Evidence for e~+e~-→γχ_(c1,2) at center-of-mass energies from 4.009 to 4.360 GeV

Using data samples collected at center-of-mass energies of √s=4.009, 4.230, 4.260, and 4.360 Ge V with the BES detector operating at the BEPC collider, we perform a search for the process e+e-→γχc J(J =0, 1, 2)and find evidence for e+e-→γχc1 and e+e-→γχc2 with statistical significances of 3.0σ and 3.4σ, respectively. The Born cross sections σB(e+e-→γχc J), as well as their upper limits at the 90% confidence level(C.L.) are determined at each center-of-mass energy.     

Photoemission of protons from4He in theΔ-resonance region

High resolution proton energy spectra from the⁴He(γ,p) reaction have been measured with tagged photons in the range E_γ = 130?525 MeV using the large Mainz NaI(T1) spectrometer atΘ _p ^lab =37.1°. Three separate reaction channels were identified, viz.⁴He(γ,p)t two-body breakup,⁴He photodisintegration via two-nucleon photon absorption processes and the quasifree pion production channel. Differential cross sections are presented for each of these channels as a function of photon energy. The sum of the two-nucleon photon absorption and the quasifree pion production differential cross sections, in the CM system, resembles that of the corresponding free-nucleon differential cross section when Fermi motion is taken into account.     

Measurements of the (γ, n0) reaction on 12C and 16O and the investigation of the reaction mechanism

Differential (γ, n₀) cross sections on ¹²C and ¹⁶O have been measured for photon energies 60 MeV ? E_γ ? 160 MeV. These results combined with the corresponding (γ, p₀) cross sections support an absorption mechanism of the photon by neutron-proton pairs.     

Effect of exchange currents in E1 sum rule and orbital g-factor in 209Bi

The peak cross section σ₀ of ²⁰⁹Bi, precisely determined via photon scattering is used to test the relation between the meson magnetic moment σg_l^meson and the GDR enhancement factor κ′. The results κ′ = 0.46±0.05 is consistent with our present knowledge of magnetic moments.     

Production of high transverse momentum prompt photons and neutral pions in proton-proton interactions at 280 GeV/c

The inclusive cross sections for production of prompt photons and π⁰ s by 280 GeV/c protons incident on a liquid hydrogen target, have been measured forp _T in the range 4.0 to 6.5 GeV/c and for |x _F |<0.45. A quantitative comparison of the prompt photon cross section with next-to-leading order QCD predictions using Duke and Owens structure functions is performed. Phenomenological fits to the π⁰ and prompt photon cross sections are given.     

Destructive interferences results in bosons anti bunching: refining Feynman’s argument

The photo-absorption cross sections for the dissociative ionization and dissociative excitation of H ₂ ⁺ are calculated for photon polarization parallel and perpendicular to the internuclear axis. The wavefunctions for the initial and final states are prepared using the Born-Oppenheimer approximation. For dissociative ionization, the cross section and angular distribution of photo-electrons are compared with those calculated with the fixed-nuclei approximation. For dissociative excitation, the cross sections for H?(N = 1～4) productions are shown.     

Pair production of Higgs boson in NMSSM at the LHC with the next-to-lightest C P-even Higgs boson being SM-like

The next-to-minimal supersymmetric standard model(NMSSM)more naturally accommodates a Higgs boson with a mass of approximately 125 Ge V than the minimal supersymmetric standard model(MSSM).In this work,we assume that the next-to-lightest CP-even Higgs boson h2 is the SM-like Higgs boson h,whereas the lightest CP-even Higgs boson h_(1)is dominantly singlet-like.We discuss the h_1h_1,h_2h_2,and h_1h_(2)pair production processes via gluon-gluon fusion at the LHC for an collision energy of 14 Te V,and we consider the cases in which one Higgsboson decays to bˉb and the other decays toγγorτ~+τ~-.We find that,for m_(h1) 62 GeV,the cross section of the gg→h_1h_(1)process is relatively large and maximally reaches 5400 fb,and the production rate of the h_1h_1→bˉbτ~+τ~-final state can reach 1500 fb,which make the detection of this final state possible for future searches of an integrated luminosity of 300 and 3000 fb~(-1).This is mainly due to the contributions from the resonant production process pp→h_2→h_1h_(1)and the relatively large branching ratio of h_1→bb and h_1→τ~+τ~-.The cross sections of the pp→h_2h_2and pp→h_1h_2 production processes maximally reach 28 fb and 133 fb,respectively.     

