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1.
We review the cross-sections for low-energy π-γ reactions in the framework of chiral perturbation theory. Charged-pion Compton scattering, π-γ → π-γ , is considered up to one-loop order where the pion's internal structure enters through the difference of the electric and
magnetic pion polarizability, απ - βπ . The ongoing COMPASS experiment aims at measuring this important structure constant with high statistics using the Primakoff
effect. In the same way, the reaction π-γ → π-π0 serves as a test of the QCD chiral anomaly (via the γ3π -coupling constant F
γ3π . Furthermore, we calculate the total cross-sections for neutral and charged pion-pair production, π-γ → π-π0π0 and π-γ → π-π+π- , which are governed by the chiral ππ -interaction. Finally, we investigate the radiative (correction) process π-γ → π-γγ and calculate the corresponding two-photon mass spectrum. This information will be useful for analyzing the π- Primakoff scattering events with photons in the final state. 相似文献
2.
A.N. Andreyev D. Ackermann P. Cagarda J. Gerl F. Heßberger S. Hofmann M. Huyse A. Keenan H. Kettunen A. Kleinböhl A. Lavrentiev M. Leino B. Lommel M. Matos G. Münzenberg C. Moore C.D. O'Leary R.D. Page S. Reshitko S. Saro C. Schlegel H. Schaffner M. Taylor P. Van Duppen L. Weissman R. Wyss 《The European Physical Journal A - Hadrons and Nuclei》1999,6(4):381-385
New neutron-deficient isotopes 188,189Po have been produced in the complete fusion reaction of 52Cr ions with a 142Nd target at the velocity filter SHIP. The evaporation residues were separated in-flight and subsequently identified on the
basis of α-γ and α-conversion electron coincidence measurements and of α-α position and time correlations. In 189Po a ground state to ground state α decay with Eα1= 7540(20) keV, T1/2= 5(1) ms and two fine structure α-decays at Eα2= 7264(15) keV and Eα3= 7316(15) keV have been observed. In 188Po (T1/2= 400+200
−150μs) a ground state to ground state α decay at Eα= 7915(25) keV and a fine structure α decay at Eα= 7350(40) keV have been found. Improved data on the α-decay of 189Bi were obtained.
Received: 15 October 1999 相似文献
3.
A. V. Guskov 《Physics of Particles and Nuclei Letters》2010,7(3):192-200
The electromagnetic structure of charged pions can be described by the electric (απ) and magnetic (βπ) polarizabilities that depend on the rigidity of pion’s internal structure as a composite particle. It is shown that the
values of απ and βπ can be precisely measured via the Primakoff reaction π− + (A, Z) → π− + (A, Z) + γ in the COMPASS experiment at CERN. 相似文献
4.
The hard X-ray yield generated with femtosecond laser pulses is studied for differently chirped irradiating laser pulses.
The radiation of a Ti:sapphire CPA laser system (29 fs, 750 μJ, 1 kHz) is focused onto an iron containing solid state target
producing incoherent hard X-ray radiation, Bremsstrahlung as well as target-specific Kα and Kβ lines. The hard X-ray yield has been optimized by introducing negative and positive group delay dispersion (GDD) and third
order dispersion (TOD) to the femtosecond laser pulse. The Kα yield could be enhanced by a factor of 1.7 and reached 1.9×108 Fe Kα photons/s in 4π with the laser pulse positively chirped, and 1.5×108 Fe Kα photons/s with the pulse negatively chirped. When the pulse energy is lowered to about 400 μJ the yield maximum at negative
chirp vanishes and only the maximum at positive chirp remains. We explain this behavior with an increased electron temperature
caused by the induced GDD and TOD in the pulse.
PACS 42.65.Re; 52.38.Ph; 52.50.Jm 相似文献
5.
We use Bloch oscillations to accelerate coherently
rubidium atoms. The variation of the velocity induced by this
acceleration is an integer number times the recoil velocity due to
the absorption of one photon. The measurement of the velocity
variation is achieved using two velocity selective Raman -pulses: the first pulse transfers atoms from the hyperfine state
5S1/2,
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to 5S1/2,
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into a narrow velocity class. After the
acceleration of this selected atomic slice, we apply the second
Raman pulse to bring the resonant atoms back to the initial state
5S1/2,
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. The populations in (F=1
and F=2) are measured separately by using a one-dimensional
time-of-flight technique. To plot the final velocity distribution
we repeat this procedure by scanning the Raman beam frequency of
the second pulse. This two -pulses system constitutes then a
velocity sensor. Any noise in the relative phase shift of the
Raman beams induces an error in the
measured velocity. In this paper
we present a theoretical and an experimental analysis of this
velocity sensor, which take into account the phase fluctuations
during the Raman pulses. 相似文献
6.
