Downstream e- identification

1. Questions raised by the Committee

2. Particle tracking in stray magnetic field

3. Cerenkov and calorimeter sizes

4. Preliminary conclusions

Gh. Grégoire

CERN - 27-29 March 2003

Progress towards answers to the International Peer Review Panel

5. Questions

MICE Collaboration Meeting

Questions raised

1. Homogeneity of response of the particle ID devices downstream ?

2. Risk of bias through loss of muons by unwanted rejection?

- position

- incident angle

- energy dependence of over-vetoing electrons

Cerenkov and calorimeter !

First elements

For the Cerenkov

Possible origins of inhomogeneity of response

- too few generated photons at some places

- non uniform light acceptance/collection across the system

Precautions

- radiator area is large enough

- highly reflective walls and surfaces

- number of reflections kept to a minimum

Remark

These precautions were already taken into account in the conceptual design presented in the proposal

… but a second iteration is needed !

What are the sizes and relative positions of the Cerenkov and the calorimeter ?

Input data

a) Sample electrons

muons

(from P. Janot)4256

10000 from the simulation of a cooling channel

Starting points

Relative populations of electrons vs muons are not normalized !

Previous presentations

http://www.fynu.ucl.ac.be/themes/he/mice

b) Latest(?) magnetic field configuration from R. Palmer (version 5)

c) proposal

V.5 Magnetic field configuration

r

z

O

Downstream ID detectors

… according to proposal !

Transverse size of Cerenkov must match the distribution of muons which reach the calorimeter

Particle tracking

- Generation of field map downstream the solenoid

zrBBzrBB zzrr ,,

- GEANT 4 tracking of Janot’s muon and electron files

- Results Electron and muon distributions (positions, momentum components)

for 0 < z < 1000 mm

0 < r < 500 mm (-500 < x, y < 500 mm)

from geometry and current densities

(TOF2 not yet taken into account)

Trajectories

r

z

r

z

1000 mm

100

0

mm

1000 mm

100

0

mm

Electrons Muons

Transverse distributions

Muons

0

500

1000

1500

2000

2500

3000

-500 -250 0 250 500X cm

0 cm

10 cm

20 cm

40 cm

60 cm

80 cm

100 cm

Electrons

0

500

1000

1500

-500 -250 0 250 500X cm

0 cm

10 cm

20 cm

40 cm

60 cm

80 cm

100 cm

Acceptance for muons

Muons

0

1000

2000

3000

-500 -250 0 250 500X mm

800 mm

200 mm

700 mm

400 mm

Calorimeter

Cerenkov

at z = 100 mm

at z 800 mm

Preliminary conclusions (1)

- Smaller Cerenkov and calorimeter compared to proposal

- Updated mechanical and optical designs to come (soon?)- No large improvement expected on homogeneity of response

= 77% Thresh = 5 .e.

Fluctuations are largely dominated by statistics

Cost

… but magnetic shielding not taken into account !

Optical response

Preliminary conclusions (2)

Correlation with the calorimeter ?

With n=1.02, [ % HE muons generating > 5 .e. ] = 0.2

1

10

100

1000

10000

0 50 100 150 200 250 300

PhotoelectronsN Electrons

MuonsEthr = 530 MeV

Unambiguously identified in calo !

… except if decays inside Cerenkov Proba ~1.5 x 10-4

(over 0.5 m at 530 MeV)

Fraction [ good  ] veto 3 x 10-7

Questions for further work

1. Confirmation of Geant 4 tracking Who? When?

2. Magnetic shielding

Rough estimate ~15 cm iron !

Influence on field and on tracking near end of solenoid ?