The study of the proton-proton collisions at the beam momentum 1581 MeV/c

The new data on the elastic pp and single-pion production reaction pp → pnπ ⁺ taken at the incident proton momentum 1581 MeV/c are presented. To extract contributions of the leading partial waves the single-pion production data are analyzed in the framework of the event-by-event maximum-likelihood method together with pp → ppπ ⁺ data measured earlier and the pp → pnπ ⁺ data taken at 1628 MeV/c. The analysis shows that at 1581 MeV/c the largest contributions stem from the ³ P ₂, ³ P ₁, ³ P ₀ and ³ F ₂ initial partial waves. From these partial waves we also deduce contributions for the production of the Δ(1232) and N(1440) states.     

Measuring the weak charge of the proton at Jefferson Lab: A search for physics beyond the standard model

The JLab Q _weak Collaboration is designing and constructing an experiment to measure the proton’s weak charge, Q _W ^p , by measuring the parity violating asymmetry in elastic electron-proton scattering at very low momentum transfer. The standard model predicts Q _W ^p = 1 ? 4 sin² θ _w from the running of the weak mixing angle sin² θ _w , corresponding to a 10σ effect in the experiment. The experiment will determine Q _W ^p with 4% combined statistical and systematic uncertainties, which leads to 0.3% uncertainty in sin² θ _w . Installation of the experiment will begin in September 2009.     

Fourier transform infrared spectra of the FO2 radical

Six infrared bands of FO₂ have been measured at high resolution using a fast-flow long-path absorption cell and a Fourier transform spectrometer. The bands have been analyzed to obtain accurate band origins, as well as rotational, centrifugal distortion, and spin-rotation parameters. In order of increasing wavenumber they are ν₃ at 579 cm⁻¹, ν₂ + ν₃ at 940 cm⁻¹, 2ν₃ at 1142 cm⁻¹, ν₁ at 1487 cm⁻¹, ν₂ + 2ν₃ at 1496 cm⁻¹, and 2ν₁ at 2948 cm⁻¹. Only ν₃ has been studied previously (by C. Yamada and E. Hirota, J. Chem. Phys. 80, 4694–4700 (1984)); the other bands are rotationally analyzed here for the first time. The ν₁ and ν₂ + 2ν₃ vibrations were found to be strongly mixed by Coriolis- and Fermi-type interactions and were thus analyzed simultaneously. 2ν₁ was also observed to be perturbed, but the perturbations were not analyzed. FO₂ now becomes one of the best-characterized unstable free radicals in terms of its rotation-vibration structure.     

Br NQR relaxation of the mixed-valence compound (NH4)4SbIIISbVBr12

⁸¹Br NQR measurements of the mixed-valence compound (NH₄)₄Sb^III Sb^VBr₁₂, which has Sb^VBr₆ ^? and Sb^IIIBr₆ ^3? octahedra in different oxidation states in the tetragonal pseudo-K₂PtCl₆ structure, were carried out by pulse method in the temperature range between 80 and 300 K. The phase transition temperature of T _c = 212 K was redetermined. The T ₁ values are quite different between Sb^VBr₆ ^? and Sb^IIIBr₆ ^3? octahedra. For all resonance lines T ₁ minima were observed at T _c. The T ₁ behavior at T _c was explained by a softening of the rotary lattice mode around a principal axis of each octahedron along the c axis of the crystal. The distinctive feature in the temperature dependence of both ⁸¹Br NQR frequencies and T ₁ values for each anion indicates that the static rotation may occur for Sb^VBr₆ ^? but not for Sb^IIIBr₆ ^3? at T _c in the low temperature phase.     

Wavenumbers,line strengths,and assignments in the Doppler-limited spectrum of formaldehyde from 2700 to 3000 cm−1

The spectrum of H₂CO from 2700 to 3000 cm^?1 has been examined at Doppler-limited resolution using a tunable difference frequency laser spectrometer at Lincoln Laboratory. The wavenumbers and strengths of 4350 absorptions have been determined with an accuracy of 0.001 cm^?1 and 5%, respectively. These data have been incorporated into the analysis of lower-resolution data from Florida State University to assign 72% of the observed absorptions to one of seven bands: ν₃ +ν₄ (a C-type band at 2655 cm^?1), ν₃ + ν₆ (a B-type band at 2719.156 cm^?1), ν₁ (an A-type band at 2782.457 cm^?1), ν₅ (a B-type band at 2843.326 cm^?1), ν₂ + ν₄ (a C-type band at 2905 cm^?1), 2ν₃ (an A-type band at 2999.5 cm^?1) and ν₂ + ν₆ (a B-type band at 3000.066 cm^?1). The band ν₃ + ν₄ has been observed for the first time, and the band center for 2ν₃ has been corrected from a value of 2972 cm^?1 to the value listed above. The effects of strong Fermi and Coriolis resonances on the spectra are discussed.     

