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Multiple particle production from e+e interactions at C.M. energies between 1.6 and 2 GeV

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Il Nuovo Cimento A (1965-1970)

Summary

Multiple particle production in electron-positron interactions has been observed in an experiment performed at Adone, the Frascati 2×1.5 GeV e+e storage ring. A total number of 239 events collected at several energies of the incident electron and positron beams between 0.8 and 1.0 GeV were analysed. The distribution of the multiplicity of charged particles produced in the final state is discussed and some upper limits on these multiplicities are reported. The observed lower limit to the total cross-section for multiple particle production in e+e interactions, averaged over the energy range explored, is 3·10−32 cm2 with a statistical error of ±10% and a systematic uncertainty of ±25%.

Riassunto

In un esperimento eseguito con Adone, l’anello di accumulazione per elettroni e positoni da 2×1.5 GeV dei Laboratori Nazionali di Frascati, è state osservata la produzione, nelle interazioni elettrone-positone, di stati finali a molte particelle. In questo lavoro si presenta l’analisi di 239 eventi raccolti a varie energie dei fasci incidenti fra 0.8 e 1.0 GeV. Si discute la distribuzione delle molteplicità delle particelle cariche nello stato finale e si danno i limiti superiori per alcune di queste molteplicità. Il limite inferiore per la sezione d’urto totale di produzione di stati finali a molte particelle nelle interazioni e+e, mediata nell’intervallo di energia esplorato, risulta essere 3·10−32 cm2 con un errore statistico del ±10% ed una incertezza sistematica del ±25%.

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References

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  3. The absorbers in the telescopesT i and in front of the CR counters set the following limits on the kinetic energyT of the observed particles: ∼80 MeV ≲ ≲T≲350 MeV. The evaluation of the corresponding corrections (due to their smallness) does not critically depend on the momentum distribution of the emitted particle; we have used the experimental momentum distribution of pions from\(p\bar p \to 2\pi ^ + + 2\pi ^ - \) annihilations (see,e.g.,C. Baltay,P. Franzini,G. Lütjens,J. C. Severiens,D. Tycko andD. Zanello:Phys. Rev.,145, 1103 (1966)).

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  4. We recall that the luminosity ℒ (essentially the product of the e+ and e beam intensities divided by their effective section) is a measurement of the machine intensity. The number of events produced is directly given by the product ℒ·σ, where σ is the cross-section of the process.

  5. Our «source» has a finite longitudinal dimension and is expected to have a Gaussian distributionN(l)=N 0 exp\(\left[ { - l^2 /2\bar l^2 } \right]\). Theoretically\(\bar l\) is expected to be\(\bar l\left( {cm} \right) = 20E_ \pm ^{\frac{3}{2}} \) and experimentally has been measured to be\(\bar l\left( {cm} \right) = \left( {22 \pm 2} \right)E_ \pm ^{\frac{3}{2}} \), whereE ± is in GeV. (Private communications from the Adone machine staff.) As far as the ∈(n)’s are concerned, their dependence on\(\bar l\) is\(\varepsilon \left( n \right) \propto l/\bar l\), but since our conclusions involve only ratios of ∈(n)’s they are independent of the actual value used for\(\bar l\).

  6. Also in the casen=2 the total number of charged and neutral particles produced in the reaction must by ≥3. In order to estimate how model dependent the values of the efficiences ∈′s are, we have calculated the ∈′s for several simple cases. If two charged pions are emitted (n=2), depending on the number of the associated π0’s, the values of the ∈′s obtained with the statistical model can be ∼30% large than the values given in Table III which were calculated under the assumption that the particles were emitted isotropically. For the higher charged multiplicity states (n>2) the values of Table III agree to better than ∼10% with the results one can obtain with any reasonable hypothesis.

  7. In eq. (4) both σeff(e+e) and ε⩾2(4) depend on the average length\(2\bar l\) of the source, but their ratio is almost independent of it.

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Bartoli, B., Coluzzi, B., Felicetti, F. et al. Multiple particle production from e+e interactions at C.M. energies between 1.6 and 2 GeV. Nuovo Cimento A (1965-1970) 70, 615–631 (1970). https://doi.org/10.1007/BF02734498

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  • DOI: https://doi.org/10.1007/BF02734498

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