Search

We have measured the branching ratio for the hyperon radiative decay [Xi][sup [minus]][r arrow][Sigma][sup [minus]][gamma] from a sample of 211[plus minus]33 events obtained in the polarized 375 GeV/[ital c] charged hyperon beam at Fermilab. We find [ital B]([Xi][sup [minus]][r arrow][Sigma][sup [minus]][gamma]/[Xi][sup [minus]][r arrow][Lambda][sup 0][pi][sup [minus]])=(1.22[plus minus]0.23[plus minus]0.06)[times]10[sup [minus]4] where the quoted errors are statistical and systematic, respectively. We have also obtained an indication that the sign of the asymmetry parameter of this decay is positive.

We have measured the asymmetry parameter (${\mathrm{\ensuremath{\alpha}}}_{\ensuremath{\gamma}}$) in the hyperon radiative decay ${\mathrm{\ensuremath{\Sigma}}}^{+}$\ensuremath{\rightarrow}p\ensuremath{\gamma} with a sample of 34 754\ifmmode\pm\else\textpm\fi{}212 events obtained in a polarized charged hyperon beam experiment at Fermilab. We find ${\mathrm{\ensuremath{\alpha}}}_{\ensuremath{\gamma}}$=-0.720\ifmmode\pm\else\textpm\fi{}0.086\ifmmode\pm\else\textpm\fi{}0.045, where the quoted errors are statistical and systematic, respectively.

We have searched for the production and decay of light super-symmetric baryons produced in 800 GeV/c proton copper interactions in a charged hyperon beam experiment. We observe no evidence for the decays R+(uud \g^~) -> S(uds \g^~) pi+ and X-(ssd \g^~) -> S(uds \g^~) pi- in the predicted parent mass and lifetime ranges of 1700-2500 Mev/c2 and 50-500 ps. Production upper limits for R+ at xF=0.47, Pt=1.4 GeV/c2 and X- at xF=0.48, Pt=0.65 GeV/c2 of less than 10^-3 of all charged secondary particles produced are obtained for all but the highest masses and shortest lifetimes predicted., 9 pages, uuencoded postscript 4 figures uuencoded, tar-compressed file (submitted to PRL)

We report the results of a polarized-${\ensuremath{\Sigma}}^{\mathrm{\ensuremath{-}}}$ beta-decay experiment carried out in the Fermilab Proton Center charged-hyperon beam. These results are based on 49 671 observed ${\ensuremath{\Sigma}}^{\mathrm{\ensuremath{-}}}$\ensuremath{\rightarrow}${\mathrm{ne}}^{\mathrm{\ensuremath{-}}}$\ensuremath{\nu}\ifmmode\bar\else\textasciimacron\fi{} decays. The ${\ensuremath{\Sigma}}^{\mathrm{\ensuremath{-}}}$ beam had a nominal momentum of 250 GeV/c and was produced by 400-GeV/c protons im- pinging on a Cu target. At a production angle of 2.5 mrad, the polarization was (23.6\ifmmode\pm\else\textpm\fi{}4.3)%. The decay asymmetries of the electron (${\ensuremath{\alpha}}_{e}$=-0.519\ifmmode\pm\else\textpm\fi{}0.104), neutron (${\ensuremath{\alpha}}_{n}$=+0.509\ifmmode\pm\else\textpm\fi{}0.102), and antineutrino (${\ensuremath{\alpha}}_{\ensuremath{\nu}}$=-0.230\ifmmode\pm\else\textpm\fi{}0.061) were measured and used to establish sign and approximate magnitude of the axial-vector-to-vector form-factor ratio ${g}_{1}$/${f}_{1}$. The form-factor ratios \ensuremath{\Vert}${g}_{1}$/${f}_{1}$\ensuremath{\Vert} and ${f}_{2}$/${f}_{1}$ were determined most sensitively from the neutron and electron center-of-mass spectra, respectively. We obtain \ensuremath{\Vert}${\mathit{g}}_{1}$/${\mathit{f}}_{1}$-0.237${\mathit{g}}_{2}$/${\mathit{f}}_{1}$\ensuremath{\Vert}=0.327\ifmmode\pm\else\textpm\fi{}0.007\ifmmode\pm\else\textpm\fi{}0.019 and ${\mathit{f}}_{2}$(0)/${\mathit{f}}_{1}$(0)=-0.96\ifmmode\pm\else\textpm\fi{}0.97\ifmmode\pm\else\textpm\fi{}0.13, where the stated errors are statistical and systematic, respectively. A general fit that includes the asymmetries and makes the conventional assumption ${g}_{2}$=0 gives the final value ${g}_{1}$(0)/${f}_{1}$(0)=-0.328\ifmmode\pm\else\textpm\fi{}0.019. The data are also compatible with positive values for ${g}_{2}$/${f}_{1}$ combined with corresponding reduced values for \ensuremath{\Vert}${g}_{1}$/${f}_{1}$\ensuremath{\Vert}. .AE

We have used the spin-precession technique to measure the ..sigma../sup -/ magnetic moment (..mu../sub ..sigma../). A ..sigma../sup -/ beam with a polarization of 22% was produced by a 400-GeV proton beam striking a Cu target at nominal production angles of +- 3 mrad. We simultaneously recorded 21X0 ..sigma../sup -/..-->..ne/sup -/nu-bar decays and 650X0 ..sigma../sup -/..-->..n..pi../sup -/ decays at ..sigma../sup -/ beam momenta of 253 and 308 GeV/c. We find that ..mu../sub ..sigma../ = -1.166 +- 0.014 +- 0.010 nuclear magnetons, where the quoted errors are statistical and systematic, respectively.

We have measured the production polarization and magnetic moment of a sample of 89{times}10{sup 3} {Xi}{sup {minus}} hyperons produced in the inclusive reaction {ital p}(400 GeV/{ital c})+Cu{r arrow}{Xi}{sup {minus}}+X. The weighted average of the polarization is {minus}0.070{plus minus}0.008{plus minus}0.010 at a {ital p}{sub {ital t}} of 0.63 GeV/{ital c}. The {Xi}{sup {minus}}'s magnetic moment yields the value {mu}{sub {Xi}}={minus}0.661{plus minus}0.036{plus minus}0.036 nuclear magnetons. The first error is statistical, the second systematic.