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Gad Eilam
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Motivated by the well known impact of rare decays of hadrons and leptons on the evolution of the Standard Model and on limits for new physics, as well as by the proposal for Giga-Z option at TESLA, we investigate the rare decay Z -> b s-bar in various extensions of the Standard Model.
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The inclusive semileptonic branching ratio is often employed to normalize other inclusive B decays. Using recent determinations of the non-perturbative parameters of the Operator Product Expansion we compute the normalization factor for the branching ratio of B->X_s gamma and find a few percent enhancement with respect to previous determinations.
The rare top quark decays mediated by a new neutral massive gauge boson that is predicted in models with extended gauge symmetries are studied. We focus on the processes $tto cV, uV$ induced at the one loop level, where $V =gamma, g$, by considering different extended models. It is found that, within a broad range of mass of the new neutral gauge boson, the models predict branching ratios for the decays in study that are competitive with respect to the corresponding branching ratios in the standard model. In order to establish bound on our branching ratios, we consider the recent experimental bounds as $m_{Z^prime}geq$ 3.8-4.5 TeV, depending on the model, which also impose restrictions on our calculation. Even in this case, the resulting branching ratios are of the same order of magnitude as that predicted by the standard model. It should be noted that for the case of two models studied here, since no experimental bound exists to compare with, the results could be important, as they are, in the best of cases, two orders of magnitude larger than the predicted by the standard model.
Rare decays involving leptons or photons in the final states are studied using 1.0 fb^{-1} of pp collisions at a centre-of-mass energy of sqrt{s}=7TeV collected by the LHCb experiment in 2011. We present results of measurements of branching ratios, angular distributions, and isospin asymmetries obtained using this data sample.
The results on rare decay processes obtained by the LHCb experiment using 1.0 fb^(-1) of pp collisions collected in 2011 at a centre-of-mass energy of sqrt(s)=7 TeV are presented. Branching fractions, angular distributions, CP and isospin asymmetries are investigated to search for new physics effects.
The rare B decays Bs(d)-->mumu, B-->K*mumu and Bs-->phigamma are studied using up to sim 0.41 fb^{-1} of pp collisions at sqrt{s} = 7 TeV collected by the lhcb experiment in 2010 and 2011. A search for the decays Bs(d)-->mumu, is performed with 0.41 fb^{-1} . The absence of significant signal leads to BR(Bs-->mumu<1.4 x 10^{-8} and BR(Bd-->mumu<3.2 x 10^{-9} at 95% confidence level. The forward-backward asymmetry, fraction of longitudinal polarization and differential branching fraction of B-->K*mumu, as a function of dimuon invariant mass, are measured in 0.31 fb^{-1}. The ratio of branching ratios of the radiative B decays B--> K*gamma and Bs-->phigamma h as been measured using 0.34fb^{-1}. The obtained value for the ratio is 1.52 pm 0.14 (stat) pm 0.10 (syst) pm 0.12 (f_s/f_d). Using the HFAG value for BR(Bd --> K^*gamma), BR(Bs-->phigamma) has been found to be (2.8 pm 0.5)times 10^{-5}.
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