A Search for GUT Monopoles with a Single Thick Scintillator at Sea Level
Experimental searches for magnetic monopoles have proliferated in recent years due to the prediction of certain Grand Unified Theories (GUTs) that monopoles should exist and be extremely massive (M ≳ 1016 GeV/c2). In contrast to monopoles of much lower mass, GUT monopoles are expected to be moving at very low speeds1 (V ∼ 10−3c) and to have a greatly reduced rate of energy loss.2 The possibility that a large reservoir of low velocity monopoles may have gone undetected has provided a challenge to experimentalists to devise new methods of detecting slow particles. Many experimenters have employed direct methods that rely only on the electromagnetic interactions of monopoles. Superconducting loop detectors, ionization detectors and various detectors based on excitation, such as scintillators, fall into this category. Of these, superconducting loop detectors are unique in that they respond to monopoles of arbitrary velocity. Several indirect techniques have been used to set impressive limits on the monopole flux. These techniques, however, often require additional assumptions regarding the velocity, charge state and the interactions of monopoles with nuclei that complicate the problem of setting hard limits on the monopole flux. For example, limits3–4 based on the Callan-Rubakov effect5 require that baryon number is not strictly conserved, an assumption that has yet to be experimentally verified.6 If monopoles do not catalyze baryon decay, then stable bound states of monopoles with nuclei may exist7, 8 and monopoles traversing the earth may pick up abundant heavy nuclei such as Al or Mn which have large magnetic moments. Such composites can be detected by tracks left in ancient mica9 or may have sufficient energy loss to stop in the earth and be detected in stable matter searches. It is possible, however, that monopoles may capture a proton in interstellar space via an Auger mechanism8 or by ordinary radiative capture in the early Universe.10 If monopoles are accompanied by a positive electric charge then Coulomb repulsion may prevent the capture of heavy nuclei and searches which depend on the enhanced stopping power of such composites may be nullified. The problem with all the indirect searches is that so many loopholes exist that it is unlikely that any will be strong enough to provide compelling evidence against monopoles. In view of the above difficulties, it seems preferable to search for monopoles with a detector which relies on as few assumptions as possible and which is sensitive to monopoles having velocities and magnetic and electric charges within a reasonable band of expected values.
KeywordsPulse Height Grand Unify Theory Fast Particle Multiple Pulse Atmospheric Muon
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- C. Goebel, Monopole Seminars at Univ. of Wisconsin, p. 51 (1981).Google Scholar
- 9.P.B. Price, Shi-lun Guo, S.P. Ahlen and R.L. Fleischer, submitted to Phys. Rev. Lett. (1983).Google Scholar
- 10.G. Fiorentini, private communication (1983).Google Scholar
- 13.S. Parke, in proceedings of this conference.Google Scholar
- 14.J.B. Birks, The Theory and Practice of Scintillation Counting, Pergamon Press, Oxford (1964).Google Scholar
- 15.T.M. Liss, G. Tarle and S.P. Ahlen, submitted to Phys. Rev. D (1984).Google Scholar
- 17.B. Cabrera, Stanford preprint, March 1983.Google Scholar
- 18.E.N. Alexeyev et al., Proc. 18th Inter. Cosmic Ray Conf., Bangalore, India 5, 52 (1983).Google Scholar
- 20.T. Mashimo et al., Univ. of Tokyo preprint UTLICEPP-83-03 (1983).Google Scholar
- 21.F. Kajino et al., Proc. 18th Inter. Cosmic Ray Conf., Bangalore, India 5, 56 (1983).Google Scholar
- 22.S. Higashi, S. Ozaki, T. Takahashi and K. Tsuji, Proc. 18th Inter. Cosmic Ray Conf. 5, 69 (1983).Google Scholar
- 25.K. Freese and M.S. Turner, Chicago EFI Preprint EFI 82/56 (1982).Google Scholar