TESTING THE STANDARD MODEL IN $t\overline{t}$ AND SINGLE TOP PRODUCTION AT THE LHC

Abstract

The top quark is the heaviest and the least studied quark of the Standard Model (SM). At the LHC several millions of top quarks will be produced every year through pair and single top production. Precision tests of the SM performed by the ATLAS and CMS collaborations (top mass, cross sections, top spin correlations and W polarization) are reviewed together with the studies of the sensitivity to new physics beyond the SM (anomalous couplings and FCNC decays) using t t and single top events. Top physics is expected to enter the era of precision measurements 1 with the start of operation of the Large Hadron Collider (LHC). Due to its large mass, close to the electroweak scale, the top quark is expected to be an eectiv e probe of the Standard Model (SM) and oer a unique window to test new physics. The top quark completes the three familly structure of the SM. It has spin 1=2, charge +2=3 and is the weak isospin partner of the b-quark. The mass, known already with a precision of 1.2% 2 , is its most precisely measured property. Once the Cabibbo-Kobayashi-Maskawa matrix ele- ment (CKM) Vtb is very close to one, the top quark decays dominantly through t ! bW . The on-shell decay width, known from the- ory with a precision better than 1% 1 , is ( t ! bW )=jVtbj 2 1:42 GeV (taking into account the W and b masses and also the QCD+EW radiative corrections). With a short lifetime, the top quark decays before hadronizing (allowing the transfer of its spin information to the decay products). For the same reason, no hadron spectroscopy should be expected at the LHC, if the SM holds and no new interactions appear associated to the top quark. 2. t t at the LHC At the LHC, 8 10 6 t t events will be pro- duced (per year, per experiment in the low luminosity phase) and used to determine the properties of the top quark.