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Chen, C.

Publications and source records attributed to Chen, C..

At least 397 records · Page 22
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DOE OSTI2017

Measurement of the e + e - → π + π - π 0 π 0 cross section using initial-state radiation at BABAR

Here, the process e + e – →π + π – 2π 0 γ is investigated by means of the initial-state radiation technique, where a photon is emitted from the incoming electron or positron. Using 454.3 fb –1 of data collected around a center-of-mass energy of √s=10.58 GeV by the BABAR experiment at SLAC, approximately 150000 signal events are obtained. The corresponding nonradiative cross section is measured with a relative uncertainty of 3.6% in the energy region around 1.5 GeV, surpassing all existing measurements in precision. Using this new result, the channel’s contribution to the leading order hadronic vacuum polarization contribution to the anomalous magnetic moment of the muon is calculated as (gπ + π – 2π 0 μ –2)/2=(17.9 ± 0.1 stat ± 0.6 syst )×10–10 in the energy range 0.85 GeV < E CM < 1.8 GeV. In the same energy range, the impact on the running of the fine-structure constant at the Z 0 -pole is determined as Δαπ + π – 2π 0 (M 2 Z )=(4.44 ± 0.02 stat ± 0.14 syst ) × 10 –4 . Furthermore, intermediate resonances are studied and especially the cross section of the process e + e – →ωπ 0 →π + π – 2π 0 is measured.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2017

Measurement of the D * ( 2010 ) + - D + Mass Difference

Here, we measure the mass difference, Δm + , between the D* (2010) + and the D + using the decay chain D* (2010) + → D + π 0 with D + → K - π + π + . The data were recorded with the BABAR detector at center-of-mass energies at and near the Υ(4S) resonance, and correspond to an integrated luminosity of approximately 468 fb -1 . We measure Δm + = (140 601.0 ± 6.8 [stat] ± 12.9 [syst] ) keV . We combine this result with a previous BABAR measurement of Δm 0 ≡ m(D* (2010) + ) - m (D 0 ) to obtain Δm D = m (D + ) - m (D 0 ) = ( 4824.9 ± 6.8 [stat] ± 12.9 [syst]) keV . These results are compatible with and approximately five times more precise than the Particle Data Group averages.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2017

A glimpse of gluons through deeply virtual compton scattering on the proton

The proton is composed of quarks and gluons, bound by the most elusive mechanism of strong interaction called confinement. In this work, the dynamics of quarks and gluons are investigated using deeply virtual Compton scattering (DVCS): produced by a multi-GeV electron, a highly virtual photon scatters off the proton which subsequently radiates a high energy photon. Similarly to holography, measuring not only the magnitude but also the phase of the DVCS amplitude allows to perform 3D images of the internal structure of the proton. The phase is made accessible through the quantum-mechanical interference of DVCS with the Bethe-Heitler (BH) process, in which the final photon is emitted by the electron rather than the proton. Here, we report herein the first full determination of the BH-DVCS interference by exploiting the distinct energy dependences of the DVCS and BH amplitudes. In the high energy regime where the scattering process is expected to occur off a single quark in the proton, these accurate measurements show an intriguing sensitivity to gluons, the carriers of the strong interaction.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2017

Observation of the topological surface state in the nonsymmorphic topological insulator KHgSb

Topological insulators represent unusual topological quantum states, typically with gapped bulk band structure but gapless surface Dirac fermions protected by time-reversal symmetry. Recently, a distinct kind of topological insulator resulting from nonsymmorphic crystalline symmetry was proposed in the KHg X ($X$ = $\mathrm{As}$, Sb, Bi) compounds. Unlike regular topological crystalline insulators, the nonsymmorphic glide-reflection symmetry in KHg X guarantees the appearance of an exotic surface fermion with hourglass shape dispersion (where two pairs of branches switch their partners) residing on its (010) side surface, contrasting to the usual two-dimensional Dirac fermion form. Here, by using high-resolution angle-resolved photoemission spectroscopy, we systematically investigate the electronic structures of KHgSb on both (001) and (010) surfaces and reveal the unique in-gap surface states on the (010) surface with delicate dispersion consistent with the "hourglass Fermion" recently proposed. Finally, our experiment strongly supports that KHgSb is a nonsymmorphic topological crystalline insulator with hourglass fermions, which serves as an important step to the discovery of unique topological quantum materials and exotic fermions protected by nonsymmorphic crystalline symmetry.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

