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B. Aubert

Publications and source records attributed to B. Aubert.

At least 19 recordsLinked to original sources

Collins asymmetries in inclusive charged $KK$ and $Kπ$ pairs produced in $e^+e^-$ annihilation

We present measurements of Collins asymmetries in the inclusive process $e^+e^- \rightarrow h_1 h_2 X$, $h_1h_2=KK,\, Kπ,\, ππ$, at the center-of-mass energy of 10.6 GeV, using a data sample of 468 fb$^{-1}$ collected by the BaBar experiment at the PEP-II $B$ factory at SLAC National Accelerator Center. Considering hadrons in opposite thrust hemispheres of hadronic events, we observe clear azimuthal asymmetries in the ratio of unlike- to like-sign, and unlike- to all charged $h_1 h_2$ pairs, which increase with hadron energies. The $Kπ$ asymmetries are similar to those measured for the $ππ$ pairs, whereas those measured for high-energy $KK$ pairs are, in general, larger.

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Measurements of Charged Current Lepton Universality and $|V_{us}|$ using Tau Lepton Decays to $e^- \barν_e ν_τ$, $μ^- \barν_μν_τ$, $π^- ν_τ$, and $\K^- ν_τ$

Using 467 $fb^{-1}$ of $e^+e^-$ annihilation data collected with the BaBar detector, we measure $\frac{\cal{B}(τ^- \to μ^- \barν_μν_τ)}{\cal{B}(τ^- \to e^- \barν_e ν_τ)} = (0.9796 \pm 0.0016 \pm 0.0036)$, $\frac{\cal{B}(τ^- \to π^- ν_τ)}{\cal{B}(τ^- \to e^- \barν_e ν_τ)} = (0.5945 \pm 0.0014 \pm 0.0061)$, and $\frac{\cal{B}(τ^- \to \K^- ν_τ)}{\cal{B}(τ^- \to e^- \barν_e ν_τ)} = (0.03882 \pm 0.00032 \pm 0.00057)$, where the uncertainties are statistical and systematic, respectively. From these precision $τ$ measurements, we test the Standard Model assumption of $μ$-$e$ and $τ$-$μ$ charge current lepton universality and provide determinations of $|V_{us}|$ experimentally independent of the decay of a kaon and which we compare with the value predicted from the unitarity of the Cabibbo-Kobayashi-Maskawa matrix.

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Correlated leading baryon-antibaryon production in e+e- --> ccbar --> Lambda_c+ antiLambda_c- X

We present a study of 649 \pm 35 e+e- --> ccbar events produced at sqrt{s}~10.6 GeV containing both a Lambda_c baryon and a Lambda_c antibaryon. The number observed is roughly four times that expected if the leading charmed hadron types are uncorrelated, confirming an observation by the CLEO Collaboration. We find a 2-jet topology in these events but very few additional baryons, demonstrating that the primary c and cbar are predominantly contained in a correlated baryon-antibaryon system. In addition to the charmed baryons we observe on average 2.6 \pm 0.2 charged intermediate mesons, predominantly pions, carrying 65% of the remaining energy.

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Observation of the chi_c2(2P) meson in the reaction gamma gamma -> D Dbar at BABAR

A search for the Z(3930) resonance in gamma gamma production of the DDbar system has been performed using a data sample corresponding to an integrated luminosity of 384 fb^-1 recorded by the BABAR experiment at the PEP-II asymmetric-energy electron-positron collider. The DDbar invariant mass distribution shows clear evidence of the Z(3930) state with a significance of 5.8 sigma. We determine mass and width values of (3926.7 +- 2.7 +- 1.1) MeV/c^2 and (21.3 +- 6.8 +- 3.6) MeV, respectively. A decay angular analysis provides evidence that the Z(3930) is a tensor state with positive parity and C-parity (J^PC = 2^++); therefore we identify the Z(3930) state as the chi_c2(2P) meson. The value of the partial width Gamma_(gamma gamma)xB(Z(3930)-> DDbar) is found to be (0.24 +- 0.05 +- 0.04) keV.

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Observation of inclusive $D^{*\pm}$ production in the decay of $Υ(1S)$

We present a study of the inclusive $D^{*\pm}$ production in the decay of $Υ(1S)$ using $(98.6 \pm 0.9)\times 10^6$ $Υ(2S)$ mesons collected with the BaBar detector at the $Υ(2S)$ resonance. Using the decay chain $Υ(2S)\to π^+ π^- Υ(1S), Υ(1S) \to D^{*\pm} X$, where X is unobserved, we measure the branching fraction $\BR[Υ(1S)\to D^{*\pm} X] = (2.52 \pm 0.13({\rm stat}) \pm 0.15({\rm syst}))%$ and the $D^{*\pm}$ momentum distribution in the rest frame of the $Υ(1S)$. We find evidence for an excess of $D^{*\pm}$ production over the expected rate from the virtual photon annihilation process $Υ(1S)\toγ^*\to c\bar c\to D^{*\pm} X$.