A study of low-lying states of 76As using the 75As(d,p) reaction

The ⁷⁵As(d, p)⁷⁶As reaction was investigated with 11 MeV deuterons. Thirty levels of the residual nucleus were identified up to about 1.8 MeV excitation energy, and angular distributions were measured. Spectroscopic factors and l_n values were obtained for low-lying transitions by means of a distorted-wave analysis of the differential cross sections. The l_n = 4 transition to the ground state of ⁷⁶As and the presence of l_n = 2 transitions to low-lying levels provide a strong support to the assumption that nuclei in this mass region have a large deformation parameter. The results are compared with the ⁷⁵As(n, γ)⁷⁶As data.     

The (γ, n) reaction on 16O between giant resonance and pion threshold

A new TOF facility has been built for measurements of differential (γ, n) cross sections to discrete final states of light nuclei in the photon energy range between giant resonance and pion threshold. The observed neutron angle θ_n can continuously be varied between 0° and 150°, and additionally measurements at 175° and 180° are possible. Differential cross sections for the reaction ¹⁶O(γ, n₀)¹⁵O are presented for E_γ = 60 MeV (40° ? θ_n ? 149°) and for θ_n = 90° (60 MeV ? E_γ ? 160 MeV). The results, combined with the corresponding (γ, p₀) cross sections, indicate an absorption mechanism of high energy photons by neutron-proton pairs.     

Transport cross sections for charged particle scattering in (dense-) cesium plasma; electrical conductivity

Transport cross sections for the electron-ion and electron-electron scattering in (dense) cesium plasmas is determined with the partial wave method. The scattering phase shifts δ_l(k) are calculated numerically by means of the usual Numerov method and the advantageous amplitude — phase method for energies E = 10^-4··· 5 ryd and for Debye screening lengths R_D = (10···10³)a₀. Besides the usual Debye potential, also a Thomas-Fermi potential is applied for the cesium electron-ion interaction. The resulting transport cross sections are compared with the Born and quasi-classical approximations. Furthermore, the electrical conductivity of fully ionized cesium plasmas is determined and compared with respective Spitzer results.     

Nuclear reaction cross sections of 16O + 16O obtained by γ-ray detection

The partial production cross sections for reaction residues produced by the fusion of ¹⁶O with ¹⁶O have been measured at E_c.m = 9–30 MeV by detecting the characteristic γ-rays with a Ge(Li) detector. The dominant products are ²⁴Mg and ²⁷A1 corresponding to 2α and αp emission from the compound nucleus, respectively. The total γ-producing cross sections σ_R were also derived by summing the partial cross sections after correction for the observed (average) γ-ray angular distributions. The trend in the total cross sections is very similar to the trends derived from an optical model or a statistical-evaporation model calculation. The partial production cross sections were compared with other experimental results at 11.9 MeV and 30 MeV and with the results of the statistical-model calculation. It is concluded that the treatment of angular momentum in the calculation is inadequate for describing the partial cross sections. Structure in the partial and total cross section excitation functions is observed with minima occurring at E_c.m. = 27, 24, 20, 17.5, and possibly 15 MeV. Some of this structure is well established by the statistical accuracy of the data and most, but perhaps not all of it, is correlated in the various channels. This structure is compared with that observed in another experiment and some of its implications are discussed.     

Analytically approximate screened calculations of atomic-field pair production cross sections

A new method is described to obtain analytically approximate screened cross sections of atomic-field pair production. The Thomas-Fermi-Csavinszky potential model is expanded at the first order and put in the place of the point Coulomb potential in the Dirac equation. That method can be very useful to calculate approximate screened cross sections for the intermediate photon energy range (5m_oc² to about 50m_oc²) where numerically exact screened cross sections are needing a prohibitive computer time and when the form factor approach based on Born approximation is not always valid.     

