Top mass determination in leptonic final states with J/psi

TL;DR

The paper proposes a novel top-quark mass determination using leptonic final states that include a J/psi from b decays in ttbar events at the LHC. It reconstructs a partial top mass from the isolated lepton and J/psi via the observable $M_lJpsi^{max}$, which shows a linear correlation with $M_{top}$ and stronger sensitivity than the muon-in-jet channel. Using leading-order generators with detector smearing, the study estimates an overall systematic on $M_{top}$ of order 0.6–1 GeV, indicating potential ~1 GeV precision. Despite the tiny branching fraction (~5.3×10^-5), the signature is clean and MC-tunable, making this method a promising complementary approach for CMS at the LHC.

Abstract

Taking advantage of large top production rates at the LHC, the leptonic final states with J/psi are explored for a precise determination of the top quark mass. The top is partially reconstructed by combining the isolated lepton from the W with the J/psi from the decays of the corresponding b-quark. The method relies, to a large extent, on the proper Monte-Carlo description of top production and decay. The main emphasis is put on the expected systematics uncertainties. Mass measurement accuracy is dominated by the current understanding of theoretical uncertainties which result in a systematic error of <~1 GeV.

Figures (4)

• Figure 1: Schematic of the top decay to leptonic final states with J$/\psi$.
• Figure 2: Example of the $\ell$J$/\psi \;$ invariant mass spectrum in 4-lepton final states. Number of events correspond to four years running at LHC high luminosity.
• Figure 3: Correlation between M$^{max} \;$ and the top-quark mass in isolated lepton plus J$/\psi \;$ (solid line) and isolated lepton plus $\mu$-in-jet (dashed line) final states.
• Figure 4: Summary on the systematics studies.