THE AFTERCLAP OF DEGENERATE CARBON IGNITION REVISITED

L'ignition du carbone et le mode de propagation de la combustion décident de manière critique du sort des étoiles qui développent des coeurs de carbone/oxygène, c'est-à-dire explosion ou implosion. Le processus le plus rapide (détonation, conduction ou convection) détermine la vitesse de propagation du front de combustion. On peut probablement éliminer la formation d'une détonation à cause de la petitesse de la surpression générée par la combustion à haute densité. Nous démontrons qu'après une courte durée de combustion par conduction, un régime de convection s'établit. Nous en tirons la conclusion que si l'ignition a lieu à densité suffisamment grande (ρ>5 x 109 g/cc) les captures d'électrons et les pertes de neutrino concomitantes causent la réimplosion du coeur de l'étoile.Whether the degenerate C-O cores, with develop in the heart of 4-8 Mθ stars, get fully disrupted or implode into neutron stars depends critically on the results of carbon ignition and on the nature of the propagation of the burning front. The velocity of this front is determined by the fastest of several processes, namely (1) detonation, (2) conductive burning, and (3) convective burning. Detonation can probably be excluded because of the small overpressures resulting from burning at high density. Since conductive burning is estimated to be very slow, the burning front is shown to propagate by convection. We conclude that if ignition occurs at sufficiently high density (ρ > 5 x 109 g/cm3), electron captures and concomitant neutrino losses will then offset the effects of burning and cause the implosion of the core

Observation of the B+^{+}→ Jψη′K+^{+} decay

International audienceThe B$^{+}$ → Jψη′K$^{+}$ decay is observed for the first time using proton-proton collision data collected by the LHCb experiment at centre-of-mass energies of 7, 8, and 13 TeV, corresponding to a total integrated luminosity of 9 fb$^{−1}$. The branching fraction of this decay is measured relative to the known branching fraction of the B$^{+}$ → ψ(2S)K$^{+}$ decay and found to be$\frac{\mathcal{B}\left({B}^{+}\to {J\psi \eta}^{\prime }{K}^{+}\right)}{\mathcal{B}\left({B}^{+}\to \psi (2S){K}^{+}\right)}=\left(4.91\pm 0.47\pm 0.29\pm 0.07\right)\times {10}^{-2},$where the first uncertainty is statistical, the second is systematic and the third is related to external branching fractions. A first look at the J/ψη′ mass distribution is performed and no signal of intermediate resonances is observed.[graphic not available: see fulltext