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Search for CP violation in the phase space of D 0 → π + π – π + π – decays
A search for time-integrated CP violation in the Cabibbo-suppressed decay D 0 → π + π – π + π – is performed using an unbinned, model-independent technique known as the energy test. This is the first application of the energy test in four-body decays. The search is performed for P-even CP asymmetries and, for the first time, is extended to probe the P-odd case. Using proton–proton collision data corresponding to an integrated luminosity of 3.0 fb –1 collected by the LHCb detector at centre-of-mass energies of $\sqrt{s}$ = 7 TeV and 8 TeV, the world's best sensitivity to CP violation in this decay is obtained. The data are found to be consistent with the hypothesis of CP symmetry with a p-value of (4.6±0.5)% in the P-even case, and marginally consistent with a p-value of (0.6±0.2)% in the P-odd case, corresponding to a significance for CP non-conservation of 2.7 standard deviations.
Expanding the Phase Space for Halide-Based Solid Electrolytes: Li–Mg–Zr–Cl Spinels
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cDVAE: VAE-guided diffusion for particle accelerator beam 6D phase space projection diagnostics
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Assessing the utility of phase-space-localized basis functions: Exploiting direct product structure and a new basis function selection procedure
In this paper we show that it is possible to use an iterative eigensolver in conjunction with Halverson and Poirier’s symmetrized Gaussian (SG) basis [T. Halverson and B. Poirier, J. Chem. Phys. 137, 224101 (2012)] to compute accurate vibrational energy levels of molecules with as many as five atoms. This is done, without storing and manipulating large matrices, by solving a regular eigenvalue problem that makes it possible to exploit direct-product structure. These ideas are combined with a new procedure for selecting which basis functions to use. The SG basis we work with is orders of magnitude smaller than the basis made by using a classical energy criterion. We find significant convergence errors in previous calculations with SG bases. For sum-of-product Hamiltonians, SG bases large enough to compute accurate levels are orders of magnitude larger than even simple pruned bases composed of products of harmonic oscillator functions.
Passive Longitudinal-Phase-Space Tailoring of Non-Ultrarelativistic Beams with Dielectric-Lined Waveguides
To date conventional use of dielectric-lined waveguides (DLWs) has mainly concerned high-gradient acceleration. In this paper we investigate an alternative use of such waveguides to impressed wakefield-induced energy correlations on non-ultra-relativistic beams. These correlations are shown to produce density modulations as the beam drifts in a free space. We explore several schemes with a single or multiple DLW structures which can lead to passive compressions and to the formation of sub-picosecond bunch trains. We finally suggest the possible use of multiple structures to bunch the beam at higher frequencies using a scheme similar to a two-stage echo enabled harmonic generation.
The kinetic origin of the fluid helicity—A symmetry in the kinetic phase space
Helicity, a topological degree that measures the winding and linking of vortex lines, is preserved by ideal (barotropic) fluid dynamics. In the context of the Hamiltonian description, the helicity is a Casimir invariant characterizing a foliation of the associated Poisson manifold. Casimir invariants are special invariants that depend on the Poisson bracket, not on the particular choice of the Hamiltonian. The total mass (or particle number) is another Casimir invariant, whose invariance guarantees the mass (particle) conservation (independent of any specific choice of the Hamiltonian). In a kinetic description (e.g., that of the Vlasov equation), the helicity is no longer an invariant (although the total mass remains a Casimir of the Vlasov’s Poisson algebra). The implication is that some “kinetic effect” can violate the constancy of the helicity. To elucidate how the helicity constraint emerges or submerges, we examine the fluid reduction of the Vlasov system; the fluid (macroscopic) system is a “sub-algebra” of the kinetic (microscopic) Vlasov system. In the Vlasov system, the helicity can be conserved if a special helicity symmetry condition holds. To put it another way, breaking helicity symmetry induces a change in the helicity. We delineate the geometrical meaning of helicity symmetry and show that for a special class of flows (the so-called epi-two-dimensional flows), the helicity symmetry is written as ∂γ = 0 for a coordinate γ of the configuration space.
Slow manifold reduction as a systematic tool for revealing the geometry of phase space
Many non-dissipative reduced plasma models can be derived from more fundamental non-dissipative models by restricting to an approximate invariant manifold. I present a general systematic procedure for finding the Hamiltonian formulation of a plasma model that can be derived in this manner. Several illustrative examples are considered in detail.
Fast and flexible control of beam longitudinal phase space for high-repetition-rate x-ray free-electron lasers
The wide-ranging requirements for the photon properties from multiple beamlines in superconducting based free-electron lasers (FELs) demand more challenging beam manipulation techniques. Shot-by-shot control of electron beam bunch length and peak current at high repetition rate up to megahertz is highly desired. In this paper, we present a comprehensive study of a method based on a 2-m-long normal conducting radio-frequency cavity to achieve fast and flexible control of beam compression and realize the full potential of the facility, including theoretical analysis, beam dynamics simulations, and conceptual cavity design for the Linac Coherent Light Source II and its high-energy upgrade. We illustrate the physical mechanism of the chirping cavity on the control of the final beam compression and propose methods to lower the requirements for the cavity parameters. The application of this method will allow tailored photon properties of individual beamlines to optimize their performance and drastically improve the multiplexing capabilities of a high-repetition rate FEL facility.
THz-driven zero-slippage IFEL scheme for phase space manipulation
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Single-shot reconstruction of core 4D phase space of high-brightness electron beams using metal grids
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Machine learning-based longitudinal phase space prediction of particle accelerators
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High resolution phase space measurements with Allison-type emittance scanners
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Knife-edge based measurement of the 4D transverse phase space of electron beams with picometer-scale emittance
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Application of a phase space beam position and size monitor for synchrotron radiation source characterization
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High dimensional characterization of the longitudinal phase space formed in a radio frequency quadrupole
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