Measurement of the running of the electromagnetic coupling at large momentum-transfer at LEP
The evolution of the electromagnetic coupling, α, in the momentum-transfer range 1800 GeV<sup>2</sup> < −Q<sup>2</sup> < 21600 GeV<sup>2</sup> is studied with about 40 000 Bhabha-scattering events collected with the L3 detector at LEP at centre-of-mass energ...
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| Autores principales: | , |
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| Formato: | Articulo |
| Lenguaje: | Inglés |
| Publicado: |
2005
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| Materias: | |
| Acceso en línea: | http://sedici.unlp.edu.ar/handle/10915/79504 |
| Aporte de: |
| Sumario: | The evolution of the electromagnetic coupling, α, in the momentum-transfer range 1800 GeV<sup>2</sup> < −Q<sup>2</sup> < 21600 GeV<sup>2</sup> is studied with about 40 000 Bhabha-scattering events collected with the L3 detector at LEP at centre-of-mass energies √s = 189–209 GeV. The running of α is parametrised as: <math><mi is="true">α</mi><mrow is="true"><mo is="true">(</mo><msup is="true"><mi is="true">Q</mi><mn is="true">2</mn></msup><mo is="true">)</mo></mrow><mo is="true">=</mo><mfrac is="true"><msub is="true"><mi is="true">α</mi><mn is="true">0</mn></msub><mrow is="true"><mn is="true">1</mn><mo is="true">−</mo><mi is="true">C</mi><mi mathvariant="normal" is="true">Δ</mi><mi is="true">α</mi><mo stretchy="false" is="true">(</mo><msup is="true"><mi is="true">Q</mi><mn is="true">2</mn></msup><mo stretchy="false" is="true">)</mo></mrow></mfrac><mo is="true">,</mo></math> where α<sub>0</sub> ≡ α(Q<sup>2</sup> = 0) is the fine-structure constant and C = 1 corresponds to the evolution expected in QED. A fit to the differential cross section of the e<sup>+</sup>e<sup>−</sup> → e<sup>+</sup>e<sup>−</sup> process for scattering angles in the range |cos θ| < 0.9 excludes the hypothesis of a constant value of α, C = 0, and validates the QED prediction with the result:
C = 1.05 ± 0.07 ± 0.14, where the first uncertainty is statistical and the second systematic. |
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