Short baseline reactor $\overline{\nu }-e$ scattering experiments and nonstandard neutrino interactions at source and detector

We investigate nonstandard interaction effects in antineutrino-electron scattering experiments with baselines short enough to ignore standard oscillation phenomena. The setup is free of ambiguities from the interference between new physics and oscillation effects and is sensitive to both semileptonic new physics at the source and purely leptonic new physics in the weak interaction scattering at the detector. We draw on the TEXONO experiment as the model system, extending its analysis of nonstandard interaction effects at the detector to include the generally allowed nonstandard interaction phase at the detector and both nonuniversal and flavor-changing new physics at the reactor source. We confirm that the current data allows for new physics constraints at the detector of the same order as those currently published, but we find that constraints on the source new physics are at least an order of magnitude weaker. The new physics phase effects are at the 5% level, noticeable in the 90% C.L. contour plots but not significantly affecting the conclusions. Based on projected increase in sensitivity with an upgraded TEXONO experiment, we estimate the improvement of sensitivity to both source and detector nonstandard interactions. We find that the bounds on source parameters improve by an order of magnitude, but do not reach parameter space beyond current limits. On the other hand, the detector new physics sensitivity would push current limits by factors of 5 to 10 smaller.

Figure 1

SM ${\sin }^2{\theta }_W$ vs ${\chi }^2$, 1(a), and our calculation of the 90% C.L. limits of Figs. 4(a) and 4(b) of Ref. [15] in Figs. 1 and 1. In Fig. 1, we show the 90% C.L. boundary for the fit to TEXONO rate data using Eq. (5) in the scattering cross section Eq. (2). The blue, red, and green curves, right to -left at the top, are for $\cos ({\varphi }_{\alpha e}^{eL}-{\varphi }_{\alpha e}^{eR})=1,0$, and $-1$, respectively. The blue curve, with $\cos ({\varphi }_{\alpha e}^{eL}-{\varphi }_{\alpha e}^{eR})=1$, corresponds to that shown in Fig. 4(c) of Ref. [15].

Figure 2

C.L. boundary regions for published TEXONO data. Upper panels [(a)–(d)]: Correlation between the source NSI parameters ($K_{ee}$) and the corresponding detector NSI parameters (${ϵ}_{ee}^{R,L}$ and ${ϵ}_{\alpha e}^{R,L}$, where $\alpha =\mu$ or $\tau$) at 90% C.L. See the text for details. Lower panels [(e)–(h)]: Correlation between the source NSI parameters ($K_{e\alpha }$) and the corresponding detector NSI parameters (${ϵ}_{\mu \mu }^{R,L}$, ${ϵ}_{\tau \tau }^{R,L}$ and ${ϵ}_{\alpha \mu }^{R,L}$, ${ϵ}_{\beta \tau }^{R,L}$, where $\alpha =e$ or $\tau$ and $\beta =e$ or $\mu$) at 90% C.L. See the text for details.

Figure 3

SM ${\sin }^2{\theta }_W$ vs ${\chi }^2$, (a), the 90% C.L. contour for NU $L$- and $R$-NSI parameters, (b), and in (c) the 90% C.L. contours for the same phase choices as in Fig. 1, but for the modeled future prospects data. All source NSI parameters are set to zero.

Figure 4

C.L. boundary regions for future prospects data. Upper panels [(a)–(d)]: Correlation between the source NSI parameter ($\mathrm{Im}{K}_{ee}$) and the corresponding detector NSI parameters (${ϵ}_{ee}^{R,L}$ and ${ϵ}_{\alpha e}^{R,L}$, where $\alpha =\mu$ or $\tau$) at 90% C.L. See the text for details. Lower panels [(e)–(h)]: Correlation between the source NSI parameter ($\mathrm{Re}{K}_{ee}$) and the corresponding detector NSI parameters (${ϵ}_{\mu \mu }^{R,L}$, ${ϵ}_{\tau \tau }^{R,L}$ and ${ϵ}_{\alpha \mu }^{R,L}$, ${ϵ}_{\beta \tau }^{R,L}$ where $\alpha =e$ or $\tau$ and $\beta =e$ or $\mu$) at 90% C.L. See the text for details.

Figure 5

Correlation between the source NSI parameters ($\mathrm{Re}{K}_{e\mu }$ and $\mathrm{Re}{K}_{e\tau }$) and the corresponding detector NSI parameters (${ϵ}_{\mu \mu }^{R,L}$, ${ϵ}_{\tau \tau }^{R,L}$ and ${ϵ}_{\alpha \mu }^{R,L}$, ${ϵ}_{\beta \tau }^{R,L}$ where $\alpha =e$ or $\tau$ and $\beta =e$ or $\mu$) at 90% C.L. See the text for details.

Figure 6

Typical antineutrino spectrum at 28 m from the core at Kuo-Sheng. The green curve is the data and the black curve inside it is the fit.