Spectral temperatures of Δ0(1232) resonances produced in p 12C and d 12C collisions at 4.2 GeV/c per nucleon

The reconstructed experimental transverse momentum (p _t ) distributions of Δ⁰(1232) resonances produced in p ¹²C and d ¹²C collisions at 4.2 A GeV/c and the corresponding spectra calculated using Modified FRITIOF model were analyzed in the framework of Hagedorn Thermodynamic Model. The spectral temperatures of Δ⁰(1232) resonances were extracted from fitting their p _t spectra with one-temperature Hagedorn function. The extracted spectral temperatures of Δ⁰(1232) were compared with the corresponding temperatures of π ^? mesons in p ¹²C and d ¹²C collisions at 4.2 A GeV/c obtained similarly from fitting the p _t spectra of π ^? by one-temperature Hagedorn function. The spectral temperatures of Δ⁰(1232) resonances agreed within uncertainties with the corresponding temperatures of π ^? mesons produced in p ¹²C and d ¹²C collisions at 4.2 A GeV/c.     

Centrality dependence of rapidity spectra of negative pions in 12 C+12 C and 12 C+181 Ta collisions at 4.2 GeV/c per nucleon

The centrality dependences of the experimental rapidity as well as transversemomentumversus rapidity spectra of negative pions were analyzed quantitatively in ¹²C+¹²C and ¹²C+¹⁸¹Ta collisions at 4.2 GeV/c per nucleon using fitting the pion spectra by Gaussian distribution function. The experimental results were compared systematically with the predictions of the Quark-Gluon-String Model (QGSM) adapted to intermediate energies.     

Study of multiparticle azimuthal correlations in central CNE, MgMg, CCu, and OPb interactions at energy of 3.7 GeV per nucleon

Azimuthal correlations between protons and between pions have been investigated in central CNe, MgMg, CCu, and OPb collisions at an energy of 3.7 GeV/nucleon. Negative (back-to-back) correlations have been observed for protons in CNe, CCu, and for π ^? mesons in CNe and MgMg collisions. For π^? mesons, positive (side-by-side) azimuthal correlations have been observed for heavy systems of CCu and OPb. The Quark-Gluon String Model satisfactorily describes the experimental results both for protons and π^? mesons.     

Inclusive yields and transverse spectra of non-strange mesons: Comparisons with the quark model,and an estimate of the fraction of “direct” pion production

Recent data on the production ofη, ?⁰, ω and other mesons in hadron-hadron collisions at intermediate energies are studied. Their transverse spectra dσ/dp_T² are all found to be approximately exponential, with similar slopes, ～3.4 (GeV/c)^?2, up to about p_T² = 2(GeV/c)². The inclusive yields of the mesons are broadly in agreement with quark model predictions. In the case of pions, a distimction is made between those directly produced and those produced indirectly via resonance decay. It is estimated that between 10% and 30% of pions are directly produced.     

Coherent two pion photoproduction on 12C

We develop the formalism for coherent two pion photoproduction in nuclei and perform actual calculations of cross sections for π⁻π⁺ and π⁰π⁰ photoproduction on ¹²C. We find that due to the isospin symmetry the cross section for π⁰π⁰ production is very small and has a maximum when the pions propagate together. However, the kinematical region where the energies and polar angles of the two π⁰ mesons are equal and their relative azimuthal angle Ø = 180° is forbidden. Conversely in the π⁻π⁺ production the pions prefer to have a relative azimuthal angle 180° and the production of the pions propagating together is suppressed. The dominant one-body mechanism in both channels is related to the excitation of the Δ isobar. Hence the reaction can serve as a source of information about Δ's properties in nucleus. We have found that the reaction is sensitive to effects of the pion and Δ renormalization in the nuclear medium, similar to those found in the coherent (γ, π⁰) reaction, but magnified because of the presence of the two pions.     

Inclusive neutron and proton energy spectra following the negative pion absorption at rest in 12C

The results of a measurement of the inclusive energy spectra of the neutrons and protons emitted following the absorption at rest of negative pions on ¹²C are presented. The spectra have been measured with the time-of-flight method with an overall resolution of 650 psec. From the neutron spectrum the rate of 1.7 × 10^?2 neutrons per stopped pion has been deduced for the single-neutron emission reaction ¹²C(π^?, n)¹¹ B. Comparisons are made with calculated spectra and other experimental spectra.     

