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Ahn, J. K.; Beckford, Brian; Beechert, Jacqueline; Bryant, Khalil; Campbell, M.; Chen, S. H.; Comfort, J. R.; Dona, Kristin; Hara, Naoya; Haraguchi, Hiroki; Hsiung, Y.; Hutcheson, M.; Inagaki, T.; Kamiji, I.; Kawasaki, Norioki; Kim, E. J.; Kim, J. L.; Kim, Y. J.; Ko, J.-W.; Komatsubara, T. K.; Kotera, Katsushige; Kurilin, A. S.; Lee, J. W.; Lim, G. Y.; Lin, C. X.; Lin, Q.; Luo, Y.; Ma, J.; Maeda, Y.; Mari, T.; Masuda, Takahiko; Matsumura, T.; McFarland, Duncan; McNeal, N.; Micallef, J.; Miyazaki, K.; Murayama, R.; Naito, D.; Nakagiri, K.; Nanjo, H.; Nishimiya, Han; Nomura, T.; Ohsugi, M.; Okuno, H.; Sasaki, Misao; Sasao, N.; Sato, Kazufumi; Satô, Tôru; Sato, Y.; Schamis, Hanna; Seki, Shu; Shimizu, Nobuhiro; Shimogawa, Tetsushi; Shinkawa, T.; Shinohara, Shuichi; Shiomi, K.; Su, Stephanie; Sugiyama, Yasuyuki; Suzuki, Shoji; Tajima, Y.; Taylor, M.; Tecchio, M.; Togawa, M.; Tung, Y. C.; Wah, Y. W.; Watanabe, H.; Woo, Jong-Kwan; Yamanaka, T.; Yoshida, Hiroshi

doi:10.1103/physrevlett.122.021802

Cited by 181 publications

(171 citation statements)

References 38 publications

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“…This corresponds to a decay branching ratio (BR) of [2] BR(K L → π 0 νν) KOTO19 = 2.1 +2.0(+4.1) −1.1(−1.7) × 10 −9 , (1.1) at 68 (95)% confidence level (CL), where the uncertainties are primarily due to statistics. This result is consistent with their previously reported 90% CL upper bound of [3] BR(K L → π 0 νν) KOTO18 < 3.0 × 10 −9 .…”

Section: Introductionsupporting

confidence: 94%

Constraints on long-lived light scalars with flavor-changing couplings and the KOTO anomaly

Dev¹,

Mohapatra

Zhang

2020

Phys. Rev. D

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Recently, the KOTO experiment at J-PARC has observed three anomalous events in the flavor-changing rare decay K L → π 0 νν, which indicates that the corresponding branching ratio is almost two orders of magnitude larger than the Standard Model (SM) prediction. Taking this intriguing result at face value, we explore model implications of its viable explanation by a long-lived light SM-singlet scalar (S) emission, i.e. K L → π 0 S, with S decaying outside the KOTO detector. We derive constraints on the parameter space of such a light scalar in the context of three simple models: (i) a real singlet scalar extension of the SM; (ii) a B − L extension where neutrino masses arise via type-I seesaw mechanism from B − L breaking; and (iii) a TeV-scale left-right symmetric model. The flavor-changing couplings needed to explain the KOTO excess in models (i) and (ii) originate from treelevel mixing of the scalar with SM Higgs field (h), and in model (iii), from the mixing of S and h with the neutral component of the heavy bidoublet Higgs field. After taking into account the stringent constraints from high-precision searches for flavor-changing charged and neutral kaon decays at NA62, E949, KOTO and CHARM experiments, as well as the astrophysical and cosmological constraints on a light scalar, such as those from supernova energy loss, big bang nucleosynthesis and relativistic degrees of freedom, we find that the light scalar interpretation of the KOTO excess is excluded in models (i) and (ii) by the supernova limit. However, there is still a narrow parameter space available in the TeVscale left-right symmetric model to explain the KOTO excess, which can be tested in future NA62 and DUNE experiments.

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Section: Introductionsupporting

confidence: 94%

Constraints on long-lived light scalars with flavor-changing couplings and the KOTO anomaly

Dev¹,

Mohapatra

Zhang

2020

Phys. Rev. D

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“…For definiteness, we takeĉ a to be the central value of the SM prediction [24] and suppose thatĉ b stems from O LNC dim-9 in Eq. (39) and has the formĉ b = F K F π Be iθ /Λ 5 where F K(π) is the kaon (pion) decay constant [4], B = − qq /(3F 2 π ) ≈ 2.8 GeV where qq is the quark [11] of recent KOTO results [1,5] and to the latest NA62 limit [6], and the red dot labeled NP corresponds to (Λ, θ) = (39 GeV, −π/4) in this model.…”

