Search for Low-Mass Dark-Sector Higgs Bosons

Recent astrophysical and terrestrial experiments have motivated the proposal of a dark sector with GeV-scale gauge boson force carriers and new Higgs bosons. We present a search for a dark Higgs boson using 516  fb^(-1) of data collected with the BABAR detector. We do not observe a significant signal and we set 90% confidence level upper limits on the product of the standard model-dark-sector mixing angle and the dark-sector coupling constant

Search for lepton-number violating processes in B^+ → h^-l^+l^+ decays

We have searched for the lepton-number violating processes B^+→h^-ℓ^+ℓ^+ with h^-=K^-/π^- and ℓ^+=e^+/μ^+, using a sample of 471±3 million BB̅ events collected with the BABAR detector at the PEP-II e^+e^- collider at the SLAC National Accelerator Laboratory. We find no evidence for these decays and place 90%-confidence-level upper limits on their branching fractions B(B^+→π^-e^+e^+)<2.3×10^(-8), B(B^+→K^-e^+e^+)<3.0×10^(-8), B(B^+→π^-μ^+μ^+)<10.7×10^(-8), and B(B^+→K^-μ^+μ^+)<6.7×10^(-8)

Study of B → X_uℓv decays in BB events tagged by a fully reconstructed B-meson decay and determination of │V_(ub)│

We report measurements of partial branching fractions for inclusive charmless semileptonic B decays B → X_uℓν and the determination of the Cabibbo–Kobayashi–Maskawa (CKM) matrix element |V_(ub)|. The analysis is based on a sample of 467×10^6 Υ(4S)→BB decays recorded with the BABAR detector at the PEP-II e^+e^- storage rings. We select events in which the decay of one of the B mesons is fully reconstructed and an electron or a muon signals the semileptonic decay of the other B meson. We measure partial branching fractions ΔB in several restricted regions of phase space and determine the CKM element |V_(ub)| based on different QCD predictions. For decays with a charged lepton momentum p_ℓ^*>1.0  GeV in the B meson rest frame, we obtain ΔB=(1.80±0.13_(stat)±0.15_(sys)±0.02_(theo))×10^(-3) from a fit to the two-dimensional M_X-q^2 distribution. Here, M_X refers to the invariant mass of the final state hadron X and q^2 is the invariant mass squared of the charged lepton and neutrino. From this measurement we extract |V_(ub)|=(4.33±0.24_(exp)±0.15_(theo))×10^(-3) as the arithmetic average of four results obtained from four different QCD predictions of the partial rate. We separately determine partial branching fractions for B^0 and B^- decays and derive a limit on the isospin breaking in B → X_uℓν decays

Cross sections for the reactions e^+e^- → K^+K^-π^+π^-,K^+K^-π^0π^0, and K^+K^-K^+K^- measured using initial-state radiation events

We study the processes e^+e^- → K^+K^-π^+π^-γ, K^+K^-π^0π^0 γ, and K^+K^-K^+K^- γ, where the photon is radiated from the initial state. About 84 000, 8000, and 4200 fully reconstructed events, respectively, are selected from 454  fb^(-1) of BABAR data. The invariant mass of the hadronic final state defines the e+e- center-of-mass energy, so that the K^+K^-π^+π^- γ data can be compared with direct measurements of the e^+e^- → K^+K^-π^+π^- reaction. No direct measurements exist for the e^+e^- → K^+K^-π^0π^0 or e^+e^- → K^+K^-K^+K^- reactions, and we present an update of our previous result based on a data sample that is twice as large. Studying the structure of these events, we find contributions from a number of intermediate states and extract their cross sections. In particular, we perform a more detailed study of the e^+e^- → ϕ(1020)ππγ reaction and confirm the presence of the Y(2175) resonance in the ϕ(1020)f_0(980) and K^+K^-f_0(980) modes. In the charmonium region, we observe the J/ψ in all three final states and in several intermediate states, as well as the ψ(2S) in some modes, and measure the corresponding products of branching fraction and electron width

Precise measurement of the e^+e^- → π^+π^-(γ) cross section with the initial-state radiation method at BABAR

A precise measurement of the cross section of the process e^+e^-→π^+π^-(γ) from threshold to an energy of 3 GeV is obtained with the initial-state radiation (ISR) method using 232  fb^(-1) of data collected with the BABAR detector at e^+e^- center-of-mass energies near 10.6 GeV. The ISR luminosity is determined from a study of the leptonic process e^+e^-→μ^+μ^-(γ)γ_(ISR), which is found to agree with the next-to-leading-order QED prediction to within 1.1%. The cross section for the process e^+e^-→π^+π^-(γ) is obtained with a systematic uncertainty of 0.5% in the dominant ρ resonance region. The leading-order hadronic contribution to the muon magnetic anomaly calculated using the measured ππ cross section from threshold to 1.8 GeV is (514.1±2.2(stat)±3.1(syst))×10^(-10)

Electron beam test of the large area Mu2e calorimeter prototype

The Mu2e calorimeter consists of 1348 pure CsI crystals coupled to two large area UV-extended Silicon Photomultipliers (SiPMs) organized in two separate annular disks. An intense R&D phase has been pursued to check if this configuration satisfies the Mu2e requirements. In May 2017, a dedicated test has been performed at the Beam Test Facility (BTF) in Frascati (Italy) where the large calorimeter prototype (Module-0) has been exposed to an electron beam in the energy range between 60 and 120 MeV. The prototype consists of 51 crystals, each one readout by two Mu2e SiPMs. We present results for timing and energy resolution both for electrons at normal incidence (0°) and at a grazing impact angle (50°) more similar to the experiment configuration. At 100 MeV, an energy resolution of 5.4% (7.4%) at normal (grazing) incidence has been achieved in good agreement with Monte Carlo expectation. In the same energy range, a time resolution of ~ XX ps (~ YY ps) has been measured at normal incidence with 1 GHz (250 MHz) sampling rate. Dependence of time and energy resolutions as a function of beam energy and impinging angle are also presented

Search for the decay B^0 → Λ^+_cppp

We report a search for the decay B^0 → Λ^+_cppp. Using a data sample of 471×10^6 BB pairs collected with the BABAR detector at the PEP-II2 storage ring at SLAC, we find no events and set an upper limit on the branching fraction B(B^0 → Λ^+_cppp)×^(B(Λ^+_c→pK^−π^+))_(0.050) <2.8×10^(−6) at 90% C.L., where we have normalized B(Λ^+_c → pK^−π^+) to the world average value