CKOV1 folded geometry 1. Optimization 2. Pion-muon separation 3. Instrumented area 4. Possible developments November 16, 2005 Gh. Grégoire Contents

DISC geometry Detecting plane Optical window 30-mm thick radiator Diam. 300 mm Curved mirror surface 500 mm Advantage: setup becomes coaxial Possibility to optimize for minimal optical aberrations and distortions 2

Optimization 3 On the basis of the « folded geometry » proposed by L. Cremaldi/D. Summers Try to minimize « thickness » of Cherenkov rings by choosing the optimum shape of the mirror Figure of merit = Inverse of « spherical aberration » i.e. compensate for focal dispersion due to angular opening of Cherenkov cone large size of object (radiator) Best solution:slightly deformed paraboloid withc -1 = 1015 mm  2 =  4 =  6 = (z and r in mm) (longitudinal and transverse) 0 < r < 300 mm parabola (transverse distance to axis of symmetry)

Side view Nice focal spot Still some residual aberrations visible 4 Beam

Simulations Momenta190 to 280 MeV/c ( in steps of 10 MeV/c ) Gaussian beams  x-y = 50 mm  x’-y’ = 25 mrad From S. Kahn’s presentation, Phone conf. March 31, 2005 Radiator30-mm thick ParticlesMuons, pions and electrons (10 kevts each) Diameter = 300 mm 5 (to match Tom’s recent beam design) FC-72 and water

Results for  ’s and  ’s 600 mm 190 MeV/c280 MeV/c Inner ringsPions Outer ringsMuons 6 Water radiator Determine ring separation (distribution of hits along y axis for x=0) X Y

Ring separation       Good  -  separation to the baseline FC-72 radiator 190 MeV/c Water radiator 280 MeV/c Cut along y-axis Y Y Thickness of ring < 20 mm 7

Instrumented area Both rings are due to muons !Inner ring190 MeV/c Outer ring280 MeV/c Water radiator FC-72 radiator 470 mm < Diameter < 600 mm Width is about 130 mm 400 mm < Diameter < 500 mm Width is about 100 mm 8

CKOV1 with variable index One simple way to reduce the size of the instrumented area is to change the index of refraction according to the momentum The two rings are still due to muons of 190 and 280 MeV/c But the radiators areFC-72 (n=1.251) at 190 MeV/c Water (n=1.33) at 280 MeV/c Diameter is about 500 mm Width is 25 mm (i.e. easily covered by a single ring of 1.5 inch PMTs ) How to match the index of refraction between n=1.251 and 1.33 for 190 < p  < 280 MeV/c ? Mixture in varying proportions of FC-72 (n=1.251) and alcohol (n=1.362) 9

Possible developments If working with radiators adapted to muon momenta the Cherenkov ring has a nearly constant diameter Possibility of a fixed annular slit to make the device really « pion-blind » detect the photons after the annular slit by six strips of wavelength shifter material, arranged as an hexagon covering the slit. In total we would need only 6 PMTs. Simplicity Cost savings To proceed further it is essential to get recent beam files for muons and pions at the position of CKOV1 (according to the latest beam design) 10 CKOV1 would become a true built-in RICH

Full RICH setup ? Annular slit 11