[Paper Review] Studies of highly-boosted top quarks near the TeV scale using jet masses at the LHC

B. Auerbach, S. Chekanov+1 more|arXiv (Cornell University)|Jan 24, 2013

Particle physics theoretical and experimental studies4 references3 citations

TL;DR

This paper proposes a data-driven analysis of jet mass distributions to detect highly-boosted top quarks in inclusive $pp$ collisions at $\sqrt{s} = 14$ TeV. Using Monte Carlo simulations with fast detector effects, it demonstrates that jet masses alone can identify top quarks if their inclusive production cross section exceeds twice the aNNLO prediction for the $t\bar{t}$ process, with $b$-tagging significantly enhancing signal-over-background ratios for observation of Standard Model $t\bar{t}$ events.

ABSTRACT

Studies of highly-boosted top quarks produced inclusively in pp collisions at 14 TeV are discussed. The hadronic decays of boosted top quarks was studied in a data-driven approach by analysing shapes of jet-mass distributions. Using Monte Carlo models after a fast detector simulation, it is shown that inclusive production of boosted top quarks can be observed if it has a cross section at least twice larger than the prediction from the approximate next-to-next-to-leading-order (aNNLO) calculation for the ttbar process. The ttbar process with the nominal aNNLO strength can be measured using the masses of jets after a b-tagging.

Motivation & Objective

• To develop a data-driven method for identifying highly-boosted top quarks in inclusive $pp$ collisions at $\sqrt{s} = 14$ TeV using only jet mass distributions.
• To assess the feasibility of observing top quarks in high-$p_T$ jets when the inclusive cross section exceeds the aNNLO prediction for the $t\bar{t}$ process by a factor of two or more.
• To evaluate the effectiveness of $b$-tagging in improving the signal-over-background ratio for $t\bar{t}$ production in high-$p_T$ jets.
• To demonstrate that jet mass shape analysis can serve as a sensitive probe for top quarks without relying on complex substructure techniques.

Proposed method

• Employing Monte Carlo simulations with fast detector simulation to model jet masses from top quark decays in high-$p_T$ jets at $\sqrt{s} = 14$ TeV.
• Analyzing the shape of jet-mass distributions to identify a bump near 170 GeV, characteristic of top quark decays, assuming a smoothly falling background.
• Using an analytic background fit function to model the QCD multijet background without a hump near 170 GeV, enabling data-driven signal extraction.
• Applying $b$-tagging to suppress QCD multijet background and enhance signal visibility for $t\bar{t}$ events.
• Evaluating systematic uncertainties by varying selection cuts and instrumental effects, with signal strength preserved under data-driven fitting.
• Comparing the signal-to-background ratio with and without $b$-tagging to quantify improvement in detectability.

Experimental results

Research questions

• RQ1 Can jet mass distributions alone provide a sensitive probe for inclusive production of highly-boosted top quarks in high-$p_T$ jets at the LHC?
• RQ2 What minimum enhancement in the top quark cross section above the aNNLO $t\bar{t}$ prediction is required to observe boosted top quarks via jet mass shape analysis?
• RQ3 How effective is $b$-tagging in improving the signal-over-background ratio for $t\bar{t}$ production in high-$p_T$ jets?
• RQ4 To what extent can a data-driven approach based on analytic background templates detect a top quark signal in the presence of a smoothly falling QCD background?

Key findings

• A signal bump near 170 GeV in the jet mass distribution can be detected if the inclusive top quark production cross section exceeds twice the aNNLO prediction for the $t\bar{t}$ process.
• The method remains robust under systematic variations such as jet energy scale shifts, as long as the data-driven fitting procedure is maintained.
• The inclusion of $b$-tagging reduces the QCD multijet background by at least a factor of two, enabling clear observation of $t\bar{t}$ events at the expected aNNLO cross section level.
• Jet mass shape analysis without substructure variables provides a viable and sensitive method for detecting highly-boosted top quarks in inclusive $pp$ collisions.
• The approach is capable of excluding exotic models such as $Z'$ and Kaluza-Klein gluons if they predict enhanced cross sections beyond the Standard Model at high $p_T$.