The equivalent photon approximation for coherent processes at colliders

We consider coherent electromagnetic processes for colliders with short bunches, in particular the coherent bremsstrahlung (CBS). CBS is the radiation of one bunch particles in the collective field of the oncoming bunch. It can be a potential tool for optimizing collisions and for measuring beam parameters. A new simple and transparent method to calculate CBS is presented based on the equivalent photon approximation for this collective field. The results are applied to theφ-factoryDAΦNE. For this collider about 5·10¹⁴ d E _γ/E _γ photons per second are expected in the photon energyE _γ range from the visible light up to 25 eV.     

The equivalent photon approximation for coherent processes at colliders

We consider coherent electromagnetic processes for colliders with short bunches, in particular the coherent bremsstrahlung (CBS). CBS is the radiation of one bunch particles in the collective field of the oncoming bunch. It can be a potential tool for optimizing collisions and for measuring beam parameters. A new simple and transparent method to calculate CBS is presented based on the equivalent photon approximation for this collective field. The results are applied to theφ-factoryDAΦNE. For this collider about 5·10¹⁴ d E _γ/E _γ photons per second are expected in the photon energyE _γ range from the visible light up to 25 eV.     

Coherent bremsstrahlung at the HERA collider

We consider a new type of radiation at colliders with short bunches—coherent bremsstrahlung (CBS) which is the radiation of the first bunch particles caused by the collective electromagnetic field of the second bunch. The number of CBS photons for a single collision isdN _λ ≈N ₀ dE _λ /E _λ > in the energy rangeE _λ ?E _c = 4γ ₁ ² ?c/l ₂. Hereγ ₁=E ₁/m ₁ c ²;l ₂ is the length of the opposing (second) bunch andN ₀ is proportional toN ₁ N ₂ ² whereN _j is thej-th bunch population. For the HERA colliderN ₀=14,E _c =73 eV in the case when photons are emitted by protons andN ₀=6·10⁷,E _c =24 keV—when photons are emitted by electrons. Unusual properties of such a coherent bremsstrahlung and the possibility to use CBS for fast beam steering and for luminosity optimization are discussed.     

Quantum effects in radiation on short bunches

The radiation caused by particles of one bunch in the collective electromagnetic field of the short oncoming bunch is studied. Quantum effects are calculated for the spectrum of radiated photons. Using this spectrum, the dependence of the relative energy loss δ on a quantum parameter K is discussed. It is shown that the behaviour of δ changes considerably with the increase of that parameter. In the classical regime (K ? 1) the energy loss is proportional to the incoming particle energy, while in the extreme quantum regime (K ? 1) the energy loss becomes a constant. The coherent e⁺e^? pair production for γe colliders as cross-channel to CBS is considered.     

Process ν → νγ in strong magnetic field with allowance for posironium contribution to photon dispersion

We have studied the radiative decay of neutrinos with relatively high energies E ? m _e in a strong magnetic field taking into account the effect of a bound electron-positron pair (positronium) on photon dispersion. The allowance for the positronium contribution to the polarization operator of the photon substantially modifies the dispersion relation for the photon and the amplitude of the process in the vicinity of the cyclotron resonance. It is shown that the probability of the ?? ?? ??? process considerably increases when the positronium contribution is taken into account.     

Coherent production of photons by neutrinos

The reaction ν+N→ν+N+γ, involving the coherent emission of a photon in a neutrino-nucleus collision, can produce “single shower” events that simulate the reaction ν+e→ν+e. The ratio of coherent photons to electrons (for an ²⁷Al target) is estimated to be 40% at E_ν=20GeV and 10% at E_ν=20 GeV. We examine the extent to which the “excess” of showers seen in the Aachen-Padova experiment could be understood by this mechanism.     

Stimulated Raman scattering in natural crystals of SrSO4, BaSO4 and PbSO4: High-order Stokes and anti-Stokes generation with?single-wavelength UV, visible, and near-IR excitation, as?well?as cascaded up-conversion nonlinear �� (3)?�� (3) lasing effects under dual-wavelength picosecond collinear coherent pumping