Features of carbon-carbon interactions at a momentum of 4.2 GeV/c per nucleon that are accompanied by the production of Λ hyperons and K S 0 mesons versus the degree of nuclei collision centrality

Experiemntal data obtained by using the 2-m propane bubble chamber of the Joint Institute for Nuclear Research (JINR, Dubna) are used to study the effect collision centrality on the spectra of Λ hyperons and K _S ⁰ mesons produced in carbon-carbon interactions at 4.2 A GeV/c. The multiplicity of participant protons having momenta in excess of 300 MeV/c is taken to be a measure of collision centrality. The features of pions and protons accompanying strange-particle production are also presented. The experimental data in question are compared with the prediction of a modified version of the FRITIOF model. It is shown that strange particles are predominantly produced in central and semicentral collisions. The average kinematical features of K _S ⁰ mesons are found to be indepedent of collision centrality. At the same time, the average transverse momentum of Λ hyperons and the average value of their emission angle increase slowly with increasing degree of collision centrality. The anisotropy of the angular distributions of both Λ hypersons and K _S/0 mesons in the c.m. frame of nucleon-nucleon collisions decreases with increasing collision centrality. The average transverse momentum of K _S ⁰ mesons is approximately 1.6 times higher than the average transverse momentum of π ^? mesons.     

Correlations associated with particles produced at small angles in pp collisions at the CERN ISR

Data on correlations between momentum analysed protons, pions or K mesons, and charged particles produced in pp collisions at the CERN ISR are presented. The charged particles were detected in a ～4π scintillation counter hodoscope. The pseudo-rapidity distributions are well described by production within the limits of cylindrical phase space, with negative kaons and antiprotons yielding narrower distributions than protons, pions and positive kaons. The azimuthal distributions show symmetry around the t-channel axis in the rest frame of the recoiling mass M_x in pp → aX (a = detected proton, pion, positive kaon).     

Investigation of the inclusive spectra of secondary protons and pions of low kinetic energies and of their wide pair correlations in π − A interactions at 43 GeV/c

The inclusive invariant cross sections for protons produced at angles of θ=90° and 60° and for positively and negatively charged pions produced at an angle of θ=90° are presented for π ^?Be, π ^?Al, and π ^?Cu interactions induced by 43-GeV/c incident π ^? mesons. The shape of the inclusive spectra of secondary hadrons, the A dependence of their cross sections, and the correlation functions for pairs of likely charged secondary hadrons at large angles of their divergence are studied. The kinematical region explored in the present article corresponded to kinetic energies of T≈0.16–0.70 GeV and T≈0.20–0.76 GeV for secondary protons and secondary pions, respectively. The angles of divergence of hadrons forming a pair, ψ, satisfied the condition cos ψ相似文献   

Formation of six-nucleon systems and nuclei in 16Op collisions at a momentum of 3.25 GeV/c per nucleon

The results obtained by studying the production of six-nucleon systems and nuclei that is accompanied by the yield of charged pions in ¹⁶Op collisions at a momentum of 3.25 GeV/c per nucleon are presented. It is shown that the correlation of the yield of mirror ³H (³He) nuclei with the production of π ⁺ (π ^?) mesons is due to the charge-exchange process involving an oxygen-nucleus proton (neutron) knocked out predominantly from an alpha-particle cluster.     

Elliptic flow of ν ands <Emphasis Type="Italic">π</Emphasis><Superscript>0</Superscript> mesons in heavy-ion collisions at 2 <Emphasis Type="Italic">A</Emphasis> GeVmesons in heavy-ion collisions at 2 <Emphasis Type="Italic">A</Emphasis> GeV

Elliptic flow of ν and π ⁰ mesons emitted at midrapidity are studied in collisions of 1.9 A GeV ⁵⁸Ni+⁵⁸Ni and 2 A GeV ⁴⁰Ca+^natCa. The observed anisotropy corresponds to a negative elliptic flow signal for ν mesons, indicating a preferred emission perpendicular to the reaction plane. In contrast, only small azimuthal anisotropies are observed for π ⁰ mesons. This may indicate that ν mesons freeze out earlier from the central interaction region than pions.     

