Fleet of ZEPLIN step up search for dark matter particles (Forwarded)

Royal Astronomical Society
London, U.K.

Issued by RAS Press Officers:

Robert Massey
Tel: +44 (0)20 7734 4582
AND
Anita Heward
Tel: +44 (0)1483 420 904

NATIONAL ASTRONOMY MEETING PRESS ROOM (16 - 20 APRIL ONLY):
Tel: +44 (0)1772 892 613
+44 (0)1772 892 475
+44 (0)1772 892 477

RAS Web site:
http://www.ras.org.uk/

RAS National Astronomy Meeting web site:
http://nam2007.uclan.ac.uk

CONTACTS:

Dr Alexander Murphy
Room 8208
James Clerk Maxwell Building
The King's Buildings
Mayfield Road
Edinburgh
EH9 3JZ
Tel : 0131 650 5285
Fax : 0131 650 7002

Prof. Tim Sumner
Imperial College London
Tel: 020 75947552

Prof. Nigel Smith
Rutherford Appleton Laboratory

PRESS INFORMATION NOTE: RAS PN 07/27 (NAM23)

EMBARGOED FOR 00:01 BST, WEDNESDAY, 18 APRIL 2007

FLEET OF ZEPLIN STEP UP SEARCH FOR DARK MATTER PARTICLES

The race for the first direct detection of dark matter will move into a
new phase in the coming months as the ZEPLIN-II instrument is joined by
ZEPLIN-III, the world's most sensitive dark matter detector.

Dr Alexander Murphy, who is presenting the first results from the
ZEPLIN-II detector at the RAS National Astronomy Meeting in Preston on
18th April said, "ZEPLIN-II is beginning its second search for dark matter
particles, deep underground in a salt and potash mine in North Yorkshire,
and we have been pouring through the first data looking for possible
interactions with dark matter. Now, just last week, we've had the go-ahead
to start operating our next generation detector, ZEPLIN-III. We will be
tweaking both detectors to improve their sensitivity all the time and,
over the next few months, we'll be able to see signals that are many times
fainter. This will give us a fantastic chance of making the first direct
detection of a dark matter particle."

The ZEPLIN-II instrument holds 31 kg of liquid xenon, cooled to a
temperature of -110 deg Celsius. Theory suggests that, from time to time,
a dark matter particle will scatter from the xenon leaving a very small
signal behind. Extremely sensitive light detectors view the xenon looking
for such a telltale sign. ZEPLIN-II, has proved the world's most sensitive
detector of this type (noble liquid technology) and is surpassed only by
the Cryogenic Dark Matter Search (CDMS), based in Minnesota, which uses a
semiconductor technology. With a few tweaks, the team expects ZEPLIN-II to
be able to match the sensitivity of CDMS within a few months.

The upgraded ZEPLIN-III, although not significantly bigger than ZEPLIN-II,
will be able to achieve a sensitivity that is a factor of 30 better than
CDMS, although it should take about two years to reach this level of
operation. This factor of 30 is especially important because the
theoretical models predict that this is the level of sensitivity needed to
have a realistic chance of seeing a signal.

The major benefit of noble liquid technology over semi-conductor
technology is that it is more easily scalable, which means that it should
allow for bigger detectors in the future. Features of ZEPLIN-III include
a much better ability to reject background events, lower radioactivity of
materials used in construction to minimise contamination and spurious
signals, and the use of higher electric fields to improve discrimination
against any remaining background.

FURTHER INFORMATION

Dark Matter

Since the 1930's it has been apparent that the Universe is made up of more
than just the things we can see. It is now widely accepted that a large
fraction of the Universe consists of 'dark matter' in the form of a new
type of fundamental particle. These dark matter particles constitute about
90% of the mass of our galaxy and are constantly passing through the Earth
itself. Evidence for this comes from a diverse, yet consistent, array of
astronomical observations and is supported by advanced theories of
particle physics that seek a deeper symmetry to explain the forces of
nature. Crucially however, no direct observation of these dark matter
particles has yet been made.

The ZEPLIN Project

The ZEPLIN Project team is composed of scientists from the Universities of
Edinburgh, Oxford and Sheffield, Imperial College London and the
Rutherford Appleton Laboratory. International collaborators include
scientists from the University of Coimbra, Portugal, the University of
California, Los Angeles, USA, Texas A&M University, USA, and the
University of Rochester, USA. UK funding is provided by the Science and
Technologies Facilities Council.

The project's first detector, ZEPLIN-I, ran between 2001 and 2004. It was
the first generation of this style of detector and had a target of 3.2 kg
of liquid xenon. For more information see
http://www.shef.ac.uk/physics/resear.../dm/zeplin.php

The ZEPLIN detectors have all been located in the Boulby Underground
Laboratory, in the Boulby Mine, near Whitby, Yorkshire, on the North East
coast of England. For more information see
http://www.pppa.group.shef.ac.uk/boulby/boulby.php

A paper on results from ZEPLIN-II, "First limits on WIMP nuclear recoil
signals in ZEPLIN-II: a two phase xenon detector for dark matter
detection" has been submitted to the journal, Journal Astroparticle
Physics. The submitted paper is available at
http://arxiv.org/PS_cache/astro-ph/p.../0701858v2.pdf

IMAGES

Images of ZEPLIN-II and ZEPLIN-III can be found at:
http://astro.ic.ac.uk/Research/ZEPLIN-III/