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 Subject "Annihilation reactions"
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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 Measurement of the Absolute Branching Fraction for Λ_c⁺ → Λe⁺ν_e(Amer Physical Soc, 2015-11-25) Ablikim, M.; Achasov, M. N.; Ai, X. C.; Albayrak, O.; Albrecht, M.; Ambrose, D. J.; Amoroso, A.; Lou, Xinchou; BESIII Collaboration; 56366505900 (Lou, X); Lou, XinchouWe report the first measurement of the absolute branching fraction for Λ_c⁺. This measurement is based on 567 pb⁻¹ of e⁺e⁻ annihilation data produced at √s = 4.599 GeV, which is just above the Λ_c⁺ Λ̅_c̅ threshold. The data were collected with the BESIII detector at the BEPCII storage rings. The branching fraction is determined to be ℬ(Λ_c⁺ → Λe⁺ν_e) = [3.63 ± 0.38(stat) ± 0.20(syst)]%, representing a significant improvement in precision over the current indirect determination. As the branching fraction for Λ_c⁺ → Λe⁺ν_e is the benchmark for those of other Λ_c⁺ semileptonic channels, our result provides a unique test of different theoretical models, which is the most stringent to date.Item Measurement of the e⁺e⁻ → K_s⁰ K^± π^∓ π⁰ and K_s⁰ K^± π^∓η Cross Sections Using Initial-State Radiation(American Physical Society, 2017-05-30) Lees, J. P.; Poireau, V.; Tisserand, V.; Grauges, E.; Palano, A.; Eigen, G.; Brown, D. N.; Izen, Joseph M.; Lou, Xinchou; BaBaR Collaboration; 0000-0003-0867-2189 (Lou, X); 250674117 (Izen, JM); Izen, Joseph M.; Lou, XinchouThe processes e⁺e⁻ → K_s⁰ K^± π^∓ π⁰ and e⁺e⁻ → K_s⁰ K^± π^∓η are studied over a continuum of energies from threshold to 4 GeV with the initial-state photon radiation method. Using 454 fb⁻¹ of data collected with the BABAR detector at the SLAC PEP-II storage ring, the first measurements of the cross sections for these processes are obtained. The intermediate resonance structures from K*⁰ (Kπ)⁰, K*(892)^±(Kπ)^∓, and K_s⁰ K^± ρ^∓ are studied. The J/ψ is observed in all of these channels, and corresponding branching fractions are measured.Item Measurement of the e⁺e⁻ → π⁺π⁻ Cross Section between 600 and 900 MeV Using Initial State Radiation(Elsevier Science BV, 2015-11-28) 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, XinchouWe extract the e⁺e⁻ → π⁺π⁻ cross section in the energy range between 600 and 900 MeV, exploiting the method of initial state radiation. A data set with an integrated luminosity of 2.93 fb⁻¹ taken at a center-of-mass energy of 3.773 GeV with the BESIII detector at the BEPCII collider is used. The cross section is measured with a systematic uncertainty of 0.9%. We extract the pion form factor |Fπ|² as well as the contribution of the measured cross section to the leading-order hadronic vacuum polarization contribution to (g - 2)μ. We find this value to be a(μ)^{ππ,LO} (600-900 MeV) = (368.2 ± 2.5(stat) ± 3.3(sys)).10⁻¹⁰, which is between the corresponding values using the BaBar or KLOE data.Item Study of ψ Decays to the Ξ⁻Ξ̅̅̅⁺ and Σ(1385)^∓ Σ̅(1385)^± Final States(Amer Physical Soc, 2016-04-04) 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, XinchouWe study the decays of the charmonium resonances J/ψ and ψ(3686) to the final states Ξ⁻Ξ̅̅̅⁺, Σ(1385)^∓ Σ̅(1385)^± based on a single baryon tag method using data samples of (223.7 ± 1.4) x 10⁶ J/ψ and (106.4 ± 0.9) x 10⁶ ψ(3686) events collected with the BESIII detector at the BEPCII collider. The decay ψ(3686) → Σ(1385)^∓ Σ(1385)^± is observed for the first time, and the measurements of the other processes, including the branching fractions and angular distributions, are in good agreement with, and much more precise than, the previously published results. Additionally, the ratios B(ψ(3686) → Ξ⁻Ξ̅⁺) / B(J/ψ → Ξ⁻Ξ̅⁺), B(ψ(3686) → Σ(1385)⁻ Σ(1385)⁺) / B(J/ψ → Σ(1385)⁻ Σ(1385)⁺) and / Β(ψ(3686) → Σ(1385)⁺ Σ(1385)⁻) / Β(J/ψ → Σ(1385)⁺ Σ(1385)⁻) are detetmindItem Two-Particle Bose-Einstein Correlations in pp Collisions at √s̅ = 0.9 and 7 TeV Measured with the ATLAS Detector(Springer, 2015-10-01) Aad, G.; Abbott, B.; Abdallah, J.; Abdel-Khalek, S.; Abdinov, O.; Aben, R.; Abi, B.; Izen, Joseph M.; Lou, Xinchou; Leyton, Michael; Namasivayam, Harisankar; Reeves, Kendall; 0000-0003-0867-2189 (Lou, X); 250674117 (Izen, JM); 250674117 (Izen, JM); Izen, Joseph M.; Leyton, Michael; Meirose, Bernhard; Namasivayam, Harisankar; Reeves, KendallThe paper presents studies of Bose–Einstein Correlations (BEC) for pairs of like-sign charged particles measured in the kinematic range pT > 100 MeV and |η| < 2.5 in proton collisions at centre-of-mass energies of 0.9 and 7 TeV with the ATLAS detector at the CERN Large Hadron Collider. The integrated luminosities are approximately 7 μb⁻¹, 190 μb⁻¹ and 12.4 nb⁻¹ for 0.9 TeV, 7 TeV minimum-bias and 7 TeV high-multiplicity data samples, respectively. The multiplicity dependence of the BEC parameters characterizing the correlation strength and the correlation source size are investigated for charged-particle multiplicities of up to 240. A saturation effect in the multiplicity dependence of the correlation source size parameter is observed using the high-multiplicity 7 TeV data sample. The dependence of the BEC parameters on the average transverse momentum of the particle pair is also investigated.