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Fang, X.

Publications and source records attributed to Fang, X..

At least 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

Search for the rare decays J / ψ → D 0 e + e - + c . c . and ψ ( 3686 ) → D 0 e + e - + c . c .

Using the data samples of (1310.6 ± 7.2) × 10 6 J / ψ events and (448.1 ± 2.9) × 106 (3686) events collected with the BESIII detector, we search for the rare decays J / ψ → D 0 e + e - + c.c. and (3686) → D 0 e + e - + c.c.. No significant signals are observed and the corresponding upper limits on the branching fractions at the 90% confidence level are determined to be B( J / ψ → D0e+e- + c.c.) < 8.5 × 10 -8 and B( (3686) → D0e+e- + c.c.) < 1.4 × 10 -7 , respectively. Our limit on B( J / ψ → D 0 e + e - + c.c.) is more stringent by two orders of magnitude than the previous results, and the B( (3686) → D 0 e + e - + c.c.) is measured for the first time.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2017

Observation of the helicity-selection-rule suppressed decay of the χ c 2 charmonium state

The decays of χ c 2 → K + K - π 0 , K S K ± π ∓ , and π + π - π 0 are studied with the ψ ( 3686 ) data samples collected with the Beijing Spectrometer (BESIII). For the first time, the branching fractions of χ c 2 → K*$\bar{K}$ , χ c 2 → $a_2^±$(1320)π ∓ /$a_2^0$(1320)π 0 , and χ c 2 → ρ( 770 ) ± π ∓ are measured. Here, K*$\bar{K}$ denotes both K* ± K ∓ and its isospin-conjugated process K* 0 $\bar{K}$ 0 +c.c., and K* denotes the resonances K*(892), $K_2^*$(1430), and $K_3^*$(1780). The observations indicate a strong violation of the helicity selection rule in χ c 2 decays into vector and pseudoscalar meson pairs. The measured branching fractions of χ c 2 → K*(892)$\bar{K}$ are more than ten times larger than the upper limit of χ c 2 → ρ ( 770 ) ± π ∓ , which is so far the first direct observation of a significant U -spin symmetry breaking effect in charmonium decays.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2017

Observation of χ c 2 → η ' η ' and χ c 0 , 2 → η η '

Using a sample of 448.1×10 6 ψ(3686) events collected with the BESIII detector in 2009 and 2012, we study the decays χ c 0,2 → η ' η ' and η η ' . The decays χ c 2 → η ' η ' , χ c 0 → η η ' and χ c 2 → η η ' are observed for the first time with statistical significances of 9.6 , 13.4 and 7.5 , respectively. The branching fractions are determined to be B( χ c 0 → η ' η ' ) = (2.19 ± 0.03 ± 0.14) × 10 -3 , B( χ c 2 → η ' η ' ) = (4.76 ± 0.56 ± 0.38) × 10 -5 , B( χ c 0 → η η ' ) = (8.92±0.84±0.65)×10 -5 and B( χ c 2 → η η ' ) = (2.27±0.43±0.25)×10 -5 , where the first uncertainties are statistical and the second are systematic. The precision for the measurement of B( χ c 0 → η ' η ' ) is significantly improved compared to previous measurements. Based on the measured branching fractions, the role played by the doubly and singly Okubo-Zweig-Iizuka disconnected transition amplitudes for χ c 0 , 2 decays into pseudoscalar meson pairs can be clarified.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2017

Improved measurements of two-photon widths of the χ c J states and helicity analysis for χ c 2 → γ γ

Based on 448.1 x 10 6 ψ(3686) events collected with the BESIII detector, the decays ψ(3686) → γχ cJ ,χ cJ → γγ(J = 0,1,2) are studied in this paper. The decay branching fractions of χ c0,2 → γγ are measured to be β(χ c0 → γγ) = (1.93 ± 0.08 ± 0.05 ± 0.05) x 10 -4 and β(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 β(ψ(3686) → γχ c0,2 ) and the total widths Γ(χ 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. Finally, 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 λ=0 γγ (χ c2 )/Γ λ=2 γγ (χ c2 ) = (0.0 ± 0.6 ± 1.2) x 10 -2 , where the uncertainties are statistical and systematic, respectively.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2017

Experimental measurement of 12 C + 16 O fusion at stellar energies

The total cross section of the 12 C + 16 O fusion reaction has been measured at low energies to investigate the role of this reaction during late stellar evolution burning phases. A high-intensity oxygen beam, produced by the 5 MV pelletron accelerator at the University of Notre Dame, impinged on a thick, ultrapure graphite target. Protons and γ rays were simultaneously measured in the center-of-mass energy range from 3.64 to 5.01 MeV for singles and from 3.73 to 4.84 MeV for coincidence events, using silicon and Ge detectors. Statistical model calculations were employed to interpret the experimental results. The emergence of a new resonance-like broad structure and a decreasing trend in the S-factor data towards lower energies (opposite to previous data) are found for the 12 C + 16 O fusion reaction. Furthermore, based on these results the uncertainty range of the reaction rate within the temperature range of late stellar burning environments is discussed.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2017