Evidence for C P violation in B + → K * ( 892 ) + π 0 from a Dalitz plot analysis of B + → K S 0 π + π 0 decays

We report a Dalitz plot analysis of charmless hadronic decays of charged B mesons to the final state K 0 S π + π 0 using the full BABAR data set of 470.9 ± 2.8 million B¯B events collected at the Υ(4S) resonance. We measure the overall branching fraction and CP asymmetry to be B(B + → K 0 π + π 0 ) = (31.8 ± 1.8 ± 2.1 +6.0 –0.0 ) × 10 –6 and A CP (B + → K 0 π + π 0 ) = 0.07 ± 0.05 ± 0.03 +0.02 –0.03 , where the uncertainties are statistical, systematic, and due to the signal model, respectively. This is the first measurement of the branching fraction for B + → K 0 π + π 0 . We find first evidence of a CP asymmetry in B + → K*(892) + π 0 decays: A CP (B + → K*(892) + π 0 ) = –0.52 ± 0.14 ± 0.04 +0.04 –0.02 . The significance of this asymmetry, including systematic and model uncertainties, is 3.4 standard deviations. As a result, we also measure the branching fractions and CP asymmetries for three other intermediate decay modes.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2017

Corrosion testing of metals in contact with calcium chloride hexahydrate used for thermal energy storage

Thermal energy storage (TES) using a phase change material (PCM) has been proposed as a supplemental cooling system to improve the performance of power plant air‐cooled condensers (ACCs). In this proposed system, frozen PCM would remove heat from plant's condensing steam during the day, which would melt the PCM. The PCM would be frozen at night as its stored heat is rejected to the cooler atmosphere. Calcium chloride hexahydrate (CaCl 2 · 6H 2 O) is an attractive material to serve as a PCM in this innovative system due to its appropriate melting temperature, low price, and relatively high latent heat of fusion. The corrosion of container materials is a major challenge in using CaCl 2 · 6H 2 O. Any material used needs to survive constant exposure to the salt for several years to ensure a long operational life for the system. In this study, the corrosion behavior of four metals in contact with CaCl 2 · 6H 2 O was experimentally investigated. Three different temperature conditions and two pH level conditions were considered under static metal exposure conditions.

Ren, S. J.↗
DOE OSTI2017

Rosenbluth Separation of the π 0 Electroproduction Cross Section Off the Neutron

Here, we report the first longitudinal/transverse separation of the deeply virtual exclusive $\pi^0$ electroproduction cross section off the neutron and coherent deuteron. Furthemore, the corresponding four structure functions $d\sigma_L/dt$, $d\sigma_T/dt$, $d\sigma_{LT}/dt$ and $d\sigma_{TT}/dt$ are extracted as a function of the momentum transfer to the recoil system at $Q^2$=1.75 GeV$^2$ and $x_B$=0.36. The $ed \to ed\pi^0$ cross sections are found compatible with the small values expected from theoretical models. The $en \to en\pi^0$ cross sections show a dominance from the response to transversely polarized photons, and are in good agreement with calculations based on the transversity GPDs of the nucleon. By combining our results with previous measurements of $\pi^0$ electroproduction off the proton, we present a flavor decomposition of the $u$ and $d$ quark contributions to the cross section.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2017

Measurement of the e + e - → K s 0 K ± π ∓ π 0 and K s 0 K ± π ∓ η cross sections using initial-state radiation

The processes e + e - → K$0\atop{S}$ K ± π ∓ π 0 and e + e - → K$0\atop{S}$ 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$0\atop{S}$K ± ρ ∓ are studied. Lastly, the J / ψ is observed in all of these channels, and corresponding branching fractions are measured.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2017

Dalitz plot analyses of J / ψ → π + π - π 0 , J / ψ → K + K - π 0 , and J / ψ → K s 0 K ± π ∓ produced via e + e - annihilation with initial-state radiation

Here, we study the processes e + e - → γ ISR J/ψ , where J/ψ → π + π - π 0 , J/ψ → K + K - π 0 , and J / ψ → K$0\atop{S}$ K ± π ∓ using a data sample of 519 fb -1 recorded with the BABAR detector operating at the SLAC PEP-II asymmetric-energy e + e - collider at center-of-mass energies at and near the Υ (nS) (n = 2 , 3 , 4) resonances. We measure the ratio of branching fractions R 1 = $B(J/ψ →K^+K^- π^0)\atop{B(J/ψ →π^+π^- π^0)}$ and R 2 = $B(J/ψ →K^0_SK^±π^∓)\atop{B(J/ψ →π^+π^- π^0)}$. We perform Dalitz plot analyses of the three J/ψ decay modes and measure fractions for resonances contributing to the decays. We also analyze the J/ψ → $π^+π^- π^0$ decay using the Veneziano model. We observe structures compatible with the presence of ρ (1450) in all three J/ψ decay modes and measure the relative branching fraction: R (p(1450)) = $Bp(1450)→K^+K^-)\atop{B(p(1450)→π^+π^-)}$ +0.307 ± 0.084 (stat) ± 0.082 (sys).

