Reaction {pi}N {yields} {pi}{pi}N near threshold
The LAMPF E1179 experiment used the {pi}{sup 0} spectrometer and an array of charged particle range counters to detect and record {pi}{sup +}{pi}{sup 0}, {pi}{sup 0} p, and {pi}{sup +}{pi}{sup 0}p coincidences following the reaction {pi}{sup +}p {yields} {pi}{sup 0}{pi}{sup +}p near threshold. The total cross sections for single pion production were measured at the incident pion kinetic energies 190, 200, 220, 240, and 260 MeV. Absolute normalizations were fixed by measuring {pi}{sup +}p elastic scattering at 260 MeV. At lower energies the experiment provided new elastic differential cross sections, 10-20% different from the SAID analysis. Relying on cosmic ray calibration runs with the {pi}{sup 0} spectrometer the detailed analysis of {pi}{sup 0} detection efficiency was confronted with a pion single charge exchange measurement using a 30 MeV {pi}{sup {minus}} beam and an extra-thin-walled LH{sub 2} target. All published data on {pi}N {yields} {pi}{pi}N are simultaneously fitted to yield a common chiral symmetry breaking parameter {xi} = -0.46{+-}0.15, consistent with the Weinberg {pi}{pi} interaction effected by the f{sub 0}(975) scalar meson. The threshold matrix element {vert_bar}a{sub 0}({pi}{sup 0}{pi}{sup +}p){vert_bar} determined by linear extrapolation yields the value of the s-wave isospin-2 {pi}{pi} scattering length {alpha}{sub 0}{sup 2}({pi}{pi}) = -0.036 {+-} 0.006 m{sub {pi}}{sup {minus}1}, within the framework of soft-pion theory.
- Research Organization:
- Virginia Univ., Charlottesville, VA (United States)
- OSTI ID:
- 111044
- Country of Publication:
- United States
- Language:
- English
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