em identification

1
e-m identification
Gh. Grégoire
University of Louvain
June 10, 2002
1. Reminder from previous presentations,
questions, remarks
2. Cerenkov option
3. Study of several optical configurations
4. Conclusions
2
A Cerenkov for e-m identification
Starting point
a) Sample
electrons
(from P. Janot)
4256
muons
10000
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
Numerical aperture (f-number) 1.5
Divergence q 20
4
Angular and energy distributions
Angle with respect to beam axis
Kinetic energy distribution
Electrons have very low energies ( Elt mp )
It is not obvious (to me) to separate e-m on
calorimetric principles at such low electron
energies!
5
C radiator n 1.25
Distribution of Cerenkov 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 Cerenkov angle distributions

With a radiator n1.25
How to identify e-m on the basis of the Cerenkov
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 C light

• detection thresh. 10 f.e
• m  ? no signal

Liquids
Gases
Definition. Contamination relative nr. of
electrons counted as muons
Ref.
http//www.fynu.ucl.ac.be/themes/he/mice (May 02,
2002)
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
Magnetic stray field
11
Case study
12
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 ( n1 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 n1.06 D300 mm t 100 mm
19
Optics for config. 1
Light spot at the detector position
e 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 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 PMs 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 simple test case
e-
26
and the intensity distribution