Differential cross sections for photoemission of deuterons from the nitrogen nucleus

Momentum distributions for inclusive photoemission of deuterons from nitrogen have been measured at laboratory angles of 43° and 50°, and for maximum energies of the bremsstrahlung photon beam of 725, 775 and 825 MeV. The double differential cross sections of deuterons emitted from nitrogen are obtained for photon energies of 750 and 800 MeV and for laboratory angles of 43° and 50°. The photon energy is determined by the photon subtraction method. Results are examined by a π⁰ photoproduction process off a quasi-deuteron in nitrogen (γ″d″→π⁰d) and by a two-step process. The two-step process means the following: first, a nucleon is produced by a photo-pion production process from a quasi-free nucleon in the nitrogen nucleus (γ″N″→πN); second, the nucleon produced at the first step picks up another nucleon in the nucleus and then a deuteron is emitted (N+A→d+anything).     

Total cross sections for photoabsorption on light nuclei in the energy range 600–1500 MeV

Experimental data of the GRAAL Collaboration on the total cross sections for photoabsorption on deuterium and carbon targets at gamma-ray energies in the range between 600 and 1500 MeV are presented. The experiment was performed in a beam of photons obtained by the method of the Compton backscattering of laser photons at the electron storage ring of the European Synchrotron Radiation Facility (ESRF, Grenoble, France) by using a wide-aperture detector covering a solid angle close to 4π. The total photoabsorption cross sections were determined by two independent methods: by subtracting the emptytarget background and by summing partial cross sections for meson photoproduction. The total cross sections for photoabsorption on quasifree protons and neutrons are shown to agree both in magnitude and in shape within a 5% precision of the measurements. In contrast to data previously available in the literature, both cross sections show distinctly the F ₁₅(1680) resonance at a photon energy of about 1 GeV. Data obtained in the present experiment for the cross sections for photoabsorption on a free and a bound nucleon are compared. This comparison reveals a substantial role of two-nucleon correlations in estimating the nuclear-medium effect on meson photoproduction.     

Experimental investigation of the reaction12C(γ, π0)X in the photon energy range between threshold and 450 MeV

The photoproduction of neutral pions on¹²C has been investigated between threshold and 450 MeV photon energy using the tagged photon beam at the Bonn 500 MeV synchrotron and a large acceptance detector. Theπ ⁰ detector consists of cylindrical wire chambers covering a solid angle of nearly 4π. Using a scintillation counter as an active¹²C target an attempt was made to separate coherent and incoherentπ ⁰ photoproduction. The measured total and differential cross sections are compared to corresponding theoretical calculations.     

Charged-pion photoproduction measurement on deuterium in the Δ(1236) region using a quasi-monochromatic photon beam

Charged-pion photoproduction spectra on hydrogen and deuterium have been measured using an in-flight positron annihilation photon beam. Pions were detected in magnetic spectrometers. The experiment consisted of π^± angular distributions at 300 MeV, and fixed-angle excitation curves at 20° (π^±) and 55° (π^±) in the photon energy range 300–460 MeV. Experimental data are compared to a calculation by Laget which includes final-state nucleon-nucleon interaction and Pauli correlations. The overall agreement is satisfactory; however, the model slightly overestimates the nucleon-nucleon rescattering contribution.     

Nuclear multifragmentation by 700–1500 MeV photons: New data of GRAAL experiment

The cross sections of carbon nucleus photodisintegration into protons and neutrons with high multiplicity for photon energies from 700 to 1500 MeV were measured. The experiment was performed at the tagged photon beam of the GRAAL setup using the wide-aperture detector LAGRANγE. It was shown that multifragmentation up to complete disintegration into separate nucleons is initiated by elementary reactions of meson photoproduction with a subsequent intranuclear cascade.     

Photoproduction of pions and etas in nuclei

We calculate the cross sections for inclusive one-pion, two-pion and eta photoproduction in nuclei in the photon energy range from 300 to 900 MeV within the framework of a semi-classical BUU transport model. Our results are compared with existing experimental data and discussed with respect to a calculation of the total photoabsorption cross section.     

Inclusive charged pion photoproduction on12C using tagged photons in the energy range (200–390) MeV

The photoproduction of charged pions on¹²C has been investigated using the tagged photon beam facility at the Bonn 500 MeV synchrotron. Pions were detected in a broad range magnetic spectrometer. Double differential cross sections for pion emission at fixed photon energies are presented. The integration of the measured distributions yields the total cross section for inclusive pion production. The data are compared to the predictions of a simple model that takes the quasifree production of pions and their subsequent scattering and reabsorption into account.     

