Search for Invisible Decays of a Dark Photon Produced in e + e − Collisions at BaBar
Not Available
Lees, J. P.↗
Engineering topics
Kim, J.
Publications and source records attributed to Kim, J..
Enhanced understanding of non-axisymmetric intrinsic and controlled field impacts in tokamaks
Here, an extensive study of intrinsic and controlled non-axisymmetric field (δB) impacts in KSTAR has enhanced the understanding about non-axisymmetric field physics and its implications, in particular, on resonant magnetic perturbation (RMP) physics and power threshold (P th ) for L–H transition. The n=1 intrinsic non-axisymmetric field in KSTAR was measured to remain as low as δB/B 0 ~ 4×10 –5 even at high-beta plasmas (β N ~ 2), which corresponds to approximately 20% below the targeted ITER tolerance level. As for the RMP edge-localized-modes (ELM) control, robust n=1 RMP ELM-crash-suppression has been not only sustained for more than ~90 τ E , but also confirmed to be compatible with rotating RMP. An optimal window of radial position of lower X-point (i.e. R x = $1.44\pm 0.02\,$ m) proved to be quite critical to reach full n=1 RMP-driven ELM-crash-suppression, while a constraint of the safety factor could be relaxed (q 95 = 5 $\pm $ 0.25). A more encouraging finding was that even when R x cannot be positioned in the optimal window, another systematic scan in the vicinity of the previously optimal R x allows for a new optimal window with relatively small variations of plasma parameters. Also, we have addressed the importance of optimal phasing (i.e. toroidal phase difference between adjacent rows) for n=1 RMP-driven ELM control, consistent with an ideal plasma response modeling which could predict phasing-dependent ELM suppression windows. In support of ITER RMP study, intentionally misaligned RMPs have been found to be quite effective during ELM-mitigation stage in lowering the peaks of divertor heat flux, as well as in broadening the 'wet' areas. Besides, a systematic survey of P th dependence on non-axisymmetric field has revealed the potential limit of the merit of low intrinsic non-axisymmetry. Considering that the ITER RMP coils are composed of 3-rows, just like in KSTAR, further 3D physics study in KSTAR is expected to help us minimize the uncertainties of the ITER RMP coils, as well as establish an optimal 3D configuration for ITER and future reactors.
3D physics↗
Thermal conductivity measurements of proton-heated warm dense aluminum
Thermal conductivity is one of the most crucial physical properties of matter when it comes to understanding heat transport, hydrodynamic evolution, and energy balance in systems ranging from astrophysical objects to fusion plasmas. In the warm dense matter regime, experimental data are very scarce so that many theoretical models remain untested. Here we present the first thermal conductivity measurements of aluminum at 0.5–2.7 g/cc and 2–10 eV, using a recently developed platform of differential heating. A temperature gradient is induced in a Au/Al dual-layer target by proton heating, and subsequent heat flow from the hotter Au to the Al rear surface is detected by two simultaneous time-resolved diagnostics. A systematic data set allows for constraining both thermal conductivity and equation-of-state models. Simulations using Purgatorio model or Sesame S27314 for Al thermal conductivity and LEOS for Au/Al release equation-of-state show good agreement with data after 15 ps. Discrepancy still exists at early time 0–15 ps, likely due to non-equilibrium conditions.
70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
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↗
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↗
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↗
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↗
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↗
Searching for large-gap quantum spin hall insulators: boron-nitride/(Pb, Sn)/α-Al 2 O 3 sandwich structures
Topological insulators hold great potential for efficient information processing and storage. Using density functional theory calculations, we predict that a honeycomb lead monolayer can be stabilized on an Al2O3 (0001) substrate to become topologically non-trivial with a sizeable band gap (~0.27 eV). Furthermore, we propose to use a hexagonal boron-nitride (h-BN) monolayer as a protection for the topological states of Pb/Al2O3 and Sn/Al2O3. Our findings suggest new possibilities for designing and protecting two-dimensional TIs for practical applications.
Wang, Hui↗
Investigation of instabilities and rotation alteration in high beta KSTAR plasmas
Not Available
Park, Y. S.↗
BigData Express - Toward Schedulable, Predictable, and High-Performance Data Transfer
DOE Data Transfer Challenges * High-performance challenges * Time-constraint challenges * Real-time data transfer * Deadline-bound data transfer * Background data transfer...
Lu, W.↗
A collimated neutron detector for RFP plasmas in MST
The neutron emissivity profile in the Madison Symmetric Torus is being reconstructed through the use of a collimated neutron detector. A scintillator-photomultiplier tube (PMT) system is employed to detect the fusion neutrons with the plasma viewing volume defined by a 55 cm deep, 5 cm diameter aperture. Effective detection of neutrons from the viewing volume is achieved through neutron moderation using 1300 lbs of high density polyethylene shielding, which modeling predicts attenuates the penetrating flux by a factor of 10{sup 4} or more. A broad spectrum of gamma radiation is also present due to the unconfined fusion proton bombardment of the thick aluminum vacuum vessel. A 15 cm cylindrical liquid scintillator of 3.8 cm diameter is used to further increase directional sensitivity. A fast (5 ns rise time) preamplifier and digitization at 500 MHz prevent pulse pile-up even at high count rates (∼10{sup 4}/s). The entire neutron camera system is situated on an adjustable inclining base which provides the differing plasma viewing volumes necessary for reconstruction of the neutron emissivity profile. This profile, directly related to the fast-ion population, allows for an investigation of the critical fast-ion pressure gradient required to destabilize a neutral beam driven Alfvénic mode which has been shown to transport fast ions.
