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A new dark sector antibaryon, denoted ψ_{D}, could be produced in decays of B mesons. This Letter presents a search for B^{+}âψ_{D}+p (and the charge conjugate) decays in e^{+}e^{-} annihilations at 10.58 GeV, using data collected in the BABAR experiment. Data corresponding to an integrated luminosity of 398 fb^{-1} are analyzed. No evidence for a signal is observed. Branching fraction upper limits in the range from 10^{-7}-10^{-5} are obtained at 90% confidence level for masses of 1.0
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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 Ï_{D}, produced in the reaction e^{+}e^{-}âγÏ_{D}, Ï_{D}âA^{'}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
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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^{±}âK^{±}a, aâγγ 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
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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 Ï(3S)âe^{±}µ^{∓} in a sample of 118 million Ï(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 B[Ï(3S)âe^{±}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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A study of the two-body decays B^{±}âX_{cc[over ¯]}K^{±}, where X_{cc[over ¯]} 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^{+}âX(3872)K^{+} at the 3σ level. The absolute branching fraction B[B^{+}âX(3872)K^{+}]=[2.1±0.6(stat)±0.3(syst)]×10^{-4} is measured for the first time. It follows that B[X(3872)âJ/ψπ^{+}π^{-}]=(4.1±1.3)%, supporting the hypothesis of a molecular component for this resonance.
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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}âh^{'-}h^{-}â^{'+}â^{+} and D^{0}âh^{'-}h^{+}â^{'±}â^{∓}, where h and h^{'} represent a K or π meson and â and â^{'} an electron or muon. The analysis is based on 468 fb^{-1} of e^{+}e^{-} annihilation data collected at or close to the Ï(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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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 (Ï_{L}) would be produced predominantly through radiation from a τ lepton. We report herein a search for e^{+}e^{-}âτ^{+}τ^{-}Ï_{L}, Ï_{L}ââ^{+}â^{-} (â=e, µ) using data collected by the BABAR experiment at SLAC. No significant signal is observed, and we set limits on the Ï_{L} coupling to leptons in the range 0.04
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We report on a precision measurement of the ratio R_{τµ}^{Ï(3S)}=B(Ï(3S)âτ^{+}τ^{-})/B(Ï(3S)âµ^{+}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 Ï(3S) mesons. The ratio is measured to be R_{τµ}^{Ï(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}^{Ï(3S)} is almost an order of magnitude smaller than the only previous measurement.
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An angular analysis of the decay B[over ¯]âD^{*}â^{-}ν[over ¯]_{â}, â∈{e,µ}, is reported using the full e^{+}e^{-} collision data set collected by the BABAR experiment at the Ï(4S) resonance. One B meson from the Ï(4S)âBB[over ¯] decay is fully reconstructed in a hadronic decay mode, which constrains the kinematics and provides a determination of the neutrino momentum vector. The kinematics of the semileptonic decay is described by the dilepton mass squared, q^{2}, and three angles. The first unbinned fit to the full four-dimensional decay rate in the standard model is performed in the so-called Boyd-Grinstein-Lebed approach, which employs a generic q^{2} parametrization of the underlying form factors based on crossing symmetry, analyticity, and QCD dispersion relations for the amplitudes. A fit using the more model-dependent Caprini-Lellouch-Neubert (CLN) approach is performed as well. Our form factor shapes show deviations from previous fits based on the CLN parametrization. The latest form factors also provide an updated prediction for the branching fraction ratio R(D^{*})≡B(B[over ¯]âD^{*}τ^{-}ν[over ¯]_{τ})/B(B[over ¯]âD^{*}â^{-}ν[over ¯]_{â})=0.253±0.005. Finally, using the well-measured branching fraction for the B[over ¯]âD^{*}â^{-}ν[over ¯]_{â} decay, a value of |V_{cb}|=(38.36±0.90)×10^{-3} is obtained that is consistent with the current world average for exclusive B[over ¯]âD^{(*)}â^{-}ν[over ¯]_{â} decays and remains in tension with the determination from inclusive semileptonic B decays to final states with charm.
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We report the observation of the rare charm decay D^{0}âK^{-}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 Ï(4S) resonance with the BABAR detector at the SLAC National Accelerator Laboratory. We find the branching fraction in the invariant mass range 0.675
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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 ÏâSΛ[over ¯]Λ[over ¯] decays based on a sample of 90×10^{6}Ï(2S) and 110×10^{6}Ï(3S) decays collected by the BABAR experiment. No signal is observed, and 90% confidence level limits on the combined Ï(2S,3S)âSΛ[over ¯]Λ[over ¯] 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 search for the rare flavor-changing neutral current process B^{+}âK^{+}τ^{+}τ^{-} using data from the BABAR experiment. The data sample, collected at the center-of-mass energy of the Ï(4S) resonance, corresponds to a total integrated luminosity of 424 fb^{-1} and to 471×10^{6} BB[over ¯] pairs. We reconstruct one B meson, produced in the Ï(4S)âB^{+}B^{-} decay, in one of many hadronic decay modes and search for activity compatible with a B^{+}âK^{+}τ^{+}τ^{-} decay in the rest of the event. Each τ lepton is required to decay leptonically into an electron or muon and neutrinos. Comparing the expected number of background events with the data sample after applying the selection criteria, we do not find evidence for a signal. The resulting upper limit, at the 90% confidence level, is B(B^{+}âK^{+}τ^{+}τ^{-})<2.25×10^{-3}.
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We search for single-photon events in 53 fb^{-1} of e^{+}e^{-} collision data collected with the BABAR detector at the PEP-II B-Factory. We look for events with a single high-energy photon and a large missing momentum and energy, consistent with production of a spin-1 particle A^{'} through the process e^{+}e^{-}âγA^{'}; A^{'}âinvisible. Such particles, referred to as "dark photons," are motivated by theories applying a U(1) gauge symmetry to dark matter. We find no evidence for such processes and set 90% confidence level upper limits on the coupling strength of A^{'} to e^{+}e^{-} in the mass range m_{A^{'}}≤8 GeV. In particular, our limits exclude the values of the A^{'} coupling suggested by the dark-photon interpretation of the muon (g-2)_{µ} anomaly, as well as a broad range of parameters for the dark-sector models.
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We measure the mass difference, Δm_{+}, between the D^{*}(2010)^{+} and the D^{+} using the decay chain D^{*}(2010)^{+}âD^{+}π^{0} with D^{+}âK^{-}π^{+}π^{+}. The data were recorded with the BABAR detector at center-of-mass energies at and near the Ï(4S) resonance, and correspond to an integrated luminosity of approximately 468 fb^{-1}. We measure Δm_{+}=(140 601.0±6.8[stat]±12.9[syst]) keV. We combine this result with a previous BABAR measurement of Δm_{0}≡m(D^{*}(2010)^{+})-m(D^{0}) to obtain Δm_{D}=m(D^{+})-m(D^{0})=(4824.9±6.8[stat]±12.9[syst]) keV. These results are compatible with and approximately five times more precise than the Particle Data Group averages.