Double Diffractive Process Factorization from ηc and γ Associated Production at Tevatron and LHC

We present a study of associated ηc and γ double diffractive production in pp^- collision based on Ingelman-Schlein model, and the framework of non-relativistic QOD factorization formalism for quarkonia production. The prediction of ηc and γ is more reliable than J/ψ production, because the associated ηc and γ production is a pure color-octet process, and the dominant contribution comes from color octet ^1S0^(8) subprocess, which is related to the color octet matrix element of ^1S0(8) of J/ψ by the heavy quark spin symmetry and the large PT J/ψ production data. We find that the ratio of diffractive to inclusive cross sections is independent of the values of color octet matrix elements, but is sensitive to the gluon factor of the Pomeron and renormalized Pomeron flux factors. So experimental measurement of this ratio can give us more information of the nature of Pomeron and test the assumption of hard diffractive factorization in hadron-hadron collisions.     

Study of the <Superscript>12</Superscript>C (<Superscript>8</Superscript>B, <Superscript>7</Superscript>Be)<Emphasis Type="Italic">X</Emphasis> knockout reaction at intermediate energies

The breakup reactions of ⁸B on a ¹²C target at 142, 285, 790, and 936MeV/nucleon have been studied. One-proton-removal cross sections, leading to the production of ⁷Be fragments in the ground and first excited states (at 0.429MeV), and the longitudinal momentum distributions of the ⁷Be fragments are obtained in the Eikonal approximation of the Glauber Model. The results of the calculations including the contribution of the ⁷Be to the ground and first excited states of ⁸B are compared with the available experimental data. One-proton-removal cross section for the ¹²C(⁸B, ⁷Be)X knockout reaction at 142, 285, 790, and 936 MeV/nucleon energy has been calculated. ⁸B and ⁷Be cross sections and momentum distribution are in a good agreement with available data.     

H<Superscript>+</Superscript><Emphasis Type="Bold">and He</Emphasis><Superscript>2+</Superscript> impact single and double ionization of lead

H⁺ and He²⁺ impact single and double ionization cross sections of ground state lead atoms have been calculated in the binary encounter approximation. Calculations of direct double ionization cross sections have been performed in the modified double binary encounter model. The accurate expressions of σ_ΔE (cross-section for energy transfer ΔE) and Hartree-Fock velocity distributions for the target electrons have been used throughout the calculations. Contributions to double ionization from Auger effect following ionization of inner shells have been considered in the present work. Our H⁺ impact single and double ionization cross sections are in good agreement with the experimental observations. In calculations of He²⁺ impact cross sections, the present theoretical approach shows limited success in the experimentally investigated region (50–350 keV amu^-1).     

Single-electron charge transfer and excitations at collisions between Bi<Superscript>4+</Superscript> ions in the kiloelectronvolt energy range

Pioneering theoretical data for single-electron charge transfer and excitations due to collisions between Bi⁴⁺ ions in the ground (6s) and metastable (6p) states are gained in the collision energy interval 5–75 keV in the center-of-mass frame. The cross sections of the processes are calculated in terms of the close-coupling method in the basis of two-electron quasi-molecular states for the Coulomb trajectory of nuclei. It is found that single-electron capture into the singlet 6s ² states of Bi³⁺ ions makes a major contribution to the charge transfer total cross section for Bi⁴⁺(6s) + Bi⁴⁺(6s) collisions (reaction 1), whereas single-electron capture into the singlet 6s6p states is the basic contributor to the total cross section in Bi⁴⁺(6s) + Bi⁴⁺(6p) collisions (reaction 2). In the collision energy interval mentioned above, the collision cross sections vary between 1.2 × 10^?17 and 1.9 × 10^?17 cm² for reaction 1 and between 3.8 × 10^?17 and 5.3 × 10^?17 cm² for reaction 2. In reaction 1, the 6s → 6p excitation cross sections vary from 0.6 × 10^?16 to 0.8 × 10^?16 cm² for the singlet channel and from 2.2 × 10^?16 to 2.8 × 10^?16 cm² for the triplet channel. The calculation results are compared with the data obtained in experiments with crossed ion beams of kiloelectronvolt energy. The fraction of metastable ions in the beams is estimated by comparing the experimental data with the weighted average theoretical results for the cross sections of reactions 1 and 2. From the data for the charge transfer cross sections, one can estimate particle losses in relativistic beams due to a change in the charge state of the ions colliding with each other in the beam because of betatron oscillations.     

