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The BaBar Collaboration

Publications and source records attributed to The BaBar Collaboration.

At least 19 recordsLinked to original sources

Measurement of the spectral function for the $τ^-\to K^-K_Sν_τ$ decay

The decay $τ^{-}\to K^{-}K_Sν_τ$ has been studied using $430\times10^6$ $e^+e^-\to τ^+τ^-$ events produced at a center-of-mass energy around 10.6 GeV at the PEP-II collider and studied with the BABAR detector. The mass spectrum of the $K^{-}K_S$ system has been measured and the spectral function has been obtained. The measured branching fraction ${\cal B}(τ^{-}\to K^{-}K_Sν_τ) = (0.739\pm 0.011(\rm stat.)\pm 0.020(\rm syst.))\times 10^{-3}$ is found to be in agreement with earlier measurements.

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Measurement of the $e^+e^-\toπ^+π^-π^0π^0$ cross section using initial-state radiation at BaBar

The process $e^+e^- \to π^+π^-2π^0γ$ is investigated by means of the initial-state radiation technique, where a photon is emitted from the incoming electron or positron. Using $454.3 \rm{fb}^{-1}$ of data collected around a center-of-mass energy of $\sqrt{s} = 10.58 \rm{GeV}$ by the BaBar experiment at SLAC, approximately 150000 signal events are obtained. The corresponding non-radiative cross section is measured with a relative uncertainty of $3.6\%$ in the energy region around $1.5 \rm{GeV}$, surpassing all existing measurements in precision. Using this new result, the channel's contribution to the leading order hadronic vacuum polarization contribution to the anomalous magnetic moment of the muon is calculated as $(g_μ^{π^+π^-2π^0}-2)/2 = (17.9 \pm 0.1_\mathrm{stat} \pm 0.6_\mathrm{syst}) \times 10^{-10}$ in the energy range $0.85\rm{GeV} < E_\mathrm{CM} < 1.8\rm{GeV}$. In the same energy range, the impact on the running of the fine structure constant at the $Z^0$-pole is determined as $Δα^{π^+π^-2π^0}(M^2_\mathrm{Z}) = (4.44 \pm 0.02_\mathrm{stat} \pm 0.14_\mathrm{syst}) \times 10^{-4}$. Furthermore, intermediate resonances are studied and especially the cross section of the process $e^+e^- \to ωπ^0 \to π^+π^-2π^0$ is measured.

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Measurement of the $D^*(2010)^+ - D^+$ mass difference

We measure the mass difference, $Δm_+$, between the $D^{*}(2010)^+$ and the $D^+$ using the decay chain $D^{*}(2010)^+\to D^+ π^0$ with $D^+\to K^-π^+π^+$. The data were recorded with the BABAR detector at center-of-mass energies at and near the $Υ(4S)$ resonance, and correspond to an integrated luminosity of approximately 468 ${\rm fb}^{-1}$. We measure $Δm_+ = \left(140\,601.0 \pm 6.8[{\rm stat}] \pm 12.9[{\rm syst}]\right)$ keV. We combine this result with a previous BABAR measurement of $Δm_0\equiv m(D^{*}(2010)^+) - m (D^0)$ to obtain $Δm_D = m(D^+) - m(D^0) = \left(4\,824.9 \pm 6.8[{\rm stat}] \pm 12.9[{\rm syst}]\right)$ keV. These results are compatible with and approximately five times more precise than the Particle Data Group averages.

