New physics from high energy tops

Abstract

Precision measurements of high energy top quarks at the LHC constitute a powerful probe of new physics. We study the effect of four fermion operators involving two tops and two light quarks on the high energy tail of the tt invariant mass distribution. We use existing measurements at a center of mass energy of 13 TeV, and state of the art calculations of the Standard Model contribution, to derive bounds on the coefficients of these operators. We estimate the projected reach of the LHC at higher luminosities and discuss the validity of these limits within the Effective Field Theory description. We find that current measurements constrain the mass scale of these operators to be larger than about 1-2 TeV, while we project that future LHC data will be sensitive to mass scales of about 3-4 TeV. We apply our bounds to constrain composite Higgs models with partial compositeness and models with approximate flavor symmetries. We find our limits to be most relevant to flavor non-universal models with a moderately large coupling of the heavy new physics states to third generation quarks.

A Monte Carlo global analysis of the Standard Model Effective Field Theory: the top quark sector

“…Another way to study the impact that the SMEFT corrections have on the description of the experimental data at high energies is to focus on the constraints provided by the tail of the invariant mass distribution m tt in top quark pair production, where energy-growing effects enhance the sensitivity to SMEFT corrections [165]. In order to highlight the impact that these energy-growing effects have on the description of the m tt tails, it is useful to compute the shift induced by the SMEFT corrections to the SM calculation separated into the contributions from different degrees of freedom.…”

Standard model EFT and the Drell-Yan process at high energy

“…It has been speculated [10] that because of the large cross section and precision of the measurements that high energy Drell-Yan could also yield a precise determination of C W . The fits of Refs.…”

“…In this approach, low scale physics is assumed to be sensitive to the presence of higher dimension operators. When a complete basis of these operators is constructed, they will affect predictions for many observables, including in Higgs physics [1,2], gauge boson pair production [3][4][5][6][7], top quark production [8][9][10], and many other processes. The measurements from different processes provide complementary information about the parameters of the EFT and potential insights into the underlying UV physics.…”

O new physics, where art thou? A global search in the top sector

“…We consider measurements in top pair production, including associated ttW and ttZ production, as well as in single top final states. Since effective interactions typically have a sizeable impact on kinematic distributions we add a set of kinematic measurements with a focus on boosted top pair production [26,27]. Finally, we include charge asymmetry [14,[28][29][30] and top decay measurements [31,32] to shed light on specific sectors of the effective Lagrangian.…”