Search for Light New Physics at B Factories

Many extensions of the Standard Model include the possibility of light new particles, such as light Higgs bosons or dark matter candidates. These scenarios can be probed using the large datasets collected by B factories, complementing measurements performed at the LHC. This review summarizes recent searches for light New Physics conducted by the BABAR and Belle experiments.Comment: 9 pages, 7 figures, Submitted to Advances in High Energy Physic

Search for Low-Mass Dark Matter at BABAR

This review briefly describes light dark matter searches performed by the BABAR experiment. Although dark matter candidates have traditionally been associated with heavy particles appearing in extensions of the Standard Model, a lighter component remains a well motivated alternative, and many scenarios of light dark matter have been recently proposed. Thanks to their large luminosities, B factories offer an ideal environment to probe these possibilities, complementing searches from direct detection and satellite experiments.Comment: 8 pages, 4 figures, submitted to Mod. Phys. Lett.

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)

Measurement of time-dependent CP asymmetry in B^0→K_S^0π^0γ decays

We measure the time-dependent CP asymmetry in B^0→K_S^0π^0γ decays for two regions of K_S^0-π^0 invariant mass, m(KS0π0), using the final BABAR data set of 467×10^6 BB pairs collected at the PEP-II e^+e^- collider at SLAC. We find 339±24 B^0→K^(*0)γ candidates and measure S_(K*γ)=-0.03±0.29±0.03 and C_(K*_γ)=-0.14±0.16±0.03. In the range 1.1<m(K_S^0π^0)<1.8  GeV/c^2 we find 133±20 B^0→K_S^0π^0γ candidates and measure S_(KS^0π^0γ)=-0.78±0.59±0.09 and C_(KS^0π^0γ)=-0.36±0.33±0.04. The uncertainties are statistical and systematic, respectively

Measurement of branching fractions of B decays to K_1(1270)π and K_1(1400)π and determination of the CKM angle α from B^0→a_1(1260)^±π^∓

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 454×10^6 BB̅ pairs produced in e^+e^- annihilation. We measure the branching fractions B(B^0→K_1(1270)^+π-+K_1(1400)^+π-)=3.1_(-0.7)^(+0.8)×10^(-5) and B(B^+→K_1(1270)^0π^++K_1(1400)^0π^+)=2.9_(-1.7)^(+2.9)×10^(-5) (<8.2×10^(-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 3.2σ is obtained for the B^+ decay mode. Based on these results, we estimate the weak phase α=(79±7±11)° from the time-dependent CP asymmetries in B^0→a1(1260)^±π^∓ decays

Measurements of the τ mass and the 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±0.12(stat)±0.41(syst)  MeV. We also measure the mass difference between the τ^+ and τ^-, and obtain (M_(τ+)-M_(τ-))/M_(AVG)^τ=(-3.4±1.3(stat)±0.3(syst))×10^(-4), where M^τ_(AVG) is the average value of M_(τ+) and M_(τ-)

Search for B^+→ℓ^+ν_ℓ recoiling against B^-→D^0ℓ^-ν̅ X

We present a search for the decay B^+→ℓ^+ν_ℓ(ℓ=τ, μ, or  e) in (458.9±5.1)×10^6 BB̅ pairs recorded with the BABAR detector at the PEP-II B-factory. We search for these B decays in a sample of B^+B^- events where one B-meson is reconstructed as B^-→D^0ℓ^-ν̅ X. Using the method of Feldman and Cousins, we obtain B(B^+→τ^+ν_τ)=(1.7±0.8±0.2)×10^(-4), which excludes zero at 2.3σ. We interpret the central value in the context of the standard model and find the B meson decay constant to be f_B^2=(62±31)×10^3   MeV^2. We find no evidence for B^+→e^+ν_e and B^+→μ^+ν_μ and set upper limits at the 90% C.L. B(B^+→e^+ν_e)<0.8×10^(-5) and B(B^+→μ^+ν_μ)<1.1×10^(-5)