46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
Measurement of the B 0 → D * - π + π - π + branching fraction
When using a sample of ( 470.9 ± 2.8 ) × 10 6 B$\bar{B}$ pairs, we measure the decay branching fraction B ( B 0 → D * - π + π - π + ) = ( 7.26 ± 0.11 ± 0.31 ) × 10 -3 , where the first uncertainty is statistical and the second is systematic. These measurement will be helpful in studies of lepton universality by measuring B ( B 0 → D * - τ + ν τ ) using τ + → π + π - π + ¯ ν τ decays, normalized to B ( B 0 → D * - π + π - π + ) .
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
LCLS-II High Energy (LCLS-II-HE): A transformative X-ray laser for science
LCLS-II-HE at SLAC will be a transformative X-ray tool for the scientific mission of DOE Basic Energy Sciences (BES) and for the nation. It represents the vital next step in the ongoing revolution in X-ray lasers, triggered by the world’s first demonstration of a hard X-ray free-electron laser (XFEL) by LCLS in 2009. Its capability moves far beyond the present generation of XFELs and the ultimate potential of storage rings, firmly maintaining the U.S. as the international leader in the science enabled by X-ray sources. The unmatched performance of this facility will serve the needs of a broad scientific user community focused on some of the most critical challenges facing our society, while providing extraordinary potential for scientific discovery and attracting the best and brightest scientific talent.
42 ENGINEERING↗
Search for a muonic dark force at BaBar
Many models of physics beyond the standard model predict the existence of new Abelian forces with new gauge bosons mediating interactions between "dark sectors" and the standard model. We report a search for a dark boson Z' coupling only to the second and third generations of leptons in the reaction e+e-→μ+μ-Z',Z'→μ+μ- using 514 fb -1 of data collected by the BABAR experiment. No significant signal is observed for Z' masses in the range 0.212-10 GeV. Lastly, limits on the coupling parameter g' as low as 7×10 -4 are derived, leading to improvements in the bounds compared to those previously derived from neutrino experiments.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
Tests of C P T symmetry in B 0 - B ¯ 0 mixing and in B 0 → c c ¯ K 0 decays
Here, using the eight time dependences e- Γt (1 + C i cos Δmt + S i sin Δmt) for the decays Y(4S)→B 0 $\bar{B}$ 0 →f j f k , with the decay into a flavor-specific state f j = ± X before or after the decay into a CP eigenstate f k =c$\bar{c}$ K S,L , as measured by the BABAR experiment, we determine the three CPT-sensitive parameters Re(z) and Im(z) in B 0 $\bar{B}$ 0 mixing and |$\bar{A}$/A| in B 0 →c$\bar{c}$ K 0 decays. We find Im(z) = 0.010 ± 0.030 ± 0.013, Re(z) = -0.065 ± 0.028 ± 0.014, and |$\bar{A}$/A|=0.999±0.023±0.01, in agreement with CPT symmetry.
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
X-ray scattering study of pyrochlore iridates: Crystal structure, electronic, and magnetic excitations
We have investigated the structural, electronic, and magnetic properties of the pyrochlore iridates Eu 2 Ir 2 O 7 and Pr 2 Ir 2 O 7 using a combination of resonant elastic x-ray scattering, x-ray powder diffraction, and resonant inelastic x-ray scattering (RIXS). The structural parameters of Eu 2 Ir 2 O 7 have been examined as a function of temperature and applied pressure, with a particular emphasis on regions of the phase diagram where electronic and magnetic phase transitions have been reported. We find no evidence of crystal symmetry change over the range of temperatures (~6 to 300 K) and pressures (~0.1 to 17 GPa) studied. We have also investigated the electronic and magnetic excitations in single-crystal samples of Eu 2 Ir 2 O 7 and Pr 2 Ir 2 O 7 using high-resolution Ir L- 3 -edge RIXS. In spite of very different ground state properties, we find that these materials exhibit qualitatively similar excitation spectra, with crystal field excitations at ~3-5 eV, spin-orbit excitations at ~ 0.5-1 eV, and broad low-lying excitations below ~0.15 eV. In single-crystal samples of "Eu-rich" Eu 2 Ir 2 O 7 (found to possess an actual stoichiometry of Eu 2.18 Ir 1.82 O 7.06 ) we observe highly damped magnetic excitations at ~45 meV, which display significant momentum dependence. Here, we compare these results with recent dynamical structure factor calculations
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Possibility of realizing quantum spin Hall effect at room temperature in stanene / A l 2 O 3 ( 0001 )
Two-dimensional quantum spin Hall (QSH) insulators with reasonably wide band gaps are imperative for the development of various innovative technologies. Through systematic density functional calculations and tight-binding simulations, we found that stanene on an α -alumina surface may possess a sizeable topologically nontrivial band gap ( ~ 0.25 eV ) at the Γ point. Furthermore, stanene is atomically bonded to but electronically decoupled from the substrate, providing high structural stability and isolated QSH states to a large extent. We conclude the underlying physical mechanism is rather general, and this finding may lead to the opening of a new vista for the exploration of QSH insulators for room temperature device applications.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