Production Of Nucleon Resonances Research Articles

Hybrid model of proton structure functions

We develop a ``hybrid'' model of the proton inelastic structure functions applicable in a wide region of invariant mass of produced states $W$ and invariant momentum transfer $Q$ including deep inelastic scattering (DIS), nucleon resonance production, as well as the region close to inelastic threshold. DIS is described in terms of the parton distributions together with higher-twist corrections from an available global QCD fit. The resonant part is addressed in terms of the Breit-Wiegner contributions from five states including the $\mathrm{\ensuremath{\Delta}}(1232)$ resonance, the $N(1440)$ Roper resonance, and three effective resonances describing the second and third resonance regions. The couplings of the nucleon resonances to photon are described in terms of helicity amplitudes. The nonresonant background is addressed in terms of DIS structure functions smoothly extrapolated to low-$W$ and low-$Q$ values with the proper behavior at the real photon limit ${Q}^{2}=0$ as well as near the inelastic threshold. We independently treat the transverse ${F}_{T}$ and the longitudinal ${F}_{L}$ structure function and fix the model parameters from a global analysis of the world hydrogen electroproduction and photoproduction cross-section data. We demonstrate a very good performance of the model by comparing our predictions with data on differential cross sections and the structure functions ${F}_{2}$ and $R={F}_{L}/{F}_{T}$.

The γp→ϕη′p reaction in an effective Lagrangian model

In this work, we investigate the production of nucleon resonances in the $\ensuremath{\gamma}p\ensuremath{\rightarrow}\ensuremath{\phi}{\ensuremath{\eta}}^{\ensuremath{'}}p$ reaction within an effective Lagrangian approach and isobar model. We first discuss the possible roles of the $N(1895)$, $N(1900)$, $N(2100)$, and $N(2120)$ productions in this reaction. By considering the $\ensuremath{\pi}$, $\ensuremath{\eta}$, and ${\ensuremath{\eta}}^{\ensuremath{'}}$ exchanges between the initial $\ensuremath{\gamma}$ and proton, we find that the excitation of the $N(1895)$ in the intermediate state gives the most important contribution near the threshold. The dominant role of the $N(1895)$ is mainly attributed to its large coupling to the $N\ensuremath{\eta}$ and $N{\ensuremath{\eta}}^{\ensuremath{'}}$ channels. Additionally, we also discuss the possibility of looking for a new nucleon resonance proposed in some recent works. We find that if this resonance indeed exists it should also show signals in the present reaction. Thus the present reaction offers the opportunities to study the properties of the $N(1895)$ and test the existence of the proposed new nucleon resonance.

Nucleon resonance production in the γp→pηϕ reaction

In this work, we perform a study of nucleon resonance production in the $\gamma p \to p\eta\phi$ reaction within an effective Lagrangian approach. In our model, we consider the excitation of the $N^*(1535)$, $N^*(1650)$, $N^*(1710)$ and $N^*(1720)$ in the intermediate state and the background term. We find that this reaction is dominated by the excitation of the $N^*(1535)$ in the near threshold region. Especially, we study the possible role of the scalar meson exchange in this reaction. It is found that the $f_0(980)$ exchange may give a significant contribution and the parity asymmetry can be used to identify its role in this reaction.

Comparison of heavy-ion transport simulations: Collision integral in a box

Simulations by transport codes are indispensable to extract valuable physics information from heavy ion collisions. In order to understand the origins of discrepancies between different widely used transport codes, we compare 15 such codes under controlled conditions of a system confined to a box with periodic boundary, initialized with Fermi-Dirac distributions at saturation density and temperatures of either 0 or 5 MeV. In such calculations, one is able to check separately the different ingredients of a transport code. In this second publication of the code evaluation project, we only consider the two-body collision term, i.e. we perform cascade calculations. When the Pauli blocking is artificially suppressed, the collision rates are found to be consistent for most codes (to within $1\%$ or better) with analytical results, or completely controlled results of a basic cascade code after eliminating the correlations within the same pair of colliding particles. In calculations with active Pauli blocking, the blocking probability was found to deviate from the expected reference values. The reason is found in substantial phase-space fluctuations and smearing tied to numerical algorithms and model assumptions in the representation of phase space. This results in the reduction of the blocking probability in most transport codes, so that the simulated system gradually evolves away from the Fermi-Dirac towards a Boltzmann distribution. As a result of this investigation, we are able to make judgements about the most effective strategies in transport simulations for determining the collision probabilities and the Pauli blocking. Investigation in a similar vein of other ingredients in transport calculations, like the mean field propagation or the production of nucleon resonances and mesons, will be discussed in the future publications.

