Preliminary Design of Electromagnetic
Calorimeter (EMC)
September 16 2002
---Lu Jun-guang
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
General Consideration
Choice of Crystal
Structure of EMC
Quality control of CsI(Tl) crystals
CsI(Tl) counter
Readout
Counter testing
Calibration and monitoring
Mechanical Structure
Question of EMC design
Summary
1. General Consideration
EMC plays an important role in the BES. The primary functions
of calorimeter are to provide precision measurement of energies
and positions of electrons and Photons. The general physics
requirements of BESIII lead to EMC based on CsI(Tl) crystals
over the entire available solid angle with performance targets,
* Energy region: 20 MeV to 2 GeV.
key energy region< 500MeV.
* Energy resolution: E / E  1% / E ( GeV )  2.7%

 5 mm / E ( GeV )
* Spatial resolution:
* Reconstruction of π0 and η
* Contributes to e/πand e/μ separation
* Provide neutral energy trigger
* With electronic noise: 200kev/each crystal
X ,Y
2. Choice of Crystal
Energy resolution of calorimeter:
 / E     
2
2
2
2
Ec
rl
pd
nois

2
cal
* EC is the intrinsic resolution due to fluctuations of
the energy deposition and the photon statistics;
• rl
is from the shower leakage including contributions
from “dead material” in front of the calorimeter
and the supporting structure;
• PD is from photodiodes directly hit by charged particles;
• noise is from electronic noise including “pile up”
at high luminosities;
• cal is from errors of calibration and non-uniformity
of the system.
The Properties of several inorganic crystal scintillators
Crystal
Density (g/㎝3)
Radiation length (㎝)
NaI(Tl)
3.67
2.59
Molière radius (cm)
4.8
DE/dX(Mev/cm)(per mip)
Nucl. Int. length (㎝)
Refractive index (480 nm)
Peak emission (nm)
Relative light output
4.8
41.4
1.85
410
100
Light yield temp.coef.(%/0C) ～0
Decay time (ns)
230
Hygroscopic
Referral cost($/㎝3)
CsI(Tl)
4.51
1.85
3.8
5.6
37
1.79
560
45 (PMT)
140 (PD)
0.3
1000
BGO
7.13
1.12
PbWO4
8.28
0.89
2.3
2.0
9.2
21.8
2.15
480
15
13.0
18
2.16
420-560
0.01
-1.6
300
-1.9
10-50
strong
slight
no
no
2
2.3
7
2.5
Figure 1. Effect of electronics noise on the energy
resolution from Monte Carlo simulation.γrays pass
through MDC and TOF. Energy is obtained by the sum
of 5 x 5 CsI(Tl) crystals, and the sum of direct energy
deposit in photodiodes with a factor of 40.
The position resolution of photon showering
Figure 2. The average position resolution of photon
showering in the calorimeter vs. photon energy.
 0 mass resolution
o
Figure 3.
 0 mass resolution vs.
momentum
The efficiency of detection for photon and  0
Figure 4. (a) photon detection efficiency vs. photo energy.
(b)  0 detection efficiency vs.  0 momentum.
Figure 5. (a) shows a measurement of a CsI(Tl) crystal Crystal:
3.5cm x 3.5cm—4.5cm x 4.5cm,25cm long coupling two
PDs(S2744-08) using 60Co source with 1.17 and 1.33 MeV γ rays. (b) the amplitude of the signal output from a photodiode
directly exposed by 60 keV-rays from an 241Am source
light output (2 x PD): ~ 5000 e /MeV
 noise  1000 e  200 keV / each counter
Effect of energy deposit in the photodiode  PD
• From measurement:
It is ~45 times of the energy deposit in the crystal.
• GEANT simulation shown the energy deposit of
photodiodes for a shower leakage is about 240 keV
which corresponds to energy deposit of 11 MeV of
CsI(Tl) crystal,
• With a small rate:
0.5 GeV 1.GeV
rate
2%
5%
So this effect is negligibly small compared to the expected
energy resolution at 1GeV (〜3%).
3. Structure of EMC
Figure 6. Configuration of the electromagnetic calorimeter
Calorimeter is composed of a barrel and two endcaps.
barrel:
inner radius: 94 cm
inner length: 276cm
polar angle 33.5o —144.7o(cosθ～0.82).
56 rings ( z direction) , each with 144 CsI(Tl) crystals
All crystals point to the collision point with a small tilt of
1o～3o in q and 1.5o in the f directions.
Endcap:
at 138 cm from the collision point,
polar angle: 21.3o—34.6o and 145.4o — 158.7o(cos θ ～0.93).
