The Reactions Gamma + Proton ---> Positive Pion Negative Pion Positive Pion Negative Pion Proton and Gamma + Proton ---> KAON(+,-) PION(-,+) Neutral Kaon Proton at 20 GEV
The reactions (gamma)p (--->) (pi)('+)(pi)('-)(pi)('+)(pi)(' -)p and (gamma)p (--->) K('(+OR-))(pi)('(-OR+))K('0)p at 20 GeV are studied from data obtained during the BC72 experiment, run at the SLAC 1 meter Hybrid Bubble Chamber facility from 1980 to 1982. The 5702 events in the first channel represent a cross section of 2.54 (+OR-) 0.24 (mu)b; the 235 events in the second channel represent a cross section of 380 (+OR-) 40 nb. The primary radial excitation of the (rho)(770), commonly called the (rho)(1600), is observed in half of the 4(pi) channel, but with parameters markedly different from what has been previously published. Production of the resonance is peripheral, exponential t dependence of 7.5 (GeV)('-2), with s-channel helicity conserved at the 90% level. A variety of methods have been used to calculate the mass and the width of the (rho)' resonance, the strongest (and new for this channel) being a maximum likelihood fit to all aspects of the 4(pi) data. Forty percent of the 4(pi) channel is associated with (DELTA)('++)(1232) production. We have studied, in particular, (gamma)p (--->) A(,n)(DELTA)('++) and see predominantly production of the A(,2) tensor meson resonance with an admixture of the pseudoscalar A(,1) mean resonance. The KK(pi) channel is dominated by K*K production. The K*K system does not appear to be associated with resonance production.
- Pub Date:
- Physics: Elementary Particles and High Energy