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Dalitz plot analyses of $J/ψ\to π^+ π^- π^0$, $J/ψ\to K^+ K^- π^0$, and $J/ψ\to K^0_S K^{\pm} π^{\mp}$ produced via $e^+ e^-$ annihilation with initial-state radiation

We study the processes $e^+ e^- \to \ γ_{\rm ISR} J/ψ$ where $J/ψ\to π^+ π^- π^0$, $J/ψ\to K^+ K^- π^0$, and $J/ψ\to K^0_S K^{\pm} π^{\mp}$ using a data sample of 519 $fb^{-1}$ recorded with the BaBar detector operating at the SLAC PEP-II asymmetric-energy $e^+ e^-$ collider at center-of-mass energies at and near the $Υ(nS)$ ($n = 2,3,4$) resonances. We measure the ratio of branching fractions $R_1 = \frac{B(J/ψ\ \to \ K^+ K^- π^0)}{B(J/ψ\ \to \ π^+ π^- π^0)}$ and $R_2 = \frac{B(J/ψ\ \to \ K^0_S K^{\pm} π^{\mp})}{B(J/ψ\ \to \ π^+ π^- π^0)}$. We perform Dalitz-plot analyses of the three $J/ψ$ decay modes and measure fractions for resonances contributing to the decays. We also analyze the $J/ψ\to π^+ π^- π^0$ decay using the Veneziano model. We observe structures compatible with the presence of $ρ(1450)$ in all the three $J/ψ$ decay modes and measure the relative branching fraction: $R(ρ(1450)) = \frac{B(ρ(1450) \ \to \ K^+ K^-)}{B(ρ(1450) \ \to \ π^+ π^-)} = 0.307 \pm 0.084 ({\rm stat}) \pm 0.082 ({\rm sys})$.

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Search for $B^{+}\rightarrow K^{+} τ^{+}τ^{-}$ at the BaBar experiment

We search for the rare flavor-changing neutral current process $B^{+}\rightarrow K^{+}τ^{+}τ^{-}$ using data from the BABAR experiment. The data sample, collected at the center-of-mass energy of the $Υ{(4S)}$ resonance, corresponds to a total integrated luminosity of 424 fb$^{-1}$ and to 471 million $B\overline{B}$ pairs. We reconstruct one $B$ meson, produced in the $Υ{(4S)}\rightarrow B^{+} B^{-}$ decay, in one of many hadronic decay modes and search for activity compatible with a $B^{+}\rightarrow K^{+} τ^{+}τ^{-}$ 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 measured branching fraction is ($1.31^{+0.66}_{-0.61}$( stat.)$^{+0.35}_{-0.25}$( sys.)$) \times 10^{-3}$ with an upper limit, at the 90\% confidence level, of $\mathcal{B}(B^{+}\rightarrow K^{+}τ^{+}τ^{-})$$< 2.25\times 10^{-3}$.

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Low-energy hadronic cross sections measurements at BaBar, and implication for the g-2 of the muon

The BaBar Collaboration has an intensive program studying the cross sections of hadron production in low-energy e+e- annihilation, accessible via initial-state radiation. Our measurements allow a significant improvement in the precision of the predicted value of the muon anomalous magnetic moment. These improvements are necessary for shedding light on the current > 3 sigma difference between the predicted and the experimental values. We have published results on a number of processes with two to six hadrons in the final state, and other final states are currently under investigation. We report here on the most recent results obtained by analysing the entire Babar dataset.

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Measurement of the branching fractions of the radiative leptonic tau decays tau -> e gamma nu anti-nu and tau -> mu gamma nu anti-nu at BaBar

We perform a measurement of the tau -> l gamma nu anti-nu (l = e, mu) branching fractions for a minimum photon energy of 10 MeV in the tau rest frame, using 431fb^-1 of e^+e^- collisions collected at the center-of-mass energy of the Upsilon(4S) resonance with the BaBar detector at the PEP-II storage rings. We find B(tau -> mu gamma nu anti-nu ) = (3.69pm0.03pm0.10)x10^-3, and B(tau -> e gamma nu anti-nu ) = (1.847pm0.015pm0.052)x10^-2, where the first quoted error is statistical, and the second is systematic. These results are substantially more precise than previous measurements.

