Lamb-Mössbauer factor in the spin crossover compound Fe(tpa)(NCS)2

The Lamb-Mössbauer factor in spin crossover compounds has been the subject of controversial discussions in the literature. For several compounds, a significantly larger Lamb-Mössbauer factor for the complex molecules in the low-spin (f _ls) than in the high-spin (f _hs) state has been reported, while for compounds studied in our laboratory such differences could not be observed. We prepared the compound Fe(tpa)(NCS)₂, thef factors of which were reported to be very different. We could not prove thef factors of this compound to be different. The implications of a different structural phase of compound prepared by us are discussed.     

The deformation producing tendency of (d 3/2−f 7/2) empirical effective interaction

The effective matrix elements in (d _3/2−f _7/2)² configuration have been recently defined by Erskineet al. and Sherret al. assuming shell clcsures for S³² and Ca⁴⁰. We have attempted to verify whether this empirically deduced (d _3/2−f _7/2)² interaction permits thed _3/2 shell to remain closed when nucleons are added to Ca⁴⁰. It is found that the Erskine interaction gives rise to ground states of thef _7/2 shell nuclei in which thed _3/2 orbit is completely filled. However that interaction over-binds Ca⁴⁰. If the centroid of the (d _3/2)² interaction is modified to fit the Ca⁴⁰ binding energy, the ground states of Cr⁴⁸ and Fe⁵² become deformed and thed _3/2 orbit is not completely filled.     

The interplay of theK + K − atom and thef 0(975) resonance

We predict that production of theK ⁺K^– atom inpd ³ He X and similar reactions exhibits a drastic missing mass spectrum due to the interplay withf ₀(975) resonance. We point out that high precision studies of theK ⁺K^– atom may shed a new light on the nature off ₀(975).Communicated by: B. Povh     

The reaction Pomeron-Pomeron →π + π − and an unusual production mechanism for thef 2 (1270)

Data are presented on Pomeron-Pomeron interactions which produce a centralπ ⁺ π ^? system in proton-proton collisions at \(\sqrt s = 62 GeV\) at the CERN Intersecting Storage Rings. This process may favor the production of gluonic bound states. A partial-wave analysis of theπ ⁺ π ^? system shows evidence for the production of the statesf ₀(975),f ₀(1400), andf ₂(1270). The fitted mass for thef ₂(1270) is about 50 MeV below the world average. In addition, the production mechanism for thef ₂(1270) is uniquely different from that for the other final states in that there is a correlation between the outgoing protons. this is consistent with a picture of two-gluon exchange with thef ₂(1270) produced by gluon fusion, and could indicate that thef ₂(1270) has a glueball component.     

Correlations in pp-collisions and two-component models

Some general consequences of charge conservation inclusive sum rules for the correlation integralsf _kandf _0k are given. It is also pointed out that the energy dependence off _korf _0k is 〈n〉 ^k fork≤7 for pp-collisions and that the data suggest all thef _k andf _0k ’s are non-zero. Further, two-component models for the charge multiplicity distribution consistent with charge conservation, are considered and compared with the data for pp-collisions.     

Ionospheric effect of the magnetospheric substorms at middle latitudes

Summary A study is made of theF2-layer effect of magnetospheric substorms over the Mediterranean area using data from several ionospheric stations for selected events in the current sunspot cycle 21. The night-time enhancements in the critical frequency of theF2-layer (f ₀ F2) and the total electron content (TEC) have been found with both premidnight and postmidnightf ₀ F2 peaks and a subsequent decrease in the minimum virtual height of theF region (h′F). It is found that the enhancements occur through the nights under steady geomagnetic conditions and that the time at which it is seen at Rome and Grocka ionospheric stations is progressively earlier as geomagnetic activity increases. It has been further shown that this type of thef ₀ F2 night-time increases is not always accompanied by an increase in TEC, although the reverse holds true during the nights of increased substorm activity. The fact that the considerable variability inf ₀ F2, TEC andh′F at the onset of the substorm expansion are preceded by the ionospheric dynamics associated with these observations can be very useful in the identification of precursor indicative of short-term variations of ionospheric propagation conditions.     

