53,464 research outputs found
Diffractive heavy pseudoscalar-meson productions by weak neutral currents
A first theoretical study for neutrino-induced diffractive productions of
heavy pseudoscalar-mesons, \eta_c and \eta_b, off a nucleon is performed based
on factorization formalism in QCD. We evaluate the forward diffractive
production cross section in perturbative QCD in terms of the light-cone wave
functions of Z boson and \eta_{c,b} mesons, and the gluon distribution of the
nucleon. The diffractive production of \eta_c is governed by the axial vector
coupling of the longitudinally polarized Z boson to Q\bar{Q} pair, and the
resulting \eta_c production cross section is larger than the J/\psi one by one
order of magnitude. The bottomonium \eta_b production, which shows up for
higher beam energy, is also discussed.Comment: 5 pages with 3 embedded figures. Talk presented at the 15th
International Spin Physics Symposium, Spin 2002, Brookhaven National
Laboratory, September 9-14, 200
Conductance of a helical edge liquid coupled to a magnetic impurity
Transport in an ideal two-dimensional quantum spin Hall device is dominated
by the counterpropagating edge states of electrons with opposite spins, giving
the universal value of the conductance, . We study the effect on the
conductance of a magnetic impurity, which can backscatter an electron from one
edge state to the other. In the case of isotropic Kondo exchange we find that
the correction to the electrical conductance caused by such an impurity
vanishes in the dc limit, while the thermal conductance does acquire a finite
correction due to the spin-flip backscattering.Comment: 5 pages, 2 figure
Single-cycle THz pulses with amplitudes exceeding 1 MV/cm generated by optical rectification in LiNbO3
Using the tilted-pulse-intensity-front scheme, we generate single-cycle
terahertz (THz) pulses by optical rectification of femtosecond laser pulses in
LiNbO3. In the THz generation setup, the condition that the image of the
grating coincides with the tilted-optical-pulse front is fulfilled to obtain
optimal THz beam characteristics and pump-to-THz conversion efficiency. The
designed focusing geometry enables tight focus of the collimated THz beam with
a spot size close to the diffraction limit, and the maximum THz electric field
of 1.2 MV/cm is obtained
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The Long Term Temperature Variation in the Lunar Subsurface
Introduction: Lunar surface heat flow values were measured directly during the Apollo missions. These experiments were carried out on Apollo 15 and 17 for about six years between July 7, 1971 and September 30, 1977. The heat flow values derived from these two measurement sites were 21 mW/m2 and 14 mW/m2 respectively [1]. Langseth et al. concluded the repre-sentative global lunar heat flow to be around 18 mW/m2 based on approximately the first 3 years of data until the end of the 1974 (see Figure 1).
Recently, Saito et al. (2006) succeeded in archiving the heat flow data from March 1 1976 until September 30th 1977 [2]. These data are very useful for identify-ing this very long-term variation because we could extend the period of data almost by a factor of two (from 3 years to 6 years) compared to the data ar-chived previously. Because an anomaly had occurred on April 28th, 1976 on the Apollo 15 experiment, the data of Apollo 15 could not be expanded. Therefore, the data obtained by Apollo 17 were used for long term analysis
Vibrationally resolved partial cross sections and asymmetry parameters for carbon K-shell photoionization of the CO_2 molecule
We have measured the vibrationally resolved partial cross sections \sigma_{v_1^{\prime}} and asymmetry parameters \beta_{v_1^{\prime}} for C K-shell photoionization of the CO2 molecule in the Σu shape resonance region above the C K-shell ionization threshold. The positions of both the maxima of \sigma_{v_1^{\prime}} and the minima of \beta_{v_1^{\prime}} move towards the C K-shell threshold with increasing symmetric stretching vibrational excitation v'1 in the C 1s single-hole state. Calculations employing the relaxed-core Hartree–Fock approach reproduce the observed vibrational effects
On the origin of magnetoresistance in SrFeMoO
We report detailed magnetization () and magnetoresistance () studies
on a series of SrFeMoO samples with independent control on anti-site
defect and grain boundary densities. These results, exhibiting a switching-like
behavior of with , establish that the is controlled by the
magnetic polarization of grain boundary regions, rather than of the grains
within a resonant tunnelling mechanism.Comment: 4 pages, 4 figure
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