Current Status and Performance of the Crystal Ball and TAPS Calorimeter

In the A2 experiment at the Mainz microtron (MAMI) electron accelerator, the production of nucleon resonances and light mesons off protons and nuclei using energy-tagged bremsstrahlung photons is studied. Decay products are measured with two electromagnetic calorimeters: Crystal Ball (CB), whose 672 NaI crystals cover almost the entire solid angle, and TAPS, which consists of 366 BaF2 and 72 PbWO4 crystals in the forward direction. Here, we report on the current performance and status of both detectors after 10 years of operation in Mainz. In addition, we present the new CB high-voltage system, a new fast readout scheme for TAPS, and the planned upgrade of the CB data-acquisition system.

Nucleon resonance production in K+N interactions

In this work, we discuss the possibility of studying nucleon resonances in the $K^+N$ interactions. Based on our model calculations, it is found that the hyperon exchange plays an important role for the excitation of nucleon resonances in the $K^+N$ interactions. Therefore, the studies on nucleon resonance production in the $K^+N$ interactions can offer us valuable information about the couplings of nucleon resonances with strange particles. By selecting suitable decay channels of nucleon resonances, some reactions are also suitable to look for missing resonances.

Dynamical coupled-channels: The key to understanding resonances

Recent developments on a dynamical coupled-channels model of hadronic and electromagnetic production of nucleon resonances are summarized.

Target-mass corrections and the Bloom-Gilman duality of the nucleon structure function

The occurrence of the Bloom-Gilman local duality in the low-order moments of the nucleon structure function is investigated for values of the squared four-momentum transfer Q 2 between ∼0.5 and 10 ( GeV/c) 2 . At variance with previous analyses truncated Cornwall-Norton moments, limited to the nucleon-resonance production regions, are considered. The role played by target-mass corrections is illustrated, showing that target-mass effects are necessary (but not sufficient) for producing the observed Bloom-Gilman duality of the nucleon structure function. The possibility of a local duality between the unphysical region at large values of the Nachtmann variable and the nucleon elastic peak contribution is analyzed. It is found that the proton magnetic form factor extracted assuming local duality is significantly below the experimental data at low and intermediate values of Q 2.

Spectator scaling in semi-inclusive inelastic lepton scattering off the deuteron and the neutron structure function

The energy and angular distributions of slow nucleons produced in semi-inclusive inelastic lepton scattering off the deuteron are investigated. It is shown that within the spectator mechanism the semi-inclusive cross section exhibits a peculiar scaling property, the spectator scaling, which can be used as a model-independent test of the dominance of the spectator mechanism itself. This property may provide a very interesting tool to obtain model-independent information on the neutron structure function both in the deep-inelastic regime and in the nucleon-resonance production regions.

First observation of the production of nucleon resonances in antiproton annihilation in liquid deuterium

First observation of the production of nucleon resonances in antiproton annihilation in liquid deuterium

A note on weak production of nucleon resonances

The resonant cross sections for weak production of nucleon resonances is extracted from experimental data on high energy\(\bar v\)-collisions and compared with predictions of theoretical models.

Production of nucleon resonances in π +d collisions

Production of nucleon resonances in π +d collisions in the energy range 1–5 GeV has been investigated in a model developed earlier as a direct means of testing the dynamic role of N ∗ exchanges found in the processes π +d → pp and dp → pd. The results which are given in the form of inclusive cross sections for π +d → p(N ∗, Δ +) show that despite the dominance of the isosbars P 33 and F 37, there are appreciable signals from the more prominent N ∗ resonances (F 15 and to some extent D 13), so as to be amenable to experimental observation. It is further argued that observation of these N ∗ should help discriminate the N ∗ exchange mechanism from other alternative such as OPE.

Electromagnetic Inelastic Form Factors of Processes eN->eN* in a Relativistic Quark Model

(Received Nove1p-ber 21, 1974) A formulation of the quark model, based on the .relativistic wave equation, is considered in connection with processes of electromagnetic excitations of nucleon, eN~eN*. The nor­ malizable solutions of the wave equation are used, arid . the electromagnetic interaction is defined .via minimal coupling. Consistent calculations of the cross-sections for .the electro­ production of nucleon resonances, without appearence of redundant, .q•-dependent factors, and photoproduction matrix elements are compared with experimental data. In particular, it is shown that at small -q•, the oscillator potential, responsible· for the· existence of the bound states of thr.ee quarks, is 'too strong.

Production of nucleon resonances by single diffraction dissociation at the CERN ISR

The single diffraction dissociation process pp → (p π + π −)p has been studied at the CERN ISR at √ s = 45 GeV and 0.1 < − t < 0.6 GeV 2. The reaction is dominated by nucleon resonance production: pp → pN (1520) and pp → pN(1688) with cross-sections (0.25 ± 0.08) mb and (0.56 ± 0.19) mb respectively.

