Reaction Pi Research Articles

Pion-pion amplitudes from low energy pion-production

The amplitudes of the process pi + N yields 2 pi + N are approximately summing all one-particle states (six nucleonpoles and one pion- pole) and allowing for the influence of more-particle states by reducing the obtained cross sections by 25%. Theoretical cross sections, including the pi - pole contributions, are adapted to the experimental cross sections of the reactions pi /sup plus or minus / + p yields 2 pi + N to yield n- pi amplitudes. Results are compared to results from previous experimental and theoretical investigations. (H.D.R.)

Evidence for resonances in K + Y(Σ, Λ) system at 1650 and 1920 MeV

The LAMBDA /sup o/ + K/sup o/ pairs produced by mesons ( pi /sup -/) at 2.8 Bev/c were investigated in freon and xenon bubble chambers. The reactions pi /sup -/ + (A) yields LAMBDA /sup o/ + K/sup o/ + m pi + (A)/sup 2/ (m =0, was studied. The assumption that a portion of the LAMBDA /sup o/ and K/sup o/ are produced in the intermediate reactions pi /sup -/ + N yields Z/sup o/ + m pi (m = 1, 2,....), where Z/sup o/ is a particle decaying according to the scheme Z/sup o/ yields LAMBDA /sup o/ + K/sup o/ + Q was tested by constructing the Q distribution of the LAMBDA /sup o/ + K/sup o/ pair production events. Distributions are presented in graphical form. The Q value to 300 Mev had a mean error of about 20 Mev; for the xenon chamber, the mean error was about 50 Mev because of multiple-scattering-increase effects on angle determination. (L.N.N.)

Final State Interaction in Kaon Production

>The final state approach is applied to the reaction pi - + P → K + Y + pi . The pi -Y and K-Y interactions are neglected and only the K- pi interaction is considered in the final state. The matrix elements for the primary interaction are determined by the use of Fermi's statistical model. The secondary interaction is handled by the use of effective range formulae, where the parameters are fitted to the experimental full width at half maximum of 23 Mev and an effective mass of 878 Mev for an I = 1/2 resonance. Both an S-wave and P-wave resonance are considered. The results indicate a κ 0 π+ Σ-/ κ + π0 Σ-- ratio of 1.7 with a small amount of K0 pi - Σ + reaction for both the S- and P-wave cases. This result is in agreement with experimental results. The calculations also indicate a κ + π0 Σ-/ κ 0 π0 Σ0 ratio of 107 for an S-wave resonance and a ratio of 0.7 for a P-wave resonance. Unfortunately, the reaction κ 0π0 Σ0is difficult to determine experimentally and no experimental results have been obtained on them as yet.

Multiple Meson Production in Proton-Proton Collisions at 2.85 Bev

Measurements are made on 753 four-prong events obtained by exposing a 20- in liquid hydrogen bubble chamber to 2,85-Bev protons. The partial cross sections observed for multiple meson production reactions are: pp +-(p + p yields p+p+ pi /sup +/+ pi /sup -/),2.67 plus or minus 0.13;pn++-,1.15 plus or minus 0.09; pp +- 0, 0.74 + 0.07; d ++-, 0.06 + 0.02; and four or more meson production, 0.04 plus or minus 0.02 mb. Production of two mesons appears to occur mainly in peripheral collisions with relatively little momentum transfer. In cases of three-meson production, however, the protons are typically deflected at large angles and are more strongly degraded in energy. The 3/2, 3/2 pion- nucleon resonance dominates the interaction; there is some indication that one or both of the T =1/2, pion-nucleon resonances also play a part. The resonance in a T = 0, three-pion state appears to be present in the pp +- 0 reaction, Results are compared with the predictions of the isobaric nucleon model and the statistical model. The cross section for the reaction pi /sup O/ + p yields pi /sup +/+ pi /sup -/ + p is derived using an expression from the one-pionmore » exchange mode. (auth)« less

Pion Production in Pion Nucleon Scattering and Pion-Pion Interaction

The reaction pi + N yields 2 pi + N is discussed. The production process is assumed to take place mainly via pi - pi interactions, which are studied using an extrapolation formula (G. F. Chew and F. E. Low, Phys. Rev., 113: 1640 (1959)). A program giving a consistent explanation to the process at 0.3 to 1.5 Bev is presented.

