Search

The original version of this chapter was published with incorrect text on page 48 last paragraph 8th and 9th lines

We report here the results of a measurement of the scattered versus unscattered neutron fluence on polyethylene determined via neutron activation of multiple natural indium foils from a deuterium-deuterium (D-D) neutron generator. The neutrons were produced by the High Flux Neutron Generator (HFNG) at the University of California, Berkeley, a specially designed source to maximize neutron flux on a sample while minimizing the total neutron yield. During the experiment, approximately 108 n/s were produced with the energies at the indium foils ranging from 2.2 to 2.8MeV. Both the angle-integrated and the partial angle differential results are consistent with the predictions of the Monte Carlo N-Particle Transport (MCNP) code, using ENDF/B-VII.1. This supports shielding calculations in the fast energy region with high-density polyethylene.

A plasma haloscope has recently been proposed as a feasible approach to extend the search for dark matter axions above 10 GHz ($\sim$ 40 $\mu$eV), whereby the microwave cavity in a conventional axion haloscope is supplanted by a wire array metamaterial. As the plasma frequency of a metamaterial is determined by its unit cell, and is thus a bulk property, a metamaterial resonator of any frequency can be made arbitrarily large, in contrast to a microwave cavity which incurs a steep penalty in volume with increasing frequency. We have investigated the basic properties of wire array metamaterials through $S_{21}$ measurements in the 10 GHz range. Excellent agreement with theoretical models is found, by which we project achievable quality factors to be of order $10^{4}$ in an actual axion search. Furthermore, schemes for tuning the array over a usable dynamic range ($30\%$ in frequency) appear practical from an engineering perspective., Comment: Published in Annalen der Physik

The axion “haloscope” technique is a well-established method to search for dark matter axions with a resonant microwave cavity and has excluded axion models over several frequency ranges with unparalleled sensitivity. This chapter describes the basics of microwave cavity searches, including overviews of the main experimental components and details on the figure of merit for these searches.

Advances in nuclear weapon technologies from – and the corresponding evolution in the threat landscape posed by – non-allied nations over the past four years underscores the exigency of the United States (U.S) in updating its stated national security policies. Here we review and suggest options for the 2022 Nuclear Posture Review (NPR) regarding the low-yield submarine-launched cruise missile (SLCM-N) and submarine-launched ballistic missile (SLBM) programs. The 2018 NPR called for programmatic changes to counteract the evolving threat environment and allow for greater deterrence flexibility. These programs include modernization of existing technologies and creation of novel weapons systems. Of these changes, two new programs were started to develop low-yield, sea-based, non-strategic weapons. These options are designed to counter any perceived gaps in U.S. regional deterrence capabilities. We enumerate several policy options likely to be considered by the Biden White House. Our proposed solution calls for maintenance of the W76-2 program and the continuance of the low-yield SLCM-N program; we present our argument along the axes of technical and cost considerations, service system preferences, tailored response capabilities, ensured support and defense of our allies, and prevention of escalation to war.

Microwave cavity experiments make a quantum leap in the search for the dark matter of the universe.

The microwave cavity technique is currently the most sensitive way of looking for dark matter axions in the 0.1 GHz–10 GHz range, corresponding to masses of 0.41 µeV–41 µeV. A particular challenge for frequencies greater than 5 GHz is designing a cavity with a large volume that contains a resonant mode that shows high coupling to dark matter axions, a high quality factor, is broadly tunable, and is free from intruder modes. For the Haloscope at Yale Sensitive to Axion Cold dark matter, we have designed and constructed an optimized high frequency cavity with a tuning mechanism that preserves a high degree of rotational symmetry, critical to maximizing its figure of merit. This cavity covers an important frequency range according to recent theoretical estimates for the axion mass, 5.5 GHz–7.4 GHz, and the design appears extendable to higher frequencies as well. This paper will discuss key design and construction details of the cavity, present a summary of the design evolution, and alert practitioners of potentially unfruitful avenues for future work.

On February 1, 2019, the United States and Russia withdrew from the three-decades old Intermediate-Range Nuclear Forces (INF) treaty. Events precipitating the withdrawal were allegations by both the United States and Russia of a variety of treaty violations. Until that point, the treaty had been a centerpiece of arms control and a key agreement of the global security architecture. The absence of such a pillar has the potential destabilize the status quo of arms control, creating significant uncertainty in global nuclear stability and security. In this paper, we present a historical review as overture to an analysis on the impacts of this development on force structure. This analysis examines the changes in U.S., Russian, and Chinese nuclear forces which may occur as a result of the treaty's demise. The article concludes with commentary on potential actions to preserve stability in a post-INF world.

