Antiproton-proton Annihilation Research Articles

Gross features of the annihilation process [formula omitted

The behaviour of the mean square of the matrix element for proton-antiproton annihilation to multipion systems has been examined with the aid of the experimental data. A simple dependence on the parameter s (the square of the energy in the c-system) is found which is independent of multiplicity.

Cosmic Gamma Rays from Metagalactic Proton–Antiproton Annihilation

Annihilation gamma radiation has a characteristic spectrum which distinguishes it from other types of cosmic gamma radiation. Such spectra are presented here, based on the results of recent accelerator experiments on antiproton annihilation and also including cosmological distortions of local annihilation gamma ray spectra.

CPViolation and Coherent Decays of Kaon Pairs

The possible experimental use of correlations between two neutral-kaon decays is discussed. Kaon pairs produced either in proton-antiproton annihilation from an $s$ state or in $\ensuremath{\phi}$ decay are in a $p$ wave, which is forbidden by Bose statistics for identical bosons. The observance of a particular decay mode, i.e., ${\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}$, for one kaon implies that the other kaon is forbidden to decay at the same time in this mode. Thus a kaon beam can be constructed that is just that coherent linear combination of ${K}_{S}$ and ${K}_{L}$ whose amplitudes for decay into this mode cancel one another. The existence of $\ensuremath{\Delta}I=\frac{3}{2}$ transitions leading to the $I=2$ final state in ${K}^{0}$ decay can be tested by looking for double decays where one of the kaons decays into ${\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}$ and the other into ${\ensuremath{\pi}}^{0}{\ensuremath{\pi}}^{0}$. This double decay is allowed at the same time only if both $\ensuremath{\Delta}I=\frac{1}{2}$ and $\ensuremath{\Delta}I=\frac{3}{2}$ amplitudes are present in the kaon decay. Detailed calculations and experimental implications are discussed.

Quark model for the production of pseudoscalar mesons in annihilation

A modification of the quark model for annihilation permits the calculation of the relative probabilities of all observed channels with pseudoscalar mesons. Agreement with the experimental data on proton-antiproton annihilations at rest into three and more mesons is obtained.

Antiproton-Proton Annihilation into Six Charged Pions and Resonance Production in thep¯p→3π+3π−π0Channel at 5.7 GeV/c

Based on 3586 six-pronged events, this work presents results on $\overline{p}p$ annihilation into six and seven pions at 5.7 GeV/c. The production of $\ensuremath{\rho}$, $\ensuremath{\omega}$, ${A}_{1}$, and ${A}_{2}$ resonances in the $\overline{p}p\ensuremath{\rightarrow}3{\ensuremath{\pi}}^{+}3{\ensuremath{\pi}}^{\ensuremath{-}}{\ensuremath{\pi}}^{0}$ channel was observed. Cross sections for the production of the $\ensuremath{\rho}$ and $\ensuremath{\omega}$ resonances are given. The partial cross sections for $\overline{p}p\ensuremath{\rightarrow}{\ensuremath{\rho}}^{0}2{\ensuremath{\pi}}^{+}2{\ensuremath{\pi}}^{\ensuremath{-}}{\ensuremath{\pi}}^{0}$ and $\overline{p}p\ensuremath{\rightarrow}\ensuremath{\omega}2{\ensuremath{\pi}}^{+}2{\ensuremath{\pi}}^{\ensuremath{-}}$ are compared with other experimental data. That the $\overline{p}p\ensuremath{\rightarrow}\ensuremath{\omega}2{\ensuremath{\pi}}^{+}2{\ensuremath{\pi}}^{\ensuremath{-}}$ cross section is small at 5.7 GeV/c shows that this reaction contributes in a rather important manner to the peak observed in the $\overline{p}p\ensuremath{\rightarrow}3{\ensuremath{\pi}}^{+}3{\ensuremath{\pi}}^{\ensuremath{-}}{\ensuremath{\pi}}^{0}$ cross section at an incident $\overline{p}$ momentum of 3 GeV/c. Our data show some indication of bumps in the (${\ensuremath{\rho}}^{0}{\ensuremath{\pi}}^{0}$), (${\ensuremath{\rho}}^{0}{\ensuremath{\rho}}^{0}$) mass for seven-pions annihilation where ${\ensuremath{\rho}}^{0}$ is defined as a (${\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}$) system having a mass combination in the ${\ensuremath{\rho}}^{0}$ band. As yet the statistics do not allow us to draw a definite conclusion about these effects. By comparison with other experimental data, it seems that the isotropy of the pion angular distribution in the c.m. system increases with the number of outgoing pions.

