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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Browsing Lou, Xinchou by Author "0000-0003-0867-2189 (Lou, X)"
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Item Amplitude Analysis of the Decays η′ → π⁺π⁻π⁰ and η′ → π⁰π⁰π⁰(American Physical Society, 2017-01-06) Ablikim, M.; Achasov, M. N.; Ai, X. C.; Albayrak, O.; Albrecht, M.; Ambrose, D. J.; Amoroso, A.; Lou, Xinchou; BESIII Collaboration; 0000-0003-0867-2189 (Lou, X); Lou, XinchouBased on a sample of 1.31 x 10⁹ J/ψ events collected with the BESIII detector, an amplitude analysis of the isospin-violating decays η′ → π⁺π⁻π⁰ and η′ → π⁰π⁰π⁰ is performed. A significant P-wave contribution from η′ → ρ^{±} π^{∓} is observed for the first time in η′ → π⁺π⁻π⁰. The branching fraction is determined to be ℬ(η′ → ρ^{±} π^{∓}) = (7.44 ± 0.60 ± 1.26 ± 1.84) x 10⁻⁴, where the first uncertainty is statistical, the second systematic, and the third model dependent. In addition to the nonresonant S-wave component, there is a significant σ meson component. The branching fractions of the combined S-wave components are determined to be ℬ(η′ → π⁺π⁻π⁰)s = (37.63 ± 0.77 ± 2.22 ± 4.48) x 10⁻⁴ and ℬ(η′ → π⁰π⁰π⁰) = (35.22 ± 0.82 ± 2.54) x 10⁻⁴, respectively. The latter one is consistent with previous BESIII measurements.Item Amplitude Analysis of the χ_{c1} → ηπ⁺π⁻ Decays(2018-05-24) Ablikim, M.; Achasov, M. N.; Ahmed, S.; Ai, X. C.; Albayrak, O.; Albrecht, M.; Ambrose, D. J.; Lou, Xinchou; BESIII Collaboration; 0000-0003-0867-2189 (Lou, X); Lou, XinchouUsing 448.0 x 10⁶ ψ(3686) events collected with the BESIII detector, an amplitude analysis is performed for ψ(3686)→γχ_{c1}, χ_{c1} → ηπ⁺π⁻ decays. The most dominant two-body structure observed is α₀(980)^± π^∓; α₀(980)^±→ηπ^±. The α₀(980) line shape is modeled using a dispersion relation, and a significant nonzero α₀(980) coupling to the η′π channel is measured. We observe χ_{c1} → α₂(1700)π production for the first time, with a significance larger than 17σ. The production of mesons with exotic quantum numbers, J^{PC} = 1⁻⁺, is investigated, and upper limits for the branching fractions χ_{c1}→π₁(1400)^±π^∓, χ_{c1} → π₁(1600)^±π^∓, and χ_{c1} → π₁(2015)^±π^∓, with subsequent π₁(X)^± → ηπ^± decay, are determined.Item Bottomonium Spectroscopy and Radiative Transitions Involving the χ_{bJ} (1p, 2p) States at BaBar(American Physical Society, 2014-12-24) Lees, J. P.; Poireau, V.; Tisserand, V.; Grauges, E.; Palano, A.; Eigen, G.; Stugu, B.; 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 use (121 ± 1) million ϒ(3S) and (98 ± 1) million ϒ(2S) mesons recorded by the BABAR detector at the PEP-II e⁺e⁻ collider at SLAC to perform a study of radiative transitions involving the χ_{bJ}(1P, 2P) states in exclusive decays with μ⁺μ⁻γγ final states. We reconstruct twelve channels in four cascades using two complementary methods. In the first we identify both signal photon candidates in the electromagnetic calorimeter (EMC), employ a calorimeter timing-based technique to reduce backgrounds, and determine branching-ratio products and fine mass splittings. These results include the best observational significance yet for the χ_{b0}(2P) → γϒ(2S) and χ_{b0}(1P) → γϒ(1S) transitions. In the second method, we identify one photon candidate in the EMC and one which has converted into an e⁺e⁻ pair due to interaction with detector material, and we