Production Of Baryon Resonances Research Articles

Vertex operators for production of baryon resonances in nucleon-gamma collisions with preserving gauge invariance and analyticity

Vertex operators for photo- and electro-production of baryon states with arbitrary spin-parity, [Formula: see text], are constructed. The operators obey gauge invariance and analyticity constraints. Analyticity is realized as a requirement of the generalized Siegert theorem for vertex form factors.

Analysis of pion production data measured by HADES in proton-proton collisions at 1.25 GeV

Baryon resonance production in proton-proton collisions at a kinetic beam energy of 1.25 GeV is investigated. The multi-differential data were measured by the HADES collaboration. Exclusive channels with one pion in the final state ($np\pi^{+}$ and $pp\pi^{0}$) were put to extended studies based on various observables in the framework of a one-pion exchange model and with solutions obtained within the framework of a partial wave analysis (PWA) of the Bonn-Gatchina group. The results of the PWA confirm the dominant contribution of the $\Delta$(1232), yet with a sizable impact of the $N$(1440) and non-resonant partial waves.

Study of quasielastic scattering using charged-currentνμ-iron interactions in the MINOS near detector

Kinematic distributions from an inclusive sample of 1.41 x 10^6 charged-current nu_mu interactions on iron, obtained using the MINOS Near Detector exposed to a wide-band beam with peak flux at 3 GeV, are compared to a conventional treatment of neutrino scattering within a Fermi gas nucleus. Results are used to guide the selection of a subsample enriched in quasielastic nu_mu Fe interactions, containing an estimated 123,000 quasielastic events of incident energies 1 < E_nu < 8 GeV, with <E_nu> = 2.79 GeV. Four additional subsamples representing topological and kinematic sideband regions to quasielastic scattering are also selected for the purpose of evaluating backgrounds. Comparisons using subsample distributions in four-momentum transfer Q^2 show the Monte Carlo model to be inadequate at low Q^2. Its shortcomings are remedied via inclusion of a Q^2-dependent suppression function for baryon resonance production, developed from the data. A chi-square fit of the resulting Monte Carlo simulation to the shape of the Q^2 distribution for the quasielastic-enriched sample is carried out with the axial-vector mass M_A of the dipole axial-vector form factor of the neutron as a free parameter. The effective M_A which best describes the data is 1.23 +0.13/-0.09 (fit) +0.12/-0.15 (syst.) GeV.

Baryon resonance production and dielectron decays in proton-proton collisions at 3.5 GeV

We report on baryon resonance production and decay in proton-proton collisions at a kinetic energy of $3.5$ GeV based on data measured with HADES. The exclusive channels $pp \rightarrow np\pi^{+}$ and $pp \rightarrow pp\pi^{0}$ as well as $pp \rightarrow ppe^{+}e^{-}$ are studied simultaneously for the first time. The invariant masses and angular distributions of the pion-nucleon systems were studied and compared to simulations based on a resonance model ansatz assuming saturation of the pion production by an incoherent sum of baryonic resonances (R) with masses $<2~$ GeV/$c^2$. A very good description of the one-pion production is achieved allowing for an estimate of individual baryon-resonance production-cross-sections which are used as input to calculate the dielectron yields from $R\rightarrow pe^+e^-$ decays. Two models of the resonance decays into dielectrons are examined assuming a point-like $RN \gamma^*$ coupling and the dominance of the $\rho$ meson. The results of model calculations are compared to data from the exclusive $ppe^{+}e^{-}$ channel by means of the dielectron and $pe^+e^-$ invariant mass distributions.

Production and Dalitz decays of baryon resonances in proton-proton interaction at = 3.16 GeV with HADES

One of the physics goals of HADES is to investigate spectral modifications of light vector mesons in strongly interacting matter via their dielectron (e+e−) decay channel. Theoretical models predict such modifications due to strong meson-baryon resonance coupling which can be also probed in elementary collisions. In 2007 electron-positron pair production has been measured in p+p reactions at a beam kinetic energy of 3.5 GeV. We present analysis results of the exclusive channels ppπ0, pnπ+, ppe+e−, which indicate contributions of higher resonances. In order to estimate production cross sections of the baryonic resonances, the results have been compared to Monte Carlo calculations based on a resonance model assuming an incoherent sum of various four-star resonances. To obtain the corresponding e+e− yields, two models of the width parametrization are applied in the simulation.

