The extended Baryon Oscillation Spectroscopic Survey of the Sloan Digital Sky Survey (SDSS-IV/eBOSS) has an extensive quasar program that combines several selection methods. Among these, the photometric variability technique provides highly uniform samples, which are unaffected by the redshift bias of traditional optical-color selections, when z = 2.7-3.5 quasars cross the stellar locus or when host galaxy light affects quasar colors at z< 0.9. We present the variability selection of quasars in eBOSS, focusing on a specific program that led to a sample of 13 876 quasars to gdered = 22.5 over a 94.5 deg2 region in Stripe 82, which has an areal density 1.5 times higher than over the rest of the eBOSS footprint. We use these variability-selected data to provide a new measurement of the quasar luminosity function (QLF) in the redshift range of 0.68 2.2. Both models are constrained to be continuous at z = 2.2. They present a flattening of the bright-end slope at high redshift. The LEDE model indicates a reduction of the break density with increasing redshift, but the evolution of the break magnitude depends on the parameterization. The models are in excellent accord, predicting quasar counts that agree within 0.3% (resp., 1.1%) to g< 22.5 (resp., g< 23). The models are also in good agreement over the entire redshift range with models from previous studies.

We present a measurement of the quasar luminosity function in the range 0.68 < z < 4 down to extinction corrected magnitude gdered = 22.5, using a simple and well understood target selection technique based on the time-variability of quasars. The completeness of our sample was derived directly from a control sample of quasars, without requiring complex simulations of quasar light-curves or colors. A total of 1877 quasar spectra were obtained from dedicated programs on the Sloan telescope (as part of the SDSS-III/BOSS survey) and on the Multiple Mirror Telescope. They allowed us to derive the quasar luminosity function. It agrees well with results previously published in the redshift range 0.68 < z < 2.6. Our deeper data allow us to extend the measurement to z = 4. We measured quasar densities to gdered < 22.5, obtaining 30 QSO per deg2 at z < 1, 99 QSO per deg 2 for 1 < z < 2.15, and 47 QSO per deg2 at z > 2.15. Using pure luminosity evolution models, we fitted our LF measurements and predicted quasar number counts as a function of redshift and observed magnitude. These predictions are useful inputs for future cosmology surveys such as those relying on the observation of quasars to measure baryon acoustic oscillations. © 2013 ESO.

We study the process e+e-→ψ(2S)π+π- with initial-state-radiation events produced at the PEP-II asymmetric-energy collider. The data were recorded with the BABAR detector at center-of-mass energies at and near the (nS) (n=2,3,4) resonances and correspond to an integrated luminosity of 520fb-1. We investigate the ψ(2S)π+π- mass distribution from 3.95 to 5.95GeV/c2, and measure the center-of-mass energy dependence of the associated e+e-→ψ(2S)π+π- cross section. The mass distribution exhibits evidence of two resonant structures. A fit to the ψ(2S)π+π- mass distribution corresponding to the decay mode ψ(2S)→J/ψπ+π- yields a mass value of 4340±16(stat) ±9(syst)MeV/c2 and a width of 94±32(stat)±13(syst)MeV for the first resonance, and for the second a mass value of 4669±21(stat) ±3(syst)MeV/c2 and a width of 104±48(stat)±10(syst)MeV. In addition, we show the π+π- mass distributions for these resonant regions. © 2014 American Physical Society.

We present updated measurements of the branching fractions for B0 meson decays to ηK0, ηη, ηφ, ηω, η′K0, η′η′, η′φ, and η′ω, and branching fractions and CP-violating charge asymmetries for B+ decays to ηπ+, ηK+, η′π+, and η′K+. The data represent the full data set of 467×106 BB̄ 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→η′K0, we find evidence for three B0 decay modes at greater than 3.0σ significance. We find B(B0→ηK0)=(1.15-0.38+0. 43±0.09)×10-6, B(B0→ηω)=(0.94-0.30+0.35±0.09) ×10-6, and B(B0→η′ω)=(1.01-0.38+0.46±0.09) ×10-6, where the first (second) uncertainty is statistical (systematic). For the B+→ηK+ decay mode, we measure the charge asymmetry Ach(B+→ηK+)=-0.36±0.11±0.03. © 2009 The American Physical Society.

