Search for the decay B^+ → τ^+ν_τ

We search for the rare leptonic decay B^+ → τ^+ν_τ in a sample of 232 × 10^6 BB̅ pairs collected with the BABAR detector at the SLAC PEP-II B-Factory. Signal events are selected by examining the properties of the B meson recoiling against the semileptonic decay B^- → D^9*0)ℓ^-ν̅_ ℓ. We find no evidence for a signal and set an upper limit on the branching fraction of B(B^+ → τ^+ν_τ)<2.8 × 10^9-4) at the 90% confidence level. We combine this result with a previous, statistically independent BABAR search for B+→τ+ντ to give an upper limit of B(B^+ → τ^+ν_τ)<2.6 × 10^(-4) at the 90% confidence level

Branching fraction limits for B^0 decays to η′η, η′π^0 and ηπ^0

We describe searches for decays to two-body charmless final states η′η, η′π^0 and ηπ^0 of B^0 mesons produced in e^+e^- annihilation. The data, collected with the BABAR detector at the Stanford Linear Accelerator Center, represent 232 × 10^6 produced BB̅ pairs. The results for branching fractions are, in units of 10^(-6) (upper limits at 90% C.L.): B(B^0 → η′η)=0.2^(+0.7)_(-0.5) ± 0.4(<1.7), B(B^0 → ηπ^0) = 0.6^(+0.5)_(-0.4) ± 0.1(<1.3), and B(B^0 → η′π^0) = 0.8^(+0.8)_(-0.6) ± 0.1(<2.1). The first error quoted is statistical and the second systematic

Measurement of time-dependent CP asymmetries in B^0→D^((*)±)π^∓ and B^0→D^±ρ^∓ decays

We present updated results on time-dependent CP asymmetries in fully reconstructed B^0→D^((*)±)π^∓ and B^0→D^±ρ^∓ decays in approximately 232×10^6 Υ(4S)→BB events collected with the BABAR detector at the PEP-II asymmetric-energy B factory at SLAC. From a time-dependent maximum-likelihood fit we obtain for the parameters related to the CP violation angle 2β+γ: a^(Dπ)=-0.010±0.023±0.007, c_(lep)^(Dπ)=-0.033±0.042±0.012, a^(D*π)=-0.040±0.023±0.010, c_(lep)D^(*π)=0.049± 0.042±0.015,a^(Dρ)=-0.024±0.031±0.009, c_(lep)^(Dρ)=-0.098±0.055±0.018, where the first error is statistical and the second is systematic. Using other measurements and theoretical assumptions, we interpret the results in terms of the angles of the Cabibbo-Kobayashi-Maskawa unitarity triangle and find |sin⁡(2β+γ)|>0.64  (0.40) at 68% (90%) confidence level

The e^+e^- → 3(π^+π^-), 2(π^+π^-π^0) and K^+K^-2(π^+π^-) cross sections at center-of-mass energies from production threshold to 4.5 GeV measured with initial-state radiation

We study the processes e^+e^- → 3(π^+π^-)γ, 2(π^+π^-π^0)γ and K^+K^-2(π^+π^-)γ, with the photon radiated from the initial state. About 20 000, 33 000 and 4000 fully reconstructed events, respectively, have been selected from 232  fb^(-1) of BABAR data. The invariant mass of the hadronic final state defines the effective e^+e^- center-of-mass energy, so that these data can be compared with the corresponding direct e^+e^- measurements. From the 3(π^+π^-), 2(π^+π^-π^0) and K^+K^-2(π^+π^-) mass spectra, the cross sections for the processes e^+e^- → 3(π^+π^-), e^+e^- → 2(π^+π^-π^0) and e^+e^- → K^+K^-2(π^+π^-) are measured for center-of-mass energies from production threshold to 4.5 GeV. The uncertainty in the cross section measurement is typically 6%–15%. We observe a structure at 1.9 GeV in both cross sections and a resonance structure with mass 1645 ± 0.008  GeV/c^2 and width 0.114 ± 0.014  GeV when the ω(782)η final state is extracted. We observe the J/ψ in all these final states and measure the corresponding branching fractions

