Meson-photon transition form factors and resonance cross-sections in e+e− collisions

Meson-photon-photon transition form factors for S-, P-, and D-wave states are calculated, the meson being treated as a non-relativistic heavy-quark-antiquark pair. The full dependence on both photon virtualities is included. Cross-section formulas for charge-conjugation even mesons with J^p = 0⁻, 0⁺, 1⁺, 2⁺, and 2⁻ in electron-positron collisions are presented and numerical results for LEP energies are given. In particular, we find two-photon event rates for χ_c1, η_c(2S), and η_b(1S) within reach of LEP.With minor modifications to incorporate SU(3)-flavour breaking we estimate rates for 18 light mesons as well, based on the observation that their two-photon decay widths agree remarkably well with measured data. Finally we point out that e⁺e⁻ cross sections for 1⁺ states do not vanish at low Q², the Landau-Yang suppression factors of the two-photon cross sections being compensated by the photon propagators.     

Cross sections of Oq+（q=1-4） electron loss in collisions with He,Ne and Ar

Electron-loss cross sections of O q+(q = 1 4) colliding with He,Ne and Ar atoms are measured in the intermediate velocity regime.The ratios of the cross sections of two-electron loss to that of one-electron loss R 21 are presented.It is shown that single-channel analysis is not sufficient to explain the results,but that projectile electron loss,electron capture by the projectile and target ionization must be considered together to interpret the experimental data.The screening and antiscreening effects can account for the threshold velocity results,but cannot explain the dependence of the ratio R 21 on velocity quantitatively.In general,the effective charge of the target atom increases with velocity increasing because the high-speed projectile ion can penetrate into the inner electronic shell of target atom.Ne and Ar atoms have similar effective charges in this velocity regime,but He atoms have smaller ones at the same velocities due to its smaller nuclear charge.     

Single electron capture in collisions of N^q＋ （q = 5, 6, 7） ions with helium

Close-coupling calculations are carried out for cross sections of the single electron capture in collisions of N^q+ (q = 5, 6, 7) ions with helium atoms in the collision velocity range from 0.3 a.u. to 1.8 a.u. The relative importances of the single ionization (SI) to the single capture (SC) are investigated for the N^q+ (q = 5, 6, 7) projectiles, respectively. The SI/SC cross section ratio for the N⁷⁺ projectile obtained from our calculations is in excellent agreement with the experimental data. The ratio curves also show us distinct behaviours when the charge of the projectile is different. The partial electron capture cross sections for different projectiles indicate that the electron on the target He atom tends to be captured by the projectile into its lower orbital of the outer shell with the decreasing projectile charge.     

Forward-backward multiplicity distributions in the Peřina-McGill scheme and analysis ine + e − collisions

A forward-backward multiplicity correlation is considered by the use of the Pe?ina-McGill formula. We obtain analytic formulae for conditional cumulants of the backward multiplicity and a conditional backward multiplicity distribution at a given forward multiplicity. The multiplicity distribution and the conditional mean multiplicity observed at \(\sqrt s = 29\) in HRS ine ⁺ e ^? collisions are analysed. We predict the conditional moments and the conditional backward multiplicity distribution. Those should be compared with the future analyses in HRS.     

Production of polarized baryons in polarized and unpolarizede + e − collisions

Polarized and unpolarizede ⁺ e ^? annihilation is considered in lowest order at energies 30–150 GeV taking γ andZ ⁰ exchange in the standardSU(2)×U(1) model into account. The fragmentation of polarized quarks into polarized baryons is described by two kinds of fragmentation functions; the first is based onSU(6) weights and empirical expressions for favoured and disfavoured fragmentation; the second is based upon a Monte Carlo model of the chain decay including helicities of quarks and hadrons. From the cross sections for \(e^ + e^ - \to q\bar q\) and the fragmentation functions we obtain predictions for the baryon polarization as function of the collision energy and of kinematical variables.     

Annihilation mechanisms of e+e− and μ+μ− production in relativistic nuclear collisions

We revise the μ⁺μ^? and $q\bar q$ annihilation mechanisms of dilepton production during relativistic nuclear collisions. We focus on the modifications caused by the specific features of in-medium pion and quark states rather than by medium modification of the ρ-meson spectral density. The main ingreditent emerging in our approach is a form-factor of the multi-pion (multi-quark) system. Replacing the usual delta-function the form-factor plays the role of distribution which, in some sense, “connects” the total 4-momenta of the annihilating and outgoing particles. The difference between the c.m.s. velocities attributed to annihilating and outgoing particles is a particular consequence of this replacement and results in the appearance of a new factor in the formula for the lepton pair production rate. We obtained that the form-factor of the multi-pion (multi-quark) system causes broadening of the rate which is most pronounced for small invariant masses, in particular, we obtain a growth of the rate for the invariant masses below two masses of the annihilating particles.     