Orthorhombic crystals of SrSO₄, BaSO₄, and PbSO₄, known as natural crystals celestine, barite, and anglesite, were found to be attractive ?? ⁽³⁾-active nonlinear optical materials. High-order Stokes and anti-Stokes picosecond generation that spans almost two octaves has been recorded with single-wavelength laser excitation in the UV, visible, and near-IR ranges. All recorded Raman induced lasing components were identified and attributed to the SRS-promoting vibration modes of the studied crystals (?? _SRS??999?cm^?1 for SrSO₄,?? _SRS??985?cm^?1 for BaSO₄ and ?? _SRS??977?cm^?1 for PbSO₄). Under dual-wavelength (?? _f1=1.06415???m + ?? _f2=0.53207???m) collinear coherent picosecond pumping several new manifestations of cascaded ?? ⁽³⁾??? ⁽³⁾ nonlinear up-conversion lasing effects were observed in BaSO₄ and SrSO₄ crystals. We classify all three studied sulfate crystals as promising SRS-active materials for Raman laser frequency converters and as efficient ?? ⁽³⁾-crystals that efficiently generate Stokes and anti-Stokes frequency combs, which can enable experiments of ultra-short pulse syntheses.     

Mössbauer spectroscopy and DFT calculations on all protonation states of the 2Fe-2S cluster of the Rieske protein

The Thermus thermophilus Rieske protein (TtRP) contains a 2Fe-2S cluster with one iron (Fe-Cys) coordinated by four sulfur atoms (2xS^2? and 2xCys) and one iron (Fe-His) by two sulfur and two nitrogen atoms (2xS^2?, His134 and His154). Here, the protein is investigated at three pH values (6.0, 8.5 and 10.5) in order to elucidate the protonation states of the His-ligands. Examination of the effect of protonation on the electronic structure of the cluster via Mössbauer spectroscopy gives a deeper understanding of the coupling of electron transfer to the protonation state of the His-ligands. Two components (1 referring to Fe-Cys and 2 to Fe-His) with parameters typical for a diamagnetic [2Fe-2S]²⁺ cluster are detected. The Mössbauer parameters and the protonation state clearly correlate: while δ remains almost pH-independent with δ ₁ (pH6.0) =?0.23 (±?0.01) mms^??1 and δ ₁ (pH10.5) =?0.24 (±?0.01) mms^??1 for Fe-Cys, it decreases for Fe-His from δ ₂ (pH6.0) =?0.34 (±?0.01) mms^??1 to δ ₂ (pH10.5) =?0.28 (±?0.01) mms^??1. ΔE _Q changes from ΔE _Q1 (pH6.0) =?0.57 (±?0.01) mms^??1 to ΔE _Q1 (pH10.5) =?0.45 (±?0.01) mms^??1 and from ΔE _Q2 (pH6.0) =?1.05 (±?0.01) mms^??1 to ΔE _Q2 (pH10.5) =?0.71 (±?0.01) mms^??1. Density functional theory (DFT)-calculations based on the crystal structure (pdb 1NYK) (Hunsicker-Wang et al. Biochemistry 42, 7303, 2003) have been performed for the Rieske-cluster with different His-ligand protonation states, reproducing the experimentally observed trend.     

Pseudo volume plasmon in arrays of doped and un-doped semiconductors

We present a theoretical work which shows that for a metamaterial consisting of a periodic array of doped and un-doped semiconductors it is possible to define a frequency ?? _t corresponding to a pseudo volume plasmon. ?? _t?depends on the thicknesses and on the dielectric constants of the components of the metamaterial and on the plasma frequency of the doped semiconductor. As its homologue in noble metal, the pseudo volume plasmon is the collective oscillation of charges present in the metallic part of the metamaterial leading to a pure longitudinal electric wave. We show that ?? _t is the degeneracy frequency between the anti-symmetric mode in a transverse magnetic field and the mode in a transverse electric field. We demonstrate that this degeneracy is due to the periodicity of the structure, which transforms the imaginary solution of a metal?Cdielectric interface into a real solution in the case of the periodic metamaterial.     

The Excited Triplet State of Azoalkanes: Electron Spin Polarization and Magnetic Field Effects During Triplet-Sensitized Photolysis of trans-Azocumene in Solution

The triplet-sensitized photodecomposition of azocumene into nitrogen and cumyl radicals is investigated by time-resolved electron paramagnetic resonance and absorption spectroscopy. The radicals are found to be created spin polarized with a yield depending on the strength of the applied magnetic field. The phenomenon arises because in triplet azocumene, the decay into radicals competes with a fast triplet-sublevel selective intersystem crossing back to the azocumene ground state. The size of the initial spin polarization of the radicals and the magnetic field effect on their yield are determined in solvents of different viscosities. Data analysis yields rate constants for the intersystem crossing and the cleavage reaction of triplet azocumene as well as its zero-field splitting D _ZFS. At room temperature in nonpolar solvents, the most probable values are: k _x ?=?k _y ?=?1.2?×?10¹¹?s^?? and k _z ?=?1.9?×?10¹⁰?s^?? for the intersystem crossing from the energetically lower and upper triplet substates, respectively, k _p ?=?1.6?×?10⁹?s^?? for the cleavage reaction and for the zero-field splitting D _ZFS?=???.4?×?10^10?s^?? (0.18?cm^??).     

