The detailed analysis is presented of an event which is interpreted as the mesonic cascade decay of a double hyperfragment produced by the capture of a E~ hyperon on a light emulsion nucleus. The most likely interprétations of the double hyperfragment are those in terms of either ^^Be'» or ^^Be".
During a systematic scan for interactions of 1. 3-and 1. 5-GeV/c K" mesons 1 in emulsions irradiated in the separated K' meson beam at CERN, 2 an event has been found which is interpreted as the production and subsequent mesonic cascade decay of a double hyper fragment. A photomicrograph and explanatory schematic drawing of the event are given in Fig. 1, AS" hyperon (track 1) emitted from the interaction of a K~ meson of momentum 1. 5 GeV/c (star A) comes to rest and is absorbed at B. A double hyperfragment (track 6) and another charged particle (track 5) are observed to come from star B. The double hyperfragment decays at C into a n~ meson (track 7), a singly charged particle (track 8), and an ordinary hyperfragment (track 9). This hyperfragment decays at D into a n~ meson (track 10) and three other charged particles (tracks 11, 12, and 13). The results of the measurements of the angles of emission and ranges of all the charged particles involved in these processes are summarized in Table I. All reasonable interpretations of this event, other than that of a H~ hyperon capture at B leading to the emission of a double hyperfragment, have been considered and discarded. 3 The ordinary hyperfragment was analyzed using only the kinematics of its decay, whereas the possible identities and decay schemes of the double hyperfragment were assigned from a study of both the production and decay processes. In particular, the Coulomb barrier argument was used to establish the fact that the H" hyperon capture occurred on a light nucleus (C,N, O) of the emulsion. The final results of this analysis are summarized in Table II.From a comparison of the binding energy B^A of the two A 0 hyperons in double hyperfragments with Bj^ for ordinary hyperfragments, one can expect to obtain information not only on the 29
We have measured the absolute differential cross section for photoproduction of neutral rho mesons from complex nuclei at a photon energy of 8.8 BeV. Using a two-parameter optical model, we have deduced a value for the total rho-nucleon cross section of 30l| mb. Application of the vector-dominance model results in a value for the rho-photon coupling of y^2/47r = 1.1 ± 0.2.We report here the results of a measurement of the photoproduction of pion pairs from complex nuclei at 8.8 BeV. These results are part of a systematic study of rho-meson photoproduction from a variety of targets (Hg through Pb), in the energy range of 5-16 BeV. Similar experiments performed at 2 to 6 BeV 1 "" 4 have produced disparate results when interpreted within the framework of the vector-dominance model (VDM). 5 Since the VDM has successfully correlated many phenomena, it is of interest to study the limits of its applicability and to resolve any theoretical or experimental inconsistencies that arise. A preliminary report of these data has been presented elsewhere. 6 The experiment was performed in the Stanford Linear Accelerator Center monochromatic photon beam using a wire spark-chamber spectrometer which was on-line to an IBM 1800 computer. This system is described elsewhere. 6 ' 7 The properties of the beam and the measurement of the spectrum are also described elsewhere. 8 The energy of the monochromatic peak was 8.85±0.02 BeV with a full width at half-maximum of 0.52 BeV. To calibrate the absolute photon flux, the spark chamber system was periodically used as a pair spectrometer. The system had a mass acceptance of -1000 MeV at any given setting, with a maximum detectable mass of -3500 MeV. The mass resolution varied from ±6 MeV at 700 MeV to ±15 MeV at 3000 MeV. The momentum transfer acceptance ranged from 0 to 0.25 (BeV/c) 2 , with a resolution of -0.0005 (BeV/c) 2 for small t increasing to 0.002 (BeV/c) 2 for large t. The apparatus detected meson decays over 80% of the decay solid angle at 9 BeV.Data were taken using targets of Be, C, Al, Cu, Ag, and Pb, ranging in thickness from 0.1 radiation length for Be to 0.3 radiation length for Pb. The target position was set to maximize the spectrometer acceptance for pion pairs with energy comparable with the energy of the monochromatic photons and mass in the vicinity of the rho. Electromagnetic attenuation of the photons and absorption of pion pairs were measured by varying the thickness of the Be target; the results were in agreement with calculations and these calculated corrections (12%) were applied to the data from all other elements. Other corrections, measured and calculated, include target-out yield (2%), track-finding inefficiency (8%), pion decay (2%), pions grazing the edges of the beam stopper (2%), and dead time (<1%). The total correction factor varies from 1.26 ±0.06 for Be to 1.35±0.09 for Pb.The energy spectrum of the pion pairs from Be is shown in Fig. 1(a). We have verified that the pion-pair yield is independent of the size of the energy cut for cuts less than ±0.75 ...
A study has been made of the production of hyperfragments by the interactions of 800-MeV/c K~ mesons in nuclear emulsion. The frequency of production, estimated to be 5.3±0.3%, is about the same as for Kr mesons at rest. The hyperfragments are emitted predominantly in the forward direction and the ratio of nonmesonic to mesonic decays has been found to be 11.5±0.6, much greater than for K~ mesons at rest. The proportion of hyperfragments of short range (range in emulsion < 5 JJ) is also much greater. These and other observations indicate that the hyperfragments are heavier than those produced by K~ mesons at rest. In at least 65±4% of cases they come from heavy emulsion nuclei, in contrast to the situation for K mesons at rest where most hyperfragments appear to originate in light emulsion nuclei. A model is proposed which can account for many of the features of the hyperfragment production process. and all interactions or decays thus found were noted. No further decay of a hyperfragment was found.
We are currently surveying the nuclear emulsion data on 77~"-mesic decays of hyperfragments in order to obtain statistically improved observations of the final-state interactions present in these events.
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