Constraining Light Colored Particles with Event Shapes

TL;DR

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, nearly an order-of-magnitude improvement over the previous model- independent bound.

Abstract

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. In the effective field theory computation, colored particles contribute in loops not only to the running of alpha_s 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 event shapes have 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 level. This is nearly an order-of-magnitude improvement over the previous model-independent bound of 6.3 GeV.

Figures (2)

• Figure 1: Theoretical prediction versus aleph data at lep 1 for the standard model and the standard model with a 25 GeV gluino. The total statistical uncertainty band includes theoretical statistical uncertainty from the Monte Carlo used to generate the NNLO fixed-order thrust distribution.
• Figure 2: Bounds on light colored particles from lep data. The darker region is completely excluded at 95% confidence. The lighter region is an uncertainty band including estimates of various theoretical uncertainties.