Measurement of positive pion production from 14N at low momentum transfer

Double differential cross sections of the reaction ¹⁴N(e, π⁺) have been measured at E₀ = 173.5 MeV for pion production angles of Θ_π = 25° and 100° which correspond to momentum transfer values of q² = 0.22 and 1.14 fm². Using the virtual photon theory single differential cross sections of the reaction ¹⁴n(γ, π⁺)¹⁴C_g.s. are extracted from the measured data. The data are compared with recent DWIA calculations and indicate a larger nuclear spin-flip transition matrix element between ¹⁴N and ¹⁴C than that obtained from β-decay. Mixing parameters for shell model wave functions of ¹⁴N and ¹⁴C ground states are derived from the data.     

Photoemission of protons from 4He in the ⊿-resonance region

High resolution proton energy spectra from the ⁴He(γ,p) reaction have been measured with tagged photons in the range E_γ = 130–525 MeV using the large Mainz NaI(Tl) spectrometer at \([Theta _p^{lab} = 37.1^circ ]\) . Three separate reaction channels were identified, viz. ⁴He(γ,p)t two-body breakup, ⁴He photodisintegration via two-nucleon photon absorption processes and the quasifree pion production channel. Differential cross sections are presented for each of these channels as a function of photon energy. The sum of the two-nucleon photon absorption and the quasifree pion production differential cross sections, in the CM system, resembles that of the corresponding free-nucleon differential cross section when Fermi motion is taken into account.     

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.     

Measurement of the absolute cross section for the elementary process of atomic field bremsstrahlung

Coincidence measurements of the absolute cross section for the production of bremsstrahlung by electrons in the field of gold atoms are reported. The incident electron energyT ₀ was 300 keV. Measurements were made for four different combinations of electron scattering angle and photon emission angle over a wide range of the relative photon energyk/T ₀ up tok/T ₀=0.83. The measured cross sections are compared with results of Bethe-Heitler and Elwert-Haug calculations     

ω Meson photoproduction from deuterium at 3.9 GeV photon energy

Measurements are presented of the cross sections for ω meson photoproduction from deuterium at an average photon energy of 3.9 GeV. The cross section for the coherent process γd → dω is found to be 1.4 ± 0.5 μb and that for the incoherent process γd → npω is 3.3 ± 0.7 μb. The forward differential cross section for γd → dω is estimated to be (dσ/dt)_t=0 = 54 ± 20 μb/GeV². This result indicates that the value of the A₂ exchange amplitude in ω photoproduction from hydrogen is less than that predicted from the measurements of the difference between the total hadron photoproduction cross sections from neutrons and protons. We note that the world data tend to show that the A₂ exchange amplitude is more consistent with zero than with the value needed to explain these differences. Measurements are also presented of the ratio of the coupling constants of the photon to the ? and ω mesons which tend to favour the vector dominance model proposed by Das, Mathur and Okubo with exact SU(3) symmetry at infinite energies.     

Reliable cross sections of partial photoneutron reactions on 188,189Os isotopes free of neutron multiplicity sorting problems

Experimental data on the cross sections of partial photoneutron reactions, obtained for ^188,189Os isotopes using quasimonoenergetic annihilation photon beams and neutron multiplicity sorting method, are analyzed. Using special criteria (transition multiplicity functions F _i = σ(γ, in)/σ(γ, xn), the ratios of the cross section of the corresponding partial reaction to the total neutron yield reaction’s cross section σ(γ, xn) = σ(γ, 1n)+ 2σ(γ, 2n) + 3σ(γ, 3n) free of the problems associated with experimental neutron multiplicity sorting), it is demonstrated that the data contain significant systematic errors. New data are evaluated for cross sections of partial photoneutron reactions (γ, 1n), (γ, 2n), (γ, 3n) and total photoneutron reaction (γ, sn) for ^188,189Os isotopes within an experimental-theoretical approach proposed earlier. It is shown that the significant systematic errors in the experimental cross sections of partial reactions can be attributed to the ambiguity of the relation between the photoneutrons’ multiplicity and their kinetic energy.     

High transverse momentum prompt photon production by π− and π+ on protons at 280 GeV/c

The inclusive cross sections for prompt photon production by π^? and π⁺ on protons have been measured with a beam momentum of 280 GeV/c using a fine grained electromagnetic calorimeter and the CERN Omega spectrometer. The transverse momentum and Feynmanx _F ranges covered are 4.0<p _T <7.0GeV/c and ?0.45<x _F <0.55 respectively. A quantitative comparison of the prompt photon cross section with next-to-leading order QCD predictions using Duke and Owens structure functions is performed.