arXiv subjects

B. Aubert

Publications and source records attributed to B. Aubert.

At least 181 records · Page 10Linked to original sources

arXiv2007

Search for the rare decay B to pi l+ l-

We have performed a search for the flavor-changing neutral-current decays B --> pi l+l-, where l+l- is either e+e- or mu+mu-, using a sample of 230 million Y(4S)-->BBbar decays collected with the BABAR detector. We observe no evidence of a signal and measure the upper limit on the isospin-averaged branching fraction to be BF(B --> pi l+ l-) < 9.1 x 10^{-8} at 90% confidence level. We also search for the lepton-flavor--violating decays B --> pi e mu and measure an upper limit on the isospin-averaged branching fraction of BF(B --> pi e mu) < 9.2 x 10^{-8} at 90% confidence level.

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arXiv2007

Observation of CP Violation in B0 -> K+pi- and B0 -> pi+pi-

We report observations of CP violation in the decays B0 -> K+pi- and B0 -> pi+pi- in a sample of 383 million Y(4S) -> BBbar events. We find 4372 +/- 82 B0 -> K+pi- decays and measure the direct CP-violating charge asymmetry Akpi = -0.107 +/- 0.018 (stat) +0.007-0.004 (syst), which excludes the CP-conserving hypothesis with a significance of 5.5 standard deviations. In the same sample we find 1139 +/- 49 B0 -> pi+pi- decays and measure the CP-violating asymmetries Spipi = -0.60 +/- 0.11 (stat) +/- 0.03 (syst) and Cpipi = -0.21 +/- 0.09 (stat) +/- 0.02 (syst). CP conservation in B0 -> pi+pi- (Spipi=Cpipi=0) is excluded at a confidence level 1-C.L. = 8 * 10^{-8}, corresponding to 5.4 standard deviations.

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arXiv2007

Search for b--> u transitions in B- -> [K+pi-pi0]_D K-

We search for decays of a B meson into a neutral D meson and a kaon, with the D meson decaying into K+pi-pi0. This final state can be reached through the b --> c transition B- -> D0K- followed by the doubly Cabibbo-suppressed D0 --> K+pi-pi0, or the b --> u transition B- --> D0bar K- followed by the Cabibbo-favored D0bar --> K+ pi-pi 0. The interference of these two amplitudes is sensitive to the angle gamma of the unitarity triangle. We present preliminary results based on 226 10^{6} e+e- --> Y(4s) --> BBbar events collected with the BABAR detector at SLAC. We find no significant evidence for these decays and we set a limit R_ADS =(BR(B- -->[K+pi-pi0]_D K-)+ BR(B+ --> [K-pi+pi0]_D K+))/(BR(B- -->[K-p i+pi0]_D K-)+ BR(B+ --> [K+pi-pi0]_D K+))<0.039 at 95% confidence level, which we translate with a Bayesian approach into r_B = |A(B- --> D0bar K-)|/|A(B- --> D0bar K-)| < 0.185 at 95% confidence level.

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arXiv2007

A study of B-meson decays to eta_c K* and eta_c gamma K(*)

We present preliminary results of a study of the two-body B-meson decays to a charmonium state (ccbar) and a K+ or K*0(892) meson using a sample of about 349 fb-1 of data collected with the BABAR detector at the PEP-II asymmetric-energy B Factory at SLAC. Here ccbar indicates either the eta_c state, reconstructed in the K_S K+- pi-+ and K+K-pi0 decay channels, or the h_c state, reconstructed in its decay to eta_c gamma. We measure BR(B0 -> eta_c K*0)=(6.1+-0.8_stat +- 1.1_syst) * 10-4, BR(B+ -> h_c K+) * BR(h_c -> eta_c gamma)<5.2 * 10-5 and BR(B0 -> h_c K*0) * BR(h_c -> eta_c gamma)<2.41 * 10^-4, at the 90% C.L.

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arXiv2007

Measurement of the tau- --> K- pi0 nu_tau Branching Fraction

A measurement of the tau- --> K- pi0 nu_tau branching fraction has been made using 230.2 fb-1 of data recorded by the BABAR detector at the PEP-II e+ e- collider, located at the Stanford Linear Accelerator Center (SLAC), at a center of mass energy sqrt{s} close to 10.58 GeV. We measure BF(tau- --> K- pi0 nu_tau) = (0.416 +/- 0.003 (stat) +/- 0.018 (syst)) %.

