Searches for New Physics at HERA

TL;DR

This paper reviews recent searches for new physics at HERA, including leptoquarks, excited fermions, contact interactions, and flavor-changing neutral currents, providing constraints on various beyond Standard Model phenomena.

Contribution

It summarizes the latest experimental results from HERA on potential new physics signals and sets new limits on several rare processes and particles.

Findings

No evidence for leptoquarks or excited fermions was found.

Stringent limits were set on flavor-changing neutral current processes.

Constraints on contact interactions and single-top production were improved.

Abstract

Recent results from searches for new physics at HERA are reviewed. Exploiting the uniqueness of lepton-hadron collisions at high energy, searches are performed for electron-quark resonant states (leptoquarks or squarks in R-parity-violating supersymmetry) or excited states of fermions. New phenomena at a very high energy scale, manifested at present energies as effective four-fermion contact interaction, are also investigated, including cases with lepton-flavor violation. Finally, the status of events with a high-energy lepton and missing transverse momentum is presented, resulting in the most stringent constraint on the flavor-changing neutral current t-u-\gamma coupling which could yield single-top production.