Proton Compton effect in the Δ(1232) energy region

The proton Compton effectγ+p→γ+p in theΔ (1232) energy region has been thoroughly studied. At the Bonn 500 MeV synchrotron differential cross sections were measured covering a large range of the CM scattering angle (50°≦θ_γ≦130°) and an energy range from 240 to 440 MeV (LAB energy of the primary photon). A contribution to the counting rate from the competing process ofπ ⁰ photoproduction was strongly suppressed by detecting both particles in the final state and by a proper choice of the endpoint energy of the gamma ray beam. The remaining contribution was monitored experimentally. The measured data were complemented by cross sections at 0° which were computed from the totalγ p cross sections with an input from a multipole analysis of single pion photoproduction. Preliminary results of this experiment have been published in Lett. Nuovo Cimento. In the meantime the experimental data were reanalyzed. The final data presented here are larger than the preliminary ones by about 15%.     

Measurement of πphotoproduction on the proton from 550 to 1500 MeV at GRAAL

Neutral pion photoproduction has been measured from 550 to 1500 MeV with the GRAAL facility, located at the ESRF in Grenoble. Differential cross-section and beam asymmetry have been measured over a wide angular range. These high-precision data improve significantly the database for the beam asymmetry in the second and third resonance regions covering for the first time the energy domain 1100-1500 MeV. New partial-wave analyses including these data are presented for which the beam asymmetry brings crucial constraints.     

Calculation of internal targets and schemes of compact devices for continuous visualization of nuclear beams at synchrotrons as exemplified by Nuclotron

An algorithm for calculating the thickness of an internal target necessary for continuous practically nondestructive visualization of circulating nuclear beams in synchrotrons is presented. Particular results are given for different operation modes of Nuclotron. The schematic diagrams of the proposed compact devices for the implementation of this diagnostics in the whole beam energy range from injection (5 MeV/nucleon) to extraction (maximum energy 6 GeV/nucleon) are shown. The sensitivity of these devices is evaluated as 10⁷–10¹⁴ single-charged nuclei on the orbit.     

Formation of two pions on nuclei in A(γ, ππN)B reactions

A model is proposed for double pion photoproduction on nuclei that is accompanied by nucleon emission. Simple models that faithfully reproduce single-particle differential cross sections are used to describe photon interactions with intranuclear nucleons. The calculated cross sections for pion photoproduction on ¹²C nuclei are compared with inclusive pion spectra measured in the second resonance region of photon energies.     

Photoproduction of ω-Mesons at ELSA and the role of azimuthal asymmetries

Measurements of ω photoproduction of the Crystal-Barrel/TAPS experiment at the ELSA accel-erator of Bonn University are presented which used linearly polarized tagged photon beam from threshold to E_γ = 1700 MeV. The azimuthal asymmetries Σ and Σ_π indicate s-channel resonance contributions on top of the established t-channel exchange processes. These findings are further enhanced by a very first measurement of the G-asymmetry which, in addition to the polarized photon beam, also requires a longitudinally polar-ized proton target. An intuitive interpretation of the specific sensitivity of the azimuthal asymmetries to the reaction mechanisms involved is given.     

Gamma ray and π0 production from hydrogen and complex nuclei by 270–375 MeV gamma rays

Measurements are reported on the differential cross section for secondary gamma ray production on hydrogen and nuclear targets at 90° in the laboratory through the interactions of primary gamma rays in the energy range 270–375 MeV. A difference method using bremsstrahlung beams at different end point energies was employed. The gamma ray detector was a high resolution Nal(Tl) spectrometer and time of flight discrimination was used to reject neutrons. For incident gamma rays in the range 270–375 MeV the first pion nucleon resonance is strongly excited and the observed gamma ray yields are consistent with those expected due to an admixture of coherent and incoherent π⁰ photoproduction in the resonance region. The experiment marks the first successful use of a large Nal(Tl) crystals as a gamma ray spectrometer at a high energy electron linear accelerator, despite the low duty cycle and its accompanying difficulties for such detectors.     

A new photoproduction model in field theory (II)

An earlier study of a gauge-invariant field-theory model for pion photoproduction is continued. The complications due to photon and nucleon spin are considered. The infinity of higher-order graphs are summed to the form of a relativistic eikonal model for photoproduction and its static limit is determined.     

