Lou, Xinchou
Permanent URI for this collectionhttps://hdl.handle.net/10735.1/2305
Dr. Lou’s research interests focus on elementary particle physics experiments at electron-position colliders, high performance cluster computing, and application of data mining techniques to other fields of research. He is currently searching for new elementary particles, measuring charmonium production with the BABAR detector located at the Stanford Linear Accelerator Center.
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Item Measurement of the Semileptonic Branching Fraction of the B_s Meson(American Physical Society, 2012-01-03) Lees, J. P.; Poireau, V.; Tisserand, V.; Garra Tico, J.; Grauges, E.; Martinelli, M.; Milanes, D. A.; Izen, Joseph M.; Lou, Xinchou; 250674117 (Izen, JM); 250674117 (Izen, JM); Lou, Xinchou; Izen, Joseph M.We report a measurement of the inclusive semileptonic branching fraction of the B_s meson using data collected with the BABAR detector in the center-of-mass energy region above the Υ(4S) resonance. We use the inclusive yield of mesons and the yield in association with a high-momentum lepton to perform a simultaneous measurement of the semileptonic branching fraction and the production rate of B_s mesons relative to all B mesons as a function of center-of-mass energy. The inclusive semileptonic branching fraction of the B_s meson is determined to be ℬ(B_s → ℓνX) = 9.5_{-2.0}^{+2.5}(stat)_{-1.9}^{+1.1}(syst)%, where ℓ indicates the average of e and μ.Item Search for B̄→Λ_c⁺Xℓ⁻ν̅_ℓ decays in Events with a Fully Reconstructed B Meson(American Physical Society, 2012-01-12) Lees, J. P.; Poireau, V.; Tisserand, V.; Garra Tico, J.; Grauges, E.; Martinelli, M.; Milanes, D. A.; Izen, Joseph M.; Lou, Xinchou; BaBar Collaboration; 250674117 (Izen, JM); 250674117 (Izen, JM); Lou, Xinchou; Izen, Joseph M.We present a search for semileptonic B decays to the charmed baryon Λc+ based on 420fb -1 of data collected at the Υ(4S) resonance with the BABAR detector at the PEP-II e +e - storage rings. By fully reconstructing the recoiling B in a hadronic decay mode, we reduce non-B backgrounds and determine the flavor of the signal B. We statistically correct the flavor for the effect of the B0 mixing. We obtain a 90% confidence level upper limit of B(B̄→Λc+X -ν ̄)/B(B̄→Λc+X)<3.5%. © 2012 American Physical Society.Item Search for CP Violation in the Decay τ⁻ → π⁻ K_S⁰(0π⁰)ν_τ(American Physical Society, 2012-02-13) Lees, J. P.; Poireau, V.; Tisserand, V.; Garra Tico, J.; Grauges, E.; Martinelli, M.; Milanes, D. A.; Izen, Joseph M.; Lou, Xinchou; BaBar Collaboration; 250674117 (Izen, JM); 250674117 (Izen, JM); Lou, Xinchou; Izen, Joseph M.We report a search for CP violation in the decay τ⁻ → π⁻ K_S⁰ (0π⁰)ν_τ using a data set of 437×106 τ-lepton pairs, corresponding to an integrated luminosity of 476 fb⁻¹, collected with the BABAR detector at the PEP-II asymmetric-energy e⁺e⁻ storage rings. The CP-violating decay-rate asymmetry is determined to be (-0.36 ± 0.23 ± 0.11)% approximately 2.8 standard deviations from the standard model prediction of (0.36 ± 0.01)%.Item Search for the Standard Model Higgs Boson in the Diphoton Decay Channel with 4.9 fb⁻¹ of pp Collision Data at √s = 7 TeV with ATLAS(American Physical Society, 2012-03-13) Aad, G.; Abbott, B.; Abdallah, J.; Abdel