Primakoff effect: Synchrotron and coulomb mechanisms of axion emission

The Primakoff effect-induced radiative emission of axions by an alternating electromagnetic field, F _a → γa, is considered for the first time. The synchrotron mechanism and the Coulomb mechanism—in the latter case, the alternating field is formed when a charge executes an infinite motion in the field of a Coulomb center—are considered as specific examples. The contributions of these effects to the axion emissivity of magnetic neutron stars and of the Sun are estimated.     

Primakoff effect in $ \eta$ -photoproduction off protons

We analyse data on forward h \eta -meson photoproduction off a proton target and extract the h \eta ? \rightarrow g \gamma g \gamma decay width utilizing the Primakoff effect. The hadronic amplitude that enters into our analysis is strongly constrained because it is fixed from a global fit to available g \gamma p ? \rightarrow p h \eta data for differential cross-sections and polarizations. We compare our results with present information on the two-photon h \eta -decay from the literature. We provide predictions for future PrimEx experiments at Jefferson Laboratory in order to motivate further studies.     

A precision measurement of the neutral Pion lifetime via the Primakoff effect

The main parameters and technical features of the PrimEx experiment conducting in Jefferson Lab (USA) are presented. One of the main parts of the PrimEx setup-electromagnetic calorimeter is described in details. Value of π⁰ meson decay width into two γ-quanta, obtained from PrimEx 2004 year data is Γ(π^o → 2γ) = 7.82 eV 2.2% (stat.) 2.1% (syst.)     

电子-质子对撞机上的Primakoff物理

Primakoff效应具有独特的动力学筛选条件,是研究原子核和粒子物理的强大的实验工具。未来电子-离子对撞机(EIC)机器具有质心能量高、亮度高、动力学范围广、本底低、探测器探测效率高以及碰撞离子种类丰富等优点。这将为我们开启一扇通往Primakoff物理研究的新时代的大门。在EIC机器上开展Primakoff物理实验可以严格检验量子色动力学的基本对称性,研究强子的电弱相互作用性质,并探索超出标准模型的新物理。Primakoff效应实验是EIC物理研究的又一亮点。     

eta-->gammagamma decay width via the Primakoff cross section

Incoherent eta photoproduction in nuclei is evaluated at forward angles within 4 to 9 GeV using a multiple scattering Monte Carlo cascade calculation with full eta-nucleus final-state interactions. The Primakoff, nuclear coherent and nuclear incoherent components of the cross sections fit remarkably well previous measurements for Be and Cu from Cornell, suggesting a destructive interference between the Coulomb and nuclear coherent amplitudes for Cu. The inelastic background of the data is consistently attributed to the nuclear incoherent part, which is clearly not isotropic as previously considered in Cornell's analysis. The respective Primakoff cross sections from Be and Cu give Gamma(eta-->gammagamma)=0.476(62) keV, where the quoted error is only statistical. This result is consistent with the Particle Data Group average of 0.510(26) keV and in sharp contrast (approximately 50%) with the value of 0.324(46) keV obtained at Cornell.     

New limits on Primakoff production of hybrid mesons

I discuss constraints on properties of isoscalarJ ^PC =1^?+ exotic hybrid mesons, assuming their dominant decay mode is ηπ. This work expands on a similar study by the Rochester-Minnesota-Fermilab collaboration, which excluded ?π as the dominant decay channel for such hybrids. The experimental limits are based on Primakoff production of such states and on a VDM argument relating their radiative widths to their ?π decay modes. Using data on coherent production of ηπ⁺ systems in π⁺ collisions with nuclei, I obtain few percent limits on the ?π branching ratios for hybrid masses ?1.5 GeV.     

Measurement of electric and magnetic polarizabilities with Primakoff reaction at COMPASS

The COMPASS spectrometer is well suited to perform precise measurements of the pion polarizabilities via the Primakoff reaction π(Z,A)→π+(Z,A)+ψ. The electric\((\bar \alpha _\pi )\) and magnetic\((\bar \beta _\pi )\) polarizabilities characterize the response of the response of the pion quark substructure to the electromagnetic field of the ψ during the πψ scattering. The results of a simulation for the foreseen 2004 setup are presented. The measurement of the pion polarizabilities allows for a test of the chiral perturbation theory (χPT) predictions.     

