[Paper Review] Perspectives for Top quark physics at High-Luminosity LHC

M. Selvaggi|arXiv (Cornell University)|Dec 15, 2015

Particle physics theoretical and experimental studies3 citations

TL;DR

This paper evaluates the prospects for top quark physics at the High-Luminosity LHC (HL-LHC), projecting that 3 ab⁻¹ of integrated luminosity will enable billion-level top quark event samples. It details experimental challenges from pile-up and radiation, and projects sensitivities to anomalous top quark couplings (e.g., |d_A,V| < 0.02) and flavor-changing neutral currents (e.g., BR(t→Zq) < 5×10⁻⁵), demonstrating the HL-LHC’s potential to probe new physics beyond the Standard Model with percent-level precision.

ABSTRACT

The High-Luminosity LHC is expected to provide $3 ab^{-1}$ of integrated luminosity. As a result billions of events containing top quarks will be detected at the CMS and ATLAS experiments, allowing for precise measurements of the top quark properties. The experimental challenges that will be faced in a high luminosity environment, with a special focus on top quark related observables are examined. We discuss prospects for measuring top quark anomalous couplings at the HL-LHC. Projections for detecting flavor changing neutral currents involving top quarks are also reviewed.

Motivation & Objective

• To assess the experimental challenges posed by high pile-up and radiation levels at the HL-LHC for top quark measurements.
• To project the sensitivity of top quark coupling measurements using effective field theory and event kinematics.
• To evaluate the potential for discovering flavor-changing neutral currents (FCNCs) in top quark decays.
• To quantify the expected improvements in branching ratio limits for rare top decays with 3 ab⁻¹ of data.

Proposed method

• Utilizes effective field theory (EFT) to model anomalous top quark couplings, including chromo-electric and chromo-magnetic dipole moments.
• Applies event-level observables such as invariant mass, transverse momentum, and jet mass distributions to probe anomalous couplings.
• Employs jet grooming and pile-up subtraction techniques to mitigate degradation in E_T^miss and jet energy resolution from high pile-up.
• Uses Monte Carlo simulations and signal-background discrimination in boosted and high-momentum regimes to enhance sensitivity.
• Analyzes final states with multiple leptons, b-jets, and missing energy to isolate rare top decays.
• Projects limits using statistical extrapolations and validated simulations from ATLAS and CMS collaborations.

Experimental results

Research questions

• RQ1 What are the key experimental challenges for top quark physics at the HL-LHC due to high pile-up and radiation?
• RQ2 How precisely can anomalous top quark couplings (e.g., chromo-dipole moments) be constrained with 3 ab⁻¹ of data?
• RQ3 Can the HL-LHC probe top quark flavor-changing neutral currents (FCNCs) at the 10⁻⁵ branching ratio level?
• RQ4 What are the projected sensitivities for rare top decays such as t→Zq and t→cH with high-luminosity data?
• RQ5 How do jet grooming and extended tracker acceptance improve top quark reconstruction in high-multiplicity environments?

Key findings

• The HL-LHC is projected to deliver 3 ab⁻¹ of integrated luminosity, enabling the observation of billions of top quark events.
• The anomalous chromo-dipole moment coupling |d_A,V| can be constrained to less than 0.02 at the HL-LHC.
• Single top s-channel production with large momentum transfer allows for a sensitivity to anomalous tensor couplings, yielding a projected limit of |g_A,V| < 0.10.
• ttZ production in the three-lepton final state enables a constraint on tensor-like couplings at |C²_Z,A|,|C²_Z,V| < 0.08.
• The top Yukawa coupling can be measured with a precision of Δy_t/y_t ≈ 10% at the HL-LHC, primarily through ttH production in H→γγ and H→ττ channels.
• For flavor-changing neutral currents, the branching ratio limit for t→Zq is projected to reach BR(t→Zq) < 5×10⁻⁵ with 3 ab⁻¹, representing a factor of 10 improvement over previous limits.