Search for narrow exotic states in p annihilations on 4He

doi:10.1016/0370-2693(84)91907-5

Physics Letters B

Volume 138, Issues 1–3, 12 April 1984, Pages 235-240

https://doi.org/10.1016/0370-2693(84)91907-5 Get rights and content

Abstract

After having found evidence for narrow exotic states in $p$ p annihilation, the production of such states on a nuclear target was studied with similar techniques. The γ spectrum associated with $p$ annihilation on ⁴He at rest was measured. The spectrum shows two peaks, at energies of 161.9 and 203.0 MeV, corresponding to intermediate narrow states of masses which seem to be related to states found in $p$ p annihilations. The confidence is better than 4σ.

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This paper reports new experimental results on the annihilation of antiprotons stopped in a⁴He gas target. The measurement was carried out with the Obelix spectrometer installed at the LEAR machine of CERN. Main results can be summarized as follows, (i) The invariant mass distribution of 2π⁺2π⁻ produced at rest is similar to those from hydrogen and deuterium targets: the peak seen in recent experiments around 1150 MeV/c² is absent, (ii) 2π angular correlations are very close to those found for hydrogen. The nuclear structure does not modify remarkably the pion production and emission, (iii) πp and pp angular correlations are strongly peaked close to 180°, in qualitative agreement with INC model predictions, (iv) The pp invariant mass distribution reveals events which may be due to η(ω) absorption; the estimated upper limit for probability of π and ω absorption is about 3 × 10⁻³. (v) Events having features compatible with two-nucleon annihilations with production of heavy mesonic systems are detected both in the 2π⁺ 2π⁻ and the 2π⁻π⁺ channels. The production rate of the 2π⁺ 2π⁻ channel is of the order of 5 × 10⁻³.
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This review concentrates on developments, both experimental and theoretical, that have occurred in the field of low energy antinucleon physics since 1983—the year in which the Low Energy Antiproton Ring opened in CERN. On the theoretical side the emphasis is on the progress made in describing $N N$ annihilation and meson branching ratios in terms of quark-antiquark rearrangement and annihilation. The related processes involving the $p - Nucleus$ system are also discussed.
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¹: Present address: BBC, Mannheim, Fed. Rep. Germany.

²: Now at ESO, Garching, Fed. Rep. Germany.

³: Now at CERN, Geneva, Switzerland.

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Physics Letters B

Abstract

References (8)

Phys. Lett.

Phys. Lett.

Nucl. Instrum. Methods

Nucl. Phys.

Cited by (13)

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Has an isotensor meson been seen in pp → π<sup>±</sup>X<sup>∓</sup>?

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