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Searches for Lepton Flavor Violation in the Decays tau -> e gamma and tau -> mu gamma

Searches for lepton-flavor-violating decay of a tau lepton to a lighter mass lepton and a photon have been performed with the entire dataset of (963 +- 7) x 10^6 tau decays collected by the BaBar detector near the Upsilon(4S), Upsilon(3S) and Upsilon(2S) resonances. The searches yield no evidence of signals and we set upper limits on the branching fractions of BR(tau -> e gamma) < 3.3 x 10^-8 and BR(tau -> mu gamma) < 4.4 x 10^-8 at 90% confidence level.

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Search for Charged Lepton Flavor Violation in Narrow Upsilon Decays

Charged lepton flavor violating processes are unobservable in the standard model, but they are predicted to be enhanced in several extensions to the standard model, including supersymmetry and models with leptoquarks or compositeness. We present a search for such processes in a sample of 99M Y(2S) decays and 117M Y(3S) decays collected with the BABAR detector. We place upper limits on the branching fractions BF(Y(nS) -> e tau) and BF(Y(nS) -> mu tau) (n = 2, 3) at the 10^(-6) level and use these results to place lower limits of order 1 TeV on the mass scale of charged lepton flavor violating effective operators.

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Model-independent search for the decay B -> l nu gamma

We present a search for the radiative leptonic decay B+ -> l+ nu gamma, where l=e,mu, using a data sample of 465 million B-meson pairs collected by the BABAR experiment. In this analysis, we fully reconstruct the hadronic decay of one of the B mesons in Upsilon(4S) -> B+B- decays, then search for evidence of B+ -> l+ nu gamma in the rest of the event. We observe no significant evidence of signal decays and report model-independent branching fraction upper limits of BR(B+ -> e+ nu gamma)<17e-6, BR(B+ -> mu+ nu gamma)< 24e-6, and BR(B+ -> l+ nu gamma)<15.6e-6 (l= e or mu), all at the 90% confidence level.

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B meson decays to charmless meson pairs containing eta or eta' mesons

We present updated measurements of the branching fractions for B0 meson decays to etaK0, etaeta, etaphi, etaomega, eta'K0, eta'eta', eta'phi, and eta'omega, and branching fractions and CP-violating charge asymmetries for B+ decays to etapi+, etaK+, eta'pi+ and eta'K+. The data represent the full dataset of 467 10^{6} BB pairs collected with the BaBar detector at the PEP-II asymmetric-energy e+e- collider at the SLAC National Accelerator Laboratory. Besides large signals for the four charged B decay modes and for B0\to eta'K0, we find evidence for three B0 decay modes at greater than 3.0sigma significance. We find B(B0\to etaK0) = (1.15^{+0.43}_{-0.38} \pm0.09)x10^{-6}, B(B0\to etaomega) = (0.94^{+0.35}_{-0.30}\pm0.09)x10^{-6}, and B(B0\to eta'omega) = (1.01^{+0.46}_{-0.38}\pm0.09)x10^{-6}, where the first (second) uncertainty is statistical (systematic). For the B+\to etaK+ decay mode, we measure the charge asymmetry A_{ch}(B+\to etaK+) = -0.36 \pm 0.11 \pm 0.03.

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Search for the B+ -> K+vv Decay Using Semi-Leptonic Tags

We present an update of the search for the flavor-changing neutral current B+ -> K+vv decay using 351 x 10^6 BB pairs collected at the Y(4S) resonance with the BABAR detector at the SLAC PEP-II B factory. Due to the presence of two neutrinos in the final state, we require the reconstruction of the companion B in the event through the decay channel B- -> D0l-v. We find 38 candidates in the data with an expected background of 31 +/- 12. This allows us to set an upper limit on the branching fraction for B+ -> K+vv of 4.5 x 10^-5 at 90% confidence level.

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Search for a low-mass Higgs boson in Y(3S)-->gamma A^0, A^0-->tau^+tau^- at BABAR

We search for a light Higgs boson, $A^0$, in the radiative decay $Υ(3S)\toγA^0$, $A^0\toτ^+τ^-$, $τ^+\to e^+ν_e \barν_τ$ or $τ^+\to μ^+ ν_μ \barν_τ$. The data sample contains 122 million $Υ(3S)$ events recorded with the \babar detector. We find no evidence for a narrow structure in the studied $τ^+τ^-$ invariant mass region of $4.03 (1.5-16)\times 10^{-5}$ across the $m_{τ^+τ^-}$ range. We also set a 90% C.L. upper limit on the $τ^+τ^-$-decay of the $η_b$ at ${\mathcal{B}}(η_b\to τ^+τ^-)<8%$.

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Study of $D_{sJ}$ decays to $D^*K$ in inclusive $e^+e^-$ interactions

We observe the decays $ $D^*_{s1}(2710)^+ \to D^*K$ and $D^*_{sJ}(2860)^+ \to D^*K$ and measure their branching fractions relative to the $D K$ final state. We also observe, in the $D^*K$ mass spectrum, a new broad structure at a mass of $(3044 \pm 8_{stat} (^{+30}_{-5})_{syst})$ $MeV/c^2$ having a width $Γ=(239 \pm 35_{stat} (^{+46}_{-42})_{syst})$ $MeV$. To obtain this result we use 470 ${\rm fb}^{-1}$ of data recorded by the BaBar detector at the PEPII asymmetric-energy $e^+e^-$ storage rings at the Stanford Linear Accelerator Center running at center-of-mass energies near 10.6 GeV.

