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A Search for Massive Magnetic Monopoles at the Baksan Underground

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A Search for Massive Magnetic Monopoles at the Baksan Underground Powered By Docstoc
					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
                      17×17×11 m3.



                                                          The “slow trigger” requires
                                                          of internal plane operation
                                                              SΩ = 1850 m2×sr
                                                               (isotropic flux)

                                                          The β ≥ 0.4 trigger requires
                                                          crossing of three horizontal
                                                          planes
                                                              SΩ = 728 m2×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




                                  3
Pylos - 2004
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 ≥ 80o)



                            No candidate for the
                             slow particles was
                             recorded


FMM ≤ 3.2 ×10-16 cm-2s-1sr-1 (90 % CL)                     5
              β ≥ 0.4, q ≥ 137/2e
The events were selected in which the energy deposition in
the facility exceeded εth = 1540 r.p. = 77 GeV
 (1 r.p. = 50 MeV)

To estimate the light yield (dL/dx) in a scintillator we use
the expression (Salamon, Ahlen, 1981)

                                               (1)

 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.

                            Pylos - 2004                       6
 Some characteristics of BUST and MACRO scintillators
                 BUST scintillator         MACRO scintillator
density, g/cm3      0.78                       0.86
H/C ratio              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-2s-1sr-1 (90 % CL)

                     Pylos - 2004            8
Pylos - 2004   9

				
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posted:5/24/2013
language:English
pages:9