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Introductory remarks Outline of physics concepts Description of the experiment Results

CDMS (Cryogenic Dark Matter Search) Long Duong (University of Minnesota) Trinity School Seminar Jan 14, 2004. Introductory remarks Outline of physics concepts Description of the experiment Results. ~ 40 physicists/students from 8 institutions work on CDMS

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Introductory remarks Outline of physics concepts Description of the experiment Results

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  1. CDMS(Cryogenic Dark Matter Search)Long Duong (University of Minnesota)Trinity School SeminarJan 14, 2004 • Introductory remarks • Outline of physics concepts • Description of the experiment • Results

  2. ~ 40 physicists/students from 8 institutions work on CDMS (experimental site is the Soudan mine in northern MN) UCB (UC at Berkeley), UCSB (UC at Santa Barbara), Santa Clara, Stanford, Colorado U, NIST (Colorado), LBL (Lawrence Berkeley Lab) CWRU (Case Western Reserve), Brown, UMN (U of Minn in Mpls), FNL (Fermi National Lab)

  3. Physics Concepts • Atomic theory of matter • Standard model of physics • Gravity • Light matter (Dark matter) • Temperature (evaporative cooling) • Ionization (or release of bound electrons) • Phonon (or lattice vibration of a solid)

  4. Electric charge of various particles e = -1 p = +1 n = 0 u = +2/3 d = -1/3

  5. Standard Model of Physics * everything is made of quarks and leptons * interactions occur via exchange of mediators Quarks (charge)Leptons (charge) u c t (+2/3) e mt (-1) d s b (-1/3) nenmnt (0) Strength Mediator Participants 1 photon all nonzero 10^(-11) W+, W-, Z0 all Higgs boson all 1000 gluon quarks only 10^(-40) graviton all

  6. Gravity: least understood of all the forces

  7. F (on sun) = G * M(bulge) * M(sun) / (R * R) + F (from other stars) = M(sun) * (V * V) / R => V = sqrt[ (G/R) M(bulge) ] + …

  8. Rotation curve of the Milky Way spiral galaxy cannot be explained only by the observed light matter. Some possible explanations: * gravity is modified on large scale * existence of a “dark” matter halo (dark matter hypothesis favored from other evidence, e.g. weak gravitational lensing studies of sky)

  9. Layout of CDMS experiment Thermal stages of a dilution refrigerator: room temp. 293 K (red) OVC (outer vacuum chamber) liquid N 77 K (yellow) liquid He 4 K (green) IVC (inner vacuum chamber) pot 1 K (light blue) still 0.6 K (light blue) cold Plate 0.05 K (dark blue) mixing chamber 0.01 K (black) Ebox Detectors (ZIP) (at 0.01 K stage) Dilution Refrigerator Icebox

  10. Temperature (kinetic theory of thermodynamics) Temperature a measure of the average energy in the random motion of a very large (~10^25) number of atoms that make the gas, liquid or solid phase of a material thermodynamic equilibrium liquid temperature = T gas pressure = P pump on gas phase liquid temp < T gas pressure < P

  11. Germanium/Silicon crystals as particle detectors • Two quantities can be measured when • a WIMP (or any particle) scatters off • some constituent of a crystal: • Lattice vibrations (phonons) • Electronic shells are excited • and electrons are freed from • being bound to a particular • nucleus (ionization) dark matter particle in the galactic halo WIMP (Weakly Interacting Massive Particle)

  12. Each ZIP detector has 4 phonon (A, B, C, D) and 2 ionization sensors (Qi, Qo)

  13. Picture of a ZIP detector phonon sensors Copper case is thermally connected to the 0.01 K layer of the icebox

  14. Two kinds of interactions with a ZIP constituent * scattering from an electron (electron recoil) * scattering from a nuclei (nuclear recoil) electron recoils (data from Cs source) nuclear recoils (data from Cf source) This is the region CDMS uses to search for WIMPs

  15. Why are we ½ mile underground to conduct the experiment? On the earth’s surface, there is a constant flux of cosmic radiation in the form of high energy muons. These muons interact with the rock, etc., to produce neutrons (cosmogenic) that pollute the WIMP search region. By going deep underground, we shield the ZIP detectors from these high energy muons. We also use a variety of lead/polyethylene shields to block neutrons, etc., that occur naturally in rocks.

  16. CDMS Shielding Scheme outer polyethylene shield muon veto paddles outer lead shield icebox inner lead shield ZIP detectors inner polyethylene shield

  17. Current World Limits for Dark Matter Searches CDMS limit using Stanford data DAMA signal region EDELWEISS limit Projected CDMS limit for Soudan data running Shaded regions are various theoretical predictions of SUSY Projected limit of a 1-ton cryoarray

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