1. e-  identification 1. Reminder from previous presentations, questions, remarks 2. Čerenkov option 3. Study of several optical configurations 4. Conclusions Gh. Grégoire June 10, 2002 University of Louvain

2. A Čerenkov for e-  identification a) Sampleelectrons muons (from P. Janot)4256 10000from the simulation of a cooling channel Starting point Relative populations of electrons vs muons are not normalized ! b) Previous presentations http://www.fynu.ucl.ac.be/themes/he/mice

3. Spatial distributions Beam spot ~300 mm diam. ~ size of the radiator Numerical aperture (f-number) = ~ 1.5 x y  xz  yz Divergence  ~ 20°

4. Angular and energy distributions Angle with respect to beam axis Kinetic energy distribution It is not obvious (to me) to separate e-  on calorimetric principles at such low electron energies! Electrons have very low energies ( E< m  )

5. Č radiator n= 1.25 n= 1.25 Distribution of light yield Distribution of Čerenkov angle ( 10 cm thick radiator ) 200-400 photoelectrons Overlap between the angle distributions

6. Questions Consequences of - large beam spot - large beam divergence - energy distributions - Overlap of Čerenkov angle distributions How to identify e-  on the basis of the Čerenkov angle ? Ref. L. Cremaldi, D. Summers (at the exit of the solenoid) Try other radiators with smaller indices ! With a radiator n=1.25

7. Contamination Gases Liquids Definition. Contamination = relative nr. of electrons counted as muons Ref. http://www.fynu.ucl.ac.be/themes/he/micehttp://www.fynu.ucl.ac.be/themes/he/mice (May 02, 2002) Assumptions - detection thresh. = 10 .e - «  »  no signal More and more low energy electrons do not give a signal Less and less muons do not give Č light

8. Tools and strategy Particle files Photon files Optics Mech. design Mathematica v.3 Zemax v.2002 Autocad 2002 ObjectsTools Status Operational Stray magnetic field not yet done ! Operational

9. General features 1. Do not put photomultipliers in the particle beam generation of spurious photons in glas window of photodetector ! « folded » optical system 2. Influence of stray magnetic field shielding needed ? 3. Detection of a small number of photons with ~ 400 nm photomultipliers with high gains and negligible noise + matching emission spectrum with photodetector response

10. Magnetic stray field * Photodetector at 1 m on the beam axis Photodetector at 1 m away from the beam axis and 1 m downstream from end of solenoid Ref. R.B. Palmer, R. Fernow Collaboration meeting 27.10.2001 * Confirmed by our own calculations with TOSCA

11. Case study End of solenoid (4 Tesla – inner diam. 500 mm) Magn. shielding (central opening diam. 400) Aerogel radiator n=1.06 300 mm x 300 mm 10 mm inside a tube with reflective inner walls Spheroidal mirror Photodetector(s)

12. Configuration # 0 Side view - Cylinder with reflective walls - Spherical mirror

13. Tracking of photons … for a single photon … for a single electron … for 3 electrons Simplest case Hypothetical detection plane … for the complete sample (4256 electrons)

14. Light collection efficiency #0 Light intensity distribution in a hypothetical detection plane 150 mm from beam axis 1. Surface of blue square = 600 mm x 600 mm Notes. Light collection efficiency  = 95 % 2. No optimization at all ! - detector plane not at a focal point … - spherical mirror 3. Perfect reflectivity 100% on all surfaces

15. Realistic configurations Design guidelinesAvoid light leaks Single photodetector Reflectivity into account Bulk scattering in aerogel ( n~1 ; = 10 mm ;  = 5° ) Coatings on all reflective surfaces Requires detailed drawings Thickness = 100 mm Overall length of setup  1000 mm Typical EMI 9356 KA diam. 200 mm Glass window BK7 5 mm thick No coating Cylindrical 300 mm diam Entrance window Al coated on its inner side Winston coneAcceptance angle 30° No chromatic effects

16. Coatings … more elaborate! Coating on all surfaces: aluminium layer 40 nm thick92% reflectivity at normal incidence independent on wavelength Could be more realistic by using actual reflectivity of Al layers on Lucite (from HARP) (… to come later!) Note.

17. Configuration # 1 - Cylinders with reflective walls - Flat mirror - PM EMI 9356KA diam. 200 mm - Winston cone (acceptance angle = 30° ) Approx. matching of optical aperture at production

18. 3D view of config. # 1 Aerogel radiator n=1.06 D=300 mm ; t = 100 mm Cylinder with reflective inner walls. Diam = 400 mm Plane mirror at 45° Winston cone Acceptance angle = 30° ; PM diam. 200 mm PM EMI 9356KA Diam. 200 mm

19. Optics for config. # 1  = 0.81 % losses when taking actual reflectivities into account Typical trajectory for a single photon Light spot at the detector position Non-meridian rays hit the Winston cone at angles larger than the acceptance angle many back/forth reflections Try to keep the optical path length as compact as possible

20. Configuration # 2 More fancy! 2 intersecting cones  /2 = 15° cut with flat mirror at 45° attempt to reduce reflections of non-meridian rays  = 59 % Conclusions Next try: one could add some additional focusing at the mirror level - worse result ! Typical trajectory for a single photon

21. Configuration #3 Spherical mirror R= 1500 mm  = 70 % Typical trajectories for 5 photons Most compact. Note. Mirror radius not optimized! Conclusion. - Extended off-axis source object - short distances w.r.t. mirror radius - larger light spot (aberrations) compared to config. #1 - (probably) no change with elliptical mirror (except cost).

22. Summary 3 configurations studied with a single PM detector + Winston cone assembly Realistic coatings, bulk scattering included 1. Plane mirror + reflecting cylinders  = 0.81 % 2. Plane mirror + reflecting cones  = 59 % 3. Spherical mirror + reflecting cylinders  = 70 %

23. Conclusions Best light collection corresponds to simplest optical system … Limited possibilities of improvements with the present configurations: - antireflection coating on the PM - optimization of parameters Other options1. No Winston cone i.e. multiple PM’s arranged in a plane Geometrical losses ! 2. Planar photodetector with a diam. of about 300 mm ? e.g. MWPC with CsI (Tl) photocathode ( COMPASS-like without imaging) How to proceed ? but Working in the UV ! Length of development Cost + delay ! When is a decision needed ? How much time for development ? Particle optics in the stray field of the solenoid

24. Typical Zemax output

25. A simple test case Entrance of particle in the optical system Sensitive plane of a hypothetical photodetector A single electron producing 20 photoelectrons distributed on a conical surface! Beam and optical axes n=1.06 Aerogel radiator e-e-

26. … and the intensity distribution Intensity distribution on a detection plane perpendicular to optical axis (for the simplest case shown before)