[Paper Review] SUSY Signatures at LHC

F. Paige|ArXiv.org|Nov 1, 2002

Particle physics theoretical and experimental studies2 references3 citations

TL;DR

This paper outlines the search for supersymmetry (SUSY) at the Large Hadron Collider (LHC), focusing on signatures involving missing transverse energy ($\not{E}_T$) and jets from gluino and squark pair production. It demonstrates that with $10\,\text{fb}^{-1}$ of luminosity, the LHC can discover TeV-scale SUSY particles up to $2\,\text{TeV}$, and proposes kinematic endpoint methods to measure SUSY particle masses despite the invisibility of the lightest supersymmetric particle ($\tilde{\chi}_1^0$).

ABSTRACT

The ATLAS and CMS Collaborations at the CERN Large Hadron Collider (LHC) have devoted considerable effort to the study of SUSY signatures and measurements. This talk provides an overview of what can be learned at the LHC if TeV-scale SUSY exists.

Motivation & Objective

• To assess the discovery potential of TeV-scale supersymmetry at the LHC using multijet + $\not{E}_T$ signatures.
• To develop and evaluate kinematic endpoint techniques for measuring SUSY particle masses when the lightest supersymmetric particle ($\tilde{\chi}_1^0$) is invisible.
• To explore model-dependent SUSY signatures under different R-parity and R-parity violation scenarios, including GMSB and AMSB models.
• To identify and characterize distinctive signals such as photons, long-lived particles, and leptonic decays to enhance discovery potential.
• To establish a systematic program for initial SUSY measurements at the LHC, integrating multiple kinematic and topological observables.

Proposed method

• Simulate SUSY events and Standard Model backgrounds using parton shower Monte Carlo programs (e.g., HERWIG, ISAJET, PYTHIA) with fast detector simulation.
• Apply kinematic cuts such as $E_T > 100, 50, 50, 50\,\text{GeV}$ for jets and $\not{E}_T > 100\,\text{GeV}$ to isolate SUSY signals.
• Use the effective mass variable $M_{\text{eff}} = \not{E}_T + \sum p_{Tj}$ as a key discriminant between signal and background.
• Reconstruct mass scales via kinematic endpoints in dilepton and $\tau\tau$ final states, exploiting momentum and polarization dependencies.
• Utilize time-of-flight and vertex resolution in the ATLAS detector to identify long-lived particles such as $\tilde{\chi}_1^0 \to \tilde{G}\gamma$ or long-lived slepton NLSPs.
• Apply endpoint analysis to $\tilde{\chi}_1^0$ decays in cascade processes to infer mass combinations, even without direct mass peaks.

Experimental results

Research questions

• RQ1 What is the reach of the LHC in discovering gluinos and squarks with masses up to $2\,\text{TeV}$ using $10\,\text{fb}^{-1}$ of integrated luminosity?
• RQ2 How can kinematic endpoints in dilepton and $\tau\tau$ final states be used to infer SUSY particle masses when the lightest supersymmetric particle is invisible?
• RQ3 What are the distinctive signatures of gauge-mediated supersymmetry breaking (GMSB) models, particularly for long-lived neutralinos or sleptons?
• RQ4 How do different R-parity violation patterns affect the detectability of SUSY signals, especially in the absence of $b$ jets?
• RQ5 What is the feasibility of measuring the lifetime of long-lived particles such as $\tilde{\chi}_1^0$ or $\tilde{\ell}$ using time-of-flight and vertex reconstruction?

Key findings

• The LHC can discover gluinos and squarks with masses up to $2\,\text{TeV}$ using only $10\,\text{fb}^{-1}$ of integrated luminosity, assuming $R$-parity conservation.
• For the mSUGRA model, the $5\sigma$ discovery reach in the multijet + $\not{E}_T$ channel extends to gluino and squark masses of approximately $1500\,\text{GeV}$ at 10% of design luminosity over one month.
• Kinematic endpoints in dilepton final states (e.g., $e^+e^-$, $\mu^+\mu^-$) allow reconstruction of the SUSY mass scale, with $100\,\text{fb}^{-1}$ of data enabling precise measurements.
• The $\tau\tau$ mass distribution shows clear sensitivity to helicity reversal and decay mode separation, with visible $\tau$ masses reconstructed using fine-grained calorimeter and tracker information.
• For GMSB models with long-lived $\tilde{\chi}_1^0 \to \tilde{G}\gamma$, the ATLAS detector can achieve a sensitivity to $c\tau \sim 100\,\text{km}$, with photon angle and time resolution enabling detection of displaced photons.
• Long-lived slepton NLSPs can be identified via time-of-flight measurements in the muon system, with lifetime estimation possible from counting events with zero, one, or two such tracks.