Role of the nuclear and electromagnetic interactions in the coherent dissociation of the relativistic <Superscript>7</Superscript>Li nucleus into the <Superscript>3</Superscript>H + <Superscript>4</Superscript>He channel

The differential cross section in the transverse momentum Q and a total cross section of (31 ± 4) mb for the coherent dissociation of a 3-A-Ge V/c ⁷Li nucleus through the ³H + ⁴He channel have been measured on emulsion nuclei. The observed Q dependence of the cross section is explained by the predominant supposition of the nuclear diffraction patterns on light (C, N, O) and heavy (Br, Ag) emulsion nuclei. The contributions to the cross section from nuclear diffraction (Q ≤ 400 Me V/c) and Coulomb (Q ≤ 50 Me V/c) dissociations are calculated to be 40.7 and 4 mb, respectively.     

Experimental investigation of ρ<Superscript>0</Superscript> photoproduction on the pion in the H1 experiment

Experimental results on quasielastic photoproduction of the ρ⁰ meson in association with a neutron, obtained at the HERA collider, are presented. The total and differential cross sections of the γp → ρ⁰ nπ⁺ reaction at the positron–proton center-of-mass energy of √s =319 GeV are measured. The data collected with the H1 detector in 2006 and 2007 correspond to an integrated luminosity of 1.16 pb^?1. The kinematic region of the photon–proton cms energy of 20 < W _γp <100 GeV, photon virtuality of Q ² < 2 GeV², and the ρ⁰ transverse momentum below 1 GeV/c is analyzed. Secondary neutrons with energies x _L > 0.35 (in proton-energy units) and emission angles below 0.75 mrad are selected. The model of double peripheral exchange, in which the ρ⁰ is elastically produced via the photon interaction with the virtual pion from the proton–neutron vertex, is employed for interpreting the results. The cross section for the ρ⁰ elastic photoproduction on the pion, γπ⁺→ ρ⁰π⁺, is extracted in the one-pion-exchange approximation. The magnitude of the cross section suggests that the γp → ρ⁰ nπ⁺ reaction is significantly affected by absorption.     

Inclusive neutral-pion production in <Emphasis Type="Italic">d</Emphasis>C and <Emphasis Type="Italic">d</Emphasis>Cu interactions at a momentum of 4.5 GeV/. per nucleon

The cross sections for inclusive neutral-pion production in the reactions d + C → π⁰ + x and d + Cu → π⁰ + x at a momentum of 4.5 GeV/c per nucleon were measured over the kinematical region specified by the inequalities Θ_π≤16° and E_π≥2 GeV (in the laboratory frame). From the ratio of the cross sections for neutral-pion generation on carbon and copper nuclei, the exponent n in the parametrization Ed³σ/d³p ～ A _T ⁿ is obtained as a function of the cumulative number X in the range 0.6 ≤ X ≤ 1.8 and as a function of the square of the transverse momentum in the range 0.04 ≤ P _t ² ≤ 0.40 (GeV/c)². The probabilities of the formation of six-quark configurations in the D, ⁴He, and ¹²C nuclei are estimated. The double-differential cross section for the reaction d + C → π⁰ + x is determined for the first time by using a data sample containing more than 40 000 neutral pions.     

One-nucleon spectroscopy of light nuclei

The capabilities and limitations of the conventional many-particle shell model and modern potential cluster models are discussed. New revaluated and more accurate calculations of one-nucleon spectroscopic characteristics of the light nuclei of 1p shell are presented. In many-particle shell model for nuclei with A = 7, 9, 11, 13, and 15 nucleon partial widths of highly excited states with the isotopic spin T = 3/2 were calculated both for “allowed” and “forbidden” transitions. One-nucleon spectroscopic factors were calculated in threebody multicluster models of ⁶Li{αnp}, ⁸Li{αtn}, and ⁹Be{ααn} nuclei. For isobar-analogue nuclei ⁷Li and ⁷Be, the spectroscopic proton S _p and neutron S _n factors for transitions to the ground and excited states of corresponding residue nuclei of the triplet ⁶Li-⁶He-⁶Be were calculated in the framework of binary potential αtand ατ models. Integral, differential and polarization characteristics of photonuclear processes ⁷Li(γ, n ₀)⁶Li, ⁶He(p, γ_{0 + 1})⁷Li, ⁷Li(γ, p ₀)⁶He, and ⁹Be(γ, p _{0 + 1})⁸Li were calculated in this approach.     