Each endcap consists of 8 rings, and vertically splits into
two half in order to open horizontally.
The entire calorimeter have 9600 CsI(Tl) crystals with a total
weight of 22 tons.
Dimension of CsI(Tl) crystals
Figure 7. Shape CsI(Tl) crystals.
Basic size of one CsI(Tl) crystal:
4cm x 4cm —5cm x 5cm, 24 cm (L)
According to GEANT simulation, about 73% of incident energy
is deposited in one segment when a ray with energy above 100
MeV enters at the center of the segment.
4. Quality control of CsI(Tl) crystals
• the tolerance of the crystal dimension as
+0, -200 µm for all side
1mm
for length
• light output :(200 µm Teflon sheet , two PD (S2744-08)
and 1 µs shaping time)
5000 e /MeV
• light uniformity (200 µm Teflon sheet and 2-inch
PMT,testing eight point in length of 24cm)
max imum  min imum
U 
 5%
average
 15%
.
for
PMT
for two PDs
Radiation hardness of crystal can be reached:
5% decrease of light output per krad
Figure 8. The setup for measuring the light output and
the uniformity of the crystal.
Light output for few vendor crystals
Figure 9. The light output nonuniformity in a 25cm-long crystal
Effect of non-uniformity of light output of crystal
on energy resolution
5. CsI(Tl) counter
Figure 11. Assembly of a CsI(Tl) crystal module.
• Wrapping:
200μm Teflon sheet + 25 μm Al +25 μm Mylar sheet
Figure 12. Light output versus thickness of Teflon and Tyvek
6. Readout
Photodiode
Hamamatsu S2744-08
photosensitive area:
1cm x 2cm
Thickness of Wafer:
300μm
Quantum efficiency(560nm):
80%
Supplies Reverse Voltage :
70 V
Capacitance :
85 PF
Dark current:
4 nA
Temp. dependence for noise:
10 %/0C
Uniformity of q. e. :
1%
Difference of q. e. :
10%
Preamplifier and amplifier
For each counter:
Two PD + Two preamplifier + One amplifier
Preamplifier noise:
~1000 e (~200kev)/counter
Shaping time of amplifier:
1μs
Figure 13. Light output and noise due to the shaping time of amplifier
Preamplifier
Post amplifier
Q Module
From Detector
CLK
Analog Sum
L1
TEST, DAC
L1 reset
SCLK, DIN , SCV
CLK
L1
Fan-out
Trigger
CLK
Buffer full
Test
Controller
L1 reset
Buffer full
L1
L1 reset
Buffer full
Figure 14. Block Diagram of the readout
V
M
E
Preamplifier
•
•
•
•
•
Low noise charge sensitive amplifier
1 AMP/diode, 2 AMPs/crystal
Average of 2 AMP outputs to improve S/N
Calibration circuit at the input
20 wire twisted cable/Ch to Post AMP
Preamplifier Specification
Gain
ENC
Dynamic Range
Output decay time
Max linear output
1mV/fc
0.16fc (80pF input capacitance)
0.5fc ~ 1500fc
50ms
2V
Post Amplifier
A
From Preamplifier
From Test Controller
To Q Module
A+B
A
CR
(RC)2
B
B
To Trigger
∑
Figure 15. Block diagram of the post amplifier
•
•
•
•
•
½(A+B), A, B can be selected
CR-(RC)2 with pole-zero cancellation shaping, t=1ms
Gain adjustable with digital potentiometer
Analogue sum for trigger
Differential connection with Pre-AMP and Q module
Q Module
×.25
Pipeline
FADC
Peak
From
Post AMP.
×1
FADC
Pipeline
Peak
×8
FADC
Pipeline
Peak
Inn. Trig
Disc.
Delay
Peak Selec.
Range
Encoding
Compress
Buffer
Out. Trig
L1
Thr. Register
Figure 16. Block diagram of Q module
• 3 FADCs sample signals from 3 different gain AMPs
• Delay samples for 1.7ms with pipeline to wait for 3.2ms trigger
latency L1
• Find peak within 3ms time window after L1 arrival
• Select peak, make range encoding & compression, store data in
buffer
• Inner trigger for radiation source calibration & adjusting gain
• 9U VME module, 32ch/module
7. Counter testing
Before construction of CsI(Tl) module
Light output of Crystal will be tested by γ source
Difference
~50%,
Uniformity ~ 5% (PMT)
~10% (PDs)
PD will be burned at 800C for 600 hours,dark current and
sensitivity checking by χ source and light pulse.
Difference ~10%
Preamplifier and amplifier will be tested by χ source irradiate
reference PD, noise and the gain difference checked
Then match them in order to have similar signal
amplitude between crystals for digitization.
