共查询到20条相似文献,搜索用时 15 毫秒
1.
Final state interaction effects inpp→ pΛK
+ andpd →3Heη reactions are explored near threshold to study the sensitivity of the cross-sections to thepΛ potential and theηN scattering matrix. The final state scattering wave functions between Λ andp andη and3He are described rigorously. The Λ production is described by the exchange of one pion and aK-meson between two protons in the incident channel. Theη production is described by a two-step model, where in the first step a pion is produced. This pion then produces anη by interacting with another nucleon 相似文献
2.
Variational Monte Carlo calculations of the ground state separation energiesB
Λ of thes-shell hypernuclei and also of
Λ
9
Be have been made for an Urbana-type central space-exchange ΛN potential consistent with Λp scattering, and also including three-body ΛNN forces. Thes-shell hypernuclei are treated asA-body systems (A = baryon number), and
Λ
9
Be is analysed as a partially nine-body problem in the Λ — 2α model. The reduction ofB
Λ due to the space-exchange ΛN potential has been calculated for thes-shell hypernuclei for a range of interactions: both ΛN and ΛN + ΛNN forces. ForA = 3,4,5 the exchange energy is approximately, 0.04, 0.15 and 0.50 MeV, respectively. For
Λ
9
Be a much more limited study gives ≅ 1.3 MeV. These values are much larger than that for ‘soft’ ΛN +NN potentials when the correlations are weak.
Preliminary results were presented at the DAE Symp. on ‘Nuclear Physics’ Vol. 32B (1989). 相似文献
3.
A. Sibirtsev J. Haidenbauer H. -W. Hammer U. -G. Meißner 《The European Physical Journal A - Hadrons and Nuclei》2006,29(3):363-367
We show that the recently measured asymmetry in helicity-angle spectra of the Λ-hyperons, produced in the reaction pp → K
+Λp reaction, and the energy dependence of the total pp → K
+Λp cross-section can be explained consistently by the same Λp final-state interaction. Assuming that there is no final-state interaction in the Σ0
p channel, as suggested by the available data for the reaction pp → K
+Σ0
p, we can also reproduce the energy dependence of the Λ/Σ0 production ratio and, in particular, the rather large ratio observed near the reaction thresholds. The nominal ratio of the
Λ and Σ0 production amplitudes squared, i.e. when disregarding the final-state interaction, turns out to be about 3, which is in line with hyperon production data from
proton and nuclear targets available at high energies. 相似文献
4.
A. Sibirtsev J. Haidenbauer H. -W. Hammer S. Krewald 《The European Physical Journal A - Hadrons and Nuclei》2006,27(3):269-285
A study of the strangeness production reaction pp → pK+Λ for excess energies of ε≤150MeV, accessible at high-luminosity accelerator facilities like COSY, is presented. Methods to
analyze the Dalitz plot distribution and angular spectra in the Jackson and helicity frames are worked out and suitable observables
for extracting information on low-lying resonances that couple to the KΛ system and for determining the Λp effective-range parameters from the final-state interaction are identified and discussed. Furthermore, the chances for identifying
the reaction mechanism of strangeness production are investigated. 相似文献
5.
Mahmood Mian 《Pramana》1993,41(2):145-149
The binding energy of the double hypernucleus
ΛΛ
6
is calculated in α + 2Λ cluster model using the method of translation invariant basis TIMO. As regards the required interaction
potentials we use a density dependent effective ΛN force and a gaussian form for ΛΛ potential. With these interactions a very reasonable value ofB
ΛΛ is obtained if the oscillator states up to the excitation quantum numberN=12 are taken into account in the expansion of wavefunction of the hypernucleus. This value ofN is much smaller than that obtained in an earlier study. This lowering inN value is attributed to a much better choice of ΛN potential used in the present study. 相似文献
6.
