View
217
Download
1
Tags:
Embed Size (px)
Citation preview
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
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)
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