Optimization of Signal Significance by Bagging Decision Trees

An algorithm for optimization of signal significance or any other classification figure of merit suited for analysis of high energy physics (HEP) data is described. This algorithm trains decision trees on many bootstrap replicas of training data with each tree required to optimize the signal significance or any other chosen figure of merit. New data are then classified by a simple majority vote of the built trees. The performance of this algorithm has been studied using a search for the radiative leptonic decay B->gamma l nu at BaBar and shown to be superior to that of all other attempted classifiers including such powerful methods as boosted decision trees. In the B->gamma e nu channel, the described algorithm increases the expected signal significance from 2.4 sigma obtained by an original method designed for the B->gamma l nu analysis to 3.0 sigma.Comment: 8 pages, 2 figures, 1 tabl

A multivariate approach to heavy flavour tagging with cascade training

This paper compares the performance of artificial neural networks and boosted decision trees, with and without cascade training, for tagging b-jets in a collider experiment. It is shown, using a Monte Carlo simulation of $WH \to l\nu q\bar{q}$ events, that for a b-tagging efficiency of 50%, the light jet rejection power given by boosted decision trees without cascade training is about 55% higher than that given by artificial neural networks. The cascade training technique can improve the performance of boosted decision trees and artificial neural networks at this b-tagging efficiency level by about 35% and 80% respectively. We conclude that the cascade trained boosted decision trees method is the most promising technique for tagging heavy flavours at collider experiments.Comment: 14 pages, 12 figures, revised versio

Measurement of branching fractions and CP-violating charge asymmetries for B-meson decays to D^(*)D^(*), and implications for the Cabibbo-Kobayashi-Maskawa angle γ

We present measurements of the branching fractions and charge asymmetries of B decays to all D^(*)D^(*) modes. Using 232×10^6 BB pairs recorded on the Υ(4S) resonance by the BABAR detector at the e^+e^- asymmetric B factory PEP-II at the Stanford Linear Accelerator Center, we measure the branching fractions B(B^0→D^(*+)D^(*-))=(8.1±0.6±1.0)×10^(-4), B(B^0→D^(*±)D^∓)=(5.7±0.7±0.7)×10^(-4), B(B^0→D^+D^-)=(2.8±0.4±0.5)×10^(-4), B(B^+→D^(*+)D^(*0))=(8.1±1.2±1.2)×10^(-4), B(B^+→D^*+D^0)=(3.6±0.5±0.4)×10^(-4), B(B^+→D^+D^(*0))=(6.3±1.4±1.0)×10^(-4), and B(B^+→D^+D^(0))=(3.8±0.6±0.5)×10^(-4), where in each case the first uncertainty is statistical and the second systematic. We also determine the limits B(B^0→D^(*0)D^(*0))<0.9×10^(-4), B(B^0→D^(*0)D^0)<2.9×10^(-4), and B(B^0→D^0D^0)<0.6×10^(-4), each at 90% confidence level. All decays above denote either member of a charge-conjugate pair. We also determine the CP-violating charge asymmetries A(B^0→D^(*±)D^∓)=0.03±0.10±0.02, A(B^+→D^(*+)D^(*0))=-0.15±0.11±0.02, A(B^+→D^(*+)D^0)=-0.06±0.13±0.02, A(B^+→D^+D^(*0))=0.13±0.18±0.04, and A(B^+→D^+D^0)=-0.13±0.14±0.02. Additionally, when we combine these results with information from time-dependent CP asymmetries in B^0→D^((*)+)D^((*)-) decays and world-averaged branching fractions of B decays to D_s^(*)D^(*) modes, we find the Cabibbo-Kobayashi-Maskawa phase γ is favored to lie in the range (0.07–2.77) radians (with a +0 or +π radians ambiguity) at 68% confidence level

Search for the charmed pentaquark candidate Θ_c(3100)^0 in e^+e^- annihilations at √s=10.58 GeV

We search for the charmed pentaquark candidate reported by the H1 collaboration, the Θ_c(3100)^0, in e^+e^- interactions at a center-of-mass (c.m.) energy of 10.58 GeV, using 124  fb^(-1) of data recorded with the BABAR detector at the PEP-II e^+e^- facility at SLAC. We find no evidence for such a state in the same pD^(*-) decay mode reported by H1, and we set limits on its production cross section times branching fraction into pD^(*-) as a function of c.m. momentum. The corresponding limit on its total rate per e^+e^-→qq event, times branching fraction, is about 3 orders of magnitude lower than rates measured for the charmed Λ_c and Σ_c baryons in such events