The Primakoff reaction study for pion polarizability measurement at COMPASS

The electromagnetic structure of charged pions can be described by the electric (α_π) and magnetic (β_π) polarizabilities that depend on the rigidity of pion’s internal structure as a composite particle. It is shown that the values of α_π and β_π can be precisely measured via the Primakoff reaction π⁻ + (A, Z) → π⁻ + (A, Z) + γ in the COMPASS experiment at CERN.     

Anomeric effect plays a major role in the conformational isomerism of fluorinated pnictogen compounds

According to our theoretical studies, the anomeric effect, an stereoelectronic interaction between lone pair and a vicinal antibonding orbital, has shown to contribute decisively for the conformational isomerism of 1‐fluoro‐N,N‐dimethylmethanamine ( 1 ) and of its corresponding P, As and Sb analogues ( 2 – 4 ). C? X bonds in 2 – 4 are larger than in the parent compound 1 , thus providing a LP_X/C? F^* interaction progressively weaker on going from 1 to 4 . However, such hyperconjugation contributed by more than 1.3 kcal mol^?1 for the stabilization of anti conformer in 4 (θ_{LP? X? C? F} = 180°), increasing to 24.1 kcal mol^?1 in 1 . An isodesmic reaction model supported these findings. Copyright © 2008 John Wiley & Sons, Ltd.     

Search for solar axions generated by the Primakoff effect with resonance absorption by <Superscript>169</Superscript>Tm

We searched for resonant excitation of the first excited state of the ¹⁶⁹Tm nucleus by axions formed inside the Sun by the Primakoff effect, A + ¹⁶⁹Tm → ¹⁶⁹Tm* → ¹⁶⁹Tm + γ (8.41keV). Gamma quanta with an energy of 8.41keV were registered by a sectionalized Si(Li) detector installed in a low-background setup. As a result, we set a new upper limit for the photon to axion coupling constant, g _Aγ (GeV⁻¹)m _A (eV) ≤ 1.06 × 10⁻⁵, which for a hadronic axion model corresponds to a mass limit of m _A ≤ 169 eV at a 90% confidence level.     

Rotational isomerism in aldehydes

A study is made of the Rydberg levels in CH₂ and CH₃ which are associated with the outer electron in a carbon 3d-orbital. A preliminary discussion of some Rydberg states in the lithium atom showed that penetration and exchange effects between the Rydberg orbital and the core were of comparable magnitude, and strongly dependent on the correct form of the Rydberg orbital wave function in the region where this overlaps the core. In the cases of CH₃ and CH₂ some conclusions of G. Herzberg about the symmetry of excited states where a 3d-orbital is involved have been confirmed, and certain other ionization potentials estimated. In CH₂ spin-orbit forces were included, but comparison with experiment is limited. The need to orthogonalize the Rydberg orbital to any core orbitals of similar overall symmetry, and to allow mixing with other orbitals (e.g. carbon 3s with carbon 3d₀) is stressed. One of the chief causes of error at present is our ignorance about the degree of validity of Koopman's theorem for situations of this kind. It is important to know to what extent the core changes its charge distribution after the ejection of the Rydberg electron.     

Density response and local field effect in the tight binding limit

The dielectric formalism is formulated for a general separable kernel in an arbitrary basis and representation. The underlying integral equation is in this case equivalent to an inhomogeneous set of linear equations. Applications to Fourier-space and real-space are presented. Furthermore it is explicitly demonstrated for the static case that in the tight binding limit local field effects do not give rise to the classical Lorentz-Lorenz relation as previously found.     

Partial conservation of seniority and nuclear isomerism

We point out the possibility of the partial conservation of the seniority quantum number when most eigenstates are mixed in seniority but some remain pure. This situation occurs in nuclei for the g(9/2) and h(9/2) shells where it is at the origin of the existence of seniority isomers in the ruthenium and palladium isotopes. It also occurs for f bosons.     

Density of states effect on resonant tunneling

We study the effect of a gaussian type of density of states distribution on the conductance of a thin amorphous junction in the presence of localized states. The absolute value of the conductance is strongly affected by the width of the distribution but is sensitive to the center of the distribution only in the case of narrow distributions. All these effects disappear once we normalize the conductance to its zero field value.