Hilger Crystals shipped the final CsI(Tl) crystal in May 1998 to Stanford University as part of a contract to supply 1500 crystals for the BaBar detector.[ Stanford Pictures... ]The complete detector barrel and end cap consists of 6720 trapezoidal shaped crystals some 35cm in length with a total volume of 6 cubic meters.[ BaBar Link... ]
Each crystal was individualy "tuned" to meet tight performance criteria and is used to detect the fundamental B and anti B particles which result in the assymmetric collision of electrons and positrons at a centre of mass energy of about 10 GeV in the PEP II collider at Stanford University.
The fundamental physics being examined is Charge - Parity (CP) Violation. By carefully reconstructing the decays of millions of particles and anti particles the BaBar detector will give an insight into the dominance of matter over anti matter in the creation of the universe, ten thousand million years ago.
Each crystal has a complex trapezoidal geometry in order that when they are assembled together almost all of the solid angle for the interactions is covered.
Also so that projective geometry is achieved, each crystal points to the interaction point -where the particles come from.
The crystals are read out using silicon photodiodes attached to one end of the crystal.
Apart from the commercial benefits of the project it has strengthened the links between Hilger and the collaborating institutes.
CsI(Tl) Crystals For BaBar Project at Stanford