A Search for Massive Magnetic Monopoles at the

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 - 2004 1

The experiment has been performed for both fast (β ≥ 0. 4) and slow (2× 10 -4 ≤ β ≤ 10 -1) 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 ≤ 10 -1 range. BUST is located at the depth of 850 m w. e. The facility dimensions are 17× 11 m 3. The “slow trigger” requires of internal plane operation SΩ = 1850 m 2×sr (isotropic flux) The β ≥ 0. 4 trigger requires crossing of three horizontal planes SΩ = 728 m 2×sr (isotropic flux) Pylos - 2004 2

2 10 -4 < β < 0. 1 “in 1” means 6 external planes “in 2” is 2 internal planes Trigger rate is ≈ 200 per day Pylos - 2004 3

Trigger is the coincidence of the signal from one of external planes with the internal plane signal delayed greater than 50 ns. Live time = 127630 hours = 14. 56 years (01. 1982 − 01. 2000) 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 - 2004 4

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) No candidate for the slow particles was recorded FMM ≤ 3. 2 × 10 -16 cm-2 s-1 sr-1 (90 % CL) 5

β ≥ 0. 4, q ≥ 137/2 e The events were selected in which the energy deposition in the facility exceeded εth = 1540 r. p. = 77 Ge. V (1 r. p. = 50 Me. V) To estimate the light yield (d. L/dx) in a scintillator we use the expression (Salamon, Ahlen, 1981) (1) where d. E/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. Pylos - 2004 6

Some characteristics of BUST and MACRO scintillators density, g/cm 3 H/C ratio BUST scintillator 0. 78 MACRO scintillator 0. 86 2. 1 2. 02 In passing of MM through the BUST, the energy deposition ε > εth/4 = 385 r. p. should be observed in each of planes intersected by MM (this value (εth/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 - 2004 7

β ≥ 0. 4 Live time = 35400 hours No candidate for the undamped energy deposition was obtained FMM ≤ 2. 5 × 10 -15 cm-2 s-1 sr-1 (90 % CL) Pylos - 2004 8

Pylos - 2004 9