Λ-hyperon lifetime in very heavy hypernuclei produced in the<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>p</mml:mi></mml:math>+U interaction

Ohm, H.; Hermes, T.; Borgs, W.; Koch, H.; Maier, R.; Prasuhn, D.; Stein, H. J.; Schult, O.W.B.; Pysz, K.; Rudy, Z.; Jarczyk, L.; Kamys, B.; Kulessa, P.; Strzalkowski, A.; Cassing, W.; Uozumi, Yusuke; Zychor, I.

doi:10.1103/physrevc.55.3062

Cited by 51 publications

(48 citation statements)

References 9 publications

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“…Such a test requires, besides the knowledge of the lifetimes of light hypernuclei, also the precise knowledge of the lifetimes for heavy hypernuclei. The existing experimental results on the lifetime of heavy hypernuclei, which have been produced in antiproton interactions with Bi and U nuclei [6], agree within the errors with the data obtained in proton induced reactions on these targets [7,8]. Experiments with electrons on Bi nuclei [9,10] lead to an order of magnitude longer lifetime, however, one has to note that the detection conditions of these experiments were not suitable for a measurement of such short lifetimes as quoted in antiproton and proton experiments.…”

supporting

confidence: 72%

“…± 14 ps) [8], but is not in agreement with the published data for p+U reaction from Ref. [7] (240 ± 60 ps). We point out, however, that a later reanalysis of the uranium data [17], in which Poisson statistics of events in position distributions was used instead the Gaussian statistics, lead to a smaller value of the lifetime (194 ± 55 ps).…”

Section: Theoretical Valuescontrasting

confidence: 39%

“…Such a method for the separation of delayed fission fragments from the prompt fission [12] has been used in all experiments measuring the lifetime of heavy hypernuclei [6,7,8,9,10,11]. Experiments with a thin target in an internal proton beam have the advantage that the recoiling hypernuclei escape with larger velocities compared to hypernuclei produced by electrons or antiprotons and therefore allow for the most accurate determination of the lifetime.…”

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confidence: 99%

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Nonmesonic decay of the Λ-hyperon in hypernuclei produced by p + Au collisions

et al. 2001

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Abstract. The lifetime of the Λ-hyperon for the nonmesonic decay ΛN → NN has been determined by a measurement at COSY Jülich of the delayed fission of heavy hypernuclei produced in proton -Au collisions at Tp=1.9 GeV. It is found that heavy hypernuclei with mass numbers A≈(180±5) and atomic numbers Z≈(74±2) fission with a lifetime τΛ=130 ± 13(stat.) ± 15(syst.) ps. This value together with the results obtained for other heavy hypernuclei in previous investigations indicates -on the confidence level of 0.9 -a violation of the phenomenological ∆I=1/2 rule for the ΛN → NN transitions as known from the weak mesonic decays of kaons and hyperons. The free Λ-hyperon undergoes almost with 100% probability the mesonic decay, i.e. Λ → π − + p or Λ → π o + n. The energy release (≈ 40 MeV) and its sharing among pion and nucleon implies (due to momentum conservation) that the energy of the nucleon is much smaller than the Fermi energy of nucleons in the nucleus. Therefore, such a process is strongly suppressed in nuclei and a different type of the hyperon decay -nonmesonic decaydominates for all but the lightest hypernuclei. This decay can be induced by neutrons (n+Λ → n+n) or by protons (p+Λ → p+n) with an energy release much higher than in the mesonic decay (≈ 180 MeV). The higher nucleon energy, due to an equal sharing of the energy among both nucleons, implies that this process is not blocked by the Pauli principle.The nonmesonic Λ -decay represents an example for the nonleptonic weak interaction of baryons with a change of strangeness (∆S = 1) and isospin (∆I= 1/2 or 3/2). Thus it is an analogue of the weak nucleon -nucleon interaction, but it involves a new degree of freedom, i.e. strangeness. The strong and Coulomb interactions preserve strangeness and therefore the weak interaction responsible for the nonmesonic decay is not masked by contributions from these two interactions. Therefore the nonmesonic decay enables to study both parity violating and parity conserving amplitudes in contrast to the nucleonnucleon interaction, where the latter amplitudes are completely masked by strong and Coulomb forces [1].The standard model of electro-weak interactions favors neither ∆I= 1/2 transitions nor the ∆I= 3/2 transitions, but experimental investigations on the properties of mesonic decays of kaons and hyperons lead to the obvious dominance of the ∆I= 1/2 part (the so called ∆I= 1/2 rule) [2]. The question arises whether this is also the case for the nonmesonic decay of the Λ-hyperon. Data from the nonmesonic decay of light hypernuclei, which were used to test this hypothesis in the phenomenological model proposed by Block and Dalitz [3], are affected by too large errors to solve this problem unambigously [4]. Another possibility for testing the validity of the ∆I= 1/2 rule is an investigation of the dependence of the hyperon lifetime for the nonmesonic decay on the mass of the hypernucleus in which the hyperon is embedded [5]. Such a test requires, besides the knowledge of the lifetimes of light hypernuclei, also the precis...

