Bulgarian Academy of Sciences

About: Bulgarian Academy of Sciences is a government organization based out in Sofia, Bulgaria. It is known for research contribution in the topics: Catalysis & Coupling constant. The organization has 17989 authors who have published 36276 publications receiving 642820 citations. The organization is also known as: Bulgarian Academy of Sciences，簡稱：BAS & Balgarska Akademiya na Naukite.

Low energy signatures of the TeV scale seesaw mechanism

Abstract: We study a type I seesaw scenario where the right-handed (RH) neutrinos, responsible for the light neutrino mass generation, lie at the electroweak scale. Under certain conditions, the strength of the charged current (CC) and neutral current (NC) weak interactions of the standard model particles with the heavy RH neutrinos can be large enough to allow the production of the latter at the LHC, opening also the possibility of observing other low energy signatures of the new physics in the electroweak precision observables as well as in searches for rare leptonic decays or neutrinoless double beta decay. In this scenario the flavor structure of the indicated CC and NC couplings of the heavy RH neutrinos is essentially determined by the low energy neutrino parameters, leading to fairly strong correlations among the new phenomena. In particular, we show that the present bound on the $\ensuremath{\mu}\ensuremath{\rightarrow}e+\ensuremath{\gamma}$ decay rate makes very difficult the observation of the heavy RH neutrinos at the LHC or the observation of deviations from the standard model predictions in the electroweak precision data. We also show that all present experimental constraints on this scenario still allow (i) for an enhancement of the rate of neutrinoless double beta decay, which thus can be in the range of sensitivity of the GERDA experiment even when the light Majorana neutrinos possess a normal hierarchical mass spectrum, and (ii) for the predicted $\ensuremath{\mu}\ensuremath{\rightarrow}e+\ensuremath{\gamma}$ decay rate to be within the sensitivity range of the MEG experiment.

Study of Z boson production in PbPb collisions at √s NN=2.76TeV

Abstract: A search for Z bosons in the mu^+mu^- decay channel has been performed in PbPb collisions at a nucleon-nucleon centre of mass energy = 2.76 TeV with the CMS detector at the LHC, in a 7.2 inverse microbarn data sample. The number of opposite-sign muon pairs observed in the 60--120 GeV/c^2 invariant mass range is 39, corresponding to a yield per unit of rapidity (y) and per minimum bias event of (33.8 +/- 5.5 (stat) +/- 4.4 (syst)) 10^{-8}, in the |y|<2.0 range. Rapidity, transverse momentum, and centrality dependencies are also measured. The results agree with next-to-leading order QCD calculations, scaled by the number of incoherent nucleon-nucleon collisions.