Results from the NOMAD experiment

The NOMAD experiment has sought ν_μ ? ν_τ oscillations by looking for the emergence of τ^? in events from the CERN SPS neutrino beam. With some improvements in the techniques of analysis in relation to the results published previously and with the inclusion of data from the 1998 run, no evidence for the oscillations has been found, which results in an updated limit on the oscillation probability [P(ν_μ → ν_τ) < 0.5 × 10^?3 at a 90% C.L.]. The corresponding limit on the oscillation mixing angle is given by sin²2θ_μτ < 1.0 × 10^?3 for large Δm ². By using a 1% contamination of ν_e in the neutrino beam, we can also rule out ν _e ? ν_τ oscillations and constrain the probability of the relevant transition as P(ν _e → ν_τ) < 3 × 10^?2 at a 90% C.L. (sin²2θ _eτ < 6 × 10^?2 at large Δm ²).     

Study of the ηπ+π− system centrally producedin the reactionpp→p f (ηπ+π−)p s at 300 GeV/c

The reactionpp→p _f (ηπ⁺π^?)p _s where the ηπ⁺π^? system is centrally produced has been studied at 300 GeV/c incident momentum at the CERN Ω spectrometer. The ηπ^± mass spectrum shows a strong δ/a ₀(980) signal having a mass of 984±4 and Γ=95±14 MeV. The ηπ⁺π^? mass spectrum shows η′ andf ₁(1285) signals over little background. A spin-parity analysis of the ηπ⁺π^? system shows evidence for aJ ^PC =1⁺⁺ peak at thef ₁(1285) mass but no evidence for the pseudoscalar states η(1270) andl/η(1440). No evidence is found for the ηππ decay of theE/f ₁(1420) meson for which we set an upper limit BR(E/f ₁(1420)→ηππ)<0.1 at 95% cl.     

Spin-Hamiltonian parameters and local rotational order parameters for Gd ion in the tetragonal phase of SrTiO3 crystal

Using a diagonalization method, the spin-Hamiltonian parameters (g factors g_||, g_⊥ and zero-field splittings b₂⁰, b₄⁰, b₂⁴, b₆⁰, b₆⁴) for Gd³⁺ ion at the 12-fold coordinated Sr²⁺ site in the tetragonal phase of SrTiO₃ at T≈4.2 and 77 K are calculated in a unified way. The calculated results are in reasonable agreement with the experimental values. The local rotational order parameters ?_l of Gd³⁺ center at the two temperatures are also obtained from the calculations. It is found that the local rotational order parameters ?_l of Gd³⁺ impurity center at both temperatures are different from the corresponding parameters ?_h in the host SrTiO₃ crystal and the changes of spin-Hamiltonian parameters with temperature are caused by the change of local rotational order parameter?_l with temperature. The results are discussed.     

Change in the size dependences of the surface properties of nanodiamond upon variation in the isotope composition

The isothermal-isomorphic dependences of the specific surface energy (σ), its isochoric temperature derivative (σ′), and surface pressure (P _sf) on the size of nanodiamonds ¹²C and ¹³C at 100 and 4300 K are calculated. It is shown that the ratio σ(¹²C)/σ(¹³C) decreases with decreasing size along both isotherms, and σ′(¹²C)/σ′(¹³C) increases with decreasing size, and this effect is higher at lower temperatures. The ratio P _sf(¹²C)/P _sf(¹³C) increases with decreasing size. The effect is stronger at higher temperatures.     