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2017

Measurement of the inclusive electron spectrum from B meson decays and determination of | V u b |

Based on the full BABAR data sample of 466.5 million $B\bar{B}$ pairs, we present measurements of the electron spectrum from semileptonic B meson decays. We fit the inclusive electron spectrum to distinguish Cabibbo-Kobayashi-Maskawa (CKM) suppressed B → X u eν decays from the CKM-favored B → X c eν decays, and from various other backgrounds, and determine the total semileptonic branching fraction B (B → Xeν) = ( 10.34 ± 0.04 stat ± 0.2 6 syst )%, averaged over B ± and B 0 mesons. We determine the spectrum and branching fraction for charmless B → X u eν decays and extract the CKM element | V ub | , by relying on four different QCD calculations based on the heavy quark expansion. While experimentally, the electron momentum region above 2.1 GeV / c is favored, because the background is relatively low, the uncertainties for the theoretical predictions are largest in the region near the kinematic endpoint. Detailed studies to assess the impact of these four predictions on the measurements of the electron spectrum, the branching fraction, and the extraction of the CKM matrix element |V ub | are presented, with the lower limit on the electron momentum varied from 0.8 GeV / c to the kinematic endpoint. We determine |V ub | using each of these different calculations and find, |V ub | = ( 3.794 ± 0.107 exp $+ 0.292\atop{ - 0.219 SF}$ $+ 0.078 \atop{- 0.068 theory}$ ) × 10 - 3 (De Fazio and Neubert), (4.563 ± 0.126 exp $+ 0.230\atop {- 0.208 SF}$ $+ 0.162\atop{- 0.163 theory}$ ) ×10 -3 (Bosch, Lange, Neubert, and Paz), (3.959 ± 0.104 exp $+ 0.164\atop{- 0.154 SF}$ $+ 0.042\atop{ - 0.079 theory}$ ) × 10 -3 (Gambino, Giordano, Ossola, and Uraltsev), (3.848 ± 0.108 exp $+ 0.084\atop{ - 0.070 theory}$) × 10 -3 (dressed gluon exponentiation), where the stated uncertainties refer to the experimental uncertainties of the partial branching fraction measurement, the shape function parameters, and the theoretical calculations.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2017

First measurement of unpolarized semi-inclusive deep-inelastic scattering cross sections from a He 3 target [First measurement of unpolarized SIDIS cross section from a 3 He target]

Here, the unpolarized semi-inclusive deep-inelastic scattering (SIDIS) differential cross sections in 3 He(e,e'π ± )X have been measured for the first time in Jefferson Lab experiment E06-010 with a 5.9 GeV e – beam on a 3 He gas target. The experiment focuses on the valence quark region, covering a kinematic range 0.12 < x bj < 0.45,1 < Q 2 < 4(GeV/c) 2 ,0.45 < z h < 0.65, and 0.05 < P t < 0.55GeV/c. The extracted SIDIS differential cross sections of π± production are compared with existing phenomenological models while the 3 He nucleus approximated as two protons and one neutron in a plane-wave picture, in multidimensional bins. Within the experimental uncertainties, the azimuthal modulations of the cross sections are found to be consistent with zero.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2017

Cross sections for the reactions e + e - → K S 0 K L 0 π 0 , K S 0 K L 0 η , and K S 0 K L 0 π 0 π 0 from events with initial-state radiation

