Author: Racha Cheaib

Publisher:

Published: 2016

Total Pages:

ISBN-13:

"The flavour changing neutral current (FCNC) process , B+ → K+ [tau]+[tau]−, is highly sup-pressed in the Standard Model (SM). This decay is forbidden at tree level and only occursat lowest order via one-loop diagrams. B+ → K+ [tau]+[tau]− thus has the potential to providea stringent test of the SM and a fertile ground for new physics searches. Contributions dueto virtual particles in the loop allow one to probe, at relatively low energies, new physicsat large mass scales. We search for the rare FCNC process B+ → K+ [tau]+[tau]− using datacollected by the BABAR detector at the SLAC National Accelerator Laboratory. The BABARdata sample corresponds to a total integrated luminosity, at the energy of the [UPSILON](4S) reso-nance, of 424.4 fb−1 and 471 million BB pairs. For this search, hadronic Btag reconstructionis employed, where one B is exclusively reconstructed via one of many possible hadronicmodes. The remaining decay products in an event are then attributed to the signal B, onwhich the search for B+ → K+ [tau]+[tau]− is performed. Each [tau] is required to decay leptonically,into either an electron or a muon and the lepton neutrinos. Furthermore, a multi-variateanalysis technique (neural network) is used to select for signal events and suppress dominantbackground modes. No significant signal is observed. The resulting branching fraction ismeasured to be B(B+ → K+[tau]+[tau]−) = 1.310.66 (stat.)+0.35(sys.) × 10−3, which is consistent −0.61 −0.25with zero at the 1.9[sigma] level, with an upper limit of 2.25 ×10−3 at the 90% confidence level." --