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

A Čerenkov for e- identification

a) Sample electrons

muons

(from P. Janot)4256

10000 from 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

Spatial distributions

0

500

1000

1500

-300 -200 -100 0 100 200 300

X (mm)

N Muons

Electrons

0

500

1000

1500

-300 -200 -100 0 100 200 300

Y (mm)

N Muons

Electrons

Beam spot ~300 mm diam. ~ size of the radiator

Numerical aperture (f-number) = ~ 1.5

x

y

0

500

1000

-40 -20 0 20 40

Theta XZ (degrees)

Muons

Electrons

0

500

1000

-40 -20 0 20 40

Theta YZ (degrees)

Muons

Electrons

xz

yz

Divergence ~ 20° sin2

1f

Angular and energy distributions

0

200

400

600

800

1000

1200

1400

0 10 20 30 40

Theta (degrees)

N

Muons

Electrons

0

200

400

600

800

1000

1200

1400

1600

1800

0 100 200 300 400 500Total energy (MeV)

N

Muons

Electrons

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 )

Č radiator n= 1.25

n= 1.25

0

1000

2000

3000

0 20 40 60 80

Cerenkov angle (degrees)

NElectrons

Muons

0

500

1000

1500

2000

2500

0 100 200 300 400 500 600 700

Photoelectrons

N Electrons

Muons

Distribution of light yield

Distribution of Čerenkov angle

( 10 cm thick radiator )

200-400 photoelectrons

Overlap between the angle distributions

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

Contamination

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0.16

0.18

0.20

1 1.02 1.04 1.06 1.08 1.1 1.12

Index of refraction

% M

uo

n c

on

tam

inati

on

Gases Liquids

Definition. Contamination = relative nr. of electrons counted as muonsRef. http://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

thresholdbelow

thresholdbelow

e

e

)(

)(

Tools and strategy

Particle files

Photon files

Optics

Mech. design

Mathematica v.3

Zemax v.2002

Autocad 2002

Objects ToolsStatus

Operational

Operational

Stray magnetic fieldnot yet done !

Operational

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

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 meeting27.10.2001

*

Confirmed by our own calculations with TOSCA

Case study

End of solenoid(4 Tesla – inner diam. 500 mm)

Magn. shielding(central opening diam. 400)

Aerogel radiator n=1.06300 mm x 300 mm 10 mminside a tube with reflective inner walls

Spheroidal mirror

Photodetector(s)

Configuration # 0

Side view - Cylinder with reflective walls- Spherical mirror

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)

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

Realistic configurations

Design guidelines Avoid 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 cone Acceptance angle 30°

No chromatic effects

Coatings

… more elaborate!

Coating on all surfaces: aluminium layer 40 nm thick 92% reflectivity at normal incidenceindependent on wavelength

Could be more realistic by using actualreflectivity of Al layers on Lucite(from HARP)

0

20

40

60

80

100

200 400 600 800

Wavelength (nm)

Re

fle

cta

nc

e (

%)

1G

2G

3G

4G

(… to come later!)

Note.

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

3D view of config. # 1

Aerogel radiator n=1.06D=300 mm ; t = 100 mm

Cylinder with reflectiveinner walls. Diam = 400 mm

Plane mirror at 45°

Winston cone

Acceptance angle = 30° ;

PM diam. 200 mm

PM EMI 9356KA

Diam. 200 mm

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

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

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).

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 %

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 options 1. 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

Typical Zemax output

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 opticalaxes

n=1.06 Aerogel radiator

e-

… and the intensity distribution

Intensity distribution on a detection plane perpendicular to optical axis (for the simplest case shown before)