Production of cumulative deuterons in collisions of oxygen nuclei with protons at a momentum of 3.25 GeV/<Emphasis Type="Italic">c</Emphasis> per nucleon

The production of cumulative nuclei of ²H in ¹⁶O _p collisions at a momentum of 3.25 GeV/c per nucleon was studied for the first time under conditions of a 4π acceptance. The parameter T ₀ characterizing the slope of the spectrum of invariant cross sections for cumulative-deuteron production in ¹⁶Op interactions was determined. The contribution to cumulative-deuteron production from the decay of the alpha-particle clusters in nuclei upon slow-pion absorption by these clusters was found on the basis of an analysis of the momentum distribution of these cumulative nuclei. The estimates obtained for the contribution of these processes from a comparison of the mean multiplicities of particles and fragments in cumulative and noncumulative events agree well with the respective result extracted from the momentum distribution of cumulative deuterons.     

Charged <Emphasis Type="Italic">ρ</Emphasis>-meson production in neutrino-induced reactions at &lt;<Emphasis Type="Italic">E</Emphasis><Subscript><Emphasis Type="Italic">ν</Emphasis></Subscript>&gt;≈ 10 GeV

The production of charged ρ mesons on nuclei and nucleons is investigated in charged current neutrino interactions at moderate energies (〈E _〉 ≈ 10 GeV), using the data obtained with SKAT bubble chamber. No strong nuclear effects are observed in ρ ⁺ and ρ ^? production. The fractions of charged and neutral pions originating from ρ decays are obtained and compared with higher-energy data. From analysis of the obtained and available data on ρ ⁺ and K*⁺(892) neutrino production, the strangeness suppression factor is extracted: λ _s = 0.18 ± 0.03. Estimation is obtained for cross section of coherent ρ ⁺ neutrino production on nuclei.     

Gamma-Rays from magellanic clouds and origin of cosmic rays

Various calculations of the integral spectrum of γ-rays from the neutral pion decays generated in ppinteractions have been analyzed. The estimate of the integral γ-ray spectrum with allowance for the behavior of the cross section of π ⁰ production in the pp → pp + nπ ⁰ + X reaction near the threshold for each channel and the proton spectrum at low energies (<1 GeV) proved to be much lower than those obtained in earlier calculations.     

Measurement of inclusive pion double charge exchange on 16O at T 0 ≥ 0.5 GeV with the SKS spectrometer at KEK

The inclusive cross section for pion double charge exchange on ¹⁶O at T ₀ = 0.5 and 0.75 GeV was measured with the superconducting kaon spectrometer (SKS) at KEK in a joint ITEP/KEK experiment. The result shows a relatively weak energy dependence of the measured cross section, which is in contradiction with its rapid drop predicted within the conventional model of two sequential single charge exchanges. The data of this experiment agree with the results that were obtained previously from similar measurements at ITEP and which are indicative of a significant contribution from the mechanism of inelastic Glauber rescatterings for T ₀ ? 0.6 GeV.     

On the dependence of the single-spin asymmetry of charged pions on kinematical variables

The experimental single-spin asymmetry (A _N ) of charged pions produced in proton-proton and proton-nucleus collisions is analyzed phenomenologically as a function of kinematical variables. It is shown that the c.m. pion threshold energy (E ₀ ^c.m. ) above which |A _N | is positive depends on the reaction energy √s and on the particle-production angle θ ^c.m.. The dependence of the single-spin asymmetry on the kinematical variables in the region specified by the inequalities 0.7 < p _T < 2.7 GeV/c and E ^c.m. > E ₀ ^c.m. exhibits a scaling behavior. The dependence of A _N on √s proves to be significant at moderate and low energies. Formulas that make it possible to predict the behavior of A _N for charged pions over a broad region of kinematical variables are derived.     

Recent STAR Spin Results and Spin Measurements at RHIC

The STAR experiment provides measurements of single and double-spin asymmetries in longitudinally and transversely polarized p + p collisions at \(\sqrt s \) = 200 and 510 GeV to deepen our understanding on the proton spin structure and dynamics of parton interactions over a wide range of collision energy, momentum and rapidity of the various produced probes. Polarized processes with W^± production allow us to study the spin-flavor structure of the proton. Recent results obtained by STAR on the double longitudinal asymmetry, A_LL, of pion and jet production at \(\sqrt s \) = 200 and 510 GeV, the single longitudinal, A_L, and transverse, A_N, asymmetry of W^± production at \(\sqrt s \) = 510 GeV are overviewed. STAR results on azimuthal single transverse asymmetry of pion in p^↑ + (p, Au) and jet + π^± in p^↑ + p collisions are discussed. The proposed Forward Calorimeter System (FCS) and Forward Tracking System (FTS) upgrades at STAR would significantly improve the capabilities of existing detectors for measurements of observables such as asymmetries of pion, jet, Drell-Yan pairs produced at forward rapidities.     

