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Particle Physics and Astronomy Research Council
Swindon, U.K.

Embargoed until: 15.00hrs, Tuesday 29th April 2003

90% of the Universe is Missing!

Part 1 of 3

The search for the missing mass of the Universe

The Universe around us is not what it appears. The stars make up less 
than 1% of its mass; all the gas clouds and other objects, less than
5%. This visible matter is mere flotsam on a sea of unknown
material -- so called 'Dark Matter' -- a descriptor which mainly
serves as an expression of our great ignorance of its nature. We know
little about that sea. We do know that about 90% of the material in
the Universe must consist of this invisible 'dark matter' in order
for stars to swirl round in galactic islands, for galaxies to cluster
together as they do, and for the Universe to look the way it does.
The mystery of the Universe's missing mass may be about to be
revealed as UK astronomers fine tune their sensitive detectors
situated 1100 metres beneath the North Yorkshire moors.

The Boulby Underground Laboratory for Dark Matter Research is
situated in a working salt and potash mine in Boulby on the North
Yorkshire coast. Here, UK scientists have installed their experiments
to detect Weakly Interacting Massive Particles [WIMPs], a prime
candidate for the missing mass of the Universe. The laboratory has
recently benefited from a £3.1M Joint Infrastructure Award [JIF],
providing enhanced underground laboratories and complementary surface
facilities to create one of the world's foremost research centres for
identifying and isolating the missing mass of the Universe.

Commenting on the new facility and its research programme Prof. Ian 
Halliday, Chief Executive of the Particle Physics and Astronomy
Research Council [PPARC], the UK's strategic science investment
agency, said," This is an outstanding research facility equipped with
some of the world's most sensitive dark matter detectors. It is a
crucial addition to the UK's resources in a research field where
British scientists are playing a world-leading role -- the race by
physicists around the globe to discover these exotic, as yet
undetected, dark matter particles. It would be a major coup for UK
science if we could win the race". 

Although billions of WIMPs are probably passing through us every
second, they hardly interact with ordinary matter and so are
extremely difficult to detect. Occasionally though they do knock into
the nuclei of atoms and the experiments at Boulby are designed to
detect these rare collisions. 

Prof. Neil Spooner of Sheffield University, one of the university
groups involved, likens detecting the elusive WIMP to playing
billiards with an invisible cue ball," You don't actually see the
WIMP, or cue ball itself, but you see the recoil of the billiard ball
as it hits. If we are successful in our quest then we are looking at
a place in the history books. This will be one of the great
discoveries of our time". 

Prof. Spooner and colleagues from the Rutherford Appleton Laboratory, 
Imperial College and the University of Edinburgh currently employ
three WIMP detectors using different materials.

In a sample of one kilogram of material, less than one WIMP a day
will hit the nucleus of an atom, causing it to recoil slightly. The
experiments will detect this recoil and record it.

However, because it happens so rarely, the detectors could also pick
up lots of other reactions -- such as cosmic rays hitting the
material, or natural radiation -- which is why the experiments are
housed 1100 metres underground. The Earth absorbs most of the
extraneous particles like cosmic rays from space, whilst the walls of
the salt mine, being very low in natural radiation, provide further
protection from the rocks of the Earth's crust.

For further information contact:

PPARC Press Office
Peter Barratt (at Boulby on Tuesday April 29th)
Tel: 01793 442025, Mobile: 0787 9602899
Email: peter.barratt{at}pparc.ac.uk

Julia Maddock (at Boulby from Sunday April 27th to April 30th)
Tel: 01793 442094, Mobile: 07901 514 975
Email: julia.maddock{at}pparc.ac.uk

Boulby Underground Laboratory for Dark Matter Research
01287 646300 or 01287 646301
(Please use these numbers if you can not contact the person you
need directly).

The UK Dark Matter Collaboration consists of: University of
Sheffield, CCLRC Rutherford Appleton Laboratory, Imperial College and
the University of Edinburgh.

Professor Neil Spooner
Department of Physics and Astronomy
University of Sheffield
Hicks Building, Hounsfield Road, Sheffield S3 7RH
Tel: +114 222 4422
Fax: +114 272 8079
Mobile: 0786 645 8107
Email: n.spooner{at}sheffield.ac.uk

Dr Nigel Smith
Particle Physics Department,
CCLRC Rutherford Appleton Laboratory,
Chilton, Didcot, Oxon, OX11 0QX
Phone: + 44 (0)1235 445151
Fax: + 44 (0)1235 446733
Email: n.j.t.smith{at}rl.ac.uk

Professor Tim Sumner
Astrophysics Group
Blackett Laboratory
Imperial College London
Prince Consort Road
London, SW7 2BZ
Tel: +44(0)2075947552
Mobile: +44(0)7876460864
Fax: +44(0)2075843465
Email: t.sumner{at}imperial.ac.uk

Dr Alex Murphy
Department of Physics & Astronomy
The University of Edinburgh
James Clerk Maxwell Building
The King's Buildings, Mayfield Road
Edinburgh EH9 3JZ
Tel: + 44 (0) 131 650 5285
Email: amurphy{at}ph.ed.ac.uk

Background notes:

UK experiments -- general methodology

WIMPs rarely interact with the matter they are passing through, (less 
than one WIMP a day will hit a nucleus in a kilogram of material) but 
this is the key to detecting their presence.

 - Continued -

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