The Syracuse HEP group was a lead institute on the BTeV experiment. Prof. Sheldon Stone was co-spokesperson, along with Joel Butler from Fermilab. The experiment was proposed in 1996, and was intended to begin running after the CDF and D0 experiments, ended their data runs in 2009. The layout of the BTeV experiment is shown below.
The BTeV experiment would have been a competitor to the LHCb Experiment at CERN, with similar physics goals, namely to search for new physics in the decays of beauty and charm hadrons.
The Syracuse group had a major role in the construction of BTeV. Our group was responsible for the design and construction of the BTeV Ring Imaging Cherenkov Detector (or RICH, for short). Cherenkov detectors exploit the fact that when charged particles exceed the speed of light in a medium with index of refraction n, they emit radiation (photons) at a characteristic angle, given by cos θ= 1/(βn), where β=v/c is the particle speed relative to the speed of light. In RICHs, a focusing mirror is use to reflect and focus the photons onto a ring at the focal plane of the mirror. Thus, the measurement of the Cherenkov angle of photons from a particle, gives a measurement of β. We also know the momentum, p, of the particle as it bends through the BTeV magnetic field. Since p = (1-β2)-1/2 mv, this allows a determination of the particle’s mass m. Knowledge of its mass is equivalent to identifying the particle type, e.g. whether it is a proton, kaon or pion.
A rendering of the BTeV RICH is shown in the figure below to the left. The BTeV RICH was to use two radiators: (1) a C4F8O gas radiator that filled most of the volume, and (2) a 1-cm thick liquid C5F12 radiator (green square in figure). The liquid radiator provided K/p separation below about 10 GeV, and the gas radiator provided about 4σ K/π separation up to 70 GeV.
The right figure above shows a top view of the BTeV RICH, and superimposed is a sketch of a test vessel built for a beam test of the BTeV RICH, carried out at Fermilab. Protons with 120 GeV momentum enter the vessel containing the C4F8O gas from the bottom. The Cherenkov photons that are radiated from the protons are reflected off a mirror at the end of the vessel and are imaged at the plane containing the MAPMT (Multi-anode PhotoMultiplier Tube) array.
A photo of the tesbeam setup is shown below. The V-shape of the vessel is evident. The protons enter from the right (moving left). The glass mirror is on the left side, and the MAPMT array is at the the other end of the vessel opposite the mirror. The MAPMT array was only partially populated to cover the region where the photons were expected to strike the array. Shown in the picture are (left to right) JC Wang, Ray Mountain and Steve Blusk.
The figure below (left) shows the photons detected by the MAPMTs for a single 120 GeV proton. The photons form a circle, as expected, and about 50 photons are detected, also consistent with expectations. From the radius, an angle can be computed, and this can be done for a large ensemble of protons. Because the protons are very high momentum (120 GeV), all Cherenkov rings should have the same radius, or equivalently, the same Cherenkov angle. The pair of plots to the right show the difference between the measured Cherenkov angle and the expected Cherenkov angle for (top) testbeam data and (bottom) simulation. The Cherenkov angle resolution in data is 109μrad, and is just a few percent larger than the expected value from simulation of 103 μrad. The resolution achieved in this first beam test was sufficient to meet the particle identification specifications for the experiment.
Additional details and results can be found in the publication:
M. Artuso et. al., Performance of a C4F8O gas radiator ring imaging Cherenkov detector using multi-anode photomultiplier tubes, Nucl. Instrum. and Methods A558 (2006) 373-387.