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Axions are hypothetical elementary particles that may help provide the answer as to why QCD preserves the discrete symmetries P and CP. Light axions also have properties that make them ideal dark-matter candidates. The Axion Dark Matter eXperiment (ADMX), has been at the forefront of the search for dark-matter axions for over a decade, and over the past few years has undergone upgrades to dramatically improve its sensitivity. I give a brief motivation for dark matter axions, discuss the hardware and software aspects of ADMX, review the 3D cavity simulations that are an integral part of the experiment, analyze the 2014 data set and present those results, and highlight some of the ongoing R&D efforts within ADMX. New limits on the axion-to-photon coupling constant are set on select frequency ranges between 600 - 800 MHz and 1050 - 1400 MHz.
The axion is a hypothetical elementary particle and cold dark matter candidate. In this RF cavity experiment, halo axions entering a resonant cavity immersed in a static magnetic field convert into microwave photons, with the resulting photons detected by a low-noise receiver. I present new limits on the axion-to-photon coupling and local axion dark matter halo mass density from a RF cavity axion search in the axion mass range 1.9-2.3 [mu]eV, broadening the search range to 1.9-3.3 [mu]eV. In addition, I report first results from an improved analysis technique, which improves the experiment sensitivity by 13%.
The axion is a hypothetical elementary particle and cold dark matter candidate. In this RF cavity experiment, halo axions entering a resonant cavity immersed in a static magnetic field convert into microwave photons, with the resulting photons detected by a low-noise receiver. The ADMX Collaboration presents new limits on the axion-to-photon coupling and local axion dark matter halo mass density from a RF cavity axion search in the axion mass range 1.9-2.3 [mu]eV, broadening the search range to 1.9-3.3 [mu]eV. In addition, we report first results from an improved analysis technique.
The nature of dark matter remains one of the preeminent mysteries in physics and cosmology. It appears to require the existence of new particles whose interactions to ordinary matter are extraordinarily feeble. One well-motivated candidate is the axion, an extraordinarily light neutral particle that may possibly be detected by looking for their conversion to detectable microwaves in the presence of a strong magnetic field. This has led to a number of experimental searches that are beginning to probe plausible axion model space and may discover the axion in the near future. These proceedings discuss the challenges of designing and operating tunable resonant cavities and detectors at ultralow temperatures. The topics discussed here have potential application far beyond the field of dark matter detection and may be applied to resonant cavities for accelerators as well as designing superconducting detectors for quantum information and computing applications. This work is intended for graduate students and researchers interested in learning the unique requirements for designing and operating microwave cavities and detectors for direct axion searches and to introduce several proposed experimental concepts that are still in the prototype stage.
Axions are peculiar hypothetical particles that could both solve the CP problem of quantum chromodynamics and at the same time account for the dark matter of the universe. Based on a series of lectures by world experts in this field held at CERN (Geneva), this volume provides a pedagogical introduction to the theory, cosmology and astrophysics of these fascinating particles and gives an up-to-date account of the status and prospect of ongoing and planned experimental searches.
The axion is a hypothetical elementary particle resulting from a solution to the "Strong-CP" problem. This serious problem in the standard model of particle physics is manifested as a 1010 discrepancy between the measured upper limit and the calculated value of the neutron's electric dipole moment. Furthermore, a light (~ [mu] eV) axion is an ideal dark matter candidate: axions would have been copiously produced during the Big Bang and would be the primary component of the dark matter in the universe. The resolution of the Strong-CP problem and the discovery of the composition of dark matter are two of the most pressing problems in physics. The observation of a light, dark-matter axion would resolve both of these problems. The Axion Dark Matter eXperiment (ADMX) is the most sensitive search for dark-matter axions. Axions in our Milky Way Galaxy may scatter off a magnetic field and convert into microwave photons. ADMX consists of a tunable high-Q RF cavity within the bore of a large, 8.5 Tesla superconducting solenoidal magnet. When the cavity's resonant frequency matches the axion's total energy, the probability of axion-to-photon conversion is enhanced. The cavity's narrow bandwidth requires ADMX to slowly scan possible axion masses. A receiver amplifies, mixes, and digitizes the power developed in the cavity from possible axion-to-photon conversions. This is the most sensitive spectral receiver of microwave radiation in the world. The resulting data is scrutinized for an axion signal above the thermal