Differentialπ−πCross Sections: Evidence for the Spin of theρMeson

Data on the reaction pi /sup +/ + p yields pi /sup +/ + p + pi /sup 0/ are reported. The data consist of a sample of 1684 events in which the proton recoiled at a momeatum bctween l00 and 400 Mev/c. Existence of a pi - pi resonance at a total mass of approximates 725 Mev is confirmed both by the extrapolation method and by using physical-region plots. Exploitation of the dominance of the pi - pi resonance effect in the physical region produces direct evidence, through angular distributions, that the resonance has spin 1. (L.N.N.)

Evidence for aT=1Pion-Pion Resonance at 575 Mev

Single pion production in the reaction pi /sup +/P yields pi /sup +/+/ pi /sup 0/+P at incident pion kinetic energies of 820, 900, and 1050 Mev was studied. Histograms showing the distribution of events as a function of the kinetic energy Q pi pi in the rest systems of the two resuitant pions are presented. Evidence for a di-pion resonance with isotopic spin T = 1 at 575 plus or minus 20 Mev is reported. (L.N.N.)

Further evidence for two di-pion resonances in single neutral pion production

Evidence that the 575 and 750-Mev 2- pi states appear in the reaction pi /sup -/ p yields pi /sup - + pi /sup 0/ Mev in the laboratory system is presented. Data are presented in graphical and tabular forms. (L.N.N.)

Associated Production in Pion-Nucleon Collisions and Effects of Resonant States

Possibilities of explaining experimental features, angular distributions, polarization, and total cross sections in the reaction pi + p yields K0 + lambda at 910 Mev by considering N?* ( pi -N third resonance), Y* ( pi -A resonance), and K (Kresonance) are investigated. Calculations are presented in graphical and tabular forms. (L.N.N.)

Helicity ofμ−Mesons; Mott Scattering of Polarized Muons

In order to find the helicity of the neutrino nu u associated with the mu meson, the reaction pi --- mu -+ nu /sub mu / is studied. The helicity is found from the asymmetry in the Mott scattering of the polarized mu - mesons produced in the reaction. It is found that the helicities of the nu mu and nu /sub e/ are equal. (T.F.H.)

Inverse Photoproduction Reactionπ−+p→γ+nin Flight

The absolute value of the cross section for the process pi /sup -/ + p yields gamma + n from which the free-neutron photoproduction cross section is immediately calculable using the principle of detailed balance was measured. The experiment was performed at 9O deg C.M. angle and a pion energy of 72 Mev. The cross section was measured by detecting the neutrons in a plastic scintillation counter. The energy of the neutrons was measured by time of flight in order to discriminate against the charge-exchange reaction pi /sup -/ + p yields pi / sup 0/ + n. (P.C.H.)

Evidence for aπ−πResonance in theI=1,J=1State

The reactions pi /sup -/ + p yields pi /sup -/ + pi /sup o/ + p, pi /sup -/ + p yields pi /sup -/ >s + pi /sup +/ + n, and pi /sup -/ + p yields pi /sup o/ + pi /sup o/ + n are studied at 1.69 Bev/c. Events with nucleon momentum transfer >400 Mev/c are excluded, in order to avoid interference from rescattering processes. The data indicate that an 1 = 1, J = 1 di-pion state exists at about 750 Mev. (T.F.H.)

Pion-Pion Interaction in Pion Production byπ+−pCollisions

The reactions pi /sup +/ + p yields pi /sup +/ + pi /sup 0/ + p and pi /sup +/ + p yields pi/sup +/ + pi /sup +/ + n are studied at 910, 1090, and 1260 Mev, in an attempt to detect a pi - pi resonance. For the outgoing pi / sup +/ pi /sup 0/ pair, peaks in the Q-values lead to a di-pion resonance with a mass of 5.0 to 5.5 pion masses and 1= 1 or 2. No resonance is observed in the outgoing pi + pi + (I = 2) pair, leading to the conclusion that the pi pi resonance is a 1 = 1 state. (T.F.H.)

Pion-Nucleon Interactions in the Region of the Higher Resonances

Reactions pi pi + p yields + pi /sub 3/ + N near a Bev are studied. Resonances in the reactions pi /sup -/ + p yields pi /sup -/ + pi /sup +/ + n and pi >s-< s + p yields pi /sup -/ + pi /sup 0/ + p are examined. It is noted that the data for the second of these reactions cannot be explained either by a one-pion exchange process, or by a process in which the two final-state pions collide, causing one of the pions to be rescattered by the proton. The pi /sup -/-p results are applied to the reaction pi /sup +/ + p yields pi /sup +/ + pi /sup 0/ + p at 800 Mev. (T.F.H.)

