Forward-backward asymmetry of top quark pair production

Abstract

We adopt a Markov chain Monte Carlo method to examine various new physics models which can generate the forward-backward asymmetry in top quark pair production observed at the Tevatron by the CDF Collaboration. We study the following new physics models: (1) exotic gluon G 0 , (2) extra Z 0 boson with flavor-conserving interaction, (3) extra Z 0 with flavor-violating u-t-Z 0 interaction, (4) extra W 0 with flavor-violating d-t-W 0 interaction, and (5) extra scalars S and S AE with flavor-violating u-t-S and d-t-S AE interactions. After combining the forward-backward asymmetry with the measurement of the top pair production cross section and the t " t invariant mass distribution at the Tevatron, we find that an axial vector exotic gluon G 0 of mass about 1 TeV or 2 TeV or a W 0 of mass about 2TeV offer an improvement over the standard model. The other models considered do not fit the data significantly better than the standard model. We also emphasize a few points that have been long ignored in the literature for new physics searches: (1) heavy resonance width effects, (2) renormalization scale dependence, and (3) next-to-leading order corrections to the t " t invariant mass spectrum. We argue that these three effects are crucial to test or exclude new physics effects in the top quark pair asymmetry.

Calculation of associated production of a top quark and aW′at the LHC

“…(10)(11)(12)(13). The ttb background is suppressed significantly, but the ttj background still overwhelms the signal.…”

“…Recently, several authors have proposed a W ′ boson with only a flavor changing (FC) d-t-W ′ interaction [11][12][13][14][15] to explain the observation of large parity violation manifest in the forward-backward asymmetry in top quark pair-production at the Tevatron [16,17]. The FC W ′ boson is also produced in association with a top quark, but it differs from the top-philic W ′ we discuss in that it decays into a top quark and a non-b quark, yielding a final state of tt plus a non-b jet [18].…”

Up asymmetries from exhilarated composite flavor structures

“…As we argue in section 3 the above choice of representation allows for a positive top A FB contribution from the axial KK gluon [84][85][86][87][88][89][90]. We assume the following representations for the leptons…”

“…We resort instead to alignment in the down sector in order to evade the CPV strong constraints in the Kaon system. The SU(3) L ×SU(3) R bulk symmetry is introduced here in order to induce a large top A FB , similarly to axigluon models in 4D [84][85][86][87][88][89][90]. The gauge field of the unbroken SU(3) V symmetry in 4D is identified to the SM massless gluon.…”

AFBtmeets LHC

“…Ultimately, models which aim to explain the Tevatron measurements [11][12][13][14][15][16][17][18][19][20][21][22][23][24] may manifest themselves in a variety of ways at the LHC. In addition to modifications of A t F B , virtually all of the candidate theories result in an increase in tt production at large invariant mass, M tt , and the differential cross section dσ tt /dM tt can be a sensitive discriminant between various models [25][26][27].…”