We report measurements of the branching fractions of neutral and charged B meson decays to final states containing a K1(1270) or K1(1400) meson and a charged pion. The data, collected with the BABAR detector at the SLAC National Accelerator Laboratory, correspond to 454×106 BB̄ pairs produced in e+e- annihilation. We measure the branching fractions B(B0→K1(1270)+π-+K1(1400) +π -)=3.1-0.7+0.8×10-5 and B(B+→ K1(1270) 0π++K1(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 B0 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 B0→a1(1260)±π decays. © 2010 The American Physical Society.

We study the reaction e+e-→e+e-π0 in the single tag mode and measure the differential cross section dσ/dQ2 and the γγ *→π0 transition form factor in the momentum transfer range from 4 to 40GeV2. At Q2>10GeV2 the measured form factor exceeds the asymptotic limit predicted by perturbative QCD. The analysis is based on 442fb-1 of integrated luminosity collected at PEP-II with the BABAR detector at e+e- center-of-mass energies near 10.6 GeV. © 2009 The American Physical Society.

We report a measurement of the branching fraction of the exclusive charmless semileptonic decay B+→ωℓ+ν, where ℓ is either an electron or a muon. We use samples of B+ mesons tagged by a reconstructed charmed semileptonic decay of the other B meson in the event. The measurement is based on a data set of 426.1 fb-1 of e+e- collisions at a center-of-mass energy of 10.58 GeV recorded with the BABAR detector at the PEP-II asymmetric-energy e +e- storage rings. We measure a branching fraction of B(B+→ωℓ+ν)=(1.35±0.21±0. 11)×10-4, where the uncertainties are statistical and systematic, respectively. We also present measurements of the partial branching fractions in three bins of q2, the invariant-mass squared of the lepton-neutrino system, and we compare them to theoretical predictions of the form factors. © 2013 American Physical Society.

We measure the rate of D0-D̄0 mixing with the observable yCP=(τKπ/τKK)-1, where τKK and τKπ are, respectively, the mean lifetimes of CP-even D0→K+K- and CP-mixed D0→K-π+ decays, using a data sample of 384fb-1 collected by the BABAR detector at the SLAC PEP-II asymmetric-energy B Factory. From a sample of D0 and D̄0 decays where the initial flavor of the decaying meson is not determined, we obtain yCP=[1.12±0.26(stat)±0.22(syst)]%, which excludes the no-mixing hypothesis at 3.3σ, including both statistical and systematic uncertainties. This result is in good agreement with a previous BABAR measurement of yCP obtained from a sample of D*+→D0π+ events, where the D0 decays to K-π+, K+K-, and π+π-, which is disjoint with the untagged D0 events used here. Combining the two results taking into account statistical and systematic uncertainties, where the systematic uncertainties are assumed to be 100% correlated, we find yCP=[1.16±0.22(stat)±0. 18(syst)]%, which excludes the no-mixing hypothesis at 4.1σ. © 2009 The American Physical Society.

We present a measurement of the B0→Λ̄pπ- branching fraction performed using the BABAR detector at the PEP-II asymmetric e+e- collider. Based on a sample of 467×106 BB̄ pairs we measure B(B0→Λ̄pπ-)=[3.07±0.31(stat)±0.23(syst)] ×10-6. The measured differential spectrum as a function of the dibaryon invariant mass m(Λ̄p) shows a near-threshold enhancement similar to that observed in other baryonic B decays. We study the Λ̄ polarization as a function of Λ̄ energy in the B0 rest frame (EΛ̄*) and compare it with theoretical expectations of fully longitudinally right-polarized Λ̄ at large EΛ̄*. © 2009 The American Physical Society.