1. Could CKOV1 become RICH? 1. Characteristics of Cherenkov light at low momenta (180 < p < 280 MeV/c) 2. Layout and characterization of the neutron beam 3. Study of the simplest optical configuration 4. Optical focusing geometries 5. Conclusions October 5, 2005 Gh. Grégoire Contents

2. Cherenkov cone 250 mm Radius of the ring Radiator 2.The identification is more difficult at the high momenta as the radii are more similar

3. Simplest configuration e, ,  Light cone centered on the beam axis Momenta parallel to beam axis (  =0)280 MeV/c 5 and 20 mm thick radiator Plane ideal mirror at 45°No optical aberrations (i.e. deformation of the Č rings) Photoelectrons for 20-mm radiator N e = 100 N  = 89 N  = 80  e = 48.2 degrees   = 44.6 degrees   = 41.9 degrees Opt. Glass BK7 n=1.5 No losses Lateral sizes fixed to get 100% light collection Flat detecting surface at 90° Particles hitting the center of the radiator (x=0 ; y=0) 3 Equal size samples Pixel size 2 x 2 mm²

4. Photon production The only (uniform) random variable is the z-coordinate of an emitted photon (radiator thickness !) affecting the « width » of the Cherenkov ring on the detecting plane Estimation of separation of pions, muons and electrons 4 neglecting the very small variation of  as a function of penetration in the radiator (energy loss)

5. Plane mirror Simple geometry 350 mm 585 mm Electrons Muons Pions 1200 mm X Y Pixel size = 2 x 2 mm 2 20-mm thick radiator ( Colors correspond to different particle species ) Sample size: 50 k pions 50 k muons 50 k electrons Diam. 250 mm 5

6. Intrinsic resolution   e 32 mm42 mm 1100 mm  R  4 mm Good separation for all particles Pixel size = 2 x 2 mm 2 6 Note. The separation of the rings and their « width » is matched to the anode sizes (2x2 and 4x4 mm²) of modern multianode photomultipliers.

7. Influence of radiator thickness Slightly smaller dispersions of radii for muons and pions (at the expense of light output) Large detecting plane due to plane mirror Optical focusing needed  100% light collection efficiency mandatory  R  3 mm   e Shifts due to refraction in the thicker radiator Conclusions At 280 MeV/c the thickness of the radiator has not much influence on imaging 7

8. Focusing geometries Non exhaustive ! Very preliminary ! Not optimized Plane mirror Spherical mirror R=-1100 mm Parabolic mirror R curv =-1500 mm  = -1  = 0 Spheroidal mirror R curv = -600 mm along X R curv =-1100 mm along Y More x-focusing obviously needed ! Goal: Č light produced at the focus to get a parallel beam after reflection and placing the detecting plane perpendicularly (for easy simulation/reconstruction)  400 mm 8 1200 mm

9. Conclusions 1. Except if there are no other physical/experimental constraints, the thickness of the radiator does not significantly affect the quality of imaging. (for reasonable thicknesses in the range 5 to 20 mm of glass) 2. Focusing geometries reduce the area of the photon detecting plane by about an order of magnitude w.r.t. a plane mirror while still keeping a good e-  -  separation 3. Could CKOV1 become RICH? But it still needs- a lot of optimization - detailed studies of aberrations with particles off axis 9 At the highest momenta in MICE - to ease the simulation and analysis The separation is easier at the lower momenta - but aberrations will not destroy the separation possibilities Yes, it is possible to separate e-  -  at the position of CKOV1 with RICH techniques With reasonable pixel sizes With acceptable radiator thicknesses