1. An alternative forward endcap calorimeter design
David Hitlin
Orsay SuperB Meeting
February 16, 2009

2. The forward EMC endcap
The higher rates and radiation does of SuperB motivate replacing the BABAR CsI(Tl) endcap with a faster, denser, more radiation hard version – we have been investigating LYSO crystals with transverse dimensions 1 Molière radius
S. GERMANI

3. { A few observations { Saves 40% of LYSO volume
The Molière radius of LYSO = 0.58 Moliere radius of CsI(Tl) (~2.07 cm vs 3.57 for CsI(Tl))
CsI crystals in the outer rings of the endcap should see rates and radiation does similar to the forward end of the barrel
This leads to consideration of the following alternative design:
Retain the mechanics of the BABAR endcap
Use 4 LYSO crystals in each existing CsI(Tl) compartment
(Option) Retain outer three rings of CsI(Tl)
A consequence is that the anticipated 10cm in front of the forward endcap does not become available for PID {
Saves cost of
new mechanics
{ Saves 40% of LYSO volume

4. The BABAR barrel and forward endcap - manufacturers
Hilger
Shanghai
Kharkov

5. Radiation dose (radfets)
The radiation dose as measured by an array of radfets has been studied by Aidan Randle-Conde and David Doll
The radiation dose is a function of polar angle
The time distribution of radiation dose does not track the integrated luminosity: it appears to have both luminosity- and current- related components (unfortunately, the currents were not included in the n-tuples)

6. Crystal response to radiation dose
The diminution of light output with radiation dose varies with crystal provider
The endcap contains three types of crystals: SIC, Kharkov and Hilger
Average over crystal provider within each ring

7. Crystal response to radiation dose
The diminution of light output with radiation dose varies with crystal provider
The endcap contains three types of crystals: SIC, Kharkov and Hilger
There is a large variation in response within each ring

8. CsI(Tl) endcap crystal nominal dimensions
Ring QTY A B C D E F Length Volume 1 EC EC EC EC EC EC EC EC EC 80 ? ? ? ? ? ? ? ?
Fill each compartment with 4 LYSO crystals (3600)
Retain Rings crystals
(1440 LYSO)
New (Rings 4-9)
2160 LYSO
Unfilled in BABAR

9. There are two alternatives employing existing mechanics
Full LYSO: 3600 crystals
= 5.0M€
Hybrid:
CsI(Tl): 360 existing crystals
LYSO: crystals =3.0M€
Saves 1440 LYSO crystals

10. Woule retain the existing BABAR endcap mechanics
The current endcap consists of 20 carbon fiber modules in two ‘D’s
Each module contains 9 rings of CsI(Tl) crystals (only the outer 8 are filled)

12. Comments
It appears to be feasible to retain the BABAR endcap mechanics, saving ~1M€
Place four LYSO crystals in each existing CsI(Tl) compartment
LYSO crystal sizes still allow two crystals/boule, which is crucial for cost
By retaining outer three CsI(Tl) rings, save additional 2M€ in crystals plus ~0.5M€ in APDs, preamps and DAQ
The alternative design is as much as 3.5-4M€ less expensive than the design we have been considering
Consequences
The 10cm that can be made available for forward particle ID with a design employing new mechanics is not available in this scheme
If we conclude that this concept has merit, we must interact with the Geometry and PID groups to study the physics consequences of
No forward PID
Less material in front of the forward EMC
The beam test module design is only slightly affected
Quotes (large quantities)
LYSO SIC, SIPAT $20/cc
APD Hamamatsu x5mm $92.80
10x10mm $203.00