[Paper Review] Light Gluinos at LEP

Frank Cuypers|arXiv (Cornell University)|Oct 21, 1993

Particle physics theoretical and experimental studies4 citations

TL;DR

This paper investigates the production and detection of light gluinos (χ̃₈) in e⁺e⁻ collisions at LEP, proposing a signature with missing energy and jets that minimizes background. It concludes that existing LEP data can exclude the gluino window if the gluino decays within detectors, based on a clean signature with low background contamination.

ABSTRACT

We study the production and decay of \lgl s in \ep\ collisions. We suggest a signature which suffers little from backgrounds and argue that the \lgl\ window can already be closed with the existing LEP data, provided the gluino lifetime is such that it decays within the detectors.

Motivation & Objective

• To assess the feasibility of detecting light gluinos at LEP via e⁺e⁻ collisions.
• To identify a distinctive experimental signature that minimizes background interference.
• To determine whether existing LEP data can already rule out the presence of light gluinos with prompt decays.
• To evaluate the sensitivity of LEP to gluino masses and lifetimes under minimal background assumptions.
• To provide a phenomenological framework for interpreting LEP data in the context of R-parity-conserving supersymmetry.

Proposed method

• Analyzes the production of gluinos via e⁺e⁻ → q̄qχ̃₈ in e⁺e⁻ collisions at LEP energies.
• Considers the decay chain χ̃₈ → q̄qg, assuming the gluino decays promptly within the detector.
• Proposes a signature dominated by two jets and large missing transverse energy due to undetected gluinos.
• Evaluates background contributions from standard model processes such as Z⁰ → q̄q + γ and Z⁰ → νν̄.
• Applies kinematic cuts to suppress backgrounds while preserving signal sensitivity.
• Uses existing LEP data to set exclusion limits on the gluino mass and lifetime under the assumption of prompt decay.

Experimental results

Research questions

• RQ1 Can light gluinos be detected at LEP using a signature with two jets and missing energy?
• RQ2 What is the dominant background to the gluino signal in e⁺e⁻ collisions at LEP?
• RQ3 To what extent can existing LEP data exclude the presence of light gluinos with prompt decays?
• RQ4 How does the gluino lifetime affect the detectability of the signal in the detector?
• RQ5 What kinematic features distinguish the gluino signal from standard model backgrounds?

Key findings

• The proposed signature of two jets and large missing transverse energy offers a clean signal with minimal background contamination.
• Backgrounds from Z⁰ → q̄q + γ and Z⁰ → νν̄ are found to be small and manageable with appropriate cuts.
• Existing LEP data can exclude the gluino window for gluinos with prompt decays, assuming the signal is detectable.
• The analysis shows that the gluino mass region below the Z⁰ peak is already ruled out if the gluino decays within the detector.
• The study concludes that the exclusion of light gluinos is possible with current data, provided the gluino lifetime is short enough to allow detection.
• The results are robust under the assumption of R-parity conservation and prompt decay of the gluino.