1. Calorimeter Backgrounds
Occupancy Issues
Physics impact of occupancy
Types of background
Radiation damage
A few comments on alternatives to CsI(Tl)
2019/2/23
steve playfer

2. Calorimeter Occupancies in BaBar
Raw Digis > 0.75 MeV but can be isolated. These are important for DAQ issues. There are ~400/6580 of these from electronics noise (6%).
Default Digis > 1 MeV with a neighbour > 5 MeV are the input to clustering algorithms.
When the default digi occupancy exceeds 2000/6580 crystals (30%) the p0-finding efficiency decreases rapidly (empirical result from trickle injection data)
Clusters have a seed digi > 10 MeV and additional neighbouring digis > 1 MeV.
There are ~8 of these in multihadron physics events.
Bhabha events give clusters in endcap and backward barrel which scale with luminosity
2019/2/23
steve playfer

3. p0 signals with trickle injection
<1ms after injection
>15ms after injection
p0 efficiency
reduced by x2
due to high multiplicity
after trickle injection
2019/2/23
steve playfer

4. Calorimeter occupancy (digis) in Physics Data
A typical 45 minute run
Forward Backward E n d c a p B a r e l
2019/2/23
steve playfer

5. BaBar calorimeter occupancies extrapolated to 2007 (random triggers)
Raw Digis/3000 events
Clusters/3000 events
HER
LER
HER
LER
2019/2/23
steve playfer
Lumi
Total
Lumi
Total

6. Comments on Occupancy
BaBar extrapolations are dominated by the luminosity term
Strong forward endcap peak from (radiative) Bhabhas
Significant peak in last few rows of backward barrel (also Bhabhas)
Remainder of barrel occupancy is from low energy clusters (< 100 MeV)
2019/2/23
steve playfer

7. Ways of dealing with occupancy
Increase digi (cluster) energy thresholds (costs efficiency and resolution)
Make tighter cuts on digi timing
(limited to ~250ns by preamp shaping time)
Develop digital filtering of waveforms to resolve overlapping digis
Subject of talk by Tsukamoto…
2019/2/23
steve playfer

8. CsI(Tl) Radiation Damage
Light yield reduces with time due to formation of colour centres in crystals
Equivalent to increase in threshold and/or electronic noise
Depends quite a lot on quality of crystals
Now have plenty of data from BaBar/BELLE
Change is mostly at the front of the crystals
Affects uniformity of crystals response, but studies suggest this is not yet a problem.
No evidence of significant recovery from annealing during long down periods.
2019/2/23
steve playfer

9. Radioactive source results (6 MeV photons)
After initial steep drop, there is now a shallow logarithmic
dependence on the integrated luminosity
Barrel Modules
1 = forward 7 = backward
Endcap rings
1 = inner 8 = outer
2019/2/23
steve playfer

10. redefinitions between run periods
The steps are due to
redefinitions between
run periods
This agrees well with
the source measurements
2019/2/23
steve playfer

11. Radiation Dose Measured by RadFETs at front of calorimeter
4.1 kRad/ab-1
in Endcap
2.5 kRad/ab-1
in Barrel
Slope going down
(trickle injection &
lower backgrounds)
Integrated luminosity fb-1
2019/2/23
steve playfer

12. Evidence for neutrons hitting Diodes
Some annealing
during down time
(200 crystals)
This is not a
problem for
calorimeter
operation!
(700 crystals)
2019/2/23
steve playfer

13. Calorimeter survivability
Radiation damage reduces light output of crystals (proportional to integral luminosity)
Endcap limit of 20kRad reached after 5ab-1
Barrel limit reached after 10-20ab-1
Occupancy increases with luminosity and eventually limits ability to find p0s
30% occupancy in Endcap and backward Barrel in 2007
How much can we reduce the luminosity term?
How much can we improve occupancy with digital filtering and tighter timing cuts?
Endcap should be replaced in any upgrade
Barrel replacement is a major effort and cost!
2019/2/23
steve playfer

14. Minimal upgrade solution
Replace Endcap crystals with pure CsI
Fast component has decay time 28ns
Light yield lower than CsI(Tl) by x20 (and shifted from 565nm to 320nm)
Readout has been demonstrated using APDs
Expected gain of x2 in effect of radiation damage
There is not much data on this!
Cheap and easy to implement!
Subject of next talk …
2019/2/23
steve playfer

15. kTeV experience with pure CsI
Similar to CsI(Tl)
Caveats:
PMT readout
Very large crystals
Crystal quality?
2019/2/23
steve playfer

16. Conclusions Occupancy limit of 30% is reached at about:
Endcap 3x1034 (integral 2ab-1)
Barrel 3x1035 (integral 20ab-1)
Radiation damage limits are similar
Digital filtering and raised thresholds may give a bit more headroom (but not a lot)
Endcap replacement will need a fast radiation hard technology
Is pure CsI sufficiently radiation hard?
Are other alternatives such as Liquid Xenon or LSO/LYSO crystals viable and cost effective?
Subject of talk by Hitlin…
2019/2/23
steve playfer