Khalek, S.; Abdelalim, A. A.; Abdesselam, A.; Abdinov, O.; Ahsan, Mahsana; Izen, Joseph M .; Lou, Xinchou; Reeves, Kendall; Wong, Wei-Cheng; ATLAS Collaboration; 250674117 (Izen, JM); 250674117 (Izen, JM); |Ahsan, Mahsana; Izen, Joseph M.; Lou, Xinchou; Reeves, Kendall; Wong, Wei-ChengA search for the standard model Higgs boson is performed in the diphoton decay channel. The data used correspond to an integrated luminosity of 4.9 fb⁻¹ collected with the ATLAS detector at the Large Hadron Collider in proton-proton collisions at a center-of-mass energy of √s̅ = 7 TeV. In the diphoton mass range 110-150 GeV, the largest excess with respect to the background-only hypothesis is observed at 126.5 GeV, with a local significance of 2.8 standard deviations. Taking the look-elsewhere effect into account in the range 110-150 GeV, this significance becomes 1.5 standard deviations. The standard model Higgs boson is excluded at 95% confidence level in the mass ranges of 113-115 GeV and 134.5-136 GeV.Item Search for the Z₁(4050)⁺ and Z₂(4250)⁺ States in B̅⁰→ χ_{c1}K⁻ π⁺ and B⁺ → χ_{c1}K_s⁰ π⁺(American Physical Society, 2012-03-16) Lees, J. P.; Poireau, V.; Tisserand, V.; Garra Tico, J.; Grauges, E.; Martinelli, M.; Milanes, D. A.; Izen, Joseph M.; Lou, Xinchou; BaBar Collaboration; 250674117 (Izen, JM); 250674117 (Izen, JM); Lou, Xinchou; Izen, Joseph M.We search for the Z₁(4050)⁺ and Z₂(4250)⁺ states, reported by the Belle Collaboration, decaying to χ_{c1}π⁺ in the decays B̅⁰ → χ_{c1}K⁻ π⁺ and B⁺ → χ_{c1}K_S⁰ π⁺ where χ_{c1} → J/ψγ. The data were collected with the BABAR detector at the SLAC PEP-II asymmetric-energy e⁺e⁻ collider operating at center-of-mass energy 10.58 GeV, and correspond to an integrated luminosity of 429 fb⁻¹. In this analysis, we model the background-subtracted, efficiency-corrected χ_{c1}π⁺ mass distribution using the Kπ mass distribution and the corresponding normalized Kπ Legendre-polynomial moments, and then test the need for the inclusion of resonant structures in the description of the χ_{c1}π⁺ mass distribution. No evidence is found for the Z₁(4050)⁺ and Z₂(4250)⁺ resonances, and 90% confidence level upper limits on the branching fractions are reported for the corresponding B-meson decay modes.Item Amplitude Analysis and Measurement of the Time-Dependent CP Asymmetry of B⁰→K_S⁰K_S⁰K_S⁰ Decays(American Physical Society, 2012-03-27) Lees, J. P.; Poireau, V.; Tisserand, V.; Garra Tico, J.; Grauges, E.; Martinelli, M.; Milanes, D. A.; Izen, Joseph M.; Lou, Xinchou; BaBar Collaboration; 250674117 (Izen, JM); 250674117 (Izen, JM); Lou, Xinchou; Izen, Joseph M.We present the first results on the Dalitz-plot structure and improved measurements of the time-dependent CP-violation parameters of the process B⁰→K_S⁰K_S⁰K_S⁰ obtained using 468×10⁶ BB̄ decays collected with the BABAR detector at the PEP-II asymmetric-energy B factory at SLAC. The Dalitz-plot structure is probed by a time-integrated amplitude analysis that does not distinguish between B⁰ and B̅⁰ decays. We measure the total inclusive branching fraction ℬ(B⁰→K_S⁰K_S⁰K_S⁰)=(6.19 ± 0.48 ± 0.15 ± 0.12)×10⁻⁶, where the first uncertainty is statistical, the second is systematic, and the third represents the Dalitz-plot signal model dependence. We also observe evidence for the intermediate resonant states ʄ₀(980), ʄ₀(1710), and ʄ₂(2010). Their respective product branching fractions