Searching for QCD Instantons via Tagging Forward Protons

Although the QCD instanton has been intensively searched for in several experiments, it has not yet been observed. Here, we study the possibility of observing heavy (\(M_{\rm inst}\gt 60\) GeV) QCD instantons at the LHC in the diffraction mode, <span class="it">i.e.</span> in events with one or two tagged leading protons which are accompanied by large rapidity gaps. The presented analysis provides a detailed look into the experimental situation and accounts for detector and pile-up effects. We show that the expected instanton signal in a single-tagged configuration is strongly affected by central detector and pile-up effects but observable. For the double-tagged approach, the combinatorial background overwhelms the expected signal. Possible improvements lie in adding time information about tracks at central and forward rapidities. Abstract Published by the Jagiellonian University 2025 authors