measure absolute product branching fractions. This method is particularly useful for measuring ϒ(3S) → γχ_{b1,2}(1P) decays. Additionally, we provide the most up-to-date derived branching fractions, matrix elements and mass splittings for χ_b transitions in the bottomonium system. Using a new technique, we also measure the two lowest-order spin-dependent coefficients in the nonrelativistic QCD Hamiltonian.Item Branching Fraction and Form-Factor Shape Measurements of Exclusive Charmless Semileptonic B Decays, and Determination of |V_{ub}|(American Physical Society, 2012-11-05) Lees, J. P.; Poireau, V.; Tisserand, V.; Tico, J. Garra; 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 report the results of a study of the exclusive charmless semileptonic decays, B0→π -+ν, B+ → π0⁺ν, B +→ω +ν, B +→η +ν, and B +→η ′+ν (=e or μ) undertaken with approximately 462×106 BB̄ pairs collected at the Υ(4S) resonance with the BABAR detector. The analysis uses events in which the signal B decays are reconstructed with a loose neutrino reconstruction technique. We obtain partial branching fractions in several bins of q2, the square of the momentum transferred to the lepton-neutrino pair, for B0→π - +ν, B +→π0 +ν, B +→ω +ν, and B +→η +ν. From these distributions, we extract the form-factor shapes f +(q2) and the total branching fractions B(B0→π -+ν)=(1.45±0.04 stat±0.06 syst)×10 -4 (combined π - and π0 decay channels assuming isospin symmetry), B(B +→ω +ν)=(1.19±0.16 stat±0.09 syst)×10 -4 and B(B +→η +ν)=(0.38±0.05 stat±0.05 syst)×10 -4. We also measure B(B +→η ′+ν)=(0.24±0. 08 stat±0.03 syst)×10 -4. We obtain values for the magnitude of the Cabibbo-Kobayashi-Maskawa (CKM) matrix element |V ub| by direct comparison with three different QCD calculations in restricted q2 ranges of B→π +ν decays. From a simultaneous fit to the experimental data over the full q2 range and the FNAL/MILC lattice QCD predictions, we obtain |V ub|=(3.25±0.31)×10 -3, where the error is the combined experimental and theoretical uncertainty. © 2012 American Physical Society.Item Branching Fraction Measurements of ψ(3686) → γχ_{cj}(2018-05-24) Ablikim, M.; Achasov, M. N.; Albrecht, M.; Ahmed, S.; Amoroso, A.; An, F. F.; An, Q.; Lou, Xinchou; BESIII Collaboration; 0000-0003-0867-2189 (Lou, X); Lou, XinchouUsing a sample of 106 million ψ(3686) decays, the branching fractions of ψ(3686) → γχ_{c0}, ψ(3686) → γχ_{c1}, and ψ(3686) → γχ_{c2} are measured with improved precision to be (9.389 ± 0.014 ± 0.332) %, (9.905 ± 0.011 ± 0.353) %, and (9.621 ± 0.013 ± 0.272) %, respectively, where the first uncertainties are statistical and the second ones are systematic. The product branching fractions of ψ(3686) → γχ_{c1}, χ_{c1} → γJ/ψ and ψ(3686) → γχ_{c2}, χ_{c2} → γJ/ψ and the branching fractions of χ_{c1} → γJ/ψ and χ_{c2} → γJ/ψ are also presented.Item Centrality and Rapidity Dependence of Inclusive Jet Production in √{S_{NN}} = 5.02 TeV Proton-Lead Collisions with the ATLAS Detector(Elsevier B.V., 2015-07-17) Abbott, B.; Abdallah, J.; Abdel Khalek, S.; Abdinov, O.; Aben, R.; Abi, B.; Abolins, M.; Izen, Joseph M.; Leyton, Michael; Lou, Xinchou; Namasivayam, Harisankar; Reeves, Kendall; ATLAS Collaboration; 0000-0003-0867-2189 (Lou, X); 250674117 (Izen, JM); 250674117 (Izen, JM); Izen, Joseph M.; Leyton, Michael; Namasivayam, Harisankar; Reeves, Kendall; Lou, XinchouMeasurements of the centrality and rapidity dependence