On the characterization of periodic signals using third-order statistical functions

In this paper the theoretical errors involved in the determination of a parameter by measuring g(³)(T,τ,τ') and n⁽³⁾(T) are pointed out. The values of this errors are calculated and compared with those obtained by measuring g(²)(T,τ) for a particular case.     

Analysis of Two Spectral Lines with Gaussian Profile by Using Photon Statistics. Comparison with Other Profile Shapes

In this paper we study the behavior of the errors involved in the determination of the parameters characterizing two spectral lines with Gaussian profile by means of the measurement of the intensity correlation function g⁽²⁾(τ) and by a multichannel system. The results obtained with both methods are compared. We also compare this results with those obtained when two lines with Lorentzian profile are analyzed.     

Two-photon correlations of luminescence at the Bose-Einstein condensation of dipolar excitons

Correlations of the luminescence intensity (the second-order correlation function g ⁽²⁾(τ)), where τ is the delay time between the photons detected in pairs) under the conditions of the Bose-Einstein condensation (BEC) of dipolar excitons has been studied in a temperature range of 0.45–4.2 K. Photoexcited dipolar excitons have been accumulated in a lateral trap in a GaAs/AlGaAs Schottky diode with a 25-nm wide single quantum well with an electric bias applied across the heterolayers. Two-photon correlations have been measured with the use of a two-beam intensity interferometer with a time resolution of }~0.4 ns according to the well-known classical Hanbury-Brown-Twiss scheme. The photon bunching has been observed at the onset of Bose-Einstein condensation manifested by the appearance of a narrow exciton condensate line in the luminescence spectrum at an increase in the optical pumping (the line width near the threshold is ?200 μeV). At the same time, the two-photon correlation function itself obeys the super-Poisson distribution, g ⁽²⁾(τ) > 1, at time scale τ_c ? 1 ns of the system coherence. The photon bunching is absent at a pumping level substantially below the condensation threshold. The effect of bunching also decreases at pumping significantly above the threshold, when the narrow exciton condensate line starts to dominate in the luminescence spectra, and finally disappears with the further increase in the optical excitation. In this region, the distribution of pair photon correlations is a Poisson distribution manifesting the united quantum coherent state of the exciton condensate. Under the same conditions, the first-order spatial correlation function g ⁽¹⁾(r) determined from the interference pattern of the luminescence signals from the spatially separated parts of the condensate at constant pumping remains noticeable at distances of no less than 4 μm. The discovered effect of photon bunching is very sensitive to temperature and decreases by several times with a temperature increase in the range of 0.45–4.2 K. Assuming that the luminescence of the dipolar excitons directly reflects the coherence properties of the gas of interacting excitons, the discovered photon bunching at the onset of condensation, where the fluctuations of the exciton density and, consequently, of the luminescence intensity are most significant, indicates a phase transition in the interacting Bose gas of excitons, which is an independent way of detecting the Bose-Einstein condensation of excitons.     

Determination of the radiative lifetime of the d3Πg state of the C2 molecule by the laser-pyrolysis technique. A feasibility study

The feasibility is studied of using the laser-pyrolysis technique for determination of the radiative lifetimes of molecules.Measurements of time-resolved spectral emission were made on spatially resolved sections of the luminous plume produced by laser illumination of a graphite target in a vacuum. The nature of certain emission continua was investigated. The effects on C₂ Swan band emission of focal spot size, illumination power density, height and width of the plasma section observed and its distance from the target were studied. Conditions were determined for measuring physically significant radiative lifetimes for the d³Π_g, v=0 and v=1 levels, of C₂. In particular, the laser flux used was 3.8×10⁸W-cm^?2 while observations were made of a plume section from 0.5 to 0.7 mm from the target. The results, τ(0,0)=235±20 ns, τ(0,1)=250±20 ns, τ(1,0)=255±20 ns, are compared with those obtained by other methods. They are in good agreement with results obtained by pulsed electron excitation. Analysis of the experimental conditions in previous experiments using the laser-pyrolysis technique for measuring τ(d³Π_g of C₂ shows that they could not have lead to meaningful results of purely molecular properties.     

