Pp Annihilation Research Articles

New results from [formula omitted]p annihilation at rest

New results on pp annihilation at rest in P-wave are reviewed. The two-body branching ratios of ππ, KK, πϱ, and πf2(1270) show a strong dependence on the angular momentum and the isospin of the initial state. The suppression of π+π−E(1420) production in P-wave suggests JPC(E) = 0−+.

π+π− mass spectrum in the [formula omitted] annihilation channel

We present a calculation of the π+π− mass spectrum in the p p → 3π process using a statistical model due to Vandermeulen. This model is based on the dominance of intermediate two-meson doorway states and reproduces global features of pp annihilation quite well. We show that the model can account not only for the resonant part of the π+π− spectrum, but also for the background.

Antiproton-helium annihilation at 1 MeV

The p − 4He annihilation cross sections have been measured in the energy range from 0.85 to 1.55 MeV (40 + 54 MeV/c) in the PS-179 experiment at the LEAR facility of the CERN using a streamer chamber in a magnetic field. The σan (0.85 + 1.55 MeV) mean value has been found to be (1541 ± 262 ± 92) mbarn. Recently Mahalanabis et al. have obtained the behaviour of the pp annihilation cross section down to zero energy and values at 40 and 50 MeV/c are given for np annihilation. Our p4He annihilation cross section is approximately twice that on free nucleon like in the interval 200–600 MeV/c.

Formula omitted] annihilation into π+π− and K +K − from atomic p states

We have obtained the branching ratios for p p annihilation at rest into π + π − and K +K − in a pure p p initial angular momentum state L = 1. A gaseous hydrogen target at normal pressure and temperature was used and events associated with transitions of the antiprotonic atom to the 2p level were selected by detecting the Balmer X-ray series. The branching ratios for p p annihilation into π + π − and K +K − from the 2p state are (4.81 ± 0.49) × 10 −3 and (2.87 ± 0.51) × 10 −4, respect The pion yield is slightly larger than in liquid hydrogen, where L = 0 annihilation dominates, while the kaon yield is suppressed by a factor of four. Using these and previous data, we derive the branching ratios for pp annihilation into all ππ and K K modes from S and P states. A measurement in gaseous hydrogen, without X-ray requirement, yields the branching ratios (4.30 ± 0.14) × 10 −3 and (6.92 ± 0.41) × 10 −4. With the known branching ratios of (3.33 ± 0.17) × 10 −3 and (1.01 ± 0.05) × 10 −3 in liquid hydrogen, we find that (50.3 ± 6.4)% of all annihilations in gas at NTP occur in the initial angular momentum state L = 1.

Transition potential in the quark model

Abstract The transition potential of p p to the hyperon-antihyperon (Y Y ) system is calculated in the constituent quark model with the 3P0 model and with the 3S1 model. The 3P0 model allows the tensor coupling between the p p and Y Y states while the 3S1 model restricts that the p p and YȲ have the same orbital angular momentum. To reproduce the relative ratios of pp annihilation into hyperon anti-hyperon qualitatively, the tensor interaction is important and the 3P0 model compares better with the experiment than the 3S1 model.

Evidence for a narrow (S) resonance in pp annihilation at 1937 MeV

A “long target” experiment designed to search for narrow structure in p p annihilation is reanalyzed and evidence is found for a narrow resonance (Γ <3 MeV) near 1937 MeV.

The “split” iota

Abstract Within the context of a five channel mixing model the possibility is considered that the E(1420) originally seen in PP annihilation at rest and originally believed to be a JPC=1++ state is actually a pseudoscalar state distinct from the ι(1460) seen in radiative ψ decay. The quark and glue content that this hypothesis implies and the consequences for branching ratios of the known pseudoscalars are discussed. The five channel mixing model includes the ground state pseudoscalars, their first radial excitations, and a glueball. Mixing terms include an SU(3) symmetric glueball-quark state coupling as well as the important two body intermediate state unitarity corrections. While a number of mathematically consistent solutions to the model are found, none are physically acceptable. It is concluded that the more likely scenario is that the E(1420) and the ι(1460) are the same state, and the fifth partner to the scheme lies in a higher mass range, above 1.7 GeV.