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arXiv2007

Measurement of the Decay B- --> D*0 e- nubar

Using 226 million $B\bar{B}$ events recorded on the $Υ(4S)$ resonance with the BABAR detector at the SLAC $e^+e^-$ storage rings PEPII, we reconstruct $B^-\to D^{*0} e^-\barν_e$ decays using the decay chain $D^{*0}\to{}D^0{}π^0$ and $D^{0}\to{}K^-π^+$. From the dependence of their differential rate on $w$, the product of the four-velocities of $B^-${} and $D^{*0}$, and using the description of the form factor $F(w)$ by Caprini et al., we obtain the preliminary results $ρ^2_{A_1} = 1.15\pm 0.06 \pm 0.08$, $F(1)\cdot|V_{cb}| = (36.3\pm 0.6 \pm 1.4)\cdot 10^{-3}$, and ${\cal B}(B^-\to D^{*0} e^-\barν_e) = (5.71\pm 0.08\pm 0.41)%$. The first errors are statistical and the second ones are systematic. \\

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arXiv2007

Measurement of Moments of the Hadronic-Mass and -Energy Spectrum in Inclusive Semileptonic $\bar{B} \to X_{c} \ell^{-} \barν$ Decays

We present a measurement of moments of the inclusive hadronic-mass and -energy spectrum in semileptonic $\bar{B} \to X_{c} \ell^{-} \barν$ decays. This study is based on a sample of 232 million $Υ(4S) \to B\bar{B}$ decays recorded by the BABAR detector at the PEP-II $e^+e^-$-storage rings. We reconstruct the semileptonic decay by identifying a lepton in events tagged by a fully reconstructed hadronic decay of the second $B$ meson. We report preliminary results for the moments $ $ with $k=1,...,6$ and $ $ with $k=2,4,6$ and $n_X^2 = m_X^2 c^4 - 2 \tildeΛ E_X + \tildeΛ^2$, with $m_X$ the mass of the hadronic system, $E_X$ its energy, and $\tildeΛ$ a constant of $0.65 \mathrm{GeV}$, for different minimal lepton momenta between 0.8 and $1.9 \mathrm{GeV}/c$ measured in the $B$-meson rest frame. These are predicted in the framework of a Heavy Quark Expansion (HQE), which allows the extraction of the total semileptonic branching fraction, the CKM-matrix element $|V_{cb}|$, and the quark masses $m_b$ and $m_c$, together with the dominant non-perturbative HQE parameters. We find as preliminary results $|V_{cb}| = (41.88 \pm 0.81) \cdot 10^{-3}$ and $m_b = (4.552 \pm 0.055) \mathrm{GeV}/c^2$.

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arXiv2007

Measurement of the Semileptonic Decays B --> D tau nubar and B --> D* tau nubar

We present preliminary measurements of branching fractions for the semileptonic decays B --> D tau nubar and B --> D* tau nubar, which are potentially sensitive to non--Standard Model amplitudes. The data sample comprises 232x10^6 Upsilon(4S) --> BBbar decays collected with the BaBar detector at the PEP-II e+e- storage ring. We obtain B(B- --> D0 tau nubar) = (0.63 +/- 0.38 +/- 0.10 +/- 0.06)%, B(B- --> D*0 tau nubar) = (2.35 +/- 0.49 +/- 0.22 +/- 0.18)%, B(B0bar --> D+ tau nubar) = (1.03 +/- 0.35 +/- 0.14 +/- 0.10)%, and B(B0bar --> D*+ tau nubar) = (1.15 +/- 0.33 +/- 0.04 +/- 0.04)%, where the uncertainties are statistical, systematic, and normalization, respectively. By combining B- and B0bar results, we also obtain the branching fractions B(B --> D tau nubar) = (0.90 +/- 0.26 +/- 0.11 +/- 0.06)% and B(B --> D* tau nubar) = (1.81 +/- 0.33 +/- 0.11 +/- 0.06)% (quoted for the B- lifetime), with significances of 3.5 sigma and 6.2 sigma.

