[Paper Review] Testing the AMSB Model via $e^+e^- \ o \ ilde{\\chi}^{+} \ ilde{\\chi}^{-} {\\gamma}$

Amitava Datta, S. Maity|arXiv (Cornell University)|Jan 1, 2001

Particle physics theoretical and experimental studies3 citations

TL;DR

This paper investigates the discovery potential of nearly invisible charginos in the minimal anomaly-mediated supersymmetry breaking (mAMSB) model at the Next Linear Collider (NLC) via the process e⁺e⁻ → γχ̃⁺χ̃⁻. Using kinematical cuts and polarized beams, it demonstrates that the entire allowed parameter space with slepton masses below 1 TeV can be probed at √s = 500 GeV, with mass measurements of charginos and sleptons offering a direct test of vacuum stability.

ABSTRACT

The possibility of detecting the signature of a nearly invisible charged wino ($\\CH$) decaying into a soft pion and the LSP ($\\LSP$), predicted by the Anomaly Mediated Symmetry Breaking model, via the process $e^+e^- \ o \ ilde{\\chi}^+ \ ilde{\\chi}^- \\gamma$ at the Next Linear Collider has been explored. Using the recenty, proposed bounds on slepton and wino masses derived from the condition of stability of the electroweak symmetry breaking vacuum and employing some standard kinematical cuts to supress the background, we find that almost the whole of the allowed parameter space with the slepton mass less than 1 TeV, can be probed at $\\sqrt{s}$ = 500 GeV. Determination of the slepton and the chargino masses from this signal is a distinct possiblity. Any violation of the above mass bounds will suggest that the standard vacuum is unstable and we are leaving in a false vacuum.

Motivation & Objective

• To assess the discovery potential of nearly invisible charginos in the mAMSB model at the Next Linear Collider.
• To determine whether the entire allowed parameter space with slepton masses below 1 TeV is accessible via the e⁺e⁻ → γχ̃⁺χ̃⁻ process.
• To explore the feasibility of measuring chargino and slepton masses from the γχ̃⁺χ̃⁻ signal as a probe of vacuum stability.
• To evaluate the role of polarized electron beams in enhancing signal sensitivity and distinguishing the mAMSB model from other models.

Proposed method

• Analyzes the process e⁺e⁻ → γχ̃⁺χ̃⁻ at √s = 500 GeV, focusing on the final state with a photon and two nearly invisible charginos.
• Applies standard kinematical cuts to suppress Standard Model backgrounds while preserving the signal from long-lived charginos decaying into LSP and soft pions.
• Uses the mAMSB model's prediction of near-degenerate chargino and LSP masses (χ̃± and χ̃⁰₁) to justify the nearly invisible decay mode χ̃± → χ̃⁰₁π±.
• Considers the impact of chargino decay length and impact parameter distributions to assess detectability in vertex detectors.
• Evaluates the potential of polarized beams to enhance signal cross sections when slepton masses are small, leveraging t-channel diagram suppression.
• Relies on theoretical bounds from electroweak vacuum stability to constrain the allowed parameter space, particularly on slepton and chargino masses.

Experimental results

Research questions

• RQ1 Can the mAMSB model's nearly invisible charginos be detected at the NLC via e⁺e⁻ → γχ̃⁺χ̃⁻ at √s = 500 GeV?
• RQ2 What fraction of the allowed parameter space with m̃l < 1 TeV is accessible under realistic kinematical cuts?
• RQ3 Can the masses of the chargino and slepton be measured from the mZ⋆ distribution and total cross section?
• RQ4 How does the use of polarized beams enhance the signal sensitivity for light sleptons in the mAMSB model?
• RQ5 What does a violation of the theoretical mass bounds imply for the stability of the electroweak vacuum?

Key findings

• The entire allowed parameter space with slepton masses below 1 TeV is probed at √s = 500 GeV, with signal cross sections ranging from 5.71 fb to 123.12 fb depending on m₀ and tanβ.
• For m₀ = 1 TeV, chargino masses up to 219 GeV can be detected at √s = 500 GeV, with the signal cross section dropping to zero for m̃χ± > 219 GeV.
• The impact parameter distribution for m̃χ± = 219 GeV shows a clear peak at b ≈ 4.5 mm, indicating observable displaced vertices.
• The decay length distribution for m̃χ± = 263 GeV at √s = 1000 GeV shows a significant tail extending to several mm, suggesting detectability in a vertex detector.
• The mZ⋆ distribution for m̃χ± = 100–200 GeV exhibits a clear peak structure, enabling mass reconstruction of the chargino.
• Violation of the theoretical mass bounds derived from vacuum stability would imply the electroweak vacuum is metastable, indicating we may be in a false vacuum.