Imprint of a new light particle at KOTO?

Abstract

Recently, the KOTO experiment reported their new preliminary result of searching for the decay $K_L\to {\pi }^0\nu \bar{\nu }$. Three candidate events were observed in the signal region, which exceed significantly the expectation based on the standard model. On the other hand, the new NA62 and previous BNL-E949 experiments yielded a consistent result and confirmed the standard model prediction in the charged meson decay $K^{+}\to {\pi }^{+}\nu \bar{\nu }$. Furthermore, the two decays are bound by a well-motivated relation from an analysis of isospin symmetry that is hard to break by the new physics of heavy particles. In this work, we study the issue by a systematic effective field theory approach with three of the simplest scenarios, in which the $K_L$ may decay into a new light neutral particle $X$, i.e., $K_L\to {\pi }^{0}X$, $K_L\to \gamma \gamma X$, or $K_L\to {\pi }^{0}XX$. We assess the feasibility of the scenarios by simulations and by incorporating constraints coming from NA62 and other relevant experiments. Our main conclusion is that the scenario $K\to \pi XX$ for a long lived scalar $X$ seems more credible than the other two when combining distributions and other experimental constraints while the region below the KOTO's blind box provides a good detection environment to search for all three scenarios for a relatively heavy $X$.

arXiv comment10 pages, with 10 figures and 4 appendices; v2: added 4 refs [9,10,17,35], no changes in wording; v3: proofred version to appear in PRD, many improvements/explanations in response to referees' comments and suggestions, added a new figure 3, conclusions not altered, 11 pages, with 11 figures and 4 appendices

References in corpus (28)

• Secluded WIMP Dark Matter
• $K_L\to {\pi }^0\nu \bar{\nu }$ Beyond the Standard Model
• Study of the decay K+ => pi+,nu,nubar in the momentum region 140<Ppi<199 MeV/c
• $K^{+}\to {\pi }^{+}\nu \bar{\nu }$ and $K_L\to {\pi }^0\nu \bar{\nu }$ in the Standard Model: Status and Perspectives
• New measurement of the K+ => pi+,nu,nubar branching ratio
• Light inflaton Hunter's Guide
• Search for $K_L\to {\pi }^0\nu \overline{\nu }$ and $K_L\to {\pi }^0{X}^0$ Decays at the J-PARC KOTO Experiment
• Z'-induced FCNC decays of top, beauty and strange quarks
• Light Scalars and the KOTO Anomaly
• New physics implications of recent search for $K_L\to {\pi }^0\nu \bar{\nu }$ at KOTO
• Vector meson exchange contributions to K --> pi gamma gamma and K(L) -> gamma lepton+ lepton-
• Precise measurement of the decay $K_L\to {\pi }^0\gamma \gamma$
• Loophole in K --> pi nu nubar Search and New Weak Leptonic Forces
• Final Results from the KTeV Experiment on the Decay KL -> pi0 gamma gamma
• Constraints on long-lived light scalars with flavor-changing couplings and the KOTO anomaly
• Implications of a new particle from the HyperCP data on Σ^+ \to p μ^+ μ^-
• A little theory of everything, with heavy neutral leptons
• A Light Scalar Explanation of $(g-2{)}_{\mu }$ and the KOTO Anomaly
• Light gauge boson interpretation for $(g-2{)}_{\mu }$ and the $K_L\to {\pi }^0+\text{(invisible)}$ anomaly at the J-PARC KOTO experiment
• Implication of $K\to \pi \nu \bar{\nu }$ for generic neutrino interactions in effective field theories
• Search for the Decay K+ -> pi+ pi0 nu nubar
• Vector-meson contributions do not explain the rate and spectrum in K_L -> pi0 gamma gamma
• Dark-sector physics in the search for the rare decays $K^{+}\to {\pi }^{+}\bar{\nu }\nu$ and $K_L\to {\pi }^0\bar{\nu }\nu$
• Study of the K0(L) --> pi0 pi0 nu nu-bar decay
• Long-lived neutral-kaon flux measurement for the KOTO experiment
• Evading the Grossman-Nir bound with $\Delta I=3/2$ new physics
• Breaking the Grossman-Nir Bound in Kaon Decays
• Three Exceptions to the Grossman-Nir Bound

Cited by in corpus (7)

• Looking forward to test the KOTO anomaly with FASER
• FCNC charmed-hadron decays with invisible singlet particles in light of recent data
• Cosmological implications of the KOTO excess
• $(g-2{)}_{\mu }$ Versus $K\to \pi +E_{miss}$ Induced by the $(B-L{)}_{23}$ Boson
• The Light Sgoldstino Phenomenology: Explanations for the Muon $(g-2)$ Deviation and KOTO Anomaly
• New Physics Searches at Kaon and Hyperon Factories
• Pionium as a source of false events in the $K\to \pi \nu \bar{\nu }$ decays