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arXiv2007

Study of B0 -> pi0 pi0, B -> pi pi0, and B -> K pi0 Decays, and Isospin Analysis of B -> pipi Decays

We present updated measurements of the branching fractions and CP asymmetries for B0 -> pi0 pi0, B+ -> pi+ pi0, and B+ -> K+ pi0. Based on a sample of 383 x 10^6 Upsilon(4S) -> B Bbar decays collected by the BABAR detector at the PEP-II asymmetric-energy B factory at SLAC, we measure B(B0 -> pi0 pi0) =(1.47 +/- 0.25 +/- 0.12) x 10^-6, B(B+ -> pi+ pi0)= (5.02 +/- 0.46 +/- 0.29) x 10^-6, and B(B+ -> K+ pi0) = (13.6 +/- 0.6 +/- 0.7) x 10^-6. We also measure the CP asymmetries C(pi0 pi0) = -0.49 +/- 0.35 +/- 0.05, A(pi+ pi0) = 0.03 +/- 0.08 +/- 0.01, and A(K+ pi0) = 0.030 +/- 0.039 +/- 0.010. Finally, we present bounds on the CKM angle $α$ using isospin relations.

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arXiv2007

Observation of $B^+\toρ^+K^0$ and Measurement of its Branching Fraction and Charge Asymmetry

We present the first observation of the decay $B^+\toρ^+K^0$, using a data sample of 348 fb$^{-1}$ collected at the $Υ(4S)$ resonance with the \babar detector.The branching fraction and charge asymmetry are measured to be $(8.0^{+1.4}_{-1.3}\pm0.6)\times10^{-6}$ and ($-12.2\pm16.6\pm2.0)%$, respectively, where the first uncertainty is statistical and the second is systematic. The significance of the observed branching fraction, including systematic uncertainties, is 7.9 standard deviations.

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arXiv2007

Amplitude Analysis of the decay D^0 --> K^- K^+ pi^0

Using 385 fb^-1 of e^+e^- collisions at the CM energies of around 10.6 GeV recorded by the BaBar experiment, we study the amplitudes of the singly Cabibbo-suppressed decay D^0 --> K^- K^+ pi^0. We measure the strong phase difference between the D0bar and D0 decays to the K^*(892)^+ K^- state to be -35.5 +/- 1.9 (stat) +/- 2.2 (syst) degrees, and their amplitude ratio to be 0.599 +/- 0.013 (stat) +/- 0.011 (syst). We observe significant contributions from the Kpi and K^-K^+ scalar and vector amplitudes, and analyze the moments of the cosine of the helicity angle in these systems. We find no evidence for charged, scalar kappa(800) state, nor for higher spin states. We also perform a model-independent partial wave analysis of the K^-K^+ system in a limited mass range around 1 GeV/c^2. We study several models for Kpi S-wave amplitude, and describe which one is favored by our data.

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arXiv2007

Search for Prompt Production of $χ_{c}$ and X(3872) in e^+e^- Annihilations

We have searched for prompt production of $χ_{c1}$, $χ_{c2}$ and X(3872) in continuum e^+e^- annihilations using a 386 fb^{-1} data sample collected around $\sqrt{s} = 10.6$ GeV with the BABAR detector using the $γJ/ψ$ decay mode. After accounting for the feed-down from $ψ(2S)\toγχ_{c1,2}$, no significant signal for prompt $χ_{c1,2}$ production is observed. We present improved upper limits on the cross-section, with the rest of the event consisting of more than two charged tracks, to be 77 fb for $χ_{c1}$ and 79 fb for $χ_{c2}$ with $e^+e^-$ center-of-mass frame $χ_c$ momentum greater than 2.0 GeV at 90% confidence level. These limits are consistent with NRQCD predictions. We also set an upper limit on the prompt production of X(3872) through the decay $X(3872)\to γJ/ψ$.

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arXiv2007

Evidence for the B0->ppbarK0 and B+->eta_cK+ decays and Study of the Decay Dynamics of B Meson Decays into ppbarh Final States

With a sample of 232x10^6 Upsilon(4S)->BBbar events collected with the BaBar detector, we study the decays of B mesons to ppbarh final states, where h=pi+,Ks,K*0 or K*+. We report evidence for the B->ppbarK*0 decay, with a branching fraction (1.5+/-0.5(stat)+/-0.4(syst))x10^-6, and for the B+->eta_cK*+ decay, with the branching fraction of Br(B+->eta_cK*+)xBr(eta_c->ppbar)=(1.57^{+0.56}_{-0.45}(stat)^{+0.46}_{-0.36}(syst))x10^-6, and provide improved measurements of the branching fractions of the other modes of this type. We also report the measurements of the charge asymmetry consistent with zero in the B+->ppbarpi+, B0->ppbarK*0 and B+->ppbarK*+ modes. No evidence is found for the pentaquark candidate Theta+ in the mass range 1.52 to 1.55 GeV/c^2, decaying into pKs, or the glueball candidate fJ(2220) in the mass range 2.2<mppbar<2.4GeV/c^2, and branching fraction limits are established for both at the 10^-7 level.