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Measurement of the D*(2010)+ natural line width and the D*(2010)+ - D0 mass difference

We measure the mass difference, Δm_0, between the D*(2010)+ and the D0 and the natural line width, Γ, of the transition D*(2010)+ -> D0 pi+. The data were recorded with the BABAR detector at center-of-mass energies at and near the Upsilon(4S) resonance, and correspond to an integrated luminosity of approximately 477 1/fb. The D0 is reconstructed in the decay modes D0 -> K- pi+ and D0 -> K- pi+ pi- pi+. For the decay mode D0 -> K- pi+ we obtain Gamma = (83.4 +- 1.7 +- 1.5) keV and Δm_0 = (145 425.6 +- 0.6 +- 1.8) keV, where the quoted errors are statistical and systematic, respectively. For the D0 -> K- pi+ pi- pi+ mode we obtain Γ= (83.2 +- 1.5 +- 2.6) keV and Δm_0 = (145 426.6 +- 0.5 +- 2.0) keV. The combined measurements yield Γ= (83.3 +- 1.2 +- 1.4) keV and Δm_0 = (145 425.9 +- 0.4 +- 1.7) keV; the width is a factor of approximately 12 times more precise than the previous value, while the mass difference is a factor of approximately 6 times more precise.

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Measurement of the D*(2010)+ meson width and the D*(2010)+ - D0 mass difference

We measure the mass difference, Δm_0, between the D*(2010)+ and the D0 and the natural line width, Γ, of the transition D*(2010)+ -> D0 pi+. The data were recorded with the BABAR detector at center-of-mass energies at and near the Upsilon(4S) resonance, and correspond to an integrated luminosity of approximately 477 1/fb. The D0 is reconstructed in the decay modes D0 -> K- pi+ and D0 -> K- pi+ pi- pi+. For the decay mode D0 -> K- pi+ we obtain Gamma = (83.4 +- 1.7 +- 1.5) keV and Δm_0 = (145 425.6 +- 0.6 +- 1.8) keV, where the quoted errors are statistical and systematic, respectively. For the D0 -> K- pi+ pi- pi+ mode we obtain Γ= (83.2 +- 1.5 +- 2.6) keV and Δm_0 = (145 426.6 +- 0.5 +- 2.0) keV. The combined measurements yield Γ= (83.3 +- 1.2 +- 1.4) keV and Δm_0 = (145 425.9 +- 0.4 +- 1.7) keV; the width is a factor of approximately 12 times more precise than the previous value, while the mass difference is a factor of approximately 6 times more precise.

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Precision Measurement of the e+e- --> K+K-(gamma) Cross Section with the Initial-State Radiation Method at BaBar

A precise measurement of the cross section for the process e+e- --> K+K-(gamma) from threshold to an energy of 5 GeV is obtained with the initial-state radiation (ISR) method using 232 fb^{-1} of data collected with the BaBar detector at e+e- center-of-mass energies near 10.6 GeV. The measurement uses the effective ISR luminosity determined from the e+e- --> mu+mu-(gamma)gamma_ISR process with the same data set. The corresponding lowest-order contribution to the hadronic vacuum polarization term in the muon magnetic anomaly is found to be a_mu^{KK, LO}=(22.93 +- 0.18_{stat} +- 0.22_{syst}) * 10^{-10}. The charged kaon form factor is extracted and compared to previous results. Its magnitude at large energy significantly exceeds the asymptotic QCD prediction, while the measured slope is consistent with the prediction.

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Study of the baryonic B decay B- -> SigmaC++ p- pi- pi-

We report the measurement of the baryonic B decay B- -> SigmaC++ p- pi- pi-. Using a data sample of 467*10^6 B B-bar pairs collected with the BaBar detector at the PEP-II storage ring at SLAC, the measured branching fraction is (2.98 +/- 0.16 (stat) +/- 0.15 (syst) +/- 0.77 (LambdaC+))*10^{-4}, where the last error is due to the uncertainty in the branching fraction of the decay LambdaC+ -> p+ K- pi+. The data suggest the existence of resonant subchannels B- -> LambdaC(2595)+ p- pi- and, possibly, B- -> SigmaC++ anti-Delta-- pi-. We see unexplained structures in m(SigmaC++ pi- pi-) at 3.25 GeV/c^2, 3.8 GeV/c^2, and 4.2 GeV/c^2.

