Engineering topics
Becker, J.
Publications and source records attributed to Becker, J..
Search for hadronic transition χ cJ →η c π + π - and observation of χ cJ →KK̄ πππ
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Precision measurements of branching fractions for ψ ′ → π 0 J / ψ and η J / ψ
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SPECTRAL ANALYSIS AND INTERPRETATION OF THE {gamma}-RAY EMISSION FROM THE STARBURST GALAXY NGC 253
Very high energy (VHE; E {>=} 100 GeV) and high-energy (HE; 100 MeV {<=} E {<=} 100 GeV) data from {gamma}-ray observations performed with the H.E.S.S. telescope array and the Fermi-LAT instrument, respectively, are analyzed in order to investigate the non-thermal processes in the starburst galaxy NGC 253. The VHE {gamma}-ray data can be described by a power law in energy with differential photon index {Gamma} = 2.14 {+-} 0.18{sub stat} {+-} 0.30{sub sys} and differential flux normalization at 1 TeV of F{sub 0} = (9.6 {+-} 1.5{sub stat}(+ 5.7, -2.9){sub sys}) Multiplication-Sign 10{sup -14} TeV{sup -1} cm{sup -2} s{sup -1}. A power-law fit to the differential HE {gamma}-ray spectrum reveals a photon index of {Gamma} 2.24 {+-} 0.14{sub stat} {+-} 0.03{sub sys} and an integral flux between 200 MeV and 200 GeV of F(0.2-200 GeV) = (4.9 {+-} 1.0{sub stat} {+-} 0.3{sub sys}) Multiplication-Sign 10{sup -9} cm{sup -2} s{sup -1}. No evidence for a spectral break or turnover is found over the dynamic range of both the LAT instrument and the H.E.S.S. experiment: a combined fit of a power law to the HE and VHE {gamma}-ray data results in a differential photon index {Gamma} = 2.34 {+-} 0.03 with a p-value of 30%. The {gamma}-ray observations indicate that at least about 20% of the energy of the cosmic rays (CRs) capable of producing hadronic interactions is channeled into pion production. The smooth alignment between the spectra in the HE and VHE {gamma}-ray domain suggests that the same transport processes dominate in the entire energy range. Advection is most likely responsible for charged particle removal from the starburst nucleus from GeV to multiple TeV energies. In a hadronic scenario for the {gamma}-ray production, the single overall power-law spectrum observed would therefore correspond to the mean energy spectrum produced by the ensemble of CR sources in the starburst region.
Observation of e⁺e⁻→ηJ/ψ at center-of-mass energy √s=4.009 GeV
Using a 478 pb⁻¹ data sample collected with the BESIII detector operating at the Beijing Electron Positron Collider storage ring at a center-of-mass energy of s√=4.009 GeV, the production of e⁺e⁻→ηJ/ψ is observed for the first time with a statistical significance of greater than 10σ. The Born cross section is measured to be (32.1±2.8±1.3) pb, where the first error is statistical and the second systematic. Assuming the ηJ/ψ signal is from a hadronic transition of the ψ(4040), the fractional transition rate is determined to be B(ψ(4040)→ηJ/ψ)=(5.2±0.5±0.2±0.5)×10⁻³, where the first, second, and third errors are statistical, systematic, and the uncertainty from the ψ(4040) resonant parameters, respectively. The production of e⁺e⁻→π0J/ψ is searched for, but no significant signal is observed, and B(ψ(4040)→π⁰J/ψ)<2.8×10⁻⁴ is obtained at the 90% confidence level.
Measurement of χ cj decaying into pn̄π⁻ and pn̄π⁻π⁰
Using a data sample of 1.06×10⁸ ψ' events collected with the BESIII detector in 2009, the branching fractions of χ cJ →pn̄π⁻ and χ cJ →pn̄π⁻π⁰ (J=0, 1, 2) are measured. (Throughout the text, inclusion of charge conjugate modes is implied if not stated otherwise.) The results for χ c⁰ →pn̄π⁻ and χ c² →pn̄π⁻ are consistent with, but much more precise than, those of previous measurements. The decays of χ c1 →pn̄π⁻ and χ cJ →pn̄π⁻π⁰ are observed for the first time.