The magnetic moments and halflives of the 5/2− states in199Hg and197Hg and the discrepancies in the experimental hyperfine fields at Hg in Fe

The Larmor-precession frequencies for¹⁹⁷Hg in Fe have been determined to beω _L = 1291 ±25 MHz at 293 K andω _L = 1334±25 MHz at 105 K. For¹⁹⁹Hg in Feω _L =1372±50 MHz has been measured at 293 K. The half-lives of the 5/2^? states in¹⁹⁷Hg and¹⁹⁹Hg have been remeasured asT _1/2(¹⁹⁷Hg)=8.1±0.16 nsec andT _1/2(¹⁹⁹Hg)=2.45±0.05 ns, respectively. The magnetic moment of the 5/2^? 158keV state in¹⁹⁹Hg was redetermined by the integral perturbed angular correlation method in an external magnetic field of 47kG asμ(5/2 ^? ) = 0.905±0.091 nm. With this new value consistency for the magnetic hyperfine fields at Hg in Fe measured with the TDPAC-method and with the NMR/ON-method is obtained. This fact is used to determine theg-factors of the 5/2^? states in¹⁹⁷Hg and¹⁹⁹Hg more precisely fromω _L -values given above:g(¹⁹⁷Hg)=0.342(6);g(¹⁹⁹Hg)=0.352(13). The magnetic moments of the first excited 2⁺ states in^198–204Hg isotopes which rely on calibrations with the¹⁹⁹Hg-g-factor, are revised.     

A tunneling spectroscopy study of the temperature dependence of the forbidden band in Bi2Te3 and Sb2Te3

Tunneling measurements of dI/dV, d ² I/dV ², and d ³ I/dV ³ were formed along the C ₃ axis (normally to layers) for Bi₂Te₃ and Sb₂Te₃ layered semiconductors in the temperature range 4.2<T>29 5 K. Temperature dependences of the forbidden band energy E _g were obtained. The forbidden band energy in Bi₂Te₃ was 0.20 eV at room temperature and increased to 0.24 eV at T=4.2 K. The E _g value for Sb₂Te₃ was 0.25 eV at 295 K and 0.26 eV at 4.2 K. The distance between the top of the higher valence band of light holes and the top of the valence band of heavy holes situated lower was found to be ΔE _V≈19 meV in Bi₂Te₃; this distance was independent of temperature. The conduction bands of Bi₂Te₃ and Sb₂Te₃ each contain two extrema with distances between them of ΔE _c≈25 and 30 meV, respectively.     

Longitudinal and transverse contributions to the threshold cross-section slope of single-pion electroproduction by a proton

The cross sections of inelastic electron scattering are measured near the threshold of single-pion production by a proton at k²=2.5, 3.5, 5.0 and 8.0 fm^? in the polarization range of the virtual photon ?=0.3–0.9. The separation of the |E₀₊|² and k²|S₀₊|² contributions to the cross-section slope at threshold is carried out and thus a new method of determining the F_A and F_π form factors is realized. The values for the axial mass and mean-square radius of the pion are obtained.     

Search for P-ODD asymmetry in the radiative cross-section of the interaction of neutrons with lead nuclei

The P-odd effect in the radiation cross section of capture of longitudinally polarized neutrons in a sample of natural lead is measured. The experiment was performed at PF1B facility at the Institut Max von Laue-Paul Langevin. The neutron polarization P _n was 92%, the total flux of polarized neutrons was ～3 × 10¹⁰ n/s, and the mean neutron wavelength was λ = 4.7 Å. Taking into account “0-test” we estimated the asymmetry: a _γ(^natPb) = (2.3 ± 3.5) × 10^?7, i.e., α _γ ≤ 8.1 × 10^?7 at 90% confidence level.     

Study of the elastic stiffness constants of thiourea by Brillouin scattering

All the elastic stiffness constants of thiourea have been measured at room temperature. The value of C₆₆(0.7 × 10¹⁰dynes/cm²) is very low. The C₁₁ and C₃₃ constants exhibit discontinuities at 169 and 202 K. The longitudinal acoustic phonons propagating in the c direction are very strongly damped in the vicinity of 202 K.     

