Nevis REU 2014 Research Program The physics experiments described on this page are offering research opportunites for undergraduates as part of the Nevis REU program.

The experimental groups participating in the Summer 2014 REU program at Nevis are:

ATLAS, Double Chooz, MicroBooNE, XENON, ATTA, VERITAS, Genesis, and RARAF.


ATLAS

contact person: John Parsons

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ATLAS is an experiment operating at the Large Hadron Collider (LHC) at CERN in Geneva, Switzerland. The LHC is the world's highest energy accelerator, and will be the premier experimental HEP collider facility for many years to come.

The foremost question of HEP is the source of so-called "electroweak symmetry breaking" (EWSB), related to the issue of the origin of mass. The ``Standard Model'' (SM) of particle physics postulates the existence of the Higgs boson to solve this issue. In July 2012, ATLAS and CMS, the two large LHC experiments, announced the discovery of a new particle with properties very much like those predicted for the Higgs boson. Whether this new particle behaves precisely as expected for the Higgs, or whether there are discrepancies that could point the way to new physics, is an area of intensive study. In addition, even with the Higgs, there are many questions that cannot be answered by the SM. Many other scenarios (eg. supersymmetry, technicolor, even the existence of extra spacetime dimensions) have been proposed. The LHC and ATLAS are designed to explore in detail physics at the TeV scale, where it is widely expected that signs of new physics should be discoverable.

The Columbia ATLAS group has played a number of roles in the experiment, including leading the development (from design through installation and commissioning) of the readout electronics of the liquid argon calorimeters, participating in the commissioning of the pixel tracking detector, a variety of software and data acquisition developments, and studies of the ATLAS detector performance and physics potential. We are now heavily involved in physics analysis with the enormous data samples recorded at proton-proton center-of-mass energies of 7 TeV in 2011 and 8 TeV in 2012. In addition, we are performing R&D aimed at developing the next generation of readout electronics for the ATLAS calorimeter system.

REU students will be based at CERN in Geneva, Switzerland and will work on analyzing the data from the first LHC physics runs. There is also the option to participate from Nevis Labs, including the possibility to be involved in the electronics development.


Double Chooz

contact person: Mike Shaevitz

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Double Chooz is an experiment located in northern France. It searches for the oscillations of electron antineutrinos produced by nuclear power reactors. Neutrinos (and also antineutrinos), of which there are three types, have been found to oscillate from one type to another. These oscillations are governed by several parameters of which one, the mixing angle θ13, was first shown to be fairly large by the Double Chooz experiment. Currently, the Double Chooz experiment has measured this mixing angle to be 9.6 ± 1.7 degrees. The value of θ13 is very important for future neutrino oscillation experiments since its value is not only crucial for interpreting these measurements but its size also determines how big CP violating effects will be.

Double Chooz has been taking data with the far detector since April 2011 and two results have been published. The Columbia group is now working on improved measurements using the additional collected data and using new techniques to enhance the oscillation signal and reduce the backgrounds. A summer REU student would be involved in developing these improvements, in helping run the experiment, and in hardware and calibration tasks. The REU student would be primarily based at Nevis Labs but may be asked to travel to France for some time period to help with running the experiment.


MicroBooNE

contact person: Mike Shaevitz

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MicroBooNE is a neutrino experiment at Fermilab which will investigate neutrino properties and interactions using the booster neutrino beam. It is a follow-up experiment to the MiniBooNE experiment which also ran in the Fermilab booster neutrino beam. MiniBooNE observed an enhanced number of low energy events over expectation with characteristics that imply the events have outgoing electrons or photons. Since electron neutrinos produce electrons in their charged current interactions, one interpretation is that these extra events are due to more electron neutrino interactions than expectation. An alternative explanation is that they are due to an unexpected number of neutrino events producing photons in the final state. In either case, the anomalous MiniBooNE signal may be from some type of new physics either within or beyond the current particle physics model.

