DARK MATTER IN THE DARK MATTER IN THE UNIVERSE?UNIVERSE?

PRESENTED BY L. KULL AT PRESENTED BY L. KULL AT THE R.H.FLEET SCIENCE THE R.H.FLEET SCIENCE

CENTER December 14,2005CENTER December 14,2005

Why be concerned about the Why be concerned about the amount of matter in the universe? amount of matter in the universe?

Start with Einstein’s Field Equations (they describe the Start with Einstein’s Field Equations (they describe the relationship between energy density and the curvature of relationship between energy density and the curvature of the universe).the universe).

Use the Robertson-Walker metric to describe the geometry Use the Robertson-Walker metric to describe the geometry of space/time (curved?) within these equations (this metric of space/time (curved?) within these equations (this metric also allows a description of a space which expands with also allows a description of a space which expands with time).time).

The result is the Friedmann Equation – today a popular The result is the Friedmann Equation – today a popular mathematical description of an expanding universe.mathematical description of an expanding universe.

This equation provides an important descriptive parameter, This equation provides an important descriptive parameter, a “critical energy density” directly related to a “flat” a “critical energy density” directly related to a “flat” universe which expands (asymptotically) forever.universe which expands (asymptotically) forever.

Could most or all of this energy density be provided by Could most or all of this energy density be provided by matter? If so, what form of matter?matter? If so, what form of matter?

Einstein’s Field Equations – A Link Einstein’s Field Equations – A Link Between Physics and GeometryBetween Physics and Geometry

Geometry – The Robertson Walker Geometry – The Robertson Walker (R-W) Line Element(R-W) Line Element

Critical Density from Friedmann Critical Density from Friedmann EquationEquation

The mass density of visible matter The mass density of visible matter (stars)(stars)

The mass of those forms of invisible The mass of those forms of invisible matter we know something about.matter we know something about.

Gas clouds (ionized and neutral) Gas clouds (ionized and neutral) In our galaxy ~1/10 of the star mass. In our galaxy ~1/10 of the star mass. In the Coma galaxy cluster~6 In the Coma galaxy cluster~6 times the star mass.times the star mass.

Planets, asteroids, dust.Planets, asteroids, dust. MACHOs Massive Compact Halo MACHOs Massive Compact Halo

Objects (black holes, neutron stars, Objects (black holes, neutron stars, dwarfs) - to be discussed.dwarfs) - to be discussed.

Neutrinos –to be discussed.Neutrinos –to be discussed.

Measuring the mass of MACHOs Measuring the mass of MACHOs (Massive Compact Halo Objects) (Massive Compact Halo Objects)

Estimates of the mass of neutrinos Estimates of the mass of neutrinos in the universe.in the universe.

A Model for the Determination of A Model for the Determination of the Baryon Energy Density of the the Baryon Energy Density of the

UniverseUniverse

Calculated Results from the ModelCalculated Results from the Model

The Baryon Density of the UniverseThe Baryon Density of the Universe

Orbital Velocity of Stars and Gas Orbital Velocity of Stars and Gas around Galaxies – best evidence around Galaxies – best evidence

for DARK MATTER for DARK MATTER

Dark Matter Detection Problem – Dark Matter Detection Problem – Big PictureBig Picture

Dark Matter Detection Problem – Dark Matter Detection Problem – Small PictureSmall Picture

Detection Mechanisms for Nuclear Detection Mechanisms for Nuclear Recoil Energy DepositionsRecoil Energy Depositions

Problem:Problem:very small signal and very small signal and VERY LARGE VERY LARGE BACKGROUNDSBACKGROUNDS

BackgroundsBackgrounds cosmic rays and secondary particles (neutrons)cosmic rays and secondary particles (neutrons) detector impurities (radioactive and non)detector impurities (radioactive and non) thermal noisethermal noise ambient natural radiation (gamma and neutron)ambient natural radiation (gamma and neutron)

Low Background Design Features•underground locations (deep mines)•exterior shielding (passive and active)•ultra pure detector material•detector cooling (cryogenic levels)

DAMA DetecrorDAMA Detecror

Target material: NaI Target material: NaI

Total target mass: 100 kgTotal target mass: 100 kg

Operating temp: ambient Operating temp: ambient

Location: Gran Sasso, ItalyLocation: Gran Sasso, Italy

DAMA Data – no confirming data DAMA Data – no confirming data from other experiments - (???)from other experiments - (???)

CDMS DetectorCDMS Detector Target material: Ge/Si Target material: Ge/Si

(100g/250g) crystals(100g/250g) crystals Total target mass:7 kgTotal target mass:7 kg Operating temp: 0.01KOperating temp: 0.01K Location: Soudan Mine, Location: Soudan Mine,

USAUSA

ZEPLIN II DetectorZEPLIN II Detector Target material: Xe (l & g)Target material: Xe (l & g) Total target mass: 30 kgTotal target mass: 30 kg Operating temp : ~3KOperating temp : ~3K Location: Boulby Mine, UKLocation: Boulby Mine, UK

Dark Matter Detection Experiments Dark Matter Detection Experiments and Collaborationsand Collaborations

Current Estimated Detection LimitsCurrent Estimated Detection Limits

Detection Techniques vs. Detection Techniques vs. Experiments/CollaborationsExperiments/Collaborations