Multiple ionization of argon in coincidence with projectile ions in 60–120 MeV Si q+-Ar collisions

A projectile ion-recoil ion coincidence technique has been employed to study the multiple ionization and the charge transfer processes in collisions of 60–120 MeV Si ^q+ (q = 4−14) ions with neutral argon atoms. The relative contribution of different ionization channels, namely; direct ionization, electron capture and electron loss leading to the production of slow moving multiply charged argon recoil ions have been investigated. The data reported on the present collision system result from a direct measurement in the considered impact energy for the first time. The total ionization cross-sections for the recoil ions are shown to scale as q ^1.7/E _p ^0.5 , where E _p is the energy in MeV of the projectile and q its charge state. The recoil fractions for the cases of total- and direct ionizations are found to decrease with increasing recoil charge state j. The total ionization fractions of the recoils are seen to depend on q and to show the presence of a ‘shell-effect’ of the target. Further, the fractions are found to vary as 1/j ² upto j = 8+. The average recoil charge state 〈j〉 increases slowly with q and with the number of lost or captured electrons from or into the projectile respectively. The projectile charge changing cross-sections σ _qq′ are found to decrease with increasing q for loss ionization and to increase with q for direct-and capture ionization processes respectively. The physics behind various scaling rules that are found to follow our data for different ionization processes is reviewed and discussed.     

Anomalous magnetic moment of theW-bosons and non-standardZ 0 W + W − coupling in polarizede − e + collisions

We study quantitatively the reactions \(e^ + e^ - \to W^ + e\bar \nu _e \) ,e _R ^? e ⁺ and the rare decay \(Z^0 \to W^ \pm l^ \mp \mathop {\nu _e }\limits^{( - )} \) forl=e, μ and τ, as a test for anomalous γW ⁺ W ^? andZ ⁰ W ⁺ W ^? structure. If κ denotes the anomalous magnetic moment of theW-boson and ω its anomalous coupling to theZ ⁰, values of |ω|>2.5 and |κ|>1.5 can be ruled out at LEP and SLC rather easily. This will put constraints on composite model building.     

Production ofH(2s) andH(2p) by electron detachment fromH − in collisions with nitrogen and oxygen

¹⁹⁹Hg Fourier Transform NMR studies of various solutions of diverse mercury salts in H₂O and D₂O or in the appropriate protonated and deuterated acids are reported for both Hg ₂ ⁺⁺ and Hg⁺⁺. In the different solutions investigated the¹⁹⁹Hg line positions depend on the concentration of the solution, on the solvents and their isotopic composition and on the temperature of the sample. A ratio of the Larmor frequency of¹⁹⁹Hg and of²H in a Hg(NO₃)₂ solution in dilute DNO₃ is given. Using this ratio and the measured chemical shifts, a ratio of the Larmor frequencies of¹⁹⁹Hg for infinite dilution relative to²H in pure D₂O is given. From this a g_I-factor for¹⁹⁹Hg is derived and compared with the g_I-factor of an optical pumping experiment. The resulting shielding constant is σ^* (hydrated¹⁹⁹Hg⁺⁺ versus¹⁹⁹Hg atom)=?24.32(5) · 10^?4. This yields an atomic reference scale for all measured NMR line shifts of mercury.     

Structure and stability of SiBn+ AND CBn+ (n = 1–4)

The structures and binding energies of small boron-rich clusters are studied using correlated wave functions and polarization basis sets. Carbon is the central atom in CB_n⁺, while SiB_n⁺ prefers planar boron networks with silicon as one of the edge atoms. These ground state structures can be explained by differences in the electronegativities of the component elements. The various fragmentation channels of SiB_n⁺ are also examined using binding energy differences.     

Low-temperature phase transitions and dynamics of ammonium in (NH4)3H(SO4)2 and [(NH4)1−x Rbx]3H(SO4)2 crystals

The (NH₄)₃H(SO₄)₂ and [(NH₄)_0.82Rb_0.18]₃H(SO₄)₂ crystals are investigated by dielectric spectroscopy, inelastic incoherent neutron scattering (IINS), and neutron powder diffraction. A comparative analysis of the data obtained is given. It is shown that the phase transitions II ? III, III ? IV, IV ? V, and V ? VII in the (NH₄)₃H(SO₄)₂ crystal are accompanied by changes in the orientation ordering of the NH ₄ ⁺ ions. In the [(NH₄)_0.82Rb_0.18]₃H(SO₄)₂ crystal, these phase transitions are completely suppressed and the long-range order inherent in the II phase is retained over the entire temperature range covered (6–300 K). It is revealed that this crystal at the temperature T _g≈70 K undergoes a transition to the dipole glass phase, which is attended by “freezing” the orientation disordering of the ammonium ions.     

