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

CrystalCsI(Tl)CsIBaF 2 CeF 3 BGOBSOPbWO 4 LSO(Ce)GSO(Ce) Density (g/cm 3 ) Melting Point (ºC) Radiation Length (cm) Molière Radius (cm) Interaction Len. (cm) Refractive Index a HygroscopicitySlight No Luminescence b (nm) (at peak) Decay Time b (ns) , Light Yield b,c (%) d(LY)/dT b (%/ ºC) ~ Radiation hardness (rad) Experiment CLEO BABAR Belle BES III KTeV, E787 TAPS L3 BELLE CMS ALICE 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  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 % 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 +80% at room T° Development of the PWO-II : Light yield increased Optimization of the PbWO 4 (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 3x3 matrix 20x20x200mm 3 PM-readout Response to high energy 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 (>10 35 )  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 or PP 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 checked 2.High energy signals  enough signal in CsI(Tl) crystals ->do not lose resolution 3.Fast/Slow  another handle for shower correction by knowing shower shape 4.Fast trigger signal using fast signal  blind to beam background 5.Much cheaper An alternative idea SNU Fast Slow

 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. E tot = E 1 *a + E 2 *b a,b : calibration factor 1)E 2 =0 : 1 st crystal interaction 2)E 1 =0 : 2 nd crystal interaction 3)Both : E tot 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 10cm Pure CsICsI(Tl) Note the difference in the emission spectrum of two X-tals E_dep_pure ->N_photon according to Intensity ->Apply transmission curve Some transmit to csi(Tl)->fast signal Other + E_dep_Tl  slow signal SNU

E10/Etot E5/Etot E10/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 (1x1x1cm 3 ) 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. 1x1x1cm 3 cubic CsI 2. 1x1x1cm 3 cubic CsI:Tl 3. 1x1x2cm 3 CsI+CsI:Tl (from 1 &2) Small size Crystal R&D KNU

X-ray emission    Pulse height Decay time Pulse height Decay time Pulse height Decay time Q: Does emission of CsI de-excite CsI:Tl ? Pure CsI CsI(Tl) KNU Am241, Cs137

KNU

310 nm 490 nm ?? Pure CsICsI(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 Tl Pure CsI KNU

Test setup for cosmic rays T.Y.Kim HYU Physics Hybrid signal shape sbelle Korea Meeting Page 20 CsI (Tl) Power Supply(HV) -1500V AmplifierFADC 400MHzLinux PC PMT (High gain Xp2206) 20cm CsI (pure) 10cm ULSNotice KoreaFedora core 6 HYU

Cosmic ray - Data T.Y.Kim HYU Physics Hybrid signal shape sbelle Korea Meeting Page 21  CsI (pure) CsI (Tl) CsI (pure) HYU

Cosmic ray - Data T.Y.Kim HYU Physics Hybrid signal shape 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 - PbWO 4 : operation at -25 o C 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