Dependence of nuclear deorientation on nuclear spin for recoils in vacuum

Time-integral measurements have been made of the vacuum deorientation of the 2⁺ and 4⁺ states in ¹⁵⁰Sm and the 6⁺ and 8⁺ states in ¹⁵⁶Gd Coulomb-excited by 133 MeV ³⁵Cl ions. The ¹⁵⁰Sm results were deduced from γ-ray angular distributions measured in coincidence with backscattered ³⁵Cl ions. In the ¹⁵⁶Gd measurements, a fixed counter array and a sandwich target were used to measure directly the differences between the γ-ray angular distributions from nuclei recoiling in vacuum and the unperturbed γ-ray angular distributions from nuclei stopped in a thick ¹⁵⁶Gd target. The measured deorientation time constants in ps are τ₂(2⁺) = 27±4; τ₂(4⁺) = 14±4; τ₂(6⁺) = 24±3; τ₂(8⁺) = 23⁺¹⁰_?6; τ₄(2⁺) = 12±2; τ₄(4⁺) = 5±3; τ₄(6⁺) = 7.6±2.5. The 8⁺ data were analyzed assuming τ₂/τ₄ = $\text{10}\text{3}$ as predicted by the Abragam-Pound theory for $\text{I ≧ 4}$ essentially independently of the degree of quadrupole admixture. The other results are consistent with this except for the 2⁺ level which shows some quadrupole effect. The present results, which show strong deorientation of high spin levels, are in contrast to earlier work on neutron deficient Er isotopes. In light of our findings we suggest that the failure to observe deorientation in the high spin states in Er is primarily due to anomalously low g-factors associated with the backbending observed in these nuclei.     

Comments on the measurements of vibrational intensity in the photoelectron spectra of N2 and CO,for the ionic ground state

Over 50 experimental values of the photoelectron intensity I(v′ = 1) (normalized to I(v′ = 0) equal to 100) for the N₂⁺, X²Σ_g⁺ photoelectron band, as well as 17 values of I(v′ = 1) for CO⁺, X²Σ⁺, are gathered or calculated from literature data, compared and discussed. Differences in the types of analyzer used, the instrumental conditions, the character of the UV light employed and the type of possible intensity corrections make such a comparison difficult, leave unexplained discrepancies and show the necessity of more systematic experimental investigations.     

Studying very light gravitino at the ILC

A collider signal with a stable gravitino of O(10) eV mass at the International Linear Collider (ILC) experiment is investigated. Such a light gravitino is generally predicted in the low-scale gauge mediation scenario of the supersymmetry breaking. We particularly focus on the case that the next lightest supersymmetric particle is stau, which eventually decays into a gravitino and a τ-lepton. With such a small gravitino mass, the lifetime of the stau is ¹⁰−15-¹⁰−11 s, and the produced stau decays before reaching the first layer of the inner detector of the ILC. It is shown, however, that the lifetime can be determined from the distribution of the impact parameter, which is obtained by observing charged tracks caused by decay products of the τ-lepton. This measurement also enables us to estimate the mass of the gravitino and determine the scale of the supersymmetry breaking. Based on a simulation study, we found that the lifetime can be measured when it is longer than ∼¹⁰−14 s and the stau mass is about 100 GeV.     

Expressions for the computer-evaluation of the four kernel functions for line formation with Doppler and Lorentz profiles

Rational approximations for the kernel functions K₁(τ), K₂(τ), M₁(τ) and M₂(τ) that describe the transfer of radiation scattered with complete redistribution over Doppler and Lorentz profiles have been obtained from their series and asymptotic expressions by the techniques of Padé approximants with a maximum relative error of less than 10^-4.     

Analysis of Depolarized Light Scattering from a Solution of Rod-Like Macromolecules Through A Laplace Transform Method

In this work, an analysis is made of the depolarized component of the light scattered by a solution of rod-like macromolecules by measuring the Laplace Transform (LT) of the time interval probability between successive photoelectrons, P(t). The study was performed in forward scattering conditions, which allows direct evaluation of the Rotational Diffusion Coefficient, Dr. Results were obtained by means of computer simulation and are compared with those obtained through the measurement of the second order correlation function, g⁽²⁾(τ), for the same experimental conditions.     