Itinerant electron metamagnetism in Y(Co1−xAlx)2

Magnetization measurements on the itinerant electron magnet Y(Co_1−xAl_x)₂ up to 350 kOe have clearly revealed metamagnetic transitions in the paramagnetic region (0.07⩽x⩽0.11). The transition is sharp for low x, suggesting itinerant electron metamagnetism to exist in YCo₂ at 1 MOe, while it is broadened and disappears upon the onset of ferromagnetism at x∼0.13.     

Rotational structure of the origin band in the 1A′ ←X1σ+ electronic transition of C4H− and C4D−

The rotational structure of the origin band for the ¹A′←X¹σt⁺ electronic transition, lying just below the electron affinity of C⁴H, was recorded by means of a two-colour resonant photodetachment technique. This allowed a determination of the rotational constants in the X¹σt⁺ ground and ¹A′ dipole bound excited state. The low lying A²II excited state of C⁴H is inferred to be the parent of the dipole bound state. The excited electronic state is deduced to have a nonlinear planar structure whereas the ground is linear according to the spectral analysis. The rotational constants have been obtained: B′; = 0.1552(2)cm^?1 for the X¹σt⁺ state, and A′ = 30.73(1), B′ = 0.1587(2), C′ = 0.1581(2)cm^?1 for the ¹A′ state.     

Complexation of hydrogen by lithium: structures,energies and vibrational spectra of Li+ (H2) n (n = 1–4), Li-H(H2) m and Li-H + (H2) m (m = 1–3)

The interaction of metals with hydrogen is of importance in several areas of technology. Lithium-hydrogen complexes are particularly amenable to theoretical study. Although no stable compound of the Li atom and H₂ has been found, a weak dative interaction forms between the σ bond of H₂ and the positively charged Li atom for Li⁺, Li-H⁺, and Li-H. At least four H₂ molecules can be complexed by Li⁺, and three by Li-H⁺ and Li-H. The presence of the Li ion does not substantially weaken the H₂ bond, nor is the energy of dissociation affected; however, the Li ion does form stable complexes with the dissociated H atoms.     

Experimental study of cross-section ratios in the collisions of Cq＋ and oq＋（q= 1-4） on atomic helium in strong-interaction region

We have measured the cross-section ratios of helium induced by C^q+ and O^q+ (q=1-4) in an energy range from 20 keV/amu to 500 keV/amu, and obtained the two-dimensional spectra by employing the coincidence method combined with the MPA-3 data acquisition system. Hence, we obtain the ratios of total single-ionization cross-sections (SI, SC, SLSI, and DLSI), total double-ionization cross-sections (DI, DC, TI, SLDI, and DLDI) and cross-sections of every process (SI, SC, SLSI, DLSI, DI, DC, TI, SLDI, and DLDI), which induce the single-ionization and double-ionization, to the total cross sections respectively. The competitive relations between the reaction-channels and the experimental data law of each reaction-channel are revealed explicitly, and the qualitative explanations involved in those results are also presented accordingly.     

Geometric structure and electron spectrum of YSi n − clusters (n = 6–17)

Results of the optimization of the geometric structure of YSi _n ^? anion clusters (n = 6–17) have been presented and their electron spectra have been calculated. Calculations have been performed by the density functional theory method. Actual geometric structures of clusters have been established by comparing the calculated and known experimental data.     

Scaling and fragmentation distributions of beam remnants in high Et proton-proton collisions at √s =27.4 GeV

Charged particle trajectories have been reconstructed in pp collisions triggered by transverse energies (E_t) ranging from 1 GeV to 20 GeV. The forward fragmentation function of negative particles in the beam jet is found to scale with E_t in variable x=2p_L/√s−E_t, and the slope is near to that found for small jet triggers in an earlier experiment. Above about E_t=8 GeV, positive particles scale and for 0.5<x<1.0 the ratio of positives to negatives is 1.73±0.2. The forward fragmentation functions at high E_t do not show the behavior expected from the fragmentation of diquarks and are more like that from quarks.Multiplicity and energy flow in various forward polar angle regions are also presented; they are compared to the beam jet predictions of ISAJET and found to be greater at wide angles and less at small.     

Production of G(1590) in 300 GeV central π−N collisions

Significant production of G(1590), a scalar glueball candidate, is observed in a study of η pairs produced in π−N central collisions at 300 GeV/c.