N. Itagaki S. Okabe K. Ikeda I. Tanihata 《The European Physical Journal A - Hadrons and Nuclei》2002,13(1-2):43-47
The structure of Be and C isotopes are investigated based on the molecular-orbit (MO) model. The low-lying states are characterized
by several configurations of valence neutrons, which are constructed as combinations of basic orbits. In 10Be, all of the observed positive-parity bands and the negative-parity bands are described within the model. The second 0+ state of 10Be has a large α-α cluster structure, and this is characterized by a (1/2+
σ)2 configuration. An enlargement of the α-α distance due to two-valence neutrons along the α-α axis makes their wave function
smooth and reduces the kinetic energy drastically. Furthermore, the contribution of the spin-orbit interaction due to coupling
between the S
z = 0 and the S
z = 1 configurations, is important. In the ground state of 12Be, the calculated energy exhibits similar characteristics, that the remarkable α clustering and the contribution of the spin-orbit
interaction make the binding of the state with (3/2-
π)2(1/2+
σ)2 configuration properly stronger in comparison with the closed p-shell (3/2-
π)2(1/2-
π)2 configuration. This is related to the breaking of the N = 8 (closed p-shell) neutron magic number. Also, the molecule-like structure of the C isotopes is investigated using a microscopic α+α+α+n+n+ . . . model. The combination of the valence neutrons in the π- and the σ-orbit is promising to stabilize the linear-chain state
against the breathing and bending modes, and it is found that the excited states of 16C are the most promising candidates for such structure.
Received: 1 May 2001 / Accepted: 4 December 2001 相似文献
7.
M. Bradley F. Palmer D. Garrison L. Ilich S. Rusinkiewicz D.E. Pritchard 《Hyperfine Interactions》1997,108(1-3):227-238
The Penning trap Ion Cyclotron Resonance (ICR) method we use to weigh atomic masses is reviewed, and our plans for future
measurements, new methods, and apparatus improvements are discussed. Our ultimate goal is to develop a new technique for measuring
atomic masses with an accuracy of a few parts in 1012. We will do this by comparing the cyclotron frequencies of two simultaneously trapped ions. In order to successfully implement
this new method we are developing a quieter, more sensitive DC SQUID-based detector and a new more harmonic trap, and we plan
to use our classical squeezing techniques to reduce the effects of thermal noise.
With our improved apparatus we will weigh Cs and Rb to help determine the fine structure constant α, weigh 29Si and 30Si as part of the current effort to replace the artifact kilogram standard with a Si crystal containing a known number of
atoms, and measure the 3H-3He mass difference to help set a limit on the mass of the electron neutrino. Our higher accuracy will also enable us to ``weigh'
the neutron capture gamma rays of 28Si, 32S, and 48Ti to help determine the molar Planck constant NAh and the fine structure constant α. Finally, with a mass measurement accuracy \sim 10-12 we will be able to ``weigh' chemical bonds.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
8.
S. Piano J. W.A. Robinson G. Burnell M. G. Blamire 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,58(2):123-126
The physics of the π phase shift in ferromagnetic
Josephson junctions may enable a range of applications for
spin-electronic devices and quantum computing. We investigate
transitions from “0” to “π” states in Nb/Fe/Nb Josephson
junctions by varying the Fe barrier thickness from 0.5 nm to 5.5 nm. From magnetic measurements we estimate for Fe a magnetic
dead
layer of about 1.1 nm. By fitting the characteristic voltage
oscillations with existing theoretical models we extrapolate an
exchange energy of 256 meV, a Fermi velocity of 1.98 ×105
m/s and an electron mean free path of 6.2 nm, in agreement with
other reported values. From the temperature dependence of the
ICRN product we show that its decay rate exhibits a nonmonotonic
oscillatory behavior with the Fe barrier thickness. 相似文献
9.