Spectral analysis by the method of consistent constraints

Two major challenges of numeric analytic continuation—restoring the spectral density, s(ω), from corresponding Matsubara correlator, g(τ)-are (i) producing the most smooth/featureless answer for s(ω), without compromising the error bars on g(τ), and (ii) quantifying possible deviations of the produced result from the actual answer. We introduce the method of consistent constraints that solves both problems.     

Lifetimes of some highly excited levels in the Pb-I spectrum measured by the hanle method

Natural lifetimes of some highly excited levels in the Pb-I spectrum have been measured by the zero field level crossing (Hanle) method. The levels were reached by optical excitation from the metastable 6p ^{2 3} P ₂ and 6p ^{2 3} P ₁ states, were a considerable population had been created by means of adc discharge in a Pb atomic beam. An atomic beam source producing atoms in metastable states is described. For the lifetimes τ of the investigated levels we find:τ(6p(1/2)6d ³ D ₁)=3.74(28) ns,τ(6p(1/2)6d ³ F ₂)=25.8(1.3) ns,τ(6p(1/2)6d ³ D ₂)=4.17_(?31) ^(?49) ns,τ(6p(1/2)6d ³ F ₃)=6.08(26) ns,τ(6p(3/2)7s)³ P ₂=5.85(27) ns. These results are compared with lifetimes derived from oscillator strengths given in the literature.     

Measurement of the spectral functions of vector current hadronic tau decays

A measurement of the spectral functions of non-strange τ vector current final states is presented, using 124 358 τ pairs recorded by the ALEPH detector at LEP during the years 1991 to 1994. The spectral functions of the dominant two- and four-pion τ decay channels are compared to published results of e ⁺ e ^- annihilation experiments via isospin rotation. A combined fit of the pion form factor from τ decays and e ⁺ e ^- data is performed using different parametrizations. The mass and the width of the ρ ^±(770) and the ρ ⁰(770) are separately determined in order to extract possible isospin violating effects. The mass and width differences are measured to be M _ρ ^± ₍₇₇₀₎ - M _ρ ⁰ ₍₇₇₀₎ = (0.0 ± 1.0) MeV/c ² and Γ _ρ ^± ₍₇₇₀₎ - Γ _ρ ⁰ ₍₇₇₀₎ = (0.1 ± 1.9) MeV/c ².     

Gyromagnetic ratios of the 4+ and 6+ rotational states of184W

The nuclear Larmor precession has been observed for the 2⁺, 4⁺ and 6⁺ rotational states of¹⁸⁴W in the hyperfine field of WFe by application of the TDPAC and the IPAC techniques. A carrier free radioactive source of^184m Re alloyed with high purity iron was used for all three measurements. From the Larmor precession observed in the 2⁺ state by TDPACω _L = 944(15) MHz and the knowng-factor the hyperfine fieldB _{300 K} ^hf (WFe)=?69.6(27)T was derived. The deviation from the result of a spin echo experiment with¹⁸³WFe extrapolated to room temperature may be caused by the Bohr-Weisskopf effect (hyperfine anomaly). IPAC measurements with the same sample polarized in an external magnetic field of 1.6T gave for the 4⁺ and 6⁺ rotational states: ω _L τ(4⁺)=0.0609(22) andω _L τ(6⁺)=0.00735(102). By use of experimentalB(E2)-values theg _R -factors were derived asg _R (4⁺)=+0.276(26) andg _R (6⁺)=+0.281(45). The directional correlation of the 537?384 keVγ-γ cascade has been analysed in terms of anE1/M2/E3 mixture for theK-forbidden 537keV transition. We obtained the mixing ratiosδ(M2/E1)=±0.086(16),δ(E3/E1)=?0.028(5) with the sign convention of Krane and Steffen.     

Pion condensation in symmetric nuclear matter

The problem of pion condensation in isospin symmetric nuclear matter is investigated in the framework of the σ-model with a residual nucleon-nucleon interaction (g′σ₁ · σ₂τ₁ · τ₂δ(x)) and Δ-isobars. The equation of state for the pion condensed phase is calculated and applied to a low-energy heavy-ion collision in the TDHF approximation. The effective particle-hole interaction and the response to spin-isospin excitation are used to determine the magnitude of the Landau-Migdal parameter g′. For a reasonable range of g′(0.5 < g′ ≦ in units of g²/4m²_N = 410 MeV · fm³) pion condensation occurs at densities above normal nuclear matter density and leads to an equation of state with no stable density isomer.     

