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1.
The low-energy part of theπ 0 spectrum associated with \(p\bar p\) annihilation at rest was measured in order to search for bound baryonium-like states. The upper limit for reaching such states via the emission of monochromaticπ 0's was found to be 8% per annihilation in the mass region of 1650 MeV. The low-energy part of the η spectrum from \(p\bar p\) annihilations at rest was also observed.  相似文献   

2.
Fermilab experiment E735 located at the CO intersection region of the $\sqrt s = 1.8$ TeV $p\bar p$ collider analysed over 900 Φ→K + K ? events. Measured were the transverse momentum spectrum, the correlation between the average transverse momentum <pt> and the charged particle multiphcityN c , as well as the probability of Φ production per charged track,N Φ /N c , versusN c . We have also made an estinate of the total inclusive cross section for Φ mesons, $\sigma (p\bar p \to \phi X) = 7.3 \pm 2.2 mb$ .  相似文献   

3.
The branching ratios of \(p\bar p\) annihilations into the neutral final states 2π0, π0γ, and 2γ are measured by stopping antiprotons in liquid hydrogen. They are \(B_{2\pi ^0 } = \left( {2.06 \pm 0.14} \right) \times 10^{ - 4} \) , \(B_{\pi ^0 \gamma } = \left( {1.74 \pm 0.22} \right) \times 10^{ - 5} \) , andB γγ<1.7×10?6 (95% c.l.).  相似文献   

4.
Results are presented on the inclusive production of π± mesons and protons in \(\bar p\) p interactions at an incident antiproton momentum of 32 GeV/c in the MIRABELLE bubble chamber, based on a sample of 55,000 inelastic events. The spectra of π+?) andp( \(\bar p\) ) are separated in the whole kinematically admitted region of phase space by a statistical method. The semi-inclusive and inclusive cross sections and the main average characteristics of π andp production are calculated. The invariant differential cross sections are studied as functions of the Fevnman scaling variablex, the rapidity and the transverse momentum. Thex distribution of π± mesons in the proton fragmentation region does not show any significant contribution from quark exchange or annihilation processes. A possible contribution of hard quark scattering on mesons or baryons is observed for large transverse momenta.  相似文献   

5.
We have investigated the properties of off-shell \(\bar K\) K and \(\bar p\) p annihilations into pions by using the interactionsK ? p → Λ + pions at 4.2 GeV/c. The properties considered are multiplicities, hadronic temperatures and angular distributions. These properties appear more akin to those of \(\bar p\) p annihilations in flight than to that of \(\bar p\) p annihilation at rest despite the fact that the annihilation energy is small.  相似文献   

6.
The production ofK * resonances has been studied in the reaction \(K^ - p \to \bar K^0 \pi ^ - p\) at 8.25 GeV/c. The data comes from a high statistics bubble chamber experiment (180 events/μb). Masses, widths and production cross-sections have been determined for the first threeK *'s. The contributions from natural and unnatural parity exchange have been obtained for theK *(890) and theK *(1420). A partial wave analysis of theK π system from threshold to 1.9 GeV provides evidence for a 0+ enhancement near 1.4 GeV which could be interpreted as the κ(1350).  相似文献   

7.
Predictions based on axiomatic field theory are obtained from the assumption that the difference between thepp and thep \(\bar p\) elastic scattering observed at the CERN ISR is caused by an “odderon-like” term in the scattering amplitude. A wide class of amplitudes violating the Pomeranchuk relation is considered. Contrary to common opinion, severe restrictions on the high-energy behaviour of the phase of the crossing-odd amplitude are shown to follow for the whole class. Less pronounced but still visible consequences follow for the phases of thepp andp \(\bar p\) amplitudes separately. We derive the corresponding high-energy bounds and correlations using the general frame of analyticity, crossing symmetry and unitarity. As a special case, the maximal odderon amplitude is discussed.  相似文献   

