CDF Collaboration(Aaltonen, T. et al), & Cabrera, S. (2011). Search for a Very Light CP-Odd Higgs Boson in Top Quark Decays from p p-bar Collisions at sqrt(s)=1.96 TeV. Phys. Rev. Lett., 107(3), 031801–8pp.
Abstract: We present the results of a search for a very light CP-odd Higgs boson a(1)(0) originating from top quark decays t -> H(+/-)b -> W(+/-(*)) a(1)(0)b, and subsequently decaying into tau(+)tau(-). Using a data sample corresponding to an integrated luminosity of 2.7 fb(-1) collected by the CDF II detector in p (p) over bar collisions at 1.96 TeV, we perform a search for events containing a lepton, three or more jets, and an additional isolated track with transverse momentum in the range 3 to 20 GeV/c. Observed events are consistent with background sources, and 95% C.L. limits are set on the branching ratio of t -> H(+/-)b for various masses of H(+/-) and a(1)(0).
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BABAR Collaboration(Lees, J. P. et al), Martinez-Vidal, F., & Oyanguren, A. (2022). Search for an Axionlike Particle in B Meson Decays. Phys. Rev. Lett., 128(13), 131802–8pp.
Abstract: Axionlike particles (ALPs) are predicted in many extensions of the standard model, and their masses can naturally be well below the electroweak scale. In the presence of couplings to electroweak bosons, these particles could be emitted in flavor-changing B meson decays. We report herein a search for an ALP, a, in the reaction B-+/- -> K(+/-)a, a -> gamma gamma using data collected by the BABAR experiment at SLAC. No significant signal is observed, and 90% confidence level upper limits on the ALP coupling to electroweak bosons are derived as a function of ALP mass, improving current constraints by several orders of magnitude in the range 0.175 GeV < m(a) < 4.78 GeV.
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Belle II Collaboration(Adachi, I. et al), Gomis, P., & Marinas, C. (2020). Search for an Invisibly Decaying Z ' Boson at Belle II in e(+)e(-) -> mu(+)mu(-) (e(+/-)mu(-/+)) Plus Missing Energy Final States. Phys. Rev. Lett., 124(14), 141801–9pp.
Abstract: Theories beyond the standard model often predict the existence of an additional neutral boson, the Z'. Using data collected by the Belle II experiment during 2018 at the SuperKEKB collider, we perform the first searches for the invisible decay of a Z' in the process e(+)e(-) -> mu(+)mu(-) Z' and of a lepton-flavor-violating Z' in e(+) e(-) -> e(+/-)mu(-/+)Z'. We do not find any excess of events and set 90% credibility level upper limits on the cross sections of these processes. We translate the former, in the framework of an L, – L, theory, into upper limits on the Z' coupling constant at the level of 5 x 10(-2) – 1 for M-z' <= 6 GeV/c(2).
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Belle II Collaboration(Abudinen, F. et al), Gomis, P., & Marinas, C. (2020). Search for Axionlike Particles Produced in e(+)e(-) Collisions at Belle II. Phys. Rev. Lett., 125(16), 161806–9pp.
Abstract: We present a search for the direct production of a light pseudoscalar a decaying into two photons with the Belle II detector at the SuperKEKB collider. We search for the process e(+)e(-) -> gamma a, a -> gamma gamma in the mass range 0.2 < m(a) < 9.7 GeV/c(2) using data corresponding to an integrated luminosity of (445 +/- 3) pb(-1). Light pseudoscalars interacting predominantly with standard model gauge bosons (so-called axionlike particles or ALPs) are frequently postulated in extensions of the standard model. We find no evidence for ALPs and set 95% confidence level upper limits on the coupling strength g(a gamma gamma) of ALPs to photons at the level of 10(-3) GeV-1. The limits are the most restrictive to date for 0.2 < m(a) < 1 GeV/c(2).
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Belle II Collaboration(Abudinen, F. et al), & Marinas, C. (2021). Search for B+ -> K+nu(nu)over-bar Decays Using an Inclusive Tagging Method at Belle H. Phys. Rev. Lett., 127(18), 181802–10pp.
Abstract: A search for the flavor-changing neutral-current decay B+ -> K+nu(nu) over bar is performed at the Belle II experiment at the SuperKEKB asymmetric energy electron-positron collider. The data sample corresponds to an integrated luminosity of 63 fb(-1) collected at the Upsilon(4S) resonance and a sample of 9 fb(-1) collected at an energy 60 MeV below the resonance. Because the measurable decay signature involves only a single charged kaon, a novel measurement approach is used that exploits not only the properties of the B+ -> K+nu(nu) over bar decay, but also the inclusive properties of the other B meson in the Upsilon(4S) -> B (B) over bar event, to suppress the background from other B meson decays and light-quark pair production. This inclusive tagging approach offers a higher signal efficiency compared to previous searches. No significant signal is observed. An upper limit on the branching fraction of B+ -> K+nu(nu) over bar of 4.1 x 10(-5) is set at the 90% confidence level.
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