A novel search technique for ultralight dark matter has been developed and carried out over a narrow range in L band, utilizing the recent Breakthrough Listen public data release of three years of observation with the Green Bank Telescope. The search concept depends only on the assumption of decay or annihilation of virialized dark matter to a quasimonochromatic radio line, and additionally that the frequency and intensity of the line be consistent with most general properties expected of the phase space of our Milky Way halo. Specifically, the search selects for a line that exhibits a Doppler shift with position according to the solar motion through a static Galactic halo, and similarly varies in intensity with the position with respect to the Galactic center. Over the frequency range $1.73-1.83$ GHz, radiative annihilation of dark matter is excluded above $\langle{\sigma}v\rangle$ = $1.2 \times 10^{-47} \text{ cm}^3 \text{ s}^{-1}$, and for decay above ${\lambda}$ = $4.1 \times 10^{-35} \text{ s}^{-1}$. The analysis of the full Breakthrough Listen GBT dataset by this method ($25,000$ spectra, $1.1-11.6$ GHz) is currently underway., Comment: Submitted to ApJ; 11 pages

A facility based on a next-generation, high-flux D-D neutron generator has been commissioned and it is now operational at the University of California, Berkeley. The current generator designed for 40Ar/39Ar dating of geological materials produces nearly monoenergetic 2.45MeV neutrons at outputs of 108n/s. The narrow energy range is advantageous relative to the 235U fission spectrum neutrons due to (i) reduced 39Ar recoil energy, (ii) minimized production of interfering argon isotopes from K, Ca, and Cl, and (iii) reduced total activity for radiological safety and waste generation. Calculations provided show that future conditioning at higher currents and voltages will allow for a neutron output of over 1010n/s, which is a necessary requirement for production of measurable quantities of 39Ar through the reaction 39K(n,p)39Ar. A significant problem encountered with increasing deuteron current was beam-induced electron backstreaming. Two methods of suppressing secondary electrons resulting from the deuterium beam striking the target were tested: the application of static electric and magnetic fields. Computational simulations of both techniques were done using a finite element analysis in COMSOL Multiphysics®. Experimental tests verified these simulations. The most reliable suppression was achieved via the implementation of an electrostatic shroud with a voltage offset of -800V relative to the target.

Many searches for axion cold dark matter rely on the use of tunable electromagnetic resonators. Current detectors operate at or near microwave frequencies and use cylindrical cavities with cylindrical tuning rods. The cavity performance strongly impacts the signal power of the detector, which is expected to be very small even under optimal conditions. There is strong motivation to characterize these microwave cavities and improve their performance in order to maximize the achievable signal power. We present the results of a study characterizing the HAYSTAC (Haloscope At Yale Sensitive to Axion Cold dark matter) cavity using bead perturbation measurements and detailed 3D electromagnetic simulations. This is the first use of bead perturbation methods to characterize an axion haloscope cavity. In this study, we measured impacts of misalignments on the order of 0.001 in and demonstrated that the same impacts can be predicted using electromagnetic simulations. We also performed a detailed study of mode crossings and hybridization between the TM$_{010}$ mode used in operation and other cavity modes. This mixing limits the tuning range of the cavity that can be used during an axion search. By characterizing each mode crossing in detail, we show that some mode crossings are benign and are potentially still useful for data collection. The level of observed agreement between measurements and simulations demonstrates that finite element modeling can capture non-ideal cavity behavior and the impacts of very small imperfections. 3D electromagnetic simulations and bead perturbation measurements are standard tools in the microwave engineering community, but they have been underutilized in axion cavity design. This work demonstrates their potential to improve understanding of existing cavities and to optimize future designs., Comment: 22 pages, 8 figures The following article has been submitted to Review of Scientific Instruments. v2: added changes made during the review process

Use of deuteron-deuteron fusion neutrons may substantially improve applicability and accuracy of the 40Ar/39Ar technique., We designed and tested a compact deuteron-deuteron fusion neutron generator for application to 40Ar/39Ar geochronology. The nearly monoenergetic neutrons produced for sample irradiation are anticipated to provide several advantages compared with conventional fission spectrum neutrons: Reduction of collateral nuclear reactions increases age accuracy and precision. Irradiation parameters within the neutron generator are more controllable compared with fission reactors. Confidence in the prediction of recoil energies is improved, and their likely reduction potentially broadens applicability of the dating method to fine-grained materials without vacuum encapsulation. Resolution of variation in the 39K(n,p)39Ar neutron capture cross section at 1.3 to 3.2 MeV and discovery of a strong resonance at ~2.4 MeV illuminate future pathways to improve the technique for 40Ar/39Ar dating.

