<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msup><mml:mrow><mml:mi mathvariant="normal">π</mml:mi></mml:mrow><mml:mrow><mml:mi mathvariant="normal">−</mml:mi></mml:mrow></mml:msup></mml:mrow></mml:math><i>p</i>→<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msup><mml:mrow><mml:mi mathvariant="normal">π</mml:mi></mml:mrow><mml:mrow><mml:mn>0</mml:mn></mml:mrow></mml:msup></mml:mrow></mml:math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msup><mml:mrow><mml:mi mathvariant="normal">π</mml:mi></mml:mrow><mml:mrow><mml:mn>0</mml:mn></mml:mrow></mml:msup></mml:mrow></mml:math><i>n</i>near threshold and chiral symmetry breaking
J. LoweBrookhaven National Laboratory, Upton, New York 11973; Case Western Reserve University, Cleveland, Ohio 44106; Central Research Institute for Physics, Budapest, Hungary; University of Birmingham, Birmingham, B15 2TT, United Kingdom Boston University, Boston, Massachusetts 02215; University of British Columbia, Vancouver, British Columbia, Canada V6T 2A6; University of New Mexico, Albuquerque, New Mexico 87131; University of Nottingham, Nottingham, NG7 2RD, United Kingdom Oxford University, Oxford, OX1 3RH, United Kingdom TRIUMF, Vancouver, British Columbia, Canada, V6T 2A3B. BassalleckUniversity of British ColumbiaHugh BurkhardtBrookhaven National Laboratory, Upton, New York 11973; Case Western Reserve University, Cleveland, Ohio 44106; Central Research Institute for Physics, Budapest, Hungary; University of Birmingham, Birmingham, B15 2TT, United Kingdom Boston University, Boston, Massachusetts 02215; University of British Columbia, Vancouver, British Columbia, Canada V6T 2A6; University of New Mexico, Albuquerque, New Mexico 87131; University of Nottingham, Nottingham, NG7 2RD, United Kingdom Oxford University, Oxford, OX1 3RH, United Kingdom TRIUMF, Vancouver, British Columbia, Canada, V6T 2A3W. FickingerBrookhaven National Laboratory, Upton, New York 11973; Case Western Reserve University, Cleveland, Ohio 44106; Central Research Institute for Physics, Budapest, Hungary; University of Birmingham, Birmingham, B15 2TT, United Kingdom Boston University, Boston, Massachusetts 02215; University of British Columbia, Vancouver, British Columbia, Canada V6T 2A6; University of New Mexico, Albuquerque, New Mexico 87131; University of Nottingham, Nottingham, NG7 2RD, United Kingdom Oxford University, Oxford, OX1 3RH, United Kingdom TRIUMF, Vancouver, British Columbia, Canada, V6T 2A3J. R. HallBrookhaven National Laboratory, Upton, New York 11973; Case Western Reserve University, Cleveland, Ohio 44106; Central Research Institute for Physics, Budapest, Hungary; University of Birmingham, Birmingham, B15 2TT, United Kingdom Boston University, Boston, Massachusetts 02215; University of British Columbia, Vancouver, British Columbia, Canada V6T 2A6; University of New Mexico, Albuquerque, New Mexico 87131; University of Nottingham, Nottingham, NG7 2RD, United Kingdom Oxford University, Oxford, OX1 3RH, United Kingdom TRIUMF, Vancouver, British Columbia, Canada, V6T 2A3M. D. HasinoffBrookhaven National Laboratory, Upton, New York 11973; Case Western Reserve University, Cleveland, Ohio 44106; Central Research Institute for Physics, Budapest, Hungary; University of Birmingham, Birmingham, B15 2TT, United Kingdom Boston University, Boston, Massachusetts 02215; University of British Columbia, Vancouver, British Columbia, Canada V6T 2A6; University of New Mexico, Albuquerque, New Mexico 87131; University of Nottingham, Nottingham, NG7 2RD, United Kingdom Oxford University, Oxford, OX1 3RH, United Kingdom TRIUMF, Vancouver, British Columbia, Canada, V6T 2A3Dezső HorváthBrookhaven National Laboratory, Upton, New York 11973; Case Western Reserve University, Cleveland, Ohio 44106; Central Research Institute for Physics, Budapest, Hungary; University of Birmingham, Birmingham, B15 2TT, United Kingdom Boston University, Boston, Massachusetts 02215; University of British Columbia, Vancouver, British Columbia, Canada V6T 2A6; University of New Mexico, Albuquerque, New Mexico 87131; University of Nottingham, Nottingham, NG7 2RD, United Kingdom Oxford University, Oxford, OX1 3RH, United