Incoherent Production Research Articles

Subthreshold and near threshold K+ meson production on light nuclei by protons

Inclusive K+-meson production in proton-nucleus collisions in the near-threshold and subthreshold energy regimes is analyzed with respect to the one-step (pN → K+YN, Y=Λ, Σ) and two-step (pN → NNπ, NN2π; πN → K+Y) incoherent production processes. An appropriate folding model is used that properly takes into account the struck-target-nucleon-removal energy and the momentum distribution (nucleon spectral function), novel elementary cross sections for proton-nucleon reaction channel close to threshold, as well as nuclear-mean-field-potential effects on the one-step and two-step kaon-creation processes. A detailed comparison of the model calculations of the K+ total and differential cross sections for the p+9Be and p+12C interactions with the existing experimental data is given, which displays both the relative role of the primary and secondary production channels at considered incident energies and those features of the cross sections that are sensitive to the high-momentum and high-removal-energy parts of the nucleon spectral function. It is found that, contrary to previous studies known in the literature, the pion-nucleon production channels do not necessarily dominate in pA collisions at subthreshold energies and that the relative strength of the proton-and pion-induced reaction channels for light target nuclei in the subthreshold energy regime is governed by the kinematics of the experiment under consideration.

On the Gerasimov-Drell-Hearn sum rule for the deuteron

The Gerasimov-Drell-Hearn sum rule is evaluated for the deuteron by explicit integration up to 550 MeV including contributions from the photodisintegration channel and from coherent and incoherent single pion production as well. The photodisintegration channel converges fast enough in this energy range and gives a large negative contribution, essentially from the 1 S 0 resonant state near threshold. Its absolute value is about the same size as the sum of proton and neutron GDH values. It is only partially cancelled by the single pion production contribution. But the incoherent channel has not reached convergence at 550 MeV.

Subthreshold K + meson production in proton–nucleus reactions and nucleon spectral function

The inclusive K+ mesons production in proton-nucleus collisions in the near threshold and subthreshold energy regimes is analyzed with respect to the one-step (pN->K+YN, Y=Lambda,Sigma) and the two-step (pN->NNpi, NN2pi; piN->K+Y) incoherent production processes on the basis of an appropriate new folding model, which takes properly into account the struck target nucleon removal energy and momentum distribution (nucleon spectral function), extracted from recent quasielastic electron scattering experiments and from many-body calculations with realistic models of the NN interaction. Comparison of the model calculations of the K+ double differential cross sections for the reaction p+C at 1.2, 1.5 and 2.5 GeV beam energies with the existing experimental data from the SATURNE experiment is given, illustrating both the relative role of the primary and secondary production channels at considered incident energies and those features of the cross sections which are sensitive to the high momentum and high removal energy part of the nucleon spectral function that is governed by nucleon-nucleon short-range and tensor correlations. In--medium modifications of the available for pion and hyperon production invariant energies squared due to the respective optical potentials are needed to account for the experimental data on K+ production in the energy region under consideration.

The spin response of the deuteron and its implication for the Gerasimov-Drell-Hearn sum rule

The spin response of the deuteron, i.e., the asymmetry of photoabsorption with respect to parallel and antiparallel spins of photon and deuteron, is calculated allowing to explicitly evaluate the Gerasimov-Drell-Hearn sum rule by integration up to a photon energy of 550 MeV including contributions from the photodisintegration channel and from coherent and incoherent single pion production as well. The photodisintegration channel converges fast enough in this energy range and gives a large negative contribution, essentially from the 1 S 0 resonant state near threshold. Its absolute value is about the same size than the sum of proton and neutron GDH values. It is only partially cancelled by the single pion production contribution. But the incoherent channel has not reached convergence at 550 MeV.

