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Register a new userSearch for exotic neutrino-electron interactions using solar neutrinos in XMASS-I
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We have searched for exotic neutrino-electron interactions that could be produced by a neutrino millicharge, by a neutrino magnetic moment, or by dark photons using solar neutrinos in the XMASS-I liquid xenon detector. We observed no significant signals in 711 days of data. We obtain an upper limit for neutrino millicharge of 5.4$times$10$^{-12} e$ at 90% confidence level assuming all three species of neutrino have common millicharge. We also set flavor dependent limits assuming the respective neutrino flavor is the only one carrying a millicharge, $7.3 times 10^{-12} e$ for $ u_e$, $1.1 times 10^{-11} e$ for $ u_{mu}$, and $1.1 times 10^{-11} e$ for $ u_{tau}$. These limits are the most stringent yet obtained from direct measurements. We also obtain an upper limit for the neutrino magnetic moment of 1.8$times$10$^{-10}$ Bohr magnetons. In addition, we obtain upper limits for the coupling constant of dark photons in the $U(1)_{B-L}$ model of 1.3$times$10$^{-6}$ if the dark photon mass is 1$times 10^{-3}$ MeV$/c^{2}$, and 8.8$times$10$^{-5}$ if it is 10 MeV$/c^{2}$.
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In theories with the large extra dimensions beyond the standard 4-dimensional spacetime, axions could propagate in such extra dimensions, and acquire Kaluza-Klein (KK) excitations. These KK axions are produced in the Sun and could solve unexplained heating of the solar corona. While most of the solar KK axions escape from the solar system, a small fraction is gravitationally trapped in orbits around the Sun. They would decay into two photons inside a terrestrial detector. The event rate is expected to modulate annually depending on the distance from the Sun. We have searched for the annual modulation signature using $832times 359$ kg$cdot$days of XMASS-I data. No significant event rate modulation is found, and hence we set the first experimental constraint on the KK axion-photon coupling of $4.8 times 10^{-12}, mathrm{GeV}^{-1}$ at 90% confidence level for a KK axion number density of $bar{n}_mathrm{a} = 4.07 times 10^{13}, mathrm{m}^{-3}$, the total number of extra dimensions $n = 2$, and the number of extra dimensions $delta = 2$ that axions can propagate in.
We propose a test for non-standard neutrino-neutrino interactions by using ultrahigh energy AGN neutrinos. Such interactions would influence the AGN neutrino flux due to collisions with cosmic background neutrinos. For typical AGN neutrinos we obtain an upper limit for the coupling constant $g<6.4cdot 10^{-3}$ if the mediator is light and $g/(M_X/MeV) <0.013$ if the mediator is heavy. We compare our results with constraints from other phenomena previously considered.
Double electron capture is a rare nuclear decay process in which two orbital electrons are captured simultaneously in the same nucleus. Measurement of its two-neutrino mode would provide a new reference for the calculation of nuclear matrix elements whereas observation of its neutrinoless mode would demonstrate lepton number violation. A search for two-neutrino double electron capture on $^{124}$Xe is performed using 165.9 days of data collected with the XMASS-I liquid xenon detector. No significant excess above background was observed and we set a lower limit on the half-life as $4.7 times 10^{21}$ years at 90% confidence level. The obtained limit has ruled out parts of some theoretical expectations. We obtain a lower limit on the $^{126}$Xe two-neutrino double electron capture half-life of $4.3 times 10^{21}$ years at 90% confidence level as well.
We conducted an improved search for the simultaneous capture of two $K$-shell electrons on the $^{124}$Xe and $^{126}$Xe nuclei with emission of two neutrinos using 800.0 days of data from the XMASS-I detector. A novel method to discriminate $gamma$-ray/$X$-ray or double electron capture signals from $beta$-ray background using scintillation time profiles was developed for this search. No significant signal was found when fitting the observed energy spectra with the expected signal and background. Therefore, we set the most stringent lower limits on the half-lives at $2.1 times 10^{22}$ and $1.9 times 10^{22}$ years for $^{124}$Xe and $^{126}$Xe, respectively, with 90% confidence level. These limits improve upon previously reported values by a factor of 4.5.
Most neutrino mass extensions of the standard electroweak model entail non-standard interactions which, in the low energy limit, can be parametrized in term of effective four-fermion operators $ u_alpha u_beta bar f f $. Typically of sub-weak strength, $epsilon_{alpha beta} G_F$, these are characterized by dimensionless coupling parameters, $epsilon_{alpha beta}$, which may be relatively sizeable in a wide class of schemes. Here we focus on non-universal (NU) flavor conserving couplings ($alpha = beta$) with electrons ($f = e$) and analyse their impact on the phenomenology of solar neutrinos. We consistently take into account their effect both at the level of propagation where they modify the standard MSW behavior, and at the level of detection, where they affect the cross section of neutrino elastic scattering on electrons. We find limits which are comparable to other existing model-independent constraints.
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