Looking forward to test the KOTO anomaly with FASER

TL;DR

The paper discusses how the FASER experiment at the LHC can independently test explanations for the KOTO anomaly, potentially confirming new physics scenarios with high-energy events and complementing kaon factory experiments.

Contribution

It demonstrates FASER's capability to probe long-lived particle models related to the KOTO anomaly and outlines its potential for early constraints and discoveries.

Findings

FASER can constrain relevant models within weeks of operation.

Potential to observe up to 10,000 high-energy events during LHC Run 3.

FASER complements kaon factory experiments in studying di-photon signatures.

Abstract

The search for light and long-lived particles at the LHC will be intensified in the upcoming years with a prominent role of the new FASER experiment. In this study, we discuss how FASER could independently probe such scenarios relevant for new physics searches at kaon factories. We put an emphasis on the proposed explanations for the recently observed three anomalous events in the KOTO experiment. The baseline of FASER precisely corresponds to the proposed lifetime solution to the anomaly that avoids the NA62 bounds on charged kaons. As a result, the experiment can start constraining relevant models within the first few weeks of its operation. In some cases, it can confirm a possible discovery with up to 10000 spectacular high-energy events in FASER during LHC Run 3. Further complementarities between FASER and kaon factories, which employ FASER capability to study di-photon signatures, are illustrated for the model with axion-like particles dominantly coupled to $SU(2)_W$ gauge bosons.