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.
Highlights
The quest for beyond the Standard Model (BSM) physics is undoubtedly among the biggest challenges in contemporary physics. It has typically been driven by the lack of answers to some fundamental questions, such as understanding the unification of the forces of nature or the mechanism of baryogenesis, as well as by hints of new physics appearing in anomalous experimental observations
Several features of its setup make it an ideal probe for light long-lived particle (LLP) produced in kaon decays: (i) Given a large expected boost factor of light particles traveling towards FASER, and the location of the detector, the experiment’s sensitivity is optimal for the precise combination of the lifetime and mass that are required to fit the anomaly
We present the results obtained for a possible larger version of the detector to operate during HL-Large Hadron Collider (LHC), dubbed FASER 2
Summary
The quest for beyond the Standard Model (BSM) physics is undoubtedly among the biggest challenges in contemporary physics It has typically been driven by the lack of answers to some fundamental questions, such as understanding the unification of the forces of nature or the mechanism of baryogenesis, as well as by hints of new physics appearing in anomalous experimental observations. Several features of its setup make it an ideal probe for light LLPs produced in kaon decays: (i) Given a large expected boost factor of light particles traveling towards FASER, and the location of the detector, the experiment’s sensitivity is optimal for the precise combination of the lifetime and mass that are required to fit the anomaly. Several useful expressions for BSM meson decay branching fractions are listed in the Appendix
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