Dark Energy?. The study of the nature of dark matter and dark energy, and their effects on the evolution and structure of the universe, are some of the most compelling scientific goals of this century, as recognized by the DOE Office of Science / HEP .
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Dark Energy? The study of the nature of dark matter and dark energy, and their effects on the evolution and structure of the universe, are some of the most compelling scientific goals of this century, as recognized by the DOE Office of Science / HEP. I am not trained in astronomy or cosmology, but the opportunity to contribute to this work is simply too exciting for me to pass up! This is a new direction for me, but I believe that my expertise in HEP, and in gravitational wave detection, puts me in a good position to make significant contributions to the study of dark energy with SNAP/JDEM.
Involvement in SNAP/JDEM • After much consultation with principle scientists in SNAP, I have applied for associate membership in the SNAP Collaboration, with the intent of ramping up to full membership within a year. • I am proposing to contribute to SNAP R&D in collaboration with the existing Caltech group led by Richard Ellis, which includes Caltech Millikan Fellow Justin Albert. • Proposed research plan (pending advice from SNAP Collaboration): • Testing and characterization of Near Infrared Focal Plane Array detectors • Development of techniques for extraction of cosmological parameters through the measurement of cosmic shear due to weak gravitational lensing • Development of SNAP simulation package • I plan to request funding for a postdoc and graduate student to pursue this and related work • It is still many years before SNAP will fly. I plan to continue to pursue my work in CMS and in LIGO for the next few years, if possible.
Type Ia Supernovae as Standard Candles • Progenitor C/O White Dwarf accreting from companion • Just before Chandrasekhar mass, thermonuclear runaway • Standard explosion from nuclear physics ("standard candle"). • From the luminosity, we can measure the distance from us • From the spectrum, we measure how fast they are moving away from us. • From this, we construct a Hubble diagram, and infer the expansion rate of the universe, and the history of the expansion rate since the Big Bang (acceleration of the universe).
Hubble diagram - SCP 0.2 0.5 1 0.6 1.0 0.2 0.4 0.8 redshift z In flat universe: M=0.28 [.085 stat][.05 syst] Prob. of fit to =0 universe: 1%
Dark Energy Exploration with SNAP Current ground based compared with Binned simulated data and a sample of Dark energy models
SNAP/JDEM Mission Design Wide field imaging from space
NIR observations in core SNAP science • NIR allows observation of SNe rest frame optical to high redshift • Tracing the effect of dark energy through cosmic time requires probing to high-redshift • Rest frame optical shifts into NIR after z=0.9 • Large wavelength coverage provides important constraints on systematic errors • Substantially enhances auxiliary science Z = 0.8 Z = 1.2 Z = 1.6 Optical Bands NIR Bands Simulated SNAP observations of high redshift SNe
NIR Science drivers Spatial and wavelength coverage: • NIR data for all SNe to constrain systematic errors focal plane to match CCDs which cover the visible • Wavelength coverage to overlap CCDs and allow B and V restframe observations to z>1.5 sensitivity from 1.0 to 1.7 m Signal-to-noise ratio: • Noise should be dominated by unavoidable zodiacal light • dark current < 0.02 e- / pixel / sec • read noise < 5 e- • Signal levels should be sufficient to allow precise observation of SNe near peak withadequate S/N out to z=1.7 within time constraints • quantum efficiency > 60%
Focal Plane Layout with Fixed Filters • FoV: ~0.3 square degrees to match CCD FoV, observe SN in every color • Wavelength coverage 0.9 – 1.7 mto observe V band out to z = 1.7 • Three optimized filters to obtain redshifted B bands out to z=1.7 • 4-fold rotational symmetry to optimize scan strategy with minimal spacecraft re-orientation
NIR detector R&D • Establish large format detectors with good QE out to 1.7 µm cutoff, operating at SNAP FPA temperature of 140o • Explore broadened technology options and vendor pool; establish competitive vendor environment • Rockwell (RSC) – MBE HgCdTe • Raytheon (RVS) – LPE HgCdTe • Sensors Unlimited/Rockwell – InGaAs • Establish facilities for testing and characterizing NIR FPA and detectors • Over the last year the SNAP infrared program has crystallized with several important developments: • NIR team assembled (Caltech, IU, JPL, UCLA, UM, GSFC) • Laboratory facilities in place and tested • Detector procurement and development program in place • Active program of device characterization under way
Proposed involvement in NIR R&D Caltech/UCLA • Caltech astronomy has a strong, experienced team of IR instrumenters, led by Keith Taylor and Roger Smith • They are involved in many projects; SNAP involvement requires more participation. • Propose to work with this team, learning the techniques and technologies; and work in close collaboration with other groups pursuing parallel goals (Michigan, JPL, GSFC). • SNAP effort requires multiple teams working together and independently to develop key technologies. • Propose to help develop a larger, more automated and flexible test facility, capable of testing and characterizing multiple detector technologies and large arrays. • Propose to recruit postdoc and grad student devoted to project.
Mount & enclosure on electronics box (dewar absent for clarity) Test dewar at Caltech OA • Molybdenum detector heater plate • Flex circuit potted into cap of light tight enclosure with silver filled epoxy: • Thermal ground • Light seal • Labyrinth for light seal
Next Generation Test dewar Fully light shielded detector Slits, holes, lenses, open, dark position with calibrated IR diode facing beam for QE crosscheck. Baffles to block scattered light Calibrated filters (CVF?) after aperture, open, or blocked Apertures, pinhole, open, blocked Stabilized Blackbody Temperature regulated blackbody, or some other calibrated light source, for QE Access hatches in top plate
Goals for automated test dewar • Capable of rapid cooling/warming cycles, cycling to LN2 temperature and back up in 24 hours or less. • Detectors would be tested under high vacuum and at temperatures ranging from 77o to the SNAP radiative-cooling temperature of 140o and up. • Chamber large enough to accommodate a mosaic of 3×3 detectors (each a bit under 4 cm square) • Illuminated in an ultra-dark chamber by calibrated light sources capable of fast pulsed illumination, with precision intensity, waveband, and position control. • Many relevant detector parameters would be measured under automated control, to maximize throughput and flexibility while minimizing variations in test procedures. • Comparable testing of devices from different manufacturers, different substrates and readout chips, different cutoff wavelengths, different AR coatings, and different filters.
Detector testing Tests would include • Dark current as a function of temperature, pixel position, settling time, exposure time, bias voltage, previous illumination history (signal persistence), and other parameters. • Electronics noise properties (frequency spectrum, bandwidth) characterized and their origins (MUX, clock, amplifier, controller, crosstalk, etc.) studied. • Quantum efficiency measured versus wavelength for various temperatures, bias voltages, and sampling schemes, ideally using a calibrated source in order to reliably measure the absolute quantum efficiency. • Intrapixel response would be studied. • Other issues, such as reflectivity, capacitive coupling between pixels within detector material, charge diffusion, fill factor, etc., could be addressed.
Conclusions • I am very excited about the opportunity to work with SNAP and Caltech colleagues on the science of SNAP/JDEM. • I am confident that I will be able to make significant contributions to the development of the mission. • I look forward to a deep exploration of the nature of dark energy and its effect on the evolution and structure of the universe.