Report of the first workshop to identify approaches and techniques in the domain of quantum sensing that can be utilized by future High Energy Physics applications to further the scientific goals of High Energy Physics.

A next-generation, high-flux DD neutron generator has been designed, commissioned, and characterized, and is now operational in a new facility at the University of California Berkeley. The generator, originally designed for 40Ar/39Ar dating of geological materials, has since served numerous additional applications, including medical isotope production studies, with others planned for the near future. In this work, we present an overview of the High Flux Neutron Generator (HFNG) which includes a variety of simulations, analytical models, and experimental validation of results. Extensive analysis was performed in order to characterize the neutron yield, flux, and energy distribution at specific locations where samples may be loaded for irradiation. A notable design feature of the HFNG is the possibility for sample irradiation internal to the cathode, just 8 mm away from the neutron production site, thus maximizing the neutron flux (n/cm2/s). The generator's maximum neutron flux at this irradiation position is 2.58e7 n/cm2/s +/- 5% (approximately 3e8 n/s total yield) as measured via activation of small natural indium foils. However, future development is aimed at achieving an order of magnitude increase in flux. Additionally, the deuterium ion beam optics were optimized by simulations for various extraction configurations in order to achieve a uniform neutron flux distribution and an acceptable heat load. Finally, experiments were performed in order to benchmark the modeling and characterization of the HFNG., Comment: 31 pages, 20 figures

A facility based on a next-generation, high-flux D-D neutron generator has been commissioned and it is now operational at the University of California, Berkeley. The current generator designed for

Four decades after its prediction, the axion remains the most compelling solution to the Strong-CP problem and a well-motivated dark matter candidate, inspiring a host of elegant and ultrasensitive experiments based on axion-photon mixing. This report reviews the experimental situation on several fronts. The microwave cavity experiment is making excellent progress in the search for dark matter axions in the microelectronvolt range and may be plausibly extended up to 100 mu eV. Within the past several years however, it has been realized that axions are pervasive throughout string theories, but with masses that fall naturally in the nanoelectronvolt range, for which a NMR-based search is under development. Searches for axions emitted from the Sun's burning core, and purely laboratory experiments based on photon regeneration have both made great strides in recent years, with ambitious projects proposed for the coming decade. Each of these campaigns has pushed the state of the art in technology, enabling large gains in sensitivity and mass reach. Furthermore each modality has also been exploited to search for more generalized axion-like particles, that will also be discussed in this report. We are hopeful, even optimistic, that the next review of the subject will concern the discovery of the axion, its properties, and its exploitation as a probe of early universe cosmology and structure formation., Comment: Published in Annual Review of Nuclear and Particle Science Vol. 65 (2015). 31 pages, 14 figures. Posted with permission from the Annual Review of Nuclear and Particle Science, Volume 65. copyright 2015 by Annual Reviews, http://www.annualreviews.org

▪ Abstract The axion, a favored dark matter candidate, is expected to have a very small mass and extraordinarily weak couplings. Although it has eluded discovery or exclusion for three decades, it remains the most compelling solution to the strong-CP problem. Axions may be detected by their resonant conversion to RF photons in a microwave cavity permeated by a magnetic field. Experiments have already set significant limits on the axion's mass and photon coupling; progress in photon detection schemes at or below the standard quantum limit will soon enable definitive searches. Similarly, axions produced in the solar burning core may be detectable by their conversion to X rays in a magnetic helioscope. Significant improvements in both mass range and sensitivity of the axion helioscope will likewise be forthcoming in the next few years.

The axion is a hypothetical particle with a mass possibly a trillion times lighter than an electron and exceedingly small couplings to ordinary matter. Yet experiments may soon detect its presence, either as dark matter or as a component of solar flux.

