A Search for Squarks of Rp-Violating SUSY at HERA

TL;DR

This paper reports a search for squarks in R-parity violating supersymmetry at HERA, setting new exclusion limits on squark masses and couplings based on the absence of observed signals in various decay channels.

Contribution

It provides the first comprehensive search for R-parity violating squarks at HERA, including direct production and pair production, and establishes new exclusion limits on their masses and couplings.

Findings

Excluded first generation squarks up to 240 GeV for certain couplings.

Excluded stop squarks up to 138 GeV for specific couplings.

No significant deviation from Standard Model predictions observed.

Abstract

A search for squarks of R-parity violating supersymmetry is performed in $ep$ collisions at HERA using H1 1994 $e^+$ data. Direct single production of squarks of each generation by $e^+$-quark fusion via a Yukawa coupling $\lambda'$ is considered. All possible R-parity violating decays and gauge decays of the squarks are taken into account. No significant deviation from the Standard Model predictions is found in the various multi-lepton and multi-jet final states studied and exclusion limits are derived. At 95% confidence level, the existence of first generation squarks is excluded for masses up to $240 \GeV $ for coupling values $\lambda' \gtrsim \sqrt{4\pi \alpha_{em}}$.The limits obtained are shown to be only weakly dependent on the free parameters of the Minimal Supersymmetric Standard Model. Stop squarks are excluded for masses up to $138 \GeV$ for coupling $\lambda' \times \cos \theta_t$ to $e^+d$ pairs $\gtrsim 0.1 \times \sqrt{4\pi \alpha_{em}}$, where $\theta_t$ is the mass mixing angle. Light stop squarks are furthermore searched for through pair production in $\gamma$-gluon fusion processes. No signal is observed and exclusion limits are derived. Masses in the range 9 to $24.4 \GeV$ are excluded at 95% confidence level for $\lambda' \times \cos \theta_t > 10^{-4}$.