Photoproduction and electroproduction

Various aspects of the electromagnetic interactions of hadrons (strongly interacting particles) are reviewed in these lectures. After a discussion of the properties of the electromagnetic current of the hadrons and the idea of vector meson dominance, the general features of photoproduction cross sections are presented and compared with the very similar behavior of purely strong interaction processes. Given this close similarity in behavior, particular photon induced reactions are then considered in some detail, illustrating the application of theoretical ideas used in treating both strong and electromagnetic processes. The particular subjects discussed in some detail are photoproduction of pions at low energy and partial wave analysis, Compton scattering, vector meson photoproduction and tests of the vector dominance model, and photoproduction of charged pions at high energy. In the second half of the lectures inelastic electron-nucleon scattering is the principal topic. After a presentation of the kinematics and structure functions of the nucleon, the principal results of the inelastic electron scattering experiments are given together with the evidence for the remarkable scaling behavior of the structure functions. This leads to a presentation of the parton model of point constituents of the nucleon and the interpretation of the experimental results in terms of the properties of the constituent partons. A different view of inelastic electron scattering in terms of strong interaction ideas is presented in the last two lectures. These concern the high energy behavior of the scattering and the application of duality concepts which tie the behavior of nucleon resonance electroproduction to the behavior of the deep inelastic scattering.     

Double pi(0) Photoproduction on the Proton at GRAAL

The double pi(0) photoproduction off the proton has been measured in the beam energy range of 0.65-1.5 GeV. The total and differential cross sections and the Sigma beam asymmetry were extracted. The total cross section measured for the first time in the third resonance region of the nucleon shows a prominent peak. The interpretation of these results by two independent theoretical models infers mostly the selective excitation of P11- and D13-nucleon resonances.     

Inflections (knees) in wide-range spectra of solar energetic protons and heavy ions: Their form,parameters, and regularities

An analysis of fluences of solar cosmic rays (SCRs), measured by the ACE (ULEIS, SIS) and GOES satellites for 1998–2006 over the wide energy range of 0.05 to 500 MeV/nucleon, is performed. It is shown that the energy spectra of the fluences have two sections described by power functions of the energy per nucleon: a hard spectrum at low energies (E < 1–10 MeV/nucleon) and a soft spectrum at high energies (E > 10–30 MeV/nucleon). The main regularities inherent to the parameters of the spectra of different particles are determined.     

Effects of the HMT on Nucleon Collective Flows within BUU Transport Model

Within the framework of a semiclassical Boltzmann-Uehling-Uhlenbeck(BUU) transport model,the high momentum tail(HMT) effects of nucleon momentum distribution in the nucleus on the nucleon collective Bows are studied in semicentral Au+Au collisions.The HMT due to the isospin-dependent short-range correlations causes a smaller value of the collective Bows.We Bnd that the HMT effects on the nucleon collective Bows are remarkable at beam energy of 300 MeV/nucleon and become weak as the incident beam energy increases.The results indicate that for the collective Bow studies at intermediate energies,the HMT of nucleon momentum distribution in nucleus should be taken into account in transport models.     

Proton-antiproton states in high energy photoproduction

Exclusive and inclusive $\text{p}\text{p}$ photoproduction (with ? 2 accompanying charged particles) have been measured in the photon energy range 44–70 GeV. The exclusive process shows no prominent features; the inclusive process shows evidence for S(1936) production as a resonant-like structure with mass 1930 ± 2 MeV and width 12 ± 7 MeV.     

In-medium spectral functions of charmonia studied by ¯p + A reactions<Superscript>a</Superscript>

We study the perspectives of resonant charmonium production in ˉp + A reactions within the Multiple Scattering Monte Carlo (MSMC) approach. We calculate the production of the resonances Ψ(2S) and Ψ(3770) on various nuclei, their propagation and decay to dileptons and D + ˉD in the medium and vacuum, respectively, employing parametrizations for the D,ˉD self-energies taken from QCD sum rule studies. The elastic and inelastic interactions of the charmonia and open-charm mesons in the medium are taken into account, too. It is found that the D,ˉD invariant-mass spectra from light and heavy nuclei are not sufficiently sensitive to the in-medium properties of the Ψ(2S) and Ψ(3770). However, a “suppression” of low-mass dileptons from the Ψ(3770) might be seen experimentally as well as a small broadening of the Ψ(2S) dilepton spectra. Received: 19 December 2002 / Accepted: 28 February 2003 / Published online: 5 June 2003