of inclusive jet production in the √s̅̅ {̅N̅N̅}=5.02 TeV proton–lead (p+Pb) collisions and the jet cross-section in √s̅=2.76 TeV proton–proton collisions are presented. These quantities are measured in datasets corresponding to an integrated luminosity of 27.8 nb⁻¹ and 4.0 pb⁻¹, respectively, recorded with the ATLAS detector at the Large Hadron Collider in 2013. The p+Pb collision centrality was characterised using the total transverse energy measured in the pseudorapidity interval −4.9 < η < −3.2 in the direction of the lead beam. Results are presented for the double-differential per-collision yields as a function of jet rapidity and transverse momentum (p_T) for minimum-bias and centrality-selected p+Pb collisions, and are compared to the jet rate from the geometric expectation. The total jet yield in minimum-bias events is slightly enhanced above the expectation in a p_T-dependent manner but is consistent with the expectation within uncertainties. The ratios of jet spectra from different centrality selections show a strong modification of jet production at all p_T at forward rapidities and for large p_t at mid-rapidity, which manifests as a suppression of the jet yield in central events and an enhancement in peripheral events. These effects imply that the factorisation between hard and soft processes is violated at an unexpected level in proton–nucleus collisions. Furthermore, the modifications at forward rapidities are found to be a function of the total jet energy only, implying that the violations may have a simple dependence on the hard parton–parton kinematics.Item Cyclopamine Tartrate, An Inhibitor of Hedgehog Signaling, Strongly Interferes with Mitochondrial Function and Suppresses Aerobic Respiration in Lung Cancer Cells(American Physical Society, 2016-03-29) del Amo Sanchez. P.; Lees, J. P.; Poireau, V.; Tisserand, V.; Grauges, E.; Palano, A.; Eigen, G.; Izen, Joseph M.; Lou, Xinchou; 0000-0003-0867-2189 (Lou, X); 250674117 (Izen, JM); Izen, Joseph M.; Lou, XinchouWe measure the time-dependent CP asymmetry in the radiative-penguin decay B0→KS0π-π+γ, using a sample of 471×106 (4S)→BB-events recorded with the BABAR detector at the PEP-II e+e- storage ring at SLAC. Using events with mKππ<1.8 GeV/c2, we measure the branching fractions of B+→K+π-π+γ and B0→K0π-π+γ, the branching fractions of the kaonic resonances decaying to K+π-π+, as well as the overall branching fractions of the B+→ρ0K+γ, B+→K∗0π+γ and S-wave B+→(Kπ)0∗0π+γ components. For events from the ρ mass band, we measure the CP-violating parameters SKS0π+π-γ=0.14±0.25±0.03 and CKS0π+π-γ=-0.39±0.20-0.02+0.03, where the first uncertainties are statistical and the second are systematic. We extract from this measurement the time-dependent CP asymmetry related to the CP eigenstate ρ0KS0 and obtain SKS0ργ=-0.18±0.32-0.05+0.06, which provides information on the photon polarization in the underlying b→sγ transition.Item Dark Photon Search in the Mass Range between 1.5 and 3.4 GeV/c²(Elsevier Science B.V., 2018-10-01) Ablikim, M.; Achasov, M. N.; Ai, X. C.; Albayrak, O.; Albrecht, M.; Ambrose, D. J.; Amoroso, A.; Lou, Xinchou; BESIII Collaboration; 0000-0003-0867-2189 (Lou, X); Lou, XinchouUsing a data set of 2.93 fb⁻¹ taken at a center-of-mass energy √s = 3.773 GeV with the BESIII detector at the BEPCII collider, we perform a search for an extra U(1) gauge boson, also denoted as a dark photon. We examine