Final Report Summary - MAMLS (Matter-antimatter and Lorentz symmetry tests)
1. Executive Summary
As stated in the original proposal, the objective of Matter-Antimatter and Lorentz Symmetry (MAMLS) tests was to conduct and develop experiments with the goal of testing the matter-antimatter symmetry of the universe, Lorentz invariance, and searching for new physics. The proposal consisted of two subprojects to be carried out in parallel. The first subproject involved measuring the magnetic moment, or g-factor, of a proton confined in a Penning trap with a fractional accuracy of 1 part-per-billion or better. Such a measurement would improve the accuracy of the known proton g-factor by an order of magnitude, and improve state-of-the art Penning trap based measurements by three orders of magnitude. The techniques developed during the experimental program would be directly applicable to measurements on antiprotons. The eventual comparison of proton and antiproton g-factors will provide a new stringent test of matter-antimatter symmetry in our universe.
The second subproject aimed to continue work started during the PhD work of Dr. Leefer, developing new tests of fundamental physics using atomic systems. At the time of proposal, such work was still largely in the conceptual phase, but included the possibility of using atomic clocks to test Lorentz symmetry or using sensitive atomic magnetometers to search for new `exotic' physics. The goal was be to develop one or more ideas to a point where a funding proposal could be made to start an experimental program.
Both subprojects were carried out with high degree of success, with additional unplanned work also arising during the final months of the fellowship. Work on the proton g-factor has primarily involved a substantial experimental upgrade. The superconducting magnet was refurbished, a new set of Penning trap electrodes was installed, new axial and cyclotron detectors were installed, and a superconducting shielding coil to stabilize the magnetic field was completed and installed. Measurements are currently underway to characterize sources of systematic errors and a new measurement of the proton g-factor is expected by the end of 2016. This work has been carried out as part of the Baryon-Antibaryon Symmetry Experiment (BASE), and a comparison of the proton g-factor with that of the anti-proton g-factor is expected within a similar time frame.
In parallel, significant progress was made toward developing new ideas for low energy tests of fundamental physics, in collaboration with theorists from the University of New South Wales, Australia. This work resulted in two published journal articles (one Physical Review Letters, one Physical Review D) providing constraints on certain models of dark model from existing parity violation measurements in atomic systems. Additionally, in collaboration with a theory PhD student at Stanford University a reanalysis of atomic spectroscopy data has placed very tight constraints on a particular model of ultralight dark matter, the results of which were published in Physical Review Letters. A direct off-shoot of this work is currently being prepared for publication.
An unplanned project opportunity arose in the final six months of the fellowship, with the formation of an international collaboration focused on developing an entirely new platform for the deterministic recombination of antiprotons and positrons to antihydrogen, on a miniaturized chip-scale architecture. Collaboration participants included senior researchers from The US, the United Kingdom, Germany, and Israel. Two participants are active members of the ALPHA collaboration. Dr. Leefer functioned as the collaboration organizer, developing a major funding proposal to start research activities. The proposal is currently being submitted to various funding agencies for evaluation. Additionally, Dr. Leefer led modeling studies of a new charged particle trapping technique that promises to enable trapping of charged particles with vastly different charge-mass ratios for more efficient recombination of antiprotons with positrons. This work has been submitted for publication in the New Journal of Physics.
2. Summary Description of Project Context and Objectives
The standard model of particle physics (SM) and the general theory of relativity (GR) are the two pillars of modern physics. Despite the success of both theories at describing most of the observable universe, however, there is ample evidence to suggest new physics remains to be discovered. The geometric theory of gravity is fundamentally distinct from the quantum theories of the electromagnetic, weak, and strong forces. The nature of dark matter and dark energy are not understood, yet together they dominate the energy content of the universe. The Big Bang model of cosmology is successful at predicting the current large scale structure of the universe, yet the SM provides no mechanism to explain the asymmetric existence of matter and antimatter (MAM) in the universe. Matter and antimatter should have been produced in equal abundance in the early universe and subsequently annihilated. The SM allows for some MAM asymmetry, but not nearly enough to account for the observable universe.
In 2012, convincing evidence for discovery of the Higgs boson at the Large Hadron Collider was obtained independently by the ATLAS and CMS collaborations. This discovery confirmed the one of the last major predictions of the SM. So far the LHC has not turned up any evidence for physics beyond the SM. In this era it is likely that a diverse range of new experimental tests must be explored before evidence is found that points the way towards solving the present mysteries of the universe. These experiments can range from high-energy searches for new particles to low-energy, precision measurements of fundamental quantities looking for small deviations from theoretical predictions.
