complexes (C 5 Me 4 R) 2 U(O-2,6- i Pr 2 C 6 H 3 )(Br) (R = Me, Et) can also be synthesized by treating (C 5 Me 4 R) 2 U(O-2,6- i Pr 2 C 6 H 3 )(Cl) (R = Me, Et) with Me 3 SiBr, respectively. Reduction of (C 5 Me 4 R) 2 UCl 2 and (C 5 Me 4 R) 2 UBr 2 (R = Me, Et) with KC 8 led to isolation of uranium(III) “ate” species [K(THF)][(C 5 Me 5 ) 2 UX 2 ] (X = Cl, Br) and [K(THF) 0.5 ][(C 5 Me 4 Et) 2 UX 2 ] (X = Cl, Br), which can be converted to the neutral complexes (C 5 Me 4 R) 2 U[N(SiMe 3 ) 2 ] (R = Me, Et). Analyses by nuclear magnetic resonance spectroscopy, X-ray crystallography, and elemental analysis are also presented.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

Insights into PG-binding, conformational change, and dimerization of the OmpA C-terminal domains from Salmonella enterica serovar Typhimurium and Borrelia burgdorferi : Characterization of OmpA C-Terminal Domain

S. Typhimurium can induce both humoral and cell-mediated responses when establishing itself in the host. These responses are primarily stimulated against the lipopolysaccharide and major outer membrane (OM) proteins of the bacterium. OmpA is one of these major OM proteins. It comprises a N-terminal eight-stranded -barrel membrane domain and a C-terminal so-called OmpA C-terminal domain (OmpACTD). The OmpACTD and its homologs are believed to bind to peptidoglycan (PG) within the periplasm, maintaining bacterial osmotic homeostasis and modulating the permeability and integrity of the outer membrane. Here we present the structures of two forms of the OmpACTD of S. Typhimurium (STOmpACTD) and one structure of the less-studied OmpACTD of Borrelia burgdorferi (BbOmpACTD). In the open form of STOmpACTD, an aspartic acid residue from a long 2-3 loop points into the binding pocket, suggesting that an anion group such as a carboxylate group from PG is favored at the binding site. In the closed form of STOmpACTD and in the structure of BbOmpACTD, a sulfate group from the crystallization buffer is tightly bound at the equivalent site. The differences between the closed and open forms of STOmpACTD, suggest a large conformational change that includes an extension of 3 helix by ordering a part of 2-3 loop. We suggest that the sulfate anion observed in these structures mimics the carboxylate group of PG when bound to STOmpACTD. In addition, the binding of PG or a ligand mimic may enhance dimerization of STOmpACTD, or possibly that of full length STOmpA.

Environmental Molecular Sciences Laboratory↗
DOE OSTI2018

Evidence of a structure in $\bar{K}^{0} \Lambda _{c}^{+}$ consistent with a charged $\Xi _c(2930)^{+}$, and updated measurement of $\bar{B}^{0} \rightarrow \bar{K}^{0} \Lambda _{c}^{+} \bar{\Lambda }_{c}^{-}$ at Belle

We report evidence for the charged charmed-strange baryon Ξ c (2930) + with a signal significance of 3.9 σ with systematic errors included. The charged Ξ c (2930) + is found in its decay to K$0\atop{S}$Λ$+\atop{c}$ in the substructure of $\bar{B}$ 0 →K$0\atop{S}$Λ$+\atop{c}$ $\bar{Λ}$ $\bar{c}$ decays. The measured mass and width are [2942.3±4.4(stat.)±1.5(syst.)] MeV/c 2 and [14.8±8.8(stat.)±2.5(syst.)] MeV, respectively, and the product branching fraction is B($\bar{B^0}$→Ξ c (2930) + $\bar{Λ}$ $\bar{c}$)B(Ξ c (2930) + →$\bar{K}^0$Λ$+\atop{c}$)=[2.37±0.51(stat.)±0.31(syst.)]×10 -4 . We also measure B($\bar{B}^{0} \rightarrow \bar{K}^{0} \Lambda _{c}^{+} \bar{\Lambda }_{c}^{-}$)=[3.99±0.76(stat.)±0.51(syst.)]×10 -4 with greater precision than previous experiments, and present the results of a search for the charmonium-like state Y(4660) and its spin partner,Y η , in the Λ$+\atop{c}$ $\bar{Λ}$ $-\atop{c}$ invariant mass spectrum. No clear signals of the Y(4660) or Y η are observed and the 90% credibility level (C.L.) upper limits on their production rates are determined. These measurements are obtained from a sample of (772±11)×10 6 $B\bar{B}$ pairs collected at the Υ(4S) resonance by the Belle detector at the KEKB asymmetric energy electron-positron collider.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2016