Dispersion Relations for Production Amplitudes

>The Logunov dispersion relation for production amplitudes is discussed. It is shown that this relation is invalid, i.e., that the production amplitude has complex singularities when regarded as a function of the Logunov variables. The reaction pi + N yields pi + pi + N is analyzed by perturbation theory, and it is found that 4 of the 5 independent variables of the reaction are ignored in the Logunov calculations. The singularities in the Logunov production amplitudes are demonstrated in Feynman diagrams. (T.F.H.)

Pion Production Branching Ratios Through the 900-Mev Resonance

The branching ratio, r = n/sub 1//n/sub 2/, for the reactions pi /sup -/ + p yields pi /sup -/ + pi /sup +/ + n and pi /sup -/ + p yields pi /sup -/ + pi /sup 0/ + p was measure d in a hydrogen bubble chamber for an incident pion energy of 905 plus or minus 2 Mev. It was found to be 1.70 plus or minus 0.17. Values of r from hydrogen bubble chamber data at energies near 900 Mev, determined by various authors, are tabulated and found to give an approximately constant r in the 800- to 1100-Mev ensrgy range. The low results of investigations by Walker et al., obtained in emulsions are discussed. (D.L.C.)

Single Pion Production in 0.96-Bevπ−−pInteractions

ABS>Photographs of interactions in a hydrogen bubble chamber irradiated by 0.96-Bev pi /sup -/ were analyzed. Measurements revealed 415 events of the reaction pi /sup -/ + p yields n + pi /sup +/ + pi /sup -/ and 267 events of the reaction pi /sup -/+ p yields p + pi /sup o/ + pi /sup -/. It is shown that the angular distributions are quite different and the observed ratio of proton to neutron events with fast pi /sup -/ is 0.9 plus or minus 0.2. Q values for the different nucleon-pion combinations were computed from the observed momenta. The distributions of Q values are plotted for pion-pion combinations in each reaction, with backward-nucleon events and forward-nucleon events plotted separately. No evidence is seen of pcaking for ( pi /sup -/ pi / sup +/), either for forward or backward neutrons or for ( pi /sup -/ pi /sup o/) forward protons. The Q distribution of ( pi /sup -/ pi /sup o/) for backward protons shows a distinct peak at about 325-Mev, which is suggestive of a 600Mev resonant di-pion'' state (T = 1 or 2). This event is being analyzed. (B.O.G.)

Parity of the Neutral Pion

A study of certain angular correlations in the decay pi /sup 0/ yields 2e /sup +/ + 2e /sup -/ is given. A total of 79 events of pi /sup 0/ production in the captive reaction pi /sup -/ + p yields pi /sup 0/ + n are analyzed. The effective frequency distribution was found to be -0.75 plus or minus 0.42 by experiment and plus or minus 0.48 theoretically, where the plus and minus sign refer to even and odd parity, respectively. It is concluded that the neutral pion is pseudoscalar. (C.J. G.)

Charge Independence in Hyperon Production

The absolute differential cross sections were measured for the reactions pi /sup -/ + p yields SIGMA /sup 0/ + K/sup 0/ and pi /sup -/ + p yields SIGMA /sup -/ + K/sup +/, using 1.09 plus or minus 0.01 Bev negative pions incident on a 10-in. liquid hydrogen bubble chamber, with an 11-kilogauss magnetic field. Results are compared to those of Brown et al. (Phys. Rev. 107, 908(1957)) both as to magnitude and as to angular dependences. (W.D.M.)

Pion Production by Pions

In order to study the direct interaction of the incident pion with a virtual pion in the meson cloud surrounding a nucleon, the reaction pi + p yields pi /sup +/ + pi /sup -/ + n was investigated in the energy range from 260 to 430 Mev. Negative pion beams impinged on a 4-in.thick liquid hydrogen target. Measurements were taken for pi /sup +/ mesons emitted at 60, 90, 125, and 160 deg in the barycentric system for incident pi /sup -/ kinetic energies of over the energy of the pi /sup +/meson at each angle to obtain the angular differential cross section. (W.D.M.)