are measured to be (2.70_{-1.19}^{+1.25} ± 0.36 ± 1.17)×10⁻⁶, (0.50_{-0.24}^{+0.46 ± 0.04 ± 0.10)×10⁻⁶, and (0.54_{-0.20}^{+0.21} ± 0.03 ± 0.52)×10⁻⁶. Additionally, we determine the mixing-induced CP-violation parameters to be S = -0.94_{-0.21}^{+0.24 ± 0.06 and C = -0.17 ± 0.18 ± 0.04, where the first uncertainty is statistical and the second is systematic. These values are in agreement with the standard model expectation. For the first time, we report evidence of CP violation in B⁰→K_S⁰K_S⁰K_S⁰ decays; CP conservation is excluded at 3.8 standard deviations including systematic uncertainties.Item Search for Lepton-Number Violating Processes in B⁺ → h⁻ l⁺ l⁺ Decays(Amer Physical Soc, 2012-04-19) Lees, J. P.; Poireau, V.; Tisserand, V.; Garra Tico, J.; Grauges, E.; Palano, A.; Eigen, G.; Izen, Joseph M.; Lou, Xinchou; BaBar Collaboration; 0000-0003-0867-2189 (Lou, X); 250674117 (Izen, JM); 250674117 (Izen, JM); Lou, Xinchou; Izen, Joseph M.We have searched for the lepton-number violating processes B +→h -- +- + with h -=K -/π - and - +=e +/μ +, using a sample of 471±3 million BB̄ 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. © 2012 American Physical Society.Item Search for the Decay D⁰ → γγ and Measurement of the Branching Fraction for D⁰ → π⁰π⁰(American Physical Society, 2012-05-18) Lees, J. P.; Poireau, V.; Prencipe, E.; Tisserand, V.; Garra Tico, J.; Grauges, E.; Martinelli, M.; Izen, Joseph M.; Lou, Xinchou; BaBar Collaboration; 250674117 (Izen, JM); 250674117 (Izen, JM); Lou, Xinchou; Izen, Joseph M.We search for the rare decay of the D⁰ meson to two photons, D⁰ → γγ, and present a measurement of the branching fraction for a D⁰ meson decaying to two neutral pions, B(D⁰ → π⁰π⁰). The data sample analyzed corresponds to an integrated luminosity of 470.5 fb⁻¹ collected by the BABAR detector at the PEP-II asymmetric-energy e⁺e⁻ collider at SLAC. We place an upper limit on the branching fraction, B(D⁰ → γγ) < 2.2 × 10⁻⁶ at 90% confidence level. This limit improves on the existing limit by an order of magnitude. We also find B(D⁰→π⁰π⁰) = (8.4 ± 0.1 ± 0.4 ± 0.3) × 10⁻⁴.Item Observation of Spin Correlation in tt̄ Events from pp Collisions at √s = 7 TeV Using the ATLAS Detector(American Physical Society, 2012-05-24) Aad, G.; Abbott, B.; Abdallah, J.; Abdel Khalek, S.; Abdelalim, A. A.; Abdesselam, A.; Abdinov, O.; Ahsan, Mahsana; Izen, Joseph M.; Lou, Xinchou; Reeves, Kendall; Wong, Wei-Cheng; ATLAS Collaboration; 250674117 (Izen, JM); 250674117 (Izen, JM); |Ahsan, Mahsana; Izen, Joseph M.; Lou, Xinchou; Reeves, Kendall; Wong, Wei-ChengA measurement of spin correlation in tt̅ production is reported using data collected with the ATLAS detector at the LHC, corresponding to an integrated luminosity of 2.1 fb⁻¹. Candidate events are selected in the dilepton topology with large missing transverse energy and at least two jets. The difference in azimuthal angle between the two charged leptons in the laboratory frame is used to extract the correlation between the top and antitop quark spins. In the helicity basis the measured degree of correlation corresponds to A_{helicity} = 0.40 _{-0.08}^{+0.09}, in agreement with the next-to-leading-order standard model prediction. The hypothesis of zero spin correlation is excluded at 5.1 standard deviations.Item Observation and Study of the Baryonic B-Meson Decays