B.G. Cheon (Hanyang), H.J.Kim (KNU), E. Won

(KU), S.S. Myoung S.K. Kim(SNU), Y.J. Kwon (Yonsei)

We, Korean group reviewed possible options for the endcap ECL from the scratch.

The goal is to see if there are alternatives to pure CsI crystal option we have.

Parameters we looked at in particular : - light yield (energy resolution) - decay time (pileup, occupancy) - radiation hardness - beam background suppression - budget and other fabrication issues

Crystal CsI(Tl)

CsI BaF2 CeF3 BGO BSO PbWO4 LSO(Ce) GSO(Ce)

Density (g/cm3) 4.51 4.51 4.89 6.16 7.13 6.8 8.3 7.40 6.71

Melting Point (ºC) 621 621 1280 1460 1050 1030 1123 2050 1950

Radiation Length (cm)

1.85 1.85 2.06 1.65 1.12 1.15 0.9 1.14 1.37

Molière Radius (cm)

3.5 3.5 3.4 3.38 2.3 2.0 2.3 2.37

Interaction Len. (cm)

37.0 37.0 29.9 23.17

21.8 18 21 22

Refractive Index a 1.79 1.95 1.50 1.60 2.15 2.06 2.2 1.82 1.85

Hygroscopicity Slight Slight

No No No No No No No

Luminescence b (nm)(at peak)

550 320 300220

340300

480 480 420 420 440

Decay Time b (ns) 1300 356

6300.9

30 300 1002.4,26

3010

40 60

Light Yield b,c (%) 45 3-4 212.7

4-5 13 3-4 0.10.6

75 30

d(LY)/dT b (%/ ºC) 0.3 -0.6 -2~0

0.05 -1.6 -2.0 -1.9 -0.3 -0.1

Radiation hardness (rad)

103 104-5 106-7 106-7 105-6 106-7 106-7 108 108

Experiment CLEO BABAR Belle

BES III

KTeV,

E787

TAPS L3BELLE

CMSALICE

PANDA

-

a. at peak of emission; b. up/low row: slow/fast component; c. measured with bi-alkali PMT

Decay time ~30 ns which is 40 times faster than CsI(Tl). Solves pileup problem.

Light yield is ~5% CsI(Tl) and peak emission is 320 nm (UV region)

Radiation hardness may be OK (need to checked carefully) up to 1035

Readout by APD or P.P. No change to geometry of calorimeter Cost is ~$4/cc Currently under R&D by sBELLE group

Decay time with 40 ns. Solves pileup problem. Smaller radiation length and Moller radius

makes shorter and finer segmentation possible.

Radiation hard to 100MRad Light output is half of CsI(Tl), and peak

emission is 420 nm Use PD, APD or P.P. for photosensor LYSO has slightly more light output than LSO,

and may be easier to obtain commercially GSO has similar characteristics but has large

thermal neutron cross section LuAG:Pr is also good candidate except the cost Currently the cost is ~$30/cc!! Italian Endcap ECL default option

Decay time with 10& 30 ns. Solves pileup problem.

Smaller radiation length and Moller radius makes shorter and finer segmentation possible.

Radiation hard to 10MRad Light output is 0.1-0.6% CsI(Tl) Cooling to -25 degree with PMT shows

reasonable performance Peak emission is 420 nm Use APD or P.P. for photosensor CMS, PANDA is using Currently the cost is ~$3/cc

Optimization of the PbWO4 and increase of the light output

4x lighter if cooled down

0 200 400 600 800 10000

20

40

60

80

100

LY

/ p

.e./M

eV

integration gate / ns

-25oC

-10oC

-0oC+10oC+25oC

400 600 800 1000 1200 14000

1000

2000

3000

/E=18.2%

coun

ts

energy / a.u.

22Na

/E=11.5%

LY=92.2pe/MeV

400 600 800 1000 1200 14000

1000

2000

3000

/E=18.2%

coun

ts

energy / a.u.

22Na

/E=11.5%

LY=92.2pe/MeV

+80% at room T°

Development of the PWO-II : Light yield increased

Optimization of the PbWO4 (collaboration RINP, Minsk and the manufacturer BTCP at Bogoroditsk, Russia)

–reduction of defects (oxygen vacancies)–reduced concentration of La-, Y-Doping–better selection of raw material–optimization of production technology

incident energy / GeV

ener

gy r

esol

uti

on

incident energy / GeV

ener

gy r

esol

uti

on

3x3 matrix20x20x200mm3

PM-readout

Response to high energy photons @MAMI, Mainz

Calor2008

Main decay time is 100 ns. Smaller radiation length and Moller radius

makes shorter and finer segmentation possible.

Radiation hard to 1-10 MRad Light output is 3-4% of CsI(Tl), and peak

emission is 480 nm Use APD or P.P. for photosensor BSO:Ce shows stronger radiation hardness Beamtest results shows reasonable resolution Cost will be cheaper than BGO (No Ge) and

growing is easier (Cubic structure, low melting) Need to produced in large quantity (~$3/cc?)=> BSO option seems OK, if 100 ns decay time is

OK

Pure CsI is baseline option, however it may be problem with higher luminesity (>1035)

L(Y)SO, PbWO4 and BSO are reasonable option. BSO seems the most reasonable next candidate

considering all characteristics if it can be produced large quantity. If we can cool down to -25 degree, PWO is the best candidate since it is being produced large quantity.

