K.T. McDonald

This Letter presents results of a search for the mixing of a sub-eV sterile neutrino based on the full data sample of the Daya Bay Reactor Neutrino Experiment, collected during 3158 days of detector operation, which contains reactor \anue candidates identified as inverse beta-decay interactions followed by neutron-capture on gadolinium. The result was obtained in the minimally extended 3+1 neutrino mixing model. The analysis benefits from a doubling of the statistics of our previous result and from improvements of several important systematic uncertainties. The results are consistent with the standard three-neutrino mixing model and no significant signal of a sub-eV sterile neutrino was found. Exclusion limits are set by both Feldman-Cousins and CLs methods. Light sterile neutrino mixing with can be excluded at 95\% confidence level in the region of eV eV. This result represents the world-leading constraints in the region of eV eV.

Daya Bay presents the first measurement of cosmogenic He isotope production in liquid scintillator, using an innovative method for identifying cascade decays of He and its child isotope, Li. We also measure the production yield of Li isotopes using well-established methodology. The results, in units of 10gcm, are 0.3070.042, 0.3410.040, and 0.5460.076 for He, and 6.730.73, 6.750.70, and 13.740.82 for Li at average muon energies of 63.9~GeV, 64.7~GeV, and 143.0~GeV, respectively. The measured production rate of He isotopes is more than an order of magnitude lower than any other measurement of cosmogenic isotope production. It replaces the results of previous attempts to determine the ratio of He to Li production that yielded a wide range of limits from 0 to 30\%. The results provide future liquid-scintillator-based experiments with improved ability to predict cosmogenic backgrounds.

The full data set of the Daya Bay reactor neutrino experiment is used to probe the effect of the charged current non-standard interactions (CC-NSI) on neutrino oscillation experiments. Two different approaches are applied and constraints on the corresponding CC-NSI parameters are obtained with the neutrino flux taken from the Huber-Mueller model with a uncertainty. Both approaches are performed with the analytical expressions of the effective survival probability valid up to all orders in the CC-NSI parameters. For the quantum mechanics-based approach (QM-NSI), the constraints on the CC-NSI parameters and are extracted with and without the assumption that the effects of the new physics are the same in the production and detection processes, respectively. The approach based on the effective field theory (EFT-NSI) deals with four types of CC-NSI represented by the parameters . For both approaches, the results for the CC-NSI parameters are shown for cases with various fixed values of the CC-NSI and the Dirac CP-violating phases, and when they are allowed to vary freely. We find that constraints on the QM-NSI parameters and from the Daya Bay experiment alone can reach the order for the former and for the latter, while for EFT-NSI parameters , we obtain for both cases.

Ampere’s force law for steady currents was not historically associated with a magnetic field, but it could have been. A magnetic field, inspired by work of Helmholtz in 1870, can be defined such that the double-differential form of Ampere’s force law is a function of a double-differential of this field. We call this field the Ampere–Weber field, B, and show that its divergence is zero everywhere, as is that of the usual, but different, magnetic field B of Maxwellian electrodynamics. The curl of the Ampere–Weber field is nonzero everywhere in static examples, in contrast to that of the usual magnetic field B. We illustrate the field B for three examples, which exhibit patterns of field lines quite different from those of the usual magnetic field. As the Ampere–Weber field is based on Ampere’s force law for steady currents, it does not extrapolate well to the Lorentz force on a moving charge in a magnetic field. That is, the Ampere …

Reactor neutrino experiments play a crucial role in advancing our knowledge of neutrinos. In this Letter, the evolution of the flux and spectrum as a function of the reactor isotopic content is reported in terms of the inverse-beta-decay yield at Daya Bay with 1958 days of data and improved systematic uncertainties. These measurements are compared with two signature model predictions: the Huber-Mueller model based on the conversion method and the SM2018 model based on the summation method. The measured average flux and spectrum, as well as the flux evolution with the Pu 239 isotopic fraction, are inconsistent with the predictions of the Huber-Mueller model. In contrast, the SM2018 model is shown to agree with the average flux and its evolution but fails to describe the energy spectrum. Altering the predicted inverse-beta-decay spectrum from Pu 239 fission does not improve the agreement with the …

We present a new determination of the smallest neutrino mixing angle θ 13 and the mass-squared difference Δ m 32 2 using a final sample of 5.55× 10 6 inverse beta-decay (IBD) candidates with the final-state neutron captured on gadolinium. This sample is selected from the complete dataset obtained by the Daya Bay reactor neutrino experiment in 3158 days of operation. Compared to the previous Daya Bay results, selection of IBD candidates has been optimized, energy calibration refined, and treatment of backgrounds further improved. The resulting oscillation parameters are sin 2 2 θ 13= 0.0851±0.0024, Δ m 32 2=(2.466±0.060)× 10− 3 eV 2 for the normal mass ordering or Δ m 32 2=−(2.571±0.060)× 10− 3 eV 2 for the inverted mass ordering.