Generalized baryon form factors and proton structure functions in the Sakai–Sugimoto model

We investigate the production of positive parity baryon resonances in proton electromagnetic scattering within the Sakai–Sugimoto model. The latter is a string model for the non-perturbative regime of large Nc QCD. Using holographic techniques we calculate the generalized Dirac and Pauli form factors that describe resonance production. We use these results to estimate the contribution of resonance production to the proton structure functions. Interestingly, we find an approximate Callan–Gross relation for the structure functions in a regime of intermediate values of the Bjorken variable.

Resonances from PHSD

The multi-strange baryon and vector meson resonance production in relativistic nucleus-nucleus collisions is studied within the parton-hadron- string dynamics (PHSD) approach which incorporates explicit partonic degrees- of-freedom in terms of strongly interacting quasiparticles (quarks and gluons) in line with an equation-of-state from lattice QCD as well as the dynamical hadronization and hadronic collision dynamics in the final reaction phase. We find a significant effect of the partonic phase on the production of multi-strange antibaryons at SPS energies due to a slightly enhanced s¯ s pair production from massive time-like gluon decay and a larger formation of antibaryons in the hadronization process. We, futhermore, obtain a visible in-medium effects in the low mass dilepton sector from dynamical vector-meson spectral functions from SIS to SPS energies whereas at RHIC and LHC energies such medium ef- fects become more moderate. In the intermediate mass regime from 1.1 to 3 GeV pronounced traces of the partonic degrees of freedom are found at SPS energies which superseed the hadronic (multi-meson) channels as well as the correlated and uncorrelated semi-leptonic D-meson decays. The dilepton production from the strongly interacting quark-gluon-plasma (sQGP) becomes already visible at top SPS energies and more pronounced at RHIC and LHC energies.

Production of baryon resonances in collisions of 4He nuclei with carbon nuclei at a momentum of 4.2 GeV/c per nucleon

Under conditions of 4π geometry, Δ0-and Δ++-resonance production in collisions of 4He nuclei with carbon nuclei at a momentum of 4.2 GeV/c per nucleon was investigated for the first time. The resonance masses and widths are estimated by analyzing the experimental and background invariant-mass distributions of (pπ±) pairs. Contributions to pion production from Δ-resonance decays, as well as from direct pion production, are determined. The results are compared with corresponding data obtained for CC collisions at the same primary momentum of 4.2 GeV/c per nucleon. By and large, the results obtained here comply with the existence of a collective mechanism of delta-isobar excitation in nuclei.

Baryon-baryon and baryon-antibaryon interaction amplitudes in the spin-momentum operator expansion method

Partial-wave scattering amplitudes in baryon-baryon and baryon-antibaryon collisions and amplitudes for the production and decay of baryon resonances are constructed in the framework of the spin-momentum operator expansion method. The approach is relativistically invariant and it allows us to perform combined analyses of different reactions imposing analyticity and unitarity directly. The role of final-state interactions (triangle and box diagrams) is discussed.

Partial decay widths of baryons in the spin-momentum operator expansion method

The cross-sections for photo- and pion-induced production of baryon resonances and their partial decay widths to the two-body and multi-body final states are calculated in the framework of the operator expansion method. The approach is fully relativistic invariant, and it allows us to perform combined analyses of different reactions imposing directly the analyticity and unitarity constraints. All formulae are given explicitly in the form used by the Crystal Barrel Collaboration in the partial-wave analysis.

Search for exotic baryons in 800 GeV/c pp → pX

We present preliminary results of the search for the pentaquark candidates Θ(1540) and Ξ(1862) using data from Fermilab experiment E690 in the reaction pp → pX at 800 GeV/c. We find that production of pentaquark resonances is heavily suppressed with respect to the production of normal baryon and antibaryon resonances.

Partial-wave decomposition of pion and photoproduction amplitudes

Partial wave amplitudes for production and decay of baryon resonances are constructed in the framework of the operator expansion method. The approach is fully relativistically invariant and allow us to perform combined analyses of different reactions imposing directly analyticity and unitarity constraints. All formulas are given explicitly in the form used by the Crystal Barrel collaboration in the (partly forthcoming) analyses of the electro-, photo- and pion induced meson production data.

