Exclusion of an Exotic Top Quark with -4/3 Electric Charge Using Soft Lepton Tagging

• Published in: Physical review letters 2010-06, Vol.105 (10)
• Main Authors: Aaltonen, T, /Helsinki Inst. of Phys, Adelman, J, /Chicago U., EFI, Alvarez Gonzalez, B, /Oviedo U. /Cantabria Inst. of Phys, Amerio, S, /INFN, Padua, Amidei, D, /Michigan U., Anastassov, A, /Northwestern U., Annovi, A, /Frascati, Antos, J, /Comenius U., Apollinari, G, /Fermilab, Appel, J, Apresyan, A, /Purdue U. /Waseda U.
• Format: Article
• Language: English
• Subjects: DECAY; ELECTRIC CHARGES; Experiment-HEP; FERMILAB COLLIDER DETECTOR; INTERMEDIATE BOSONS; LEPTONS; LUMINOSITY; PHYSICS OF ELEMENTARY PARTICLES AND FIELDS; STANDARD MODEL; T QUARKS
• ISSN: 0031-9007; 1079-7114

We present a measurement of the electric charge of the top quark using p{bar p} collisions corresponding to an integrated luminosity of 2.7 fb{sup -1} at the CDF II detector. We reconstruct t{bar t} events in the lepton+jets final state and use kinematic information to determine which b-jet is associated with the leptonically- or hadronically-decaying t-quark. Soft lepton taggers are used to determine the b-jet flavor. Along with the charge of the W boson decay lepton, this information permits the reconstruction of the top quark's electric charge. Out of 45 reconstructed events with 2.4 {+-} 0.8 expected background events, 29 are reconstructed as tt with the standard model +2/3 charge, whereas 16 are reconstructed as t{bar t} with an exotic -4/3 charge. This is consistent with the standard model and excludes the exotic scenario at 95% confidence level. This is the strongest exclusion of the exotic charge scenario and the first to use soft leptons for this purpose.