3. Description of the main S&T results/foregrounds
The main S&T results for each subproject are as follows.
Proton g-factor
The proton g-factor measurement was significantly delayed due to problems with the superconducting magnet that generates the confining field for the Penning trap. Unpredictable boil-off events and near quenches occurred on multiple occasions, in addition to a drastically reduced standing time for the liquid helium reservoir. The significant age of the magnet prevented professional servicing, so the magnet refurbishing was performed completely in-house by our group. Tasks included: magnet discharge, disassembly, cleaning, reassembly, recharging, and shimming. In total this process took nearly one year to complete due to a lack of prior experience and lack of proper documentation of the magnet.
In parallel with the magnet refurbishment a new set of Penning trap electrodes was installed, new axial and cyclotron detectors were installed, and a superconducting shielding coil was completed and installed. As this work was primarily a technical upgrade to the apparatus, no publications were produced. A progress report was presented at the 2015 Deutsche Physikalische Gesellschaft Frühjahrstagung in Heidelberg, DE.
Despite the unexpected delays, a new measurement of the proton g-factor is anticipated within 2016. Before the magnet refurbishing, significant progress was made towards implementing phase detection methods for measurement of the proton cyclotron frequency and detection of axial frequency shifts due to spin flips. After the magnet refurbishing and equipment upgrades, the phase detection methods dramatically deteriorated for reasons that are still poorly understood, but may be a result of worse magnetic field homogeneity for excited protons. It was decided to continue the measurement with conventional image current detection methods, which were significantly improved with the detector upgrades. In late 2015 a technical review paper summarizing the Baryon Antibaryon Symmetry Experiment (BASE) was published in the European Physical Journal – Special Topics. The publication detailed the motivation and progress of the proton and antiproton g-factor experiments carried out by the Mainz collaboration.
New tests of fundamental physics
Significant progress was made toward developing new ideas for low energy tests of fundamental physics, in collaboration with theorists from the University of New South Wales, Australia. This work resulted in two published journal articles (one Physical Review Letters, one Physical Review D) providing constraints on certain models of dark model from existing parity violation measurements in atomic systems. Additionally, in collaboration with a theory PhD student at Stanford University a reanalysis of atomic spectroscopy data has placed very tight constraints on a particular model of ultralight dark matter, the results of which were published in Physical Review Letters in 2015.
Building on the work in 2015, the collaboration with Victor Flambaum of UNSW continued. A manuscript is currently under preparation that details a model of low-mass scalar dark matter with non-zero coupling to standard model fields. In such a model conventional matter and energy acts as a source for the new scalar field, which can be observed through precise measurement of atomic energy levels in the modulated presence of a test mass. This works provides an entirely new method for dark matter searches in addition to providing a model for comparison of well-known fifth force type experiments with atomic clock comparisons. The manuscript is expected to be finished in mid 2016.
Future tests of matter antimatter symmetry
New work was started in the later part of 2015, relating to developing a new technological platform for the efficient production of antihydrogen at European facilities such as the CERN or the future FAIR/FLAIR facility in Germany. A collaboration of physicists from the US, Germany, the United Kingdom, and Israel was formed and organized by Dr. Leefer with the intention of developing a hybrid atom-ion, chip-scale device for trapping and combing antiprotons and positrons, and capturing the resulting neutral antihydrogen with a deep atom trap. Miniaturization of the trap geometry is expected to enable more precise control of the produced antihydrogen, enabling eventual precision spectroscopy for ultrasensitive tests of matter antimatter symmetry.
To date the collaboration activities have produced a detailed project timeline and proposal outlining major challenges and work packages to overcome them. The proposal was unsuccessfully submitted as a FET-open proposal, and is now being evaluated for submission to other funding platforms. Initial development work is expected to continue within available resources.
In addition to proposal development, Dr. Leefer led an analysis effort to study a novel solution to one of the key challenges for antihydrogen recombination: how to confine antiprotons and positrons, with vastly different charge-mass ratios, in the same volume. A literature search led to the idea of using a two-frequency Paul trap for independent tailoring of confining forces for the two charged particle species. The analysis covered an exploration of stability criteria for such traps as well as numerical modeling of the relative efficiency of antihydrogen recombination compared to single-frequency Paul traps. The work has been submitted for publication in the New Journal of Physics in early 2016 and is currently under review.