Backward yields of pions, protons, and deuterons in relativistic 28Si+Pb collisions at 14.6 [formula omitted

The production of pions, protons and deuterons is studied at a laboratory angle of 144° in 28Si+Pb collisions at 14.6 GeV/ c per nucleon. The centrality dependence of the pion yields is studied over the full impact parameter range using a zero degree calorimeter. The results are compared with the hadronic cascade model RQMD. These calculations are generally in agreement with the experimental results. According to these calculations, the pion yield in our acceptance is completely dominated by Δ-decay at freeze-out. Our measurements thus support the importance of baryon resonance production as one of the central features of relativistic heavy ion collisions at AGS energies. Although the strength of the pion spectrum is adequately described for kinetic energies above 50 MeV, an additional very soft component is observed in the pion spectra which is not predicted by RQMD. This very soft component accounts for a significant fraction of the total pion yield in this rapidity range but remains unexplained.

Quantum interference effects in (e, e′p) reactions

The response to longitudinally polarized electrons in coincident out-of-plane (e, e′p) reaction is discussed to study the role of final state interactions and quantum interference between different reaction channels, i.e. between direct (quasi) elastic proton emission and baryon resonance production. The high-energy suppression of this effect due to colour transparency is also discussed. Results are given for the 12C(e, e′p) 11B g.s. reaction.

Charmed particle production in hadron-hadron collisions

In the framework of Quark--Gluon--String Model developed recently in ITEP we calculate spectra of charmed particles $D$, $D_s$, $\Lambda_c$, $\Xi_c$, $\Omega_c$ in hadron--hadron collisions taking into account the decays of $S$--wave resonances like $D^*$, $D^*_s$, $\Sigma_c$, $\Sigma^*_c$, $\Xi^*_c$, $\Xi'_c$, and $\Omega^*_c$. We describe the bulk of the existing data on $D$, $D^*$, and $\Lambda_c$ production in $\pi p$ and $pp$ collisions and predict the yield of charmed particles in $\Sigma^-p$ and $\Xi^-p$ reactions at hyperon beam energies of $340\;GeV/c$ and $600\;GeV/c$. Because of significant production of baryon resonances our predictions for unfavored fragmentation differ from predictions of other models which do not take resonance production into account.

Detailed balance for the production and the reabsorption of baryon resonances and heavy-ion collisions

A new detailed balance derived by Danielewicz and Bertsch, which takes into account the finite width of baryon resonances, for cross sections of baryon resonance production and reabsorption is used in a hadronic transport model for relativistic heavy-ion collisions. By comparing calculations done with the commonly used detailed balance and the new detailed balance we study effects of the detailed balance on heavy-ion reaction dynamics, pion spectra, pion rapidity and transverse-momentum distributions.

InclusiveK *'s and∑ *'s production in 360 GeV/cpp interactions using the European hybrid spectrometer

We have studied the inclusive production of strange meson and baryon resonances in 360 GeV/cpp interactions. Cross sections forK *+(892) andK *−(892) are estimated to be 4.42±0.62 mb and 2.54±0.47 mb respectively and those for∑ +(1385) and∑ −(1385) are 0.67±0.11 mb and 0.26±0.07 mb respectively. Longitudinal and transverse momentum distributions forK *(892) and Σ(1385) are presented, as well as for their decay productsK 0 and Λ. An estimation is given on theK *(1430) and∑ *(1915) productions.

Inclusive resonance production in 7.3 GeV/c $$\bar pp$$ interactions

We present results on inclusive baryon and meson resonance production in\(\bar pp\) interactions at 7.3 GeV/c. Total inclusive and semi-inclusive cross sections are given for Δ(1232),∑*(1385), ϱ0,f andK*±(892) production. For the meson resonances separation into annihilation and non-annihilation components has been made, the annihilation component being dominant at this energy. We find that the energy dependence of inclusive cross sections for ϱ0 production inpp interactions and\(\bar pp\) non-annihilations shows a type of scaling behaviour previously reported for ϕ, ψ, ψ′ and ϒ production inpp interactions.Δ++, ϱ0 andK*± production are studied in terms of Feynmanx,y* andpT2. For the vector mesons we compare they* andx dependences with the predictions of simple quark models.

Baryons in dual unitarization and dynamical thresholds

Baryon exchange and baryon resonance production is introduced in the dual unitarisation scheme. The dynamical threshold for the production of meson and baryon resonances is incorporated. It is shown that the intercepts of the ω and the f, which are generated by baryons, are suppressed by the above dynamical threshold effects to α ω(0) ⋍ 0 and α f(0) < 0. The pomeron is shifted slightly upwards by baryon production. An upper limit is determined for the ratio of the crossed and uncrossed produced baryon lines. The breaking of the Freund-Rosner-Walz rule is discussed.

ρ exchange and density matrices in baryon resonance production

ρ exchange and density matrices in baryon resonance production