Effects of the overlap between wave functions of impurity centers on the activation energy of hopping conduction

The hopping conductivity σ₃ has been studied in samples of slightly counterdoped crystalline Si: B with a boron concentration of 2×10¹⁶ cm^?3<N<10¹⁷ cm^?3 and a compensation of 10^?4≤K≤10^?2. It is found that at K≤10^?3 the activation energy ε₃ is not lower (as it must be according to classical notions at finite K) but larger than the value ε_N=e ² N ^1/3/κ, where e is the electronic charge and κ is the dielectric constant. With decreasing N, the energy ε₃ drops slower and, with decreasing K, grows faster than follows from the standard theory. At K≤10^?4, ε₃ is higher than ε _N by a factor of 1.5–2. The result is explained by the effect of the overlap between wave functions of neighboring impurity centers on the structure of the impurity band.     

Diagnostics of the solar corona structure by the refraction effects on radio emission

The solar disc radio brightness distribution observed at RATAN-600 can be interpreted as the angular directivity of the disk center emission at viewing anglesΘ=arcsin(R/R₀) over an angular range of R<0.9R ₀ at several wavelengths in the 2.0–32 cm region. These spectra can be treated as an emission enhancement due to refraction effects in free-free corona emission. The model simulations show good agreement with the observations and lead to estimation of the electron density N_e=1·10 ⁹ cm^?3 and emission measureEM=6·10 ²⁶ cm^?5 for the quiet Sun.     

Neutron-interferometric measurement of the coherent scattering length of the isotopes of silver

Employing a new measuring scheme with the D 18 Neutron Interferometer at the ILL, Grenoble, the thermal neutron coherent scattering lengthb _c for bound atoms of natural Ag,¹⁰⁷Ag and¹⁰⁹Ag have been measured at the wavelengthλ=1.8742 Å. The results, corrected for composition and density of the actual samples, are nat Ag:b _c =5.922 (7) fm¹⁰⁷Ag:¹⁰⁷ b _c =7.555 (11) fm¹⁰⁹Ag:¹⁰⁹ b _c =4.165 (11) fm The result is in agreement with an earlier value obtained with the interferometer for nat Ag (5.932 (6)) using a different measuring scheme and a totally different sample. For nat Ag and¹⁰⁷Ag the values determined interferometrically are ?0.05 and ?0.08 fm smaller, repectively, than those measured with the Christiansen filter method.     

The effect of fast neutron irradiation on the optical modulation spectra of GaAs

The electroreflectance and wavelength-modulated reflectance spectra of GaAs were measured before and after several reactor irradiation periods. High resistivity n type GaAs crystals were irradiated at a temperature between 300 and 310 K up to a fast neutron fluence of 3.3 × 10¹⁷n/cm². The E₀ and E₀+Δ_o peaks shift nonlinearly toward lower energy, the change reaching a maximum value of about ? 50 meV at 10¹⁷n/cm². At this fluence an additional peak appears at 1.33 eV. The E₁ and E₁+Δ₁ peaks move almost linearly toward higher energy with increasing fast neutron fluence, the shift being about + 25 meV at 2 × 10¹⁷n/cm². The results are discussed taking into account infrared absorption measurements and the calculations made by McNichols, Hayes and Ginell concerning the metallic GaAs precipitates. The effect of possible internal stress produced by the fast neutron bombardment on the modulation spectra is also discussed.     

Two-nucleon T = 0 transfer reactions in the 0p shell

The ¹⁶O(d, α)¹⁴N, ¹⁴N(d, α)¹²C and ¹²C(d, α)¹⁰B reactions at E_d = 40MeV and the ¹²C(α d)1¹⁴N at E_α = 55 MeV were investigated. A total of seventeen transitions are analysed in terms of one-step, zero-range DWBA calculations, using the two-particle coefficients of fractional parentage obtained from the Cohen-Kurath Op shell wave functions. For most transitions, fair agreement is obtained between experiment and calculation, possible exceptions being the transition to the E_x = 4.43 MeV, J^π = 2⁺ state in ¹²C and to the E_x = 2.15 MeV, J^π = 1⁺ state in ¹⁰B, for which the calculations predict too much L = 0 strength. Where possible, a comparison with previous (p, ³He) results is made. In ¹⁴N a state at E_x = 11.04 MeV was observed for which the values (J_π; T) = (3⁺; 0) are suggested. In ¹²C we found, in addition to the well known T = 0 states, two relatively sharp T = 0 states at E_x = 19.50 ± 0.10 and 20.55 ± 0.10 MeV. The shape and strength of the angular distribution for the transitions to these states can be approximately accounted for by the calculations, although no one-to-one correspondence between observed and predicted levels could be established.