The NPDGamma collaboration reports results from the first phase of a measurement of the parity violating up-down asymmetry Aγ with respect to the neutron spin direction of γ-rays emitted in the reaction n + p → d + γ using the capture of polarized cold neutrons on the protons in a liquid parahydrogen target. One expects parity-odd effects in the hadronic weak interaction (HWI) between nucleons to be induced by the weak interaction between quarks. Aγ in n + p → d + γ is dominated by a ∆I = 1, 3 S1 − 3 P1 parity-odd transition amplitude in the n-p system. The first phase of the measurement was completed at the Los Alamos Neutron Science Center spallation source (LANSCE) with the result Aγ = (−1.2 ± 2.1 stat. ± 0.2 sys.) × 10 −7 . We also report the first measurement of an upper limit for the parity allowed left right asymmetry in this reaction, with the result Aγ,LR = (−1.8 ± 1.9 stat. ± 0.2 sys.) × 10 −7 . In this paper we give a detailed report on the theoretical background, experimental setup, measurements, extraction of the parity-odd and parity-allowed asymmetries, analysis of potential systematic effects, and the LANSCE results. The asymmetry has an estimated size of 5 × 10 −8 and the aim of the NPDGamma collaboration is to measure it to 1 × 10 −8 . The second phase of the measurement will be performed at the Spallation Neutron Source (SNS) at Oak Ridge National Laboratory.
The layered MnBi2nTe3n+1 family represents the first intrinsic antiferromagnetic topological insulator (AFM TI, protected by a combination symmetry S ) ever discovered, providing an ideal platform to explore novel physics such as quantum anomalous Hall effect at elevated temperature and axion electrodynamics. Recent angle-resolved photoemission spectroscopy (ARPES) experiments on this family have revealed that all terminations exhibit (nearly) gapless topological surface states (TSSs) within the AFM state, violating the definition of the AFM TI, as the surfaces being studied should be S -breaking and opening a gap. Here we explain this curious paradox using a surface-bulk band hybridization picture. Combining ARPES and first-principles calculations, we prove that only an apparent gap is opened by hybridization between TSSs and bulk bands. The observed (nearly) gapless features are consistently reproduced by tight-binding simulations where TSSs are coupled to a Rashba-split bulk band. The Dirac-cone-like spectral features are actually of bulk origin, thus not sensitive to the S -breaking at the AFM surfaces. This picture explains the (nearly) gapless behaviour found in both Bi2Te3-and MnBi2Te4-terminated surfaces and is applicable to all terminations of MnBi2nTe3n+1 family. Our findings highlight the role of band hybridization, superior to magnetism in this case, in shaping the general surface band structure in magnetic topological materials for the first time.
We report the first observation of the parity-violating gamma-ray asymmetry A np γ in neutronproton capture using polarized cold neutrons incident on a liquid parahydrogen target at the Spallation Neutron Source at Oak Ridge National Laboratory. A np γ isolates the ∆I = 1, 3 S1 → 3 P1 component of the weak nucleon-nucleon interaction, which is dominated by pion exchange and can be directly related to a single coupling constant in either the DDH meson exchange model or pionless effective field theory. We measured A np γ = (−3.0 ± 1.4(stat.) ± 0.2(sys.)) × 10 −8 , which implies a DDH weak πN N coupling of h 1 π = (2.6 ± 1.2(stat.) ± 0.2(sys.)) × 10 −7 and a pionless EFT constant of C 3 S 1 → 3 P 1 /C0 = (−7.4 ± 3.5(stat.) ± 0.5(sys.)) × 10 −11 MeV −1 . We describe the experiment, data analysis, systematic uncertainties, and implications of the result.
We study different ways of symmetry fractionalization in Z2 spin liquids on the triangular lattice. Our classification can be used to identify the symmetry fractionalization in the Z2 spin liquid reported in recent density-matrix-renormalization-group simulations for J1-J2 spin model on the triangular lattice. We find 64 types of symmetry enriched Z2 spin liquid states on triangular lattice. Besides 8 states constructed in Schwinger-boson parton wavefunctions, 12 more states can be realized in Abrikosov-fermion parton construction. Within a larger gauge group than SU (2), the rest 40 states are also found in a spin-3/2 system. Among 20 types of Abrikosov-fermion Gutzwillerprojected wavefunctions, No.B5 state is a promising candidate for the Z2 spin liquid for J1-J2 spin model on the triangular lattice. No.B5 lies close to Dirac spin liquid (DSL). However, variational Monte Carlo simulation find that DSL has a good variational energy and J1-J2 spin model cannot open a gap for spinons on top of DSL to stabilize No.B5 state.
Among all the monitoring data which could be captured in a machining process, the cutting forces could convey key knowledge on the conditions of the process. When the machining involves a single cutting edge the relationship between the output forces (measured with off-the-shelf dynamometers) and condition of the process, is somehow straight forward. However, when multiple cutting edges are in contact with the workpiece, the conventional dynamometers, that cannot separate the reaction forces on each cutting edge, loose significant information that could be used to in-detail monitor the machining process. To this end, this paper presents a novel concept of instrumented wireless milling cutter system with embedded thin film sensors in each cutting inserts, thus the cutting forces acting on each cutting edge could be monitored without reducing the stiffness and dynamic characteristics of the machining system. For this to happen, a dedicated milling force decoupling model for the developed instrumented milling cutter system is proposed and calibrated, and for the first time the accurate online estimation of the separate inserts' working conditions is achieved. The validation demonstrates a satisfactory agreement between the forces measured from the dynamometer and the proposed monitoring system prototype with the error less than 10%. Furthermore, the experimental results also indicate that the monitoring system prototype could also identify the tool insert conditions such as worn and chipped, which could be of high relevance to the analysis of the insert failure mechanism and its progress. Not only the proposed method and easy implementable but above all, it allows the monitoring of the condition (e.g. worn, chipped) of each insert, ability that has not been previously reported.
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