The activation of materials due to the exposure to cosmic rays may become an important background source for experiments investigating rare event phenomena. DarkSide-20k is a direct detection experiment for galactic dark matter particles, using a two-phase liquid argon time projection chamber filled with 49.7 tonnes (active mass) of Underground Argon (UAr) depleted in 39Ar. Here, the cosmogenic activity of relevant long-lived radioisotopes induced in the argon and other massive components of the set-up has been estimated; production of 120 t of radiopure UAr is foreseen. The expected exposure above ground and production rates, either measured or calculated, have been considered. From the simulated counting rates in the detector due to cosmogenic isotopes, it is concluded that activation in copper and stainless steel is not problematic. Activation of titanium, considered in early designs but not used in the final design, is discussed. The activity of 39Ar induced during extraction, purification and transport on surface, in baseline conditions, is evaluated to be 2.8% of the activity measured in UAr from the same source, and thus considered acceptable. Other products in the UAr such as 37Ar and 3H are shown to not be relevant due to short half-life and assumed purification methods.

In 1915, Einstein computed the precession of the perihelion of Mercury [1] as the first application of his new theory of general relativity, finding that advance in angle θ of the perihelion with respect to the Sun (assumed to be spherical and not rotating) to be,

Readers of articles 1, 2 in this Journal on the fact that a golf ball may roll into the “cup”(vertical cylinder) and then roll back out may be interested in a vectorial analysis of this phenomenon given by Milne (1948) in a little-known textbook. 3 I have transcribed his argument 4 and given another example of his method. 5

A recent article in this journal by Narayan 1 illustrated that magnetic forces do not obey Newton’s third law of action and reaction via the example of two “point” electric dipoles whose moments pi ¼ p0, iektxi grow exponentially with time. He correctly found that F12 þ F21 þ dPEM/dt ¼ 0, where PEM ¼Ð E  B dVol/4pc (in Gaussian units, with c as the speed of light in vacuum) is the electromagnetic-field momentum associated with the two dipoles. 2 This is an example of a general result by Page and Adams 3 published in this journal many years ago, in the so-called Darwin approximation 4–6 that keeps terms only to order v2/c2 (which ignores electromagnetic radiation), where v is velocity. Narayan’s demonstration is nice in that it holds to all orders of v/c. However, Narayan mistakenly claimed that “there are no electromagnetic fields in the far field zone,” and hence,“no radiation is emitted” in his example, based on …

Readers of articles 1, 2 in this Journal on the fact that a golf ball may roll into the “cup”(vertical cylinder) and then roll back out may be interested in a vectorial analysis of this phenomenon given by Milne (1948) in a little-known textbook. 3 I have transcribed his argument 4 and given another example of his method. 5

Nuclear reactors are uniquely powerful, abundant, and flavor-pure sources of antineutrinos that continue to play a vital role in the US neutrino physics program. The US reactor antineutrino physics community is a diverse interest group encompassing many detection technologies and many particle physics topics, including Standard Model and short-baseline oscillations, BSM physics searches, and reactor flux and spectrum modelling. The community’s aims offer strong complimentary with numerous aspects of the wider US neutrino program and have direct relevance to most of the topical sub-groups composing the Snowmass 2021 Neutrino Frontier. Reactor neutrino experiments also have a direct societal impact and have become a strong workforce and technology development pipeline for DOE National Laboratories and universities.This white paper, prepared as a submission to the Snowmass 2021 community organizing exercise, will survey the state of the reactor antineutrino physics field and summarize the ways in which current and future reactor antineutrino experiments can play a critical role in advancing the field of particle physics in the next decade. As it is directed towards the Snowmass 2021 Neutrino Frontier, Sections 4 through 9 are organized around specific Topical Groups within that Frontier, with the relevant Topical Group specified in each Section’s title. Finally, to enable quick reference to the document’s main themes, two to four ‘Key Takeaways’ are provided at the beginning of each Section.

Reactor neutrino experiments play a crucial role in advancing our knowledge of neutrinos. A precise measurement of reactor electron antineutrino flux and spectrum evolution can be key inputs in improving the knowledge of neutrino mass and mixing as well as reactor nuclear physics and searching for physics beyond the standard model. In this work, the evolution of the flux and spectrum as a function of the reactor isotopic content is reported in terms of the inverse-beta-decay yield at Daya Bay with 1958 days of data and improved systematic uncertainties. These measurements are compared with two signature model predictions: the Huber-Mueller model based on the conversion method and the SM2018 model based on the summation method. The measured average flux and spectrum, as well as their evolution with the 239Pu fraction, are inconsistent with the predictions of the Huber-Mueller model. In contrast, the SM2018 model is shown to agree with the average flux and its evolution but fails to describe the energy spectrum. Altering the predicted IBD spectrum from 239Pu does not improve the agreement with the measurement for either model. The models can be brought into better agreement with the measurements if either the predicted spectrum due to 235U is changed or the predicted 235U, 238U, 239Pu, and 241Pu spectra are changed in equal measure

