Known hadrons are composed of three valence quarks (barions) and valence quarkantiquark pair (mesons). Belle collaboration discovered an interesting state X(3872) in 2003, which is most likely a mesonic molecule D0bar D*0. In spite of many attempts to provide theoretical evidence for the existence of this interesting state, our results present the first unambiguous evidence for its existence within the framework of abinitio lattice QCD. We find a state in a dynamical simulation of scattering Dbar D* in the channel with J+=1++ and I=0. This is the first simulation that establishes a candidate for X(3872) in addition to the nearby scattering states D bar D* and J/psi mega, which inevitably have to be present in dynamical QCD. The Dbar D* scattering phase shift is extracted using the Luscher formalism and we find large and negative D bar D* scattering length a0=1.7+ 0.4 fm. The extrapolation of the resulting phase shift indicates a pole 11+ 7 MeV below DD* threshold and we relate this pole to experimental nearthreshold state X(3872). The detailed study of the composition of the resulting state indicates a large Dbar D* component, as supported by the previous phenomenological studies claiming that this is a mesonic molecule.
COBISS.SI-ID: 2613348
B physics offers important tests of the Standard Model at low energies. Recently, BaBar observed significant deviations from the Standard Model expectations in the semileptonic B→D/D*τυ mathτ decays. Interestingly, the measured leptonic B τν branching fraction also deviates from CKM unitarity predictions. Motivated by these results we investigate the most general set of lowest dimensional effective operators leading to modifications ofb c(u) (semi)tauonic transitions. Allowing for general flavor violation, we find that among possible operator structures, new contributions from rightright vector and rightleft scalar quark currents provide viable explanations of the anomalies. In addition, we identify a number of B→D/D*τυ mathτ transition observables with the power to discriminate among the various effective operators' contributions. They are the differential decay rate, longitudinalD polarization fraction, D τ opening angle asymmetry and the τ helicity asymmetry.
COBISS.SI-ID: 25811495
We explored the implications of the recent experimental evidence for charm CP violation both within the standard model (SM) and beyond. In the absence of reliable methods to evaluate the hadronic matrix elements involved, we estimated qualitatively the magnitude of the non SM contributions required to generate the observed central value. In the context of an effective theory, we listed the operators that can give rise to the measured CP violation and investigated constraints on them from other processes.
COBISS.SI-ID: 25741863
Experimental measurments of the cross section and forwardbackward asymmetry at Tevatron are in disagreement with the Standard model predictions. The measured forwardbackward asymmetry in the t tbar production at the Tevatron might be explained by the additional exchange of a colored weak singlet scalar which appears in the variation of grand unfied model o the fundamental interactions.
COBISS.SI-ID: 23517735
We compute the branching ratios for the rare top quark decays t to c gamma and t to c Z mediated by effective flavor changing neutral couplings at the nexttoleading order in QCD including the effects due to operator mixing.
COBISS.SI-ID: 23788583