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Register a new userReactions forming C(0,+)n=2,10, Cn=2,4H(0,+) and C3H(0,+) in the gas phase: semi empirical branching ratios
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The aim of this paper is to provide a new set of branching ratios for interstellar and planetary chemical networks based on a semi empirical model. We applied, instead of zero order theory (i.e. only the most exoergic decaying channel is considered), a statistical microcanonical model based on the construction of breakdown curves and using experimental high velocity collision branching ratios for their parametriza- tion. We applied the model to ion-molecule, neutral-neutral, and ion-pair reactions implemented in the few popular databases for astrochemistry such as KIDA, OSU and UMIST. We studied the reactions of carbon and hydrocarbon species with electrons, He+, H+, CH+, CH, C, and C+ leading to intermediate complexes of the type Cn=2,10, Cn=2,4 H, C3 H2, C+n=2,10, Cn=2,4 H+, or C3 H+2 . Comparison of predictions with measurements supports the validity of the model. Huge deviations with respect to database values are often obtained. Effects of the new branching ratios in time dependant chemistry for dark clouds and for photodissociation region chemistry with conditions similar to those found in the Horsehead Nebula are discussed.
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Using the entire data sample of $980$ $fb^{-1}$ integrated luminosity collected with the Belle detector at the KEKB asymmetric-energy $e^{+}e^{-}$ collider, we present an amplitude analysis measuring the branching fractions of the Cabibbo-allowed, $W$-exchange resonant decay $Xi_{c}^{0} rightarrow Xi^{0} phi (to K^+ K^-)$ with a polarized $phi$ and the non-resonant decay via a direct process $Xi_{c}^{0} rightarrow Xi^{0} K^+ K^-$. We present these measurements, relative to the normalization mode $Xi^{-}pi^{+}$, and find branching ratios $frac{mathcal{B}(Xi_{c}^{0} rightarrow Xi^{0} phi (rightarrow K^{+}K^{-}))}{mathcal{B}(Xi_{c}^{0} rightarrow Xi^{-} pi^{+})} = 0.036 pm 0.004 (stat.) pm 0.002 (syst.)$ and $frac{mathcal{B}(Xi_{c}^{0} rightarrow Xi^{0} K^{+} K^{-})}{mathcal{B}(Xi_{c}^{0} rightarrow Xi^{-} pi^{+})} = 0.039 pm 0.004 (stat.) pm 0.002 (syst.)$ which suggest that only minor cusping peaks occur in the combinatorial background of $Omega^{*-} to Xi^{0}K^{-}$ due to these $Xi_{c}^{0}$ decays.
We precisely measured pi^0 branching ratios of 5_Lambda-He and 12_Lambda-C hypernuclei produced via (pi^+,k^+) reaction. Using these pi^0 branching ratios with the pi^- branching ratios and the lifetimes, we obtained the pi^0 decay widths and the non-mesonic weak decay widths at high statistics with the accuracy of ~5 % (stat) for both hypernuclei.
We present Atacama Large Millimeter/sub-millimeter Array (ALMA) observations towards 27 low-redshift ($0.02< z<0.2$) star-forming galaxies taken from the Valparaiso ALMA/APEX Line Emission Survey (VALES). We perform stacking analyses of the $^{12}$CO($1-0$), $^{13}$CO($1-0$) and C$^{18}$O($1-0$) emission lines to explore the $L$ ($^{12}$CO($1-0$))/$L$($^{13}$CO($1-0$))) (hereafter $L$($^{12}$CO)/$L$($^{13}$CO)) and $L$($^{13}$CO($1-0$))/$L$(C$^{18}$O($1-0$)) (hereafter $L$($^{13}$CO)/$L$(C$^{18}$O) line luminosity ratio dependence as a function of different global galaxy parameters related to the star formation activity. The sample has far-IR luminosities $10^{10.1-11.9}$L$_{odot}$ and stellar masses of $10^{9.8-10.9}$M$_{odot}$ corresponding to typical star-forming and starburst galaxies at these redshifts. On average we find a $L$($^{12}$CO)/$L$($^{13}$CO) line luminosity ratio value of 16.1$pm$2.5. Galaxies with evidences of possible merging activity tend to show higher $L$($^{12}$CO)/$L$($^{13}$CO) ratios by a factor of two, while variations of this order are also found in galaxy samples with higher star formation rates or star formation efficiencies. We also find an average $L$($^{13}$CO)/$L$(C$^{18}$O) line luminosity ratio of 2.5$pm$0.6, which is in good agreement with those previously reported for starburst galaxies. We find that galaxy samples with high $L_{text{IR}}$, SFR and SFE show low $L$($^{13}$CO)/$L$(C$^{18}$O) line luminosity ratios with high $L$($^{12}$CO)/$L$($^{13}$CO) line luminosity ratios, suggesting that these trends are produced by selective enrichment of massive stars in young starbursts.
The cross sections for the reactions pp -> p Lambda^0K^+ and pn -> n Lambda^0K^+ are calculated near threshold of the final states. The theoretical ratio of the cross sections R = sigma(pn -> n Lambda^0K^+)/ sigma(pp ->pLambda^0K^+) = 3 shows the enhancement of the pn interaction with respect to the pp interaction near threshold of the strangeness production N Lambda^0K^+. Such an enhancement is caused by the contribution of the np interaction in the isospin-singlet state, which is stronger than the $pn$ interaction in the isospin-triplet state. For the confirmation of this result we calculate the cross sections for the reactions pp -> pp pi^0, pi^0 p -> Lambda^0 K^+ and pi^-p -> Lambda^0 K^0 near threshold of the final states. The theoretical cross sections agree well with the experimental data.
Differential cross sections and hyperon polarizations have been measured for $bar{K}^0 n$, $pi^0 Lambda$, and $pi^0 Sigma^0$ production in $K^- p$ interactions at eight $K^-$ momenta between 514 and 750 MeV/$c$. The experiment detected the multiphoton final states with the Crystal Ball spectrometer using a $K^-$ beam from the Alternating Gradient Synchrotron of BNL. The results provide significantly greater precision than the existing data, allowing a detailed reexamination of the excited hyperon states in our energy range.
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