Magnetic monopoles naturally arise in grand unified gauge theories and are believedto carry a mass of ~ 10^(17) GeV/c^2. Strange quark matter (nuclearites) may be the trueQCD ground state and its mass could vary from ~ 100 GeV/c^2 to the neutron star mass.Both of them could travel at any velocities from 3.7 x 10^(-5)c to ~ 10^(-2)c. Experimentaldiscovery of either one would have profound implications. This thesis presents a searchwith the MACRO detector for both of them and any other supermassive particles that arescintillating, slow-moving and highly-penetrating.
The MACRO detector is a large underground detector located at Gran Sasso, Italy,with the primary goal of searching for magnetic monopoles at a flux level beyond theastrophysical Parker bound. It employs liquid scintillator counters, streamer tubes andtrack-etch detectors. When completed, it will have an acceptance of 10,000 m^2sr.
This search is conducted with the large liquid scintillator detector in the first supermoduleof the MACRO detector, which has an acceptance of 870 m^2sr. A specialized slowmonopole trigger is based on the time of passage of slow particles through each scintillatorcounter and enables the detection of supermassive particles with velocities as lowas ~ 10^(-4)c. A second trigger is based on the time of flight between different scintillatorlayers and covers relatively fast velocity range up to 2 x 10^(-2)c. The scintillator waveformsare recorded for both triggers. Both triggers collected data over a period of two years fromOctober 1989 to November 1991. The data were analyzed to search for slow particles. Theabsence of candidates establishes an upper limit on the flux of supermassive particles at 8.7 x 10^(-15) cm^(-2)sr^(-1)sec^(-1) for 3 x 10^(-3) < β < 2 X 10^(-2) and at 5.6 x 10 ^(-15)cm^(-2)sr^(-1)sec^(-1) for β_0 < β < 3 x 10^(-3).The low velocity cutoff β_0 depends on the type of supermassive particles. For magnetic monopoles, the cutoff based on the Ficenec et al. slow proton scintillation measurement is β_0 = 1.8 x 10^(-4) , and the pessimistic cutoff based on the most conservative Ahlen-Tarle light yield model is β_0 = 7 x 10^(-4).For dyons or monopoleproton composites, the model independent cutoff is β_0 = 9 x 10^(-5). Bracci et al. have argued that most likely bare monopoles have bound protons in the early universe, making this dyon search more significant. The application of this flux limit to other supermassiveparticles including nuclearites is described in Chapter 5.