8.
\(N\bar N\) annihilation into three pseudoscalar mesons especially πππ and \(K\bar K\pi \) are studied in the quark pair creation model or the3 P 0 model in which two \(q\bar q\) pairs are annihilated and two \(q\bar q\) pairs are created with quantum numbers of the vacuum or3 P 0. The correlations of two pions to form ?,f 2 and the resonance AX(1565) which is recently found by the ASTERIX group are taken into account. A proper treatment of the symmetry among the three pions in the final state shows that the \({}^{31}S_0 p\bar p\) annihilation into ?π is suppressed in agreement with the experiment. We calculate the cosθ distribution or the distribution of the Dalitz plot as the function of the angle between the direction of emission of one decay pion in the resonance centre of mass and the line of flight of the resonance. The interferences of π+ρ+, π?ρ+ and π0ρ0 in the isospin 0 channels and π±ρ? and π0 f 2 in the isospin 1 channel reproduce the peaks. The cos θ distribution for the P-wave \(p\bar p\) annihilation into πAX depends strongly on the size of the pion since the amplitude interfers with the π±ρ? amplitude which is sensitive to the size of the pion. The same model qualitatively explains the \(p\bar p\) annihilation into \(K\bar K\pi \) in whichK or \(\bar K\) and π are correlated to formK* \(\bar K\) or \(\bar K\) *K final states. We can qualitatively reproduce different patterns of the cos θ distribution for theK *+ andK *0.  相似文献   

9.
InclusiveK s 0 , Λ and \(\bar \Lambda\) -production has been investigated in \(\bar p\) p-interactions at 22.4 GeV/c. Total and topological cross sections and multiplicity characteristics of neutral strange particles have been determined. DifferentialK s 0 and Λ-cross sections and also characteristics of annihilation processes with neutral kaon production have been studied. It is shown that the difference of the shapes of the invariantx-distributions forK-mesons in the fragmentation region for annihilation and non-annihilation processes can be described in the framework of the “dual” valon model, but not by considering the current (undressed) quark recombination mechanisms only. The polarization of Λ and \(\bar \Lambda\) -hyperons has been measured.  相似文献   

10.
Data on the reactionsv μ p→ μ? pπ+ and \( \bar v_\mu p \to \mu ^ + p\pi ^ - \) in the Δ(1232) region are presented and a test of the PCAC hypothesis, using a modified version of the Adler model, is performed. The analysis is based on 1081 events in the neutrino and on 180 events in the antineutrino reaction, obtained in a bubble chamber experiment with BEBC at CERN. The experimental cross-sections for an invariant hadronic massW<1.4 GeV and an (anti-)neutrino energyE v L >10 GeV are determined to be (0.628±0.059)·10?38 cm2 for the neutrino and (0.168±0.023)·10?38 cm2 for the antineutrino reaction. TheQ 2 andW distributions, the density matrix elements of the Δ resonance, and moments of the pion angular distribution are discussed. The data are found to be in good agreement with the Adler model in theQ 2 region below 1 GeV2. A maximum likelihood fit for the axial massm A in the axial-vector form factor yields a value ofm A =1.31±0.12 GeV. At lowQ 2 the data confirm the PCAC hypothesis and the discrepancy, formerly observed between the experimental and theoretical cross-sections forv μ p→ μ? pπ+ at low momentum transfers (Q 2?0.2 GeV2), is understood as being due to inadequate pion ‘off-mass-shell’ corrections.  相似文献   

11.
The nonlinear relation between the mean effective polarizability $ \bar \gamma $ of molecules and the local-field anisotropy in uniaxial liquid crystals is demonstrated. Stringent constraints on $ \bar \gamma $ from below, indicative of the dependence of $ \bar \gamma $ on the liquid-crystal state and the change of the “ $ \bar \gamma $ = const” paradigm, are established. The theoretical results are confirmed by experiments with nematic liquid crystals having high and low birefringences.  相似文献   

12.
13.
We present the first results on the production of fast (p>10 GeV/c)p, \(\bar p\) , Λ and \(\bar \Lambda \) from π± hydrogen and nucleus interactions at 30 GeV/c using the CERN Ω′ spectrometer. We have used five nuclear targets (C, Al, Cu, Sn, Pb) to study theA-dependence of the inclusive particle distributions in the region 0.3<x F <0.6. The high statistical level of our experiment allows us to demonstrate the differentA-behaviour of baryon and antibaryon inclusive reactions. We relate this difference to the final state interaction inside a nucleus using the formation-zone model.  相似文献   

