1. Monte Carlo studies of the configuration of the charge identifier
Paolo Maestro
Università di Siena/INFN-Pisa
1st CaloCube collaboration meeting
Firenze 20/6/2014

2. Charge Identifier System for CaloCube
Study how to improve PID capability with a different configuration of sensitive elements on the faces of the calorimeter.
Basic idea: replace the cubes on the calorimeter surface with a stack of thinner scintillating squared tiles in order to perform multiple measurement of dE/dx of the incident nuclei.
Advantages:
Multiple dE/dx samples would allow to tag and remove early interacting nuclei which represent a a dangerous background in secondary/primary abundance measurement
Pixel geometry of the tiles would allow to isolate the ionization signal generated by the incoming particle, reducing the effect of back-scattered shower particles, thereby minimizing the probability of misidentification.
Possible additional materials to shield the backscattering
Easier and cheaper technology than silicon arrays.
Charge identifier system integrated in the calorimeter (same R&D for sensors and electronic)

3. Monte Carlo simulation: geometry
FLUKA version b.5 (feb. 2014)
CaloCube: 20×20×20 cubes with 3.6 cm side spaced by 0.4 cm
CHarge Identifier: 2 layers of 30×30 squared tiles (4×4×0.9 cm3) with no gaps between tiles.
Layer#0 placed on the CaloCube surface. Layer#1 placed upstream CaloCube at a distance of 25 cm.
CHI1
CHI0
CHI layer
CALOCUBE 
Beam
Generated 1,10, 100, 1000 TeV
with normal incidence in x=2 y=2 z=-80

4. Monte Carlo simulation: output
Two approaches are pursued aimed at studying the nature and effect of backscattered particles:
Analyzing the distributions of energy deposited in the CHI tiles.
Use EVENTBIN cards to collect hits in CHI layers.
tracing the backscattered particles emerging from CaloCube and reaching the CHI Layers.
FLUKA routine “mgdraw.f” was modified to tag and dump the “albedo” tracks.
For each tracks several information are recorded in a USERDUMP file: particle ID, track ID, kinetic energy, energy deposited in steps along the track, parent ID, parent interaction code, age, track length, point of generation, traversed regions.
Using this information is possible to reconstruct a posteriori the connections (kinship) between tracks and distinguish primary backscattered particles from secondaries (daughters).

5. Backscattered particlesn g
Blue: backscattered primaries (from interacting events)
entering CHI0 && CHI1
Black: backscattered secondaries (generated
from primaries reaching CHI) entering CHI0 && CHI1
Red: backscattered secondaries (generated
from primaries NOT reaching CHI) entering CHI0 && CHI1
1 TeV protons e p p m K p0
Zgen: z coordinate of generation point
CHI1
CHI0
CALOCUBE

6. Radial distribution of the impact point of albedo tracks on CHI layers
All particle Charged particle Neutron Gamma

7. Impact point of albedo tracks for different zgen intervals
CHI layer 1
0<zgen<16
CCUBE layers 0-3
zgen<-2
CHI layer 1
-2<zgen<0
CHI layer 0
Charged particles are mostly d-rays
Electrons from g interactions
Albedo particles generated in CCUBE
and reaching CHI are mostly n and g
16<zgen<32
CCUBE layers 4-7
32<zgen<48
CCUBE layers 8-11
48<zgen<80
CCUBE layers 12-19
Charged are mostly delta rays in the core of primary particle (proton) in CHI layers
In the halo are from photon (compton photoelectric if near i.e. in CHI layers): secondary back. electrons. Pair production from the bulk of CCUBE primary electrons
Moller Babha secondary electrons. Primary electrons from bremmstrahlung.
All particles Charged particle Neutron Photons

8. Impact point of albedo tracks for different zgen intervals
CCUBE layers 0-3
zgen<-2
CHI layer 1
-2<zgen<0
CHI layer 0
CHI layer 0
16<zgen<32
CCUBE layers 4-7
32<zgen<48
CCUBE layers 8-11
48<zgen<80
CCUBE layers 12-19
All particles Charged particle Neutron Gamma

9. Energy deposited by albedo particles in CHI tiles

10. Energy deposited in the CHI tiles crossed by the beam particle
1 TeV protons
10 TeV protons
Red : CaloCube placed downstream CHI layers
Black: CHI layers alone, CaloCube removed

11. Energy deposited in the CHI tiles crossed by the beam particle
1 TeV protons
10 TeV protons
Protons interacting in CHI layers ~5.5%
Red : CaloCube placed downstream CHI layers
Black: CHI layers alone, CaloCube removed

12. Energy deposited in the CHI tiles crossed by the beam particle (2)
100 TeV protons
1000 TeV protons
Red : CaloCube placed downstream CHI layers
Black: CHI layers alone, CaloCube removed

13. CHI0
CHI1
CHI1 – no CCube

14. Backscatter hits hit threshold = 1 MeV (~0.2 mip)
no. backscatter hits total energy deposited mean edep per hit
CHI 0
100 TeV protons
CHI 1

15. no. backscatter hits total energy deposited mean edep per hit
CHI 0
1000 TeV protons
CHI 1

17. Hit energy density vs. radial distance
1 TeV p
10 TeV p
−− CHI 0
−− CHI 1
100 TeV p
1000 TeV p

18. Summary and future work
Distance the CHI from the CCUBE surface allows to reduce the effect of worsening of
backscattered particles on the charge measurement.
However with current configuration, charge assessment is critical for proton above hundreds of TeV.
Possible improvements
With current configuration:
Reduce tile surface to 2x2 cm2 or less to collect less albedo signals in a single tile.
Thinner tiles to reduce the probability of interaction of nuclei in the CHI.
Use a pair of nearby layers to correlate signals.
Is it feasible practically ? In which size and shapes can CsI crystals be machined?
Study in details the energy spectra of albedo particles. Investigate if it is possible to shield albedo photons ?
Cerenkov could be exploited to measure the heavy nuclei charge. Study the Cerenkov signals produced by albedo particles.