1. General Consideration 2. Choice of Crystal 3. Structure of EMC 4. Quality control of CsI(Tl) crystals 5. CsI(Tl) counter 6. Readout 7. Counter testing 8. Calibration and monitoring 9. Mechanical Structure10. Question of EMC design 11. Summary

Preliminary Design of Electromagnetic Calorimeter (EMC) September 16 2002

---Lu Jun-guang

EMC plays an important role in the BES. The primary functionsof calorimeter are to provide precision measurement of energiesand positions of electrons and Photons. The general physicsrequirements of BESIII lead to EMC based on CsI(Tl) crystalsover the entire available solid angle with performance targets,

* Energy region: 20 MeV to 2 GeV. key energy region< 500MeV.

* Energy resolution: * Spatial resolution: * Reconstruction of π0 and η * Contributes to e/πand e/μ separation * Provide neutral energy trigger * With electronic noise: 200kev/each crystal

1. General Consideration

)GeV(E/mm5Y,X

%7.2)GeV(E/%1E/E

2. Choice of Crystal

Energy resolution of calorimeter:

* 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.

22222/calnoispdrlEc

E

The Properties of several inorganic crystal scintillators

Crystal NaI(Tl) CsI(Tl) BGO PbWO 4

Density (g/ ㎝ 3) 3.67 4.51 7.13 8.28

Radiation length ( ㎝ ) 2.59 1.85 1.12 0.89

Molière radius (cm) 4.8 3.8 2.3 2.0

DE/dX(Mev/cm)(per mip) 4.8 5.6 9.2 13.0

Nucl. Int. length ( ㎝ ) 41.4 37 21.8 18

Refractive index (480 nm) 1.85 1.79 2.15 2.16

Peak emission (nm) 410 560 480 420-560

Relative light output 100 45 (PMT) 15 0.01

140 (PD)

Light yield temp.coef.(%/0C) ～ 0 0.3 -1.6 -1.9

Decay time (ns) 230 1000 300 10-50

Hygroscopic strong slight no no

Referral cost($/ ㎝ 3) 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.

mass resolution0

Figure 3. mass resolution vs. momentum

o

0

The efficiency of detection for photon and 0

Figure 4. (a) photon detection efficiency vs. photo energy. (b) detection efficiency vs. momentum.00

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

countereach/keV200e1000noise

Effect of energy deposit in the photodiode

• From measurement:

It is ~45 times of the energy deposit in the crystal.

• GEANT simulation shown the energy deposit of photod

iodes for a shower leakage is about 240 keV which corr

esponds 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%).

PD

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 and 1.5o in the 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 (S2744-0

8) and 1 µs shaping time) 5000 e /MeV• light uniformity (200 µm Teflon sheet and 2-inch PM

T,testing eight point in length of 24cm)

PDstwofor%15

PMTfor%5average

imumminimummaxU

. 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

Figure 14. Block Diagram of the readout

From DetectorPost amplifier Q Module

TestController

Fan-outTrigger

TEST, DAC

CLK

CLK

L1

VME

L1 reset

Buffer full

CLK

L1

L1 reset

Buffer full

L1

L1 reset

Buffer fullSCLK, DIN , SCV

Analog Sum

Preamplifier

Preamplifier

Gain 1mV/fcENC 0.16fc (80pF input capacitance)Dynamic Range 0.5fc ~ 1500fcOutput decay time 50sMax linear output 2V

• 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

Figure 15. Block diagram of the post amplifier

• ½(A+B), A, B can be selected• CR-(RC)2 with pole-zero cancellation shaping, =1s• Gain adjustable with digital potentiometer• Analogue sum for trigger• Differential connection with Pre-AMP and Q module

A+B

A

B

CR (RC)2

From Test Controller

To Q Module

To Trigger∑

A

B

From Preamplifier

Post Amplifier

Q Module

• 3 FADCs sample signals from 3 different gain AMPs• Delay samples for 1.7s with pipeline to wait for 3.2s trigger latency L1• Find peak within 3s 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

×.25 Pipeline

×1

×8

Pipeline

Pipeline

Peak Selec.Range

EncodingCompress

Peak

Peak

Peak

Buffer

From Post AMP.

FADC

FADC

FADC

Disc. Delay L1

Out. TrigInn. Trig

Thr. Register

Figure 16. Block diagram of Q module

7. Counter testingBefore 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

CalibrationBefore calorimeter assembling, each counter will be pre-calibrate

dusing cosmic ray in the Lab .Has cosmic ray running for 1 month after the installation ofBESIII finishedAt normal performance:1. Calibration system of electronics every day (gains, pedestals a

nd linearity) 2. Temperature corrections for CsI crystal with temperature co

efficient 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 monitore

d 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

ii

ii ADCdEE

25

1iij EE

N

1j2j

2ii

25

1iexp

2)/EE(

expE25

j

iADC

i

is the data of light output of the crystal i .

is the fraction of light output of the crystal i.

are the fraction and error of energy deposited in ,defined by MC

,

5.0minmax

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