Dark Matter – Investigating the Universe's Hidden Secrets

Physics Dark matter – investigating the universe’s hidden secrets One of the biggest mysteries of the Universe is that, through DARKLIGHT Physicists like Professors Richard Milner and observations, we know we can only account for a sixth of the mass Peter Fisher from the Massachusetts Institute out there. The rest is put down to a mysterious substance called ‘dark of Technology (MIT) are seeking to find out matter’, and we need physics beyond the Standard Model of particle what dark matter is. The two now lead an physics to explain it. Professor Richard Milner and Professor Peter MIT-conceived experiment called Detecting A Resonance Kinematically with eLectrons from the Massachusetts Institute of Technology (MIT) are helping Fisher Incident on a Gaseous Hydrogen Target – or us get closer to understanding the mystery with a new experiment, soon DarkLight for short. The experiment will use to begin its first set of data collection. the latest technology to look beyond the Standard Model, to try and delve into the world of dark matter. The MIT DarkLight group led by Milner and Fisher includes four he Standard Model of particle galaxies by studying how the galaxies move. PhD researchers, five graduate students, physics describes the most But when the total mass from everything we several undergraduate students, and basic building blocks of matter, can actually see is added up, there is a huge technical support from the Bates Research from electrons to quarks, and amount missing. Particles described by the and Engineering Center. MIT theoretical the forces that govern the way Standard Model, the ones we can see, only physicist Professor Jesse Thaler and his they interact. It is arguably one of the best make up a sixth of the mass of the Universe group have provided key calculations that Tscientific theories to date, describing with – so where is the rest of the mass coming have guided the design of the DarkLight great accuracy how atoms stick together, from? experiment. how radioactivity works in the sun and how the Universe was formed. But it is This mysterious substance has been given In 2013, a paper was published in the incomplete. There are a few observations we the name ‘dark matter’, because it does not journal Physical Review Letters, revealing cannot explain using the Standard Model, interact with light the way normal matter the potential of electron beams for use in and one of these is called dark matter. does, so we cannot see it. It could be one particle physics experiments. One year later, kind of particle, or it could be thousands of in 2014, a group of physicists from MIT, When astronomers peer into the Universe, different particles, but at the moment we do alongside others from Hampton University, they can measure the amount of mass in not know. Arizona State University and Temple University, were awarded a grant to build the first phase of the DarkLight experiment, at Schematic of the Low High-voltage the Thomas Jefferson National Laboratory Electron gun Energy Recirculator power supply in Virginia. Facility at Jefferson Injector Laboratory 1/4 Cryomodule 2nd The experiment will send powerful beams of Recirculation electrons through a linear accelerator on to Arc a target of hydrogen atoms, which they will UV Light To scatter off to create electron and positron Experimental pairs. For this purpose, the DarkLight Labs experiment uses one of the most powerful Darklight Detector Superconducting RF electron beams in the world, located at Linac Cryomodules Jefferson Laboratory, Newport News, THz LightLab 3A to Virginia, USA. Recirculation DARK PHOTONS AND NEW FORCES Beam Dump UV Wiggler The experiment was originally motivated by the possibility of a new A’ gauge boson, Dark matter could be one kind of 1st Recirculation Arc UV OpticalCavity giving rise to a dark (massive) photon. DarkLight is designed to search for new particle, or it could be thousands particles having a mass between 10 and 90 MeV, so we need energies up to about 100 of different particles – at the MeV to see it. The dark photon, if it exists, moment we do not know 6 www.researchfeatures.com Physics Detail RESEARCH OBJECTIVES Prof Milner and Prof Fisher's current What is your involvement in the theoretical expectation and does research mainly focuses on particle DarkLight experiment? bring it in line with the measure value. physics in the areas of dark matter We realised that an experiment to look We note that physicists are mounting detection and the development of new for electron-positron final-states in a more precise determination of the kinds of particle detectors. elastic electron-proton scattering at muon magnetic moment and results are low energies offered a unique means to expected within several years. FUNDING search for new physics that could bear