Spin Dependent Interactions?

1
Dark Matters
Mavourneen Wilcox Physics 711 Presentation
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Overview

• Definition
• Current Understanding
• Some Methods of Detection
• Final Remark

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Definition of Dark Matter

• Matter that can be observed by its gravitational
  effects, but does not emit light.

Dark Matter
Luminous Matter
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Strong Gravitational Lensing

• HST image of background blue galaxies lensed by
  orange galaxies in a cluster
• Einsteins rings can be formed for the correct
  alignment

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Rotation Curves of Galaxies
What we expect
Mass of a galaxy grows with radius. Requires dark
matter halo.
What we observe
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Hot or Cold

• Dark Matter Comes in two forms

Hot Dark Matter (HDM) -A form of non-baryonic
dark matter with individual
particle masses not more than 10-
100 eV/c2 (e.g., neutrinos) -relativistic
velocities Cold Dark Matter (CDM) -a form of
non-baryonic dark matter with typical mass
around 1 GeV/c2 (e.g., WIMPs) -able to form
smaller structures like galaxies -more massive
and slower
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Baryons vs. Non-Baryons

• CDM may be made of two types of matter

Baryons -Strongly interacting fermions -Ordinary
matter such as MACHOs, white, red or
brown dwarfs, black holes, neutron stars, gas
and dust. Non-Baryons -Formed during the Big
Bang -Suitable candidate not directly observed
yet are WIMPs or other Supersymmetric particles
and axions.
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MACHOs
MAssive Compact Halo Objects

• Brown Dwarfs
• Exist in the halo of galaxies
• Attempts to explain Cold Dark Matter without new
  particles

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WIMPs
Weakly Interacting Massive Particles

• Undiscovered non-baryonic particle
• Interacts only through the weak and gravitational
  forces
• High mass corresponds to a lower kinetic energy,
  making the particle cold

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General Consensus

• No WIMPs have been directly observed
• Groups studying MACHOs have not found enough
  objects to account for the missing mass problem

• Cold Dark Matter probably is a mixture of both
  baryonic and
  non-baryonic matter
• We still do not know for sure

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Detecting Wimps

• Several groups are currently running experiments
  to find WIMPs

• Cryogenic Dark Matter Search (CDMS)
• Cryogenically cooled GE and SI crystals
• DAMA Experiment
• Scintillation detectors
• Zeplin
• Liquid Xenon
• EDELWEISS
• GE Cryogenic
• All detect the collisions between a WIMP and a
  target nuclei

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Collision between a WIMP and target nuclei
A wimp will strike a target nucleus in the
detector material head on and cause an elastic
recoil.
The recoil energy depends on the mass and
velocity of The WIMP together with the Mass of
the target nucleus.
The energy can be measured in several ways,
depending on the Detector. A scintillation
photon may be emitted, an electric charge may be
liberated or a phonon may cause a slight rise in
temperature in the cryogenic material.
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Direct Search Principle
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DAMA

• Experiment running since 1996
• Located at Gran Sasso Lab, Italy, at a depth of
  1400 meters
• 9 ? 9.7 kg low-activity NaI (sodium-iodide)
  scintillator crystals, each viewed by 2 PMTs
• Known technology
• Low cost
• Large mass
• 107,000 kg-days exposure through July 2002
• Annual modulation in wimp signal 6.3s

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Signal of WIMPs
Earth motion through the galactic halo produce
asymmetries distinctive of WIMPs.

• Earth orbital motion around
• the Sun (15 km/s)

Annual modulation of the WIMP interaction rate.
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DAMA Results
Figure 10 Model independent residual rate for
single hit events, in the (24), (25) and (26)
keV energy intervals as a function of the time
elapsed since January 1-st of the first year of
data taking. The experimental points present the
errors as vertical bars and the associated time
bin width as horizontal bars. The superimposed
curves represent the cosinusoidal functions
behaviors expected for a WIMP signal with
a period equal to 1 year and phase at 2nd June
the modulation amplitudes have been obtained by
best fit. See text. The total exposure is 107731
kg day.
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CDMS II Overview

• Located at the Soudan mine in sunny Minnesota
• CDMS II is 2341 feet below the surface

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CDMS II

• Aim to measure nuclear recoil energy in Ge or Si
  semiconductor crystals following ?10- nucleon
  elastic scattering. Measure, or place upper
  limits on, WIMP-nucleus cross-sections.
• Both recoiling nuclei and electrons (due to
  photon background) produce phonons and
  electron-hole pairs (ionization) within the
  crystal. Two parameters characterize particle
  events.
• Ionization/phonon ratio (ionization yield)
  differs for electron and nuclear recoil. Allows
  for event-by-event discrimination.

