RESUMEN
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
RESUMEN
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
RESUMEN
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
RESUMEN
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).
RESUMEN
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.
RESUMEN
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
RESUMEN
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.
RESUMEN
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.
RESUMEN
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
RESUMEN
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.
RESUMEN
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.
RESUMEN
We present first evidence that the cosine of the CP-violating weak phase 2ß is positive, and hence exclude trigonometric multifold solutions of the Cabibbo-Kobayashi-Maskawa (CKM) Unitarity Triangle using a time-dependent Dalitz plot analysis of B^{0}âD^{(*)}h^{0} with DâK_{S}^{0}π^{+}π^{-} decays, where h^{0}∈{π^{0},η,ω} denotes a light unflavored and neutral hadron. The measurement is performed combining the final data sets of the BABAR and Belle experiments collected at the Ï(4S) resonance at the asymmetric-energy B factories PEP-II at SLAC and KEKB at KEK, respectively. The data samples contain (471±3)×10^{6}BB[over ¯] pairs recorded by the BABAR detector and (772±11)×10^{6}BB[over ¯] pairs recorded by the Belle detector. The results of the measurement are sin2ß=0.80±0.14(stat)±0.06(syst)±0.03(model) and cos2ß=0.91±0.22(stat)±0.09(syst)±0.07(model). The result for the direct measurement of the angle ß of the CKM Unitarity Triangle is ß=[22.5±4.4(stat)±1.2(syst)±0.6(model)]°. The measurement assumes no direct CP violation in B^{0}âD^{(*)}h^{0} decays. The quoted model uncertainties are due to the composition of the D^{0}âK_{S}^{0}π^{+}π^{-} decay amplitude model, which is newly established by performing a Dalitz plot amplitude analysis using a high-statistics e^{+}e^{-}âcc[over ¯] data sample. CP violation is observed in B^{0}âD^{(*)}h^{0} decays at the level of 5.1 standard deviations. The significance for cos2ß>0 is 3.7 standard deviations. The trigonometric multifold solution π/2-ß=(68.1±0.7)° is excluded at the level of 7.3 standard deviations. The measurement resolves an ambiguity in the determination of the apex of the CKM Unitarity Triangle.
RESUMEN
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.
RESUMEN
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}.
RESUMEN
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.
RESUMEN
We report on measurements of the decays of B¯ mesons into the semileptonic final states B¯âD^(*)π^(+)π^(-)â^(-)ν¯, where D^(*) represents a D or D^(*) meson and â^(-) is an electron or a muon. These measurements are based on 471×10^(6) BB ¯ pairs recorded with the BABAR detector at the SLAC asymmetric B factory PEP-II. We determine the branching fraction ratios R_{π^{+}π^{-}}^{(*)}=B(B[over ¯]âD^{(*)}π^{+}π^{-}â^{-}ν[over ¯])/B(B[over ¯]âD^{(*)}â^{-}ν[over ¯]) using events in which the second B meson is fully reconstructed. We find R_{π^{+}π^{-}}=0.067±0.010±0.008 and R_{π^{+}π^{-}}^{*}=0.019±0.005±0.004, where the first uncertainty is statistical and the second is systematic. Based on these results and assuming isospin invariance, we estimate that B[over ¯]âD^{(*)}ππâ^{-}ν[over ¯] decays, where π denotes either a π^{±} and π^{0} meson, account for up to half the difference between the measured inclusive semileptonic branching fraction to charm hadrons and the corresponding sum of previously measured exclusive branching fractions.
RESUMEN
We present a measurement of the asymmetry A_{CP} between same-sign inclusive dilepton samples â^{+}â^{+} and â^{-}â^{-} (â=e, µ) from semileptonic B decays in Ï(4S)âBB[over ¯] events, using the complete data set recorded by the BABAR experiment near the Ï(4S) resonance, corresponding to 471×10^{6} BB[over ¯] pairs. The asymmetry A_{CP} allows comparison between the mixing probabilities P(B[over ¯]^{0}âB^{0}) and P(B^{0}âB[over ¯]^{0}), and therefore probes CP and T violation. The result, A_{CP}=[-3.9±3.5(stat)±1.9(syst)]×10^{-3}, is consistent with the standard model expectation.
RESUMEN
We present a search for a neutral, long-lived particle L that is produced in e+ e- collisions and decays at a significant distance from the e+ e- interaction point into various flavor combinations of two oppositely charged tracks. The analysis uses an e+ e- data sample with a luminosity of 489.1 fb(-1) collected by the BABAR detector at the Ï(4S), Ï(3S), and Ï(2S) resonances and just below the Ï(4S). Fitting the two-track mass distribution in search of a signal peak, we do not observe a significant signal, and set 90% confidence level upper limits on the product of the L production cross section, branching fraction, and reconstruction efficiency for six possible two-body L decay modes as a function of the L mass. The efficiency is given for each final state as a function of the mass, lifetime, and transverse momentum of the candidate, allowing application of the upper limits to any production model. In addition, upper limits are provided on the branching fraction B(BâXsL), where Xs is a strange hadronic system.
RESUMEN
Dark sectors charged under a new Abelian interaction have recently received much attention in the context of dark matter models. These models introduce a light new mediator, the so-called dark photon (A^{'}), connecting the dark sector to the standard model. We present a search for a dark photon in the reaction e^{+}e^{-}âγA^{'}, A^{'}âe^{+}e^{-}, µ^{+}µ^{-} using 514 fb^{-1} of data collected with the BABAR detector. We observe no statistically significant deviations from the standard model predictions, and we set 90% confidence level upper limits on the mixing strength between the photon and dark photon at the level of 10^{-4}-10^{-3} for dark photon masses in the range 0.02-10.2 GeV. We further constrain the range of the parameter space favored by interpretations of the discrepancy between the calculated and measured anomalous magnetic moment of the muon.
RESUMEN
We present results of a search for CP violation in B0- B0 mixing with the BABAR detector. We select a sample of B0âD*- Xâ+ ν decays with a partial reconstruction method and use kaon tagging to assess the flavor of the other B meson in the event. We determine the CP violating asymmetry ACP≡[N(B0B0)-N(B0B0)]/[N(B0B0)+N(B0B0)]=(0.06±0.17(-0.32)(+0.38))%, corresponding to ΔCP=1-|q/p|=(0.29±0.84(-1.61)(+1.88))×10(-3).