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Ultrarelativistic magnetic monopole search with the ANITA-II balloon-borne radio interferometer

M. Detrixhe et al. (ANITA Collaboration)
Phys. Rev. D 83, 023513 – Published 19 January 2011
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Article Text
  • MAGNETIC MONOPOLES
  • ANITA
  • MONOPOLE ENERGY LOSS IN MATTER
  • MONOPOLE SIMULATION
  • ANITA EXPERIMENTAL MONOPOLE DETECTION…
  • MONOPOLE SELECTION AND EVENT YIELD
  • CROSS-CHECK ANALYSIS
  • LIVE TIME
  • SYSTEMATIC ERRORS
  • PARTICLE FLUX LIMIT CALCULATION
  • SUMMARY
  • ACKNOWLEDGEMENTS
    • References

    Abstract

    We have conducted a search for extended energy deposition trails left by ultrarelativistic magnetic monopoles interacting in Antarctic ice. The nonobservation of any satisfactory candidates in the 31 days of accumulated ANITA-II (Antarctic Impulsive Transient Antenna) flight data results in an upper limit on the diffuse flux of relativistic monopoles. We obtain a 90% C.L. limit of order 10−19  (cm2 s  sr)−1 for values of Lorentz factor, γ, 1010≤γ at the anticipated energy Etot=1016  GeV. This bound is stronger than all previously published experimental limits for this kinematic range.

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    • Received 19 August 2010

    DOI:https://doi.org/10.1103/PhysRevD.83.023513

    © 2011 American Physical Society

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    Vol. 83, Iss. 2 — 15 January 2011

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    Images

    • Figure 1
      Figure 1

      Total energy loss versus γ for 1016  GeV monopoles, showing stochastic variation averaged over 50 m intervals. Lines show average contributions from different processes.

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    • Figure 2
      Figure 2

      Path geometry of monopoles coming from above (air→ice) or below (rock→ice) illuminating ANITA. Red/pink arrows indicate monopole trajectories which can result in a significant signal measured at the balloon. For isotropic monopole flux, the fraction of monopoles satisfying this geometry is of order ∼1%. (For the sake of illustration, ray curvature through the firn has been neglected, although this feature is incorporated into our simulation.)

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    • Figure 3
      Figure 3

      Simulated voltage vs time (as measured at the data acquisition system) in a single ANITA VPol antenna channel; γ=109.

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    • Figure 4
      Figure 4

      Minimum time between successive triggers (in-flight data).

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    • Figure 5
      Figure 5

      T4 distribution for Monte Carlo monopole signal simulations compared with DB data (points). Note that, for our simulations, we conservatively use Tmin=120  ns. Also overlaid is a fit to the DB data showing the extrapolation into the region T4<500  ns, used to estimate the expected anthropogenic background for the signal sample.

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    • Figure 6
      Figure 6

      Time between first and fourth event trigger (T4) distribution for ANITA-II monopole search sample; the monopole event selection requirement (T4<500  ns) is indicated by vertical line.

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    • Figure 7
      Figure 7

      Time domain (top four panels), as well as frequency domain (bottom four panels) voltage distributions for the four channels in one of the four search sample events passing the T4<500  ns requirement.

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    • Figure 8
      Figure 8

      Time domain (top four panels), as well as frequency domain (bottom four panels) voltage distributions for the four channels in one of the DB events with T4≈500  ns.

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    • Figure 9
      Figure 9

      T4 distribution for Monte Carlo simulations and DB sample, for events passing PFP<10−7 requirement. Note the diminution of dedicated background events populating the T4∼500  ns region, in comparison to Fig. 5.

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    • Figure 10
      Figure 10

      Timing diagram, illustrating the sequence of filling and emptying event data buffers. Four rapid triggers (“TRIG”) initiate data HOLD in buffers A, B, C and D, and decrements the Buffer Depth (BD) variable. Once all buffers are filled, DEAD time is incurred during the clear (CLR) and reset cycles.

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    • Figure 11
      Figure 11

      Comparison of the simulated readout time model with data. “Simulated” quantities refer to outputs of the live time model, as the effective readout time is varied. At an effective readout time of 73 ms, the simulated live time (blue, short dashed) matches the known live time (cyan, dotted), implying a BD=4 live time slightly less than 106  s.

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    • Figure 12
      Figure 12

      Comparison of ANITA upper limit on diffuse monopole flux with other results. Save for RICE, other experimental results have been extrapolated up to our sensitive kinematic interval. In performing this extrapolation, the limits for γ≥109 have been weakened by a factor of 2, to account for increasing Earth opacity.

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