A joint determination of the reactor antineutrino spectra resulting from the fission of U 235 and Pu 239 has been carried out by the Daya Bay and PROSPECT Collaborations. This Letter reports the level of consistency of U 235 spectrum measurements from the two experiments and presents new results from a joint analysis of both data sets. The measurements are found to be consistent. The combined analysis reduces the degeneracy between the dominant U 235 and Pu 239 isotopes and improves the uncertainty of the U 235 spectral shape to about 3%. The U 235 and Pu 239 antineutrino energy spectra are unfolded from the jointly deconvolved reactor spectra using the Wiener-SVD unfolding method, providing a data-based reference for other reactor antineutrino experiments and other applications. This is the first measurement of the U 235 and Pu 239 spectra based on the combination of experiments at low-and …

This Letter reports the first measurement of high-energy reactor antineutrinos at Daya Bay, with nearly 9000 inverse beta decay candidates in the prompt energy region of 8–12 MeV observed over 1958 days of data collection. A multivariate analysis is used to separate 2500 signal events from background statistically. The hypothesis of no reactor antineutrinos with neutrino energy above 10 MeV is rejected with a significance of 6.2 standard deviations. A 29% antineutrino flux deficit in the prompt energy region of 8–11 MeV is observed compared to a recent model prediction. We provide the unfolded antineutrino spectrum above 7 MeV as a data-based reference for other experiments. This result provides the first direct observation of the production of antineutrinos from several high-Q β isotopes in commercial reactors.

I once read that a theoretical physicist is someone who will approximate a four-legged table as one with either one or two legs to simplify the problem and will then conclude that it is unstable. I was reminded of that quote when I read the paper by Rostamian et al. in this journal. 1 They considered a point mass projectile bouncing up an incline, assuming that the projectile and the surface were both ideal rather than physical objects. It is standard if not universal practice to make simplifying assumptions when developing a physical model, but sometimes it can be taken too far. I tried the experiment using a real ball on a real surface and found that none of their assumptions or conclusions were valid. The time intervals between successive bounces were not equal, the rebound velocity was not equal for all impacts, the angle of incidence to the normal was not equal to the angle of reflection, the friction force was not …

We will evaluate the resistance R via Ohm’s Law, R= V/I, by calculating the current I that flows when a potential difference V is established between the two contacts. For a thin disk, the current flow is 2-dimensional. Since J= σE, where J is the current density and E is the electric field, the electric field is 2-dimensional also. And, since E=− Vφ, where φ is the electric potential, the potential is 2-dimensional as well. The form of the 2-dimensional potential is well approximated (for distances more than δ/2 from the centers of the contacts) by considering a cylinder of radius a, rather than the disk, with a line charge density λ that passes through the center of one contact, and line charge− λ that passes through the center of the other contact. The electric field from the wire of charge density λ has magnitude (in Gaussian units),

Certain land and sea “yachts”, with no internal power source, are capable of “sailing” directly into to the wind, and also “sailing” directly downwind faster than the wind. Such behavior is not possible for “yachts” that are propelled only by the force of the wind on “fixed sails” attached to the “yachts”, 1 which leads many people to assume that no variant of a “yacht” could exhibit the stated behavior. However, the “yachts” that achieve this counterintuitive performance do so with the aid of wind-powered propellers (turbines) rather than classic sails. There exist numerous YouTube videos [1]-[42] showing aspects of this performance, but skepticism as to postings on “social media” is such that these are doubted by many people. 2

The prediction of reactor antineutrino spectra will play a crucial role as reactor experiments enter the precision era. The positron energy spectrum of 3.5 million antineutrino inverse beta decay reactions observed by the Daya Bay experiment, in combination with the fission rates of fissile isotopes in the reactor, is used to extract the positron energy spectra resulting from the fission of specific isotopes. This information can be used to produce a precise, data-based prediction of the antineutrino energy spectrum in other reactor antineutrino experiments with different fission fractions than Daya Bay. The positron energy spectra are unfolded to obtain the antineutrino energy spectra by removing the contribution from detector response with the Wiener-SVD unfolding method. Consistent results are obtained with other unfolding methods. A technique to construct a data-based prediction of the reactor antineutrino energy …

Discuss the volume densities ρ+ and ρ−< 0 of positive and negative electric charges in a wire that carries a steady current, assuming that in the lab frame the positive charges are at rest and the current is due to negative charges (electrons) that all have speed v. This problem seems to have been first considered in 1877 by Clausius [1, 2], who argued that the force on an electric charge at rest outside the wire is zero in the lab frame of the wire, but it was noticed [3, 4] that this implies a nonzero force in the rest frame of the charges whose motion in the lab constitutes the electrical current there. 1