MicroBooNE will have the capability to distinguish between electrons and photons by using a time projection chamber (TPC) filled with 175 tons of liquid argon. This detector will have excellent spatial and energy resolution and will be able to differentiate between an electron from an electron neutrino interaction and a photon; an electron will produce a track originating at the main interaction vertex, while a photon which will travel some distance from the vertex before converting and producing a track. Its superb pattern recognition capabilities will also allow improved measurements of several neutrino cross sections. MicroBooNE will also be a test setup for future very large (~100 kton) liquid argon detectors planned for studies of CP violation in neutrino interactions, proton decay and Super Novae detection. It will allow R&D on liquid argon purity, mechanical configurations and electronic designs.

The Columbia neutrino group at Nevis Labs have been involved in the design and construction of the readout electronics for the liquid argon detector and the phototubes that detect the scintillation light from the liquid argon. The group will also be involved in coding a simulation program for neutrino interactions in liquid argon and in developing pattern recognition analysis procedures to distinguish between neutrino interactions and background events and between electrons and photons.

MicroBooNE will complete construction and start taking initial data this spring. This summer will be an intense time for looking at the first data, developing neutrino event reconstruction software, and updating the oscillation physics simulations. We would plan for the REU student to be based at Nevis Labs and be involved in all of these efforts along with possibly helping with special tests of the TPC and phototube readout hardware.


The XENON Dark Matter Experiment
contact person: Elena Aprile

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There is a wide range of astronomical evidence that the stars in all galaxies, including our own, are immersed and gravitationally bound in a much larger cloud of non-luminous matter, typically an order of magnitude greater in total mass. The existence of this dark matter is consistent with evidence from large-scale galaxy surveys and microwave background measurements. The conclusion from all evidence strongly supports that the majority of matter in the universe is non-baryonic. The nature of dark matter remains unknown, and the resolution of the dark matter puzzle is of fundamental importance to cosmology, astrophysics and elementary particle physics. A leading explanation, theoretically motivated by supersymmetry theory, is the existence of new weakly interacting massive particles (WIMPs), formed in the early universe and subsequently clustered in association with normal matter. These could in principle be detected in terrestrial experiments by collisions with ordinary nuclei, giving observable low energy (< 100 keV) nuclear recoils.

XENON is one such experiment, aiming at the direct detection of WIMPs with a large volume time projection chamber (TPC) filled with liquid xenon as WIMP target and detection medium. Through the simultaneous measurement of the ionization and scintillation signals produced in LXe by radiation and through its 3D event localization capability, the XENON TPC is able to discriminate nuclear recoils produced by WIMPs (and neutrons), from electron recoils produced by gamma and beta background. The XENON concept was tested at Nevis Laboratories with several small scale prototypes, culminating with the XENON10 detector, yielding the best sensitivity for dark matter searches in 2007. After the successful operation of this detector, the collaboration led by Columbia University and involving groups at UCLA and Rice universities in addition to European, Israeli and Chinese groups, is now operating the next generation TPC at the 100 kg scale.

The XENON100 experiment is currently taking data at the Laboratori Nazionali de Gran Sasso (LNGS), Italy, one of the largest underground laboratories worldwide. With the first science run, XENON100 provided a factor 100 increase in sensitivity with respect to its predecessor, becoming the most sensitive dark matter experiment in the world. These results have challenged the dark matter interpretation of other running experiments. The second science run, 225 live-days, lowered the WIMP-nucleon cross section limit to 2x10^{-45}cm^{2} for a WIMP mass of 55 GeV. The attached figure shows the XENON100 results from the 225 live-days science run.

After the successful operation of XENON100, Columbia University is leading the effort for the construction of the next detector in the XENON program, XENON1T. With a total mass of ~2.2 tons and the use of new photosensors and materials, this detector will improve the sensitivity of XENON100 by more than a factor 100, and it will be able to explore cross sections down to 2x10^{-47}cm^{2}. The experiment is currently under construction at LNGS. In addition, the XENON1T Demonstrator, a setup that will test the new technologies to be used in the actual detectors, is currently being operated at the Nevis Laboratories of Columbia University.

