FASER2

Abstract:

We present the first statistically significant detection of neutrino oscillations in the high-energy regime ($>$ 20 GeV) from an analysis of IceCube Neutrino Observatory data collected in 2010-2011. This measurement is made possible by the low energy threshold of the DeepCore detector ($\sim 20$ GeV) and benefits from the use of the IceCube detector as a veto against cosmic ray-induced muon background. The oscillation signal was detected within a low-energy muon neutrino sample (20 -- 100 GeV) extracted from data collected by DeepCore. A high-energy muon neutrino sample (100 GeV -- 10 TeV) was extracted from IceCube data to constrain systematic uncertainties. Disappearance of low-energy upward-going muon neutrinos was observed, and the non-oscillation hypothesis is rejected with more than $5\sigma$ significance. In a two-neutrino flavor formalism, our data are best described by the atmospheric neutrino oscillation parameters $\Delta m^2_{23}= (2.3^{+0.6}_{-0.5})\cdot 10^{-3}$ eV$^2$ and $\sin^2(2 \theta_{23})>0.93$, and maximum mixing is favored.

Abstract:

The CDMS-II collaboration has reported 3 events in a Si detector, which are consistent with being nuclear recoils due to scattering of Galactic dark matter particles with a mass of about 8.6 GeV and a cross-section on neutrons of about 2 x 10^-41 cm^2. While a previous result from the XENON10 experiment has supposedly ruled out such particles as dark matter, we find by reanalysing the XENON10 data that this is not the case. Some tension remains however with the upper limit placed by the XENON100 experiment, independently of astrophysical uncertainties concerning the Galactic dark matter distribution. We explore possible ways of ameliorating this tension by altering the properties of dark matter interactions. Nevertheless, even with standard couplings, light dark matter is consistent with both CDMS and XENON10/100.

Abstract:

We report on the observation of two neutrino-induced events which have an estimated deposited energy in the IceCube detector of 1.04 $\pm$ 0.16 and 1.14 $\pm$ 0.17 PeV, respectively, the highest neutrino energies observed so far. These events are consistent with fully contained particle showers induced by neutral-current $\nu_{e,\mu,\tau}$ ($\bar\nu_{e,\mu,\tau}$) or charged-current $\nu_{e}$ ($\bar\nu_{e}$) interactions within the IceCube detector. The events were discovered in a search for ultra-high energy neutrinos using data corresponding to 615.9 days effective livetime. The expected number of atmospheric background is $0.082 \pm 0.004 \text{(stat)}^{+0.041}_{-0.057} \text{(syst)}$. The probability to observe two or more candidate events under the atmospheric background-only hypothesis is $2.9\times10^{-3}$ ($2.8\sigma$) taking into account the uncertainty on the expected number of background events. These two events could be a first indication of an astrophysical neutrino flux, the moderate significance, however, does not permit a definitive conclusion at this time.