Diffractive Scattering Factorization from J/ψ and γ Associated Production in HERA ep Collisions

Using three sets of Pomeron structure functions, the cross sections of J/ψ and γ associated productionvia resolved photon and proton diffractive scatting in ep collision are investigated. It is found that the cross sectionscalculated with various gluon distribution functions of Pomeron are different. The discrepancy is about 1.8 times fordifferential cross sections and 1.7 times for total cross sections. The experimental studies of the process could give valuableinsight in the diffractive production mechanism and test the color-octet mechanism for heavy quarkonium production ina new environment.     

Evaluation of the <Superscript>52</Superscript>Cr–<Superscript>52</Superscript> Cr Interaction via Spin-Flip Scattering

In order to evaluate g ₀, the interaction strength of a pair of ⁵²Cr atoms with total spin S = 0, a specially designed s-wave scattering of the pair has been studied theoretically. Both the incident atom and the target atom trapped by a potential are polarized previously but in reverse directions. Due to spin-flips, the outgoing atom may have spin component μ ranging from −3 to 3. The outgoing channels are classified by μ. The effect of g ₀ on the s-wave cross sections of each of these μ- channels has been predicted. In particular, when the parameters of the trapping potential are given around their optimal values so that the cross sections can be maximized, distinguished features of the dependence of the cross sections on g ₀ are found. These features are helpful for evaluating g ₀.     

H<Superscript>+</Superscript> and He<Superscript>2+</Superscript> impact charge transfer cross sections of magnesium

H⁺ impact single and He²⁺ impact single and double electron capture cross sections of magnesium atoms have been calculated in the modified binary encounter approximation (BEA). The accurate expressions of ion impact s_DE\sigma _{\Delta {E}} (cross section for energy transfer DE\Delta E) and Hartree-Fock momentum distributions of the target electrons have been used throughout the calculations. On the basis of the present work it is concluded that inner shell captures by H⁺ and He²⁺ ions incident on magnesium atoms contribute partly to single electron capture and partly to transfer ionization cross sections. The calculated He²⁺ impact double electron capture cross sections of magnesium are in reasonably good agreement with the experimental observations. This indicates the success of the present theoretical approach in study of charge transfer cross sections of atoms as indirect mechanisms do not interfere with double electron capture processes in this case.     

Excitation of the BaI <Superscript>1</Superscript><Emphasis Type="Italic">P</Emphasis> levels in collisions of slow electrons with barium atoms

Excitation of the singlet P levels of the barium atom by slow monoenergetic electrons is studied experimentally. In the four series studied, the dependence of the excitation cross sections on the principal quantum number of the upper level was found to be irregular. Such behavior of the cross sections is associated with the fact that the BaI singlet series are strongly perturbed. The absolute excitation cross sections and the branching ratios obtained are compared with the data of previous studies.     

J/\psi +{\mathrm{jet}} diffractive production in the direct photon process at HERA

We present a study of the diffractive production in direct photon processes at HERA based on the factorization theorem for lepton-induced hard diffractive scattering and the factorization formalism of the non-relativistic QCD (NRQCD) for quarkonia production. Using the diffractive gluon distribution function extracted from HERA data on diffractive deep inelastic scattering and diffractive dijet photon production, we demonstrate that this process is measurable at DESY HERA. The experimental study of this process can give valuable insight in the diffractive production mechanism and test the color-octet mechanism for heavy quarkonia production in a new environment. Received: 13 September 1999 / Revised version: 31 December 1999 / Published online: 6 April 2000     

Charge exchange collisions of H<Superscript>+</Superscript>/D<Superscript>+</Superscript> ions with alkaline Earth atoms (Ca,Mg)

The Classical Trajectory Monte Carlo (CTMC) Method has been used to calculate the differential, partial and total single electron capture cross sections for the collision of H⁺/D⁺ with Ca and Mg atoms in the energy range of 1–100 keV. The differential cross sections at angles near the diffraction limit (<0.1^○) in both systems show a forward peak followed by an asymptotic fall at higher angles. Total and partial capture cross sections are found to be in good agreement with the experimental observations. Oscillations in the partial capture cross sections have been explained due to the swapping of the field electron. Isotope effect in the electron transfer is reported to be negligible.     

The knockout reaction of <Superscript>15</Superscript>C on a <Superscript>9</Superscript>Be target at intermediate energies

In this work, neutron knockout reactions of ¹⁵C on a ⁹Be target at energy 103 and 250 MeV/nucleon are studied. Using the Eikonal approximation of the Glauber model, total neutron removal cross sections, the stripping and diffractive cross sections as well as ¹⁴C longitudinal momentum distributions are determined in both ¹⁵C ground state and exited states of the wave function. We compared the results of our calculations with the available experimental data obtained recently. The calculated cross sections of ¹⁵C and ¹⁴C reactions, as well as the momentum distribution are in relatively good agreement with available data.     

