Could CKOV1 become RICH?

1. Characteristics of Cherenkov light at low momenta (180 < p < 280 MeV/c)

2. Layout and characterization of the neutron beam

3. Study of the simplest optical configuration

4. Optical focusing geometries

5. Conclusions

October 5, 2005

Gh. Grégoire

Contents

Cherenkov cone

n=1.5

0

100

200

300

150 200 250 300

Momentum (MeV/c)

Rad

ius

(mm

)

Electrons

Muons

Pions

n=1.25

0

100

200

300

150 200 250 300

Momentum (MeV/c)

Rad

ius

(mm

)

Electrons

Muons

Pions

250 mm

Radius of the ring

Radiator

nc 1

cos

2

.The identification is more difficult at the high momenta as the radii are more similar

Simplest configuration

e, ,

Light cone centered on the beam axis

Momenta parallel to beam axis (=0)

280 MeV/c

5 and 20 mm thick radiator

Plane ideal mirror at 45° No optical aberrations (i.e. deformation of the Č rings)

Photoelectrons for 20-mm radiator

Ne = 100N = 89N = 80

e = 48.2 degrees = 44.6 degrees

= 41.9 degrees

Opt. Glass BK7 n=1.5

No losses

Lateral sizes fixed to get 100% light collection

Flat detecting surface at 90°

Particles hitting the center of the radiator (x=0 ; y=0)

3

Equal size samples

Pixel size 2 x 2 mm²

Photon production

222

2 11

2

nddz

Nd

The only (uniform) random variable is the z-coordinate of an emitted photon (radiator thickness !)

affecting the « width » of the Cherenkov ring on the detecting planeEstimation of separation of pions, muons and electrons

4

neglecting the very small variation of as a function of penetration in the radiator (energy loss)

Plane mirror

Simple geometry

350 mm

585 mm

Electrons

Muons

Pions

1200 mm

12

00

m

mX

Y

Pixel size = 2 x 2 mm2

20-mm thick radiator

( Colors correspond to different particle species )

Sample size:50 k pions

50 k muons

50 k electronsDiam. 250 mm

5

Y=0

0.0

200.0

400.0

600.0

800.0

1000.0

1200.0

-600 -400 -200 0 200 400 600

X (mm)

Y=0

0.0

200.0

400.0

600.0

800.0

1000.0

1200.0

400 450 500 550X (mm)

Intrinsic resolution

e

32 mm 42 mm1100 mm

R 4 mmGood separation for all particles

Pixel size = 2 x 2 mm2

6

Note. The separation of the rings and their « width » is matched to the anode sizes (2x2 and 4x4 mm²) of modern multianode photomultipliers.

Y=0

0.0

200.0

400.0

600.0

800.0

1000.0

1200.0

400 450 500 550X (mm)

Radiator 5 mm

Radiator 20 mm

Influence of radiator thickness

• Slightly smaller dispersions of radii for muons and pions

(at the expense of light output)

• Large detecting plane due to plane mirror

Optical focusing needed

100% light collection efficiency mandatory

R 3 mm

e

• Shifts due to refraction in the thicker radiator

Conclusions • At 280 MeV/c the thickness of the radiator has not much influence on imaging

7

Focusing geometries

Non exhaustive ! Very preliminary ! Not optimized

Plane mirror

Spherical mirror

R=-1100 mm

Parabolic mirror

Rcurv=-1500 mm = -1

= 0

Spheroidal mirror

Rcurv= -600 mm along X

Rcurv=-1100 mm along Y

More x-focusing obviously needed !

Goal: Č light produced at the focus to get a parallel beam after reflection and placing the detecting plane perpendicularly (for easy simulation/reconstruction)

400 mm

8

12

00

mm

1200 mm

Conclusions

1. Except if there are no other physical/experimental constraints, the thickness of the radiator does not significantly affect the quality of imaging. (for reasonable thicknesses in the range 5 to 20 mm of glass)

2. Focusing geometries reduce the area of the photon detecting plane by about an order of magnitude w.r.t. a plane mirror

while still keeping a good e-- separation

3. Could CKOV1 become RICH?

But it still needs

- a lot of optimization

- detailed studies of aberrations with particles off axis

9

At the highest momenta in MICE

- to ease the simulation and analysis

The separation is easier at the lower momenta

- but aberrations will not destroy the separation possibilities

Yes, it is possible to separate e-- at the position of CKOV1 with RICH techniques With reasonable pixel

sizesWith acceptable radiator thicknesses