Formfaktor des π-Mesons und Struktur der Nukleonen

Recent measurements of electron-proton scattering at Stanford have shown that the electric and magnetic form factors are not equal. Therefore, the isotopic vector parts of the form factorsG _e ^v andG _m ^v are recalculated with unsubtracted dispersion relations in the 2π-approximation. For the isotopic scalar parts we useG _e ^s (s)≈G _e ^v (s) andG _m ^s (s)≈ 0 which is known to be valid for moderate energy-momentum transfers. We obtain a simple closed expression for the electromagnetic form factor of the pionF _π in terms of the scattering lengtha ₁ and the effective ranger ₁ of the π-π-scattering in the stateL=T=1.a ₁ is roughly known from pion production by pions. With this value and a suitabler ₁,F _π has a resonance in the region of time-like energy-momentum transfer; and the pion rms-radius becomes\(\overline {v_\pi ^2 } = (0.82 \times 10^{ - 13} cm)^2 \). The calculated anomalous magnetic moment, the electric and the magnetic rms-radii of the proton are then within 10% of the experimental values, the electric charge within 30%. Moreover, the proton form factors are different from each other and up to an energy-momentum transfer of\(s = \frac{{ - q^2 }}{{m_\pi ^2 }} = 23\) within the experimental error of the new measurements. The deviations for higher values of the energy-momentum transfer may be explained in terms of the isotopic scalar parts of the form factors. In this case the electric form factor of the neutron will be different from zero in that region and the magnetic form factor of proton and neutron will no longer be equal. For comparison with other experiments we also calculate the π⁺?π^? cross section with neglect of other states thanL=T=1. Under this assumption the π?π cross section has a resonance for low energy-momentum transfer.     

Heavy-quark production in p $$\bar p$$ collisions and unintegrated gluon distributions

The inclusive production of heavy (c and b) quarks in high-energy p\(\bar p\) collisions are considered within the semihard approach in QCD. The dependence of the cross section for heavy-quark production, σ(p_T>p _T ^min ), on unintegrated gluon distributions is studied. The results of this consideration are compared with experimental data obtained by the D0 and CDF Collaborations at Tevatron.     

Analysis of the production of Higgs boson pairs at the one-loop level in the minimal supersymmetric standard model

Within theminimal supersymmetric standardmodel, the amplitudes and total cross sections for the processes e ⁺ e ^? → hh, e ⁺ e ^? → hH, e ⁺ e ^? → HH, and e ⁺ e ^? → AA are calculated in the first order of perturbation theory with allowance for a complete set of one-loop diagrams in the m _e → 0 approximation. Analytic expressions are obtained for the quantities under consideration; numerical results are presented in a graphical form. It is shown that the cross section for the process e ⁺ e ^? → hh is larger than those for the other processes (and is on the same order of magnitude as the cross section for the corresponding processes in the Standard Model). In the case of the collision energy equal to √s = 500 GeV, an integrated luminosity in the region ∫ ? ≥ 500 fb^?1, and a longitudinal polarization of the e ⁺ e ? beams used, 520, 320, and 300 production events are possible in the processes e ⁺ e ^? → hh (at M _h = 115 GeV), e ⁺ e ^? → HH, and e ⁺ e ^? → AA (at M _H,A = 120 GeV), respectively. Even at M _H,A ≈ 500 GeV and √s = 1.5 TeV, not less than 200 events for each of the processes can be accumulated. The cross section for the process e ⁺ e ^? → hH is small (about 10^?2 fb), which complicates the detection of the sought signal significantly.     

<Emphasis Type="Italic">η</Emphasis><Superscript>7</Superscript>Li Scattering in the <Emphasis Type="Italic">αt</Emphasis>-Cluster Model

The cross sections for elastic and inelastic η-meson scattering on ⁷Li nuclei are obtained on the basis of the αt-cluster representation of the target nucleus. The experimentally known values of the parameters of elastic ηα and αt scattering are used in exactly solving three-body Faddeev equations with separable two-body potentials. The η⁷Li elastic-scattering scattering length found from respective calculations is a_η7Li = ?0.310 ? i0.198 fm.     

Calculation of the energy dependence of the fusion cross section and total cross sections for peripheral reactions on the basis of an analysis of data on elastic heavy-ion scattering: Strongly bound ions

A method is proposed for calculating the energy dependence of the fusion cross section (in general, the sum of the cross sections for complete and incomplete fusion, quasifission, and reactions of deep-inelastic scattering) σ _F (E) and the total cross section for peripheral (or quasielastic) reactions, σ _D (E). The method is based on an analysis of a limited set of angular distributions for the elastic scattering in a given pair of nuclei. The predictive power of the method is illustrated by considering the ¹⁶O + ²⁰⁸Pb, ¹⁶O + ⁴⁰Ca, and ¹⁶O + ²⁸Si systems. For each of these systems, the calculations were performed at energies in the range extending from subbarrier values to those exceeding the barrier height substantially. The results of the calculations are found to be in good agreement with relevant experimental data, whereby the reliability of the method is confirmed. By virtue of this, it is proposed to employ the method to study the energy dependences σ _F (E) and σ _D (E) in collisions involving unstable nuclei, for which it is difficult to determine experimentally the above dependences because of a low intensity of secondary beams.     

