Top Quark Pairs at High Invariant Mass - A Model-Independent Discriminator of New Physics at the LHC

TL;DR

High invariant mass top pair production may provide an early indicator for new physics beyond the standard model andForward-backward asymmetry and CP-odd variables can be constructed to further delineate the nature of new physics.

Abstract

We study top quark pair production to probe new physics at the LHC. We propose reconstruction methods for $t\bar{t}$ semileptonic events and use them to reconstruct the $t\bar{t}$ invariant mass. The angular distribution of top quarks in their c.m. frame can determine the spin and production subprocess for each new physics resonance. Forward-backward asymmetry and CP-odd variables can be constructed to further delineate the nature of new physics. We parametrize the new resonances with a few generic parameters and show high invariant mass top pair production may provide an early indicator for new physics beyond the Standard Model.

Figures (4)

• Figure 1: (a) The $W$ and top mass reconstructions from the ($M_W$, $m_t$) scheme, with the procedure Step I (solid) and Step II (dashed). (b) Differential cross section versus $\cos{\theta}_{b\,W}$ with no invariant mass cut (dotted), and with cuts of 600 GeV (dashed) and 1000 GeV (solid).
• Figure 2: $t\bar{t}$ invariant mass distributions reconstructed from (a) the ($M_W$, $m_t$) scheme, and (b) the small angle selection scheme. Both plots featured a 1 TeV resonance with a total width of 2% (solid), 5% (dashed), and 20% (dotted) of the resonance's mass.
• Figure 3: Normalization factor versus the resonance mass for the scalar (dashed) with a width-mass ratio of $20\%$, vector (dot-dashed) with 5%, and graviton (solid) 2%, respectively. The region above each curve represents values of $\omega$ that give 5$\sigma$ or greater statistical significance with 10 fb$^{-1}$ integrated luminosity.
• Figure 4: Polar angular distributions for the top quark in the c.m. frame, (a) Signal only by the ($M_W$, $m_t$) scheme for a scalar (dashed), a vector (dots), and a graviton from $q\bar{q}$ (solid) or from $gg$ (dot-dashed); (b) number of events for the SM $t\bar{t}$ background (solid) with 1$\sigma$ statistical error bars, and the background plus a vector resonance (dashed).