Consistent treatment of color transparency effects in diffractive electroproduction of vector mesons off nuclei

Nuclear transparency for incoherent real and virtual photoproduction of vector mesons off nuclei depends crucially on the interplay of the initial-state and final-state interactions. We develop a consistent description of initial-state and final-state interactions based on the coupled-channel multiple-scattering theory. We present detailed predictions for incoherent production of ss and cc mesons. The onset of initial-state interactions is controlled by the production length lP, and we find strong variations of nuclear transparency when lP rises with energy and becomes comparable to the radius of the target nucleus RA. For ss mesons, the regime lP∼RA corresponds to precisely the kinematic range of the HERA-HERMES experiment, whereas for cc mesons the same condition will be met at the ENC electron-nucleus collider at GSI. In spite of the subasymptotic values of Q2 and v, we find a complex pattern of color transparency-induced effects whose experimental study may provide information on several issues relevant to the understanding of QCD, both in the perturbative and nonperturbative regimes.

Coherent, semicoherent and incoherent pion production in heavy-ion reactions

Two types of coherent pion production in heavy-ion collisions are studied and calculations are performed for 12C against 12C collisions. The first one, doubly coherent production, produces a pion in one nucleus leaving it in its ground state, while the second nucleus is excited to the 1 +, T = 1 state. The second process, semicoherent production, also leaves in its ground state the nucleus where the pion is produced while the second one is broken. The cross sections for forward pions are compared to the standard incoherent production process. We observe that at energies below 130 MeV/ A the semicoherent process dominates the cross section for forward pion angles while at large energies around 800 MeV/ A it represents a fraction of around 30% of the incoherent cross section. The doubly coherent process leads to smaller cross sections, still in the measurable range for energies above 200 MeV/ A.

Intermittency for coherent and incoherent current ensemble model

We investigate the origin of intermittency for multiparticle distribution in momentum space, following the idea that there is a kind of power law distribution of the space-time region of hadron emission. Using the formalism of current ensamble model to describe boson sources we discuss intermittency exponents for the coherent and incoherent (chaotic) particle production scheme.

Decisive test of colour transparency in exclusive virtual photoproduction of vector mesons

The exclusive production of vector mesons in deep inelastic scattering is a hard scattering process with the well controlled size of quark configurations which dominate the production amplitude. This allows an unambiguous prediction of colour transparency effects in the coherent and incoherent production of vector mesons on nuclei. We demonstrate how the very mechanism of colour transparency leads to a belated onset of colour transparency effects as a function of Q 2. We conclude that the Q 2 dependence of the exclusive ϱ 0-meson production on nuclei and nucleons observed in the Fermilab E665 experiment gives a solid evidence for the onset of colour transparency. We propose the scaling relation between the ϱ 0 and the J/ Ψ production, which further tests the mechanism of colour transparency in exclusive (virtual) photoproduction.

Production of Higgs bosons in central ultrarelativistic heavy-ion collisions

The incoherent production of minimal and non-minimal, intermediate-mass Higgs bosons in central ultrarelativistic heavy-ion collisions is considered. In comparison to pp colliders, the increased number of nucleon-nucleon collisions prevailing in the heavy-ion collision raises the production cross sections by more than three orders of magnitude to about 10-100 nb for the standard-model Higgs boson, depending on its mass and on the collider energy at the LHC and SSC. For specific parameters the production cross sections for the Higgs bosons of the minimal supersymmetric extension of the standard model are even larger by one to three orders of magnitude.

Electromagnetic pair production in relativistic heavy ion collisions

We survey the phenomenon of pair production by the transient electromagnetic fields produced in relativistic heavy-ion collisions, as it impinges upon atomic, nuclear, and particle physics, and the design of accelerators and detectors. The subject is naturally divided between coherent production in peripheral collisions, and incoherent production in central collisions. We discuss examples illustrating both régimes.

Coherent and incoherent η-photoproduction from nuclei

Elastic and inelastic η-photoproduction from complex nuclei is studied in a distorted-wave impulse approximation (DWIA) framework. The elementary operator is obtained by using a dynamical model which employs the reactions πN→ πN, πN→ ππN and π −p→ ηn to fix the hadronic vertex as well as the isobar propagators and the process γN→ πN to constrain the electromagnetic vertex. The nuclear structure input for the inelastic transitions has been extracted from electron-scattering form factors. The η final-state interaction has been included via a simple optical potential using the ηN t-matrix as an input. We find that coherent η-production is dominated by the D 13(1520) isobar while spin-flip transitions to excited nuclear states are sensitive to the S 11(1535) resonance. Predictions are given for coherent production on 4He, 12C and 40Ca, as well as incoherent production on 6Li, 10B and 12C.

