Bard: Interpreting New Frontier Energy Collider Physics

No systematic procedure currently exists for inferring the underlying physics from discrepancies observed in high energy collider data. We present Bard, an algorithm designed to facilitate the process of model construction at the energy frontier. Top-down scans of model parameter space are discarded in favor of bottom-up diagrammatic explanations of particular discrepancies, an explanation space that can be exhaustively searched and conveniently tested with existing analysis tools.Comment: 3 pages, 2 figure

Probing Models with Near Degeneracy of the Chargino and LSP at a Linear e+e- Collider

For some choices of soft SUSY--breaking parameters, the LSP is a stable neutralino, the NLSP is a chargino almost degenerate in mass with the LSP (with mass difference $\sim m_{\pi}-$few GeV), and all other sparticles are relatively heavy. We discuss the potential of a \sqrt{s}\sim 600\gev $e^+e^-$ collider for studying such models.Comment: 37 pages, 13 figures; revised version includes additional reference

Technihadron Production and Decay at LEP2

The simple "straw-man" model of low-scale technicolor contains light color--singlet technihadrons, which mix with the electroweak gauge bosons. We present lepton collider production rates at the parton level, and show that experiments at LEP2 may be sensitive to the presence of technirho and techniomega states with masses 10-20 GeV beyond the center-of-mass energy because of the mixing. The exact sensitivity depends on several parameters, such as the technipion mass, the technipion mixing angle, and the charge of the technifermions. In an appendix, we describe the implementation of the model into the event generator PYTHIA for particle-level studies at lepton and hadron colliders.Comment: 18 pages (5 figures) in Latex forma

A Brief Introduction to PYTHIA 8.1

The PYTHIA program is a standard tool for the generation of high-energy collisions, comprising a coherent set of physics models for the evolution from a few-body hard process to a complex multihadronic final state. It contains a library of hard processes and models for initial- and final-state parton showers, multiple parton-parton interactions, beam remnants, string fragmentation and particle decays. It also has a set of utilities and interfaces to external programs. While previous versions were written in Fortran, PYTHIA 8 represents a complete rewrite in C++. The current release is the first main one after this transition, and does not yet in every respect replace the old code. It does contain some new physics aspects, on the other hand, that should make it an attractive option especially for LHC physics studies.Comment: 27 page

PYTHIA 6.3 Physics and Manual

The PYTHIA program can be used to generate high-energy-physics `events', i.e. sets of outgoing particles produced in the interactions between two incoming particles. The objective is to provide as accurate as possible a representation of event properties in a wide range of reactions, with emphasis on those where strong interactions play a role, directly or indirectly, and therefore multihadronic final states are produced. The physics is then not understood well enough to give an exact description; instead the program has to be based on a combination of analytical results and various QCD-based models. This physics input is summarized here, for areas such as hard subprocesses, initial- and final-state parton showers, beam remnants and underlying events, fragmentation and decays, and much more. Furthermore, extensive information is provided on all program elements: subroutines and functions, switches and parameters, and particle and process data. This should allow the user to tailor the generation task to the topics of interest.Comment: 8 + 454 page

Can a light technipion be discovered at the Tevatron if it decays to two gluons?

In multiscale and topcolor-assisted models of walking technicolor, light, spin-one technihadrons can exist with masses of a few hundred GeV; they are expected to decay as rho_T -> W pi_T. For technirho masses ~200 GeV and technipion masses ~100 GeV, the process pbar p -> rho_T -> W pi_T has a cross section of about a picobarn at the Tevatron. We demonstrate the detectability of this process with simulations appropriate to Run II conditions, for the challenging case where the technipion decays dominantly into two gluons.Comment: 11 pages, LaTeX, including figure

The Matrix Element Method: Past, Present, and Future

The increasing use of multivariate methods, and in particular the Matrix Element Method (MEM), represents a revolution in experimental particle physics. With continued exponential growth in computing capabilities, the use of sophisticated multivariate methods-- already common-- will soon become ubiquitous and ultimately almost compulsory. While the existence of sophisticated algorithms for disentangling signal and background might naively suggest a diminished role for theorists, the use of the MEM, with its inherent connection to the calculation of differential cross sections will benefit from collaboration between theorists and experimentalists. In this white paper, we will briefly describe the MEM and some of its recent uses, note some current issues and potential resolutions, and speculate about exciting future opportunities.Comment: 3 pages, no figures. Snowmass white paper. Minor revisions. References adde