Here, we study the processes e + e - → K$0\atop{S}$ K$0\atop{L}$ π 0 γ , K $0\atop{S}$ K$0\atop{L}$ η γ , and K$0\atop{S}$ K$0\atop{L}$ π 0 π 0 γ , where the photon is radiated from the initial state, providing cross section measurements for the hadronic final states over a continuum of center-of-mass energies. The results are based on 469 fb -1 of data collected at or near the Υ ( 4 S ) resonance with the BABAR detector at SLAC. We present the first measurements of the e + e - → K$0\atop{S}$ K$0\atop{L}$ π 0 , K$0\atop{S}$ K$0\atop{L}$ η , and K$0\atop{S}$ K$0\atop{L}$ π 0 π 0 cross sections up to a center-of-mass energy of 4 GeV and study their intermediate resonance structures. We observe J / ψ decays to all of these final states for the first time, present measurements of their J / ψ branching fractions, and search for ψ (2S) decays.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2017

Search for B + → K + τ + τ - at the BaBar Experiment

We search for the rare flavor-changing neutral current process B + → K + τ + τ - using data from the BABAR experiment. The data sample, collected at the center-of-mass energy of the Υ ( 4 S ) resonance, corresponds to a total integrated luminosity of 424 fb - 1 and to 471 × 1 0 6 B$\bar{B}$ pairs. We reconstruct one B meson, produced in the Υ ( 4 S ) → B + B - decay, in one of many hadronic decay modes and search for activity compatible with a B + → K + τ + τ - decay in the rest of the event. Each τ lepton is required to decay leptonically into an electron or muon and neutrinos. Comparing the expected number of background events with the data sample after applying the selection criteria, we do not find evidence for a signal. The resulting upper limit, at the 90% confidence level, is B ( B + → K + τ + τ - ) < 2.25 × 10 - 3 .

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2017

Signature of type-II Weyl semimetal phase in MoTe 2

Topological Weyl semimetal (TWS), a new state of quantum matter, has sparked enormous research interest recently. Possessing unique Weyl fermions in the bulk and Fermi arcs on the surface, TWSs offer a rare platform for realizing many exotic physical phenomena. TWSs can be classified into type-I that respect Lorentz symmetry and type-II that do not. Here, we directly visualize the electronic structure of MoTe 2 , a recently proposed type-II TWS. Using angle-resolved photoemission spectroscopy (ARPES), we unravel the unique surface Fermi arcs, in good agreement with our ab initio calculations that have nontrivial topological nature. Our work not only leads to new understandings of the unusual properties discovered in this family of compounds, but also allows for the further exploration of exotic properties and practical applications of type-II TWSs, as well as the interplay between superconductivity (MoTe 2 was discovered to be superconducting recently) and their topological order.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Rosenbluth Separation of the π 0 Electroproduction Cross Section

In this paper, we present deeply virtual $\pi^0$ electroproduction cross-section measurements at $x_B$=0.36 and three different $Q^2$ values ranging from 1.5 to 2 GeV$^2$, obtained from Jefferson Lab Hall A experiment E07-007. The Rosenbluth technique is used to separate the longitudinal and transverse responses. Results demonstrate that the cross section is dominated by its transverse component and, thus, is far from the asymptotic limit predicted by perturbative quantum chromodynamics. Nonetheless, an indication of a nonzero longitudinal contribution is provided by the measured interference term $\sigma_{LT}$. Results are compared with several models based on the leading-twist approach of generalized parton distributions (GPDs). In particular, a fair agreement is obtained with models in which the scattering amplitude includes convolution terms of chiral-odd (transversity) GPDs of the nucleon with the twist-3 pion distribution amplitude. Finally, this experiment, together with previous extensive unseparated measurements, provides strong support to the exciting idea that transversity GPDs can be accessed via neutral pion electroproduction in the high-Q 2 regime.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2016

Analysis of citation networks as a new tool for scientific research

The rapid growth of scientific publications necessitates new methods to understand the direction of scientific research within fields of study, ascertain the importance of particular groups, authors, or institutions, compute metrics that can determine the importance (centrality) of particular seminal papers, and provide insight into the social (collaboration) networks that are present. We present one such method based on analysis of citation networks, using the freely available CiteSpace Program. We use citation network analysis on three examples, including a single material that has been widely explored in the last decade (BiFeO 3 ), two small subfields with a minimal number of authors (flexoelectricity and Kitaev physics), and a much wider field with thousands of publications pertaining to a single technique (scanning tunneling microscopy). Interpretation of the analysis and key insights into the fields, such as whether the fields are experiencing resurgence or stagnation, are discussed, and author or collaboration networks that are prominent are determined. Such methods represent a paradigm shift in our way of dealing with the large volume of scientific publications and could change the way literature searches and reviews are conducted, as well as how the impact of specific work is assessed.

97 MATHEMATICS AND COMPUTING↗