1. Idee per lo sviluppo del Charge Identifier
Paolo Maestro
Univ. di Siena/INFN-Pisa
CaloCube Startup meeting
Firenze 22/1/2014

2. State of the art
Precise measurement of CR nuclei charge Z is mandatory to identify individual chemical elements in the cosmic ray flux for composition/spectrum studies.
Different techniques have been exploited so far:
combination of Cerenkov/scintillation counters (CRN, HEAO-3-C2)
redundant identification in magnetic spectrometers (AMS, PAMELA) : ToF scintillating paddles, silicon microstrips, ring imaging Cherenkov
pixelated silicon arrays in calorimetric experiments (CREAM, ATIC)
segmented scintillator arrays (CALET)
CREAM Silicon Charge Detector
Excellent charge resolution: ~ 0.2 e (C-Si), 0.4 e (Fe)
Perfectly linear from H to Fe

3. 2013 beam test Beam Tracker (Si pixel+strips) CaloCube
Pb 30 (13) GeV/n
Fragmented ions A/Z=2
Charge tagging with 12 dE/dx samples (4 Si pixel + 8 Si-strip layers)
Beam Tracker
(Si pixel+strips)
CaloCube
Excellent charge resolution: ~ 0.1 e B/C

4. CALET Charge Detector (CHD)
2 layers of scintillator paddles (10x32x448 mm3)
readout by 2x14 photomultipliers
Fragmented ion charge distribution measured with CHD at SPS

5. CHD prototype response
The relation between deposited energy and light emission is not linear. Can be parametrized with Tarle’s formula (“halo” model)
Effective dynamic range Z=1-40
In BC region, the charge resolution is 0.15 e from the combined CHD layer measurements.

6. Charge identification in CALOCUBE
GOAL: develop a Charge Identifier System (CIS) integrated in the calorimeter, characterized by fine segmentation and capable of single-element discrimination
BASIC idea proven at the ion beam test
Energy deposited in the central crystal of
1st layer selecting events which have not suffered an inelastic interaction in the first two layers (~0.2 lI)
The signals in the two layers are required to be consistent with the dE/dx of a fully stripped ion of charge Z.

7. CaloCube prototype: charge separation
13 GeV/amu beam
30 GeV/amu beam
Li-O
Li-O
Pulse height distribution in the 1st layer central cube using a high purity sample of nuclei tagged with the Beam Tracker.
F-S
F-S

8. Single crystal cube response
Signal dependence
on Z2
Signal saturation?
Hi/Lo gain scale not well linked?
13 GeV/amu beam
30 GeV/amu beam
Charge resolution
Quite poor charge separation (~0.3 e at O)
but the prototype was not optimized for this purpose

9. 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)

10. Activities for WP2
Design and optimize the CIS configuration with Monte Carlo studies. Study the effect of backscattering and spallation in degrading the CIS performance and possible solutions to reduce it.
Characterization and tests in laboratory of the active elements of the CIS.
Design of the CIS mechanical structure. Study of its mechanical integration with the CALOCUBE.
Study of the integration of the CIS with the front-end and readout system of CALOCUBE.
Tests of CIS prototypal structures with atmospheric muons.
Construction of a reduced scale CIS prototype and test with accelerator beams.
Assembly of the CIS and integration with CALOCUBE medium-size prototype.
Development and integration of the DAQ systems.
Test of the medium-size CIS prototype at accelerators with relativistic ion beams.