1. Where are we? What do we want to do next? Some thoughts
Adam Para
August 7, 2007

2. What Tools Do We Have?
Stand-alone GEANT4 for a single medium with total ionization energy deposition and Cherenkov energy deposition. (Hans + Eiko) ROOT analysis macros.
Stand-alone GEANT4 for longitudinally segmented detector with absorber/scintillator/Cherenkov structure. Not all different layers must be present. In the ‘Cherenkov’ layer the ionization energy is read out as well. (Hans + Eiko). Note that this in principle should supersede the first one. And it does! ROOT analysis macros.
SLIC-based simulation with longitudinal and transverse segmentation. Standard distribution of SLIC. (Hans+Jeremy) JAS and ROOT analysis. A given volume can be either scintillator or Cherenkov (to be improved)

3. What Do We Know: Case I Homogeneous Calorimeter (Eiko + Niki)
In case of a homogeneous calorimeter with both ionization and Cherenkov energy measured separately
a very good hadron energy resolution of 25%/sqrt(E) can be achieved.
Average corrected response to hadrons and electrons is the same
Response to hadrons and electrons is linear
Correction function is practically independent of the measured energy

4. Jet energy resolution is somewhat better than the single hadron energy resolution
Jet response and energy resolution is independent on the jet composition and fragmentation

5. What Do We Know: Case II Functionally Segmented Calorimeter (Eiko + Niki + George + Franco + Roberto)
The case studied so far involves longitudinally segmented calorimeter with ionization or Cherenkov or none readout. All detector volumes constructed from the same material (lead glass). This simplifies the problems of neutron component of the hadron shower.
Resolution depends on the geometry (thickness) of the scintillation/other layers (sampling fluctuations + other effects)
Good resolution requires large sampling fraction AND thin detector layers

6. ‘Global’ compensation, based on the total amount of light possible, but energy resolution improvement in general modest
Global compensation works equally well (or poorly) for jets as it does for single particles.
Further improvement of energy resolution by using ‘local’ compensation possible but not trivial. Using only transverse segmentation and additional improvement of energy resolution of the order of ~7% possible.

7. Next Steps I Homogeneous Calorimeter simulation/analysis: Clean-up
Write a paper
Need more cases plots?? What??
Optimize the detector (anticipating a possible cost implications): is it necessary to read out both scintillation and Cherenkov from the entire volume? Or perhaps it is sufficient to read out scintillation? Cherenkov? from a smaller volume ? Notice: This step requires that both the Cherenkov and the scintillation light is read out from the same volume in a transversely segmented detector

8. Next Steps II Sampling calorimeter (glass only):
Complete the survey of possible geometries/thicknesses
Continue investigations of possible local compensation algorithms (longitudinal only)
Investigate compensation algorithms using transverse segmentation

9. Next Steps III
Sampling calorimeter with cherenkov radiator (heavy lead glass) and plastic scintillator.
This is a case where Cherenkov-based and neutron-based compensation may be possible.
Investigate resolution as a function of layer thicknesses
Investigate global and local compensation algorithms

10. From Simulations to Real Detectors. A Possible Strategy?
Homogeneous detector offers the best performance, it seems.
Its practical realization requires separation of Cherenkov and scintillation light from the same detector. This has been demonstrated (kind of) in the case of lead tungstate.
Lead tungstate is a very heavy material. It offers an attractive possibility of 6-7 l calorimeter in a limited volume, like SiD.

11. Very heavy scintillating glasses (>8g/cm3) have been produced
Very heavy scintillating glasses (>8g/cm3) have been produced. So far they seem to have poor transmission for Cherenkov, but this can be possibly improved. Perhaps lead glass can be doped with scintillating agent without too much of Cherenkov losses?
Homogeneous detector does not require any segmentation. But it allows for any depth/transverse segmentation as required by other physics considerations. Signals can be summed.
Construction of a calorimeter from ‘smallish’ building blocks/crystals cad reduce the production(growing) cost of crystals and make it affordable.

12. Possible Calorimeter Design
Propose the calorimeter base on lead tungstate (baseline), while encouraging R&D on alternatives using heavy glasses.
Decouple the spatial measurements (two/multiparticle separation, position, direction) in the EM by inserting two-three layers of pixel silicon detector
All crystals read-out via silicon photodetectors
Crystals glued into full-depth towers
Crystal sizes of the order of 2.5×5×5 cm in the EM ‘section’ to 10×5×5 cm in the HAD section

13. Testing?
Get samples of lead tungstate. If possible with the (natural) slow scitillation (more light!). Demostrate Cherenkov/scintillation separation by timing.
Construct EM prototype: 10 x 10 x 25 cm, build out of 5 x 5 x 2.5 crystals (40 crystals) with three layers of silicon. Demonstrate the spatial measurements. Establish the silicon photodetectors as a viable readout. Demonstrate the energy resolution using Cherenkov AND scintillation light.
(perhaps) construct EM prototype with Lead glass/lead tungstate separated functions (Cherenkow/scintillation). Evaluate the resolution, validate the simulation studies

14. Construct the full scale hadronic calorimeter 1 x 1 x 1. 2 m
Construct the full scale hadronic calorimeter 1 x 1 x 1.2 m. Demonstrate the compensation/energy resolution for single hadrons. ~5000 channels
Perhaps… The cost of such a calorimeter is likely to be dominated by the cost of lead tungstate. Perhaps it would be sufficient to have only central core with dual readout and use scintillating glass for tail/side catcher?
In the meantime/in parallel: investigate doping of lead glass, investigate transparent scintillating glasses