There are opportunities for REU students working in the XENON group to spend the majority of their time at LNGS in Italy, helping with the construction and commissioning of the XENON1T experiment, or at Nevis participating in the ongoing construction, operation and analysis of the data from the XENON1T Demonstrator.


The ATTA Experiment
contact person: Elena Aprile

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As described above, the nature of dark matter is a central question in cosmology, astrophysics and particle physics, and is being aggressively pursued with a variety of experimental and theoretical approaches. A key requirement for XENON, and a challenge for all dark matter searches, is control and reduction of background to an ultra-low level (<0.0001 events/keV/kg/day before any rejection). Traces of radioactive isotopes in the noble liquid targets contribute an intrinsic background. For Xe targets, the isotope of concern is 85-Kr, a long-lived beta emitter, with a 85-Kr/Kr abundance of 10^{-11}. The contamination of Kr in Xe must be reduced to the part per trillion (ppt) level, in order for the 85-Kr background to be negligible in an experiment like XENON1T. This is achieved by cryogenic distillation or adsorption-based separation. For the XENON100 experiment, we are using a cryogenic distillation tower to separate Kr from Xe, however we lack a reliable and rapid method to measure the ultra-low Kr contamination we expect (<1 ppt) to achieve with the distillation process. The Atom Trap Trace Analysis (ATTA) method, originally developed for radioactive dating with rare Kr isotopes, by Prof. Lu's group at Argonne National laboratory, shows the potential to accomplish this task.

An ATTA system based on laser cooling, trapping, and counting single atoms, with the specific purpose to determine the number of radioactive Kr atoms in Xe samples, has been built at Columbia University. The goal of the experiment is to assess whether the Kr/Xe contamination has been reduced to the ppt level, as necessary for the next generation of sensitive dark matter searches based on LXe. The ATTA instrument consists of a high-vacuum system with an injected gas sample that generates a metastable atomic beam through a radio frequency discharge excitation of the contaminant atoms. The metastable atoms are slowed and trapped using magneto-optical techniques, and counted by detecting their laser flourescence with a sensitive photodetector. An all-diode laser system supplies the light for transverse cooling, slowing, and trapping metastable atoms. The system will be tuned to count, with high signal-to-noise, single Kr atoms that periodically arrive in the trap. The project is a collaborative effort between the XENON Dark Matter group led by Prof. Aprile and the atomic, molecular, and optical (AMO) group led by Prof. Zelevinsky, in the Physics Department of Columbia University. The project exploits the considerable expertise available at Columbia in these two research areas. It is carried out directly by the two faculty members together with a postdoctoral researcher and two physics graduate research assistants.

REU students will be based in New York and will participate in the testing and calibration of the apparatus, and the ongoing development of the supporting optical equipment.


VERITAS/CTA

contact person: Brian Humensky

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VERITAS is an array of four imaging air Cherenkov telescopes located at the Whipple Observatory on Mt. Hopkins, about one hour south of Tucson, AZ. VERITAS is dedicated to the study of gamma-ray astrophysics in the energy range from 100 GeV to 30 TeV. The Fermi Gamma-ray Space Telescope operates in a complementary gamma-ray range, covering 100 MeV to 100 GeV. Together with other similar ground- and space-based instruments (HAWC, H.E.S.S., MAGIC, AGILE), these experiments provide a unique window on the most powerful cosmic particle accelerators, including jets associated with supermassive black holes, shock waves in supernova remnants and the nebulae surrounding energetic pulsars, and the complex physics of X-ray binary systems. Very-high-energy gamma rays can also probe some of the most important questions in particle physics and cosmology: the search for dark matter, Lorentz invariance violation, and the strength of the magnetic field in intergalactic space. We are also deeply involved in a world-wide project to develop and build a next-generation ground-based instrument, the Cherenkov Telescope Array, with a factor of 10 better sensitivity and much broader energy range.

