Physics reach of a low threshold scintillating argon bubble chamber in coherent elastic neutrino-nucleus scattering reactor experiments

The physics reach of a low threshold (100 eV) scintillating argon bubble chamber sensitive to coherent elastic neutrino-nucleus scattering ($\mathrm{CE}\nu \mathrm{NS}$) from reactor neutrinos is studied. The sensitivity to the weak mixing angle, neutrino magnetic moment, and a light $Z^{\prime }$ gauge boson mediator are analyzed. A Monte Carlo simulation of the backgrounds is performed to assess their contribution to the signal. The analysis shows that world-leading sensitivities are achieved with a one-year exposure for a 10 kg chamber at 3 m from a $1{\mathrm{MW}}_{th}$ research reactor or a 100 kg chamber at 30 m from a $2000{\mathrm{MW}}_{th}$ power reactor. Such a detector has the potential to become the leading technology to study $\mathrm{CE}\nu \mathrm{NS}$ using nuclear reactors.

Figure 1

Signal and neutron background rates above threshold for setups A (top) and B (bottom). Backgrounds in setup A come from reactor and cosmogenic neutrons while only cosmogenic neutrons are shown in setup B. The assumed normal cumulative distribution function (Gaussian CDF) to describe the nucleation efficiency and its systematic uncertainty, as described in the calibration section, are also presented (green).

Figure 2

Conceptual design of the configuration for setup A at the ININ experimental hall. The distance between the reactor core center and the bubble chamber is 3 m. Accuracy of a few mm is expected based on survey work developed at ININ.

Figure 3

RGE running of the weak mixing angle in the $\overline{\mathrm{MS}}$ renormalization scheme [43, 44], as a function of the energy scale $\mu$. The expected measurements and $1\sigma$ uncertainties for setups A, B and B(1.5) are shown in solid purple, solid orange, and dashed orange, respectively. Measurements from other experiments are also presented. Figure adapted from [43]. A value of ${0.209}_{-0.069}^{+0.072}$ has been extracted from the CsI COHERENT data [45] (not shown in this plot). The three setups shown in the plot have all the same value of $\mu \sim 17\mathrm{MeV}$.

Figure 4

Exclusion limits (95% C.L.) in the $g^{\prime }-M_{Z^{\prime }}$ plane. The solid purple, solid orange and dashed orange lines represent the limits for setups A, B and B(1.5), respectively. The dash-dotted gray curve is the exclusion set by CONNIE [61]. The shaded brown and yellow regions correspond to the exclusions set by COHERENT, using CsI [1] and LAr [2, 62] detectors, respectively. Exclusion regions for dark photon searches from BABAR [63] and LHCb [64] are shown in light gray, and from beam dump experiments [65, 66, 67, 68, 69, 70, 71, 72, 73, 74] are shown in blue. These limits were obtained in the framework of Ref. [75]. The exclusion region from an ATLAS search for dilepton resonances [76] is also shown in light gray, using the software developed in Ref. [77].

Figure 5

Limits for the neutrino magnetic moment. The solid purple, solid orange and dashed orange lines represent the limits for setups A, B and B(1.5), respectively. The shaded brown and yellow regions correspond to the exclusions set by COHERENT, using CsI [1] and LAr [2, 62] detectors, respectively. The GEMMA [80] and Borexino [81] values are 90% C.L. bounds.