Theoretical study of charge-exchange and excitation processes in collisions of He<Superscript>+</Superscript> ions with C<Superscript>5+</Superscript>, N<Superscript>6+</Superscript>, and O<Superscript>7+</Superscript> hydrogen-like ions

Data on the cross sections for single-electron charge exchange and excitation in collisions of He⁺ ions with C⁵⁺, N⁶⁺, and O⁷⁺ ions in the He⁺ ion energy range of 0.2–3.0 MeV are obtained for the first time. The cross sections for the single-electron charge transfer into the singlet and triplet 1snl states of C⁴⁺, N⁵⁺, and O⁶⁺ (2≤n≤5) ions and for the 1s → 2p _{0, ±1} electronic excitation of He⁺(1s) ions are calculated. The calculations were performed by solving close-coupling equations on the basis of ten two-electron quasi-molecular states.     

Soft-core Interaction for the <Superscript>4,6</Superscript>He + <Superscript>64</Superscript>Zn Fusion Reactions

In this paper, the cross section of the ⁴He + ⁶⁴Zn and ⁶He + ⁶⁴Zn reactions, at bombarding energies above and below the fusion barrier, has been investigated. Soft-core nucleon-nucleon interaction and the Monte Carlo method have been employed for studying the nuclear potential of the projectile-target system. One adjustable parameter has been chosen in this study. This parameter can change the depth of the soft-core potential. It has to be adjusted so that the calculated elastic scattering and fusion cross sections are in acceptable agreement with experimental data. Our results indicate that an increase in energy decreases the depth parameter of the soft-core nucleon-nucleon potential obtained from careful analysis the ⁴He + ⁶⁴Zn and ⁶He + ⁶⁴Zn reactions. Likewise, by comparing the results obtained from both reactions, one can observe that the calculated depth parameter for the reaction related to ⁶He is larger than that for ⁴He at the same energy, in particular at the sub-barrier energies. We try to explain this behavior.     

Higgs and Z<Superscript>′</Superscript> phenomenology in B–L extension of the standard model at LHC

The phenomenology of the low scale U(1)_B–L extension of the standard model and its implications at LHC energies is presented. In this model, an extra gauge boson corresponding to B–L gauge symmetry and an extra SM singlet scalar (heavy Higgs boson) are predicted. We show a detailed analysis of both heavy and light Higgs bosons decay and production in addition to the possible decay channels of the new gauge boson. We find that the cross sections of the SM-like Higgs production are reduced by ∼20–30%, while its decay branching ratios remain intact. The extra Higgs boson has relatively small cross sections and the branching ratios of Z^′→l⁺l^- are of order ∼20% to be compared to ∼3% of the SM results. Hence, the search for Z^′ is accessible via a clean dilepton signal at LHC.     

Physical criteria for the reliability of data on the photodisintegration of the <Superscript>89</Superscript>Y nucleus

Experimental photonuclear reaction cross sections obtained in experiments using quasimonoenergetic annihilation, monoenergetic tagged photons, and bremsstrahlung γ-radiation are analyzed using physical criteria for the reliability of data on the ⁸⁹Y nucleus. It is found that the reliability of data on the cross sections of partial reactions (γ, 1n) and (γ, 2n), obtained by means of photoneutron multiplicity sorting, is highly doubtful. Reliable cross sections of reactions (γ, 1n) and (γ, 2n) are obtained using the experimental–theoretical method (ETM) for evaluating using both experimental cross sections of neutron yield reaction σ^exp(γ, xn) that are free of neutron multiplicity problems, and theoretically calculated F _i ^theor ratios of the cross sections of definite (i) partial reactions to cross section σ^theor(γ, xn). It is shown that the evaluated cross sections differ noticeably from the experimental data.     

The Reliability of Cross Sections of Partial Photoneutron Reactions for <Superscript>98</Superscript>Mo

The cross sections of partial photoneutron reactions for ⁹⁸Mo were evaluated. These cross sections are free from the shortcomings of various methods for neutron multiplicity determination used at the beams of quasimonoenergetic annihilation photons and bremsstrahlung radiation. New data on the cross sections of reactions (γ, 1n), (γ, 2n), and (γ, 3n) were obtained using the experimental–theoretical method for evaluation of cross sections of partial reactions satisfying the introduced physical reliability criteria. It is demonstrated that considerable deviations of the experimental cross sections from the evaluated ones result from an inaccurate sorting of neutrons between channels with a multiplicity of 1, 2, and 3.     

