Forward Tagger - JLab12

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Forward Tagger

Hardware Projects

The Forward Tagger is designed to detect electron scattered at small angle to perform quasi-real photo-production experiments with the CLAS spectrometer. In electron scattering on nuclear targets, the diffusion of electrons at angles of the order of a degree can be interpreted as due to the exchange of virtual photons with Q2 of the order of 10-3-10-2 GeV2, which are equivalent to real photons. The Forward Tagger, together with the CLAS12 spectrometer, will allow physicists to perform photo-production measurements utilizing the high quality electron beam provided by the CEBAF accelerator.The Forward Tagger (FT) will be installed inside the CLAS12 spectrometer, in between the Forward and the Central Detectors. I twill consist of an electromagnetic calorimeter (FT-Cal) to accurately measure the energy of the electron, of a tracker (FT-Trk) to precisely determine the scattering angles and of a scintillating hodoscope (FT-Hodo) to distinguish electrons from photons. The FT-Cal will be based on Lead-Tungstate crystals coupled to Avalanche PhotoDiode sensor for the scintillating light readout. The crystals will be kept at a temperature close to 0C, to enhance their light emission and improve the calorimeter performances in terms of energy resolution.The tracker will be formed by two pairs of Micromegas detectors with strip readout.

The strip of the two layers of each pair will be roated by 90 to determine the (x,y) coordinates of the electron impact point with spatial resolution of the order of 200 um. The hodoscope will be formed by plastic scintillator tiles, coupled to Silicon Photomultipliers via Wavelength Shifting Fibers. These technologies allowed to develop a compact design for a high performance detector system. The FT will detect electrons in the angular and energy ranges of 2.5-4.5 and 0.5-4.5 GeV, respectively, at the nominal luminosity of the CLAS12 spectrometer of 1035cm-2s-1. The new equipment will operate in magnetic field and high-radiation environment due to the proximity with the beamline. The expected energy resolution is of ~ 2.5% for 1-GeV electrons. The Forward Tagger project involves an international collaboration including Universities and Research Institutes of four nations, as INFN, IPN-Orsay (France), CEA-Saclay (France), the University of Edinburgh (UK), the James Madison University (USA), the Norfolk State University (USA), the Ohio University (USA) and Jefferson Lab. Financial contribution for the design and construction of the detector have been provided by INFN, the UK Research Council, the US Department of Energy and National Science foundation and the European Union.The Forward Tagger is presently in the construction phase and will be installed at Jefferson Lab in the Fall of 2015.

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