Incoherent two-photon production of the Higgs boson in relativistic heavy-ion collisions.

Cross sections for the incoherent production of the Higgs boson in ultrarelativistic heavy-ion collisions through two-photon processes are calculated by the direct Monte Carlo integration of Feynman diagrams incorporating nuclear-structure functions.

Many-body theory of high-energy heavy-ion reactions

The description of heavy-ion collisions up to bombarding energies of a few GeV per nucleon requires nonperturbative many-body approaches far from equilibrium which include the selfconsistent mean-field dynamics with its momentum-dependent forces as well the residual nucleon-nucleon collisional history. In this review we present such approaches within the framework of quantum correlation dynamics in the nonrelativistic as well as in the relativistic case and derive selfconsistent transport equations for the baryonic phase-space distribution. This quantity allows us to follow the space-time evolution of the reaction, to determine the degree of thermalization and to calculate one-body as well as collective observables. We explicitly study the approximations performed in the derivation of the respective transport theory in the nonrelativistic domain. Furthermore, we analyze the sensitivity of flow observables to the scalar and vector part of the nuclear selfenergy and try to extract information on the nuclear equation of state in comparison with experimental data. In the last part of this article we compare the theoretical predictions for differential particle yields with the available data where we adopt the incoherent on-shell nucleon-nucleon production mechanism. Detailed comparisons are presented for hard photons at bombarding energies from 15 MeV/u to 125 MeV/u, for dileptons at 1 GeV/u and for mesons (π's, η's, K +'s) from 30 MeV/u to 2 GeV/u. We finally discuss selection criteria for optimal probes with respect to the experimental determination of the nuclear equation of state at high densities.

A Monte Carlo program for the simulation of scintillation camera characteristics

There is a need for mathematical modelling for the evaluation of important parameters for photon imaging systems. A Monte Carlo program which simulates medical imaging nuclear detectors has been developed. Different materials can be chosen for the detector, a cover and a phantom. Cylindrical, spherical, rectangular and more complex phantom and source shapes can be simulated. Photoelectric, incoherent, coherent interactions and pair production are simulated. Different detector parameters, e.g. the energy pulse-height distribution and pulse pile-up due to finite decay time of the scintillation light emission, can be calculated. An energy resolution of the system is simulated by convolving the energy imparted with an energy-dependent Gaussian function. An image matrix of the centroid of the events in the detector can be simulated. Simulation of different collimators permits studies on spatial resolution and sensitivyt. Comparisons of our results with experimental data and other published results have shown good agreement. The usefulness of the Monte Carlo code for the accurately simulation of important parameters in scintillation camera systems, stationary as well as SPECT (single-photon emission computed tomography) systems, has been demonstrated.

Coherent and incoherent particle production off nuclei at high energies

The Glauber-Gribov model for hadronnucleus scattering is extended to multiproduction processes by supplimenting it with the AGK cutting rules. In contrast to the standard Glauber approach neither smallness of the interaction radius compared to the nuclear radii nor Gaussian form of theh-N-interaction profile function are assumed. We consistently use the theory of superciritical Pomeron. However all the results are more general and do not depend on the specific parametrization of the Pomeron pole amplitude. The inelastic screening due to the low mass diffractive excitations is also included. The cross-sections of coherent and incoherent diffractive production of the low mass hadronic states are calculated. We comment on the novel features of particle-nucleus interactions at superhigh energies when the interaction region blows up to the nucleus size. Specifically, one encounters here the rapid rise of the coherent interaction cross-sections and strong suppression of incoherent quasielastic processes.

Cross sections and angular distributions for 12C( γ, π0)

Absolute cross sections and angular distributions for the production of neutral pions from 12C by monochromatic photons have been measured near threshold. The contribution of incoherent pion production is found to be less than 10% for E γ ⩽168 MeV. Both the absolute cross section and the angular distribution indicate that a quantitative analysis requires final-state interactions of the produced π 0 with the surrounding nucleons to be taken into account.