on US National Science Foundation and US understanding the elusive dark matter. When do you expect the results of Department of Energy, Office of Science The mass region 10 to 100 MeV is difficult the 17 MeV search to be gathered to access at high energies. Thus, we were and analysed by? COLLABORATORS motivated to propose the experiment. If funding and beam time become The DarkLight experiment is carried We oversee the collaboration and the available in a timely way, we expect to out by a collaboration of physicists sizable MIT group that leads it. have data within two years. However, and engineers from MIT, Jefferson government funding of science in the Laboratory, Arizona State University, Why are you personally interested in US at present is uncertain. Hampton University, Temple University in the search for dark matter? the US and from CEA-Saclay in France. Schematic layout of the Dark matter is a profound mystery at What would it mean if we found a DarkLight experiment this time. Astrophysical observations particle or force not described by BIO tell us that the amount of dark matter the Standard Model? Prof Peter Fisher is a Professor significantly exceeds the amount of It would be a huge deal for in the MIT Physics Department would be exciting because it would interact visible matter, which is what physicists physicists. Newton gave us the and currently serves as with both light and dark matter. This would have studied since the dawn of history. gravitational force. Maxwell department head. Prof Fisher provide a window through which we could If we wish to understand the physical described electricity and received a BS Engineering study the mysterious properties of dark universe, we must understand dark magnetism in his famous equations. Physics from Berkeley in 1983 matter. Recent theoretical work has shown matter. Quantum mechanics has allowed us and a PhD in Nuclear Physics from that DarkLight is sensitive to a broad class to describe and generalise these Caltech in 1988. of new (fifth) forces. How could the dark photon explain the fundamental forces. Discovery of muon magnetic moment mystery? a new interaction beyond those Prof Richard Milner is a This new force could also explain another The dark photon or a similar new particle described in the present Standard Professor in the MIT Physics mystery in the Standard Model. The muon, can produce a new contribution to the Model would be revolutionary. Department. He received his a heavier cousin of the electron, has been BSc in Experimental Physics an enigma for some time. Although it is in 1978 and MSc in Theoretical 207 times more massive, the particle acts Physics in 1979 from University like a tiny magnet – just like the electron. College Cork, Ireland. He later received But curiously, in 2001, an experiment at the If we wish to understand the a PhD in Nuclear Physics from Caltech in Brookhaven National Lab (BNL) in New York 1984. measured the particle’s magnetic moment physical universe, we must and found it was larger than the predictions understand dark matter CONTACT of the Standard Model. This could have Professor Richard Milner been a statistical fluke, or it could mean Photograph of experiment as installed in Jefferson Laboratory, September 2016 Massachusetts Institute of Technology something else is at play. If a new force 77 Massachusetts Avenue exists, it may explain this discrepancy. Cambridge, MA 01239-4301 optimised the design of the experiment One of the first sets of data to be taken If it does exist, this mysterious particle After this run, future data taking with the USA Construction of the initial phase of Profs and its ability to gather data. As of now, it by the experiment will be a search for a could hint at a fifth fundamental experiment will be looking for electron Milner and Fisher’s experiment was is ready to go, with the first phase of the particle with a mass around 17 MeV for force – beyond the Standard Model, positron pairs with masses between 30 E: [email protected] completed in August 2016, and is ready for experiment due to be finished in the next electron positron pair decays. This search at because the data does not fit with and 70 MeV. New accelerators are under T: +1 (617) 258-5439 testing. In the past year, the researchers several years. 17 MeV is exciting because an experiment any previous experiments. It may or construction at Cornell University, New York W: http://web.mit.edu/physics/people/ at the Hungarian Academy for Science’s may not be a dark photon, but even if and at the University of Mainz, Germany faculty/milner_richard.html Institute for Nuclear Research, in Drebecen, it is not, a new kind of particle would to pursue the DarkLight experimental Hungary, found something surprising when bring completely new possibilities for approach.

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