FLAVIDAS · The physics of flavor in visible and dark sectors

The physics of flavor in visible and dark sectors

The project focussed on two major open problems of high energy physics: the origin of flavour structure in the Standard Model and beyond, and the nature of Dark Matter (DM). The aim of the project was to: (i) investigate the implications of flavour symmetries at future low energy machines and at CERN LHC, and (ii) develop a model independent description of direct DM searches and explore their relevance for astrophysical and collider signatures of DM. Since the start of the project we have investigated the implications of ?avour symmetries at future low energy machines and at CERN LHC. We have shown that the D0 Collaboration reported 3.2 sigma deviation from the standard model prediction in the like-sign dimuon asymmetry can be explained within Minimal Flavour Violation hypothesis. Assuming that new physics contributes only to Bd and Bs meson mixing, we showed that the data can be analysed without using the theoretical calculation of the decay width difference in Bs mesons allowing for robust interpretations. We found that this framework gives a good fit to all measurements, including the measurements of time dependent CP asymmetries in J/Psi phi final state at Tevatron. The data allow universal new physics with similar contributions relative to the SM in the Bd and Bs systems, but flavours a larger deviation in Bs than in Bd mixing. The general minimal flavour violation framework with flavour diagonal CP violating phases can account for the former and remarkably even for the latter case. This observation makes it simpler to speculate about which extensions with general flavour structure may also fit the data. The results of the study were published in Phys. Rev. Lett. 105 (2010) 131601. We have explored the possibilities to search for dark sector using the Higgs boson decays, if these are predominantly into a hidden sector, producing lepton jets instead of the standard Higgs signatures. We proposed a search strategy for such a signal at hadron colliders. A promising channel is the associated production of the Higgs with a Z or W, where the dominant background is Z or W plus QCD jets. The lepton jets can be discriminated from QCD jets by cutting on the electromagnetic fraction and charge ratio. The former is the fraction of jet energy deposited in the electromagnetic calorimeter and the latter is the ratio of energy carried by charged particles to the electromagnetic energy. We used a Monte Carlo description of detector response to estimate QCD rejection efficiencies of order 0.01 per jet. The expected Higgs mass reach is about 155 GeV at the Tevatron with 10 inverse femtobarns of data and about 135 GeV at the 7 TeV LHC with 1 inverse femtobarn. The results were published in Phys. Rev. Lett. 105 (2010) 241801. We have developed the model independent description of direct DM searches including interactions with leptons. Dark matter interacting predominantly with leptons instead of nuclear matter has received a lot of interest recently. We investigated the signals expected from such 'leptophilic Dark Matter' in direct detection experiments and in experiments looking for Dark Matter annihilation into neutrinos in the Sun. The results were presented at IDM 2010 conference, and published on the arxiv 1011.1398, awaiting publication in the proceedings.

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