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Observation of the dependence on drift field of scintillation from nuclear recoils in liquid argon

T. Alexander et al. (SCENE Collaboration)
Phys. Rev. D 88, 092006 – Published 26 November 2013
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  • ACKNOWLEDGEMENTS
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    Abstract

    We have exposed a dual-phase liquid argon time projection chamber (LAr-TPC) to a low energy pulsed narrow-band neutron beam, produced at the Notre Dame Institute for Structure and Nuclear Astrophysics, to study the scintillation light yield of recoiling nuclei. Liquid scintillation counters were arranged to detect and identify neutrons scattered in the LAr-TPC and to select the energy of the recoiling nuclei. We report the observation of a significant dependence (up to 32%) on the drift field of liquid argon scintillation from nuclear recoils of energies between 10.8 and 49.9 keV. The field dependence is stronger at lower energies. Since it is the first measurement of such an effect in liquid argon, this observation is important because, to date, estimates of the sensitivity of LAr-TPC dark matter searches are based on the assumption that the electric field has only a small effect on the light yield from nuclear recoils.

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    • Received 25 June 2013

    DOI:https://doi.org/10.1103/PhysRevD.88.092006

    © 2013 American Physical Society

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    Measurement of scintillation and ionization yield and scintillation pulse shape from nuclear recoils in liquid argon

    H. Cao et al. (SCENE Collaboration)
    Phys. Rev. D 91, 092007 (2015)

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    Vol. 88, Iss. 9 — 1 November 2013

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    Images

    • Figure 1
      Figure 1

      A schematic of the experimental setup. The zoomed-in view of the TPC shows the PMTs, field shaping rings and PTFE support structure. It does not include the inner reflector.

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    • Figure 2
      Figure 2

      GEANT4-based simulation of the energy deposition in the SCENE detector at the 10.8 keV setting. Blue line: All scatters in the LAr-TPC producing coincidences in either neutron detector and surviving the timing cuts discussed in the text. Red line: Single elastic scatters surviving the same cuts.

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    • Figure 3
      Figure 3

      Distributions of pulse-shape discrimination vs time of flight for data taken in the 10.8 keV configuration at 1000  V/cm. All variables are defined in the text. Panel (a) refers to the LAr-TPC and panel (b) to the neutron detectors.

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    • Figure 4
      Figure 4

      (a) Surviving primary scintillation light (S1) distributions for 10.8 keV nuclear recoils as the neutron selection cuts described in the text are imposed sequentially. Data were collected with a field of 1000  V/cm. The high energy peak is from the Kr83m source in use for continuous monitoring of the detector. (b) Final S1 distributions for the 10.8 keV nuclear recoils at a null field at 1000  V/cm.

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    • Figure 5
      Figure 5

      Distributions of pulse-shape discrimination vs time of flight for data taken in the 49.9 keV configuration at 1000  V/cm. All variables are defined in the text. Panel (a) refers to the LAr-TPC and panel (b) to the neutron detectors. For these data, the polyethylene cylinders blocking the line of sight between the LiF target and the neutron detectors were removed due to geometric constraints. Accidental direct neutron coincidence events appear as the first “Neutron” blob around 80 ns in panel (b).

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    • Figure 6
      Figure 6

      (a) Surviving S1 distributions for 49.9 keV nuclear recoils as the neutron selection cuts described in the text are imposed sequentially. Data were collected with a field of 1000  V/cm. The high energy peak is from the Kr83m source in use for continuous monitoring of the detector. (b) Final S1 distributions for the 49.9 keV nuclear recoils at a null field at 1000  V/cm.

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    • Figure 7
      Figure 7

      Variation of the S1 scintillation yield for 10.8 to 49.9 keV nuclear recoils as a function of a drift field normalized to the value at a null field. Error bars on the data points taken at a nonzero field are statistical only and include the uncertainty on the zero-field value.

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