Section: Lnv Amplitudes From ∆I = 1/2 Interaction Onlymentioning

confidence: 99%

“…(41) on the Λ-θ plane. We depict the predictions of this toy scenario for Λ ∈ [1, 60] GeV and θ ∈ [−π, π] with the green region on the right panel and compare them to an interpretation [11] of the recent KOTO results [1,5] as well as to the latest NA62 limit [6]. Clearly this model has parameter space which can explain the anomaly in the new preliminary KOTO data [1] but the NP scale has to be of order tens of GeV, as the left plot indicates, this will be discussed in detail in our upcoming publication.…”

Section: Lnv Amplitudes From ∆I = 1/2 Interaction Onlymentioning

confidence: 99%

Breaking the Grossman-Nir bound in kaon decays

Dong

Tandean

et al. 2020

J. High Energ. Phys.

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The ratio B(K L → π 0 νν)/B(K + → π + νν) of the branching fractions of kaon decays K L → π 0 νν and K + → π + νν has a maximum of about 4.3 under the assumption that the underlying interactions change isospin by ∆I = 1/2. This is referred to as the Grossman-Nir (GN) bound, which is respected by the standard model (SM) and by many scenarios beyond it. Recent preliminary results of the KOTO and NA62 Collaborations searching for these kaon modes seem to imply a violation of this bound. The KOTO findings also suggest that B(K L → π 0 νν) could be much larger, by nearly two orders of magnitude, than that predicted in the SM. In this work we study the possibility of violating the GN bound in an effective field theory approach with only SM fields. We show that the bound holds, in addition to the original GN scenarios, whether or not the kaon decays conserve lepton number. We demonstrate that the inclusion of ∆I = 3/2 operators can lead to a violation of the GN bound and illustrate with an example of how the KOTO numbers may be reached with a new physics scale of order tens of GeV.Recently the KOTO Collaboration has presented a preliminary report on its latest search for the flavor-changing neutral current (FCNC) decay of neutral kaon K L into a neutral pion π 0 and an unobserved neutrino pair (2ν), having achieved a single event sensitivity of 6.9 × 10 −10 and showing 3 candidate events in the signal region [1]. Should these turn out to be real signal events, they would imply a branching fraction of B(K L → π 0 2ν) 2.1 × 10 −9 , which is greater by almost two orders of magnitude than the standard model (SM) prediction [2-4]: B(K L → π 0 νν) SM = (3.0 ± 0.2) × 10 −11 . If confirmed in the future, this huge enhancement seen by KOTO would constitute early evidence for new physics (NP) beyond the SM in the quark sector. For comparison, KOTO [5] earlier set the limit B(K 0 L → π 0 2ν) KOTO15 < 3.0 × 10 −9 at 90% confidence level (CL).

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“…at the 95% confidence level (CL). They update the upper limit on the decay rate of K + → π + νν from BNL E949 [5,6] and the limit on the branching ratio B(K L → π 0 νν) from the 2015 run at KOTO itself [7] B KOTO15 K L →π 0 νν < 3.0 × 10 −9 ,…”

Section: Introductionmentioning

confidence: 99%

Implication of K→πνν¯ for generic neutrino interactions in effective field theories

Schmidt

2020

Phys. Rev. D

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In this work we investigate the implication of K → πνν from the recent KOTO and NA62 measurements for generic neutrino interactions and the new physics scale in effective field theories. The interactions between quarks and left-handed Standard Model (SM) neutrinos are first described by the low energy effective field theory (LEFT) below the electroweak scale. We match them to the chiral perturbation theory (χPT) at the chiral symmetry breaking scale to calculate the branching fractions of Kaon semi-invisible decays and match them up to the SM effective field theory (SMEFT) to constrain new physics above the electroweak scale. In the framework of effective field theories, we prove that the Grossman-Nir bound is valid for both dim-6 and dim-7 LEFT operators, and the dim-6 vector and scalar operators dominantly contribute to Kaon semi-invisible decays based on LEFT and chiral power counting rules. They are induced by multiple dim-6 lepton-number-conserving operators and one dim-7 lepton-number-violating operator in the SMEFT, respectively. In the lepton-number-conserving s → d transition, the K → πνν decays provide the most sensitive probe for the operators with τ τ component and point to a corresponding new physics scale of Λ NP ∈ [47 TeV, 72 TeV] associated with a single effective coefficient. The lepton-number-violating operator can also explain the observed K → πνν discrepancy with the SM prediction within a narrow range Λ NP ∈ [19.4 TeV, 21.5 TeV], which is consistent with constraints from Kaon invisible decays. *

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Search for KL→π0νν¯ and

Cited by 181 publications

References 38 publications

Constraints on long-lived light scalars with flavor-changing couplings and the KOTO anomaly

Constraints on long-lived light scalars with flavor-changing couplings and the KOTO anomaly

Breaking the Grossman-Nir bound in kaon decays

Implication of K→πνν¯ for generic neutrino interactions in effective field theories

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