BSO and PWO costs ~3$/cc & can be used with 20cm length with finer segmentation.

Detail study and comparison of different candidates coupled with photo sensor are necessary to select the best performance one.

APD orPP

Pure CsI Used CsI(Tl)

Endcap ECL upgrade : 11 M USD (8.2M for crystals)Crystal costs ¼ of full crystal 2 M total <5 M should be OK

Logic (and probably advantages)

1.Radiation damage only to front ~10 cm of crystals need to be checked2.High energy signals enough signal in CsI(Tl) crystals ->do not lose resolution3.Fast/Slow another handle for shower correction by knowing shower shape4.Fast trigger signal using fast signal blind to beam background5.Much cheaper

An alternative idea

SNU

FastSlow

A phoswich ('phosphor sandwich') is a combination of scintillators with dissimilar pulse shape characteristics optically coupled to each other and to a common PMT. Pulse shape analysis distinguishes the signals from the two scintillators, identifying in which scintillator the event occurred.

Etot = E1*a + E2*ba,b : calibration factor1) E2=0 : 1st crystal

interaction2) E1=0 : 2nd crystal

interaction3) Both : Etot can be

calculated

Idea: re-use (possibly) un-damaged rear part of endcap CsI(Tl) crystals

CsI(Tl)Pure CsI

SNU

CsI 8cm*8cm*30cm

-15cm +15cm

Gamma: 100 MeV 200 MeV 400 MeV 500 MeV 1 GeV

10cmPure CsICsI(Tl)

Note the difference in the emission spectrum of two X-tals

E_dep_pure

->N_photon according to Intensity

->Apply transmission curveSome transmit to csi(Tl)->fast signalOther + E_dep_Tl slow signal

SNU

E10/Etot

E5/Etot

E10/EtotE10/Etot

E10/Etot>0.5 >0.7

10MeV: 83% 82%100MeV: 86% 73%1GeV: 51% 13%

One Crystal

SNU

100 MeV

200 MeV

500 MeV 1 GeV

E(pure) vs. E(CsI(Tl))

E=a*E(Tl )+ b*E(pure)fit to each energy distribution

σ /E

E

5 cm

Energy resolution is 2% at 1 GeV

SNU

30cm*30cm*30cm

Two Belle type of crystals were received from KEK and cut into test samples (1x1x1cm3) for this study. They are polished and wrapped with Teflon sheet.

Maxium 40 keV x-ray energy is used for luminescence test

2” bi-alkali high gain PMT is used for 662 keV gamma and 5.5 MeV alpha-ray test.

Configuration 1. 1x1x1cm3 cubic CsI2. 1x1x1cm3 cubic CsI:Tl3. 1x1x2cm3 CsI+CsI:Tl (from 1 &2)

Small size Crystal R&D

KNU

X-ray

X-rayX-ray

X-rayemission

emission

emission

emission

Pulse heightDecay time

Pulse heightDecay time

Pulse heightDecay time

Q: Does emission of CsI de-excite CsI:Tl ?

Pure CsI

CsI(Tl)

KNU

Am241, Cs137

KNU

310 nm490 nm ??

Pure CsI CsI(Tl)

550 nm

Pure to Tl

490 nm

Tl to pure

550 nm

Strange enhancement !!!

Because of the mystery above, we cannot draw any conclusions

KNU

Am-241(alpha)

Cs137(gamma)

Am-241(alpha)

Am-241(alpha)

Pure to TlPure CsI

KNU

Test setup for cosmic rays

T.Y.Kim HYU Physics

Hybrid signal shape measurement @ sbelle Korea Meeting Page 20

CsI

(Tl)

Power Supply(HV)

-1500V

Amplifier FADC 400MHz

Linux PC

PMT

(High gain

Xp2206) 20cm

CsI

(pure)10cm

ULS Notice Korea

Fedora core 6

HYU

Cosmic ray - Data

T.Y.Kim HYU Physics

Hybrid signal shape measurement @ sbelle Korea Meeting Page 21

CsI (pure)

CsI

(Tl)

CsI

(pure)

HYU

Cosmic ray - Data

T.Y.Kim HYU Physics

Hybrid signal shape measurement @ sbelle Korea Meeting Page 22

CsI (Tl)

CsI

(Tl)

CsI

(pure)

HYU

Phoswich option may reduce the budget significantly (5 cm pure CsI costs < 5M US $).

Geant4 simulation (very preliminary) shows the energy resolution is ~ 2% at 1 GeV.

E = a*E(pure) + b*E(CsI(Tl)) seems to make everything complicated.

Phoswich x-ray luminescence shows a strange behavior (need to understand, calibration issue?).

Phoswich fast and slow components are 50:50 % in the signal.

More R&D is needed to understand situation better.

Pure CsI is a default option We are looking at - LSO : expensive but others look fine- BSO : decay time 100ns, no mass production- PbWO4 : operation at -25 oC is desired

as feasible alternative options Phoswich[CsI:CsI(Tl)] has been studied. We would like to continue R&D efforts to reduce

number of options, if not one option