CKOV1 folded geometry

1. Optimization2. Pion-muon separation

3. Instrumented area

4. Possible developments

November 16, 2005

Gh. Grégoire

Contents

DISC geometry

Detecting plane

Optical window

30-mm thick radiator

Diam. 300 mm

Curved mirror surface

500 mm

Advantage: setup becomes coaxial

Possibility to optimize for minimal optical aberrations and distortions

2

Optimization

3

On the basis of the « folded geometry » proposed by L. Cremaldi/D. Summers

• Try to minimize « thickness » of Cherenkov rings by choosing the optimum shape of the mirror

• Figure of merit = Inverse of « spherical aberration » 

i.e. compensate for focal dispersion due to

• angular opening of Cherenkov cone

• large size of object (radiator)

• Best solution:slightly deformed paraboloid6

64

42

22

2

1rrrrcz

with c-1 = 1015 mm

2 = - 3.386 10-5

4 = - 1.530 10-

106 = - 1.204 10-

16

(z and r in mm)

(longitudinal and transverse)

0 < r < 300 mm

parabola

(transverse distance to axis of symmetry)

Side view

Nice focal spot

Still some residual aberrations visible

4

Beam

Simulations

• Momenta 190 to 280 MeV/c ( in steps of 10 MeV/c )

• Gaussian beams x-y = 50 mm

x’-y’ = 25 mrad

From S. Kahn’s presentation, Phone conf. March 31, 2005

• Radiator 30-mm thick

• Particles Muons, pions and electrons (10 kevts each)

Diameter = 300 mm

5

(to match Tom’s recent beam design)

FC-72 and water

Results for ’s and ’s

60

0 m

m

600 mm 600 mm

190 MeV/c 280 MeV/c

Inner rings Pions

Outer rings Muons

6

Water radiator

Determine ring separation

(distribution of hits along y axis for x=0)

X

Y

Ring separation

0

500

1000

-300 -200 -100 0 100 200 300

0

1000

2000

-300 -200 -100 0 100 200 300

y (mm)

0

1000

2000

200 220 240 260 280 300

y (mm)

Good - separation to the baseline

FC-72 radiator

190 MeV/c

Water radiator

280 MeV/c

Cut along y-axis

Cut along y-axis

Y

Y

Thickness of ring < 20 mm

7

Instrumented area

Both rings are due to muons ! Inner ring 190 MeV/c

Outer ring 280 MeV/c

Water radiator

FC-72 radiator

470 mm < Diameter < 600 mm

Width is about 130 mm

400 mm < Diameter < 500 mm

Width is about 100 mm

8

CKOV1 with variable index

One simple way to reduce the size of the instrumented area is to change the index of refraction according to the momentum

The two rings are still due to muons of 190 and 280 MeV/c

But the radiators are FC-72 (n=1.251) at 190 MeV/c

Water (n=1.33) at 280 MeV/c

Diameter is about 500 mm

Width is 25 mm (i.e. easily covered by a single ring of 1.5 inch PMTs )

How to match the index of refraction between n=1.251 and 1.33 for 190 < p < 280

MeV/c ?Mixture in varying proportions of FC-72 (n=1.251) and alcohol (n=1.362)

9

Possible developments

• If working with radiators adapted to muon momenta

• the Cherenkov ring has a nearly constant diameter

Possibility of a fixed annular slit to make the device really « pion-blind »

• detect the photons after the annular slit by six strips of wavelength shifter material, arranged as an hexagon covering the slit. In total we would need only 6 PMTs.

Simplicity

Cost savings

• To proceed further it is essential to get recent beam files for muons and pions at the position of CKOV1 (according to the latest beam design)

10

CKOV1 would become a true built-in RICH

Full RICH setup ?

Annular slit 1

1