Before installing the calorimeter structure
Each counter will be tested by using cosmic-ray. It will
provide a pre-calibration of counters, Cosmic-ray
measurement is one way to reach a required 1%
accuracy.
Beam test of a CsI(Tl) matrix
We plan to perform a beam test of a 6×6 crystal
matrix when all elements of a detector module is
ready. It will help us to debug the system, obtain the
first hand experience for calibration, cross check
Monte Carlo simulation, and finalize the system
design.
Figure 17. The setup for the cosmic-ray measurement
7. Calibration and monitoring
Environmental control and monitoring
Temperature of preamplifier will be controlled by the cooling pipe
system :~25oC ± 1o
Humidity will be controlled by flushed with dry air or nitrogen
~5% ± 3%
Temperature monitoring
About 600 LTM8802 temperature sensors distributed around
the calorimeter,using precision of 0.5oC
Humidity monitoring
About 200 sensors are distributed and linked to the slow
control system, using precision of 3%
Radiation dose monitoring (50～300 rad/year)
About 80 sensors distributed around the calorimeter, using a
sensitivity level of 0.5 rad
Calibration
Before calorimeter assembling, each counter will be pre-calibrated
using cosmic ray in the Lab .
Has cosmic ray running for 1 month after the installation of
BESIII finished
At normal performance:
1. Calibration system of electronics every day (gains, pedestals
and linearity)
2. Temperature corrections for CsI crystal with temperature
coefficient of 0.3%/Co
3. Cosmic-ray muons can be used periodically to check absolute
light yield and the detector performance.
4. The ultimate energy calibration using e+e-,γe+e- and πo events.
Bhabha event rate: ~0.6 kHz. 4000 events/counter-day.
5. The effects of radiation damage of crystals have been
monitored by a Xe lamp-fiber system
Figure 18. Overview of the Xenon lamp-fiber monitor system
parameter of light output of crystal fitted use bb events
E i  dEi
i
 ADC i
Ej 
25
 Ei
i 1
ADC i is the data of light output of the crystal i .
 i is the fraction of light output of the crystal i.
 max   min  0.5
N
2  
( Eexp 
j 1
25

i 1
E i /  i )2
 2j
Eexp ,  j are the fraction and error of energy
deposited in  25 ,defined by MC
9. Mechanical Structure
72 slots in φ
14 in Z
each compartment:
8 crystals
Steel bar 144 piece
Inner wall (Al) :
1.6 mm (T)
compartment wall:
0.5mm (T)
Figure 20. Support structure of the barrel calorimeter
Figure 21. Assembly structure of the crystal module in the
compartment
Process to assemble crystals will start at the top of platform.
1. Uninstall two reinforce steel bars and plastic super-Modules
2. Insert two rows of crystals one by one.
3. Install the two reinforce steel bars,bridge bars and fix
the elastic jig, then press each crystal tightly.
4. Install the cooling pipes and inserts cables and fibers.
5. Using the Xe lamp-fiber system to test the signal of each crystal.
6. Install the bar of the outer wall
10. Question of EMC design
• It is short that CsI(Tl) calorimeter with a length of
13X0 .
suitable length: 15X0 (28cm)
cost: ~8.64 M$ (13X0) +1.87M$ (add 2X0)
energy resolution: 3.7% to 2.6% for 1GeV
• There are not compartment wall in between crystals
for calorimeter support.
effect of 0.5mm Al fins for 2x4 crystal module on
energy resolution: ~ + 0.5%.
Figure 24-a The shower leakage and the leakage fluctuation for
CsI(Tl) calorimeter with a length of 24cm.
Figure 24-b The contribution to the energy resolution
for length of CsI(Tl) crystals.
Figure 25. relative energy deposition and energy resolution for
different thicknesses of the air and materials in the inter-crystal
Fig 26. Relative energy deposition and energy resolution for
different tilt angle of crystal to point the interaction point
11. Summary
• A basic design of BEMC is to use CsI(Tl) crystals.
suggested use 13X0 in length.
• Covering the polar angle of cosθ～0.93.
• Expected performance:
E/E ~ 1%/√E + 2.7% , x,y ≤ 5mm/√E
• Quality of crystal:
light output: 5000 e /MeV, uniformity: ~10%
wrapping:
200μm Teflon sheet
• Readout: adopt two PD S2744-08 in each crystal.
• Electronics
noise:
~1000 e (~200 keV)/counter
shaping time: 1 μs
• Single crystal calibration will used Bhabha event and
Xenon flusher for monitoring
Thanks