Simon Rainville Michael P. Bradley James V. Porto James K. Thompson David E. Pritchard 《Hyperfine Interactions》2001,132(1-4):177-187
We report new values for the atomic masses of the alkali 133Cs, 87Rb, 85Rb, and 23Na with uncertainties ≤ 0.2 ppb. These results, obtained using Penning trap single ion mass spectrometry, are typically two
orders of magnitude more accurate than previously measured values. Combined with values of h/m
atom from atom interferometry measurements and accurate wavelength measurements for different atoms, these values will lead to
new ppb-level determinations of the molar Planck constant N
A
h and the fine structure constant α. This route to α is based on simple physics. It can potentially achieve the several ppb
level of accuracy needed to test the QED determination of α extracted from measurements of the electron g factor. We also demonstrate an electronic cooling technique that cools our detector and ion below the 4 K ambient temperature.
This technique improves by about a factor of three our ability to measure the ion's axial motion.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
10.
J. S. Bakos G. P. Djotyan P. N. Ignácz M. Á. Kedves M. Serényi Zs. Sörlei J. Szigeti Z. Tóth 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2006,37(1):59-66
The spatial displacement of the 85Rb atoms in a
Magneto-Optical Trap (MOT) under the influence of series of frequency
modulated light pulse pairs propagating opposite to each other is measured
as a function of the time elapsed after the start of the pulse train, and
compared with the results of simulations. Adiabatic excitation and
consecutive de-excitation take place between the ground
52S1/2 (F=3) and the 52P3/2 (F'=2, 3, 4) excited levels as the result of
the interaction. The displacement of the 85Rb atoms is calculated as
the solution of simple equation of motion where the expelling force is that
arising from the action of the frequency modulated light pulses. The
restoring and friction forces of the MOT are taken into account also. The
system of Bloch equations for the density matrix elements is solved
numerically for transitions between six working hyperfine levels of the atom
interacting with the sequence of the frequency modulated laser pulses.
According to these simulations, the momentum transferred by one pulse pair
is always smaller than the expected 2ħk, (1) where ħ is the Plank constant and
k=2π/λ where λ is the wavelength, (2) having a maximum
value in a restricted region of variation of the laser pulse peak intensity
and the chirp. 相似文献
11.
V. I. Ritus 《Journal of Experimental and Theoretical Physics》2006,102(4):582-602
The symmetry manifests itself in exact relations between the Bogoliubov coefficients for processes induced by an accelerated
point mirror in 1 + 1 dimensional space and the current (charge) densities for the processes caused by an accelerated point
charge in 3 + 1 dimensional space. The spectra of pairs of Bose (Fermi) massless quanta emitted by the mirror coincide with
the spectra of photons (scalar quanta) emitted by the electric (scalar) charge up to the factor e
2/ħc. The integral relation between the propagator of a pair of oppositely directed massless particles in 1 + 1 dimensional space
and the propagator of a single particle in 3 + 1 dimensional space leads to the equality of the vacuum-vacuum amplitudes for
the charge and the mirror if the mean number of created particles is small and the charge e = √ħc. Due to the symmetry, the mass shifts of electric and scalar charges (the sources of Bose fields with spin 1 and 0 in 3 +
1 dimensional space) for the trajectories with a subluminal relative velocity β12 of the ends and the maximum proper acceleration w
0 are expressed in terms of the heat capacity (or energy) spectral densities of Bose and Fermi gases of massless particles
with the temperature w
0/2π in 1 + 1 dimensional space. Thus, the acceleration excites 1-dimensional oscillation in the proper field of a charge,
and the energy of oscillation is partly deexcited in the form of real quanta and partly remains in the field. As a result,
the mass shift of an accelerated electric charge is nonzero and negative, while that of a scalar charge is zero. The symmetry
is extended to the mirror and charge interactions with the fields carrying spacelike momenta and defining the Bogoliubov coefficients
αB,F. The traces trαB,F, which describe the vector and scalar interactions of the accelerated mirror with a uniformly moving detector, were found
in analytic form for two mirror trajectories with subluminal velocities of the ends. The symmetry predicts one and the same
value e
0
= √ħc for the electric and scalar charges in 3 + 1 dimensional space. Arguments are adduced in favor of the conclusion that this
value and the corresponding value α0 = 1/4π of the fine structure constant are the bare, nonrenormalized values.
The text was submitted by the author in English. 相似文献
12.
