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A Search for Massive Magnetic A Search for Massive Magnetic Monopoles at the BaksanMonopoles at the BaksanUnderground Scintillation Underground Scintillation

TelescopeTelescope

Yu.F. Novoseltsev, M.M. Boliev, A.V. Butkevich, Yu.F. Novoseltsev, M.M. Boliev, A.V. Butkevich, S.P.Mikheev, V.B. PetkovS.P.Mikheev, V.B. Petkov

Institute for Nuclear Research of RAS

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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 17×17×11 m3.

The “slow trigger” requires

of internal plane operation

SSΩΩ = 1850 m = 1850 m22××sr sr

(isotropic flux)(isotropic flux)

The β ≥ 0.4 trigger requires

crossing of three horizontal crossing of three horizontal

planesplanes

SSΩΩ = 728 m = 728 m22××srsr

(isotropic flux)(isotropic flux)

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““in 1” means in 1” means

6 external planes 6 external planes

““in 2” is 2 internal in 2” is 2 internal

planes planes

Trigger rate is Trigger rate is

≈≈ 200 per day200 per day

22ββ < 0.1 < 0.1

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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 = 127630 hours = 14.56 years Live time = 127630 hours = 14.56 years (01.1982 (01.1982 − 01.2000)− 01.2000)

Only events with three hit planes were considered as Only events with three hit planes were considered as slow particle candidates (because a background from slow particle candidates (because a background from stopping of muons with subsequent stopping of muons with subsequent μμ - e decay was - e decay was rather large)rather large)

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All triggered events can be All triggered events can be subdivided into 3 groups:subdivided into 3 groups:

44 % 44 % − − μμ-e decays-e decays

54.6 % 54.6 % − random coincidence− random coincidence

1.4 % 1.4 % − relativistic muons − relativistic muons which have flight time > 50 nswhich have flight time > 50 ns

(large zenith angles (large zenith angles θθ ≥ 80 ≥ 80oo))

No candidate for the slow particles was recorded

FMM ≤ 3.2 ×10-16 cm-2s-1sr-1 (90 % CL)

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ββ ≥≥ 0.4, q 0.4, q ≥≥ 137/2e 137/2e

The events were selected in which the energy deposition in The events were selected in which the energy deposition in

the facility exceeded the facility exceeded εεthth = 1540 r.p. = 77 GeV = 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 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)(1)

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Some characteristics of BUST and MACRO scintillatorsSome characteristics of BUST and MACRO scintillators

BUST scintillatorBUST scintillator MACRO scintillatorMACRO scintillator

density, g/cmdensity, g/cm33 0.780.78 0.860.86

H/C ratioH/C ratio 2.12.1 2.022.02

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 by MM (this value (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

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ββ ≥≥ 0.4 0.4

Live time = 35400 hoursLive time = 35400 hours

No candidate for the undamped energy deposition was obtained

FMM ≤ 2.5 ×10-15 cm-2s-1sr-1 (90 % CL)

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