ArDM  - Argon Dark Matter experiment

 
 

Astronomical observations give strong evidence for the existence of non-luminous and non-baryonic matter, presumably composed of a new type of elementary particle.  A possible candidate is the Weakly Interacting Massive Particle (WIMP). If they exist, WIMPs should form a cold thermal relic gas, which could be detected via elastic collisions with nuclei of ordinary matter. The detection of these WIMPs is based on the capability of measuring the recoils of target nuclei with kinetic energy in the range of 10-100 keV. The signal is therefore quite elusive and is expected to be a rare event given the weak coupling between WIMPs and ordinary matter.


Noble liquid detectors using Xenon or Argon can efficiently act as targets for Weakly Interacting Massive Particles (WIMP) detection. Xenon or Argon provide a high event rate because of their high density and high atomic number and large target masses are readily conceivable.  They have high scintillation and ionization yields because of their low ionization potentials.  Both scintillation and ionization are measurable and can be used to very effectively discriminate between nuclear recoils and gamma/electron backgrounds.


The use of noble liquid gases to detect WIMP dark matter is currently the subject of intense R&D carried out by a number of groups worldwide. In these detectors, one relies on the simultaneous detection of the ionization charge and of the scintillation light produced during a nuclear recoil event.  A main subject for any such detector is the method of the readout for the ionization and scintillation. 

 

In 2004 we have initiated the Argon Dark Matter experiment. The goal of this project is to design, assemble and operate a bi-phase ≅1 ton Argon detector with independent ionization and scintillation readout, to demonstrate the feasibility of a noble gas ton-scale experiment with the required performance to efficiently detect and sufficiently discriminate backgrounds for a successful WIMP detection. 

 

Given the challenging nature of the experiment which requires innovations both at the level of the detection methods and at the level of background rejection, our immediate plan is to fully design and acquire the needed equipments to setup and operate the 1 ton prototype at CERN. The operation of the prototype will involve cryogenic, LAr purification, HV system, drift volume, charge amplification plus readout, and light readout.  It will allow us to define and set up all the necessary equipment and infrastructure for a safe operation of the detector.

Our first milestone is a proof of principle and stability studies, and further optimization of the design for a highly efficient γ-ray and beta electron (39Ar) rejection vs.  nuclear recoils. 


Assuming the successful operation of the prototype, we will consider a deep underground operation. With the assumed recoil energy threshold of 30 keVr, a WIMP-nucleon cross-section of 10-44 cm2 would yield 1 events per day per ton.

Illustration of the principle of operation of a double phase dark matter detector.