14.
Experiments have been performed at 5 GPa on liquid Fe-FeS in order to determine Fe and S self-diffusivity as a function of temperature. The viscosity of the sample was then obtained using the Stokes-Einstein relation. The results are in excellent agreement with previous experiments where the viscosity of a material of the same composition under similar conditions was measured directly. These results support high, near-metallic, values of diffusivity and low viscosity in liquid Fe-S up to a few hundred K above the eutectic temperature, in contrast with some previous studies. Moreover, these results fully confirm the validity of the Stokes-Einstein relation between viscosity and diffusion coefficients for Fe0.61S0.39.  相似文献   

15.
A partial wave analysis of theK \(\bar K\) system produced by 8.25 GeV/cK ? mesons in the reaction \(K^ - p \to K\bar K\Lambda ^{ 0} \) has been performed, taking into account the information provided by the Λ0 decay. Thef′ region is dominated byD 0 (?) andD 1 (+) waves. We see no evidence for the production of new 0++ states in the mass region 1.05 to 1.75 GeV.  相似文献   

16.
The elastic and inelastic \(\bar p\) p cross sections at 70 GeV/c have been determined in an experiment performed at CERN using BEBC equipped with a TST. The topological cross sections were measured and the moments of the inelastic multiplicity distribution are 〈n c 〉=6.16±0.09, 〈n c 〉/D=2.04±0.05 andf 2 cc =2.97±0.03. The average number of Dalitz pairs per inelastic event is (3.12±0.09)×10?2. Assuming that these all arise from π0 decay the average π0 multiplicity is \(\langle n_{\pi ^0 } \rangle = 2.71 \pm 0.14\) . The \(\bar p\) p?pp cross section differences lead to an annihilation cross section σ A = 4.42±0.41 mb and the moments of the annihilation multiplicty distribution are 〈n A 〉=8.0±0.3, 〈n A 〉/D=2.5±0.2 andf 2 A?? =?1.4±0.3. An independent check of σ A was made by investigating fast forward charged and neutral secondary interactions in the TST and in the surrounding neon-hydrogen mixture, and gives a value σ A = 5.0±1.6 mb. The ratio of fast \(\bar n\) to \(\bar p\) production in non-annihilation interactions at 70 GeV/c is found to be 0.45±0.11.  相似文献   

17.
18.
The spectra of leading and nonleading charmed baryons (Λc and $\bar \Lambda _c$ ) and the asymmetries between these spectra measured in Σ? A, π ? A, and pA collisions at p L =600 GeV/c in the E781 experiment are simultaneously described within the framework of the Quark-Gluon String Model (QGSM). It is shown that the charmed baryon spectra can be fitted by QGSM curves calculated with the parameter of diquark fragmentation, $a_f^{\Lambda _c } = 0.006$ . It was found in this experiment that the asymmetry between the spectra of Λc and $\bar \Lambda _c$ in π ? A collisions is of nonzero value. It might be described in our model only assuming that the string junction is transferred from target proton into the kinematical region of pion projectile fragmentation.  相似文献   

19.
We calculate the amplitude of $gg\to b\bar{b}$ production for the colour singlet, J z =0, di-gluon state at $\mathcal{O}(\alpha_{\mathrm{S}}^{2})$ order. We consider the cancellation and a realistic cut-off, of the infrared divergent terms. We show that the one-loop radiative QCD contributions effectively reduce the Born level result for the central exclusive $b\bar{b}$ cross section at the LHC. This process is essentially the only irreducible QCD background to the exclusive $H\to b\bar{b}$ signal.  相似文献   

20.
We studied the dielectric properties of nano-sized liquid water samples confined in polymerized silicates MCM-41 characterized by pore sizes 3–10 nm. Freezing temperature suppression in nanopores helps keep the water samples in liquid form at temperatures well below 0°C and thus effectively study the properties of supercooled liquid water. We report the first direct measurements of the dielectric constant by the dielectric spectroscopy method and demonstrate very clear signatures of the second-order phase transition of ferroelectric nature at temperatures next to the λ-point in the supercooled bulk water in full agreement with the recently developed model of the polar liquid.  相似文献   

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