Many scenarios of physics beyond the standard model predict the existence of new gauge singlets, which might be substantially lighter than the weak scale. The experimental constraints on additional ...scalars with masses in the MeV to GeV range could be significantly weakened if they interact predominantly with leptons rather than quarks. At an e+e− collider, such a leptophilic scalar (ϕL) would be produced predominantly through radiation from a τ lepton. We report herein a search for e+e−→τ+τ−ϕL, ϕL→ℓ+ℓ− (ℓ=e, μ) using data collected by the BABAR experiment at SLAC. No significant signal is observed, and we set limits on the ϕL coupling to leptons in the range 0.04<mϕL<7.0 GeV. These bounds significantly improve upon the current constraints, excluding almost entirely the parameter space favored by the observed discrepancy in the muon anomalous magnetic moment below 4 GeV at 90% confidence level.
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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→γγ 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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We report on a precision measurement of the ratio R_{τμ}^{ϒ(3S)}=B(ϒ(3S)→τ^{+}τ^{-})/B(ϒ(3S)→μ^{+}μ^{-}) using data collected with the BABAR detector at the SLAC PEP-II e^{+}e^{-} collider. The ...measurement is based on a 28 fb^{-1} data sample collected at a center-of-mass energy of 10.355 GeV corresponding to a sample of 122 million ϒ(3S) mesons. The ratio is measured to be R_{τμ}^{ϒ(3S)}=0.966±0.008_{stat}±0.014_{syst} and is in agreement with the standard model prediction of 0.9948 within 2 standard deviations. The uncertainty in R_{τμ}^{ϒ(3S)} is almost an order of magnitude smaller than the only previous measurement.
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Collider searches for dark sectors, new particles interacting only feebly with ordinary matter, have largely focused on identifying signatures of new mediators, leaving much of dark sector structures ...unexplored. In particular, the existence of dark matter bound states (darkonia) remains to be investigated. This possibility could arise in a simple model in which a dark photon (A^{'}) is light enough to generate an attractive force between dark fermions. We report herein a search for a J^{PC}=1^{--} darkonium state, the ϒ_{D}, produced in the reaction e^{+}e^{-}→γϒ_{D}, ϒ_{D}→A^{'}A^{'}A^{'}, where the dark photons subsequently decay into pairs of leptons or pions, using 514 fb^{-1} of data collected with the BABAR detector. No significant signal is observed, and we set bounds on the γ-A^{'} kinetic mixing as a function of the dark sector coupling constant for 0.001<m_{A^{'}}<3.16 GeV and 0.05<m_{ϒ_{D}}<9.5 GeV.
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We report on the first search for electron-muon lepton flavor violation (LFV) in the decay of a b quark and b antiquark bound state. We look for the LFV decay ϒ(3S)→e^{±}μ^{∓} in a sample of ...118 million ϒ(3S) mesons from 27 fb^{-1} of data collected with the BABAR detector at the SLAC PEP-II e^{+}e^{-} collider operating with a 10.36 GeV center-of-mass energy. No evidence for a signal is found, and we set a limit on the branching fraction Bϒ(3S)→e^{±}μ^{∓}<3.6×10^{-7} at 90% C. L. This result can be interpreted as a limit Λ_{NP}/g_{NP}^{2}>80 TeV on the energy scale Λ_{NP} divided by the coupling-squared g_{NP}^{2} of relevant new physics (NP).
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Recent investigations have suggested that the six-quark combination uuddss could be a deeply bound state (S) that has eluded detection so far, and a potential dark matter candidate. We report the ...first search for a stable, doubly strange six-quark state in ϒ→SΛover ¯Λover ¯ decays based on a sample of 90×10^{6}ϒ(2S) and 110×10^{6}ϒ(3S) decays collected by the BABAR experiment. No signal is observed, and 90% confidence level limits on the combined ϒ(2S,3S)→SΛover ¯Λover ¯ branching fraction in the range (1.2-1.4)×10^{-7} are derived for m_{S}<2.05 GeV. These bounds set stringent limits on the existence of such exotic particles.
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We present a search for nine lepton-number-violating and three lepton-flavor-violating neutral charm decays of the type $D^0 → h'^-h^-ℓ'^+ℓ^+$ and $D^0 → h'^-h^+ℓ'^±ℓ^∓$, where $h$ and $h'$ represent ...a $K$ or $π$ meson and $ℓ$ and $ℓ '$ an electron or muon. The analysis is based on $468 fb^{-1}$ of $e^+e^-$ annihilation data collected at or close to the $Υ(4S)$ resonance with the BABAR detector at the SLAC National Accelerator Laboratory. No significant signal is observed for any of the twelve modes, and we establish 90% confidence level upper limits on the branching fractions in the range $(1.0 – 30.6) × 10^{-7}$. The limits are between 1 and 3 orders of magnitude more stringent than previous measurements.
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A study of the two-body decays B±→Xcc¯K±, where Xcc¯ refers to one charmonium state, is reported by the BABAR Collaboration using a data sample of 424 fb−1. The absolute determination of branching ...fractions for these decays are significantly improved compared to previous BABAR measurements. Evidence is found for the decay B+→X(3872)K+ at the 3σ level. The absolute branching fraction BB+→X(3872)K+=2.1±0.6(stat)±0.3(syst)×10−4 is measured for the first time. It follows that BX(3872)→J/ψπ+π−=(4.1±1.3)%, supporting the hypothesis of a molecular component for this resonance.
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We report the observation of the rare charm decay D0 → K-π+e+e- , based on 468 fb-1 of e+e- annihilation data collected at or close to the center-of-mass energy of the γ ( 4 S ) resonance with the ...BABAR detector at the SLAC National Accelerator Laboratory. We find the branching fraction in the invariant mass range 0.675<m ( e+e- ) <0.875 GeV / c2 of the electron-positron pair to be B ( D0 → K-π+e+e- ) = ( 4.0±0.5±0.2±0.1 ) ×10-6 , where the first uncertainty is statistical, the second systematic, and the third due to the uncertainty in the branching fraction of the decay D0 → K-π+π+π- used as a normalization mode. The significance of the observation corresponds to 9.7 standard deviations including systematic uncertainties. This result is consistent with the recently reported D0 → K-π+μ+μ- branching fraction, measured in the same invariant mass range, and with the value expected in the standard model. In a set of regions of m ( e+e- ) , where long-distance effects are potentially small, we determine a 90% confidence level upper limit on the branching fraction B ( D0 → K-π+e+e- ) <3.1×10-6 .
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