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Dark matter search with the BDX-MINI experiment

M. Battaglieri, M. Bondí, A. Celentano, P. L. Cole, M. De Napoli, R. De Vita, L. Marsicano, N. Randazzo, E. S. Smith, M. Spreafico, and M. H. Wood
Phys. Rev. D 106, 072011 – Published 28 October 2022
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  • INTRODUCTION AND THEORETICAL FRAMEWORK
  • EXPERIMENTAL SETUP
  • EXPECTED SIGNAL AND SIMULATION
  • DATA ANALYSIS
  • RESULTS
  • FUTURE PERSPECTIVES: THE BDX EXPERIMENT
  • SUMMARY AND OUTLOOK
  • ACKNOWLEDGMENTS
    • References

    Abstract

    BDX-MINI is a beam dump experiment optimized to search for light dark matter produced in the interaction of the intense CEBAF 2.176 GeV electron beam with the Hall A beam dump at Jefferson Lab. The BDX-MINI detector consists of a PbWO4 electromagnetic calorimeter surrounded by a hermetic veto system for background rejection. The experiment accumulated 2.56×1021 EOT in six months of running. Simulations of fermionic and scalar dark matter interactions with electrons of the active volume of the BDX-MINI detector were used to estimate the expected signal. Data collected during the beam-off time allowed us to characterize the background dominated by cosmic rays. A blind data analysis based on a maximum-likelihood approach was used to optimize the experiment sensitivity. An upper limit on the production of light dark matter was set using the combined event samples collected during beam-on and beam-off configurations. In some kinematic regions of interest, this pilot experiment is sensitive to the parameter space covered by some of the most sensitive experiments to date, which demonstrates the discovery potential of the next generation beam dump experiment planned at intense electron beam facilities.

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    • Received 4 August 2022
    • Accepted 4 October 2022

    DOI:https://doi.org/10.1103/PhysRevD.106.072011

    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
    Hypothetical particle physics modelsParticle dark matter
    1. Physical Systems
    Hypothetical gauge bosons
    1. Techniques
    Particle accelerators
    Particles & Fields

    Authors & Affiliations

    M. Battaglieri1,2, M. Bondí3,4, A. Celentano2, P. L. Cole5, M. De Napoli6, R. De Vita2, L. Marsicano2,*, N. Randazzo6, E. S. Smith1, M. Spreafico7,2, and M. H. Wood8

    • 1Thomas Jefferson National Accelerator Facility, Newport News, Virginia 23606, USA
    • 2Istituto Nazionale di Fisica Nucleare, Sezione di Genova, Genova 16146, Italy
    • 3Istituto Nazionale di Fisica Nucleare, Sezione di Roma2, Roma 00133, Italy
    • 4Universitá di Roma Tor Vergata, Roma 00133, Italy
    • 5Lamar University, 4400 MLK Boulevard, P.O. Box 10046, Beaumont, Texas 77710, USA
    • 6Istituto Nazionale di Fisica Nucleare, Sezione di Catania, Catania 95125, Italy
    • 7Universitá degli Studi di Genova, Genova 16126, Italy
    • 8Canisius College, Buffalo, New York 14208, USA

    • *Corresponding author. luca.marsicano@ge.infn.it

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    Issue

    Vol. 106, Iss. 7 — 1 October 2022

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    Images

    • Figure 1
      Figure 1

      Schematic representation of the location of the wells relative to the Hall A beam dump. From left to right, the Hall A aluminum-water beam dump (blue-green), the concrete beam vault walls (gray), the dirt (brown), and the two vertical pipes. The detector was located in the well closest to the accelerator, Well-1.

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    • Figure 2
      Figure 2

      Sketch of the “BDX-MINI” detector. The detector is located inside a well, illustrated in Fig. 1, whose wall is shown as the outer PVC cylinder in this sketch. The detector package fits inside the stainless steel vessel.

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    • Figure 3
      Figure 3

      LDM particle flux (in arbitrary units) downstream of the Hall A beam dump for fermionic LDM of mχ=10  MeV, as a function of the particle energy Eχ and polar angle ζχ.

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    • Figure 4
      Figure 4

      IV-O detection efficiency stability over the entire measurement period.

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    • Figure 5
      Figure 5

      Top panel: in black, the ECAL total energy distribution for the beam-on data sample, with and without the veto system’s anticoincidence cut. In blue, the beam-off anticoincidence data sample, properly normalized to take into account the difference in running time. Bottom panel: the ratio between the beam-on and the scaled beam-off anticoincidence distributions.

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    • Figure 6
      Figure 6

      Vertical cosmic muon rate as function of time measured during beam-off (top panel) and beam-on data taking (middle panel). The comparison between beam-on and beam-off rate in terms of standard deviations is shown in the bottom panel.

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    • Figure 7
      Figure 7

      Deposited energy spectrum in the BDX-MINI ECAL for anticoincidence events associated to simulated beam-related (red) and measured beam-unrelated (green) background, compared to the simulated signal. The expected energy distribution for fermionic LDM with mχ=6.3  MeV was selected and arbitrarily normalized for illustration.

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    • Figure 8
      Figure 8

      Plot of the functions αj(g) for the illustrative case of fermionic LDM with mχ=8.5  MeV. The graphs show the results obtained from the Monte Carlo runs performed with different energy calibration scales, while the functions are the corresponding polynomial interpolations. The case g=1 corresponds to a perfect agreement between the real detector response and the one implemented in the Monte Carlo simulation.

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    • Figure 9
      Figure 9

      The function C(g) describing the effects of a variation of the BDX-MINI ECAL energy scale, computed for mχ=6  MeV, for the fermionic (black) and scalar (red) case. Each point is the result obtained processing Monte Carlo signal events through the full reconstruction chain, with a fixed variation of the energy scale. The two curves are the results of a best fit with a second order function, with the constraint C(1)=1.

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    • Figure 10
      Figure 10

      Expected sensitivity for different energy. The average exclusion limit is obtained using the procedure presented in text. Different colors correspond for different cuts on the minimum energy. The same bin width and energy range was used for all the cuts (the last bin size was set to include events with energy up to 600 MeV). The sensitivity is strongly dependent on the energy cut for χ masses of few MeV.

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    • Figure 11
      Figure 11

      BDX-MINI exclusion limits assuming αD=0.1 and mA′=3mχ are shown as red lines: the continuous line represents the exclusion limit for scalar LDM and the dashed line for fermionic LDM. The projected exclusion limits of the full-size BDX experiment for scalar LDM are shown in green. The thick black lines represent the relic target [8, 16]. The other colored lines show the exclusion limits from BABAR [41], NA64 [19, 42], MiniBooNE [43], E137 [18, 22], and COHERENT [44].

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