Exclusive ρ0 and Φ production in deep inelastic muon scattering

Data are presented on exclusive ρ0 and ϕ production in deep inelastic muon scattering from a target consisting mainly of nitrogen. The ratio of the total cross sections for ρ0 and ϕ production is found to be 9∶(1.6±0.4) at 〈Q2〉=7.5 GeV2, consistent with theSU(3) prediction of 9∶2. Thet dependence for exclusive ρ0 production is found to become shallover asQ2 increases and, for largeQ2, thet dependence is typical of that for a hard scattering process. Furthermore, the ratio of the cross sections for coherent: incoherent production from nitrogen is found to decrease rapidly withQ2. Such behaviour indicates that even for exclusive vector meson production the virtual photon behaves predominantly as an electromagnetic probe.

Coherent π 0 production in neutrino reactions

We have calculated the cross section and angular distribution of the neutral current process ν + N → ν + N + π 0 involving the coherent interaction of a neutrino with a complex nucleus. A contrast is made to incoherent production ν + n → ν + n + π 0 on a single nucleon. The results are compared with observations from some recent experiments.

Fragmentation of12C nuclei in emulsion at 50 GeV/c

A total of 85212C-emulsion nucleus interactions at 4.2 GeV/c per incident nucleon was investigated. At least one charged projectile fragment was observed in 733 events, in which the multiplicity and angular distributions ofZ=1,2, and ≧3 projectile fragments were studied. Five events were observed in which12C projectile nuclei were fragmented into twoZ=3 fragments. Thus the cross section of this process is about 6×10−3 of the inelastic cross section. The angular distribution of projectile fragments becomes narrower as the fragment charge increases. At all values of fragment charges, a pronounced peak in the angular distribution can be observed at zero emission angle. In this paper, only the projectile-fragmentation events possessing no heavily ionizing particle (n h =0 events) have been investigated. Our sample contains 84 of these events, i.e., about 10% of the total inelastic events. The number of events withZ max, the charge of the emitted principal fragment, equal to 1, 2, 3, 4, and 5 are 11, 52, 13, 4, and 4, respectively. Of these 84 events, 36 interactions have a total charge of emitted projectile fragmentsZ * equal to 6, i.e., as much as the beam chargeZ p . Of the 36 events, 17 produce no charged pions and of the 17 events, 10 only represent the dissociation of12C→3α, i.e., 1.2% of the total inelastic interactions. The number of events withZ *=5, 4, 3, 2, and 1 are 27, 14, 4, 2, and 1, respectively. The average number of produced charged pions per one interacting projectile nucleon was estimated to be 1.2±0.1. This value agrees with the corresponding one in elementary interaction at the same energy per nucleon, a result pertaining to the incoherent production model in collision of two nuclei. In this class of events,n h =0, the number of stars in which H, He, Li, Be, and B isotopes were detected are 59, 58, 13, 4, and 4, respectively. The projected angular distributions ofZ=1 and 2 projectile fragments are Gaussian shaped, narrow, consistent with isotropy, and depend on the fragment. These distributions are consistent with quantum mechanical calculations using the sudden approximation and shell-model functions. From the angular measurements ofα-particle tracks in the dissociation12C→3α events, the distribution ofα-particle transverse momentum inside the carbon projectile nucleus was deduced. It seems that the dissociation of12C→3α happens via an intermediate8Be state.

Electromagnetic production of trimuons in muon scattering: Bethe-Heitler reactions with muon and heavy-lepton pairs

We analyze the Bethe-Heitler production of muon and heavy-lepton pairs using high-energy muon beams on a variety of targets. We give results for coherent production from a nucleus, for incoherent production from individual protons and neutrons, and for deep-inelastic production. Differential distributions are presented for the final leptons and the effects of experimental cuts are considered. This work complements our previous study of trimuon production via muon radiation, Compton radiation, and hadronic final-state interactions.