The cryogenic storage ring CSR Review of Scientific Instruments 87, 063115 (2016); https://doi

A search for nuclear-bound states of the 77 meson has been carried out. Targets of lithium, carbon, oxygen, and aluminum were placed in a /r"^ beam at 800 MeV/c. A predicted T] bound state in ^^O* {Ex « 540 MeV) with a width of « 9 MeV was not observed. A bound state of a size j of the predicted cross section would have been seen in this experiment at a confidence level of 3CT {P> 0.9987).PACS numbers: 25.80.-e, 21.90.+f, 27.20.+n This Letter describes a search for a novel nuclear excitation involving the creation of a bound r] meson in the nuclear medium. The concept is similar in spirit to a number of ideas which have recently been vigorously pursued. Some familiar examples are A hypernuclear states, Z hypernuclear states, antiprotonic nuclear states, and various dibaryon resonances. In each case an attractive particle-nucleus potential is required together with some mechanism to inhibit the decay process, such as strangeness conservation in the case of the A.Several suggestions of the existence of bound states of the 7] meson in a wide range of nuclei have recently been published. ^"^ The suggestions of this novel nuclear excitation are based on bound-state formation through the attractive N-T] channel of the TV* (1535), where A^*(1535) is the {KN) resonance with (/,/'') = (T, y") and mass 1535 MeV/c^. This resonance dominates 77 production near threshold. Bhalerao and Liu'* have shown, by a coupled-channels analysis, that the lowenergy rfN interaction is attractive with a scattering length of 0.28 + 0.202/ fm. The attractive interaction is a consequence of the threshold being below the A^*(1535) resonance.Liu and his collaborators have examined the consequences of this attractive interaction in the formation of a bound-77 state as a function of mass number. Their study indicates that nuclear bound states could exist for mass numbers larger than A^\Q. At low mass numbers, only 5-state bound r/'s are predicted. At larger mass numbers, p and d states could become bound. Both binding energies and widths increase with A. The optimum case, in their analysis, is \^0, formed from the in^.p) reaction on *^0 at a momentum near 740 MeV/c. ^ At an angle near 15°, the momentum transfer is favorable for the transition involving the conversion of a p-shell neutron to an ^-shell ry. For higher mass numbers, the increase in predicted width would make this excitation more difficult to see over the continuum {K^,p) background which is present.An experiment to test these predictions was devised with the positive pion beam available at the low-energy separated beam I at the Brookhaven alternating-gradient synchrotron (AGS), and the Moby Dick spectrometer. The experimental arrangement is virtually identical with that used for the production and measurement of hypernuclei, and it has been described in detail in a number of publications (see Milner et al.^ and related references). The only differences involve the selection of pions, rather

Data obtained by the associated production of A hypernuclei through the (n + ,K + ) reaction are presented for a wide range of mass numbers. The special features which make this reaction useful are pointed out. The reaction is shown to be an excellent probe of A single-particle states, as demonstrated by the excitation of deeply bound states which are interpreted as the weak coupling of a A to neutronhole states of the core. The A binding energies and ground-state production cross sections for JvBe, 'AC, '&>, 2 2Si, ^Ca, 5 A V, and ^Y are presented.

Until recently, the spectroscopy of A-hypernuclei has been studied by use of the well-known, strangeness-exchanging (K,n) reactions. These reactions are typically characterized by small momentum transfer, q < qp, where qp is the Fermi momentum. They populate preferentially states of low angular momentum and are effective in producing "substitutior.al states" in which the A has the same orbital as the neutron it replaces (AL=0).

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Evidence for the presence of alpha-particle clustering in 218 Ra comes from a number of observables: binding energy, S 2n9 Q a , ^(J^), 6 a 2 , and F a . That this clustering is a signature for the new dipole collectivity suggested by Iachello and Jackson follows from observation of simultaneous enhancement of selected El 9 E2, and E3 deexcitation transition matrix elements; of these the El enhancement is most pronounced as would be expected for dipole collectivity.PACS numbers: 21.10. Re, 21.60.Gx, 27.80,+w The existence of alpha clustering in the lowlying states of light nuclei, particularly in the 16 O-20 Ne region, is now well established. 1 Recently published 2 systematics for ground-state alpha-particle widths for heavy nuclei also indicate large reduced alpha-particle widths in the vicinity of the Z= 50 and 82 shell closures. It bears noting that the largest ground-state reduced alpha-particle width for any heavy nucleus yet reported is that 2 for 218 Ra; it exhausts 75% of the Wigner sum-rule limit. These large groundstate reduced widths (0 a 2 ) suggest that configurations such as a +A 2 may indeed exist in the vicinity of shell closures. If the overlap between the alpha cluster and the core nucleus (A 2 ) is small (as suggested by the large 9 a 2 ), it may be appropriate to view these states as physically real molecular alpha-particle cluster states. Such states could then be viewed as the nuclear equivalents of the HBr or HI diatomic molecules which also invoice consitituents of very different sizes.Recently, the possible importance of such alphaparticle clustering in heavy nuclei was emphasized and a phenomenological description was proposed 3 in which the cluster states are associated with a new molecular dipole degree of freedom. 4 The model is developed within the context of a spectrum-generating algebra to emphasize the intrinsic symmetries involved; in this case the cluster is characterized by the length and orientation of the vector separating the a. and A 2 centers of mass and thus is associated with a dipole degree of freedom and with 5 and P (-1 ^ l± ^1) bosons-the generators of U(4).In addition to such molecular states it would be expected, of course, to find the normal quadrupole collective states in the low-energy excitation spectra of these heavy nuclei-and indeed dipole and quadrupole states having the same J 7r would be expected to mix. The result of such mixing of the normal quadrupole ground-state band having a sequence 0 + , 2 + , 4 + , 6 + ,..., and the molecular dipole band 3 having sequence 0 + , 1 ~, 2 + , 3", 4 + ,... then leads to low-lying 1" states, as observed, 5 a sequence 0 + , 2 + , 1", 4 + , 3", again as observed, as well as large ground-state alphaparticle reduced widths and small relative alphaparticle hindrance factors for excited states. In addition, higher-lying states-0 2 + , 2 2 ,-with small hindrance factors are expected. For highspin states it remains possible that the mixing of the ground-state band and the cluster band may not be as important, leaving the i...

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