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  • Open Access

Search for slow magnetic monopoles with the NOvA detector on the surface

M. A. Acero et al. (NOvA Collaboration)
Phys. Rev. D 103, 012007 – Published 11 January 2021
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  • INTRODUCTION
  • SIMULATION
  • ON-LINE TRIGGER ALGORITHM
  • EVENT SELECTION
  • RESULTS
  • CONCLUSION
  • ACKNOWLEDGMENTS
    • References

    Abstract

    We report a search for a magnetic monopole component of the cosmic-ray flux in a 95-day exposure of the NOvA experiment’s Far Detector, a 14 kt segmented liquid scintillator detector designed primarily to observe GeV-scale electron neutrinos. No events consistent with monopoles were observed, setting an upper limit on the flux of 2×10−14  cm−2 s−1 sr−1 at 90% C.L. for monopole speed 6×10−4<β<5×10−3 and mass greater than 5×108  GeV. Because of NOvA’s small overburden of 3 meters-water equivalent, this constraint covers a previously unexplored low-mass region.

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    • Received 10 September 2020
    • Accepted 22 December 2020

    DOI:https://doi.org/10.1103/PhysRevD.103.012007

    Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. Funded by SCOAP3.

    Published by the American Physical Society

    Physics Subject Headings (PhySH)

    1. Research Areas
    Cosmic ray composition & spectraHypothetical particle physics modelsParticle astrophysics
    1. Physical Systems
    Magnetic monopoles
    1. Techniques
    Neutrino detection
    Gravitation, Cosmology & AstrophysicsParticles & Fields

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    Issue

    Vol. 103, Iss. 1 — 1 January 2021

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    Images

    • Figure 1
      Figure 1

      Schematic of a corner of the NOvA detector. The z direction is to the right, perpendicular to the 15.5-meter-long cells, the ends of which are shown.

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    • Figure 2
      Figure 2

      Hit selection in the trigger algorithm. Cells near the +x edge in the xz view are shown. Filled boxes represent hits in a 5 ms window; size is proportional to signal strength. The dotted red line shows the path of a simulated monopole; hits off this line are zero bias data. Hits above the horizontal dashed line are considered to be on the detector edge.

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    • Figure 3
      Figure 3

      Trigger and overall selection efficiency as a function of angle in the xz view, for monopoles that cross at least 10 m of the detector with β=10−3. Efficiency in the yz view has the same form.

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    • Figure 4
      Figure 4

      Correlation coefficient rmin2 (top) and the time gap fraction fmax (bottom) of monopole candidates. In each plot, events are shown only if they pass every selection except the one shown in that plot (displayed as a dashed line with arrow), i.e., for the top (bottom) plot, selections 1–4 and 6 (1–5) were applied. Each Monte Carlo simulation is normalized to the data for display purposes.

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    • Figure 5
      Figure 5

      Top: reconstructed monopole speed vs rmin2 for events passing selections 1–3 and 6. Data events are shown as gray circles, and simulation for β=10−3 both as red squares and as a heat map. Events must be in the dashed box in the lower right to be selected. Bottom: Same for fmax and events passing selections 1–3 and 5. Events must be in the lower left to be selected.

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    • Figure 6
      Figure 6

      Solid angle coverage as a function of monopole speed and mass. Horizontal dashed lines indicate the boundaries of the search sensitivity in speed. Vertical dashed lines indicate the reference masses used to generate limits shown in Fig. 7 and Table 1.

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    • Figure 7
      Figure 7

      Upper limits on the magnetic monopole flux. Results are shown of experiments [7, 8, 18] that do not assume proton decay catalysis [19] nor ultrarelativistic monopoles [20]. In each region of speed-flux space, the experiment with the best mass reach is shown. NOvA sets the only limits around β=10−3 for monopoles lighter than 1010  GeV.

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