[Paper Review] Event Generators for Discovery Physics

M. Mangano, Giovanni Ridolfi+41 more|ArXiv.org|Feb 1, 1996

Scientific Research and Discoveries19 citations

TL;DR

This paper reviews Monte Carlo event generators for new physics at colliders, focusing on Higgs boson, supersymmetry (SUSY), and leptoquark signals. It evaluates tools like PYTHIA, ISAJET, and Lq2, emphasizing accurate matrix element calculations, spin correlations, and detector-level simulation for discovery and parameter extraction, concluding that current theoretical uncertainties do not hinder discovery potential but affect precision measurements of new physics properties.

ABSTRACT

Review of Monte Carlo event generators for signals of new particles at LEP2. The areas covered include SUSY, HIGGS and Leptoquarks.

Motivation & Objective

• To evaluate the state-of-the-art Monte Carlo event generators for new physics signals at e+e− colliders.
• To assess the impact of theoretical approximations—especially spin correlations and interference effects—on discovery potential and parameter determination.
• To provide a comparative overview of available public generators for Higgs, SUSY, and leptoquark processes.
• To identify key technical and theoretical challenges in modeling exotic final states with high precision.
• To guide experimentalists and phenomenologists in selecting appropriate generators for signal simulation and analysis.

Proposed method

• Systematic review and comparison of 15+ event generators across three new physics sectors: Higgs, SUSY, and leptoquarks.
• Evaluation of matrix element calculations including full 4-fermion amplitudes, interference between signal and background diagrams, and initial state radiation (ISR).
• Use of CERNLIB routines (e.g., DIVON4) for numerical integration and importance sampling in multi-dimensional phase space.
• Integration with JETSET and PYTHIA for parton showering, hadronization, and decay modeling in generators like Lq2.
• Implementation of effective Lagrangians for leptoquark couplings and decay widths using quantum numbers and coupling constants.
• Benchmarking of generators via cross-checks and comparisons of cross sections, branching ratios, and kinematic distributions.

Experimental results

Research questions

• RQ1 How do different event generators model Higgs production in e+e− collisions, and what is the impact of including full 4-fermion amplitudes?
• RQ2 To what extent do spin correlations in SUSY decays affect the accuracy of parameter extraction, even when discovery remains robust?
• RQ3 How do theoretical uncertainties in matrix element calculations influence the projected discovery reach for new physics?
• RQ4 What are the key technical differences between multi-purpose SUSY generators and single-channel event generators?
• RQ5 How well do leptoquark generators like Lq2 reproduce the full kinematics and decay branching ratios from effective field theory?

Key findings

• For Higgs boson searches, full 4-fermion matrix elements including interference between signal and background diagrams are essential, especially when b-quark masses are non-zero.
• Spin correlations in SUSY decays, though negligible for discovery, significantly affect the determination of electroweak properties of new particles.
• The Lq2 generator uses CERNLIB’s DIVON4 for fast numerical integration and provides accurate cross sections and branching ratios for scalar and vector leptoquarks.
• Event generators such as PYTHIA, ISAJET, and SUSYGEN offer varying levels of precision, with single-channel generators providing higher accuracy for specific final states.
• Theoretical uncertainties in current generators do not compromise the discovery potential of new physics signals, but they do affect precision measurements of model parameters.
• The inclusion of initial state radiation and correct 4-momentum reconstruction is critical for realistic detector-level simulations.