Measurement of CP observables for the decays B^± → D^0_(CP)K^±

We present a study of the decay B^- → D^0_(CP)K^± and its charge conjugate, where D^0_CP) is reconstructed in CP-even, CP-odd, and non-CP flavor eigenstates, based on a sample of 232 x 10^6 Y(4S) → BB decays collected with the BABAR detector at the PEP-II e^+e^- storage ring. We measure the partial-rate charge asymmetries A_(CP±) and the ratios R_(CP±) of the B → D^0K decay branching fractions as measured in CP^± and non-CP D^0 decays: A_(CP±) 0:35 ± 0.13(stat) ± 0.04(syst), A_(CP-)= -0.06 ± 0.13(stat) ± 0.04(syst), R_(CP+) = 0.90 ± 0.12(stat) ± 0.049syst), and R_(CP-) = 0:86 ± 0.10(stat) ± 0.05(syst)

Search for the rare decays B^0 → D_s^((*)+)a-_(0(2))

We have searched for the decays B^0 → D_s^+a^-_0, B^0 → D_s^(*+)a^-_0, B^0 → D_s^+a^-_2 and B^0 → D_s^(*+)a^-_2 in a sample of about 230 × 10^6 Υ(4S) → BB̅ decays collected with the BABAR detector at the PEP-II asymmetric-energy B Factory at SLAC. We find no evidence for these decays and set upper limits at 90% C.L. on the branching fractions: B(B^0 → D_s^+a^-_0)<1.9 × 10^(-5), B(B^0 → D_s^(*+)a^-_0)<3.6 × 10^(-5), B(B^0 → D_s^+a^-_2)<1.9 × 10^(-4), and B(B^0 → D_s^(*+)a^-_2)<2.0 × 10^(-4)

Measurements of the Absolute Branching Fractions of B^±→K^±X_(cc)

We study the two-body decays of B^± mesons to K^± and a charmonium state X_cc in a sample of 210.5  fb^(-1) of data from the BABAR experiment. We perform measurements of absolute branching fractions B(B^±→K^±X_(cc)) using a missing mass technique, and report several new or improved results. In particular, the upper limit B(B^±→K^±X(3872))4.2% will help in understanding the nature of the recently discovered X(3872)

Measurement of the B⁰ → J/ψπ⁺π⁻ Branching Fraction

We present a measurement of the branching fraction for the decay of the neutral B meson into the final state J/ψπ+π−. The data set contains approximately 56×106 B¯B pairs produced at the Υ(4S) resonance and recorded with the BABAR detector at the PEP-II asymmetric-energy e+e− storage ring. The result of this analysis is B(B0→J/ψπ+π−)=(4.6±0.7±0.6)×10−5, where the first error is statistical and the second is systematic. In addition, we measure B(B0→J/ψρ0)=(1.6±0.6±0.4)×10−5

Measurement of the B^0 → J/ψπ^+π^− Branching Fraction

We present a measurement of the branching fraction for the decay of the neutral B meson into the final state J/ψπ+π−. The data set contains approximately 56 × 10^6 BB pairs produced at the Υ(4S)resonance and recorded with the BABAR detector at the PEP-II asymmetric-energy e^+e^− storage ring. The result of this analysis is B(B^0 → J/ψπ^+π^−)=(4.6 ± 0.7 ± 0.6) × 10^(−5), where the first error is statistical and the second is systematic. In addition, we measure B(B^0 → J/ψρ^0) = (1.6 ± 0.6 ± 0.4) × 10^(−5)

Les Houches Guidebook to Monte Carlo Generators for Hadron Collider Physics

Recently the collider physics community has seen significant advances in the formalisms and implementations of event generators. This review is a primer of the methods commonly used for the simulation of high energy physics events at particle colliders. We provide brief descriptions, references, and links to the specific computer codes which implement the methods. The aim is to provide an overview of the available tools, allowing the reader to ascertain which tool is best for a particular application, but also making clear the limitations of each tool.Comment: 49 pages Latex. Compiled by the Working Group on Quantum ChromoDynamics and the Standard Model for the Workshop ``Physics at TeV Colliders'', Les Houches, France, May 2003. To appear in the proceeding