the initial state radiation reactions e⁺e⁻ → e⁺e⁻γ(ISR) and e⁺e⁻ → μ⁺μ⁻γ(ISR) for this search, where the dark photon would appear as an enhancement in the invariant mass distribution of the leptonic pairs. We observe no obvious enhancement in the mass range between 1.5 and 3.4 GeV/c² and set a 90% confidence level upper limit on the mixing strength of the dark photon and the Standard Model photon. We obtain a competitive limit in the tested mass range.Item Determination of the Spin and Parity of the Z_c (3900)(American Physical Society, 2017) Ablikim, M.; Achasov, M. N.; Ai, X. C.; Albayrak, O.; Albrecht, M.; Ambrose, D. J.; Amoroso, A.; Lou, Xinchou; 0000-0003-0867-2189 (Lou, X); Lou, XinchouThe spin and parity of the Z_{c}(3900)^{±} state are determined to be J^{P} =1⁺ with a statistical significance larger than 7σ over other quantum numbers in a partial wave analysis of the process e⁺e⁻ → π⁺π⁻J/ψ. We use a data sample of 1.92 fb⁻¹ accumulated at √s̅=4.23 and 4.26 GeV with the BESIII experiment. When parametrizing the Z_{c}(3900)^{±} with a Flatté-like formula, we determine its pole mass M_{pole} = (3881.2 ± 4.2_{stat} ± 52.7_{syst}) MeV/c² and pole width Γ_{pole} = (51.8 ± 4.6_{stat} ± 36.0_{syst}) MeV. We also measure cross sections for the process e⁺e⁻→ Z_{c}(3900)^{±}π⁻ + c.c.→ J/ψπ⁺π⁻ and determine an upper limit at the 90% confidence level for the process e⁺e⁻→ Z_{c}(4020)^{±}π⁻ + c.c.→J/ψπ⁺π⁻Item Evidence for CP Violation in B⁺ → K*(892)⁺π⁰ from a Dalitz Plot Analysis of B⁺ → K_s⁰π⁺π⁰ Decays(American Physical Society, 2017-10-02) Lees, J. P.; Poireau, V.; Tisserand, V.; Grauges, E.; Palano, A.; Eigen, G.; Stugu, B.; Izen, Joseph M.; Lou, Xinchou; BaBar Collaboration; 0000-0003-0867-2189 (Lou, X); 250674117 (Izen, JM); Izen, Joseph M.; Lou, XinchouWe report a Dalitz plot analysis of charmless hadronic decays of charged B mesons to the final state K_s⁰ π⁺π⁰ using the full BABAR data set of 470.9 ± 2.8 million BB̅ events collected at the Υ(4S) resonance. We measure the overall branching fraction and CP asymmetry to be Β(B⁺ → K⁰ π⁺π⁰) = (31.8 ± 1.8 ± 2.1_{-0.0}^{+6.0}) x 10⁻⁶ and A_{CP}(B⁺ → K⁰ π⁺π⁰) = 0.07 ± 0.05 ± 0.03_{-0.03}^{+0.02}, where the uncertainties are statistical, systematic, and due to the signal model, respectively. This is the first measurement of the branching fraction for B⁺ → K⁰ π⁺π⁰. We find first evidence of a CP asymmetry in B⁺ → K*(892)⁺π⁰ decays: A_{CP}(B⁺ → K*(892)⁺π⁰) = -0.52 ± 0.14 ± 0.04_{-0.02}^{+0.04}. The significance of this asymmetry, including systematic and model uncertainties, is 3.4 standard deviations. We also measure the branching fractions and CP asymmetries for three other intermediate decay modes.Item Evidence for the Baryonic Decay B̅→ D⁰ΛΛ̅(2014-06-06) Lees, J. P.; Poireau, V.; Tisserand, V.; Grauges, E.; Palano, A.; Eigen, G.; Stugu, B.; Lou, Xinchou; Izen, Joseph M.; BaBar Collaboration; 0000-0003-0867-2189 (Lou, X); 250674117 (Izen, JM); 250674117 (Izen, JM); Lou, Xinchou; Izen, Joseph M.Evidence is presented for the baryonic B meson decay B̅⁰ → D⁰ΛΛ̅ based on a data sample of 471 x 10⁶ BB̅ pairs collected with the BABAR detector at the PEP-II asymmetric e⁺e⁻ collider located at the SLAC National Accelerator Laboratory. The branching fraction is determined to beℬ(B̅⁰ → D⁰ΛΛ̅) = (9.8_{-2.6}^{+2.9} ± 1.9) x 10⁻⁶, corresponding to a significance of 3.4 standard deviations including additive systematic uncertainties. A