Observation of χ cJ decays to ΛΛ¯¯¯π⁺π⁻
Decays of the χ cJ states (J=0, 1, 2) to ΛΛ¯¯¯π⁺π⁻, including processes with intermediate Σ(1385), are studied through the E1 transition ψ'→γχ cJ using 106×10⁶ ψ' events collected with the BESIII detector at BEPCII. This is the first observation of χcJ decays to the final state ΛΛ¯¯¯π⁺π⁻. The branching ratio of the intermediate process χ cJ →Σ(1385) ± Σ¯¯¯(1385) ∓ is also measured for the first time, and the results agree with the theoretical predictions based on the color-octet effect.
Study of J/ψ→pp̄ and J/ψ→nn̄
The decays J/ψ→pp̄ and J/ψ→nn̄ have been investigated with a sample of 225.2×10⁶ J/ψ events collected with the BESIII detector at the BEPCII e⁺e⁻ collider. The branching fractions are determined to be B(J/ψ→pp̄)=(2.112±0.004±0.031)×10⁻³ and B(J/ψ→nn̄)=(2.07±0.01±0.17)×10⁻³. Distributions of the angle θ between the proton or antineutron and the beam direction are well described by the form 1+αcos ²θ, and we find α=0.595±0.012±0.015 for J/ψ→pp̄ and α=0.50±0.04±0.21 for J/ψ→nn̄. Our branching-fraction results suggest a large phase angle between the strong and electromagnetic amplitudes describing the J/ψ→NN¯¯¯ decay.
First observation of the isospin violating decay J/ψ→ΛΣ̄⁰+c.c.
Using a sample of (225.2±2.8)×10⁶ J/ψ events collected with the BESIII detector, we present results of a study of J/ψ→γΛΛ¯¯¯ and report the first observation of the isospin violating decay J/ψ→ΛΣ¯¯¯⁰+c.c., in which Σ¯¯¯⁰ decays to γΛ¯¯¯. The measured branching fractions are B(J/ψ→Λ¯¯¯Σ⁰)=(1.46±0.11±0.12)×10⁻⁵ and B(J/ψ→ΛΣ¯¯¯⁰)=(1.37±0.12±0.11)×10⁻⁵. We search for Λ(1520)→γΛ decay, and find no evident signal, and an upper limit for the product branching fraction B(J/ψ→ΛΛ¯¯¯(1520)+c.c.)×B(Λ(1520)→γΛ)<4.1×10⁻⁶ is set at the 90% confidence level. We also report the observation of η c →ΛΛ¯¯¯ in J/ψ→γη c , η c →ΛΛ¯¯¯ and measure the branching fraction B(η c →ΛΛ¯¯¯)=(1.16±0.12(stat)±0.19(syst)±0.28(PDG))×10⁻³.
High compositional homogeneity in In-rich InGaAs nanowire arrays on nanoimprinted SiO{sub 2}/Si (111)
We report improved homogeneity control of composition-tuned In{sub 1-x}Ga{sub x}As (x < 0.4) nanowire (NW) arrays grown by catalyst-free molecular beam epitaxy (MBE) on nanoimprinted SiO{sub 2}/Si (111) substrates. Using very high As/(Ga+In) ratios at growth temperatures of 550 Degree-Sign C enabled uniform incorporation of the respective group-III elements (In,Ga) over the investigated composition range, confirmed by high-resolution x-ray diffraction (HRXRD) and energy dispersive x-ray spectroscopy. Low-temperature (20 K) photoluminescence of these In-rich In{sub 1-x}Ga{sub x}As NW ensembles reveal state-of-the-art linewidths of {approx}29-33 meV. These are independent of Ga content, suggesting an overall low degree of phase separation. In contrast, self-assembled, non-periodic In{sub 1-x}Ga{sub x}As NW arrays show larger inhomogeneity with increased peakwidths in 2{theta}-{omega} HRXRD scans as well as broadened Raman modes. These results demonstrate the excellent potential of site-selective MBE growth of high-periodicity non-tapered In{sub 1-x}Ga{sub x}As NW arrays with low size and composition dispersion for optimized device integration on Si.