AION/Magis

Abstract:

We propose an alternate, calculable mechanism of dark matter genesis, "thermal freeze-in," involving a Feebly Interacting Massive Particle (FIMP) interacting so feebly with the thermal bath that it never attains thermal equilibrium. As with the conventional "thermal freeze-out" production mechanism, the relic abundance reflects a combination of initial thermal distributions together with particle masses and couplings that can be measured in the laboratory or astrophysically. The freeze-in yield is IR dominated by low temperatures near the FIMP mass and is independent of unknown UV physics, such as the reheat temperature after inflation. Moduli and modulinos of string theory compactifications that receive mass from weak-scale supersymmetry breaking provide implementations of the freeze-in mechanism, as do models that employ Dirac neutrino masses or GUT-scale-suppressed interactions. Experimental signals of freeze-in and FIMPs can be spectacular, including the production of new metastable coloured or charged particles at the LHC as well as the alteration of big bang nucleosynthesis.

Abstract:

A combined mass and particle identification fit is used to make the first observation of the decay B̄s0→Ds±K□ and measure the branching fraction of B̄s0→Ds±K□ relative to B̄s0→Ds+π-. This analysis uses 1.2fb-1 integrated luminosity of pp̄ collisions at s=1.96TeV collected with the CDF II detector at the Fermilab Tevatron collider. We observe a B̄s0→Ds±K□ signal with a statistical significance of 8.1σ and measure B(B̄s0→ Ds±K□)/B(B̄s0→Ds+π-)=0.097±0.018(stat)±0. 009(syst). © 2009 The American Physical Society.