Role of the nuclear and electromagnetic interactions in the coherent dissociation of the relativistic 7Li nucleus into the 3H + 4He channel

Abstract

The differential cross section in the transverse momentum Q and a total cross section of (31 ± 4) mb for the coherent dissociation of a 3-A-GeV/c 7 Li nucleus through the 3 H+ 4 He channel have been measured on emulsion nuclei. The observed Q dependence of the cross section is explained by the predominant supposition of the nuclear diffraction patterns on light (C, N, O) and heavy (Br, Ag) emulsion nuclei. The contributions to the cross section from nuclear diffraction (Q ≤ 400 MeV/c) and Coulomb (Q ≤ 50 MeV/c) dissociations are calculated to be 40.7 and 4 mb, respectively. The properties of the nuclei and mechanisms of the reactions induced by the Coulomb and nuclear interactions in nucleus-nucleus collisions have been studied for more than five decades [1-4]. These investigations have been recently expanded to the relativistic energy range [5-8].It is known that the nuclear diffraction mechanism of the reactions at low momentum transfers Q (similar to optical diffraction), which was predicted as early as the 1950s [9][10][11][12], becomes significant at energies of about hundreds of MeVs and higher along with the Coulomb interaction. Diffraction is characterized by the observed oscillations of the cross sections for the elastic scattering of particles and nuclei, dσ/dQ, with the main maximum at small angles ϑ λ/R, where λ is the de Broglie wavelength of the incident particle and R is the radius of the nuclear interaction region. It is also known [12] that the diffraction mechanism can induce the coherent dissociation of the incident nucleus (without the excitation of the target nucleus) and the production of particles. The dissociation of the 12 C nucleus into three α particles was observed at relativistic energies [13,14]. However, the direct observation of the diffraction pattern with the counter technique (measurement of dσ/dQ) in the nuclear dissociation remains a sufficiently complex problem. The energy spectra of the charged particles at given angles [15,16] are normally used in such experiments.Among numerous reactions accompanying the collisions of relativistic nuclei (multifragmentation, meson production), we take a comparatively simple channel of coherent (elastic) dissociation of the 7 Li nucleus (λ 0.01 fm), which corresponds to the twocluster structure of the 7 Li nucleus and is convenient for the application of the developed theoretical approaches to the description of such reactions.The cross section dσ/dQ for the elastic dissociation of the 7 Li nucleus is measured in the experiment in order to analyze the diffraction pattern of the process and to determine the contribution from the electromagnetic dissociation. According to previous nuclear emulsion measurements [8], the chosen reaction is characterized by very small nucleus emission angles and correspondingly low values Q ≤ 0.45 GeV/c; under these conditions, the simultaneous manifestation of the Coulomb and nuclear diffraction mechanisms of the process can be expected [5]. The Q regions of the contributions from the Coulomb and nuclear intera...

Dissociation of relativistic 7Be nuclei through the 3He+4He channel on a proton target

“…A comparatively large number of such events observed in a nuclear emulsion [6,7,10,11] is indicative of a high probability for two-cluster components in the wave functions that describe primary nuclei. This idea was confirmed in interpreting the results obtained by measuring the Q dependence of the differential cross section for the two-cluster fragmentation of a 7 Li nucleus on photoemulsion nuclei at the projectile momentum of 3 GeV/c per nucleon [12,13]. Within the two-body model of the 7 Li nucleus [14,15] and with the aid of the cluster version of diffraction theory [16,17] developed by analogy with the Akhiezer-Sitenko theory [18] of deuteron breakup to a neutron and a proton, diffraction patterns (versus the momentum transfer) were obtained for the dissociation channel 7 Li → 3 H+ 4 He in the cases of the reactions on light (C, N, and O) and heavy (Ag and Br) emulsion nuclei.…”

“…A similar form of the momentum-transfer dependence of cross sections and a close value of the total cross section, 8 ± 2 mb, were obtained earlier in [19] for the dissociation of 7 Li nuclei on protons through the 3 H+ 4 Не channel. An interpretation of the observed cross sections for the two-cluster dissociation of relativistic 7 Li and 7 Be nuclei on protons and a comparative analysis of the results concerning the dissociation of 7 Li nuclei on complex photoemulsion nuclei [12] are given in [23]. With the aim of additionally testing theory, it would be of interest to perform similar investigations of the two-cluster fragmentation process 6 Li → 2 H+ 4 He.…”

Nuclear track emulsion in search for the Hoyle-state in dissociation of relativistic 12C nuclei

“…Its average value P T sum (RMS) is equal to 190 ± 19 (118) MeV/c corresponding to the nuclear-diffraction mechanism. In the case of electromagnetic dissociation on Ag and Br nuclei composing NTE the limitation is expected to be P T sum < 100 MeV/c [9]. It is surprising that such a "fragile" formation of three α-particles as HS can arise in relativistic collisions as an ensemble which is "bouncing off" with the transverse momentum P T sum characteristic for strong interactions rather than electromagnetic ones.…”

Coherent dissociation of relativistic 12N nuclei

“…The mean value of <P T ( 11 C + p)> = 300 ± 52 MeV/c, together with RMS = 104 ± 37 MeV/c, is indicative of the nuclear-diffraction type of the dissociation process in question [8] and of the presence of the bounce-off effect. The branching fraction of the 11 C + p channel proved to be (9 ± 5)%.…”

“…4). On this basis, the contributions of 8 Be nuclei was estimated at a level of (4 ± 2)%. For the neighboring nuclei of 12 , it was about 20%.…”