B→D^{(*)}pp̅ (π)(π)(American Physical Society, 2012-05-30) Del Amo Sanchez, P.; Lees, J. P.; Poireau, V.; Prencipe, E.; Tisserand, V.; Garra Tico, J.; Grauges, E.; Izen, Joseph M.; Lou, Xinchou; BaBar Collaboration; 250674117 (Izen, JM); 250674117 (Izen, JM); Lou, Xinchou; Izen, Joseph M.We present results for B-meson decay modes involving a charm meson, protons, and pions using 455×10⁶ BB̄ pairs recorded by the BaBar detector at the SLAC PEP-II asymmetric-energy e⁺e⁻ collider. The branching fractions are measured for the following ten decays: B̅⁰→D⁰pp̄, B̅⁰→D*⁰pp̄, B̅⁰→D⁺pp̄π⁻, B̅⁰→D*⁺pp̄π⁻, B⁻→D⁰pp̄π⁻, B⁻→D*⁰ pp̄π⁻, B̅⁰→D⁰pp̄→D0pp̄π⁻π⁺, B̅⁰→D*⁰pp̄π⁻π⁺, B⁻→D*⁺pp̅π⁻, B⁻→D⁰pp̄π⁻, B⁻→D*⁰pp̄π⁻, B̅⁰→D⁰pp̄π⁻π⁺, B̅⁰→D*⁰pp̄π⁻π⁺, B⁻→D⁺pp̄π⁻π⁻, and B⁻→D*⁺pp̄π⁻π⁻. The four B⁻ and the two five-body B̅⁰ modes are observed for the first time. The four-body modes are enhanced compared to the three- and the five-body modes. In the three-body modes, the M(pp̄) and M(D^{(*)⁰}p) invariant-mass distributions show enhancements near threshold values. In the four-body mode B̅⁰→D⁺pp̄π⁻, the M(pπ⁻) distribution shows a narrow structure of unknown origin near 1.5 GeV/c². The distributions for the five-body modes, in contrast to the others, are similar to the expectations from uniform phase-space predictions.Item Search for Gluinos in Events with Two Same-Sign Leptons, Jets, and Missing Transverse Momentum with the ATLAS Detector in pp Collisions at √s̅=7 TeV(American Physical Society, 2012-06-15) Aad, G.; Abbott, B.; Abdallah, J.; Abdel Khalek, S.; Abdelalim, A. A.; Abdesselam, A.; Abdinov, O.; Abi, B.; Ahsan, Mahsana; Izen, Joseph M.; Lou, Xinchou; Reeves, Kendall; Wong, Wei-Cheng; ATLAS Collaboration; 250674117 (Izen, JM); 250674117 (Izen, JM); |Ahsan, Mahsana; Izen, Joseph M.; Lou, Xinchou; Reeves, Kendall; Wong, Wei-ChengA search is presented for gluinos decaying via the supersymmetric partner of the top quark using events with two same-sign leptons, jets, and missing transverse momentum. The analysis is performed with 2.05 fb⁻¹ of integrated luminosity from pp collisions at √s̅=7 TeV collected by the ATLAS detector at the LHC. No excess beyond the standard model expectation is observed, and exclusion limits are derived for simplified models where the gluino decays via the supersymmetric partner of the top quark and in the minimal supergravity and constrained minimal supersymmetric standard model framework. In those scenarios, gluino masses below 550 GeV are excluded at 95% C.L. within the parameter space considered, significantly extending the coverage with respect to existing limits. Depending on the model parameters, gluino masses up to 750 GeV can also be excluded at 95% C.L.Item Search for Supersymmetry in pp Collisions at √s=7TeV in Final States with Missing Transverse Momentum and b-Jets with the ATLAS Detector(American Physical Society, 2012-06-15) Aad, G.; Abbott, B.; Abdallah, J.; Abdel Khalek, S.; Abdelalim, A. A.; Abdesselam, A.; Abdinov, O.; Ahsan, Mahsana; Izen, Joseph M.; Lou, Xinchou; Reeves, Kendall; Wong, Wei-Cheng; ATLAS Collaboration; 250674117 (Izen, JM); 250674117 (Izen, JM); |Ahsan, Mahsana; Izen, Joseph M.; Lou, Xinchou; Reeves, Kendall; Wong, Wei-ChengThe results of a search for supersymmetry in events with large missing transverse momentum and heavy-flavor jets using an integrated luminosity