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Sources of Background
Detectors must effectively discriminate between
Nuclear Recoils (Neutrons, WIMPs) Electron
Recoils (gammas, betas)
Use Ge and Si based detectors with two-fold
interaction signature - Ionization signal -
Athermal phonon signal
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CDMS II Setup

• Neutrons interact with matter in a similar way to
  WIMPs. No discrimination between Neutron and WIMP
  events.
• Soudan Mine
• Cosmic ray muons induce neutron production in
  matter. 800m rock overburden reduces muon flux
  by 5 x 104.
• Shielding
• 0.5cm of Cu, 22.5cm of Pb, 50cm of polyethylene
  provide shielding from neutron background of
  rock. Cu is low background and provides shielding
  from Pb background.
• Active Muon Veto
• A scintillator identifies 99 of all muon
  induced neutron events.

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Data analysis

• Fig 10. shows cuts (black lines) for neutron and
  gamma calibration. Blue dots nuclear recoils.
  Red dots electron recoil.
• Gives a low rate of misidentified surface
  events.
• Fig 11. shows plot of calibration data.
• Solid curves are the 2s electron-recoil band.
• Dashed curves are 2s nuclear-recoil band.
• Efficiency of combined cuts 0.4 in 20 keV 100
  keV range.

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Data Analysis 2

• Fig 12. shows a data plot for an exposure of 19.4
  kg day following timing and ionization cuts.
  Black vertical line is the 10 keV analysis
  threshold.
• Note missing nuclear recoil events. No candidate
  WIMP events for total exposure.
• Triangles and plus marks are Surface electrons
• Null result used to set upper limit on
  WIMP-nucleus rate/cross-section.

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CDMS II Limit

• Factor of 4 below best previous limits set by
  EDELWEISS
• New analysis methods and increased exposure
  promises 20x improvement over current limit
• Set an upper limit on the WIMP-nucleon
  cross-section of 4X10-43 cm2 at the 90 C.L. at a
  WIMP mass of 60Gev/c2 for coherent scalar
  interactions and a standard wimp halo.

• Whats Next?
• Currently operating 2 towers
• Adding 3 new towers over the next 6 months (4kg
  Ge, 1.4kg Si)

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The XENON Project

• A 1 tonne Liquid Xenon experiment for a sensitive
  Dark Matter Search
• Elena Aprile
• Columbia University

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The XENON Experiment Design Overview

• The XENON design is modular.
• An array of 10 independent 3D position
  sensitive LXeTPC (Time projection Chamber)
  modules, each with a 100 kg active Xe mass, is
  used to make the 1-tonne scale experiment.
• The TPC fiducial LXe volume is self-shielded by
  a few cm thick layer of additional LXe. The
  active scintillator shield is very effective for
  charged and neutral background rejection.
• One common vessel of 60 cm diameter and 60 cm
  height is used to house the TPC teflon and copper
  rings structure filled with the 100 kg Xe target
  and the 50 kg Xe for shielding.

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The XENON TPC Principle of Operation

• 30 cm drift gap to maximize active target ? long
  electron lifetime in LXe demonstrated
• 5 kV/cm drift field to detect small charge from
  nuclear recoils ? internal HV multiplier
  (Cockroft Walton type)
• Electrons extraction into gas phase to detect
  charge via proportional scintillation (1000 UV
  g/e/cm)? demonstrated
• Internal CsI photocathode with QE31 (Aprile et
  al. NIMA 338,1994) to enhance direct light
  signal and thus lower threshold ? demonstrated
• PMTs readout inside the TPC for direct and
  secondary light ? need PMTs with low activity
  from U/Th/K

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The XENON TPC Signals Nuclear Recoil
Discrimination

• Redundant information from charge (secondary
  light) signal (S2) and primary scintillation
  light (S1) signal from PMTs and CsI photocathode
• Background (g,e,a) produce electron recoils with
  S2/S1 gtgt0
• WIMPs (and neutrons) produce nuclear recoils with
  S2/S11
• 3D event localization for effective background
  rejection via fiducial volume cuts

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XENON Summery

• The XENON experiment is proposed as an array of
  ten independent, self shielded, 3D position
  sensitive LXeTPCs each with 100 kg active mass.
• The detector design, largely based on established
  technology and gt10 yrs experience with LXe
  detectors development at Columbia, maximizes the
  fiducial volume and the signal information useful
  to distinguish the rare WIMP events from the
  large background.
• With a total mass of 1-tonne, a nuclear recoil
  discrimination gt 99.5 and
• a threshold of 10 keV, the projected
  sensitivity for XENON is ? 0.0001 events/kg/day
  in 3 yrs operation, covering most SUSY
  predictions.

