CERN Hybrid Oscillation Research apparatus
CHORUS in brief
In the CHORUS experiment, we have analysed the interactions of a pure neutrino beam of a particular type (the muon neutrino νµ) generated by the large CERN SPS accelerator between 1994 and 1997. Our detector has an extremely high spatial resolution and is very sensitive to the detection of interactions generated by another type of neutrino (the tau-neutrino ντ). This would have been the sign of an oscillation between the two types of neutrinos. The search is now complete and no tau neutrino event has been found. This places a new limit on the νµ-ντ oscillation probability in the domain of neutrino masses relevant for astrophysics and cosmology. The observation of such a neutrino oscillation phenomenon would demonstrate that neutrinos have mass like all the other constituents of matter and can thus contribute to the dark matter of the Universe – i.e. matter whose existence is inferred only through its gravitational effects. There is evidence that this matter is mainly composed of particles that have survived from the Big-Bang and are not the usual protons, neutrons and electrons that constitute the ordinary matter. Big-Bang cosmology indeed predicts that there are about 1 billion times more neutrinos than protons in the Universe.
For more on neutrino oscillation, click here
A 1-plot summary of CHORUS results on neutrino oscillation
The figure above shows the domain of excluded values for the two physics parameters that govern the oscillation phenomenon between two families of neutrino - in this case nm and nt - the mixing angle θ and the square of the mass difference ∆m2. The green lines are the CHORUS limits for two kinds of statistical analyses, in purple, the result obtained by the sister experiment NOMAD and in black the limit obtained from a combined analysis. The regions of values above the curves are excluded by the non-observation of oscillation.
More on the CHORUS detector
The CHORUS detector is an hybrid detector that includes a very-high spatial resolution photographic "nuclear" emulsion target in which the signature of the very short track (~1mm) left by the short lived t- lepton created in the nt interaction can be efficiently observed, and a set of electronic detectors (trackers, calorimeters and spectrometers) to predict the position of the events in the target and perform the kinematics analysis. The figure to the right is a schematic representation of the detector showing the emulsion target region, the hadron and muon spectrometers and the calorimeter, all instrumented with planes of trackers of appropriate resolution
Charm particles in CHORUS:
The analysis of the production and decay of charm particles (one of the constituents is a charm quark) in neutrino interactions is the main by-product of the spatial resolution of the CHORUS experiment as statistical samples of one to two orders of magnitude larger in size than previously available are being gathered. The event on figure below is the production of 
a meson and its subsequent decay chain 
.The dots are the grains left by the charged particles in the nuclear emulsion. Note the scale.
You want to know more?
Click here to know more on CHORUS, here to access the list of CHORUS publications, here for a link to CERN and here to access the site of the neutrino oscillation industry and related sites in the domain of astrophysics and cosmology.
Or contact Pierre Vilain or Gaston Wilquet at IIHE-ULB
What next?
OPERA is the next generation neutrino oscillation experiment in which we involved.
CHORUS Collaboration
The CHORUS collaboration consists of about 110 physicists working in 25 laboratories in 9 countries from Europe, Russia and Far-East.
CHORUS at IIHE
Engineers and physicists from IIHE who have worked for CHORUS :
Patrio Annis, Jean-Paul Dewulf, Redouane El Aidi, Magali Gruwé, Chantal Mommaerts, Guy Van Beek, Muriel Vander Donckt, Bart Van de Vyver, Pierre Vilain and Gaston Wilquet.
Main hardware contributions of IIHE to CHORUS:
· Scintillating fibres trackers of the hadron spectrometer
· Image intensifiers and CCD camera read-out of trackers
· Trigger
· Large emulsion trackers
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Main contributions to the analysis:
· Conceptual design of the experiment
· Monte-Carlo simulation programme
· Trackers alignment, track reconstruction and hadron momentum measurement
· Analysis of the t- -> hadrons decay channel
· Semi-leptonic branching ratio of charm hadron decays and measurement of Vcd
