Evidence for an excess of soft photons in hadronic decays of Z(0)

• Published in: The European physical journal. C, Particles and fields Vol. 47; no. 2; p. 273
• Main Authors: Abdallah, J., Botner, Olga, Brenner, Richard, Ekelöf, Tord, Ellert, Mattias, Hallgren, Allan, Tegenfeldt, Fredrik, Zupan, M.
• Format: Journal Article
• Language: English
• Published: 2006
• Subjects: Elementarpartikelfysik; Elementary particle physics; Fysik; NATURAL SCIENCES; NATURVETENSKAP; Physical Sciences; Physics; Subatomic Physics; Subatomär fysik
• ISSN: 1434-6044; 1434-6052
• DOI: 10.1140/epjc/s2006-02568-8

Soft photons inside hadronic jets converted in front of the DELPHI main tracker (TPC) in events of qq disintegrations of the Z(0) were studied in the kinematic range 0.2 < E-y < I GeV and transverse momentum with respect to the closest jet direction P-T < 80 MeV/c. A clear excess of photons in the experimental data as compared to the Monte Carlo predictions is observed. This excess (uncorrected for the photon detection efficiency) is (1.17 +/- 0.06 +/- 0.27) x 10(-3) gamma/jet in the specified kinematic region, while the expected level of the inner hadronic bremsstrahlung (which is not included in the Monte Carlo) is (0.340 +/- 0.001 +/- 0.038) X 10(-3) gamma/jet. The ratio of the excess to the predicted bremsstrahlung rate is then (3.4 +/- 0.2 +/- 0.8), which is similar in strength to the anomalous soft photon signal observed in fixed target experiments with hadronic beams.