2γ and 3γ annihilation as calibration processes for high energy <Emphasis Type="Italic">e</Emphasis><Superscript>+</Superscript><Emphasis Type="Italic">e</Emphasis><Superscript>−</Superscript> colliders

Born differential cross sections and the lowest-order radiative correction to them are obtained in the kinematics of large-angle final photon emissions in high-energy electron-positron annihilation processes. Taking into account the possible emission of real soft and hard photons in collinear kinematics, we show the validity of the Drell-Yan form of the differential cross section with the nonsinglet structure functions of the initial leptons. The leading and next-to-leading contribution to the cross sections is obtained. The relevant numerical estimations are presented. The text was submitted by the authors in English.     

Study of fusion and nucleon transfer channels in the <Superscript>197</Superscript>Au + <Superscript>6</Superscript>He reaction in an energy range of <Superscript>6</Superscript>He to 20 Mev/A

New data on the cross sections of reactions occurring during the interaction of ⁶He nuclei with ¹⁹⁷Au at energies of ⁶He from 40 to 120 MeV are presented. The experiments were performed in the ACCULINNA secondary beam separator of the Laboratory of Nuclear Reactions, Joint Institute for Nuclear Research. To identify the reaction products, the activation method for measuring the gamma activity of the target assembly of thin foils was used. The excitation functions for fusion reactions involving the evaporation of up to ten neutrons from the compound nucleus as well as reactions with the emission of charged particles and nucleon transfer in the investigated energy region are obtained. Data analysis was carried out using two codes: ALICE-MP and NRV. The cross sections for the (⁶He, xn) reactions occurring through the compound nucleus are mostly in agreement with the results of model calculations based on the statistical approach. It is shown that, up to the energies of 114 MeV, the cross-section drop in the complete fusion reactions is negligible. The experimental excitation functions of reactions leading to the formation of isotopes of mercury and gold (transfer reaction) indicate that the main contribution to their formation is made by direct processes and that evaporation reactions (⁶He, pxn) and (⁶He, αxn) play a minor role, as is evidenced by a comparison of the measured cross sections with the calculation results.     

Microscopic interpretation of the (<Emphasis Type="Italic">t</Emphasis>, <Superscript>3</Superscript>He) reaction at 130 MeV on <Superscript>90</Superscript>Zr and isovector monopole strength

The 130-MeV primary tritium beam of the AGOR facility with an intensity of up to 10⁸ pps and the Big Bite Spectrometer experimental setup have been used to study the (t, ³He) reaction between 0° and 5° lab angles on ¹²C and ⁹⁰Zr targets. The standard ray-tracing procedure has allowed us to obtain excitation-energy spectra up to 30 MeV in six angular bins for each residual nucleus, with an average energy resolution of 350 keV. We have used the DWBA reaction mechanism model to reproduce those spectra and their angular distributions. In this approximation, the form factor was treated as a folding of an effective projectile-nucleon interaction with a transition density. The effective projectile-nucleon interaction has been adjusted to reproduce the 0° cross section of the 1⁺ ground state of ¹²B populated in the ¹²C(t, ³He) reaction. We have employed RPA wave functions of excited states to construct the form factors. This DWBA+RPA analysis is used to compare calculated and experimental cross sections directly and to discuss the giant resonance excitations in the ⁹⁰Y nucleus. In this talk, we give some details on this analysis. We show that there are important contributions of L = 2 transitions in the observed cross sections for the 1⁺ final states that explain the previous difficulties in clearly identifying the monopole strength distributions. We then have a better indication of where the L = 0 part is located with this reaction and its microscopic analysis. The text was submitted by the author in English.     

Investigation of the dynamics of gluon distributions in the production of heavy quarks and quarkonia at the LEP2 collider

The inclusive production of heavy quarks and quarkonia in photon-photon collisions at the LEP2 collider is considered within the semihard (k _T-factorization) QCD approach. The dependence of the total and differential cross sections for the production of heavy (c and b) quarks and D* and J/ψ mesons on the choice of unintegrated gluon distribution is studied. The transition of a $c\bar c$ charmed pair to observed J/ψ mesons is described on the basis of the color-singlet model. The results of the calculations are compared with currently available experimental data obtained by the L3, OPAL, ALEPH, and DELPHI Collaborations. It is shown that the polarization properties of J/ψ mesons at the LEP2 collider are sensitive to the behavior of unintegrated gluon distributions. This means that experimental investigations of the polarization properties of quarkonia in photon-photon collisions may provide a direct test of the dynamics of gluon distributions in the photon.