Sergey V. Donskov Anatoly K. Likhoded Alexey V. Luchinsky Vladimir D. Samoylenko 《Central European Journal of Physics》2010,8(3):393-399
The decay η′ → ηπ
0
π
0 is studied in the framework of isobar model. It is shown, that good agreement with the experiment is achieved if α
0- and σ-meson contributions are taken into account. The contribution of α
0-meson is dominant, but σ-meson is necessary to reproduce the form of the Dalitz plot. Instead of the usual Breit-Wigner form of σ-meson propagator we use parametrization of the ππ-amplitude, which satisfies analyticity, crossing, unitarity and chirality constraints. This amplitude has a pole in the complex
plane, which corresponds to σ-meson and describe experimental data on ππ-scattering in K
e4 decay. 相似文献
13.
H. Müller S.-W. Chiow Q. Long C. Vo S. Chu 《Applied physics. B, Lasers and optics》2006,84(4):633-642
We report on progress towards a measurement of the fine structure constant α to an accuracy of 5×10-10 or better by measuring the ratio h/mCs of the Planck constant h to the mass of the cesium atom mCs. Compared to similar experiments, ours is improved in three significant ways: (i) simultaneous conjugate interferometers, (ii) multi-photon Bragg diffraction between same internal states, and (iii) an about 1000-fold reduction of laser phase noise to -138 dBc/Hz. Combining that with a new method to simultaneously stabilize the phases of four frequencies, we achieve 0.2 mrad effective phase noise at the location of the atoms. In addition, we use active stabilization to suppress systematic effects due to beam misalignment. PACS 03.75.Dg; 06.20.Jr; 06.30.Ft; 39.20.+q; 03.65.Ta 相似文献
14.
Optical nutation at the Raman-active transition 6P
1/2−6P
3/2 of thallium atoms (ω
R
/2πc=7793 cm −1) under resonant Raman excitation by a biharmonic picosecond pulsed field, giving rise to substantial motion of the population,
is detected. Optical nutation appears as an oscillatory behavior of the energy of the anti-Stokes scattering of probe pulses,
which follow with a fixed delay, as a function of the product of the energies of the excitation pulses. As a result of the
dynamic Stark effect, which decreases the frequency of the transition under study, resonance excitation conditions are satisfied
for negative initial detunings of the Raman excitation frequency from resonance. The Raman scattering cross section for the
transition under study is estimated by comparing the experimental data with the calculations.
Pis’ma Zh. éksp. Teor. Fiz. 70, No. 1, 7–12 (10 July 1999) 相似文献
15.
A.N. Andreyev K. Van de Vel A. Barzakh A. De Smet H. De Witte D.V. Fedorov V.N. Fedoseyev S. Franchoo M. Górska M. Huyse Z. Janas U. Köster W. Kurcewicz J. Kurpeta V.I. Mishin K. Partes A. Plochocki P. Van Duppen L. Weissman 《The European Physical Journal A - Hadrons and Nuclei》2002,14(1):63-75
Alpha-decay properties of the neutron-deficient isotope 185Pb were studied at the PSB-ISOLDE (CERN) on-line mass separator using the resonance ionisation laser ion source (RILIS). The
nuclei of interest were produced in a 1.4 GeV proton-induced spallation reaction of a uranium graphite target. In contrast
to previous studies, two α-decaying isomeric states were identified in 185Pb. The relative production of the isomers, monitored by their α-counting rates, could be significantly changed when a narrow-bandwidth
laser at the RILIS setup was used to scan through the atomic hyperfine structure. Based on the atomic hyperfine structure
measurements, along with the systematics for heavier odd-mass lead isotopes, the spin and the parity of these states were
interpreted as 3/2- and 13/2+ and their nuclear magnetic moments were deduced. The α-decay energy and half-life value for the I
π = 13/2+ isomer are E
α = 6408(5) keV, T
1/2 = 4.3(2) s, respectively; while for the I
π = 3/2- isomer ( T
1/2 = 6.3(4) s) two α-decays with E
α1 = 6288(5) keV, I
α1 = 56(2)% and E
α2 = 6486(5) keV, I
α2 = 44(2)% were observed. By observing prompt α-γ coincidences new information on the low-lying states in the daughter isotope
181Hg was obtained.
Received: 7 February 2002 / Accepted: 19 February 2002 相似文献
16.
G. Chen J. G. Chen Y. J. Yang J. Q. Lin 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2010,57(1):145-149
We numerically calculate the high-order harmonic generation (HHG)
power spectra from a one-dimensional model atom irradiated by linearly
polarised 12 fs two-colour laser pulses composed of a fundamental pulse from
Ti:sapphire laser and its second harmonic. It is found that a distinct
double plateau structure appears when the relative phase of the two pulses
is set as π/8, 2π/8 or 3π/8, and the double plateau structure
disappears when the relative phase is set as 4π/8, 5π/8, 6π/8
or 7π/8. The relative-phase-dependent plateau structure is explained by
the temporal profile of the synthesised electric fields as well as the
semi-classical “three-step” model. Moreover, our numerical result shows
that cut-off frequencies of the two-colour pulse HHG spectra can be exactly
predicted by use of the semi-classical “three-step” model. 相似文献
17.