On induced double-nucleon emission. III. 12C, (π−, NN) and short-range correlations

The reaction channel (π^?, NN) for the absorption of bound negative pions by nuclei is used as a means to study nuclear short range correlations. A three-body partial-wave analysis has been carried out for the final-state scattering which includes a Reid soft-core nucleon-nucleon interaction and an optical potential. This coupled-channel formalism rapidly converges as we eliminate the asymptotic single-nucleon and deuteron interactions. It is found that for ¹²C reasonable agreement with experiment cannot be obtained in this model without modification of the high relative-momentum components of bound shell model pair wave functions.     

Nucleons after pion absorption

We calculate energy spectra and angular distributions of single and correlated spectra after the absorption of stopped pions in nuclei. We assume: The pion is abosrbed by a pair of nucleons; these primary nucleons may leave the nucleus directly or only after one or more collisions with other nucleons. We propose a multiple scattering expansion for the intranuclear cascade after pion absorption. Various experimental data are successfully described in shape and absolute magnitude. The ratio R_np = R(π^?np → nn)/R (π^? pp → np) is determined from the experimental proton spectra: R_np = 13 ± 6.     

Pion-production in heavy-ion collisions at SIS energies

We investigate the production of pions in heavyion collisions in the energy range of 1–2 GeV/A. The dynamics of the nucleus-nucleus collisions is described by a set of coupled transport equations of the Boltzmann-Uehling-Uhlenbeck type for baryons and mesons. Besides theN(938) and theΔ(1232) we also take into account nucleon resonances up to masses of 1.95 GeV/c² as well asπ-,η- andρ-mesons. We study in detail the influence of the higher baryonic resonances and the 2π-production channels (NN→NNππ) on the pion spectra in comparison toπ ^? data fromAr+KCl collisions at 1.8 GeV/A andπ ⁰-data forAu+Au at 1.0GeV/A. We, furthermore, present a detailed comparison of differential pion angular distributions with the BEVALAC data forAr+KCl at 1.8 GeV/A. The general agreement obtained indicates that the overall reaction dynamics is well described by our novel transport approach.     

A measurement of the charge asymmetry in the decay η → π+π−πo

An experiment has been carried out at the Rutherford Laboratory to look for a possible asymmetry in the eta decay to three pions. Eta mesons were produced in the process π^?p→ ηn. The experiment produced 165311 decays η → π⁺π^?π^o from which we determined a value for the charge asymmetry A = (0.0028 ± 0.0026). We see no evidence for C-violation in this decay.     

Charged particle emission following the absorption of stopped π− in 12C, 59Co and 197Au

Energy spectra of charged particles (p, d, t, ³He, α) emitted following the absorption of stopped π^? in ¹²C, ⁵⁹Co and ¹⁹⁷Au have been measured. The results are compared with results from neutron spectroscopy and discussed in the context of the quasi-deuteron model of π^? absorption.     

The four-pion final state in pp annihilations at 5.7 GeV/c

577 events from $\text{p}\text{p}\text{→2π}{}^{\mathrm{+}}\text{2π}{}^{\mathrm{?}}$ annihilations at 5.7 GeV/c are analyzed. Single-particle spectra are studied and an effective matrix element in the form Π_i=1⁴ exp(?Bp_Ti²) is determined. The rates for production of ?° and f⁰ mesons are estimated and the influence of resonances on the angular distributions of pions and dipions is investigated. Transverse momenta correlations can be explained using peripheral phase space.     

Rapidity and azimuthal correlations in π − p and π −C collisions at 40 GeV/c

New results are presented that were obtained from an analysis of experimental data on rapidity and azimuthal correlations in π ^? p and π ^?C collisions at 40 GeV/c. Some nonstandard methods for seeking correlations are developed. Dynamical correlations associated with fluctuations of the number of intranuclear collisions at a given multiplicity are discovered in π ^?C collisions. It is shown that the Lund model cannot describe the experimental data being discussed.     

Observation of a γ transition in the Λ4H hypernucleus

The γ spectra induced by stopped K^? mesons in a ⁷Li target were obtained in coincidence with the accompanying charged pions. A thorough analysis of these spectra indicates that the observed 1.09 MeV line can be ascribed to a γ transition in the ⁴_ΛH hypernucleus.