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e- m identification

e- m identification. Gh. Grégoire. University of Louvain. June 10, 2002. 1. Reminder from previous presentations, questions, remarks. 2. Čerenkov option. 3. Study of several optical configurations. 4. Conclusions. A Čerenkov for e- m identification. Starting point. a) Sample. 4256.

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e- m identification

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

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

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

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

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

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

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

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

  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 l ~ 400 nm + matching emission spectrum with photodetector response photomultipliers with high gains and negligible noise

  10. 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 Photodetector at 1 m on the beam axis * Magnetic stray field

  11. 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) Case study

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

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

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

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

  16. Coatings … more elaborate! Coating on all surfaces: aluminium layer 40 nm thick 92% reflectivity at normal incidence independent on wavelength Note. Could be more realistic by using actual reflectivity of Al layers on Lucite (from HARP) (… to come later!)

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

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

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

  21. Configuration #3 Most compact. Spherical mirror R= 1500 mm Typical trajectories for 5 photons 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). e = 70 %

  22. Summary 3 configurations studied with a single PM detector + Winston cone assembly Realistic coatings, bulk scattering included 1. Plane mirror + reflecting cylinders e = 0.81 % 2. Plane mirror + reflecting cones e = 59 % 3. Spherical mirror + reflecting cylinders e = 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 Particle optics in the stray field of the solenoid i.e. multiple PM’s arranged in a plane Other options 1. No Winston cone Geometrical losses ! 2. Planar photodetector with a diam. of about 300 mm ? e.g. MWPC with CsI (Tl) photocathode ( COMPASS-like without imaging) but Working in the UV ! Length of development Cost + delay ! How to proceed ? When is a decision needed ? How much time for development ?

  24. Typical Zemax output

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

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

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