Antiproton-proton annihilation into kaons and pions in the momentum region 3 to 4 GeV/c

A total of 1121 unambiguously identified events of the type $$\bar pp \to \bar KKn\pi $$ (n=1÷5) at momentum 3.0, 3.6 and 4.0 GeV/c have been analysed, and partial cross-section for the various channels are given. The total cross-sections for annihilation into two kaons with pions is estimated to be (5.1±0.4) mb or 14% of all annihilations. The amounts of resonant K*(890), ρ, ω and associated K*K* production in the various channels are determined. Evidence for the E-meson, a KKπ resonance at 1700 MeV, and a K*π resonance at 1265 MeV is presented. Study of 955 unfitted events containing two charged particles, a K 1 0 and ≥2 neutral secondaries gives rise to a four-standard-deviation peak in a strangeness-zero mass spectrum at (1820±12) MeV with a width (Γ) of (50±23) MeV. The angular distributions favour a peripheral rather than a statistical or core-core model of the annihilation process. The possible usefulness of weighting the various combinations in accord with this observation, to accentuate enhancements in the invariant-mass distribution, is discussed. A method of separating each annihilation into its most likely two-body final-state configuration based on maximizing the four-momentum transfer (u) in the cross-channel is presented as well as some examples of the enhancements in mass spectra obtained using this method.

Antiproton-proton annihilations into five pions at 5.7 GeV/c

A study of 872 events of the reaction\(\bar pp \to \pi ^ + \pi ^ + \pi ^ - \pi ^ - \pi ^0 \) is reported. The cross-section for this reaction is found to be (0.9±0.1) mb. The positive pions tend to be emitted in the direction of the proton and the negative pions in the direction of the antiproton. The forward to backward and polar to equatorial ratios(F−B/(F+B) and(P−E)/(P+E) are found to be 0.17±0.02 and 0.27±0.02 respectively, the former value corresponding to an excess of two-thirds of a π+ or a π− per event in the backward or forward direction respectively in the c.m.s. There is a considerable amount of\(\rho ^{0^ \pm } \) and f0 resonance production but no A1, A2 or B meson production has been observed. No evidence for an associated production of resonances has been found which makes any simple interpretation of the annihilation process in terms of three-meson final states diffcult. In the π+π−π0 mass distribution an enhancement is seen with a mass (2207±13) MeV and width (62±52) MeV which could correspond to the neutrally charged state of the peak observed by Chikovaniet al. at 2195 MeV. A simple model is proposed which explains part of the data on four- and five-pion annihilations. *** DIRECT SUPPORT *** A09E0041 00009

Further study of the E-meson in antiproton-proton annihilations at rest

In the study of the annihilation\(\bar pp \to K\bar K\pi \pi \pi \) at rest, we observed an important enhancement in the\(\left( {K\bar K\pi } \right)\) neutral system. We show that this enhancement is the manifestation of a resonance, which we call the E0 meson, with quantum numbersM=(1425±7) MeV, Γ=(80±10) MeV,IGJP=0+0− and branching ratio\(E \to K*\bar K\left( {\bar K*K} \right)/E \to \left( {K\bar K} \right)\pi - 1\).