corresponding to 2.05fb -1 of pp collisions at √s=7TeV recorded with the ATLAS detector at the Large Hadron Collider are reported. No significant excess is observed with respect to the prediction for standard model processes. Results are interpreted in a variety of R-parity conserving models in which scalar bottoms and tops are the only scalar quarks to appear in the gluino decay cascade, and in an SO(10) model framework. Gluino masses up to 600-900GeV are excluded, depending on the model considered. © 2012 CERN. Published by the American Physical Society.Item Study of CP Violation in Dalitz-Plot Analyses of B⁰→K⁺K⁻K_S⁰, B⁺→K⁺K⁻K⁺, and B⁺→K_S⁰ K_S⁰K⁺(American Physical Society, 2012-06-22) Lees, J. P.; Poireau, V.; Tisserand, V.; Garra Tico, J.; Grauges, E.; Milanes, D. A.; Palano, A.; Izen, Joseph M.; Lou, Xinchou; BaBar Collaboration; 250674117 (Izen, JM); 250674117 (Izen, JM); Lou, Xinchou; Izen, Joseph M.We perform amplitude analyses of the decays B⁰→K⁺K⁻K_S⁰, B⁺→K⁺K⁻K⁺, and B⁺→K_S⁰K_S⁰K⁺, and measure CP-violating parameters and partial branching fractions. The results are based on a data sample of approximately 470 × 10⁶ BB̄ decays, collected with the BABAR detector at the PEP-II asymmetric-energy B factory at the SLAC National Accelerator Laboratory. For B⁺→K⁺K⁻K⁺, we find a direct CP asymmetry in B⁺→φ(1020)K₊ of A_{CP}=(12.8±4.4±1.3)%, which differs from zero by 2.8σ. For B⁰→K⁺K⁻K_S⁰, we measure the CP-violating phase β_{eff}(φ(1020)K_S⁰)=(21±6±2)°. For B⁺→K_S⁰K_S⁰K⁺→K_S⁰K_S⁰K⁺, we measure an overall direct CP asymmetry of A _{CP}=(4_{-5}^{+4} ± 2)%. We also perform an angular-moment analysis of the three channels and determine that the ʄχ(1500) state can be described well by the sum of the resonances ʄ₀(1500), ʄ′₂(1525), and ʄ₀(1710).Item Search for Supersymmetry in Events with Three Leptons and Missing Transverse Momentum in √s = 7 TeV pp Collisions with the ATLAS Detector(American Physical Society, 2012-06-29) Aad, G.; Abbott, B.; Abdallah, J.; Abdel Khalek, S.; Abdelalim, A. A.; Abdinov, O.; Abi, B.; Ahsan, Mahsana; Izen, Joseph; Lou, Xinchou; Reeves, Kendall; Wong, Wei-Cheng; ATLAS Collaboration; 250674117 (Izen, JM); 250674117 (Izen, JM); |Ahsan, Mahsana; Izen, Joseph M.; Lou, Xinchou; Reeves, Kendall; Wong, Wei-ChengA search for the weak production of charginos and neutralinos decaying to a final state with three leptons (electrons or muons) and missing transverse momentum is presented. The analysis uses 2.06 fb⁻¹ of √s=7 TeV proton-proton collision data delivered by the Large Hadron Collider and recorded with the ATLAS detector. Observations are consistent with standard model expectations in two signal regions that are either depleted or enriched in Z-boson decays. Upper limits at 95% confidence level are set in R-parity conserving phenomenological minimal supersymmetric and simplified models. For the simplified models, degenerate lightest chargino and next-to-lightest neutralino masses up to 300 GeV are excluded for mass differences from the lightest neutralino up to 300 GeV.Item Search for the Decay Modes B^± → h^± τℓ(American Physical Society, 2012-07-16) Lees, J. P.; Poireau, V.; Tisserand, V.; Garra Tico, J.; Grauges, E.; Milanes, D. A.; Palano, A.; Izen, Joseph M.; Lou, Xinchou; BaBar Collaboration; 250674117 (Izen, JM); 250674117 (Izen, JM); Lou, Xinchou; Izen, Joseph M.We present