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Evidence for an excess of B -> D(*) Tau Nu decays

Based on the full BaBar data sample, we report improved measurements of the ratios R(D(*)) = B(B -> D(*) Tau Nu)/B(B -> D(*) l Nu), where l is either e or mu. These ratios are sensitive to new physics contributions in the form of a charged Higgs boson. We measure R(D) = 0.440 +- 0.058 +- 0.042 and R(D*) = 0.332 +- 0.024 +- 0.018, which exceed the Standard Model expectations by 2.0 sigma and 2.7 sigma, respectively. Taken together, our results disagree with these expectations at the 3.4 sigma level. This excess cannot be explained by a charged Higgs boson in the type II two-Higgs-doublet model. We also report the observation of the decay B -> D Tau Nu, with a significance of 6.8 sigma.

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Precision Measurement of the B to X_s γPhoton Energy Spectrum, Branching Fraction, and Direct CP Asymmetry A_{CP}(B to X_{s+d}γ

The photon spectrum in the inclusive electromagnetic radiative decays of the $B$ meson, $B \to X_{s} γ$ plus $B \to X_{d} γ$, is studied using a data sample of $(382.8 \pm 4.2) \times 10^6$ $Υ(4S) \to B\overli\ ne{B}$ decays collected by the \babar\ experiment at SLAC. The spectrum is used to extract the branching fraction ${\cal B}(B \to X_{s} γ)=(3.21 \pm 0.33)\times 10^{-4}$ for $E_γ>1.8 \gev$ and the direct CP asymmetry $A_{CP}(B \to X_{s+d} γ)=0.057 \pm 0.063$. The effects of detector resolution and Doppler smearing are unfolded to measure the photon energy spectrum in the $B$ meson rest frame.

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A Measurement of the Semileptonic Branching Fraction of the B_s Meson

We report a measurement of the inclusive semileptonic branching fraction of the B_s meson using data collected with the BaBar detector in the center-of-mass (CM) energy region above the Upsilon(4S) resonance. We use the inclusive yield of phi mesons and the phi yield in association with a high-momentum lepton to perform a simultaneous measurement of the semileptonic branching fraction and the production rate of B_s mesons relative to all B mesons as a function of CM energy. The inclusive semileptonic branching fraction of the B_s meson is determined to be B(B_s to l nu X)=9.5 (+2.5/-2.0)(stat)(+1.1/-1.9)(syst)%, where l indicates the average of e and mu.

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Observation of the rare decay B+->K+pi0pi0 and measurement of the quasi-two body contributions B+->K*(892)+pi0, B+->f0(980)K+ and B+->chic0K+

We report an analysis of the charmless hadronic decays of charged B meson to the final state K+pi0pi0, using a data sample of 470+/-2.8 million BBbar events collected at the Y(4S) resonance. We observe an excess of signal events, with a significance above 10 standard deviations including systematic uncertainties, and measure the branching fraction and CP asymmetry to be B(B+->K+pi0pi0)=(16.2+/-1.2+/-1.5)x10^-6 and A_CP(B+->K+pi0pi0)=-0.06+/-0.06+/-0.04, where the uncertainties are statistical and systematic respectively. Additionally we study the contributions of the B+->K*(892)+pi0, B+->f0(980)K+ and B+->chic0K+ quasi-two body decays. We report the world's best measurements of the branching fractions and CP asymmetry of the B+->K+pi0pi0 and B+->K*(892)+pi0 channels.