The competition between fusion-fission and deeply inelastic reactions in the medium mass systems

The competition between fusion-fission and deeply inelastic reactions in the Cl + Ni system has been studied by investigating the exit channelQ-value dependence of theZ-distributions of fission-like fragments. TheZ-, kinetic energy- and angular distributions of the fission-like fragments produced in the³⁷Cl +⁶⁴Ni system atE _lab=170, 186 MeV and in the²⁸Si +⁷⁴Ge system atE _lab=176 MeV have been measured by counter telescopes. TheZ-distribution of the³⁷Cl +⁶⁴Ni system was found to be essentially the same as that of the³⁵Cl +⁶²Ni system at the same bombarding energy. It is shown that this result can not be explained by the statistical fusion fission model but is consistent with a deeply inelastic model. A systematic study of the fission-like phenomenon in this mass region indicates that the maximum angular momenta for fusion reactions as well as the minimum angular momenta for DIC can be reproduced by the Bass model in the sliding limit (f=1.0) while the maximum angular momenta for fully energy-damped deeply inelastic reactions are governed by the strong interaction radius as predicted by the successive critical distance fusion model. The significance of these results are discussed.Communicated by V. Metag     

Bethe-ansatz solution of the groundstate of a model for mixed-valent Ce and Yb impurities in metals

We consider an impurity model consistent of the 4f ⁰-singlet and a multiplet of total angular momentumj of the 4f ¹ configuration hybridized with conduction states of the metal. The model is solved by Bethe-ansatz and related to theU limit of the Anderson model. If thef-level is far below the Fermi level the equations are reduced to the Bethe-ansatz solution of the Coqblin-Schrieffer model. Approximate analytical results valid in the mixed valence regime are given. A numerical solution for the impurity groundstate energy,f-level occupancy and charge susceptibility as a function of thef-level energy and in the absence of a magnetic field is presented.On a Heisenberg fellowship of the Deutsche Forschungsgemeinschaft     

Radiative decay ofJ/ψ into γ π+ π−

The radiative decayJ/ψ → γ π⁺ π^? has been studied using the 8.6 millionJ/ψ produced in the DM2 experiment at the DCIe ⁺e^? storage rings at Orsay. The π⁺ π^? mass spectrum shows a cleanf ₂ (1270) signal, and the possible presence of two other states at thef ₂ (1720) andf ₄ (2030) masses. For thef ₂ (1270), the branching ratio BR(J/ψ →γf)xBR(f→π⁺ π^?) is measured to be (7.50±0.30±1.12)×10^?4, and the spin analysis prefers theJ=2 assignment, with helicity parametersx=0.83±0.06 andy=0.01±0.06. The existence of higher mass states is discussed.     

Structural phase transitions in Pd0.8 Si0.2 and Pd0.75 Si0.20 Ag0.05 alloys observed by pac

The phase transition in the alloys Pd_0.8 Si_0.2 and Pd_0.75 Si_0.20 Ag_0.05 have been investigated through the quadrupole interaction of¹¹¹Cd impurities. The quadrupole interactions were measured by means of the TDPAC technique from room temperature up to about 870 K. The variation of the quadrupole interaction with temperature in the alloy PdSiAg shows aT ^3/2 dependence below and above 629 K, with coefficientsB=5.43(25)·10⁻⁵ K^−3/2 andB=3.70(15)·10⁻⁵ K^−3/2, respectively. This demonstrates that the alloy undergoes a phase transition around 629 K. The existence of two electric field gradients observed in the alloy PdSi,V _zz (1)=3.47(54)·10¹⁷ V/cm² andV _zz (2)=2.29(36)·10¹⁷ V/cm², indicates that there are two different¹¹¹Cd sites. The corresponding fractionsf ₁ andf ₂ strongly depend on temperature. Below 520 K, most¹¹¹Cd nuclei are subject to the higher EFGV _zz (1) (f ₁≈70%), whereas above 520 Kf ₁ falls rapidly to zero andV _zz (2) becomes dominant. The temperature dependences of thef ₁ andf ₂ reveal a picture of the phase transition between the two crystal structures.     