Muon Capture on Deuteron and 3He

We present the results of a recent simultaneous study of the muon capture reactions ²H(?? ^?, ?? _?? )nn and ³He(?? ^?, ?? _?? )³H. The initial and final A = 2 and 3 nuclear wave functions are obtained from the Argonne v ₁₈ or chiral N3LO two-nucleon potential, in combination with, respectively, the Urbana IX or chiral N2LO three-nucleon potential in the case of A?=?3. The weak current consists of polar- and axial-vector components. The former are related to the isovector piece of the electromagnetic current via the conserved-vector-current hypothesis. These and the axial currents are derived either in a meson-exchange or in a chiral effective field theory (??EFT) framework. In the first case, there is one parameter which is fixed by reproducing the Gamow-Teller matrix element in tritium ??-decay (GT^EXP). In the second case, the low-energy constants, two in the polar and one in the axial-vector current, are fixed, respectively, by reproducing the A?=?3 magnetic moments and GT^EXP. The total rates are found to be 392.0 ± 2.3 s^?1 for A?=?2, and 1484 ± 13 s^?1 for A?=?3, where the spread accounts for the model dependence relative to the adopted interactions and currents (and cutoff sensitivity in the ??EFT currents).     

Preparation and characterisation of isotopically enriched Ta2O5 targets for nuclear astrophysics studies

Level energies in two-quasiparticle (2qp) structures in ¹⁵⁶ ₆₁Pm₉₅ are evaluated using the phenomenological rotor-particle model for odd-odd deformed nuclei with the inclusion of the residual p-n interaction contribution. Using these results as location guides, the experimental data from a recent ¹⁵⁶Nd decay study are used to construct a level scheme for ¹⁵⁶Pm with excitation energies upto 550 keV, wherein 26 (out of 30) ????s reported in ¹⁵⁶Nd decay are incorporated. Spin-parities and configuration assignments are suggested for 15 levels, in addition to the two isomers, in this energy domain. These investigations point to the need for information on higher-energy ????s and on ??-?? and ??-?? coincidence data from ¹⁵⁶Nd ??-decay to confirm these assignments.     

Optical anisotropy of orthorhombic InS

The optical anisotropy of InS single crystals in the range of photon energy from 1.8 to 3.5 eV has been studied by absorption, electroreflectance and wavelength-derivative reflectance measurements. These systematic optical measurements for the polarizations, E//a and E//b, have revealed that the transition at the fundamental absorption edge of InS is allowed for E//b, and there exist three distinct doublet transitions having different selection rules in the photon energy region from 2 to 3.5 eV; Bo and B^'₀doublet allowed only for E//b, A₀ and A^'₀ allowed only for E//a, and E₁ and E^'₁ allowed for both polarizations. The observed results are discussed based on the anisotropic nature of two chemical bonds in InS, cation-cation and cation-anion.     

O−−-Lücken-Dipole in Rubidiumhalogenidkristallen

Dielectric loss measurements are reported for RbCl, RbBr, and RbJ crystals containing O^??ions. The frequency and temperature dependence can be approximated by a Debye curve. The dipole moment is interpreted as being due to O^?? ions associated with anion vacancies. Activation energies for reorientation of the dipole are 0.60 eV for RbCl, 0.56 eV for RbBr, and 0.50 eV for RbJ. The deviations of the experimental dielectric loss curves from a Debye curve are interpreted. The dielectric losses decrease and the center uv absorption changes during annealing due to association of the centers into aggregates. A detailed analysis of the kinetics for RbBr indicates the formation of O^??-pair centers as the first step. The activation energy for association isE ₂=0.79 eV.     

Bounds for Entanglement via an Extension of Strong Subadditivity of Entropy

Let ?? ₁₂ be a bipartite density matrix. We prove lower bounds for the entanglement of formation E_f(?? ₁₂) and the squashed entanglement E_sq(?? ₁₂) in terms of the conditional entropy S ₁₂ ? S ₁ and prove that these bounds are sharp by constructing a new class of states whose entanglements can be computed, and for which the bounds are saturated.     

