2,015 research outputs found

    On the electromagnetic form factors of the proton from generalized Skyrme models

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    We compare the prediction of Skyrme-like effective Lagrangians with data for electromagnetic form factors of proton and consider the possibility of fixing the parameters of these higher-order Lagrangians. Our results indicate that one or two-parameter models can lead to better agreement with the data but more accurate determination of the effective Lagragian faces theoretical uncertainties.Comment: 8 pages, 2 figures, revte

    Optical Lattice Induced Light Shifts in an Yb Atomic Clock

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    We present an experimental study of the lattice induced light shifts on the 1S_0-3P_0 optical clock transition (v_clock~518 THz) in neutral ytterbium. The ``magic'' frequency, v_magic, for the 174Yb isotope was determined to be 394 799 475(35)MHz, which leads to a first order light shift uncertainty of 0.38 Hz on the 518 THz clock transition. Also investigated were the hyperpolarizability shifts due to the nearby 6s6p 3P_0 - 6s8p 3P_0, 6s8p 3P_2, and 6s5f 3F_2 two-photon resonances at 759.708 nm, 754.23 nm, and 764.95 nm respectively. By tuning the lattice frequency over the two-photon resonances and measuring the corresponding clock transition shifts, the hyperpolarizability shift was estimated to be 170(33) mHz for a linear polarized, 50 uK deep, lattice at the magic wavelength. In addition, we have confirmed that a circularly polarized lattice eliminates the J=0 - J=0 two-photon resonance. These results indicate that the differential polarizability and hyperpolarizability frequency shift uncertainties in a Yb lattice clock could be held to well below 10^-17.Comment: Accepted to PR

    Proton decay of high-lying states in odd nuclei

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    In the framework of the quasiparticle-phonon model, we study the non-statistical proton decay of excited states in odd nuclei towards low-lying collective states. Partial cross sections and branching ratios for the proton decay of the high angular momentum states in 41^{41}Sc, 59^{59}Cu and 91^{91}Nb %{\it excited by means of the (7^{7}Li,6^{6}He) reaction} are evaluated. The calculated branching ratios predict strong direct proton decays to the low-lying vibrational states in 41^{41}Sc and 91^{91}Nb. A general agreement with existing experimental data is found.Comment: 12 pages, 2 figures, Latex, accepted for publication in Nucl. Phys.

    Frequency evaluation of the doubly forbidden 1S03P0^1S_0\to ^3P_0 transition in bosonic 174^{174}Yb

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    We report an uncertainty evaluation of an optical lattice clock based on the 1S03P0^1S_0\leftrightarrow^3P_0 transition in the bosonic isotope 174^{174}Yb by use of magnetically induced spectroscopy. The absolute frequency of the 1S03P0^1S_0\leftrightarrow^3P_0 transition has been determined through comparisons with optical and microwave standards at NIST. The weighted mean of the evaluations is ν\nu(174^{174}Yb)=518 294 025 309 217.8(0.9) Hz. The uncertainty due to systematic effects has been reduced to less than 0.8 Hz, which represents 1.5×10151.5\times10^{-15} in fractional frequency.Comment: 4 pages, 3 figure -Submitted to PRA Rapid Communication

    Sub-femtosecond absolute timing precision with a 10 GHz hybrid photonic-microwave oscillator

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    We present an optical-electronic approach to generating microwave signals with high spectral purity. By circumventing shot noise and operating near fundamental thermal limits, we demonstrate 10 GHz signals with an absolute timing jitter for a single hybrid oscillator of 420 attoseconds (1Hz - 5 GHz)

    Anisotropy of the Seebeck Coefficient in the Cuprate Superconductor YBa2_{2}Cu3_{3}Oy_{y}: Fermi-Surface Reconstruction by Bidirectional Charge Order

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    The Seebeck coefficient SS of the cuprate YBa2_{2}Cu3_{3}Oy_{y} was measured in magnetic fields large enough to suppress superconductivity, at hole dopings p=0.11p = 0.11 and p=0.12p = 0.12, for heat currents along the aa and bb directions of the orthorhombic crystal structure. For both directions, S/TS/T decreases and becomes negative at low temperature, a signature that the Fermi surface undergoes a reconstruction due to broken translational symmetry. Above a clear threshold field, a strong new feature appears in SbS_{\rm b}, for conduction along the bb axis only. We attribute this feature to the onset of 3D-coherent unidirectional charge-density-wave modulations seen by x-ray diffraction, also along the bb axis only. Because these modulations have a sharp onset temperature well below the temperature where S/TS/T starts to drop towards negative values, we infer that they are not the cause of Fermi-surface reconstruction. Instead, the reconstruction must be caused by the quasi-2D bidirectional modulations that develop at significantly higher temperature.Comment: 7 pages, 5 figure

    Unbound exotic nuclei studied by projectile fragmentation

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    We call "projectile fragmentation" of neutron halo nuclei the elastic breakup (diffraction) reaction, when the observable studied is the neutron-core relative energy spectrum. This observable has been measured in relation to the Coulomb breakup on heavy target and recently also on light targets. Such data enlighten the effect of the neutron final state interaction with the core of origin. Projectile fragmentation is studied here by a time dependent model for the excitation of a nucleon from a bound state to a continuum resonant state in a neutron-core complex potential which acts as a final state interaction. The final state is described by an optical model S-matrix so that both resonant and non resonant states of any continuum energy can be studied as well as deeply bound initial states. It turns out that due to the coupling between the initial and final states, the neutron-core free particle phase shifts are modified, in the exit channel, by an additional phase. Some typical numerical calculations for the relevant observables are presented and compared to experimental data. It is suggest that the excitation energy spectra of an unbound nucleus might reflect the structure of the parent nucleus from whose fragmentation they are obtained.Comment: Proceedings of the 11th Conference on Problems in Theoretican Nuclear Physics, Cortona, Italy, 2006. World Scientifi

    Hyperpolarizability and operational magic wavelength in an optical lattice clock

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    Optical clocks benefit from tight atomic confinement enabling extended interrogation times as well as Doppler- and recoil-free operation. However, these benefits come at the cost of frequency shifts that, if not properly controlled, may degrade clock accuracy. Numerous theoretical studies have predicted optical lattice clock frequency shifts that scale nonlinearly with trap depth. To experimentally observe and constrain these shifts in an 171^{171}Yb optical lattice clock, we construct a lattice enhancement cavity that exaggerates the light shifts. We observe an atomic temperature that is proportional to the optical trap depth, fundamentally altering the scaling of trap-induced light shifts and simplifying their parametrization. We identify an "operational" magic wavelength where frequency shifts are insensitive to changes in trap depth. These measurements and scaling analysis constitute an essential systematic characterization for clock operation at the 101810^{-18} level and beyond.Comment: 5 + 2 pages, 3 figures, added supplementa

    Generation of Ultrastable Microwaves via Optical Frequency Division

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    There has been increased interest in the use and manipulation of optical fields to address challenging problems that have traditionally been approached with microwave electronics. Some examples that benefit from the low transmission loss, agile modulation and large bandwidths accessible with coherent optical systems include signal distribution, arbitrary waveform generation, and novel imaging. We extend these advantages to demonstrate a microwave generator based on a high-Q optical resonator and a frequency comb functioning as an optical-to-microwave divider. This provides a 10 GHz electrical signal with fractional frequency instability <8e-16 at 1 s, a value comparable to that produced by the best microwave oscillators, but without the need for cryogenic temperatures. Such a low-noise source can benefit radar systems, improve the bandwidth and resolution of communications and digital sampling systems, and be valuable for large baseline interferometry, precision spectroscopy and the realization of atomic time
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