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The Precision Reactor Oscillation and Spectrum Experiment, PROSPECT, has made world-leading measurements of reactor antineutrinos at short baselines. In its first phase, conducted at the High Flux Isotope Reactor (HFIR) at Oak Ridge National Laboratory, PROSPECT produced some of the strongest limits on eV-scale sterile neutrinos, made a precision measurement of the reactor antineutrino spectrum from $^{235}$U, and demonstrated the observation of reactor antineutrinos in an aboveground detector with good energy resolution and well-controlled backgrounds. The PROSPECT collaboration is now preparing an upgraded detector, PROSPECT-II, to probe yet unexplored parameter space for sterile neutrinos and contribute to a full resolution of the Reactor Antineutrino Anomaly, a longstanding puzzle in neutrino physics. By pressing forward on the worlds most precise measurement of the $^{235}$U antineutrino spectrum and measuring the absolute flux of antineutrinos from $^{235}$U, PROSPECT-II will sharpen a tool with potential value for basic neutrino science, nuclear data validation, and nuclear security applications. Following a two-year deployment at HFIR, an additional PROSPECT-II deployment at a low enriched uranium reactor could make complementary measurements of the neutrino yield from other fission isotopes. PROSPECT-II provides a unique opportunity to continue the study of reactor antineutrinos at short baselines, taking advantage of demonstrated elements of the original PROSPECT design and close access to a highly enriched uranium reactor core.
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The muon is playing a unique role in sub-atomic physics. Studies of muon decay both determine the overall strength and establish the chiral structure of weak interactions, as well as setting extraordinary limits on charged-lepton-flavor-violating processes. Measurements of the muons anomalous magnetic moment offer singular sensitivity to the completeness of the standard model and the predictions of many speculative theories. Spectroscopy of muonium and muonic atoms gives unmatched determinations of fundamental quantities including the magnetic moment ratio $mu_mu / mu_p$, lepton mass ratio $m_{mu} / m_e$, and proton charge radius $r_p$. Also, muon capture experiments are exploring elusive features of weak interactions involving nucleons and nuclei. We will review the experimental landscape of contemporary high-precision and high-sensitivity experiments with muons. One focus is the novel methods and ingenious techniques that achieve such precision and sensitivity in recent, present, and planned experiments. Another focus is the uncommonly broad and topical range of questions in atomic, nuclear and particle physics that such experiments explore.
The ALICE detector has been commissioned and is ready for taking data at the Large Hadron Collider. The first proton-proton collisions are expected in 2009. This contribution describes the current status of the detector, the results of the commissioning phase and its capabilities to contribute to the understanding of both pp and PbPb collisions
In the past few decades, numerous searches have been made for the neutrinoless double-beta decay (0$ ubetabeta$) process, aiming to establish whether neutrinos are their own antiparticles (Majorana neutrinos), but no 0$ ubetabeta$ decay signal has yet been observed. A number of new experiments are proposed but they ultimately suffer from a common problem: the sensitivity may not increase indefinitely with the target mass. We have performed a detailed analysis of the physics potential by using the Jiangmen Underground Neutrino Observatory (JUNO) to improve the sensitivity to 0$ ubetabeta$ up to a few meV, a major step forward with respect to the experiments currently being planned. JUNO is a 20 kton low-background liquid scintillator (LS) detector with 3%/$sqrt{E text{(MeV)}}$ energy resolution, now under construction. It is feasible to build a balloon filled with enriched xenon gas (with $^{136}$Xe up to 80%) dissolved in LS, inserted into the central region of the JUNO LS. The energy resolution is $sim$1.9% at the $Q$-value of $^{136}$Xe 0$ ubetabeta$ decay. Ultra-low background is the key for 0$ ubetabeta$ decay searches. Detailed studies of background rates from intrinsic 2$ ubetabeta$ and $^{8}$B solar neutrinos, natural radioactivity, and cosmogenic radionuclides (including light isotopes and $^{137}$Xe) were performed and several muon veto schemes were developed. We find that JUNO has the potential to reach a sensitivity (at 90% C. L.) to $T^{0 ubetabeta}_{1/2}$ of $1.8times10^{28}$ yr ($5.6times10^{27}$ yr) with $sim$50 tons (5 tons) of fiducial $^{136}$Xe and 5 years exposure, while in the 50-ton case the corresponding sensitivity to the effective neutrino mass, $m_{betabeta}$, could reach (5--12) meV, covering completely the allowed region of inverted neutrino mass ordering.
In dark matter direct detection experiments, neutron is a serious source of background, which can mimic the dark matter-nucleus scattering signals. In this paper, we present an improved evaluation of the neutron background in the PandaX-II dark matter experiment by a novel approach. Instead of fully relying on the Monte Carlo simulation, the overall neutron background is determined from the neutron-induced high energy signals in the data. In addition, the probability of producing a dark-matter-like background per neutron is evaluated with a complete Monte Carlo generator, where the correlated emission of neutron(s) and $gamma$(s) in the ($alpha$, n) reactions and spontaneous fissions is taken into consideration. With this method, the neutron backgrounds in the Run 9 (26-ton-day) and Run 10 (28-ton-day) data sets of PandaX-II are estimated to be 0.66$pm$0.24 and 0.47$pm$0.25 events, respectively.
We report the Neutrino-less Double Beta Decay (NLDBD) search results from PandaX-II dual-phase liquid xenon time projection chamber. The total live time used in this analysis is 403.1 days from June 2016 to August 2018. With NLDBD-optimized event selection criteria, we obtain a fiducial mass of 219 kg of natural xenon. The accumulated xenon exposure is 242 kg$cdot$yr, or equivalently 22.2 kg$cdot$yr of $^{136}$Xe exposure. At the region around $^{136}$Xe decay Q-value of 2458 keV, the energy resolution of PandaX-II is 4.2%. We find no evidence of NLDBD in PandaX-II and establish a lower limit for decay half-life of 2.4 $ times 10^{23} $ yr at the 90% confidence level, which corresponds to an effective Majorana neutrino mass $m_{beta beta} < (1.3 - 3.5)$ eV. This is the first NLDBD result reported from a dual-phase xenon experiment.
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