Evidence for e + e - → γ η c ( 1 S ) at center-of-mass energies between 4.01 and 4.60 GeV

In this paper, we present first evidence for the process e + e - → γη c (1S) at six center-of-mass energies between 4.01 and 4.60 GeV using data collected by the BESIII experiment operating at BEPCII. We measure the Born cross section at each energy using a combination of twelve η c (1S) decay channels. We also combine all six energies under various assumptions for the energy-dependence of the cross section. Finally, if the process is assumed to proceed via the Y (4260), we measure a peak Born cross section σ peak (e + e - → γη c (1S)) = 2.11 ± 0.49(stat.) ± 0.36(syst.) pb with a statistical significance of 4.2σ.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2017

Determination of the Spin and Parity of the Z c ( 3900 )

In this paper, the 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 - &rarr; &pi; + &pi; - J/Ψ. We use a data sample of 1.92 fb -1 accumulated at $ \sqrt{s}=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/c 2 and pole width Γ pole = (51.8± 4.6 stat ± 36.0 syst ) MeV. Finally, we also measure cross sections for the process e + e - &rarr; Z c (3900) + &pi; - + c.c. &rarr; J/Ψ&pi; + &pi; - and determine an upper limit at the 90% confidence level for the process e + e - &rarr; Z c (4020) + &pi; - + c.c. &rarr; J/Ψ &pi; + &pi; - .

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2017

Branching fraction measurements of ψ ( 3686 ) → γ χ c J

In this paper, using a sample of 106 million ψ(3686) decays, the branching fractions of ψ(3686) &rarr; γχ c0 , ψ(3686) &rarr; γχ c1 , and ψ(3686) &rarr; 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. Finally, the product branching fractions of ψ(3686) &rarr; γχ c1 , χ c1 &rarr; γJ/ψ and ψ(3686) &rarr; γχ c2 , χ c2 &rarr; γJ/ψ and the branching fractions of χ c1 &rarr; γJ/ψ and χ c2 &rarr; γJ/ψ are also presented.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2017

Quenching measurements and modeling of a boron-loaded organic liquid scintillator

Organic liquid scintillators are used in a wide variety of applications in experimental nuclear and particle physics. Boron-loaded scintillators are particularly useful for detecting neutron captures, due to the high thermal neutron capture cross section of 10 B. These scintillators are commonly used in neutron detectors, including the DarkSide-50 neutron veto, where the neutron may produce a signal when it scatters o protons in the scintillator or when it captures on 10 B. Reconstructing the energy of these recoils is complicated by scintillation quenching. Understanding how nuclear recoils are quenched in these scintillators is an important and dicult problem. In this article, we present a set of measurements of neutron-induced proton recoils in a boron-loaded organic liquid scintillator at recoil energies ranging from 57-467 keV, and we compare these measurements to predictions from different quenching models. We and that a modified Birks' model whose denominator is quadratic in dE=dx best describes the measurements, with χ 2 /NDF = 1:6. This result will help model nuclear recoil scintillation in similar detectors and can be used to improve their neutron tagging efficiency.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2017

Development of a solenoid spectrometer for nuclear astrophysical studies of fusion reactions near stellar energies

Here, a solenoid spectrometer for nuclear astrophysics (SSNAP) has been developed to study heavy-ion fusion reactions of astrophysical importance near stellar energies. Charged particles follow helical trajectories within the strong magnetic field of a superconducting solenoid. The 12 C( 12 C,p) 23 Na reaction was studied as the first measurement using the solenoid spectrometer at the University of Notre Dame within the energy range of E c.m. = 4.0 to 6.0 MeV. This experiment demonstrated that the solenoid spectrometer is able to provide outstanding capability for detection of light charged particles produced by nuclear fusion reactions having a relatively wide energy range.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2017

Analysis of $D$ + → $K¯$ 0 $e$ + $ν$ $e$ and $D$ + → $π$ 0 $e$ + $ν$ $e$ semileptonic decays

Using 2.93 fb –1 of data taken at 3.773 GeV with the BESIII detector operated at the BEPCII collider, we study the semileptonic decays D + → K¯ 0 e + ν e and D + → π 0 e + ν e . Here, we measure the absolute decay branching fractions B(D + → K¯ 0 e + ν e ) = (8.60 ± 0.06 ± 0.15) × 10 –2 and B(D + → π 0 e + ν e ) = (3.63 ± 0.08 ± 0.05) × 10 –3 , where the first uncertainties are statistical and the second systematic. We also measure the differential decay rates and study the form factors of these two decays. With the values of |V cs | and |V cd | from Particle Data Group fits assuming CKM unitarity, we obtain the values of the form factors at q 2 = 0, $f$ $^{K}_{+}$(0) = 0.725 ± 0.004 ± 0.012 and $f$ $^{π}_{+}$(0) = 0.622 ± 0.012 ± 0.003. Taking input from recent lattice QCD calculations of these form factors, we determine values of the CKM matrix elements |V cs | = 0.944 ± 0.005 ± 0.015 ± 0.024 and |V cd | = 0.210 ± 0.004 ± 0.001 ± 0.009, where the third uncertainties are theoretical.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