Multi-photon events with large missing energy in e+e− collisions at s=192–209 GeV

• Published in: Physics letters. B Vol. 602; no. 3-4; pp. 167 - 179
• Main Authors: Ainsley, C., Alexander, G., Amaral, P., Anagnostou, G., Asai, S., Azuelos, G., Bailey, I., Barillari, T., Barlow, R.J., Bechtle, P., Behnke, T., Biebel, O., Boutemeur, M., Brown, R.M., Burckhart, H.J., Campana, S., Carnegie, R.K., Ciocca, C., Csilling, A., Dado, S., De Roeck, A., De Wolf, E.A., Desch, K., Duchovni, E., Duckeck, G., Fabbri, F., Ferrari, P., Fiedler, F., Fleck, I., Gagnon, P., Giacomelli, P., Gross, E., Günther, P.O., Harel, A., Hauschild, M., Hawkes, C.M., Hawkings, R., Hemingway, R.J., Horváth, D., Jovanovic, P., Keeler, R.K., Kellogg, R.G., Kennedy, B.W., Kluth, S., Kobayashi, T., Komamiya, S., Krämer, T., Krieger, P., von Krogh, J., Kruger, K., Kuhl, T., Kupper, M., Levinson, L., Lillich, J., Lloyd, S.L., Ludwig, J., Mader, W., Martin, A.J., Mashimo, T., McKenna, J., McPherson, R.A., Meijers, F., Menges, W., Merritt, F.S., Mihara, S., Miller, D.J., Mohr, W., Neal, H.A., O'Neale, S.W., Pater, J.R., Pinfold, J., Plane, D.E., Quadt, A., Rabbertz, K., Roney, J.M., Runge, K., Saeki, T., Schieck, J., Scott, W.G., Seuster, R., Skuja, A., Smith, A.M., Stahl, A., Strom, D., Tarem, S., Tran, P., Trigger, I., Tsur, E., Ueda, I., Vértesi, R., Verzocchi, M., Vossebeld, J., Watson, A.T., Watson, N.K., Wengler, T., Wermes, N., Wilson, G.W., Wolf, G., Wyatt, T.R., Yamashita, S.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 25.11.2004; Elsevier Science
• Subjects: Exact sciences and technology; Physics; The physics of elementary particles and fields; Upper bound; Supersymmetric field theory; Kinematics; Standard model; Pair production; Collision energy; Positron annihilation; GeV range; Neutrino production; Cross sections; Neutralino; Gravitinos
• ISSN: 0370-2693; 1873-2445
• DOI: 10.1016/j.physletb.2004.09.059

Events with a final state consisting of two or more photons and large missing transverse energy have been observed in e+e− collisions at centre-of-mass energies in the range 192–209 GeV using the OPAL detector at LEP. Cross-section measurements are performed within the kinematic acceptance of the selection and compared with the expectations from the Standard Model process e+e−→νν¯γγ(γ). No evidence for new physics contributions to this final state is observed. Upper limits on σ(e+e−→XX)⋅BR2(X→Yγ) are derived for the case of stable and invisible Y. In the case of massive Y the combined limits obtained from all the data range from 10 to 60 fb, while for the special case of massless Y the range is 20 to 40 fb. The limits apply to pair production of excited neutrinos (X=ν*,Y=ν), to neutralino production (X=χ˜20,Y=χ˜10) and to supersymmetric models in which X=χ˜10 and Y=G˜ is a light gravitino.