A new analysis could sharpen the search for a top-quark bound state

A proposed method for studying top quarks at the Large Hadron Collider may improve sensitivity by up to 12 percent.

Editorial illustration — not from the study.

The study applies a reconstruction technique to simulated events in which a top quark and an antitop quark decay into two b-jets, two oppositely charged leptons and two neutrinos. The method helps resolve which particles belong to each part of the event and estimates the effects of the neutrinos, whose presence cannot be measured directly.

The researchers compared four reconstruction approaches and proposed using two angular measurements to distinguish a possible top-quark bound state from the much more common background of ordinary top-quark pair production. Their preliminary results indicate an improvement in sensitivity of up to 12 percent over the current Run 3 strategy.

How the search could improve

The researchers showed how Recursive Jigsaw Reconstruction could be used to study a possible top-quark bound state, known as toponium, near the top-antitop production threshold. They compared four methods implemented in the RestFrames software package and used the reconstructed event rest frames to obtain additional measurements. Two angular variables were proposed to improve discrimination between the possible toponium signal and ordinary top-antitop production. The preliminary results indicate that this approach could improve sensitivity by as much as 12 percent over the current strategy for the Large Hadron Collider’s Run 3 configuration.

Why the threshold matters

Toponium would be a short-lived bound state involving a top quark and an antitop quark. Studying events near the top-antitop threshold could provide additional information about how these particles interact in this energy region. The proposed reconstruction approach offers a way to use more of the event’s kinematic information, including information from intermediate rest frames, when searching for the possible state.

Evidence and caveats

This is a proposed analysis based on a non-relativistic quantum chromodynamics model implemented in MadGraph5_aMC@NLO, rather than a report of a new observation in LHC collision data. The results are described as preliminary. The study focuses on one final-state pattern with two b-jets, two oppositely charged leptons and missing energy from two neutrinos, and the reported 12 percent improvement is a sensitivity estimate for the Run 3 strategy. The abstract does not provide the statistical significance, event yields or an independent experimental validation of the method.

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