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Evidence for the eta_b(1S) Meson in Radiative Upsilon(2S) Decay

We have performed a search for the eta_b(1S) meson in the radiative decay of the Upsilon(2S) resonance using a sample of 91.6 million Upsilon(2S) events recorded with the BABAR detector at the PEP-II B factory at the SLAC National Accelerator Laboratory. We observe a peak in the photon energy spectrum at E_gamma = 609.3 {+4.6} {-4.5} (stat) +/- 1.9 (syst) MeV, corresponding to an eta_b(1S) mass of 9394.2 {+4.8} {-4.9} (stat) +/- 2.0 (syst) MeV/c^2. The branching fraction for the decay Upsilon(2S) --> gamma eta_b(1S) is determined to be [3.9 +/-1.1 (stat) {+1.1} {-0.9} (syst)] x 10^(-4). We find the ratio of branching fractions B[Upsilon(2S) --> gamma eta_b(1S)]/B[Upsilon(3S) --> gamma eta_b(1S)] = 0.82 +/- 0.24 (stat) {+0.20}{-0.19} (syst).

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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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Measurements of the $τ$ Mass and Mass Difference of the $τ^{+}$ and $τ^{-}$} at BaBar

We present the result from a precision measurement of the mass of the $τ$ lepton, $M_τ$, based on $423 fb^{-1}$ of data recorded at the $Υ(4S)$ resonance with the BaBar detector. Using a pseudomass endpoint method, we determine the mass to be $1776.68 \pm 0.12 (stat) \pm 0.41 (syst) MeV$. We also measure the mass difference between the $τ^+$ and $τ^-$, and obtain $(M_{τ^{+}}-M_{τ^{-}})/M^τ_{AVG} = (-3.4 \pm 1.3 (stat) \pm 0.3 (syst)) \times 10^{-4}$, where $M^τ_{AVG}$ is the average value of $M_{τ^+}$ and $M_{τ^-}$.

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Study of B Meson Decays with Excited eta and eta' Mesons

Using 383 million BBbar pairs from the BaBar data sample, we report results for branching fractions of six charged B-meson decay modes, where a charged kaon recoils against a charmless resonance decaying to KKbar* or etapipi final states with mass in the range (1.2-1.8)gev/c^2. We observe a significant enhancement at the low KK*bar invariant mass which is interpreted as B+ --> eta(1475)K+, find evidence for the decay B+ --> eta(1295)K+, and place upper limits on the decays B+ --> eta(1405)K+, B+ --> f_1(1285)K+, B+ --> f_1(1420)K+, and B+ --> phi(1680)K+.

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Observation of the baryonic B-decay B0bar -> Lambda_c^+ antiproton K^- pi^+

We report the observation of the baryonic B-decay B0bar -> Lambda_c^+ antiproton K^- pi^+, excluding contributions from the decay B0bar -> Lambda_c^+ anti-Lambda K^-. Using a data sample of 467*10^6 BBbar pairs collected with the BABAR detector at the PEP-II storage ring at SLAC, the measured branching fraction is (4.33 +/- 0.82_stat +/- 0.33_syst +/- 1.13_Lambda_c^+)*10^-5. In addition we find evidence for the resonant decay B0bar -> Sigma_c(2455)^++ antiproton K^- and determine its branching fraction to be (1.11 +/- 0.30_stat +/- 0.09_syst +/- 0.29_Lambda_c^+)*10^-5. The errors are statistical, systematic, and due to the uncertainty in the Lambda_c^+ branching fraction. For the resonant decay B0bar -> Lambda_c^+ antiproton K^*0 we obtain an upper limit of 2.42*10^-5 at 90% confidence level.

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Measurement of branching fractions of B decays to K1(1270)pi and K1(1400)pi and determination of the CKM angle alpha from B0 --> a1(1260)+/- pi-/+

We report measurements of the branching fractions of neutral and charged B meson decays to final states containing a K_1(1270) or K_1(1400) meson and a charged pion. The data, collected with the BaBar detector at the SLAC National Accelerator Laboratory, correspond to 454 million B Bbar pairs produced in e^+ e^- annihilation. We measure the branching fractions BF(B^0 --> K_1(1270)^+ π^- + K_1(1400)^+ π^-) = 3.1^{+0.8}_{-0.7} x10^{-5} and BF(B^+ --> K_1(1270)^0 π^+ + K_1(1400)^0 π^+) = 2.9^{+2.9}_{-1.7} x10^{-5} (<8.2 x10^{-5} at 90% confidence level), where the errors are statistical and systematic combined. The B^0 decay mode is observed with a significance of 7.5σ, while a significance of 3.2σis obtained for the B^+ decay mode. Based on these results, we estimate the weak phase α= (79 +/- 7 +/- 11)^{\circ} from the time dependent CP asymmetries in B^0 --> a_1(1260)^{+/-} π^{-/+} decays.

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