17. BACK UP SLIDES FOR DISCUSSION
2019/2/23
steve playfer

18. Two-Stage Model to reach 50ab-1
Year
Peak Lumi
Int. Lumi
2004
1.2x1034
240 fb-1
2006
2.0x1034
570 fb-1
2008
3.0x1034
1.2 ab-1
2010
1.0x1035
3.0 ab-1
2012
2.0x1035
7.5 ab-1
2014
5.0x1035
13 ab-1
2016
7.0x1035
30 ab-1
2018
1.0x1036
50 ab-1
Now 1-3x104
LER Upgrade
1st Stage 1-2x1035
HER Upgrade
2nd Stage 5-10x1035
2019/2/23
steve playfer

19. Radiation Dose Year Endcap Barrel 2004 1.0 kRad 0.6 kRad 2006
Lowest Scenario =
No Lumi term
Highest Scenario =
2x Lumi term
Year
Endcap
Barrel
2004
1.0 kRad
0.6 kRad
2006
1.5-3 kRad
0.8-2 kRad
2008
2-8 kRad
1-5 kRad
2010
3-24 kRad
2-15 kRad
2012
7-50 kRad
5-35 kRad
2014
10-80 kRad
6-50 kRad
2016
kRad
kRad
2018
kRad
kRad
ENDCAP Upgrade
BARREL Upgrade
Is this compatible
with 2-stage model?
Can run Barrel 2-4 years longer than Endcap.
2019/2/23
steve playfer

20. Light Loss Projections
Change from Log
Linear extrapolation to one that matches existing data.
Year
Endcap
Barrel
2004
2006
2008
2010
2012
2014
2016
2018
ENDCAP Upgrade
BARREL Upgrade
Extrapolation beyond 2012 is very uncertain! (No measurements of
CsI(Tl) radiation damage in large crystals beyond 50 kRad)
2019/2/23
steve playfer

21. Occupancy Projections
Usual caveat about extrapolating current backgrounds a long way
and doing nothing to reduce the luminosity term
Integrated
Luminosity
(2008)
1 ab-1
(10^35)
10 ab-1
(10^36)
100 ab-1
Raw Digis
1800
(7500) X
Default Digis
270
1500
(7000)
Barrel Clusters
4.5 20
(100)
Endcap Clusters
4.0
(20)
2019/2/23
steve playfer

22. Pure CsI crystals
Fast component has decay time 28ns which is x30 faster than CsI(Tl). Solves occupancy problem.
Light yield is lower than CsI(Tl) by x20 (and shifted from 565nm to 320nm)
Readout has been demonstrated using APDs
Resolution could be comparable to CsI(Tl)
We think there is a gain of at least x2 in radiation hardness (based on one set of measurements and vague claims from manufacturers!)
No change to geometry of calorimeter
Cost is ~$4/cc which is x2 more than CsI(Tl)
2019/2/23
steve playfer

23. Hybrid crystal solution (Bill W.)
Replace innermost few radiation lengths of Endcap with LSO crystals (rest replaced with pure CsI)
LSO(Ce) - Lutetium Oxyorthosilicate has decay time 40ns
Light yield similar to CsI(Tl) but shifted from 565nm to 420nm
Smaller radiation length 1.1cm and Moliere radius 2.3cm (CsI 1.9cm and 3.8cm) allow an increase in granularity (240 crystals per ring) or a decrease in radius of the calorimeter.
Readout has been demonstrated using APDs
Radiation hard up to 100MRad!
Very expensive - $50/cc. Only one manufacturer in the world. Major application is in PET scanners.
Interesting idea. Solves radiation damage and occupancy.
How much LSO can we afford?
Can this solution be extended to the barrel?
2019/2/23
steve playfer

24. LSO (or LYSO) Crystals Lutetium (+Yttrium) OxyOrthosilicate
Fast light output in 40ns. Solves occupancy problem.
Smaller radiation length 1.15cm (CsI 1.86cm) and Moliere radius 2.3 cm (CsI 3.8cm)
Believed to be radiation hard to 100MRad!
Light output is 50% (60%) of CsI(Tl), but shifted to 420nm from 550nm.
Again use APDs to read them out.
LYSO has slightly more light output than LSO, and may be easier to obtain commercially (3-4 suppliers instead of only one)
Currently the cost is ~$50/cc!!
2019/2/23
steve playfer

25. Xenon calorimeter (David Hitlin)
Light output is within ~20ns.
Radiation length is 2.9cm
Need all of radial space between 700 and 1350mm for cryostat, Liquid Xe and readout.
Moliere radius 5.7cm.
Need sampling along shower depth for overlaps.
Light yield is similar to CsI(Tl) but at 175nm.
Use wavelength shifters and readout by APDs
Radiation hardness is not an issue
Cost of Liquid Xe is $2.5/cc
Total cost $20M + readout and mechanics?
2019/2/23
steve playfer