SBS - GEM - JLab12

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Hardware Projects > SBS

The Super Bigbite Spectrometer is a new detector assembly designed for high precision experiments with the 12 GeV JLab beam, that will access unexplored kinematics regions and observables not measured yet
(visit the web page). Installed in the Hall A, SBS will provide a solid angle of about 70 msr (tunable), pretty good resolutions: vertex (< 2mm), momentum (dp/p 0.5% at 4 GeV/c) and angular (about 1 mr), configuration flexibility (for optimal experimental setup), and most of all it will be able to operate at very high luminosity up to 10^39 (cm^2 s)^-1. Measurements of the nucleon form factors at high Q^2 and of relevant Transverse Momentum Dependent quark distribution functions in the neutron, are the key experiments of the physics program of SBS. Challenging aspects of the new spectrometer are the two charged particle trackers based on the GEM (Gaseous Electron Multiplier) technology which has been invented and developed an the end of the ‘90s at CERN by F.Sauli and collaborators (show the document). The GEM detector has demonstrated to be able to sustain the large particle flux of the high luminosity experiments. Members of JLab12 are responsible of the design and development of the front tracker, which will reconstruct the tracks of the primary charged particles, those coming from the scattering process in the target region.

The front tracker is made of 6 large chambers (40x150 cm^2 each), about the largest used in experiments for fundamental physics (outside CERN), located after the dipole magnet (adapted 48D48 from Brookhaven National Laboratory). Each chamber is composed of 3 independent modules, of size 40x50 cm^2 with active area above 90%, in triple GEM configuration with 2dimensional strip readout, that will stand a photon flux of the order of 250 MHz/cm^2 with a single hit resolution of about 70 m. The GEM technology is probably the mandatory choice to fulfill such challenge requirements while keeping the cost relatively low.In fact, the independence of the electron multiplication process from the ionization and charge collection permit the GEM chamber to tolerate high particle flux and at the same time to provide resolution at the level of few tens of m. Moreover, the production processes and materials are rather common in electronics industry. Two small microstrip silicon planes (10x20 cm^2), before the 48D48 magnet, will complete the front tracker, extending the detection arm length, and therefore improving the overall tracking capability, with small effect on background flux and costs. Both detectors will be readout by the same electronics specifically developed around the APV25 chip. Groups from Bari (gas system and test), Catania (simulation, assembling, mechanical design), Genova (readout electronics), Sanità (coordination, simulation, design, analysis) and Rome (silicon microstrip) collaborate to the development of the front tracker.

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