search for the related baryonic B meson decay B̅⁰ → D⁰Σ⁰Λ̅ with Σ⁰ → Λγ is performed and an upper limit ℬ(B̅⁰ → D⁰Σ⁰Λ̅ + B̅⁰ → D⁰ΛΣ̅⁰ < 3.1 x 10⁻⁵ is determined at 90% confidence level.Item Evidence for the Decay B⁰ → ωω and Search for B⁰ → ωφ(American Physical Society, 2014-03-05) Lees, J. P.; Poireau, V.; Tisserand, V.; Grauges, E.; Palano, A.; Eigen, G.; Stugu, B.; Lou, Xinchou; Izen, Joseph M.; BaBar Collaboration; 0000-0003-0867-2189 (Lou, X); 250674117 (Izen, JM); 250674117 (Izen, JM); Lou, Xinchou; Izen, Joseph M.We describe searches for B meson decays to the charmless vector-vector final states ωω and ωφ with 471 x 10⁶ BB̅ pairs produced in e⁺e⁻ annihilation at √s̅ = 10.58 GeV using the BABAR detector at the PEP-II collider at the SLAC National Accelerator Laboratory. We measure the branching fraction ℬ(B⁰ → ωω) = (1.2 ± 0.3_{-0.2}^{+0.3}) x 10⁻⁶, where the first uncertainty is statistical and the second is systematic, corresponding to a significance of 4.4 standard deviations. We also determine the upper limit ℬ(B⁰ → ωφ) < 0.7 x 10⁻⁶ at 90% confidence level. These measurements provide the first evidence for the decay B⁰ → ωω, and an improvement of the upper limit for the decay B⁰ → ωφ.Item Evidence for the Singly Cabibbo Suppressed Decay Λ_c⁺ → pη and Search for Λc+ →pπ⁰(2018-05-24) Ablikim, M.; Achasov, M. N.; Ahmed, S.; Ai, X. C.; Albayrak, O.; Albrecht, M.; Ambrose, D. J.; Lou, Xinchou; BESIII Collaboration; 0000-0003-0867-2189 (Lou, X); Lou, XinchouWe study the singly Cabibbo suppressed decays Λ_c⁺ → pη and Λ_c⁺ → pπ⁰ using Λ_c⁺Λ̅_c⁻ pairs produced by e⁺e⁻ collisions at a center-of-mass energy of √s̅ = 4.6 GeV. The data sample was collected by the BESIII detector at the BEPCII collider and corresponds to an integrated luminosity of 567 pb⁻¹. We find the first evidence for the decay Λ_c⁺ → pη with a statistical significance of 4.2σ and measure its branching fraction to be ℬ(Λ_c⁺ → pη) = (1.24 ± 0.28(stat) ± 0.10(syst)) x 10⁻³. No significant Λ_c⁺ → pπ⁰ signal is observed. We set an upper limit on its branching fraction ℬ(Λ_c⁺ → pπ⁰) < 2.7 x 10⁻⁴ at the 90% confidence level.Item Evidence of Two Resonant Structures in e⁺e⁻ → π⁺π⁻h_c(American Physical Society, 2017-03-01) Ablikim, M.; Achasov, M. N.; Ahmed, S.; Ai, X. C.; Albayrak, O.; Albrecht, M.; Ambrose, D. J.; Lou, Xinchou; BESIII Collaboration; 0000-0003-0867-2189 (Lou, X); Lou, XinchouThe cross sections of e⁺e⁻ → π⁺π⁻h_c at center-of-mass energies from 3.896 to 4.600 GeV are measured using data samples collected with the BESIII detector operating at the Beijing Electron Positron Collider. The cross sections are found to be of the same order of magnitude as those of e⁺e⁻→ π⁺π⁻J/ψ and e⁺e⁻ → π⁺π⁻ψ(2S), but the line shape is inconsistent with the Y states observed in the latter two modes. Two structures are observed in the e⁺e⁻ → π⁺π⁻h_c cross sections around 4.22 and 4.39 GeV/c², which we call Y(4220) and Y(4390), respectively. A fit with a coherent sum of two Breit-Wigner functions results in a mass of (4218.4_{-4.5}^{+5.5} ± 0.9) MeV/c² and a width of (66.0_{-8.3}^{+12.3} ± 0.4) MeV for the Y(4220), and a mass of (4391.5_{-6.8}^{+6.3} ± 1.0) MeV/c² and a width of (139.5_{-20.6}^{+16.2} ± 0.6) MeV for the Y(4390), where the first uncertainties are statistical and the second ones systematic. The statistical significance of Y(4220) and Y(4390) is 10σ over one structure assumption. .Item Exclusive