Kingdom TRIUMF, Vancouver, British Columbia, Canada, V6T 2A3G. KochBrookhaven National Laboratory, Upton, New York 11973; Case Western Reserve University, Cleveland, Ohio 44106; Central Research Institute for Physics, Budapest, Hungary; University of Birmingham, Birmingham, B15 2TT, United Kingdom Boston University, Boston, Massachusetts 02215; University of British Columbia, Vancouver, British Columbia, Canada V6T 2A6; University of New Mexico, Albuquerque, New Mexico 87131; University of Nottingham, Nottingham, NG7 2RD, United Kingdom Oxford University, Oxford, OX1 3RH, United Kingdom TRIUMF, Vancouver, British Columbia, Canada, V6T 2A3K. D. LarsonBrookhaven National Laboratory, Upton, New York 11973; Case Western Reserve University, Cleveland, Ohio 44106; Central Research Institute for Physics, Budapest, Hungary; University of Birmingham, Birmingham, B15 2TT, United Kingdom Boston University, Boston, Massachusetts 02215; University of British Columbia, Vancouver, British Columbia, Canada V6T 2A6; University of New Mexico, Albuquerque, New Mexico 87131; University of Nottingham, Nottingham, NG7 2RD, United Kingdom Oxford University, Oxford, OX1 3RH, United Kingdom TRIUMF, Vancouver, British Columbia, Canada, V6T 2A3J. MillerBrookhaven National Laboratory, Upton, New York 11973; Case Western Reserve University, Cleveland, Ohio 44106; Central Research Institute for Physics, Budapest, Hungary; University of Birmingham, Birmingham, B15 2TT, United Kingdom Boston University, Boston, Massachusetts 02215; University of British Columbia, Vancouver, British Columbia, Canada V6T 2A6; University of New Mexico, Albuquerque, New Mexico 87131; University of Nottingham, Nottingham, NG7 2RD, United Kingdom Oxford University, Oxford, OX1 3RH, United Kingdom TRIUMF, Vancouver, British Columbia, Canada, V6T 2A3A. J. NobleBrookhaven National Laboratory, Upton, New York 11973; Case Western Reserve University, Cleveland, Ohio 44106; Central Research Institute for Physics, Budapest, Hungary; University of Birmingham, Birmingham, B15 2TT, United Kingdom Boston University, Boston, Massachusetts 02215; University of British Columbia, Vancouver, British Columbia, Canada V6T 2A6; University of New Mexico, Albuquerque, New Mexico 87131; University of Nottingham, Nottingham, NG7 2RD, United Kingdom Oxford University, Oxford, OX1 3RH, United Kingdom TRIUMF, Vancouver, British Columbia, Canada, V6T 2A3B. L. RobertsBrookhaven National Laboratory, Upton, New York 11973; Case Western Reserve University, Cleveland, Ohio 44106; Central Research Institute for Physics, Budapest, Hungary; University of Birmingham, Birmingham, B15 2TT, United Kingdom Boston University, Boston, Massachusetts 02215; University of British Columbia, Vancouver, British Columbia, Canada V6T 2A6; University of New Mexico, Albuquerque, New Mexico 87131; University of Nottingham, Nottingham, NG7 2RD, United Kingdom Oxford University, Oxford, OX1 3RH, United Kingdom TRIUMF, Vancouver, British Columbia, Canada, V6T 2A3D. K. RobinsonBrookhaven National Laboratory, Upton, New York 11973; Case Western Reserve University, Cleveland, Ohio 44106; Central Research Institute for Physics, Budapest, Hungary; University of Birmingham, Birmingham, B15 2TT, United Kingdom Boston University, Boston, Massachusetts 02215; University of British Columbia, Vancouver, British Columbia, Canada V6T 2A6; University of New Mexico, Albuquerque, New Mexico 87131; University of Nottingham, Nottingham, NG7 2RD, United Kingdom Oxford University, Oxford, OX1 3RH, United Kingdom TRIUMF, Vancouver, British Columbia, Canada, V6T 2A3M. SakittBrookhaven National Laboratory, Upton, New York 11973; Case Western Reserve University, Cleveland, Ohio 44106; Central Research Institute for Physics, Budapest, Hungary; University of Birmingham, Birmingham, B15 2TT, United Kingdom Boston University, Boston, Massachusetts 02215; University of British Columbia, Vancouver, British Columbia, Canada V6T 2A6; University of New Mexico, Albuquerque, New Mexico 87131; University of Nottingham, Nottingham, NG7 2RD, United Kingdom Oxford University, Oxford, OX1 3RH, United Kingdom TRIUMF, Vancouver, British Columbia, Canada, V6T 