T.Yu. Tretyakova D.E. Lanskoy 《The European Physical Journal A - Hadrons and Nuclei》1999,5(4):391-398
Properties of light neutron-rich Λ hypernuclei (16
ΛC, 12
ΛBe, and 11
ΛLi) are calculated within the Skyrme-Hartree-Fock approach. Interplay between hypernuclear interaction features and properties
of these hypernuclei is studied. Response of weakly bound neutron states to hyperon addition depends generally on core distortion
by hyperon, and it is essentially different for the different states. This response is especially sensitive to details of
the ΛN interaction for 1p
1/2 states. Implications of the nuclear spin-orbit potential and nuclear incompressibility in the neutron-rich system properties
are inferred. Dependence of the Λ binding energies in hypernuclei on Z at fixed A is discussed.
Received: 16 December 1998 相似文献
7.
The forces of interaction as reflected in the cosθ plane analytic structures of the helicity amplitudes of Σ−-p and Λ-p scattering are optimally exploited using the conformal mapping technique of Cutkosky and coworkers. A suitable parametrization
of these amplitudes in the mapped variable is then chosen so that it can see the zeros better. These zeros are then located
by making a good fit to the differential scattering cross-section curves. The effect of these zeros upon the cross-sections
is discussed. Values for the phase shifts and coupling parameters between channels of fixedJ values are also computed. 相似文献
8.
N. Kaiser 《The European Physical Journal A - Hadrons and Nuclei》1999,5(1):105-110
We analyze the recent total cross section data for pp→pΛK
+ near threshold measured at COSY. Using an effective range approximation for the on-shell pΛ S-wave final state interaction we extract from these data the combination ?= (2|K
s|2+|K
t|2)−1/2= 0.38 fm4 of the singlet (K
s) and triplet (K
t) threshold transition amplitudes. We present an exploratory calculation of various (tree-level) vector and pseudoscalar meson
exchange diagrams. Pointlike ω-exchange alone and the combined (ρ0,ω,K*+)-exchange can explain the experimental value of ?. The pseudoscalar meson exchanges based on a SU(3) chiral Lagrangian turn
out to be too large. However, when adding π0-exchange in combination with the resonant πN→S
11(1650) →KΛ transition and introducing monopole form factors with a cut-off Λc= 1.5 GeV one is again able to reproduce the experimental value of ?. More exclusive measurements are necessary to reveal
the details of the pp→pΛK
+ production mechanism.
Received: 28 October 1998 / Revised version: 12 January 1999 相似文献
9.
R. Kotte 《Physics of Particles and Nuclei Letters》2011,8(9):969-972
Results on Λp femtoscopy are reported at the lowest energy so far. At a beam energy of 1.76.A GeV, the reaction Ar + KCl was studied with
HADES at SIS18/GSI. A high-statistics and high-purity Λ sample was collected, allowing for the investigation of Λp correlations at small relative momenta. The experimental correlation function is compared to corresponding model calculations
allowing the determination of the space-time extent of the Λp emission source. The Λp radius is found significantly smaller than that for Au + Au/Pb + Pb collisions in the AGS, SPS and RHIC energy domains, but
larger than that for electroproduction from He. Taking into account all available data, we find the Λp source radius to increase almost linearly with the number of participants to the power of one-third. 相似文献
10.
P. Zh. Aslanyan 《Physics of Particles and Nuclei》2009,40(4):525-557
Exotic strange multibaryon states have been observed in the effective mass spectra of: Λπ±, Λπ+π−, Λp, Λpp, Λπp, ΛΛ and ΛK
s
0, K
s
0
p, K
s
0π± subsystems. The measured Λ/π+ ratio for average multiplicities from the pC reaction is equal to (5.3 ± 0.8) × 10−2, and it is approximately two times larger than the Λ/π+ ratio simulated by the FRITIOF model and than that of experimental pp reactions at the same energy. The observed wellknown resonances Σ*+ (1385) and K*± (892) from PDG are good tests of this method. The mean value of the mass for the Σ*−(1385) resonance is shifted to 1370 MeV/c
2 and the width is two times larger than the same value from PDG. Such kind of behavior for the width and invariant mass of
Σ*− (1385) resonance is interpreted as an extensive contribution from stopped Ξ− → Λπ− and medium effect. There is enhancement of the production contribution for all observed hyperons. A few events were registered
by hypothesis of light H
0 and heavy H
0, + dihyperons. Dihyperons were observed by weak decay channels: (Σ−
p), (Λpπ−), (Λpπ0), and (K
−
pp).