Relaxationszeiten für die Umorientierung von Quecksilberatomen im metastabilen 63 P 2-Zustand durch Stöße

From the linewidth of the radiofrequency resonance between the Zeeman levels of the 6³ P ₂ state the lifetimeT _m of the metastable Hg atoms in a certain magnetic sublevel was derived as a function of the Hg vapour pressure. The lifetime of the metastable stateT(6³ P ₂) was determined under the same experimental conditions by optical absorption measurements. In the pressure range from 2·10^?3 to 2.4·10^?2 mm HgT(6³ P ₂) was longer thanT _m by one to two orders of magnitude. This result means thatT _m is only dependent on disorienting collisions and is practically not affected by the collisional destruction of the metastable state. ThusT _m is the relaxation time for the disorientation of the metastable atoms by collisions. The pressure dependence of the relaxation time indicates that the disorientation is achieved by two-body collisions with ground state Hg atoms. The disorientation cross section was found to be (2.1±0.2)·10^?14 cm².     

High transverse momentum identified particle spectra in 200 GeV collisions from STAR

Significant baryon over meson enhancement was measured at RHIC in the intermediate transverse momentum range of p _T =2?4 GeV/c (“baryon-meson puzzle”). With STAR detector we were able to extend particle identification towards higher transverse momentum offering further insights into the particle production mechanisms at intermediate to high p _T . In this paper we present results on charged pion, proton and anti-proton spectra and ratios at intermediate to high p _T exploiting the relativistic rise of the specific ionization energy loss measured in the STAR Time Projection Chamber. These measurements provide valuable information about the production mechanisms of particles at intermediate p _T in relativistic heavy ion collisions, e.g. coalescence/recombination versus jet fragmentation.     

Application of a folding-model optical potential to analyzing inelastic pion–nucleus scattering and the in-medium effect on a pion–nucleon amplitude

The folding-model optical potential is generalized in such a way as to apply it to calculating the cross sections for inelastic scattering of π ^±-mesons on ²⁸Si, ⁴⁰Ca, ⁵⁸Ni, and ²⁰⁸Pb nuclei at the energies of 162, 180, 226, and 291 MeV leading to the excitation of the 2⁺ and 3^? collective states. In doing this, use is made of known nucleon-density distributions in nuclei and the pion–nucleon scattering amplitude whose parameters were obtained previously by fitting the elastic scattering cross sections for the same nuclei. Thus, the values of quadrupole (β ₂) and octupole (β ₃) deformations of nuclei appear here as the only adjustable parameters. The scattering cross section is calculated by solving the relativistic wave equation, whereby effects of relativization and distortion in the entrance and exit scattering channels are taken exactly into account. The cross sections calculated in this way for inelastic scattering are in good agreement with respective experimental data. The importance of the inclusion of in-medium effects in choosing parameters of the pion–nucleon amplitude is emphasized.     

Radiative parton energy loss and jet quenching in high-energy heavy-ion collisions

We study within the light-cone path integral approach [3] the effect of the induced gluon radiation on high-p _T hadrons in high-energy heavy-ion collisions. The induced gluon spectrum is represented in a new form which is convenient for numerical simulations. For the first time, computations are performed with a realistic parameterization of the dipole cross section. The results are in reasonable agreement with the suppression of high-p _T hadrons in Au + Au collisions at \(\sqrt s = 200\)GeV observed at RHIC.     

The analysis of <Emphasis Type="Italic">π</Emphasis><Superscript>−</Superscript>-meson spectra in semicentral CC and CTa collisions at a momentum of 4.2 GeV/<Emphasis Type="Italic">c</Emphasis> per nucleon in terms of light-front variables

The inclusive spectra of pions produced in CC and CTa collisions at a momentum of 4.2 GeV/c per nucleon are analyzed in terms of light-front variables ξ and ζ. The phase space of the secondary pions is divided into two parts with very different angular and momentum distributions. In one of these parts, the thermal equilibrium assumption seems to be in good agreement with the data. Corresponding temperatures T are extracted, and their dependence on (A_PA_T)^1/2 is studied: T decreases linearly with increasing (A_PA_T)^1/2. The results are compared with the predictions of the quark-gluon string model (QGSM). The QGSM satisfactorily reproduces the experimental data.