2A3M. E. SeviorBrookhaven National Laboratory, Upton, New York 11973; Case Western Reserve University, Cleveland, Ohio 44106; Central Research Institute for Physics, Budapest, Hungary; University of Birmingham, Birmingham, B15 2TT, United Kingdom Boston University, Boston, Massachusetts 02215; University of British Columbia, Vancouver, British Columbia, Canada V6T 2A6; University of New Mexico, Albuquerque, New Mexico 87131; University of Nottingham, Nottingham, NG7 2RD, United Kingdom Oxford University, Oxford, OX1 3RH, United Kingdom TRIUMF, Vancouver, British Columbia, Canada, V6T 2A3NW TannerBrookhaven National Laboratory, Upton, New York 11973; Case Western Reserve University, Cleveland, Ohio 44106; Central Research Institute for Physics, Budapest, Hungary; University of Birmingham, Birmingham, B15 2TT, United Kingdom Boston University, Boston, Massachusetts 02215; University of British Columbia, Vancouver, British Columbia, Canada V6T 2A6; University of New Mexico, Albuquerque, New Mexico 87131; University of Nottingham, Nottingham, NG7 2RD, United Kingdom Oxford University, Oxford, OX1 3RH, United Kingdom TRIUMF, Vancouver, British Columbia, Canada, V6T 2A3C. E. WalthamBrookhaven National Laboratory, Upton, New York 11973; Case Western Reserve University, Cleveland, Ohio 44106; Central Research Institute for Physics, Budapest, Hungary; University of Birmingham, Birmingham, B15 2TT, United Kingdom Boston University, Boston, Massachusetts 02215; University of British Columbia, Vancouver, British Columbia, Canada V6T 2A6; University of New Mexico, Albuquerque, New Mexico 87131; University of Nottingham, Nottingham, NG7 2RD, United Kingdom Oxford University, Oxford, OX1 3RH, United Kingdom TRIUMF, Vancouver, British Columbia, Canada, V6T 2A3T. M. WarnerBrookhaven National Laboratory, Upton, New York 11973; Case Western Reserve University, Cleveland, Ohio 44106; Central Research Institute for Physics, Budapest, Hungary; University of Birmingham, Birmingham, B15 2TT, United Kingdom Boston University, Boston, Massachusetts 02215; University of British Columbia, Vancouver, British Columbia, Canada V6T 2A6; University of New Mexico, Albuquerque, New Mexico 87131; University of Nottingham, Nottingham, NG7 2RD, United Kingdom Oxford University, Oxford, OX1 3RH, United Kingdom TRIUMF, Vancouver, British Columbia, Canada, V6T 2A3D. M. WolfeBrookhaven National Laboratory, Upton, New York 11973; Case Western Reserve University, Cleveland, Ohio 44106; Central Research Institute for Physics, Budapest, Hungary; University of Birmingham, Birmingham, B15 2TT, United Kingdom Boston University, Boston, Massachusetts 02215; University of British Columbia, Vancouver, British Columbia, Canada V6T 2A6; University of New Mexico, Albuquerque, New Mexico 87131; University of Nottingham, Nottingham, NG7 2RD, United Kingdom Oxford University, Oxford, OX1 3RH, United Kingdom TRIUMF, Vancouver, British Columbia, Canada, V6T 2A3
1991lv
ABI
Аннотация
Total cross sections, angular, and mass distributions for the reaction ${\mathrm{\ensuremath{\pi}}}^{\mathrm{\ensuremath{-}}}$p\ensuremath{\rightarrow}${\mathrm{\ensuremath{\pi}}}^{0}$${\mathrm{\ensuremath{\pi}}}^{0}$n have been measured for ${\mathit{p}}_{\mathrm{\ensuremath{\pi}}}^{\mathrm{\ensuremath{-}}}$(lab)=7--140 MeV/c above threshold. The threshold amplitude was used to determine a value for the chiral-symmetry-breaking parameter, \ensuremath{\xi}, of -0.98\ifmmode\pm\else\textpm\fi{}0.52. The \ensuremath{\pi}\ensuremath{\pi} scattering lengths ${\mathit{a}}_{\mathit{I}}$ for isospin I=0 and 2 are derived from this result, together with a current-algebra sum rule. The results are ${\mathit{a}}_{0}$=(0.207\ifmmode\pm\else\textpm\fi{}0.028)${\mathit{m}}_{\mathrm{\ensuremath{\pi}}}^{\mathrm{\ensuremath{-}}1}$ and ${\mathit{a}}_{2}$=(-0.022\ifmmode\pm\else\textpm\fi{}0.011)${\mathit{m}}_{\mathrm{\ensuremath{\pi}}}^{\mathrm{\ensuremath{-}}1}$. These values are consistent with chiral symmetry broken by the Weinberg \ensuremath{\pi}\ensuremath{\pi} interaction and the effects of the ${\mathit{f}}_{0}$(975) scalar meson.
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