Transcript No Slide Title

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.
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Involvement in SNAP/JDEM
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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
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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.
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Hubble diagram – low z
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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).
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Hubble diagram - SCP
0.2
0.5
1
0.2
In flat universe: M=0.28 [.085 stat][.05 syst]
Prob. of fit to =0 universe: 1%
0.4
0.6
0.8
1.0
redshift z
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Supernova Cosmology
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SNAP: The Third Generation
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Dark Energy Equation of State
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Dark Energy Exploration with SNAP
Current ground based compared with
Binned simulated data and a sample of
Dark energy models
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SNAP/JDEM Mission Design
Wide field imaging from space
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NIR observations in core SNAP science
NIR allows observation of SNe
rest frame optical to high
redshift
Z = 0.8
Tracing the effect of dark
energy through cosmic
time requires probing to
high-redshift
Optical
Bands
Rest frame optical shifts
into NIR after z=0.9
NIR
Bands
Large wavelength
coverage provides
important constraints on
systematic errors
Z = 1.2
Z = 1.6
Simulated SNAP observations of high redshift SNe
Substantially enhances
auxiliary science
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NIR Science drivers
Spatial and wavelength coverage:
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NIR data for all SNe to constrain systematic errors
 focal plane to match CCDs which cover the visible
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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:
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Noise should be dominated by unavoidable zodiacal light
— dark current < 0.02 e- / pixel / sec
— read noise < 5 e-
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Signal levels should be sufficient to allow precise observation of SNe
near peak with adequate S/N out to z=1.7 within time constraints
— quantum efficiency > 60%
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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 m
to 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
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NIR detector R&D
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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
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Proposed involvement in NIR R&D
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Caltech astronomy has a
strong, experienced team of IR
instrumenters, led by Keith
Taylor and Roger Smith
Caltech/UCLA
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They are involved in many
projects; SNAP involvement
requires more participation.
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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).
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SNAP effort requires multiple
teams working together and
independently to develop key
technologies.
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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.
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Test dewar at Caltech OA
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Molybdenum detector heater plate
Flex circuit potted into cap of light tight
enclosure with silver filled epoxy:
— Thermal ground
— Light seal
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Labyrinth for light seal
Mount & enclosure on
electronics box
(dewar absent for clarity)
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Next Generation Test dewar
Access hatches in top plate
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
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Goals for automated test dewar
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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.
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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.
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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.
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