Theoretical investigation into electron density redistribution in theS 0→S 1 transition for (H2O) n ,n=2–6, complexes with hydrogen bonding

The association of theH ₂ O molecule and the effect of UV radiation on complexes with hydrogen bonds were studied. Complete ab initio calculations of the S₀ and S₁ states were performed for the(H ₂ O) _n ,n=2–6, complexes. Changes in the effective atomic charges, bond orders, and electron densities on the bonds were analyzed. The analysis and the calculated cross sections of potential surfaces along theOH bonds reveal that one of theOH complex bonds is in decay. The electron excitation is shown to be localized at a molecule of the(H ₂ O) _n ,n=2–6, complex, while for theH ₂ O complexes withn>2 the excitation involves, for the most part, a freeOH _f bond of the water molecule that does not participate in the formation of the hydrogen bondO...H. A direct correlation is observed between the behavior of theOH _f bond and the changes in the atomic charges Q(O) and Q(H_f) reflecting the electron density redistribution. V. D. Kuznetsov Siberian Physical-Technical Institute at Tomsk State University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 8–12, May, 1999.     

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.     

Study of the centrally producer ππ andK \bar K systems at 85 and 300 GeV/c

We have studied the andK systems centrally produced in proton proton collisions at 300 GeV/c and ⁺/p proton collisions at 85 GeV/c using the CERN spectrometer. Clear evidence forS ^*/f _o(975) production is observed. An analysis performed on the ^{+ –} mass spectrum in the 1.0 GeV region, using a coupled channel formalism, shows that it is possible to describe theS ^*/f _o(975) effect with one single resonance once interference of theS ^*/f _o(975) with theS-wave background is introduced. The resultingS ^*/f _o(975) parameters arem _o =979±4MeV,g =0.28±0.04,g _K =0.56±0.18 corresponding to a pole position on sheet II at (1001±2)–i(36±4) MeV. Evidence is also found for a structure having a mass of 1472±12 MeV and a width of 195±33 MeV.     

Tests of the infinite mass effective theory and properties of the charming and beautiful mesons

Using an operator product expansion (OPE) in the inverse of the heavy quark massM _Q and a dispersive approach, we rederive theB andB ^* couplings and the Isgur-Wise function predicted by the infinite mass effective theory (IMET). We find that, at the subtraction pointM _Q and using VDM for the spectral function, these observables are governed by the universal light quark condensate. We also find that the corrections induced by finite values ofM _c andM _b are large and are due to the splitting _b between the ground state and its radial excitation. We review the determinations of the different decay constants, couplings and masses from QCD spectral sum rules (QSSR). Forf _B andf _D , we conclude the optimum average:f _B =(1.59±0.09±0.27)f andf _D =(1.31±0.12)f , where the main error is due to the quark mass, while the first one inf _B is due to the non-perturbative terms and to the choice of the continuum thresholdt _c from the onset of sum rule variable stability until thet _c -stability regions. We also find that the vector coupling _V satisfies approximately the IMETM _Q ^3/2 mass dependence scaling law, whilef _P obeys in units of GeV:f P/f(4.6±0.4)M _Q ^–1/2 (1–1.56/M _Q +0.88/M _Q ² ), forM _Q M _c . We also predict the flavour independence:M _P -M _Q 0.6-0.7 GeV andM _V -M _Q 0.7-0.8 GeV of the mass differences between the mesons and the corresponding quark. Finally we find that theBDev _e form factorf ₊(0)(0.55±0.10) deviates from the naive expectation (f ₊(0)=1).     