At Columbia and Barnard, the science problems we focus on are in the areas of dark matter searches, the origins of Galactic cosmic rays, and the physics of active galactic nuclei. In many dark matter scenarios, the particles that make up the dark matter can either annihilate with each other, or decay (with a very long lifetime). In either case, one of the final products will be high-energy gamma rays. The mass of the dark matter particle is poorly constrained; above a few hundred GeV, detection of gamma rays from regions of space with unusually high concentrations of dark matter (such as dwarf spheroidal galaxies, or the central region of the Milky Way galaxy) becomes one of the most promising avenues for identifying dark matter.

For just over 100 years we have known that the earth is bombarded by energetic charged particles, cosmic rays, without a clear understanding of their origins. Cosmic rays can range in energy up to 10^20 eV. Up to 10^15 eV or so, cosmic rays are believed to be accelerated within our galaxy, and only recently has unambiguous evidence for cosmic-ray acceleration in supernova remnants (SNRs) emerged, particularly from Fermi-LAT. It remains an open question whether SNRs are the sole, or even the primary, source, along with how the acceleration process works, and how cosmic rays escape from SNRs and diffuse into the galaxy from the regions surrounding them. Deep studies of known Galactic accelerators and surveys of classes of objects will allow us to address this question, as well as explore the details of the acceleration process.

Active galactic nuclei (AGN) are supermassive black holes at the centers of galaxies which are actively accreting material; energy released from the accretion disk somehow powers the formation of relativistic jets of material moving outward from the black holes, as well as acceleration of particles to very high energies. Where and how this particle acceleration occurs, and how it connects to the structure and formation of these remarkable jets, are a few of the questions being addressed by studies of AGN from the radio through the gamma-ray bands.

Projects working on hardware or simulations for the next-generation Cherenkov Telescope Array are available, and there may be opportunities to work on analysis of VERITAS and Fermi data as well. All of these projects would be based at Nevis Labs.


Genesis

contact person: Daniel Savin

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We have constructed a novel merged-beams apparatus to study the cosmic origins of organic chemistry. With this, we are measuring reactions of atomic C with molecular hydrogen ions forming the first organic molecules. We are also studying atomic O reacting with molecular hydrogen ions forming precursors to water. The rate coefficients we measure are a critical component of the astrochemical models used to predict interstellar molecular abundances and to analyze spectroscopic observations of molecule-bearing cosmic sources.

Initial studies focus on the reactions C + H3+ → CH+ + H2 and O + H3+ → OH+ + H2, important first steps in leading to interstellar organic chemistry. Starting with a C- or O- beam, we will use laser photodetachment to generate a neutral atomic beam; the residual anions will then be removed leaving a pure neutral beam. Subsequently an H3+ beam will be merged with the atomic beam. Since the beams will be co-propagating, we are able to study reactions down to collision energies of the order of ten meV (less than ~ 80 K). Reactions will be studied using an electrostatic analyzer to separate and detect the charged end products, allowing us to determine absolute reaction cross sections.

REU students working on Genesis would be based at Nevis Labs.


Radiological Research Accelerator Facility (RARAF)

contact person: David Brenner

The Radiological Research Accelerator Facility (RARAF) is dedicated to providing user-friendly radiation sources and bio-labs for research in biology, radiation biology, and radiation physics. Our sources include a unique single-cell/single-particle microbeam irradiator that allows irradiation of single cells or parts of cells with exactly one (or more) charged particle(s). This provides a unique opportunity for scientists to study both structure and function of individual cells and, particularly, their response to damage.

RARAF involves a unique interaction of physics, engineering, and biology, and there are opportunities for research projects in the fields of beam line development (e.g., development of a neutron microbeam), beamline focusing and targeting, applications for biological systems (e.g., self-referencing microprobes), and automated cellular and sub-cellular imaging, both in terms of hardware and software.

Whatever the project, it is important to be able to talk to, and listen to, the on-site and visiting biologists, to make sure that what is being built is really what is needed.

REU students working on RARAF would be based at Nevis Labs.


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