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NUCLEAR REACTIONS 34S(t, 3He),~4Mg(t, 3He), E =23.0 MeV; measured o(8). P deduced levels. New mass of 3 P. No evidence for previously reported state in 24Na.are due to the 3 S(t, 3He)3 P reaction. 15The S(t, 'He)"P reaction has been used to study the mass and low-lying excited states of P, using 23 MeV tritons and a quadrupole-dipole-dipole spectrometer. The mass excess of "P is -24545 (20) keV. Excited states have been observed at E"=423, 1605, 2225, 2309, and (3345) keV (+10 keV). Spectra of the ' Mg(t, 'He) Na reaction show no evidence for a previously reported state at E"=2.46 MeV in Na.

The reaction '2C('Li, t)' 60 has been studied at E('Li) = 34 MeV with the LASL tandem accelerator and QDDD magnetic spectrometer. Angular distributions to levels with E, < 11 MeV have been obtained from 0°to 90°, including 0°. The results have been analyzed with finite-range distorted-wave Born approximation theory. The a-particle spectroscopic factors and reduced widths obtained are compared with those calculated with group theory (SU(3)) and other models. The analysis of data for the 7.1 and 9.6 MeV J* = 1levels, which areof great importance in stellar helium boring, yields a ratio, R, of dimensionless reduced a-widths B;(7.1 MeV)/B;(9.6 MeV) = 0.3510.13. The observed line width of the 9.6 MeV level (r~.m. = 390f60 keV) is less than the accepted value (r~.o. = 510±60 keV) and implies B;(9.6 MeV) x 0.6. These results as well as data for the 6.92 MeV J`= 2* and 10 .35 MeV J`= 4* "a-cluster' states indicate 0.09 < B;(7.1 MeV) < 0.33 with a mean value 0;(7 .1 MeV) = 0.14f 0.04. The implication for stellar helium burning is discussed. NUCLEAR REACTIONS '2C('Li, t), E = 34 MeV ; measured a(E B), r~.m.. 'eQ levels deduced S reduced ;~;. Inferred stellar helium fusion rate. Magnçtic spectrometer .

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Angular distributions of single nucleon transfer reactions populating single particle states in the reactions 138Ba(14C, 15N)137Cs and 138Ba(14C, 13C)139Ba have been studied. The shapes of the angular distributions show differences for different final configurations. Using the reaction asymmetry it is possible to describe these differences consistently for all transitions by a spin-orbit potential. The polarisation of the outgoing fragments is discussed and its dependence on final configurations is explained. The spin-orbit potentials deduced from the reaction asymmetry are large, as compared to predictions of folding potentials. They are, however, consistent with measurements of spin-flip probabilities. The origin of the L-S interaction is to be found in coupling effects of second order in the heavy ion reaction. I. MotivationRecent studies of direct reactions with heavy ions have shown that there are various observable effects connected with the spins of the interacting nuclei [1][2][3]. The most obvious effects, known from work with light particles, are related to the polarisation of reaction products produced in reactions and to analysing powers in reactions induced by polarised projectiles [4]. Polarisation and non-vanishing analysing powers can be produced by the vector coupling of angular momenta and spins in a surface reaction where only particular coupling schemes are strongly favoured. The clearest case for this circumstance can be found in the polarisation of final spins in Coulomb excitation [5]. This dynamic polarisation can be produced in any direct reaction in a one step interaction. The notion of an interaction potential containing the scalar product of orbital angular momentum and spin, L-S, is the second alternative. The L.S interaction can be due to the primary spin dependence of the nucleon-nucleon interaction [6]. The interplay of the dynamical polarisation with this L.S interaction produces a great variety of phenomena arising from the spin degrees of freedom in nuclear reactions (see for example [4]). The first studies of the spin dependent interactions of heavy ions [7][8][9][10] have shown that strong effects are observed, which, if attributed to an L.S interaction, cannot be traced back to the spin dependence of the nucleon-nucleon interaction. Models for the L.S interaction of heavy ions [11][12][13], where the nucleon-nucleon interaction is folded with the nuclear densities, tend to give L.S potentials whose strength is generally a factor 10-100 too small. It was realised recently that different channel couplings due to transfer reactions and inelastic excitations can contribute in second order to the polarisation and effectively be responsible for the spin dependent interactions [14][15][16]. The case with heavy ions is rather interesting because it offers possibilities to study different origins of the spin dependent interactions. The present work presents data on reaction asymmetries (introduced in [2,9]) for 15N

(to be submitted to Zeit. Phys. C} for muons, and ~ 40% for electrons.level, on any new source of lepton pairs is ~ 20% of the hadronic decay contribution of the major hadronic sources is set by the data. The upper limit, at 90% confidence decays, and there is no need to invoke any "unconventional" source. The normalisation the low-mass spectrum can be explained satisfactorily by lepton pairs from hadronic p-Be collisions at 450 GeV/ c at the CERN SPS. For both electron and muon pairsWe report on the production of low-mass electron pairs and muon pa.irs in Area. An overview of the apparatus is shown in Figure la. The main components are OCR OutputThe HELIOS spectrometer is situated in the H8 beam line of the CERN SPS North 2.2 Apparatus reliably and stably throughout the experiment.The intensity was ~ 106 per burst. The targeting of the beam on to the wire worked 0.1%), a transverse diameter less than 50 pm and divergence ~ 0.2 mrad at the target.eriment to match the wire target. This beam has excellent momentum resolution (6p/ p A special 450 GeV/ c proton f'micro"-bea.m was developed for the HELIOS exp from the decay of hadrons produced in the interaction.of only 125 pm diameter, in order to minimize the radiation length traversed by photons the design. Accordingly, we have used a 4 cm long (10% interaction length) Be wire target experiment, and so the suppression of e'*'c" pairs from conversions was a key feature ofThe study of low-mass lepton pairs was one of the prime motivations of the HELIOS analysis is presented in section 4, and in section 5 results are summarised and conclusions ing, and data-taking, followed by the event reconstruction and selection in section 3. TheThe plan of this paper is as follows. In section 2 we describe the apparatus, trigger any "unconventional" source. Upper limits on any new source are presented.can be accounted for by lepton pairs from the decay of hadrons, and there is no need forThe main result is that low-mass lepton pairs, produced centrally at `/E 2 29 GeV, a measurement of the total charged multiplicity of the event.electron identincation by both transition radiation and calorimetry; a double measurement of the momentum (or energy) of both muons and electrons;Other noteworthy points are:of certain Dalitz decay modes;the measurement of photons as well as charged leptons, affording direct measurement the detector, producing two essentially independent measurements of lepton pairs; the analysis of both electron pairs and muon pairs, emphasising different aspects of from conventional sources. The most important features of the experimental approach are:Be collisions (\/Z cx 29 GeV) in the central rapidity region, is compared to the expectationIn this paper the production of electron and muon pairs, produced in 450 GeV/ c p their production level in ordinary hadronic collisions.plasma formation in relativistic heavy-ion collisions [3]: it is essential then to understand process Furthermore, lepton pairs have been suggested as a signature for quark-gluon implied by conven...