Observation of B^0 Meson Decay to a_1^±(1260)π^∓

We present a measurement of the branching fraction of the decay B^0→a_1^±(1260)π^∓ with a_1^±(1260)→π^∓π^±π^±. The data sample corresponds to 218×10^6 BB pairs produced in e^+e^- annihilation through the Υ(4S) resonance. We measure the branching fraction B(B^0→a_1^±(1260)π^∓)B(a_1^±(1260)→π^∓π^±π^±)=(16.6±1.9±1.5)×10^(-6), where the first error quoted is statistical and the second is systematic

Measurements of the semileptonic decays B[overbar]→Dℓν[overbar] and B[overbar]→D^*ℓν[overbar] using a global fit to DXℓν[overbar] final states

Semileptonic B[overbar] decays to DXℓν[overbar](ℓ=e or μ) are selected by reconstructing D^0ℓ and D^+ℓ combinations from a sample of 230×10^6 Υ(4S)→BB[overbar] decays recorded with the BABAR detector at the PEP-II e^+e^- collider at SLAC. A global fit to these samples in a three-dimensional space of kinematic variables is used to determine the branching fractions B(B^-→D^0ℓν[overbar])=(2.34±0.03±0.13)% and B(B^-→D^(*0)ℓν[overbar])=(5.40±0.02±0.21)% where the errors are statistical and systematic, respectively. The fit also determines form-factor parameters in a parametrization based on heavy quark effective theory, resulting in ρ_D^2=1.20±0.04±0.07 for B[overbar]→Dℓν[overbar] and ρ_(D*)^2=1.22±0.02±0.07 for B[overbar]→D^*ℓν[overbar]. These values are used to obtain the product of the Cabibbo-Kobayashi-Maskawa matrix element |V_(cb)| times the form factor at the zero recoil point for both B[overbar]→Dℓν[overbar] decays, G(1)|V_(cb)|=(43.1±0.8±2.3)×10^(-3), and for B[overbar]→D^*ℓν[overbar] decays, F(1)|V_(cb)|=(35.9±0.2±1.2)×10^(-3)

Search for the decay τ-→3π^-2π^+2π^0ν_τ

A search for the decay of the τ lepton to five charged and two neutral pions is performed using data collected by the BABAR detector at the PEP-II asymmetric-energy e^+e^- collider. The analysis uses 232  fb^(-1) of data at center-of-mass energies on or near the Υ(4S) resonance. We observe 10 events with an expected background of 6.5_(-1.4)^(+2.0) events. In the absence of a signal, we set the limit on the branching ratio B(τ-→3π^-2π^+2π^0ν_τ)<3.4×10^(-6) at the 90% confidence level. This is a significant improvement over the previously established limit. In addition, we search for the decay mode τ-→2ωπ-ν_τ. We observe 1 event with an expected background of 0.4+1.0/-0.4 events and calculate the upper limit B(τ-→2ωπ-ν_τ)<5.4×10^(-7) at the 90% confidence level. This is the first upper limit for this mode

Study of the decay B^0→D^(*+)ωπ^-

We report on a study of the decay B^0→D^(*+)ωπ^- with the BABAR detector at the PEP-II B-factory at the Stanford Linear Accelerator Center. Based on a sample of 232×10^6 BB decays, we measure the branching fraction B(B^0→D^(*+)ωπ^-)=(2.88±0.21(stat.)±0.31(syst.))×10^(-3). We study the invariant mass spectrum of the ωπ^- system in this decay. This spectrum is in good agreement with expectations based on factorization and the measured spectrum in τ-→ωπ-ν_τ. We also measure the polarization of the D^(*+) as a function of the ωπ^- mass. In the mass region 1.1 to 1.9 GeV we measure the fraction of longitudinal polarization of the D^(*+) to be ΓL/Γ=0.654±0.042(stat.)±0.016(syst.). This is in agreement with the expectations from heavy-quark effective theory and factorization assuming that the decay proceeds as B^(-0)→D^(*+)ρ(1450)-, ρ(1450)^-→ωπ^-