The text was submitted by the author in English. 相似文献
11.
The ΛΛ binding energy (B
ΛΛ) of the s- and p-shell hypernuclei are calculated variationally in the cluster model and multidimensional integrations are
performed using Monte Carlo. A variety of phenomenological Λ-core potentials consistent with the Λ-core energies and a wide
range of simulated s-state ΛΛ potentials are taken as input. The B
ΛΛ of ΛΛ6He is explained and ΛΛ5He and ΛΛ5H are predicted to be particle stable in the ΛΛ-core model. The results for s-shell hypernuclei are in excellent agreement
with those of non-VMC calculations. The ΛΛ10Be in ΛΛαα model is overbound for combinations of ΛΛ and Λα potentials. A phenomenological dispersive three-body force, V
Λαα, consistent with the B
Λ of Λ9Be in the Λαα model underbinds ΛΛ10Be. The incremental ΔB
ΛΛ values for the s- and p-shell cannot be reconciled, consistent with the finding of earlier analyses.
相似文献
12.
L. S. Geng E. Oset M. Döring 《The European Physical Journal A - Hadrons and Nuclei》2007,32(2):201-211
We evaluate theoretically the radiative decay widths into γΛ and γΣ
0 of the two poles of the Λ(1405) found in chiral unitary theories and we find quite different results for each of the two poles. We show that, depending
on which reaction is used to measure the Λ(1405) radiative decays, one gives more weight to one or the other pole, resulting in quite different shapes in the γΛ(Σ
0) invariant-mass distributions. Our results for the high-energy pole agree with those of the empirical determination of the
γΛ and γΣ
0 radiative widths (based on an isobar model fitting of the K-p atom data), which are sometimes referred to as “experimental data”. We have made a detailed study of the K
-
p→π
0
γΛ(Σ
0) and π
-
p→K
0
γΛ(Σ
0) reactions and have shown that they, indeed, lead to different shapes for the γΛ(Σ
0) invariant-mass distributions. 相似文献
13.
T. Maruta S. Ajimura K. Aoki A. Banu H. Bhang T. Fukuda O. Hashimoto I. Hwang S. Kameoka B. H. Kang E. H. Kim J. H. Kim M. J. Kim Y. Miura Y. Miyake T. Nagae M. Nakamura S. N. Nakamura H. Noumi S. Okada Y. Okayasu H. Outa H. Park P. K. Saha Y. Sato M. Sekimoto T. Takahashi H. Tamura K. Tanida A. Toyoda K. Tsukada T. Watanabe 《The European Physical Journal A - Hadrons and Nuclei》2007,33(3):255-258
The proton decay asymmetry, αNM
p , of the polarized Λ -hypernuclei, 5
ΛHe , 12
ΛC and 11
ΛB , has been investigated to understand the reaction mechanism of the non-mesonic weak-decay process. These Λ -hypernuclei
were produced in the highest statistics ever via the (π+, K
+) reaction at 1.05GeV/c by using the SKS spectrometer at KEK 12GeV PS. The results show that the αNM
p are very small for these s -shell and p -shell hypernuclei. 相似文献
14.
A. Ramos V. K. Magas E. Oset H. Toki 《The European Physical Journal A - Hadrons and Nuclei》2007,31(4):684-686
We critically revise the recent claims of a deeply bound K-pp state associated to a peak seen in the Λp invariant-mass spectrum following nuclear K- absorption reactions measured by the FINUDA Collaboration. An explicit theoretical simulation shows that the peak is simply
generated from a two-nucleon absorption process, like K
-
pp→Λp, followed by final-state interactions of the produced particles with the residual nucleus. 相似文献
15.
