R. Armenteros

pp annihilation into π+π− and K+K− from atomic p states

Abstract 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.

K−p cross sections from440 to 800 MeV/c

Abstract K − p reactions have been studied at 19 different momenta between 436 and793 MeV/ c . This interval corresponds to a mass of theK¯N system from 1535 to 1695 MeV. About 400 000 photographs were taken in the 81 cm Saclay hydrogen bubble chamber exposed to a separated K − beam at the CERN proton-synchrotron. A total of about 100 000 events were analysed, from which partial and differential cross sections were determined. Polarizations were obtained for the two-body reactions where the decay of the Λ or Σ hyperon allowed their measurement. Data for all the channels are presented here.

The KN interaction from 800 to 1200 MeV/c (I). K−p cross sections

K−p reactions have been studied at 23 different momenta between 777 and 1226 MeV/c. This interval corresponds to a mass range of the KN system from 1688 to 1897 MeV. About 350 000 photographs were taken in the 81 cm Saclay hydrogen bubble chamber, exposed to a separated K− beam at the CERN proton synchrotron. A total of about 100 000 events were analysed and partial and differential cross sections were determined; polarisations were also obtained for those reactions where the decay of the Λ or Σ+ hyperon allowed their measurement. The data for all the channels are presented here except those corresponding to two-prong configurations, which make the subject of a separate investigation.

Measurement of the strong-interaction shift and broadening of the ground state of the pp̄ atom☆☆☆

Abstract The Kα X-rays from pp atoms formed in H2 gas at normal temperature and pressure are unambiguously identified by coincidences with L X-rays populating the 2P level. Background due to inner bremsstrahlung is suppressed by selecting events annihilating into neutral final states only. The Kα line is observed with a significance of more than 25 standard deviations at an energy of 8.67 (15) keV. From fits to the Kα line we obtain a strong-interaction shift and width of the 1S level, averaged over the unresolved spin singlet and triplet contributions, of ΔE + iΓ/2 = [−0.70(15) + i0.80(20)] keV.

Observation and quantum numbers determination of the E(1420) meson in π−p interactions at 3.95 GeV/c

In a high statistics (90 events/μb) bubble chamber experiment, the reactions π−p→Ks0K±π∓n have been studied at 3.95 GeV/c. A significant enhancement is observed in the (KKπ) system which we attribute to the production of the E(1420) meson. For its mass, M, and width, Λ, we find M=1426±6 MeV and Γ=40±15 MeV. The E(1420) quantum numbers are determined to be IGJP=0+1+ with a branching ratio E→K∗ K+c.cE→[δπ+(K∗ K+ c.c.)]=0.86±0.12, where δ→KK. The cross section for the reaction π−p→En, with E→K0K±π±, is 8.2±1.0 μb. Forward and backward productions are observed in the approximate ratio 2:1. The SU(3) assignment of the E(1420) meson is discussed.

pp annihilation into K0K0 in hydrogen gas

Abstract The annihilation channels p p→KsKs and KsKL at rest have been observed in hydrogen gas at normal temperature and pressure. The channel KsKs has also been observed from the atomic 2p orbital. The branching fraction for p p→K0 K 0 from initial L = 1 angular momentum p p states is (8.8±2.3)×10−5 and is suppressed by one order of magnitude compared to L = 0 states.

First observation of K X-rays from pp atoms☆☆☆

Abstract K and L series X-rays have been observed from p p atoms formed in hydrogen gas at NTP in association with annihilations into neutral particles. The total K X-ray yield is (6.5 ± 3.2) × 10 −3 per stopped antiproton. A model-dependent fit of the K X-ray spectrum gives a K α energy of 8.9±0.3 keV, corresponding to a strong interaction shift of (−0.5±0.3) keV.

The reactions K−p → K−p and K−p → Kon between 600 and 1200 MeV/c

Data on K−p → K−p, K− → Kon and on the K−p total cross section between 600 and 1200 MeV/c are analysed in terms of resonant and non-resonant partial-wave amplitudes.

STUDY OF THE REACTION K

Data on K−p → K−p, K− → Kon and on the K−p total cross section between 600 and 1200 MeV/c are analysed in terms of resonant and non-resonant partial-wave amplitudes.

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Abstract The reactions K−p → ΛπO and K−n → Λπ− in the centre-of-mass energy range from ≈1.6 to ≈1.9 GeV have been interpreted in terms of an energy-independent partial-wave analysis. Solutions are presented and the possible existence of new resonant states is discussed.