As stated in the original proposal, the objective of Matter-Antimatter and Lorentz Symmetry (MAMLS) tests was to conduct and develop experiments with the goal of testing the matter-antimatter symmetry of the universe, Lorentz invariance, and searching for new physics. The proposal consisted of two subprojects to be carried out in parallel. The first subproject involved measuring the magnetic moment, or g-factor, of a proton confined in a Penning trap with a fractional accuracy of 1 part-per-billion or better. Such a measurement would improve the accuracy of the known proton g-factor by an order of magnitude, and improve state-of-the art Penning trap based measurements by three orders of magnitude. The techniques developed during the experimental program would be directly applicable to measurements on antiprotons. The eventual comparison of proton and antiproton g-factors will provide a new stringent test of matter-antimatter symmetry in our universe.
The second subproject aimed to continue work started during the PhD work of Dr. Leefer, developing new tests of fundamental physics using atomic systems. At the time of proposal, such work was still largely in the conceptual phase, but included the possibility of using atomic clocks to test Lorentz symmetry or using sensitive atomic magnetometers to search for new `exotic' physics. The goal was be to develop one or more ideas to a point where a funding proposal could be made to start an experimental program.
Both subprojects were carried out with high degree of success, with additional unplanned work also arising during the final months of the fellowship. Work on the proton g-factor has primarily involved a substantial experimental upgrade. The superconducting magnet was refurbished, a new set of Penning trap electrodes was installed, new axial and cyclotron detectors were installed, and a superconducting shielding coil to stabilize the magnetic field was completed and installed. Measurements are currently underway to characterize sources of systematic errors and a new measurement of the proton g-factor is expected by the end of 2016. This work has been carried out as part of the Baryon-Antibaryon Symmetry Experiment (BASE), and a comparison of the proton g-factor with that of the anti-proton g-factor is expected within a similar time frame.
In parallel, significant progress was made toward developing new ideas for low energy tests of fundamental physics, in collaboration with theorists from the University of New South Wales, Australia. This work resulted in two published journal articles (one Physical Review Letters, one Physical Review D) providing constraints on certain models of dark model from existing parity violation measurements in atomic systems. Additionally, in collaboration with a theory PhD student at Stanford University a reanalysis of atomic spectroscopy data has placed very tight constraints on a particular model of ultralight dark matter, the results of which were published in Physical Review Letters. A direct off-shoot of this work is currently being prepared for publication.
An unplanned project opportunity arose in the final six months of the fellowship, with the formation of an international collaboration focused on developing an entirely new platform for the deterministic recombination of antiprotons and positrons to antihydrogen, on a miniaturized chip-scale architecture. Collaboration participants included senior researchers from The US, the United Kingdom, Germany, and Israel. Two participants are active members of the ALPHA collaboration. Dr. Leefer functioned as the collaboration organizer, developing a major funding proposal to start research activities. The proposal is currently being submitted to various funding agencies for evaluation. Additionally, Dr. Leefer led modeling studies of a new charged particle trapping technique that promises to enable trapping of charged particles with vastly different charge-mass ratios for more efficient recombination of antiprotons with positrons. This work has been submitted for publication in the New Journal of Physics.
2. Summary Description of Project Context and Objectives
The standard model of particle physics (SM) and the general theory of relativity (GR) are the two pillars of modern physics. Despite the success of both theories at describing most of the observable universe, however, there is ample evidence to suggest new physics remains to be discovered. The geometric theory of gravity is fundamentally distinct from the quantum theories of the electromagnetic, weak, and strong forces. The nature of dark matter and dark energy are not understood, yet together they dominate the energy content of the universe. The Big Bang model of cosmology is successful at predicting the current large scale structure of the universe, yet the SM provides no mechanism to explain the asymmetric existence of matter and antimatter (MAM) in the universe. Matter and antimatter should have been produced in equal abundance in the early universe and subsequently annihilated. The SM allows for some MAM asymmetry, but not nearly enough to account for the observable universe.
In 2012, convincing evidence for discovery of the Higgs boson at the Large Hadron Collider was obtained independently by the ATLAS and CMS collaborations. This discovery confirmed the one of the last major predictions of the SM. So far the LHC has not turned up any evidence for physics beyond the SM. In this era it is likely that a diverse range of new experimental tests must be explored before evidence is found that points the way towards solving the present mysteries of the universe. These experiments can range from high-energy searches for new particles to low-energy, precision measurements of fundamental quantities looking for small deviations from theoretical predictions.