Production rate and decay lifetime measurements ofBs0 mesons at LEP usingDs and? mesons

The study of the properties of inclusive production ofD _s mesons and of events in which a and a muon are present in the same jet provides two independent measurements of the probability,f _s ^w , for a heavy quark to hadronize into a strangeB orD meson. The data sample analysed corresponds to 243,000 hadronicZ ⁰ decays. The combined value of these measurements isf _s ^w =0.19±0.06±0.08. From the flight distance distributions ofD _s and of (-lepton) secondary vertices, with the lepton emitted at high transverse momentum relative to the jet axis, two values are obtained for theB _s ⁰ meson lifetime. Combining these measurements with a previous result based on the study ofD _s- events, theB _s ⁰ meson lifetime is measured to be: 0.96±0.37 ps.     

Connection between elastic scattering and inclusivek T 2 distribution

A connection between the elastic scattering and the inclusive one-particlek _T ² distribution is pointed out in the context of thes channel unitarity. One of the implications of this connection is that the slope of thek _T ² distribution atk _T ² =0 is about a factor two larger than the slope of the elastic scattering att=0.     

L-S coupling and the magnetic moment of6Li from three-body models

Recently, the shell structure of⁶Li was calculated from three-body models (pn) where the only input is the required nucleon-nucleon and alpha-nucleon interactions. There it was learned, within the framework ofj-j coupling for the two valence nucleons with their coordinate's origin on the alpha particle, that orbitals beyond thep-shell, e.g. thes-d shell, play a significant role in the structure of⁶Li. In the present work, we extend these calculations to thef-shell. Thef-shell orbital probabilities add 4% to the normalization, thus bring all the models to within 3–5% of complete convergence. We then use thej-j coupling orbital amplitudes up to thef-shell to construct the corresponding amplitudes forL-S coupling. We find theL-S orbital probabilities, and compare them with theL-S component probabilities calculated directly by recoupling the three-body wave function from its natural Jacobi-coordinate form. The⁶Li magnetic moment is determined from the directL-S probabilities. The most realistic models yield magnetic moments about 2.5% higher than experiment.     

Four-quark states and nucleon-antinucleon annihilation within the quark model with QCD vacuum-induced interaction

The spectrum of , J^p=0⁺, 2⁺ mesons is discussed. We have shown that due to instanton-induced forces the physical states are strong mixtures of theSU _f (3) group basis states. The cross-sections for annihilation of the system into mesons are obtained. Thea ₀(980) meson is considered as meson consisting of 9 _f and 36 _f plets. The branchings are also predicted for the cross-sections for production of thea ₀(980) and tensor mesons in annihilation.     

The effect of an electromagnetic wave-field pressure on the propagation of slow tm waves along the plasma layer

Angular distributions of the⁴⁸Ti(d, t)⁴⁷Ti and⁴⁷Ti(d, t)⁴⁶Ti reactions have been measured atE _d =19.5 MeV and analyzed by DWBA. The data suggest an explanation of the⁴⁸Ti(d, t)⁴⁷Ti ground state transition by means of a [f ₇ ^2/5 ·f _5/2]₀₊ neutron component in the ground state of⁴⁸Ti.     

The πN partial waves at low energies and in the unphysical region

The real parts of theπN partial wave amplitudesf _l± ^(?) have been calculated from fixed-t dispersion relations, using phase shifts up to 2 GeV and the reggeizedp-exchange model at higher energies. The comparison with Ref _l± ^(?) as calculated directly from phase shifts shows to what extent the input is consistent with the fixed-t relation. The result is also of interest for the test of simple models, in particular for the comparison with predictions from current algebra. — A new evaluation of the partial wave dispersion relation forf ₀₊ ^(?) is presented. Combined with the first method it shows that the determination of thep-coupling parameter is based on an assumption which is difficult to justify.