Ab Initio Reaction Kinetics of CH 3 O$\dot{C}$(=O) and $\dot{C}$H 2 OC(=O)H Radicals

The dissociation and isomerization kinetics of the methyl ester combustion intermediates methoxycarbonyl radical (CH3O$\dot{C}$(=O)) and (formyloxy)methyl radical ($\dot{C}$H2OC(=O)H) are investigated theoretically using high-level ab initio methods and Rice–Ramsperger–Kassel–Marcus (RRKM)/master equation (ME) theory. Geometries obtained at the hybrid density functional theory (DFT) and coupled cluster singles and doubles with perturbative triples correction (CCSD(T)) levels of theory are found to be similar. We employ high-level ab initio wave function methods to refine the potential energy surface: CCSD(T), multireference singles and doubles configuration interaction (MRSDCI) with the Davidson–Silver (DS) correction, and multireference averaged coupled-pair functional (MRACPF2) theory. MRSDCI+DS and MRACPF2 capture the multiconfigurational character of transition states (TSs) and predict lower barrier heights than CCSD(T). The temperature- and pressure-dependent rate coefficients are computed using RRKM/ME theory in the temperature range 300–2500 K and a pressure range of 0.01 atm to the high-pressure limit, which are then fitted to modified Arrhenius expressions. Dissociation of CH3O$\dot{C}$(=O) to $\dot{C}$H3 and CO2 is predicted to be much faster than dissociating to CH3$\dot{O}$ and CO, consistent with its greater exothermicity. Isomerization between CH3O$\dot{C}$(=O) and $\dot{C}$H2OC(=O)H is predicted to be the slowest among the studied reactions and rarely happens even at high temperature and high pressure, suggesting the decomposition pathways of the two radicals are not strongly coupled. The predicted rate coefficients and branching fractions at finite pressures differ significantly from the corresponding high-pressure-limit results, especially at relatively high temperatures. Finally, because it is one of the most important CH3$\dot{O}$ removal mechanisms under atmospheric conditions, the reaction kinetics of CH3$\dot{O}$ + CO was also studied along the PES of CH3O$\dot{C}$(=O); the resulting kinetics predictions are in remarkable agreement with experiments.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

CARBON-RICH PRESOLAR GRAINS FROM MASSIVE STARS: SUBSOLAR {sup 12}C/{sup 13}C AND {sup 14}N/{sup 15}N RATIOS AND THE MYSTERY OF {sup 15}N

Carbon-rich grains with isotopic anomalies compared to the Sun are found in primitive meteorites. They were made by stars, and carry the original stellar nucleosynthesis signature. Silicon carbide grains of Type X and C and low-density (LD) graphites condensed in the ejecta of core-collapse supernovae. We present a new set of models for the explosive He shell and compare them with the grains showing {sup 12}C/{sup 13}C and {sup 14}N/{sup 15}N ratios lower than solar. In the stellar progenitor H was ingested into the He shell and not fully destroyed before the explosion. Different explosion energies and H concentrations are considered. If the supernova shock hits the He-shell region with some H still present, the models can reproduce the C and N isotopic signatures in C-rich grains. Hot-CNO cycle isotopic signatures are obtained, including a large production of {sup 13}C and {sup 15}N. The short-lived radionuclides {sup 22}Na and {sup 26}Al are increased by orders of magnitude. The production of radiogenic {sup 22}Ne from the decay of {sup 22}Na in the He shell might solve the puzzle of the Ne-E(L) component in LD graphite grains. This scenario is attractive for the SiC grains of type AB with {sup 14}N/{sup 15}N ratios lower than solar, and provides an alternative solution for SiC grains originally classified as nova grains. Finally, this process may contribute to the production of {sup 14}N and {sup 15}N in the Galaxy, helping to produce the {sup 14}N/{sup 15}N ratio in the solar system.

79 ASTRONOMY AND ASTROPHYSICS↗