A study of the quark rearrangement model of nucleo-antinucleon annihilation

A model of proton-antiproton annihilation via quark rearrangement suggested by Rubinstein and Stern is examined in detail. This model predicts that all final states are three-meson states, made from the set π, η, X, ρ, ω, and allows a computation of their relative rates. Its predictions are compared with experimental data at rest and at several energies in flight. The model is found not to be able to account for more than 25% of the annihilations at rest, event when maximum freedom is given to certain extra parameters. The model underestimates the importance of high-multiplicity states in annihilations, in flight and also fails to predict the more detailed features of these data. A number of interesting aspects of the data are uncovered and possible directions along which the model might be modified are suggested.

Euler angles for three and four identical particle systems: (I). A determination of the Euler angles and applications to some angular distributions for four-body decays

By a new method, we determine the third Euler angle for a three identical particle system. We treat all particles on the same level. We choose the Euler angles for the Li atom and for a four identical particle system. We give a relation for an angular distribution connected with the decay of a resonance into four identical spinless particles. We study also the angular distribution of a pion issued from the proton-antiproton annihilation in four particles.

W-meson production in proton-antiproton annihilations

The cross-sections for W-meson production with a single pion or kaon in proton-antiproton annihilations have been calculated using a model in which single-meson intermediate states dominate. Considerations of unitary symmetry and ω-π mixing, previously discussed in connection with annihilation into strongly interacting mesons only as well as W-meson decays, have been combined in the calculations. We find that the predicted cross-sections are large enough to suggest that W mesons may be observable in annihilation reactions at high energies.

Evidence for the existence of mesons decaying to four pions

Evidence is presented for the production in antiproton-proton annihilations of mesons with masses (1717 ± ± 7) MeV and (1832 ± 6) MeV with narrow widths decaying to four charged pions in a neutral mode.

Proton-antiproton annihilation into two pseudoscalar mesons in brokenSU 6W

Proton-antiproton annihilation into two pseudoscalar mesons in brokenSU 6W

Determination of the Nucleon's Isotopic Spectral Functions

We employ the method of exact inversion, discussed in an earlier paper, to determine the nucleon's isotopic spectral functions from their corresponding real form factors. Specific analytic expressions, as suggested by previous pole fits, are used for the real form factors and these give spectral functions that have all the required analytic properties. The constraint that the electric and magnetic form factors are equal at the threshold for proton-antiproton annihilation into an electron-positron pair is used throughout. We find that the complex proton's form factors are zero at the annihilation threshold and using this observation we compare our results with the predictions of the internal symmetry theories.

The proton-antiproton annihilation at rest as predicted by theSU 6-covariantS-matrix formalism and byW-spin analysis

The proton-antiproton annihilation at rest into two mesons is calculated by two methods: (i) on the basis of theSU6 -covariantS-matrix formalism recently proposed byRothleitner andStech, and (ii) by assuming the additional invariance under the group (SU6) W proposed byLipkin andMeshkov. In the first case the calculations give only few relations between transition amplitudes, whereas the larger symmetry group (SU6) W actually determines all amplitudes up to a common factor. While agreement with experiment seems to be poor in some cases for the (SU6) W , so far there are no experimental data available to test the relations of case (i).

Current algebras and annihilations into two mesons

Using current algebras in the low energy limit, we derive relations between electron-positron annihilations into two pseudoscalar mesons and meson-meson scattering. We also obtain some relations for proton-antiproton annihilations at rest.

Two-prong proton-antiproton annihilation with formation of a pair of charged mesons

The cross-section for the two-prong, proton antiproton, annihilation with formation of a pair of charged mesons (π± or K±) is calculated, starting from the Sakurai theory of strong interactions and introducing the vector mesons ρ, ϕ etc. in the intermediate state. The agreement with experiments can be obtained if convenient form factors are introduced in the interactions.

Antiproton-Proton Annihilation at Rest into Two Pseudoscalar Mesons and SU(6) Symmetry

Antiproton-Proton Annihilation at Rest into Two Pseudoscalar Mesons and SU(6) Symmetry

Proton-antiproton annihilation into two mesons

Proton-antiproton annihilation into two mesons

Antiproton-Proton Annihilation at Rest into Two Pseudoscalar Mesons and su(6) Symmetry

Antiproton-Proton Annihilation at Rest into Two Pseudoscalar Mesons and su(6) Symmetry