Bremsstrahlung Model Calculation of High-Energy Nucleon-Nucleon Scattering

A model calculation of nucleon-nucleon scattering is presented which results in an amplitude that in the elastic high-energy limit realizes the Wu-Yang idea regarding the relation between the elastic form factor of the nucleon and the differential cross section, and which is consistent with the behavior of the differential cross section for the production of nucleon resonances. The calculation makes use of results obtained with the same model in the study of electroproduction.

Proton-proton elastic scattering and nucleon resonance production at high energies

Abstract Angular distributions of proton-proton elastic scattering have been measured for incident beam momenta of 10.0, 12.0, 14.2 and 24.0 GeV/ c over a range of lab scattering angles from 12 to 152 mrad. This is equivalent to a range of four-momentum transfer squared from about 0.1 to 6.7 GeV 2 at the highest momentum. Nucleon resonance production in the two-body reaction p + p → p + X has been studied at 24.0 GeV/ c incident momentum from 13.5 to 112 mrad by measuring the proton momentum spectra from the elastic peak down to a momentum corresponding to a missing mass of about 2.6 GeV. The new data are compared with previous results and theoretical models.

Nucleon resonance production in high-energy pp collisions

The expe r imen ta l and theore t ica l s tudy of near fo rward different ial cross-sect ions for react ions of form pp-->pJ~* has been the subjec t of m u c h effort in recent years . E x p e r i m e n t a l in format ion , ma in ly ob ta ined f rom (~ missing mass ~ expe r imen t s (1), for the h igh-energy region ( laboratory m o m e n t a g rea te r t h a n about 5 GeV/c) ind ica tes t ha t p roduc t ion of the iV*(1400) and the .N'*(1690) is essent ia l ly energy i n d e p e n d e n t and the different ial cross-section in each case is pa r ame t r i z ed as de/dr = A exp [bt] for small t, as in pp elast ic scat ter ing. I n resonance p roduc t ion A is m u c h smal ler t h a n in elast ic scat ter ing, whi le the re appears to be subs tan t i a l va r i a t ion in t he va lues of b f rom resonance to resonance. Fo r t he J~*(1400) and J~*(1690) b is ~ 1 4 (GeV/e) -~ and ~ 7 (GeV/c) -2, respec t ive ly , compared wi th b ~-~ 9 for elast ic scat ter ing. The basis for our calcula t ion is t h a t t he p ro ton and these p roduced J~* ' s m a y be considered as the g round s ta te and exc i ted spat ia l s ta tes of the same th r ee -qua rk sys tem (2-4). The ba ryon sca t te r ing ampl i tudes are t h e n bu i l t up f rom t h e qua rk scatt e r ing ampl i tudes , the p roduc t ion of J~* ' s differing because each has a charac te r i s t i c in te rna l spat ia l w a v e funct ion. A s imi lar ca lcu la t ion has a l ready been car r ied ou t by ttENDRV and TREFIL (5) for r : p ~ ~ j~* . T h e y considered t h e p ion-baryon ampl i t ude to be bui l t up f rom the p ion-quark ampl i tudes us ing Glauber theory (8). I n our discussion of pp-+ pJ~* we must , for consis tency, consider all t he ba ryons to be compos i te th ree -qua rk systems. F o r t he reac t ion A § B + C ~ D w i t h A and C iVy-body and B and D iVy-body composi te systems, the reac t ion ampl i tude is in Glauber t h e o r y (s) r e la ted to the scatte r ing (assumed elastic) of the cons t i tuen t par t ic les by t h e following re la t ions :

Momentum transfer dependence of nucleon resonance production in proton-proton collisions at 24 GeV/c

Nucleon resonance production in the two-body reaction p + p → p + N ∗ has been studied at 24 GeV/ c incident momentum for angles from 12 to 117 mrad by measuring proton momentum spectra from the elastic peak down to a momentum corresponding to a missing mass of about 2.6 GeV.

Isospin analysis of pion and nucleon resonance production in NN collisions

After a brief survey of isospin relations for the general reaction NN→N′N′ + kπ ( k = 1, 2, 3, …), cases of k = 2, 3 and resonance formation are discussed. The reaction NN → N′ Δπ is found particularly suitable for the isospin analysis, and its cross sections are given in terms of various isospin exchange amplitudes. Another eventually feasible example is NN → N′ Δϱ.

The production of nucleon resonances in proton-proton collisions at high energy and large momentum transfers

Experimental results are presented on the excitation of the nucleon isobars N ∗(1518) and N ∗(1688) in proton-proton collisions at an incident momentum of 19.2 GeV/ c and in the range of four-momentum squared 0.6 ⩽7 z. sfnc; t| ⩽ 5.8 GeV 2.