Measurements of b → sγ Transition Rate and Photon Energy Spectrum(American Physical Society, 2012-10-17) 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); Izen, Joseph M.; Lou, XinchouWe use 429 fb⁻¹ of e⁺e⁻ collision data collected at the Υ(4S) resonance with the BABAR detector to measure the radiative transition rate of b → sγ with a sum of 38 exclusive final states. The inclusive branching fraction with a minimum photon energy of 1.9 GeV is found to be ℬ(B̅ → Χ_sγ) = (3.29 ± 0.19 ± 0.48) x 10⁻⁴ where the first uncertainty is statistical and the second is systematic. We also measure the first and second moments of the photon energy spectrum and extract the best-fit values for the heavy-quark parameters, m_b and μ_π², in the kinetic and shape function models.Item Fiducial and Differential Cross Sections of Higgs Boson Production Measured in the Four-Lepton Decay Channel in pp Collisions at √s̅ = 8 TeV with the ATLAS Detector(Elsevier B. V., 2014-09-28) Aad, G.; Abbott, B.; Abdallah, J.; Abdel Khalek, S.; Abdinov, O.; Aben, R.; Abi, B.; Izen, Joseph M.; Leyton, Michael; Lou, Xinchou; Namasivayam, Harisankar; Reeves, Kendall; ATLAS Collaboration; 0000-0003-0867-2189 (Lou, X); 250674117 (Izen, JM); 250674117 (Izen, JM); 250674117 (Izen, JM); Izen, Joseph M.; Leyton, Michael; Namasivayam, Harisankar; Reeves, Kendall; Lou, XinchouMeasurements of fiducial and differential cross sections of Higgs boson production in the H → ZZ* → 4ℓ decay channel are presented. The cross sections are determined within a fiducial phase space and corrected for detection efficiency and resolution effects. They are based on 20.3 fb⁻¹ of pp collision data, produced at √s̅ = 8 TeV centre-of-mass energy at the LHC and recorded by the ATLAS detector. The differential measurements are performed in bins of transverse momentum and rapidity of the four-lepton system, the invariant mass of the subleading lepton pair and the decay angle of the leading lepton pair with respect to the beam line in the four-lepton rest frame, as well as the number of jets and the transverse momentum of the leading jet. The measured cross sections are compared to selected theoretical calculations of the Standard Model expectations. No significant deviation from any of the tested predictions is found..Item An Improved Limit for Γ_{ee} of X(3872) and Γ_{ee} Measurement of ψ(3686)(Elsevier, 2015-08-07) Ablikim, M.; Achasov, M. N.; Ai, X. C.; Albayrak, O.; Albrecht, M.; Ambrose, D. J.; Amoroso, A.; Lou, Xinchou; BESIII Collaboration; 0000-0003-0867-2189 (Lou, X); Lou, XinchouUsing the data sets taken at center-of-mass energies above 4 GeV by the BESIII detector at the BEPCII storage ring, we search for the reaction e⁺e⁻→ γ(ISR}X(3872) → γ{ISR}π⁺π⁻J/ψ via the Initial State Radiation technique. The production of a resonance with quantum numbers JPC=1⁺⁺ such as the X(3872) via single photon e+e- annihilation is forbidden, but is allowed by a next-to-leading order box diagram. We do not observe a significant signal of X(3872), and therefore give an upper limit for the electronic width times the branching fraction Γ{ee} ^{X(3872)} ℬ(X(3872) → π⁺π⁻J/ψ) < 0.13 eV at the 90% confidence level. This measurement improves upon existing limits by a factor of 46. Using the same final state, we also measure the electronic width of the ψ(3686) to be Γ {ee} ^{ψ(3686)} = 2213 ± 18{stat} ± 99{sys} eV. © 2015 The Authors.Item Improved Limits