1 A Search for Massive Magnetic Monopoles at the Baksan Underground Scintillation Telescope A Search for Massive Magnetic Monopoles at the Baksan Underground Scintillation Telescope Yu.F. Novoseltsev, M.M. Boliev, A.V. Butkevich, S.P.Mikheev, V.B. Petkov Institute for Nuclear Research of RAS Pylos

2 The experiment has been performed for both fast (β ≥ 0.4) and slow (2 × ≤ β ≤ ) monopoles. In the velocity range β ≥ 0.4, we made use of "the cascade trigger" (large energy deposition in the facility), the time-flight method was used for 2×10 -4 ≤ β ≤ range. BUST is located at the depth of 850 m w.e. The facility dimensions are 17×17×11 m 3. The “slow trigger” requires of internal plane operation SΩ = 1850 m 2 × sr SΩ = 1850 m 2 × sr (isotropic flux) (isotropic flux) The β ≥ 0.4 trigger requires crossing of three horizontal crossing of three horizontal planes planes SΩ = 728 m 2 × sr SΩ = 728 m 2 × sr (isotropic flux) (isotropic flux) Pylos

3 “in 1” means 6 external planes 6 external planes “in 2” is 2 internal planes planes Trigger rate is ≈ 200 per day ≈ 200 per day 2    β <    β < 0.1 Pylos

4 Trigger is the coincidence of the signal from one of Trigger is the coincidence of the signal from one of external planes with the internal plane signal delayed external planes with the internal plane signal delayed greater than 50 ns. greater than 50 ns. Live time = hours = years ( − ) ( − ) Only events with three hit planes were considered as slow particle candidates (because a background from stopping of muons with subsequent μ - e decay was rather large) Pylos

5 All triggered events can be subdivided into 3 groups: All triggered events can be subdivided into 3 groups: 44 % − μ-e decays 54.6 % − random coincidence 1.4 % − relativistic muons which have flight time > 50 ns (large zenith angles θ ≥ 80 o ) (large zenith angles θ ≥ 80 o ) No candidate for the slow particles was recorded F MM ≤ 3.2 × cm -2 s -1 sr -1 (90 % CL)

6 β ≥ 0.4, q ≥ 137/2e The events were selected in which the energy deposition in the facility exceeded ε th = 1540 r.p. = 77 GeV the facility exceeded ε th = 1540 r.p. = 77 GeV (1 r.p. = 50 MeV) (1 r.p. = 50 MeV) To estimate the light yield (dL/dx) in a scintillator we use the expression (Salamon, Ahlen, 1981) the expression (Salamon, Ahlen, 1981) where dE/dx is the total energy loss, A = 0.03, B is the quenching parameter, F is the fraction of energy loss which results from excitations outsite the core. (1) Pylos

7 Some characteristics of BUST and MACRO scintillators BUST scintillator BUST scintillator MACRO scintillator MACRO scintillator density, g/cm 3 density, g/cm H/C ratio H/C ratio In passing of MM through the BUST, the energy deposition by MM (this value ( ε > ε th /4 = 385 r.p. should be observed in each of planes intersected by MM (this value ( ε th /4 ) determines the least velocity of MM (β ≈ 0.4)) The energy deposition have to be the undamped one in contrast to the cascade Pylos

8 β ≥ 0.4 Live time = hours No candidate for the undamped energy deposition was obtained F MM ≤ 2.5 × cm -2 s -1 sr -1 (90 % CL) Pylos

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