The pp̄ interaction with an annihilation potential derived from the quark rearrangement model

Abstract The s-wave pp annihilation potential is derived from the quark rearrangement model. Combining the G -parity transformed OBEP of Bryan and Phillips and the derived s-wave annihilation potential we solve the multichannel N / D equation by the Pade approximant method. For the p- and d-waves we introduce a phenomenological annihilation potential from a few-meson decay mode. We can reproduce the annihilation cross section by choosing two parameters: the strength of the s-wave annihilation potential and the strength of the p- and d-wave annihilation potential. We find p-wave quasi-bound states near the threshold but their energy and width are sensitive to the energy dependence of the effective phase-space function x ( E ).

Pp̄ Annihilation at rest into mesons in the quark rearrangement model and the quark annihilation modelt

Abstract pp annihilation at rest into mesons is calculated in the quark rearrangement model in which 3 quarks and 3 antiquarks rearrange into 3 mesons and in the quark annihilation model in which one or two quark-antiquark pairs are annihilated and a quark-antiquark pair is created to form two or three mesons. The constants of the quark-meson coupling are adjusted such that the meson-nucleon interactions agree with experiment. The radial dependences of the quark-meson couplings are all assumed to be the same. This is determined by the vector-meson-quark interaction derived from the charge form factor of the proton. In the case of the decay into three mesons both rearrangement and annihilation models explain with similar reliability the branching ratio of the decay products. In the case of the decay into two-meson annihilation gives a better agreement with experiment than rearrangement.

A Simple Explanation of Negative Correlation Data in Formulap Annihilations

Negative correlation data in pp annihilations at low energies are explained by a simple model, in which the normalized cross section for the negative-charged multiplicity is represented by binomial distribution. It satisfies the multiplicity cutoff required by the energy conservation and shows an approximate KNO scaling.

Measurement of [formula omitted] annihilation cross sections into charged particles in the momentum range 374–680 MeV/ c

pp annihilation cross sections into 2-, 4- and 6-prong topologies, and the exclusive annihilation cross sections for the π + π −, K +K −, π + π − π 0, π + π + π − π −, π + π + π − π − π 0, π + π + π + π − π − π −, and π + π + π + π − π − π − π 0 channels in the momentum range 374–680 MeV/ c were measured. No prominent structure was observed in the momentum dependence of any of the above cross sections, but a small enhancement in the cross section was observed at 490 MeV/ c corresponding to the S meson mass in the topological, and π + π − π 0 and π + π + π − π − π 0 cross sections. If the extensive of the S meson with a mass and width of 1935.5 and 2.8 MeV/ c 2 is assumed, our measurement gives a total resonant annihilation cross section into charged particles of 10.0±3.0 mb.

A study of second-order interference for pions produced in various hadronic interactions

Second-order interference of pion pairs of equal charge is observed in good statistics samples of 16 GeV/ c π +p and K −p interactions (2 × 10 6 and 10 6 pion pair combinations, respectively) and in a smaller sample of pp annihilations at rest. The effective radius R of the pion source is found to be approximately 1.4 fm for all three types of interaction. The interference does not appear to be “total”, about 60–80% of the like pairs interfering. It is shown that the numerical results for the radius R, for the depth cτ of the source “photosphere” and for the fraction λ of the interfering pairs are sensitive to any dynamical correlation in the background, and hence depend on the background chosen. It is argued that further refinements in the theoretical formulation of the phenomenon and in the experimental approach are needed for truly quantitative results.

Exclusive annihilation processes in [formula omitted] interactions and comparisons between [formula omitted] non-annihilations and pp interactions

We give cross sections for annihilation and non-annihilation reactions in pp interactions at 8.8 GeV. The non-annihilation data are compared with pp data from the same experiment. We compare data on resonance production and on the impact parameter structure of the final states in pp annihilation and non-annihilation and pp interactions. We investigate the charge structure of the 2 π + 2 π − π 0 final state, and find it consistent with a simple quark model.