Radiative decay and autoionization in the4 D-states of the 3d 94s5s configuration in CuI

The CuI 3d ⁹4s5s ⁴ D-states, which lie above the ionization limit, were populated by stepwise collisional and laser excitation. With respect to their total angular momentum, the⁴ D-states have completely different decay modes. Whereas the lifetimesτ(⁴ D _7/2)=8.2(4)·10^?9s andτ(⁴ D _1/2)=7.9(6)·10^?9 s are determinrd by radiative transitions and were measured by time-resolved spectroscopy, the lifetimesτ(⁴ D _5/2)=1.59(6)·10^?12s andτ(⁴ D _3/2)=1.28(5)·10^?12s are due to autoionization and were deduced from the widths of the excitation signals observed by ion detection.     

Theg-factor of the 8+ isomer of142Eu

Theg-factor of the 8⁺ isomer of¹⁴²Eu with mean lifeτ=9 ns, has been measured by the time-differential perturbedγ ray angular distribution (TDPAD) method. The 8⁺ isomer was populated with the reaction¹¹⁴Cd(³²S,p3n)¹⁴²Eu at 155 MeV. The obtained valueg(8⁺)=0.51(3) agrees with shell model calculations using effective single-particle moments taken from neighbouring nuclei. A main configurationπh_11/2?(vh _11/2)^?1 has been confirmed for the 8⁺ isomer.     

The g-factor of the yrast 4+ state in 20Ne from transient-field precession measurements

Transient field precessions of the first excited 2⁺ and 4⁺ states in ²⁰Ne nuclei traversing polarized gadolinium have been measured. The deduced g-factor of the 4⁺ state, g = + 0.08(20), agrees with our earlier reported value of g = ? 0.10(19) measured in iron by the same technique. The significant reduction in the value of the $\text{g-}\text{factor}\text{,}\text{g}\text{?}\text{= ? 0.01(14)}$, relative to that of the 2 ⁺ state, g = + 0.54(4), is incompatible with the pure T = 0 character expected for low-lying states in this self-conjugate nucleus. In addition, the lifetime of the 4⁺ state has been measured to be τ = 95(13) fs, in agreement with a previous measurement.     

A study of the γ-ray decays from single particle states in 91Zr and 93Mo

Lifetimes have been measured in ⁹¹Zr and ⁹³Mo by the Doppler shift attenuation method through the ⁹⁰Zr(¹³C, ¹²C)⁹¹Zr and the ⁹²Mo(¹³C, ¹²C)⁹³Mo reactions. Gamma rays were observed in coincidence with the back scattered particles and the reactions took place at sub-Coulomb energies. The lifetimes measured in ⁹¹Zr are τ(1205) = 250⁺⁹⁰_?70 fs, τ(1467) = 280⁺¹⁶⁰_?110 fs, τ(2042) < 30 fs, τ(2558) = 180⁺⁹⁰_?60 fs. The lifetimes measured in ⁹³Mo are τ(1361) = 170⁺⁸⁰_?40 fs, τ(1494) = 60 ± 40 fs, τ(1697) = 440⁺²³⁰_?130 fs, τ(2705)=160⁺⁸⁰_?60fs These results are compared with the expectations of the shell model and the $\text{3}\text{s}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{→ 2}\text{d}{}_{\mathrm{<mtext>5</mtext><mtext>2</mtext>}}\text{E}\text{2}$ transition is shown to be very enhanced.     

Measurement of theg-factor of the 21 + state of192Pt in an external magnetic field

Theg-factor of the 2₁ ⁺ state of¹⁹²Pt has been measured by the IPAC technique in an external magnetic field as:g(2₁ ⁺,¹⁹²Pt)=+0.287(17). An additional IPAC experiment with an¹⁹²IrFe sample was performed with the same level in order to investigate the hyperfine field. The result:ω _L τ(2₁ ⁺,¹⁹²PtFe)=0.1115(9) gives the hyperfine field:B _hf ^4.2k (PtFe)=126.8(71) T. The result of an LTNO experiment with the same level is compatible with the assumption that 100% of the¹⁹²Ir atoms were on unique sites.