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arXiv2007

Search for the Decays B0->e+e-gamma and B0->mu+mu-gamma

We present results of a search for the decays $B^0 \to \ell^+\ell^-γ$ ($\ell=e$, $μ$). The search is performed using $320\times 10^{6}$ $B\bar{B}$ pairs collected at the $Υ(4S)$ resonance with the BABAR detector at the PEP-II $B$ Factory at SLAC. We find no significant signal and set the following branching fraction upper limits at the 90% confidence level: $\mathcal{B}(B^0\to e^+e^-γ)<1.2\times 10^{-7}$ and $\mathcal{B}(B^0\to μ^+μ^-γ)<1.5\times 10^{-7}$.

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arXiv2007

Evidence of a Broad Structure at an Invariant Mass of 4.32 GeV/$c^2$ in the Reaction $e^+e^-\toπ^+π^-ψ(2S)$ Measured at BaBar

We present a measurement of the cross section of the process $e^+e^-\toπ^+pi^-ψ(2S)$ from threshold up to 8 GeV center-of-mass energy using events containing initial-state radiation, produced at the PEP-II $e^+e^-$ storage rings. The study is based on 298 fb$^{-1}$ of data recorded with the BaBar detector. A structure is observed in the cross-section not far above threshold, near 4.32 GeV. We also investigate the compatibility of this structure with the Y(4260) previously reported by this experiment.

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arXiv2007

Measurement of Decay Amplitudes of B -->(c cbar) Kstar with an Angular Analysis, for (c cbar)=J/psi, psi(2S) and chi_c1

We perform the first three-dimensional measurement of the amplitudes of $B\to ψ(2S) K^*$ and $B\to χ_{c1} K^*$ decays and update our previous measurement for $B\to J/ψK^*$. We use a data sample collected with the BaBar detector at the PEP2 storage ring, corresponding to 232 million $B\bar B$ pairs. The longitudinal polarization of decays involving a $J^{PC}=1^{++}$ $χ_{c1}$ meson is found to be larger than that with a $1^{--}$ $J/ψ$ or $ψ(2S)$ meson. No direct {\it CP}-violating charge asymmetry is observed.

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arXiv2007

A Search for B+ -> tau+ nu

We present a search for the decay B+ -> tau+ nu using 383x10^6 BBbar pairs collected at the Y(4S) resonance with the BABAR detector at the SLAC PEP-II B-Factory. A sample of events with one reconstructed semileptonic B decay (B- -> D0 l nu X)) is selected, and in the recoil a search for B+ -> tau+ nu is performed. The tau is identified in the following channels: tau+ -> e nu nubar, tau+ -> mu nu nubar, tau+ -> pi+ nu, and tau+ -> pi+ pi0 nu. We measure a branching fraction of B(B+ -> tau+ nu)=(0.9 +- 0.6(stat.) +- 0.1(syst.)) x 10^-4. In the absence of a significant signal, we calculate an upper limit at the 90% confidence level of B(B+ -> tau+ nu) < 1.7 x 10^-4. We calculate the product of the B meson decay constant f_B and |V_ub| to be f_B x |V_ub| = (7.2^{+2.0}_{-2.8}(stat.) +- 0.2 (syst.)) x 10^-4 GeV.

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arXiv2007

Amplitude Analysis of the B+- ->phi K*(892)+- Decay

We perform an amplitude analysis of B+- -> phi(1020) K*(892)+- decay with a sample of about 384 million BBbar pairs recorded with the BABAR detector. Overall, twelve parameters are measured, including the fractions of longitudinal f_L and parity-odd transverse f_perp amplitudes, branching fraction, strong phases, and six parameters sensitive to CP-violation. We use the dependence on the Kpi invariant mass of the interference between the JP=1- and 0+ Kpi components to resolve the discrete ambiguity in the determination of the strong and weak phases. Our measurements of f_L=0.49+-0.05+-0.03, f_perp=0.21+-0.05+-0.02, and the strong phases point to the presence of a substantial helicity-plus amplitude from a presently unknown source.

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