Nonlinear model-Boltzmann equations and exact solutions

The present paper is devoted to the subject of photonuclear reactions of the type (γ, p), (γ, n), (γ, np), (γ, nn), (γ, pp) as well as nucle on capture reactions as (p, γ) at intermediate photon energies. The theoretical part of this paper reviews and extends earlier calculations of the authors up t gamma energies of E_γ ≈ 400 MeV. The paper is not intended to give a review on different theoretical approaches which have been underta ken in the past. Instead, emphasis is put on the dynamical aspects of the photonuclear reactions in order to see which elementary processes govern the reactions at different photon energies. In view of the success of the present treatment up to E_γ ≈ 120 MeV photon energy, we tempt the predictive power of the model up to photon energies of E_γ ≈ 400 MeV for the reactions in ⁴He and ¹⁶O.     

Muon Capture on Light Nuclei

This work investigates the muon capture reactions ²H(?? ^?, ?? _?? )nn and ³He(?? ^?, ?? _?? )³H and the contribution to their total capture rates arising from the axial two-body currents obtained imposing the partially-conserved-axial-current (PCAC) hypothesis. The initial and final A = 2 and 3 nuclear wave functions are obtained from the Argonne v ₁₈ two-nucleon potential, in combination with the Urbana IX three-nucleon potential in the case of A?=?3. The weak current consists of vector and axial components derived in chiral effective field theory. The low-energy constant entering the vector (axial) component is determined by reproducting the isovector combination of the trinucleon magnetic moment (Gamow-Teller matrix element of tritium beta-decay). The total capture rates are 393.1(8) s^?1 for A = 2 and 1488(9) s^?1 for A?=?3, where the uncertainties arise from the adopted fitting procedure.     

Quantum physics of an elementary system in de Sitter space

We present the coherent states of a scalar massive particle on 1+3-de Sitter space. These states are vectors in Hilbert space, and they are labeled by points in the associated phase space. To do this, we use the fact that the phase space of a scalar massive particle on 1+3-de Sitter space is a cotangent bundle “T ^?(S ³)” which is isomorphic with the complex sphere “ $S_{\mathbb{C}}^{3}We present the performances of a 330?g zinc molybdate (ZnMoO₄) crystal working as scintillating bolometer as a possible candidate for a next generation experiment to search for neutrinoless double beta decay of ¹⁰⁰Mo. The energy resolution, evaluated at the 2615?keV ??-line of ²⁰⁸Tl, is 6.3?keV FWHM. The internal radioactive contaminations of the ZnMoO₄ were evaluated as <6???Bq/kg (²²⁸Th) and 27±6???Bq/kg (²²⁶Ra). We also present the results of the ?? vs ??/?? discrimination, obtained through the scintillation light as well as through the study of the shape of the thermal signal alone.     

Resonance structure of strength functions for first-forbidden β +/EC transitions

Experimental data obtained by measuring the fine structure of the strength function S _?? (E) in spherical and deformed nuclei were analyzed. The use of modern nuclear-spectroscopy methods made it possible to reveal the nuclear-deformation-induced splitting of peaks in S _?? (E) for transitions of the Gamow-Teller type. For first-forbidden transitions, the resonance nature of S _?? (E) was proven experimentally both for spherical and for deformed nuclei. It is shown that, at some values of the excitation energy, the intensity of first-forbidden transitions in nuclei can be commensurate with the intensity of Gamow-Teller transitions.     

Total photonuclear absorption cross section for Pb and for heavy nuclei in the Δ-resonance region

The partial sum σ⁽²⁾(E_γ) = Σ_i?2 σ(γ, in…), representing the inclusive cross section for all reaction channels in which at least two neutrons are emitted, has been measured with a quasimonochromatic photon beam obtained by the in-flight annihilation of monoenergetic positrons, and neutron multiplicity counting. These experimental results, taken with photon energies E_γ from 145 up to 440 MeV for Pb and with photon energies E_γ= 235 MeV and 330 MeV for Al, Cu, Zr, Sn, Ho, Ta and U, are subsequently used to determine the total photonuclear absorption cross section σ(tot: E_γ) and to study the dependence upon the mass number A of the normalized cross section σ(tot: E_γ)/A. These results are then compared with other information on the total photonuclear absorption cross section.