Title: Large acceptance magnetic spectrometer for the 12 GeV2 GEp experiment

Authors: @@@ GEp spokespeople ? suggestion very welcome @@@

The JLab beam energy upgrade combined to high intensity and longitudinally polarization will offer new
opportunities to improve our understanding of the nucleon structure.
In this direction, the HallA experiment GEp5, will investigate the electromagnetic form factors ratio GE/GM of the proton at high Q2, 
by the measurement of the polarization transferred from the longitudinal polarized electron of the beam to the elastically 
scattered proton. 

GEp5 is the last of a series of successful experiments that measured a linear decrease of the GE/GM 
ratio with Q2, breaking up 
our view of the mechanism of the electron scattering and
renewing critical interest on our understanding on the nucleon structure from form factor measurements.

The foreseen GEp5 measurements at higher Q2, will extend the previous measurement to region where a possible
deviation from linearity could be expected; data can be compared with expectations 
from perturbative QCD and can give new hints on the role of the elusive measurement of the
quark orbital angular momentum.

To compensate the large drop of the elastic cross section with Q2, 
the GEp5 experiment needs to run at the highest beam polarization and luminosity, 
with large acceptance detectors and high efficiency proton polarimeter.

These requirements are fulfilled by the development of a new liquid hydrogen target and 
the new Super Bigbite Spectrometer (SBS).
SBS will use a conventional setup with state of the art detectors:
an existing dipole magnet from BNL, with large gap and field integral up to 2 Tm
will be properly adapter to reach forward scattering angles; 
large Gaseous Electron Multiplier (GEM) based chambers
will be used both as tracker for the primary proton and the scattered secondary in the polarimeter.
A newly designed shashlik calorimeter with rather high segmentation will complete the detector setup.

Details of the Super Bigbite Spectrometer will be gived at the meeting as well as a short summary of 
the GEp experiment and its physics motivations.