F.P. Heßberger S. Hofmann I. Kojouharov D. Ackermann S. Antalic P. Cagarda B. Kindler B. Lommel R. Mann A.G. Popeko S. Saro J. Uusitalo A.V. Yeremin 《The European Physical Journal A - Hadrons and Nuclei》2002,15(3):335-342
The radioactive decay of 217Pa was investigated by means of α-γ-spectroscopy. Fine structure in the ground-state α-decay was established. Ambiguities
in the fine structure of the α-decay of the previously known isomeric state could be clarified by α-γ-coincidence measurements.
A previously unknown α-transition of E
α = (8306 ± 5) keV was detected and identified by means of delayed α-α- and α-γ-γ-coincidence measurements. A second isomeric
state decaying by α-emission was not observed. The quality of the previously reported data of the α-decay fine structure of
217Th was improved.
Received: 29 April 2002 / Accepted: 17 June 2002 / Published online: 19 November 2002
RID="a"
ID="a"e-mail: f.p.hessberger@gsi.de
Communicated by J. ?yst? 相似文献
18.
M. Schumacher 《The European Physical Journal A - Hadrons and Nuclei》2006,30(2):413-422
The t-channel contribution to the difference of electromagnetic polarizabilities of the nucleon, (α - β)t, can be quantitatively understood in terms of a σ-meson pole in the complex t-plane of the invariant scattering amplitude A
1(s, t) with properties of the σ-meson as given by the quark-level Nambu-Jona-Lasinio model (NJL). Equivalently, this quantity may
be understood in terms of a cut in the complex t-plane where the properties of the σ-meson are taken from the ππ → σ → ππ, γγ → σ → ππ and Nˉ → σ → ππ reactions. This equivalence may be understood as a sum rule where the properties of the σ-meson as predicted by
the NJL model are related to the f
0(600) particle observed in the three reactions. In the following, we describe details of the derivation of (α - β)t making use of predictions of the quark-level NJL model for the σ-meson mass.
An erratum to this article is available at . 相似文献
19.
R.O. Grondin W. Porod J. Ho D.K. Ferry G.J. Iafrate 《Superlattices and Microstructures》1985,1(2):183-186
While many predicted superlattice behaviors depend on the presence of Bloch oscillations, the existence of such oscillations remains problematical. Here, we consider procedures by which their existence within a superlattice could be detected. We first set upper and lower bounds on the necessary fields. We then demonstrate that while a negative differential mobility is expected, no resonant peak occurs in this mobility at the Bloch frequency. However, we provide two ways of directly observing Bloch oscillations. In the first, we note the existence of structures in the dc velocity-field characteristic when an externally applied RF field has a frequency which is harmonically related to the Bloch frequency. The second approach is to measure the velocity fluctuation noise spectra, which should have a peak at the field-tunable Bloch frequency. 相似文献
20.
Pedro Freitas 《Communications in Mathematical Physics》2001,217(2):375-382
We consider the problem of minimizing the eigenvalues of the Schr?dinger operator H=−Δ+αF(κ) (α>0) on a compact n-manifold subject to the restriction that κ has a given fixed average κ0.
In the one-dimensional case our results imply in particular that for F(κ)=κ2 the constant potential fails to minimize the principal eigenvalue for α>αc=μ1/(4κ0
2), where μ1 is the first nonzero eigenvalue of −Δ. This complements a result by Exner, Harrell and Loss, showing that the critical value
where the constant potential stops being a minimizer for a class of Schr?dinger operators penalized by curvature is given
by α
c
. Furthermore, we show that the value of μ1/4 remains the infimum for all α >α
c
. Using these results, we obtain a sharp lower bound for the principal eigenvalue for a general potential.
In higher dimensions we prove a (weak) local version of these results for a general class of potentials F(κ), and then show that globally the infimum for the first and also for higher eigenvalues is actually given by the corresponding
eigenvalues of the Laplace–Beltrami operator and is never attained.
Received: 17 July 2000 / Accepted: 11 October 2000 相似文献