on B⁰ Decays to Invisible (+γ) Final States(American Physical Society, 2012-09-27) Lees, J. P.; Poireau, V.; Tisserand, V.; Grauges, E.; Palano, A.; Eigen, G.; Stugu, B.; Izen, Joseph M.; Lou, Xinchou; BaBar Collaboration; 0000-0003-0867-2189 (Lou, X); 250674117 (Izen, JM); 250674117 (Izen, JM); Izen, Joseph M.; Lou, XinchouWe establish improved upper limits on branching fractions for B⁰ decays to final states where the decay products are purely invisible (i.e., no observable final state particles) and for final states where the only visible product is a photon. Within the Standard Model, these decays have branching fractions that are below the current experimental sensitivity, but various models of physics beyond the Standard Model predict significant contributions for these channels. Using 471 x 10⁶ BB̅ pairs collected at the Υ(4S) resonance by the BABAR experiment at the PEP-II e⁺e⁻ storage ring at the SLAC National Accelerator Laboratory, we establish upper limits at the 90% onfidence level of 2.4 x 10⁻⁵ for the branching fraction of B⁰ → invisible and1.7 x 10⁻⁵ for the branching fraction of B⁰ → invisible + γ.Item Improved Measurements of Branching Fractions for η_c → φφ and ωφ(Amer Physical Soc, 2017-05-11) Ablikim, M.; Achasov, M. N.; Ai, X. C.; Albayrak, O.; Albrecht, M.; Ambrose, D. J.; Amoroso, A.; Lou, Xinchou; BESIII Collaboration; 0000-0003-0867-2189 (Lou, X); Lou, XinchouUsing (223.7 ± 1.4) x 10⁶ J/ψ events accumulated with the BESIII detector, we study η_c decays to φφ and ωφ final states. The branching fraction of η_c → φφ is measured to be Br(η_c → φφ) = (2.5 ± 0.3_{-0.7}^{+0.3} ± 0.6) X 10⁻³, where the first uncertainty is statistical, the second is systematic, and the third is from the uncertainty of Br(J/ψ → γη_c). No significant signal for the double Okubo-Zweig-Iizuka suppressed decay of η_c → ωϕ is observed, and the upper limit on the branching fraction is determined to be Br(η_c → ωϕ) < 2.5 × 10⁻⁴ at the 90% confidence level.Item Improved Measurements of Two-Photon Widths of The χ(cJ) States and Helicity Analysis For χ(c2) → γγ(Amer Physical Soc, 2018-10-01) Ablikim, M.; Achasov, M. N.; Ahmed, S.; Albrecht, M.; Amoroso, A.; An, F. F.; An, Q.; Lou, Xinchou; BESIII Collaboration; 0000-0003-0867-2189 (Lou, X); Lou, XinchouBased on 448.1 x 10⁶ ψ(3686) events collected with the BESIII detector, the decays ψ(3686) → γ χ(cJ), χ(cJ) → γγ(J = 0, 1, 2) are studied. The decay branching fractions of χ(c0,2) → γγ are measured to be ℬ(χ(c0) → γγ) = (1.93 ± 0.08 ± 0.05 ± 0.05) x 10⁻⁴ and ℬ(χ(c2) → γγ) = (3.10 ± 0.09 ± 0.07 ± 0.11) x 10⁻⁴ which correspond to two-photon decay widths of Γ(γγ)(χ(c0)) = 2.03 ± 0.08 ± 0.06 ± 0.13 keV and Γ(γγ)(χ(c2)) = 0.60 ± 0.02 ± 0.01 ± 0.04 keV with a ratio of R = Γ(γγ)(χ(c2))/Γ(γγ)(χ(c0)) = 0.295 ± 0.014 ± 0.007 ± 0.027, where the uncertainties are statistical, systematic and associated with the uncertainties of ℬ(ψ(3686) → γχ(c2)) and the total widths Γχ(c0,2), respectively. For the forbidden decay of χ(c1) → γγ, no signal is observed, and an upper limit on the two-photon width is obtained to be Γ(γγ)(χ(c1)) < 5.3 eV at the 90% confidence level. The ratio of the two-photon widths between helicity-zero and helicity-two components in the decay χ(c2) → γγ is also measured to be f(0/2) = Γ(γγ)(λ=0) (χ(c2)) / Γ(γγ)(λ=2) (χ(c2) = (0.0 ± 0.6 ± 1.2) x 10(-2), where the uncertainties are statistical and systematic, respectively.