Recent determinations of cosmological parameters point to a flat Universe, whose total energy density is composed of about two-thirds vacuum energy and one-third matter. Ordinary baryonic matter is relegated to a small fraction of the latter, within which the luminous part is an order of magnitude smaller yet. Particle dark matter, i.e., one or more relic particle species from the big bang, is thus strongly suggested as the dominant component of matter in the Universe. The axion, a hypothetical elementary pseudoscalar arising from the Peccei-Quinn solution to the strong-$\mathrm{CP}$ problem, is a well-motivated candidate. If the axion exists, it must be extremely light, in the mass range of ${10}^{\ensuremath{-}6}--{10}^{\ensuremath{-}3}\mathrm{eV},$ and possess extraordinarily feeble couplings to matter and radiation. Nevertheless, as proposed by Sikivie in 1983, the axion's two-photon coupling lends itself to a feasible search strategy with currently available technology. In this scheme, axions resonantly convert to single microwave photons by a Primakoff interaction, in a tunable microwave cavity permeated by a strong magnetic field. Present experiments utilizing heterostructure transistor microwave amplifiers have achieved total system noise temperatures of $\ensuremath{\sim}3\mathrm{K}$ and represent the world's quietest spectral radio receivers. Exclusion regions have already been published well into the band of realistic axion model couplings, within the lowest decade of mass range. Recent breakthroughs in the development of near-quantum-limited superconducting quantum interference device amplifiers should reduce the system noise temperature to $\ensuremath{\sim}100\mathrm{mK}$ or less. Ongoing research into using Rydberg-atom single-quantum detectors as the detector in a microwave cavity experiment could further reduce the effective noise temperature. In parallel with improvements in amplifier technology, promising concepts for higher-frequency cavity resonators are being explored to open up the higher decades in mass range. Definitive experiments to find or exclude the axion may therefore be at hand in the next few years. As the microwave cavity technique measures the total energy of the axion, a positive discovery could well reveal fine structure of the signal due to flows of nonthermalized axions. Manifesting diurnal and sidereal modulation, such detailed features would contain a wealth of information about the history, structure, and dynamics of our Milky Way galaxy.

The axion, a hypothetical elementary particle, emerged from a compelling solution to the Strong-CP problem in QCD. Subsequently, the axion was recognized to be a good Cold Dark Matter candidate. Although dark matter axions have only feeble couplings to matter and radiation, extremely sensitive searches are underway around the world. We review the state of experiments searching for the axion through its coupling to photons. Besides answering an outstanding question in particle physics, the discovery of dark matter axions may provide a detailed history of the formation of our Milky Way galaxy through the structure of the axion signal.

The article of record as published may be found at http://dx.doi.org/101063/1.3489552 I comment on the status and future prospects of the field of axion searches in the context of the seminal contributions of Pierre Sikivie.

A resonantly‐enhanced photon‐regeneration experiment to search for the axion or axion‐like particles is discussed. Photons enter a strong magnetic field and some are converted to axions; the axions can pass through an opaque wall and some may convert back to photons in a second high‐field region. The photon regeneration is enhanced by employing matched Fabry‐Perot optical cavities, with one cavity within the axion generation magnet and the second within the photon regeneration magnet. The optics for this experiment are discussed, with emphasis on the alignment of the two cavities.

New upper limits on the spin-independent interaction of WIMPs and nucleons marks the latest volley in the worldwide effort to detect and identify particle dark matter.

A resonantly-enhanced photon-regeneration experiment to search for the axion or axion-like particles is described. This experiment is a shining light through walls study, where photons travelling through a strong magnetic field are (in part) converted to axions; the axions can pass through an opaque wall and convert (in part) back to photons in a second region of strong magnetic field. The photon regeneration is enhanced by employing matched Fabry-Perot optical cavities, with one cavity within the axion generation magnet and the second within the photon regeneration magnet. Compared to simple single-pass photon regeneration, this technique would result in a gain of (F/pi)^2, where F is the finesse of each cavity. This gain could feasibly be as high as 10^(10), corresponding to an improvement in the sensitivity to the axion-photon coupling, g_(agg), of order (F/pi)^(1/2) ~ 300. This improvement would enable, for the first time, a purely laboratory experiment to probe axion-photon couplings at a level competitive with, or superior to, limits from stellar evolution or solar axion searches. This report gives a detailed discussion of the scheme for actively controlling the two Fabry-Perot cavities and the laser frequencies, and describes the heterodyne signal detection system, with limits ultimately imposed by shot noise., Comment: 10 pages, 5 figures

The possibilitis of electroproduction experiments at a facility such as the proposed European electron accelerator are discussed. Examples given are from studies of hadronization, color transparency, backward production, virtual Compton scattering and target spectator decay. Some conclusions about machine parameters are drawn.

This chapter will cover the search for dark matter axions based on microwave cavity experiments proposed by Pierre Sikivie. We will start with a brief overview of halo dark matter and the axion as a candidate. The principle of resonant conversion of axions in an external magnetic field will be described as well as practical considerations in optimizing the experiment as a signal-to-noise problem. A major focus of this chapter will be the two complementary strategies for ultra-low noise detection of the microwave photons – the “photon-as-wave” approach (i.e., conventional heterojunction amplifiers and soon to be quantum-limited SQUID devices), and the “photon-as-particle” approach (i.e.,Rydberg-atom single-quantum detection). Experimental results will be presented; these experiments have already reached well into the range of sensitivity to exclude plausible axion models, for limited ranges of mass. The chapter will conclude with a discussion of future plans and challenges for the microwave cavity experiment.