W. Schroeder 《The European Physical Journal A - Hadrons and Nuclei》2007,31(4):503-505
The strangeness production program at the COSY-TOF experiment is discussed. The apparatus is shown emphasizing the technique
to measure delayed decays. Results obtained for the reactions pp→K
+
Λp and pp→K
0
Σ
+
p are discussed. 相似文献
16.
B. Saghai J. -C. David B. Juliá-Dıaz T. -S. H. Lee 《The European Physical Journal A - Hadrons and Nuclei》2007,31(4):512-514
Differential cross-section and single polarization observables in the process γp→K
+
Λ are investigated within a constituent-quark model and a dynamical coupled-channel formalism. The effects of two new nucleon
resonances and of the K
*(892)- and K1(1270)-exchanges are briefly presented. 相似文献
17.
Bianchi Type-I cosmological models containing perfect fluid with time varying G and Λ have been presented. The solutions obtained represent an expansion scalar θ bearing a constant ratio to the anisotropy in the direction of space-like unit vector λ
i
. Of the two models obtained, one has negative vacuum energy density, which decays numerically. In this model, we obtain Λ
∼ H
2, Λ ∼ R
44/R and Λ ∼ T
−2 (T is the cosmic time) which is in accordance with the main dynamical laws for the decay of Λ. The second model reduces to a
static solution with repulsive gravity.
相似文献
18.
L. Roca C. Hanhart E. Oset U. -G. Meißner 《The European Physical Journal A - Hadrons and Nuclei》2006,27(3):373-380
The Λ(1520)-resonance has been recently studied in a unitarized coupled-channel formalism with πΣ(1385), KΞ(1530), ˉN and πΣ as constituents blocks. We provide a theoretical study of the predictions of this model in physical observables of
the pp → pK+K-p and pp → pK+π0π0Λ reactions. In particular, we show that the ratio between the π0π0Λ and K-p mass distributions can provide valuable information on the ratio of the couplings of the Λ(1520)-resonance to πΣ(1385) and
ˉN than the theory predicts. Calculations are done for energies which are accessible in an experimental facility like COSY at
Jülich or the developing CSR facility at Lanzhou. 相似文献
19.
20.
H. Bhang S. Ajimura K. Aoki A. Banu T. Fukuda O. Hashimoto J. I. Hwang S. Kameoka B. H. Kang E. H. Kim J. H. Kim M. Kim T. Maruta Y. Miura Y. Miyake T. Nagae M. Nakamura S. N. Nakamura H. Noumi S. Okada Y. Okayasu H. Outa H. Park P. K. Saha Y. Sato M. Sekimoto S. Shin T. Takahashi H. Tamura K. Tanida A. Toyota K. Tsukada T. Watanabe H. J. Yim 《The European Physical Journal A - Hadrons and Nuclei》2007,33(3):259-263
Recent exclusive coincidence measurements of non-mesonic weak decays (NMWD) reported for the ratio of the partial decay width
of neutron-induced-to-proton-induced NMWD, Γn/Γp , values of 0.45±0.11±0.03 and 0.51±0.13±0.04 for 5lam and 12
Λ
C , respectively. These observations agree well with the improved theoretical Γn/Γp ratios which are in the range of 0.3-0.7. It appears that the long-standing discrepancy between the experimental and theoretical
values of Γn/Γp has finally been solved. However, when compared to the results of intra-nuclear cascade (INC) calculations, the observed
numbers of both single nucleons and coincident nucleon pairs are strongly quenched. The quenching of the proton yield observed
previously has been interpreted as an increase of the Γn/Γp ratio. On the other hand, significant contributions from the two-nucleon-induced three-body process ΛNN → nNN are predicted. Indeed, the angular correlation of the emitted nucleon pairs in the NMWD of 12
Λ
C showed not only decay events in back-to-back kinematics, but also events with non-back-to-back kinematics. In this paper
we show that the difficulties to extract the correct Γn/Γp ratio from the proton spectra is related to the three-body weak-interaction process which strongly quenches the nucleon yields. 相似文献