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supporting

confidence: 72%

Section: Theoretical Valuescontrasting

confidence: 39%

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confidence: 99%

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Nonmesonic decay of the Λ-hyperon in hypernuclei produced by p + Au collisions

et al. 2001

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“…On the other hand, although our calculations do not deem it necessary, it should be possible to further increase the ratio of signal to background using delayed fission of pion absorption fragments, a technique used with success in the production of Λ hypernuclei in [13] and tentatively suggested for the present reaction [14]. The set up for the experiment is suited to present experimental facilities, particularly those of low energies, and the cross sections predicted are of the order of those presently being measured with high precision in the (γ,p) reaction [10], which makes this reaction a very practical method to produce deeply bound pionic atoms.…”

Section: Introductionmentioning

confidence: 99%

Deeply bound pionic atoms from the (γ,p) reaction in nuclei

Hirenzaki

Oset

2002

Physics Letters B

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We study the (γ, p) reaction on 208 P b leading to 207 P b with a bound pion attached to it in the lowest 1s or 2p pionic levels. The reaction can be made recoilless to optimize the production cross section but we must choose a bit higher photon energy to overcome the Coulomb barrier in the proton emission. The cross sections obtained are easily measurable and can be larger than 50 per cent of the background from inclusive (γ,p). This makes it a clear case for the detection of the pionic atom signals, converting this reaction into a practical tool to produce deeply bound pionic atoms.

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“…A renewed interest in the subject of strangeness production in proton-nucleus, pion-nucleus, and kaon-nucleus reactions appeared since the observation of hypernucleus bound states for some nuclei such as [1][2][3][4][5][6][7]. The energy level density, branching ratio of non-mesonic to mesonic decays, and hypernucleus lifetime have been investigated.…”

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confidence: 99%

Hot hypernucleus formation in high-energy photonuclear reactions

Gonçalves¹,

Oliveira²,

Medeiros³

et al. 2004

Braz. J. Phys.

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The probability of a compound residual hot hypernucleus formation at the end of pre-equilibrium phase of high energy photonuclear reactions is calculated with a time dependent Monte Carlo Multicollisional Cascade (MCMC) approach. The emission of hadrons during the rapid phase of the reaction is discussed and characteristics of the residual nucleus are obtained. Results for mass and charge distributions of the formed hot hypernucleus are shown and its excitation energy is discussed.A renewed interest in the subject of strangeness production in proton-nucleus, pion-nucleus, and kaon-nucleus reactions appeared since the observation of hypernucleus bound states for some nuclei such as -7]. The energy level density, branching ratio of non-mesonic to mesonic decays, and hypernucleus lifetime have been investigated. Another important subject is the effect of the Pauli exclusion principle on the suppression of mesonic decay in favor of the non-mesonic decay of hyperons, mainly for heavy target nuclei. Moreover, the many-body re-scattering Λ-N also contributes to the thermalization of the hyperon, and increases its probability of being confined in the nuclear environment [6,7]. Indeed, static calculations based on studies of the hyperon-nucleon potential [8,9], chiral perturbation theory [10], and statistical models [11] have provided some insight on the properties of hypernuclei such as their mass shifts, wave functions, fissioning path, and attachment probabilities of hyperons in nuclei.Theoretical and experimental interest in photonuclear kaon-production reactions has grown from the observation of new nuclear Λ-bound states, which have been experimentally detected through the excitation of the target nucleus by incident photons with energy in the range 0.8-1.4 GeV [4,12]. Also, new phenomena related to the inclusion of a Λ in the nuclear structure, such as the halo effects Λ C, which can be thought of as a Λ-particle attached to the 12 C nucleus, and the Λ-bound p-states are 11 MeV above the s-state. By measuring the spin-orbit splitting, and the gamma emission during the transition p → s, one can obtain information on the signature of the hypernucleus existence [14].In the photomesonic energy region, the gamma-nucleus reaction has been explored in the framework of a two-step interaction model. First, a rapid intranuclear cascade is developed through a sequence of hadronic binary collisions. Subsequently, the hot residual nucleus slowly reaches its final configuration through a sequence of particle-evaporation processes in competition with the residual-nucleus fission process.We have shown that quasi-free kaon production in photonuclear reactions can be an important issue to determine the strangeness content of the residual nuclei at the end of the rapid cascade phase [15]. These reactions permit to study the in-medium effects on the photonuclear absorption and the strangeness-production mechanism. The many-body cascade calculation proposed in Refs. [15,16] for the rapid phase of the photonuclear reaction takes int...

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Λ-hyperon lifetime in very heavy hypernuclei produced in thep+U interaction

Cited by 51 publications

References 9 publications

Nonmesonic decay of the Λ-hyperon in hypernuclei produced by p + Au collisions

Nonmesonic decay of the Λ-hyperon in hypernuclei produced by p + Au collisions

Deeply bound pionic atoms from the (γ,p) reaction in nuclei

Hot hypernucleus formation in high-energy photonuclear reactions

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