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Evolution of Direct Searches
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LSST (The Large Synoptic Survey Telescope)

• At least 8.4 meter telescope
• About 10 square degree field of view with high
  angular resolution
• Resolve all background galaxies and find
  redshifts
• Goal is 3D maps of universe back to half its
  current age

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Other Features

• A camera with over 3 billion pixels
• LSST's camera will produce 20 million megabytes
  of data every night.
• A single ten-second exposure will detect sources
  at 24th magnitude
• LSST will detect and classify 840 million
  persistent sources. Over time, LSST will survey
  30,000 square degrees. By adding together the
  first five years of data, the all-sky map will
  reach 27th magnitude, and its database will
  contain over three billion sources, not counting
  transient events.

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LSST will map the Dark Matter Universe

• From the warping of the visible matter, dark
  matter clumps can be seen, mapped and charted
  over their development.
• To see the dark matter, one "inverts" the cosmic
  mirage it produces.
• Analysis of all the distorted images produces a
  unique map of the space-time warp caused by the
  unseen dark matter in the foreground cluster.

HST image of the cluster of galaxies, CL00241654
Analysis of all the distorted images in the HST
picture above .
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LSST will map the Dark Matter Universe
Here the a image of the distribution of mass from
the previous image is shown as a two-dimensional
surface, where the height of the orange surface
represents the amount of mass at that point in
the image. This mass distribution shows that
most of the dark matter is not clinging to the
galaxies in the cluster (the narrow, high peaks),
but instead is smoothly distributed.
Kochanski, Dellantonio,Tyson
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Pan-STARRS

• Panoramic Survey Telescope Rapid Response
  System
• Developed at the University of Hawaii's Institute
  for Astronomy
• The Pan-STARRS design is weighted towards
  detecting potentially hazardous objects in our
  Solar System like earth bound asteroids and
  comets but will be ideal for making three
  dimensional maps of the distribution of dark
  matter in clusters of galaxies.

PS1 - the Prototype Telescope
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Pan-STARRS

• Four comparatively small telescopes, each with a
  3 degree field
• A single observation with the broad-band filter
  will reach a 5 s depth of 24th magnitude.
• Determine positions on an individual image to
  within 0.07 arcseconds, based on an image size of
  0.6 arcseconds FWHM, and a signal-to-noise ratio
  of 5.
• 30,000 square degrees can be observed from
  Hawaii. PanStarrs looks at about 7 square degrees
  in each 30 seconds exposure, so in an eight-hour
  night it can map about 6,000 square degrees.
• Therefore it takes about a week to survey the
  whole sky once, using one filter.

4, 1.8-m concave primary mirror that follow the
Richey-Chretien design
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Final Thought

• The discovery of cold dark-matter particles
  would be one of the most important in the history
  of physics. It would clarify many questions
  concerning the birth, evolution and final destiny
  of our universe. A definitive confirmed discovery
  would certainly merit a Nobel prize and a
  distinguished place in history for those who
  provided the intellectual leadership
• Frank T Avignone

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References

• UKDMC http//hepwww.rl.ac.uk/ukdmc/ukdmc.html
• Microlensing planet search http//bustard.phys.nd
  .edu/MPS/
• Neutrinoless double ß-decay http//www.rcnp.osaka
  -u.ac.jp/kudomi/ELE5.html
• WIMP direct detection http//gaitskell.brown.edu/
  physics/dm/0009_IDM2000_York_Gaitskell/
• CDMS Collaboration http//cdms.berkeley.edu/
• Pan-STARRS WEBSITE http//pan-starrs.ifa.hawaii.ed
  u/public/
• http//www.lsst.org/lsst_home.shtml
• Perkins, D. H. Introduction to High Energy
  Physics, 4th Ed. 2000. CUP.
• Roos, M. Introduction to Cosmology, 3rd Ed. 2003.
  Wiley
• Liddle, A.R. An Introduction to Modern Cosmology.
  2nd Ed. 2003. Wiley.
• D.S. Akerib et al. "First Results from the
  Cryogenic Dark Matter Search in the Soudan
• Underground Lab". astro-ph/0405033.
• T. Saab, Search for Weakly Interacting Massive
  Particles with the Cryogenic Dark Matter Search
  Experiment, PhD Dissertation, Stanford University
  Aug. 2002.

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Web Resources

• Jonathan Dursis Dark Matter Tutorials Java
  applets
• http//www.astro.queensu.ca/dursi/dm-tutor
  ial/dm0.html
• MACHO project http//wwwmacho.mcmaster.ca/
• National Center for Supercomputing Applications
  http//www.ncsa.uiuc.edu/Cyberia/Cosmos/MystDarkMa
  tter.html
• Pete Newburys Gravitational Lens movies
  http//www.iam.ubc.ca/newbury/lenses/research.htm
  l
• http//www.dmtelescope.org/dark_home.shtml