Search for invisibly decaying Higgs bosons with large decay width using the OPAL detector at LEP

Abbiendi, G. and Ainsley, C. and Akesson, P. F. and Alexander, G. and Anagnostou, G. and Anderson, K. J. and Asai, S. and Axen, D. and Bailey, I. and Barberio, E. and Barillari, T. and Barlow, R. J. and Batley, R. J. and Bechtle, P. and Behnke, T. and Bell, K. W. and Bell, P. J. and Bella, G. and Bellerive, A. and Benelli, G. and Bethke, S. and Biebel, O. and Boeriu, O. and Bock, P. and Boutemeur, M. and Braibant, S. and Brown, R. M. and Burckhart, H. J. and Campana, S. and Capiluppi, P. and Carnegie, R. K. and Carter, A. A. and Carter, J. R. and Chang, C. Y. and Charlton, D. G. and Ciocca, C. and Csilling, A. and Cuffiani, M. and Dado, S. and De Roeck, A. and De Wolf, E. A. and Desch, K. and Dienes, B. and Dubbert, J. and Duchovni, E. and Duckeck, G. and Duerdoth, I. P. and Etzion, E. and Fabbri, F. and Ferrari, P. and Fiedler, F. and Fleck, I. and Ford, M. and Frey, A. and Gagnon, P. and Grunhaus, J. and Gruwe, M. and Gupta, A. and Hajdu, C. and Hamann, M. and Hanson, G. G. and Harel, A. and Hauschild, M. and Hawkes, C. M. and Hawkings, R. and Herten, G. and Heuer, R. D. and Hill, J. C. and Horvath, D. and Igo-Kemenes, P. and Ishii, K. and Jeremie, H. and Jovanovic, P. and Junk, T. R. and Kanzaki, J. and Karlen, D. and Kawagoe, K. and Kawamoto, T. and Keeler, R. K. and Kennedy, B. W. and Kluth, S. and Kobayashi, T. and Kobel, M. and Komamiya, S. and Kraemer, T. and Krasznahorkay, A. and Krieger, P. and von Krogh, J. and Kuhl, T. and Kupper, M. and Lafferty, G. D. and Landsman, H. and Lanske, D. and Lellouch, D. and Letts, J. and Levinson, L. and Lillich, J. and Lloyd, S. L. and Loebinger, F. K. and Lu, J. and Ludwig, A. and Ludwig, J. and Mader, W. and Marcellini, S. and Martin, A. J. and Mashimo, T. and Maettig, P. and McKenna, J. and McPherson, R. A. and Meijers, F. and Menges, W. and Merritt, F. S. and Mes, H. and Meyer, N. and Michelini, A. and Mihara, S. and Mikenberg, G. and Miller, D. J. and Mohr, W. and Mori, T. and Mutter, A. and Nagai, K. and Nakamura, I. and Nanjo, H. and Neal, H. A. and Nisius, R. and O'Neale, S. W. and Oh, A. and Oreglia, M. J. and Orito, S. and Pahl, C. and Pasztor, G. and Pater, J. R. and Pilcher, J. E. and Pinfold, J. and Plane, D. E. and Pooth, O. and Przybycien, M. and Quadt, A. and Rabbertz, K. and Rembser, C. and Renkel, P. and Roney, J. M. and Rossi, A. M. and Rozen, Y. and Runge, K. and Sachs, K. and Saeki, T. and Sarkisyan, E. K. G. and Schaile, A. D. and Schaile, O. and Scharff-Hansen, P. and Schieck, J. and Schoerner-Sadenius, T. and Schroeder, M. and Schumacher, M. and Seuster, R. and Shears, T. G. and Shen, B. C. and Sherwood, P. and Skuja, A. and Smith, A. M. and Sobie, R. and Soeldner-Rembold, S. and Spano, F. and Stahl, A. and Strom, D. and Stroehmer, R. and Tarem, S. and Tasevsky, M. and Teuscher, R. and Thomson, M. A. and Torrence, E. and Toya, D. and Tran, P. and Vannerem, P. and Vertesi, R. and Verzocchi, M. and Voss, H. and Vossebeld, J. and Ward, C. P. and Ward, D. R. and Watkins, P. M. and Watson, A. T. and Watson, N. K. and Wells, P. S. and Wengler, T. and Wermes, N. and Wilson, G. W. and Wilson, J. A. and Wolf, G. and Wyatt, T. R. and Yamashita, S. and Zer-Zion, D. and Zivkovic, L. (2007) Search for invisibly decaying Higgs bosons with large decay width using the OPAL detector at LEP. European Physical Journal C: Particles and Fields, 49 (2). pp. 457-472. ISSN 1434-6044

Abstract

This paper describes a topological search for an invisibly decaying Higgs boson, H, produced via the Bjorken process (e(+)e(-)-> HZ). The analysis is based on data recorded using the OPAL detector at LEP at centre-of-mass energies from 183 to 209 GeV corresponding to a total integrated luminosity of 629 pb(-1). In the analysis only hadronic decays of the Z boson are considered. A scan over Higgs boson masses from 1 to 120 GeV and decay widths from 1 to 3000 GeV revealed no indication for a signal in the data. From a likelihood ratio of expected signal and standard model background we determine upper limits on cross-section times branching ratio to an invisible final state. For moderate Higgs boson decay widths, these range from about 0.07 pb (M-H=60 GeV) to 0.57 pb (M-H=114 GeV). For decay widths above 200 GeV the upper limits are of the order of 0.15 pb. The results can be interpreted in general scenarios predicting a large invisible decay width of the Higgs boson. As an example we interpret the results in the so-called stealthy Higgs scenario. The limits from this analysis exclude a large part of the parameter range of this scenario experimentally accessible at LEP 2.