General features of charged particle production in ? interactions at 100 GeV/c

We present new data on charged particle production in pp interactions at 100 GeV/c. Comparisons are made between pp annihilations (estimated by differences) between corresponding pp and pp data samples) and e+e− annihilation into hadrons. A technique for separating the inclusive proton and pion spectra is described and the resulting pion spectra are studied in terms of Feynman x, rapidity and pT. Comparison with pp data allows us to estimate the pion spectra in pp annihilations and we find agreement with predictions of Mueller-Regge theory. We also present results on semi-inclusive π± and proton production, give updated topological cross sections and describe further attempts to isolate effects due to annihilations. Finally we investigate the diffractive excitation of the antiproton into low-mass states by studying events with a slow recoil proton.

First observation of X-rays from antiprotonic hydrogen

We have observed the Balmer series of antiprotonic hydrogen atoms formed in gaseous hydrogen at 4 atm. The yield of L X-rays was determined to be (6 ± 3)% per stopped antiproton. The 2P state is dominantly depopulated via pp annihilation and not by radiative transitions to the 1S state.

Inclusive production of [formula omitted] annihilations at 0.76 GeV/ c

The production of K ∗±(892) and K S 0 are studied in pp annihilations at 0.76 GeV/ c. Longitudinal and transverse momentum distributions are presented. The ratio σ( K ∗+) σ dir ( K 0 ) is found to be 0.09 ± 0.09, where σ dir(K 0) refers to kaons which do not arise from decay of the resonances. The ratio of strange to non-strange directly produced vector mesons is K dir ∗+ ϱ dir 0 = 0.054 ± 0.005 , compared to the corresponding ratio for the pseudoscalar mesons K dir 0 π dir − = 0.021 ± 0.003 . It is deduced that (50±5)% of all K S 0 are indirectly produced through the decay of the meson resonances and consequently (50±5)% are directly produced.

Measurement of neutral to charged pion ratio in [formula omitted] annihilations in the 2200 MeV mass region

The relative probability distribution of π ±and π 0 mesons in pp annihilation was measured in 10 MeV bins from 2.15 to 2.23 GeV. No significant variation in probabilities was found, and mean values are consistent with those reported at 2.28 GeV. Observed multiplicity distributions are consistent with two-body cascading on the statistical model under equal weighting of G = ±1 states.

ωπ structures in pp annihilations between 1.50 and 2.04 GeV/c

A study of 54930 events of type pp to pi + pi + pi - pi - pi 0 shows evidence for two nearly mass degenerate enhancements in the omega pi mass plots at a mass near to 1200 MeV/c2. This result is in agreement with that reported from annihilations at rest by Frenkiel et al. (see Nucl. Phys., vol.B47, p.61 of 1972).

Granddaughter trajectories in $$\bar pp$$ annihilations

We have fitted the differential cross-section data for pp annihilations to π−π+ and K−K+ with a model consisting of resonances together with a constituent interchange model background. We find strong evidence for meson resonances of mass 2.11, 2.3 and 2.48 GeV/c2 with spins of 3, 4 and 5 respectively. We also have weaker evidence for a J=2 resonance near threshold. Together with the ρ′(1600) these resonances from a « granddaughter » Regge trajectory approximately two units of angular momentum below ther> A2 trajectory.

Multihadron production in nucleon-antinucleon annihilation at rest in the statistical bootstrap model

Inclusive, semi-inclusive and exclusive invariant single particle distributions and average transverse momenta and energies are discussed in the statistical bootstrap model. The shape of inclusive distributions and average transverse momenta are confronted with available data on pp, pn and e+e− annihilations. Good agreement is found using the parameter of the model as determined in part I from the multiplicity distribution in pp annihilation at rest. Furthermore the approach to the asymptotic behaviour in the statistical bootstrap model is discussed.