Solid Forward Calorimeter
Contents
general design ideas
from Eugene Chudakov
a brief explanation is given in the proposal to PAC34, page 57-58.
A preshower I simulated gave a factor of 3 in e/pi rejection, which is important.
The resolution I used was 10/sqrt(E). With the shashlyk technology one can get 10% at 1 Gev easily, with a rad. hard scintillator. A better resolution of about 3-4%/sqrt(E) was obtained (KOPIO) with a high Sc/Pb ratio, but also with a rad. soft scintillator (there is a brief discussion in the proposal).
In order to make sure which resolution is enough one has to consider all the aspects including the pattern reconstruction. A poor reconstruction may lead to a more stringent requirement on the calorimeter resolution. The coordinate resolution is also very important, since tracking should start with the hit in the calorimeter.
I would suggest to assume 10%/sqrt(E) with a preshower, take some cell size to provide about 1 cm window for the shower center, and develop an algorithm for track reconstruction (Richard Holmes made some preliminary calculations). This is a critical issue, since the background in GEMs will be very high, and the calorimeter tagging is important. I used some assumptions on the GEM X-Y matching and resolutions, based on the SBB proposal in Hall A, which might be optimistic (Bogdan told me that they were concerned about it).
from Paul Souder
The Ecal has the following functions:
1. Provide a trigger.
2. Provide an energy for tracking.
3. Reject pions.
4. Study systematic errors.
Effect of resolution:
Pion rejection: the rejection factor is inversely proportional to the resolution. The asymmetry of the pions cn be measured, so the correction due to pion contamination can be made. However, if it is too big, complex systematic errors enter and the statistics is degraded.
Energy for tracking: The idea is that given a hit and an Ecal energy, one can compute where other possible hist are. This is the key to the tracking algorithm. We need a tracking Monte Carlo to determine which resolution dominates: multiple scattering, detector resolution, or Ecal resolution.
Trigger: Poor resolution may increase trigger rate.
Systematic errors: If the tracking and Ecal both have good resolution, the comparison is useful for minimizing systematic errors such as Q2.
Summary: The excellent resolution available with the sashlyk Ecal is useful. How much poorer resolution we can tolerate requires the Monte Carlo.