background. ADMX first operated from 1995-2005 and produced exclusion limits on the energy of dark-matter axions from 1.9 [mu] eV to 3.3 [mu] eV. In order to improve on these limits and continue the search for plausible dark-matter axions, the system was considerably upgraded from 2005 until 2008. In the upgrade, the key technical advance was the use of a dc Superconducting QUantum Interference Device (SQUID) as a microwave amplifier. The SQUID amplifier's noise level is near the allowed minimum from quantum mechanics, allowing ADMX to reduce its thermal noise background by up to 100x. However, SQUIDs are extremely sensitive to magnetic fields, such as those within in ADMX. Integrating a SQUID amplifier into ADMX presented a serious technical challenge. Commissioning the SQUID amplifier was a major focus of my thesis work. This work demonstrates the successful use of a SQUID amplifier in ADMX during operations from 2008-2010. Compared to other dark-matter candidates, the axion's mass and the axion's coupling strength to normal matter and radiation are rather tightly constrained. This allows for the near-definitive elimination or detection of dark-matter axions. A successful detection in ADMX would immediately lead to a determination of the axion's spectral line shape. This shape encodes the history of the Milky Way's formation and is therefore of high scientific importance. The imperfectly-constrained Milky Way dark-matter halo, however, produces remnant uncertainties of the axion signal in both its spectral line-shape and its total intensity, complicating the ADMX search. This work investigates proposed features of dark-matter halo models which enhance ADMX's sensitivity. From these models, this work presents the corresponding exclusion limits for both the local axion density and axion-to-photon coupling strength for axions with mass in the 3.36 [mu] eV to 3.69 [mu] eV region.
The Axion is a well motivated hypothetical elementary particle that must exist in nature if the strong CP problem of QCD is explained by the spontaneous breaking of a Peccei-Quinn symmetry. Not only would the discovery of the axion solve deep issues in QCD, an axion with a mass of [mu]eV - meV could account for most or all of the missing mass in our galaxy and finally reveal the composition of dark matter. The Axion Dark Matter experiment (ADMX) seeks to resolve these two critical problems in physics by looking for the resonant conversion of dark-matter axions to microwave photons in a strong magnetic field. Utilizing state of the art electronics and dilution refrigerator cryogenics, ADMX is the world's leading haloscope search for axions - able to discover or rule out even the most pessimistically coupled QCD axions. With multi-TM0N0 functionality and with the commissioning of the new high-frequency Sidecar experiment, ADMX is also sensitive to a wide range of plausible axion masses. Here I motivate axions as ideal dark matter candidates, review techniques for detecting them and give a detailed description of the ADMX experiment. I discuss my contributions to the construction of the ADMX dual-channel receiver, which is the most sensitive microwave receiver on earth. I discuss the data acquisition, data taking and real-time analysis software. The primary focus of this work, however, is the ADMX Sidecar experiment which is a miniature axion haloscope that fits inside of the ADMX insert and has the capability of searching for axion masses between 16[mu]eV - 24[mu]eV on the TM010 and 26.4 - 30[mu]eV on the TM020 mode. I discuss analysis of the Sidecar data and exclude axion-to-two-photon coupling g[alpha] [gamma] [gamma]
We describe the status of a sensitive search for halo axions with masses in the [mu]eV range. A tunable large-volume and low-loss microwave cavity is operated at low temperature in a strong magnetic field. Resonant Primakoff conversion of axions into photons takes place when the cavity frequency is matched to the axion mass. No positive signal has been found so far, and we are able to exclude hadronic axions as the dominant halo component over a significant axion mass range. Future plans for a detector upgrade are outlined.
This wide-ranging presentation of applied superconductivity, from fundamentals and materials right up to the details of many applications, is an essential reference for physicists and engineers in academic research as well as in industry. Readers looking for a comprehensive overview on basic effects related to superconductivity and superconducting materials will expand their knowledge and understanding of both low and high Tc superconductors with respect to their application. Technology, preparation and characterization are covered for bulk, single crystals, thins fi lms as well as electronic devices, wires and tapes. The main benefit of this work lies in its broad coverage of significant applications in magnets, power engineering, electronics, sensors and quantum metrology. The reader will find information on superconducting magnets for diverse applications like particle physics, fusion research, medicine, and biomagnetism as well as materials processing. SQUIDs and their usage in medicine or geophysics are thoroughly covered, as are superconducting radiation and particle detectors, aspects on superconductor digital electronics, leading readers to quantum computing and new devices.