Current R&D

Prototype Operation

The scintillator hcal prototype will be exposed to a hadron test beam at Fermilab during the 2005-2007 period [11]. Hadrons in the momentum range 1-50 GeV are of interest. We are hoping to collect O($10^6$) events per setting (energy, angle and particle type) for a total of $\approx$ $10^8$ events. With $\approx$ 10K channels, the prototype is comparable in channel count to the full calorimetric systems of some of the current collider experiments. Thus a large investment in manpower and resources will be required. Our expertise and location implies that we will be playing a major role in the assembly, commissioning and operation of the prototype. Already one of us (VZ) has been named as one of the two 'Experimental Contacts' for the full ILC calorimeter test beam program. Substantial amount of our resources will also be required to calibrate and analyze the data being collected.

The operation of the scintillator-based hadron calorimeter prototype will deliver a wealth of information. It is however clear that R&D will need to continue in parallel to carry the design forward and optimize it for its realization in an ILC detector. The 2-3 year LC test beam program will permit us to make incremental changes to the initial design which can then be tested in the beam without having to assemble an entirely new device. In this regard the two major areas of concentration will be:


Electronics Development

A detector consisting of a few million channels requires a high degree of integration. The small size, low bias and magnetic field immunity of the SiPMs has already allowed us to take the first step towards this goal. The photo-conversion occurs right at the tile thus integrating the light transport and conversion functions on the tile itself. The next logical step is to bring an equivalent level of integration to the electrical signal path. While individual cables per tile are feasible for the prototype containing a few thousand channels, they are not a viable option for a device with a few million channels. Our objective is the design and fabrication of a readout system with the required mechanical and electronics integration such that data from many tiles could be sent off the detector on a few conductors. The strategy is to have a PC board inside the detector which will connect directly to the SiPMs and carry the necessary electronics and signal/bias traces. The goal is to have robust and cheap electronics with the following functionality:

  1. Preamplification (gain of 10-20) .
  2. Multiple thresholds (cascading discriminators or time over base are possible options).
  3. Good time resolution.
  4. Electronic charge injection.
  5. Temperature monitoring.

For the full detector the most economical solution will be a custom ASIC which encompasses all of the above mentioned functionalities. For our R&D studies however we will be interested in fabricating a prototype system of 500-1000 channels (10% of the channel count for the test beam hadron calorimeter prototype) with discrete elements. This will help us identify and solve electrical and mechanical issues associated with such a design at a fraction of the cost required to develop an ASIC. It will be fairly straightforward to test a prototype of this system with the current hadron calorimeter prototype under construction. This task will be carried out in collaboration with Fermilab electrical engineering department.


Calibration

The current calibration system relies on transport of LED light through clear fibers to the individual tiles. The LED's in turn are themselves monitored with a PIN-diode system. For a system with a few million channels this solution can easily get out of hand. Our objective will be the design and prototyping of a robust calibration system which is scalable. We propose to do this by separating the relative and absolute calibration functions. For the absolute calibration we would aim to develop a scheme based on a radioactive source. This may take the shape of a movable wire source or the deposition of radioactive material near the tiles themselves. For a quick monitoring of the gain a LED system may still be useful. The gain of a SiPM can be tracked by monitoring the distance between the photo peaks. Since only the difference between the peaks is relevant the instabilities in the absolute amount of light emitted by the LED's is not a critical issue. This obviates the need for a PIN-diode monitoring system. Further simplification may be obtained by shining the LED directly on the tiles. The R&D will focus on the mechanical and electrical aspects of this arrangement. Of special interest on the mechanical side would be the challenge to keep the layer thickness to a minimum while on the electrical side the cross talk induced on the signal traces due to the proximity of the LED will need to be addressed.