This paper presents a large solid angle measurement of the positive pion absorption cross section on 4He and its decomposition into partial channels. The total absorption cross sections at incident pion kinetic energies of Tπ+=70, 118, 162, and 239 MeV are 35±5, 52±4, 51±5, and 27±2 mb, respectively. These values are lower than those reported in some previous experiments. At all pion energies a large fraction of the absorption cross section is due to multinucleon channels.
Data with (C=PRC) are taken from PR C56, 1872.
A systematic study of the spectra and yields of K+ and K− is reported by experiment E866 as a function of centrality in Au+Au collisions at 11.6A GeV/c. The invariant transverse spectra for both kaon species are well described by exponentials in mt, with inverse slope parameters that are largest at midrapidity and which increase with centrality. The inverse slopes of the K+ spectra are slightly larger than the inverse slopes of the K− spectra. The kaon rapidity density peaks at midrapidity with the K+ distribution wider in rapidity than K−. The integrated total yields of K+ and K− increase nonlinearly and steadily with the number of projectile participants. The yield per participant for kaons is two to three times larger than the yield from N−N collisions. This enhancement suggests that the majority of kaons in central Au+Au reactions are produced in secondary hadronic collisions. There is no evidence for an onset of additional kaon production from a possible small volume of baryon-rich quark-gluon plasma. The differences between K+ and K− rapidity distributions and transverse spectra are consistent with a lower phase space for K− production due to a higher energy threshold. These differences also exclude simple thermal models that assume emission from a common equilibrated system.
In this case FRAGB=NUCLEAR FRAG + PROTONS.
In this case FRAGB = NUCLEAR FRAG + PROTONS.
The production of Λ hypernuclei was studied in proton reactions with Bi nuclei and the lifetime of the produced heavy hypernuclei was measured by the observation of delayed fission using the recoil shadow method. The measurements were performed at 1.9 GeV proton energy whereas the background was determined at 1.0 GeV. From the distribution of the fission fragments in the shadow region the lifetime τ=[161±7( statist. )±14( system. )] ps was obtained and from a comparison of counting rates of prompt and delayed fission fragments the production cross section of hot Λ hypernuclei was determined to be (350±140) μ b.
No description provided.
The reaction pp → K + Λp was measured exclusively at the cooler synchrotron COSY at beam momenta of p Beam = 2.50 GeV/c and p Beam = 2.75 GeV/c using the TOF detector. Angular and momentum distributions were obtained for the full phase space of the reaction products. Total cross sections were extracted to be (2.7 ± 0.3) μ b and (12.0 ± 0.4) μ b, respectively. The polarization of the Λ -hyperon was determined as a function of its transversal momentum and was found to be negative for transverse momentum transfers of p T ≥ 0.3 GeV/c. The results together with existing data are compared with phenomenological parametrizations and model calculations on the basis of meson exchange.
Axis error includes +- 10/10 contribution (Overall normalization error).
Associated strangeness production in the reactions γp → K + Λ and γp → K + Σ 0 was measured with the SAPHIR detector at the electron stretcher ring ELSA at Bonn. Data on total and differential cross sections and on hyperon polarizations are presented. The total cross section for Λ production shows a strong threshold enhancement whereas the Σ 0 data have a maximum at about E γ =1.45 GeV. Along with the angular decomposition of the differential cross section into polynomials, this suggests resonance production. However, the angular distributions of both hyperon polarizations vary only slightly with the photon energy. Λ and Σ 0 polarizations show opposite signs and change sign over the angular range.
Total cross section for the reaction GAMMA P --> K+ LAMBDA.
Total cross section for the reaction GAMMA P --> K+ SIGMA0.
Differential cross section for the reaction GAMMA P --> K+ LAMBDA in the GAMMA energy range 0.90 to 1.10 GeV in three energy bins.
New experimental results on the π + d → π + π − pp and π + d → π + π + nn reactions at T π 1 = 283 MeV are presented. In-plane coincidence data were taken with the CHAOS spectrometer using pions from the M11 channel at TRIUMF. Because of the quasi-free nature of the pion-production reaction, the present study is equivalent to studying the elementary π + N → π + π ± N reactions on protons and neutrons simultaneously. These exclusive measurements provide a set of many-fold differential cross sections which are an ideal testing ground for microscopic models describing the πN → ππN reaction. The interpretation of the data relies on a model which is based on effective chiral Lagrangians to describe the piece of the reaction that includes only π's and N 's, and on effective Lagrangians to account for intermediate Δ's and N ∗ ' s . The measured many-fold differential cross sections are used to constrain some parameters of the model (ξ, f Δ , C, g N ∗ Δπ and g N ∗ Nπ ). Finally, the π + π ± invariant mass distributions display no evidence of strongly interacting pion pairs in either the I = J = 0 or the I = 2 J = 0 channels.
No description provided.
No description provided.
Enhanced production of ΛΛ pairs, above the prediction of a two-step process model, is observed near threshold (around the masses of 2.23 – 2.26 GeV/c 2 ) in the 12 C(K − ,K + ) reaction at P K − = 1.66GeV/c using a scintillating fiber target. The differential cross section for the ΛΛ production averaged over 2.3° ≤ $$ K + ≤ 14.7° in the momentum region 0.95 ≤ p K + ≤ 1.3GeV/c was found to be 7.6 ± 1.3 μb/sr, and that for the enhancement approximately 3 μb/sr.
No description provided.
No description provided.
No description provided.
We determine the top quark mass m_t using t-tbar pairs produced in the D0 detector by \sqrt{s} = 1.8 TeV p-pbar collisions in a 125 pb^-1 exposure at the Fermilab Tevatron. We make a two constraint fit to m_t in t-tbar -> b W^+bbar W^- final states with one W boson decaying to q-qbar and the other to e-nu or mu-nu. Likelihood fits to the data yield m_t(l+jets) = 173.3 +- 5.6 (stat) +- 5.5 (syst) GeV/c^2. When this result is combined with an analysis of events in which both W bosons decay into leptons, we obtain m_t = 172.1 +- 5.2 (stat) +- 4.9 (syst) GeV/c^2. An alternate analysis, using three constraint fits to fixed top quark masses, gives m_t(l+jets) = 176.0 +- 7.9 (stat) +- 4.8 (syst) GeV/C^2, consistent with the above result. Studies of kinematic distributions of the top quark candidates are also presented.
No description provided.
Enhanced production of strange baryons and anti-baryons at central rapidity in S-W and S-z.sbnd;S with respect to p-A reactions has been reported by the CERN experiments WA85 and WA94. The WA97 experiment is extending such a study to Pb Pb collisions making use of the newly developed silicon pixel detectors. Results on Λ, Ξ − and Ω − production in Pb Pb collisions at 158 A GeV/ c at central rapidity are presented. Transverse mass spectra and particle ratios are presented. Hyperon yields are given as a function of the collision centrality and compared with those obtained from p-Pb collisions using the same experimental setup.
No description provided.
No description provided.
No description provided.
We have observed a clear peak below the Σ+-production threshold in the 4He(K−,π−) reaction at 600MeV/c and θKπ=4∘. This is confirmation of the existence of the bound state of Σ4He, which was reported in the 4He(stoppedK−,π−) reaction. As in the case of stopped kaons, no such peak was found in the 4He(K−,π+) spectrum. Quantitatively reliable parameters for this level have been established. The binding energy and the width of the bound state are 4.4±0.3(stat)±1(syst) MeV and 7.0±0.7(stat)−0.0+1.2(syst) MeV, respectively.
$HE4/S represents the HE4/SIGMA+ bound state.
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