https://doi.org/10.1140/epjc/s10052-006-0170-x
Regular Article - Experimental Physics
Search for invisibly decaying Higgs bosons with large decay width using the OPAL detector at LEP
1
School of Physics and Astronomy, University of Birmingham, Birmingham, B15 2TT, UK
2
Dipartimento di Fisica dell’ Università di Bologna and INFN, 40126, Bologna, Italy
3
Physikalisches Institut, Universität Bonn, 53115, Bonn, Germany
4
Department of Physics, University of California, Riverside, CA, 92521, USA
5
Cavendish Laboratory, Cambridge, CB3 0HE, UK
6
Ottawa-Carleton Institute for Physics, Department of Physics, Carleton University, Ottawa, Ontario, K1S 5B6, Canada
7
CERN, European Organisation for Nuclear Research, 1211, Geneva 23, Switzerland
8
Enrico Fermi Institute and Department of Physics, University of Chicago, Chicago, IL, 60637, USA
9
Fakultät für Physik, Albert-Ludwigs-Universität Freiburg, 79104, Freiburg, Germany
10
Physikalisches Institut, Universität Heidelberg, 69120, Heidelberg, Germany
11
Department of Physics, Indiana University, Bloomington, IN, 47405, USA
12
Queen Mary and Westfield College, University of London, London, E1 4NS, UK
13
III Physikalisches Institut, Technische Hochschule Aachen, Sommerfeldstrasse 26–28, 52056, Aachen, Germany
14
University College London, London, WC1E 6BT, UK
15
Department of Physics, Schuster Laboratory, The University, Manchester, M13 9PL, UK
16
Department of Physics, University of Maryland, College Park, MD, 20742, USA
17
Laboratoire de Physique Nucléaire, Université de Montréal, Montréal, Québec, H3C 3J7, Canada
18
Department of Physics, University of Oregon, Eugene, OR, 97403, USA
19
CCLRC Rutherford Appleton Laboratory, Chilton, Didcot, Oxfordshire, OX11 0QX, UK
20
Department of Physics, Technion – Israel Institute of Technology, Haifa, 32000, Israel
21
Department of Physics and Astronomy, Tel Aviv University, Tel Aviv, 69978, Israel
22
International Centre for Elementary Particle Physics and Department of Physics, University of Tokyo, Tokyo, 113-0033, Japan
23
Kobe University, Kobe, 657-8501, Japan
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Particle Physics Department, Weizmann Institute of Science, Rehovot, 76100, Israel
25
Institut für Experimentalphysik , Universität Hamburg/DESY, Notkestrasse 85, 22607, Hamburg, Germany
26
Department of Physics, University of Victoria, P O Box 3055, Victoria, BC, V8W 3P6, Canada
27
Department of Physics, University of British Columbia, Vancouver, BC, V6T 1Z1, Canada
28
Department of Physics, University of Alberta, Edmonton, AB, T6G 2J1, Canada
29
Research Institute for Particle and Nuclear Physics, 1525, Budapest, PO Box 49, Hungary
30
Institute of Nuclear Research, 4001, Debrecen, PO Box 51, Hungary
31
Sektion Physik, Ludwig-Maximilians-Universität München, Am Coulombwall 1, 85748, Garching, Germany
32
Max-Planck-Institute für Physik, Föhringer Ring 6, 80805, München, Germany
33
Department of Physics, Yale University, New Haven, CT, 06520, USA
34
TRIUMF, Vancouver, Canada V6T 2A3,
35
University of Alberta, Edmonton, Alberta, Canada
36
Institute of Nuclear Research, Debrecen, Hungary
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Institute of Physics, Academy of Sciences of the Czech Republic, 18221, Prague, Czech Republic
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Department of Experimental Physics, University of Debrecen, Debrecen, Hungary
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MPI München, München, Germany
40
Research Institute for Particle and Nuclear Physics, Budapest, Hungary
41
Dept of Physics, University of Liverpool, Liverpool, L69 3BX, UK
42
Dept. Physics, University of Illinois at Urbana-Champaign, Urbana-Champaign, USA
43
Manchester University, Manchester, M13 9PL, UK
44
Dept of Physics and Astronomy, University of Kansas, Lawrence, KS, 66045, USA
45
Dept of Physics, University of Toronto, Toronto, Canada
46
Bergische Universität, Wuppertal, Germany
47
University of Mining and Metallurgy, Cracow, Poland
48
University of California, San Diego, USA
49
The University of Melbourne, Victoria, Australia
50
IPHE Université de Lausanne, 1015, Lausanne, Switzerland
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IEKP Universität Karlsruhe, Karlsruhe, Germany
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Physics Department, University of Antwerpen, 2610, Antwerpen, Belgium
53
Technische Universität, Dresden, Germany
54
High Energy Accelerator Research Organisation (KEK), Tsukuba, Ibaraki, Japan
55
University of Pennsylvania, Philadelphia, Pennsylvania, USA
56
TRIUMF, Vancouver, Canada
57
CERN, Geneva 23, Switzerland
58
DESY, Hamburg, Germany
* e-mail: David.Plane@cern.ch
Received:
8
August
2006
Revised:
30
November
2006
Published online:
6
December
2006
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 (MH=60 GeV) to 0.57 pb (MH=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.
© Springer-Verlag Berlin Heidelberg, 2007