Search for excited fermions and leptoquarks at HERA

TL;DR

This paper reports on searches for excited fermions and leptoquarks at HERA, setting new exclusion limits and constraining their properties based on data collected between 1994 and 1999.

Contribution

It provides the first comprehensive exclusion limits for excited fermions and leptoquarks at HERA, including lepton-flavor violating channels and contact interaction constraints.

Findings

No evidence of excited fermions or leptoquarks was observed.

New exclusion limits were established for various decay channels.

Contact interaction analyses further restrict the parameter space.

Abstract

Recent results on searches for new particles at the electron-proton collider HERA are reported. Based on roughly 40pb-1 of e^+p data taken in the years 1994-1997, the H1 and ZEUS collaborations have derived new exclusion limits for the direct production of excited fermion states and of leptoquarks in different decay channels, including lepton-flavor violating decays. The results of searches for contact interactions further constrain the parameter space for such particles and their couplings in the high-mass regime, where direct production is kinematically prohibited. Also preliminary analyses of the e^-p data taken in 1998 and 1999 do not find signals of new physics.