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Studies of tau- -> eta.K-.nu and tau- -> eta.pi-.nu at BaBar and a search for a second-class current

We report on analyses of tau lepton decays $τ^- \to ηK^- ν_τ$ and $τ^- \to ηπ^- ν_τ$, with $η\to π^+ π^- π^0$, using 470 fb$^{-1}$ of data from the Babar experiment at PEP-II, collected at center-of-mass energies at and near the $Υ(4S)$ resonance. We measure the branching fraction for the $τ^- \to ηK^- ν_τ$ decay mode, $\Br(τ^- \to ηK^- ν_τ) = (1.42\pm0.11\text{(stat)}\pm0.07\text{(syst)})\times10^{-4}$, and report a 95% confidence level upper limit for the second-class current process $τ^- \to ηπ^- ν_τ$, $\Br(τ^- \to ηπ^- ν_τ) < 9.9\times10^{-5}$.

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B-meson decays to eta' rho, eta' f0, and eta' K*

We present measurements of B-meson decays to the final states eta'rho, eta'f0, and eta'K*, where K* stands for a vector, scalar, or tensor strange meson. We observe a significant signal or evidence for eta'rho+ and all the eta'K* channels. We also measure, where applicable, the charge asymmetries, finding results consistent with no direct CP-violation in all cases. The measurements are performed on a data sample consisting of 467 x 10^6 B-Bbar pairs, collected with the BaBar detector at the PEP-II e+e- collider at the SLAC National Accelerator Laboratory. Our results favor the theoretical predictions from perturbative QCD and QCD Factorization and we observe an enhancement of the tensor K_2*(1430) with respect to the vector K*(892) component.

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Measurement of CP violation observables and parameters for the decays $B^{\pm}\to D K^{*\pm}$

We study the decay $B^-\to DK^{*-}$ using a sample of 379$\times 10^6$ $Υ(4S)\to B\bar{B}$ events collected with the BABAR detector at the PEP-II $B$-factory. We perform a "GLW" analysis where the $D$ meson decays into either a CP-even ($CP+$) eigenstate ($K^+K^-$, $π^+π^-$), CP-odd ($CP-$) eigenstate ($K^0_Sπ^0$, $K^0_Sϕ$, $K^0_Sω$) or a non-CP state ($K^-π^+$). We also analyze $D$ meson decays into $K^+π^-$ from a Cabibbo-favored $\bar{D}^0$ decay or doubly suppressed $D^0$ decay ("ADS" analysis). We measure observables that are sensitive to the CKM angle $γ$: the partial-rate charge asymmetries ${\cal A}_{CP\pm}$, the ratios ${\cal R}_{CP\pm}$ of the B-decay branching fractions in $CP\pm$ and non-CP decay, the ratio ${\cal R}_{ADS}$ of the charge-averaged branching fractions, and the charge asymmetry ${\cal A}_{ADS}$ of the ADS decays: ${\cal A}_{CP+}= 0.09\pm0.13 \pm 0.06$, ${\cal A}_{CP-}=-0.23\pm 0.21\pm 0.07$, ${\cal R}_{CP+} =2.17 \pm 0.35 \pm 0.09$,${\cal R}_{CP-} =1.03\pm 0.27\pm 0.13$, ${\cal R}_{ADS}=0.066\pm0.031\pm0.010$, and ${\cal A}_{ADS}=-0.34\pm0.43\pm 0.16$, where the first uncertainty is statistical and the second is systematic. Combining all the measurements and using a frequentist approach yields the magnitude of the ratio between the Cabibbo-suppressed and favored amplitudes, $r_B$ = 0.31 with a one (two) sigma confidence level interval of [0.24, 0.38] ([0.17, 0.43]). The value $r_B=0$ is excluded at the 3.3 sigma level. A similar analysis excludes values of $γ$ in the intervals $[0, 7]^{\circ}, [55, 111]^{\circ}$, and $[175, 180]^{\circ}$ ([85, 99]$^{\circ}$) at the one (two) sigma confidence level.

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