Liquid argon scintillation response to electronic recoils between $2.8$–$1275~{rm keV}$ in a high light yield single-phase detector. (arXiv:2003.14248v3 [physics.ins-det] UPDATED)

Liquid argon scintillation response to electronic recoils between $2.8$–$1275~{rm keV}$ in a high light yield single-phase detector. (arXiv:2003.14248v3 [physics.ins-det] UPDATED)
<a href="http://arxiv.org/find/physics/1/au:+Kimura_M/0/1/0/all/0/1">M.Kimura</a>, <a href="http://arxiv.org/find/physics/1/au:+Aoyama_K/0/1/0/all/0/1">K.Aoyama</a>, <a href="http://arxiv.org/find/physics/1/au:+Tanaka_M/0/1/0/all/0/1">M.Tanaka</a>, <a href="http://arxiv.org/find/physics/1/au:+Yorita_K/0/1/0/all/0/1">K.Yorita</a>

We measure the liquid argon scintillation response to electronic recoils in
the energy range of $2.82$ to $1274.6~{rm keV}$ at null electric field. The
single-phase detector with a large optical coverage used in this measurement
yields $12.8 pm 0.3 ~ (11.2 pm 0.3)~{rm photoelectron/keV}$ for
$511.0$-${rm keV}$ $gamma$-ray events based on a photomultiplier tube single
photoelectron response modeling with a Gaussian plus an additional exponential
term (with only a Gaussian term). It is exposed to a variety of calibration
sources such as $^{22}{rm Na}$ and $^{241}{rm Am}$ $gamma$-ray emitters, and
a $^{252}{rm Cf}$ fast neutron emitter that induces quasimonoenergetic
$gamma$ rays through a $(n, n’gamma)$ reaction with $^{19}{rm F}$ in
polytetrafluoroethylene. In addition, the high light detection efficiency of
the detector enables identification of the $2.82$-${rm keV}$ peak of
$^{37}{rm Ar}$, a cosmogenic isotope in atmospheric argon. The observed light
yield and energy resolution of the detector are obtained by the full-absorption
peaks. We find up to approximately $25%$ shift in the scintillation yield
across the energy range and $3%$ of the energy resolution for the
$511.0$-${rm keV}$ line. The Thomas-Imel box model with its constant parameter
$varsigma=0.033 ^{+0.012} _{-0.008}$ is found to explain the result. For
liquid argon, this is the first measurement on the energy-dependent
scintillation yield down to a few ${rm keV}$ at null field and provides
essential inputs for tuning the argon response model to be used for physics
experiments.

We measure the liquid argon scintillation response to electronic recoils in
the energy range of $2.82$ to $1274.6~{rm keV}$ at null electric field. The
single-phase detector with a large optical coverage used in this measurement
yields $12.8 pm 0.3 ~ (11.2 pm 0.3)~{rm photoelectron/keV}$ for
$511.0$-${rm keV}$ $gamma$-ray events based on a photomultiplier tube single
photoelectron response modeling with a Gaussian plus an additional exponential
term (with only a Gaussian term). It is exposed to a variety of calibration
sources such as $^{22}{rm Na}$ and $^{241}{rm Am}$ $gamma$-ray emitters, and
a $^{252}{rm Cf}$ fast neutron emitter that induces quasimonoenergetic
$gamma$ rays through a $(n, n’gamma)$ reaction with $^{19}{rm F}$ in
polytetrafluoroethylene. In addition, the high light detection efficiency of
the detector enables identification of the $2.82$-${rm keV}$ peak of
$^{37}{rm Ar}$, a cosmogenic isotope in atmospheric argon. The observed light
yield and energy resolution of the detector are obtained by the full-absorption
peaks. We find up to approximately $25%$ shift in the scintillation yield
across the energy range and $3%$ of the energy resolution for the
$511.0$-${rm keV}$ line. The Thomas-Imel box model with its constant parameter
$varsigma=0.033 ^{+0.012} _{-0.008}$ is found to explain the result. For
liquid argon, this is the first measurement on the energy-dependent
scintillation yield down to a few ${rm keV}$ at null field and provides
essential inputs for tuning the argon response model to be used for physics
experiments.

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