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A search for {sigma} hypernuclear states in p -shell hypernuclei has been performed with the Moby Dick spectrometer and the low energy separated beam (LESB-2) at the Brookhaven Alternating Gradient Synchrotron (BNL AGS). Unlike some previously published reports, no narrow states have been observed for targets of {sup 6}Li and {sup 9}Be in (K{sup -}, {pi}{sup {+-}}) reactions, either for bound state or continuum regions. Together with the previously reported J=0 , T=1/2 bound state in {sup 4}{sub {sigma}} He , these results demonstrate the crucial role of isospin in {sigma} hypernuclei. (c) 1999 The American Physical Society.

We have observed a clear peak below the {Sigma}{sup +} -production threshold in the {sup 4}He( K{sup {minus}},{pi}{sup {minus}}) reaction at 600 MeV/c and {theta}{sub K{pi}}=4{sup {circ}} . This is confirmation of the existence of the bound state of {sup 4}{sub {Sigma}}He , which was reported in the {sup 4}He(stopped K{sup {minus}},{pi}{sup {minus}}) reaction. As in the case of stopped kaons, no such peak was found in the {sup 4}He(K{sup {minus}} ,{pi}{sup +}) spectrum. Quantitatively reliable parameters for this level have been established. The binding energy and the width of the bound state are 4.4{plus_minus}0.3(stat){plus_minus}1(syst ) MeV and 7.0{plus_minus}0.7(stat){sup +1.2}{sub {minus}0.0}(syst) MeV, respectively. {copyright} {ital 1998} {ital The American Physical Society}

A spectroscopic study of the $_{\ensuremath{\Lambda}}^{12}\mathrm{C}$ hypernucleus by the (${\ensuremath{\pi}}^{+}, {K}^{+}$) reaction has been performed using a new superconducting kaon spectrometer (INS-SKS) at the KEK 12 GeV Proton Synchrotron with an energy resolution of 2 MeV (FWHM). In addition to two prominent peaks which correspond to the $s$ and $p$ orbitals of a $\ensuremath{\Lambda}$ hyperon, for the first time two smaller peaks were clearly observed at excitation energies of 2.6 and 6.9 MeV. These two peaks are interpreted as states where the $^{11}\mathrm{C}$ excited core and a $\ensuremath{\Lambda}$ hyperon in the $s$ orbit are weakly coupled. The excitation energies and the cross sections of these peaks provide information on the $\ensuremath{\Lambda}N$ interaction.

An experiment demonstrating the production of double-Lambda hypernuclei in (K(-),K(+)) reactions on (9)Be was carried out at the D6 line in the BNL alternating-gradient synchrotron. The technique was the observation of pions produced in sequential mesonic weak decay, each pion associated with one unit of strangeness change. The results indicate the production of a significant number of the double hypernucleus (4)(double Lambda)H and the twin hypernuclei (4)(Lambda)H and (3)(Lambda)H. The relevant decay chains are discussed and a simple model of the production mechanism is presented. An implication of this experiment is that the existence of an S = -2 dibaryon more than a few MeV below the double Lambda mass is unlikely.

An experiment demonstrating the production of double-Lambda hypernuclei in (K(-),K(+)) reactions on (9)Be was carried out at the D6 line in the BNL alternating-gradient synchrotron. The technique was the observation of pions produced in sequential mesonic weak decay, each pion associated with one unit of strangeness change. The results indicate the production of a significant number of the double hypernucleus (4)(double Lambda)H and the twin hypernuclei (4)(Lambda)H and (3)(Lambda)H. The relevant decay chains are discussed and a simple model of the production mechanism is presented. An implication of this experiment is that the existence of an S = -2 dibaryon more than a few MeV below the double Lambda mass is unlikely.

Measurements of the semileptonic weak neutral-current reactions ..nu../sub ..mu../p..--> nu../sub ..mu../p and nu-bar/sub ..mu../p..-->..nu-bar/sub ..mu../p which yield the absolute differential cross sections dsigma(..nu../sub ..mu../p)/dQ/sup 2/ and dsigma(nu-bar/sub ..mu../p)/dQ/sup 2/ described. The weak-neutral-current parameter, sin/sup 2/theta/sub W/, is determined to be sin/sup 2/theta/sub W/ = 0.220 +- 0.016 (stat)/sub -0.031//sup +0.023/(syst).

The result of a measurement of sigma(..nu../sub ..mu../+e/sup -/..--> nu../sub ..mu../+e/sup -/) is presented. With use of neutrinos of mean energy 1.5 GeV from the Brookhaven National Laboratory alternating gradient synchrotron and a massive, active, high-resolution detector, a signal of 51 +- 9 events with a average signal-to-background ratio greater than 2:1 is observed. sigma(..nu../sub ..mu../e/sup -/..--> nu../sub ..mu../+e/sup -/) = (1.60 +- 0.29(stat) +- 0.26(sys)) E/sub ..nu../ (GeV) x 10/sup -42/ cm/sup 2/ is obtained.

Large-angle cross sections for ..gamma..d..--> pi../sup 0/d are systematically measured in a photon energy range between 500 and 1000 MeV. A good fit is obtained by use of a Glauber model calculation which includes the dibaryon resonances /sup 3/F/sub 3/(2.26) and /sup 1/G/sub 4/(2.51), but the fit has an unusual nature in the role of resonance and nonresonance contributions.

This paper describes measurements of the semileptonic weak-neutral-current reactions $\ensuremath{\nu}_{\ensuremath{\mu}}p\ensuremath{\rightarrow}\ensuremath{\nu}_{\ensuremath{\mu}}p$ and $\overline{\ensuremath{\nu}}_{\ensuremath{\mu}}p\ensuremath{\rightarrow}\overline{\ensuremath{\nu}}_{\ensuremath{\mu}}p$ which yield the absolute differential cross sections $\frac{d\ensuremath{\sigma}(\ensuremath{\nu}_{\ensuremath{\mu}}p)}{d{Q}^{2}}$ and $\frac{d\ensuremath{\sigma}(\overline{\ensuremath{\nu}}_{\ensuremath{\mu}}p)}{d{Q}^{2}}$. The weak-neutral-current parameter, ${{sin}^{2}\ensuremath{\theta}}_{\mathrm{W}}$, is determined to be ${{sin}^{2}\ensuremath{\theta}}_{\mathrm{W}}=0.220\ifmmode\pm\else\textpm\fi{}0.016(\mathrm{stat}.)_{\ensuremath{-}0.031}^{+0.023}(\mathrm{syst}.)$.