We point out that photon regeneration-experiments that search for the axion, or axion-like particles, may be resonantly enhanced by employing matched Fabry-Perot optical cavities encompassing both the axion production and conversion magnetic field regions. Compared to a simple photon regeneration experiment, which uses the laser in a single-pass geometry, this technique can result in a gain in rate of order ${\cal F}^2$, where ${\cal F}$ is the finesse of the cavities. This gain could feasibly be $10^{(10-12)}$, corresponding to an improvement in sensitivity in the axion-photon coupling, $g_{a\gamma\gamma}$ , of order ${\cal F}^{1/2} \sim 10^{(2.5-3)}$, permitting a practical purely laboratory search to probe axion-photon couplings not previously excluded by stellar evolution limits, or solar axion searches., Comment: 4 pages, 2 figures

We investigate the potential for detecting and studying Higgs bosons in {gamma}{gamma} and e{gamma} collisions at future linear colliders with energies below a TeV. Our study incorporates realistic {gamma}{gamma}spectra based on available laser technology, and NLC and CLIC acceleration techniques. Results include detector simulations. We study the cases of: (a) a SM-like Higgs boson based on a devoted low energy machine with {radical}s{sub ee} {le} 200 GeV; (b) the heavy MSSM Higgs bosons; and (c) charged Higgs bosons in e{gamma} collisions.

Lee A. BERNSTEIN, Darren L. BLEUEL, Joseph A. CAGGIANO, Charles CERJAN, Richard J. FORTNER, Julie GOSTIC, Patrick M. GRANT, Narek GHARIBYAN, Christian HAGMANN, Robert HATARIK, Eugene A. HENRY, Daniel SAYRE, Dieter H. G. SCHNEIDER, Wolfgang STOEFFL, Dawn A. SHAUGHNESSY, Dennis P. McNABB, Charles B. YEAMANS, Natalia P. ZAITSEVA, Joshua A. BROWN1), Brian H. DAUB1), Nicholas M. BRICKNER1), Paul F. DAVIS1), Bethany L. GOLDBLUM1), Karl A. VAN BIBBER1), Jasmina VUJIC1), Mohammad S. BASUNIA2), Richard B. FIRESTONE2), Aaron M. HURST2) and Andrew M. ROGERS2)

We review the current status of axions as dark matter. Motivation, models, constraints and experimental searches are outlined. The axion remains an excellent candidate for the dark matter and future experiments, particularly the Axion Dark Matter eXperiment (ADMX), will cover a large fraction of the axion parameter space., 17 pages, 1 figure; contribution to NJP focus issue, "Dark Matter and Particle Physics"

A proposal for an internal gas-jet target and forward spectrometer for the PEP storage ring is described. The beam structure, allowable luminosity (l = 1033cm−2s−1 for H2, D2 decreasing as Z−1.75 for nuclear targets) and energy (Ee ≦ 15 GeV) make the ring ideal for multiparticle coincidence studies in the scaling regime, where perturbative QCD may be an apt description of some exclusive and semi-inclusive reactions.

The history of visual track detectors is as old as the history of nuclear physics itself. Possessing a combination of assets and liabilities peculiar to each technique, visual detectors invariably figured among the first investigations in each new chapter of nuclear and particle physics and frequently made the most significant discoveries. The expansion cloud chamber made possible the discovery of the neutron in 1932, the muon five years later, and the first observations of strange particles in 1947. Such chambers were productive even in the era of modern high-energy accelerators such as the Brookhaven Cosmotron in the early 1950s. Emulsion stacks identical to those used in the pioneering studies of cosmic rays in the upper atmosphere are used today in charmed particle decay studies and in investigations of projectile fragmentation systematics, where a potentially very significant mean-free-path anomaly has recently been reported (Fr 80, Fr 84). And without question, no advance in nuclear instrumentation has had such singular impact as the development of the hydrogen bubble chamber, whose accomplishments are too numerous to cite here. Small wonder then that visual techniques have so tenaciously resisted extinction in the face of the onslaught of the electronic revolution. They have yielded ground reluctantly, only to reappear in hybrid experiments and rejuvenated by technical innovation.

This white paper summarizes the workshop "U.S. Cosmic Visions: New Ideas in Dark Matter" held at University of Maryland on March 23-25, 2017., Comment: 102 pages + references