a search for the lepton flavor violating decay modes B^± → h^± τ ℓ (h=K, π, ℓ = e, μ) using the BABAR data sample, which corresponds to 472 × 10⁶ BB̄ pairs. The search uses events where one B meson is fully reconstructed in one of several hadronic final states. Using the momenta of the reconstructed B, h, and ℓ candidates, we are able to fully determine the τ four-momentum. The resulting τ candidate mass is our main discriminant against combinatorial background. We see no evidence for B ^± → h^± τ ℓ decays and set a 90% confidence level upper limit on each branching fraction at the level of a few times 10⁻⁵.Item Measurement of the Azimuthal Anisotropy for Charged Particle Production in √{S_{NN}} = 2.76 TeV Lead-Lead Collisions with the ATLAS Detector(American Physical Society, 2012-07-24) Aad, G.; Abbott, B.; Abdallah, J.; Abdel Khalek, S.; Abdelalim, A. A.; Abdesselam, A.; Abdinov, O.; Ahsan, Mahsana; Izen, Joseph M.; Lou, Xinchou; Reeves, Kendall; 0000-0003-0867-2189 (Lou, X); 250674117 (Izen, JM); 250674117 (Izen, JM); Lou, Xinchou; Izen, Joseph M.Differential measurements of charged particle azimuthal anisotropy are presented for lead-lead collisions at √{S_{NN}} = 2.76 TeV with the ATLAS detector at the LHC, based on an integrated luminosity of approximately 8 μb⁻¹. This anisotropy is characterized via a Fourier expansion of the distribution of charged particles in azimuthal angle relative to the reaction plane, with the coefficients vn denoting the magnitude of the anisotropy. Significant v₂–v₆ values are obtained as a function of transverse momentum (0.5 < p_T < 20 GeV), pseudorapidity (|η| < 2.5), and centrality using an event plane method. The ν_n values for n ≥ 3 are found to vary weakly with both η and centrality, and their p_T dependencies are found to follow an approximate scaling relation, v_{1/n / n} (p_T) ∝ v{1/2 / 2} (p_T), except in the top 5% most central collisions. A Fourier analysis of the charged particle pair distribution in relative azimuthal angle (Δφ = φ_a − φ_b) is performed to extract the coefficients v_{n,n} = (cos nΔφ). For pairs of charged particles with a large pseudorapidity gap (|Δη = η_a−η_b| > 2) and one particle with pT < 3 GeV, the v₂,₂ – v₆,₆ values are found to factorize as v_{n,n}(p_T^a, pp_T^b) ≈ v_n(p_T^a) ν_n (p_T^b) in central and midcentral events. Such factorization suggests that these values of v₂,₂ – v₆,₆ are primarily attributable to the response of the created matter to the fluctuations in the geometry of the initial state. A detailed study shows that the v₁,₁ (p_T^a,p_T^b) data are consistent with the combined contributions from a rapidity-even v₁ and global momentum conservation. A two-component fit is used to extract the v₁ contribution. The extracted v₁ is observed to cross zero at p_T ≈ 1.0 GeV, reaches a maximum at 4–5 GeV with a value comparable to that for v₃, and decreases at higher p_T.Item Cross Sections for the Reactions e⁺e⁻ → K⁺ K⁻ π⁺π⁻, K⁺ K⁻ π⁰π⁰, and K⁺ K⁻K⁺ K⁻ Measured Using Initial-State Radiation Events(Amer Physical Soc, 2012-07-26) Lees, J. P.; Poireau, V.; Prencipe, E.; Tisserand, V.; Garra Tico, J.; Grauges, E.; Martinelli, M.; Izen, Joseph M.; Lou, Xinchou; BaBar Collaboration; 56366505900 (Lou, X); 250674117 (Izen, JM); 250674117 (Izen, JM); Lou, Xinchou; Izen, Joseph M.We study the processes e⁺e⁻ → K⁺ K⁻ π⁺π⁻γ, K⁺ K⁻ π⁰π⁰γ, and K⁺ K⁻ K⁺ K⁻ γ, where the photon is radiated from the initial state. About 84000, 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 ⁻ π⁰π⁰ 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)f⁰(980) and K⁺ K⁻ f⁰ (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.Item Search for the Decay Modes D⁰ → e⁺e⁻, D⁰ → μ⁺μ⁻, and D⁰ → e^{±} μ^{∓}(Amer Physical Soc, 2012-08-01) Lees, J. P.; Poireau, V.; Tisserand, V.; Garra Tico, J.; Grauges, E.; Palano, A.; Eigen, G.; Izen, Joseph M.; Lou, Xinchou; BaBar Collaboration; 0000-0003-0867-2189 (Lou, X); 250674117 (Izen, JM); 250674117 (Izen, JM); Lou, Xinchou; Izen, Joseph M.We present searches for the rare decay modes D0→e +e -, D0→μ +μ -, and D0→e ±μ ∓ in continuum e +e -→cc̄ events recorded by the BABAR detector in a data sample that corresponds to an integrated luminosity of 468fb -1. These decays are highly Glashow-Iliopoulos-Maiani suppressed but may be enhanced in several extensions of the standard model. Our observed event yields are consistent with the expected backgrounds. An excess is seen in the D0→μ +μ - channel, although the observed yield is consistent with an upward background fluctuation at the 5% level. Using the Feldman-Cousins method, we set the following 90% confidence level intervals on the branching fractions: B(D0→e +e -)<1. 7×10 -7, B(D0→μ +μ -) within 0.6, 8.1]×10 -7, and B(D0→e ±μ ∓)<3.3×10 -7. © 2012 American Physical Society.Item Study of B̅ → X_u ℓν̅ decays in BB̅ events tagged by a fully reconstructed B-meson decay and determination of |V_{ub}|(American Physical Society, 2012-08-07) Lees, J. P.; Poireau, V.; Tisserand, V.; Garra Tico, J.; Grauges, E.; Martinelli, M.; Milanes, D. A.; Izen, Joseph M.; Lou, Xinchou; BaBar Collaboration; 0000-0003-0867-2189 (Lou, X); 250674117 (Izen, JM); 250674117 (Izen, JM); Lou, Xinchou; Izen, Joseph M.We report measurements of partial branching fractions for inclusive charmless semileptonic B decays B̄→X ulν̄ and the determination of the Cabibbo-Kobayashi-Maskawa (CKM) matrix element |V ub|. The analysis is based on a sample of 467×106 Υ(4S)→BB̄ 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 pl*>1.0GeV 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-q2 distribution. Here, M X refers to the invariant mass of the final state hadron X and q2 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 B̄→X ulν̄ decays. .Item Measurement of Branching Fractions and Rate Asymmetries in the Rare Decays B → K^{(*)}ℓ⁺ℓ⁻(American Physical Society, 2012-08-24) Lees, J. P.; Poireau, V.; Tisserand, V.; Garra Tico, J.; Grauges, E.; Palano, A.; Eigen, G.; Izen, Joseph M.; Lou, Xinchou; BaBar Collaboration; 0000-0003-0867-2189 (Lou, X); 250674117 (Izen, JM); 250674117 (Izen, JM); Lou, Xinchou; Izen, Joseph M.In a sample of 471 x 106 BB̅ events collected with the BABAR detector at the PEP-II e⁺e⁻ collider we study the rare decays B → K^{(*)}ℓ⁺ℓ⁻, where ℓ⁺ℓ⁻ is either e⁺e⁻ or μ⁺μ⁻. We report results on partial branching fractions and isospin asymmetries in seven bins of dilepton mass-squared. We further present CP and lepton-flavor asymmetries for dilepton masses below and above the J/ψ resonance. We find no evidence for CP or lepton-flavor violation. The partial branching fractions and isospin asymmetries are consistent with the Standard Model predictions and with results from other experiments.