3. Description of the main S&T results/foregrounds
The main S&T results for each subproject are as follows.
Proton g-factor
The proton g-factor measurement was significantly delayed due to problems with the superconducting magnet that generates the confining field for the Penning trap. Unpredictable boil-off events and near quenches occurred on multiple occasions, in addition to a drastically reduced standing time for the liquid helium reservoir. The significant age of the magnet prevented professional servicing, so the magnet refurbishing was performed completely in-house by our group. Tasks included: magnet discharge, disassembly, cleaning, reassembly, recharging, and shimming. In total this process took nearly one year to complete due to a lack of prior experience and lack of proper documentation of the magnet.
In parallel with the magnet refurbishment a new set of Penning trap electrodes was installed, new axial and cyclotron detectors were installed, and a superconducting shielding coil was completed and installed. As this work was primarily a technical upgrade to the apparatus, no publications were produced. A progress report was presented at the 2015 Deutsche Physikalische Gesellschaft Frühjahrstagung in Heidelberg, DE.
Despite the unexpected delays, a new measurement of the proton g-factor is anticipated within 2016. Before the magnet refurbishing, significant progress was made towards implementing phase detection methods for measurement of the proton cyclotron frequency and detection of axial frequency shifts due to spin flips. After the magnet refurbishing and equipment upgrades, the phase detection methods dramatically deteriorated for reasons that are still poorly understood, but may be a result of worse magnetic field homogeneity for excited protons. It was decided to continue the measurement with conventional image current detection methods, which were significantly improved with the detector upgrades. In late 2015 a technical review paper summarizing the Baryon Antibaryon Symmetry Experiment (BASE) was published in the European Physical Journal – Special Topics. The publication detailed the motivation and progress of the proton and antiproton g-factor experiments carried out by the Mainz collaboration.
New tests of fundamental physics
Significant progress was made toward developing new ideas for low energy tests of fundamental physics, in collaboration with theorists from the University of New South Wales, Australia. This work resulted in two published journal articles (one Physical Review Letters, one Physical Review D) providing constraints on certain models of dark model from existing parity violation measurements in atomic systems. Additionally, in collaboration with a theory PhD student at Stanford University a reanalysis of atomic spectroscopy data has placed very tight constraints on a particular model of ultralight dark matter, the results of which were published in Physical Review Letters in 2015.
Building on the work in 2015, the collaboration with Victor Flambaum of UNSW continued. A manuscript is currently under preparation that details a model of low-mass scalar dark matter with non-zero coupling to standard model fields. In such a model conventional matter and energy acts as a source for the new scalar field, which can be observed through precise measurement of atomic energy levels in the modulated presence of a test mass. This works provides an entirely new method for dark matter searches in addition to providing a model for comparison of well-known fifth force type experiments with atomic clock comparisons. The manuscript is expected to be finished in mid 2016.
Future tests of matter antimatter symmetry
New work was started in the later part of 2015, relating to developing a new technological platform for the efficient production of antihydrogen at European facilities such as the CERN or the future FAIR/FLAIR facility in Germany. A collaboration of physicists from the US, Germany, the United Kingdom, and Israel was formed and organized by Dr. Leefer with the intention of developing a hybrid atom-ion, chip-scale device for trapping and combing antiprotons and positrons, and capturing the resulting neutral antihydrogen with a deep atom trap. Miniaturization of the trap geometry is expected to enable more precise control of the produced antihydrogen, enabling eventual precision spectroscopy for ultrasensitive tests of matter antimatter symmetry.
To date the collaboration activities have produced a detailed project timeline and proposal outlining major challenges and work packages to overcome them. The proposal was unsuccessfully submitted as a FET-open proposal, and is now being evaluated for submission to other funding platforms. Initial development work is expected to continue within available resources.
In addition to proposal development, Dr. Leefer led an analysis effort to study a novel solution to one of the key challenges for antihydrogen recombination: how to confine antiprotons and positrons, with vastly different charge-mass ratios, in the same volume. A literature search led to the idea of using a two-frequency Paul trap for independent tailoring of confining forces for the two charged particle species. The analysis covered an exploration of stability criteria for such traps as well as numerical modeling of the relative efficiency of antihydrogen recombination compared to single-frequency Paul traps. The work has been submitted for publication in the New Journal of Physics in early 2016 and is currently under review.