Constraining Light Colored Particles with Event Shapes

David E Kaplan,Matthew D Schwartz

doi:10.1103/physrevlett.101.022002

David E Kaplan, Matthew D Schwartz

Open Access

https://doi.org/10.1103/physrevlett.101.022002

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Journal: Physical Review Letters	Publication Date: Jul 11, 2008
Citations: 29	License type: cc-by

Affiliation: Johns Hopkins University

Abstract

Using recently developed techniques for computing event shapes with soft-collinear effective theory, CERN Large Electron Positron Collider event shape data are used to derive strong model-independent bounds on new colored particles. In the effective field theory computation, colored particles contribute in loops not only to the running of alphas but also to the running of hard, jet, and soft functions. Moreover, the differential distribution in the effective theory explicitly probes many energy scales, so even shapes have a strong sensitivity to new particle thresholds. Using thrust data from ALEPH and OPAL, colored adjoint fermions (such as a gluino) below 51.0 GeV are ruled out to 95% confidence. This is nearly an order-of-magnitude improvement over the previous model-independent bound of 6.3 GeV.

Highlights

Using recently developed techniques for computing event shapes with Soft-Collinear Effective Theory, lep event shape data is used to derive strong model-independent bounds on new colored particles
Despite the fact that particle physics experiments have been running at and above 91 GeV center of mass energies for over two decades, it is not known if the standard model represents the complete particle content below this scale
For particles which carry no standard model quantum numbers, the only hope of producing them at colliders is through the Higgs, if there is a Higgs, and if they couple to it, or indirectly through off-shell intermediate states

Summary

Introduction

Using recently developed techniques for computing event shapes with Soft-Collinear Effective Theory, lep event shape data is used to derive strong model-independent bounds on new colored particles. The gluino is a color octet and should have a large production cross section at hadron colliders, a nonnegligible contribution to four-jet events at lep, and a significant effect on the running of αs. Some of the current model-independent bounds come from fitting the 1-loop β-function coefficient – which is sensitive to the number of flavors, nf – to values of αs measured at different energies.

Results

Conclusion