PROCEEDINGS OF SPIE. The next generation of crystal detectors

Transcription

1 PROCEEDGS OF SPE SPEDigitalLibrary.org/conference-proceedings-of-spie The next generation of crystal detectors Ren-Yuan Zhu Ren-Yuan Zhu, "The next generation of crystal detectors," Proc. SPE 9593, Hard X-Ray, Gamma-Ray, and eutron Detector Physics XV, 9593T (4 September 25); doi:.7/ Event: SPE Optical Engineering + Applications, 25, San Diego, California, United States Downloaded From: on 2/4/27 Terms of Use:

2 The ext Generation of Crystal Detectors Ren-Yuan Zhu* a a , HEP, California nstitute of Technology, Pasadena, CA 925, USA ABSTRACT Crystal detectors have been used widely in high energy and nuclear physics experiments, medical instruments and homeland security applications. ovel crystal detectors are continuously being discovered and developed in academia and in industry. n high energy and nuclear physics experiments, total absorption electromagnetic calorimeters (ECAL) made of inorganic crystals are known for their superb energy resolution and detection efficiency for photon and electron measurements. A crystal ECAL is thus the choice for those experiments where precision measurements of photons and electrons are crucial for their physics missions. For future HEP experiments at the energy and intensity frontiers, however, the crystal detectors used in the above mentioned ECALs are either not bright and fast enough, or not radiation hard enough. Crystal detectors have also been proposed to build a Homogeneous Hadron Calorimeter (HHCAL) to achieve unprecedented jet mass resolution by duel readout of both Cherenkov and scintillation light, where development of cost-effective crystal detectors is a crucial issue because of the huge crystal volume required. This paper discusses several R&D directions for the next generation of crystal detectors for future HEP experiments. Keywords: Crystal, scintillator, calorimeter, radiation damage, fast timing. TRODUCTO Crystal detectors have been used widely in high energy and nuclear physics experiments, medical instruments and homeland security applications. ovel crystal detectors are continuously being discovered and developed in academia and industry. Table Existing Crystal Calorimeters in High Energy Physics Date Experiment Accelerator C. Ball SPEAR L3 LEP CLEO CESR C. Barrel LEAR KTeV FAL BaBar SLAC BELLE KEK CMS CER Crystal Type a:tl BGO Cs:Tl Cs:Tl Cs Cs:Tl Cs:Tl PWO B-Field(T) rinner (m) Crystal number 672,4 7,8,4 3,3 6,58 8,8 76, Crystal Depth(X) to Crystal Volume(m 3 ) Light Output(p.e./MeV) 35,4 5, 2, 4 5, 5, 2 Photo-detector PMT Si PD Si PD WS+Si PD PMT Si PD Si PD Si APD Gain of Photo-detector Large 4, 5 σ/channel(mev) Small Dynamic Range *zhu@hep.caltech.edu; phone (626) ; fax (626) Hard X-Ray, Gamma-Ray, and eutron Detector Physics XV, edited by Larry Franks, Ralph B. James, Michael Fiederle, Arnold Burger, Proc. of SPE Vol. 9593, 9593T 25 SPE CCC code: X/5/$8 doi:.7/ Proc. of SPE Vol T- Downloaded From: on 2/4/27 Terms of Use:

3 n high energy physics (HEP) and nuclear physics (P) experiments, total absorption electromagnetic calorimeters (ECAL) made of inorganic crystals are known for their superb energy resolution and detection efficiency for photon and electron measurements []. A crystal ECAL is thus the choice for those experiments where precision measurements of photons and electrons are crucial for their physics missions. Examples are the Crystal Ball a:tl ECAL, the L3 BGO ECAL and the BaBar Cs:Tl ECAL in lepton colliders, the ktev Cs ECAL and the CMS PWO ECAL in hadron colliders and the Fermi Cs:Tl ECAL in space. Table lists existing crystal calorimeters in high energy physics. For future HEP experiments at the energy and intensity frontiers, however, the crystal detectors used in the above mentioned ECALs are either not bright and fast enough, or not radiation hard enough. Crystals have also been proposed to build a Homogeneous Hadron Calorimeter (HHCAL) to achieve unprecedented jet mass resolution by duel readout of both Cherenkov and scintillation light [2], where development of cost-effective crystal detectors is a crucial issue because of the huge crystal volume required [3]. This paper discusses several R&D directions for the next generation crystal detectors for future HEP experiments. increases, m and recovers during LHC stops. 2. PERFORMACE OF PWO CRYSTALS Table shows that the CMS lead tungstate (PbWO 4 or PWO) crystal calorimeter, consisting of 76, crystals of m 3, is the largest crystal calorimeter ever built. Because of its superb energy resolution and detection efficiency, the CMS eonslqeoos PWO 78 ECAL has played an important role for the discovery of the Higgs boson by the CMS experiment [4]. One crucial issue < is crystal s >' radiation damage in the severe radiation environment at LHC, which requires precision monitoring to correct variations di M l of crystal transparency [5]. After two years of operation up to 7% loss of light output was observed in the CMS PWO crystals at large rapidity in situ at LHC as shown in Figure when the LHC was running at a luminosity of up to 5 33 cm -2 s - and a half of its designed energy [6]. The damage in PWO crystals increases when the luminosity. BTCP-262R L.O.= 9.3 p.e./mev (2 ns, 2. C). rta-. Q.9 }} t} } + }}} o W V f rv 4 W ru co - sanoqasl svilslsl s-ma Sonimul EgOF) OHJ.6.5 dose rate (rad/h): 5 5 recovery Time (hours) 4 Figure. Monitoring response of CMS PWO crystals observed during LHC run. Figure 2. Dose rate dependent light output loss observed in a PWO crystal The radiation damage of PWO crystals shown in Figure is well understood. t is caused by radiation induces absorption, or color center formation, and is dose rate dependent [7]. Figure 2 shows that light output of a PWO crystal reached an equilibrium during irradiation under a defined dose rate, indicating a dose rate dependent radiation damage caused by colour center dynamics. At equilibrium the speed of the color center formation (damage) equals to the speed of the color center annihilation (recovery), so that the colour center density, or the radiation induced absorption, does not change unless the applied dose rate changes [7]. Proc. of SPE Vol T-2 Downloaded From: on 2/4/27 Terms of Use:

4 4 E 3.5 BTCP-PWO _._....._..._......:_..._......: EWRAC=.26`Log(X+)+.8Lóg2(X+) Light Output Loss ( %) p E C.5 w 2 3 Dose rate ( rad /n 4 Figure 3. EWRAC values are shown as a function of dose rate for mass produced PWO Figure 4. Predicated light output loss as a function of luminosity and rapidity Figure 3 shows emission weighted radiation induced absorption coefficient (EWRAC) as a function of the γ-ray dose rate measured for a batch of mass-produced BTCP PWO crystals [8]. The EWRAC values of all crystals are less than m - up to 4 rad/h, indicating no damage to the light response uniformity for PWO crystals used in the CMS ECAL barrel, where the maximum dose rate is expected to be a few hundreds rad/h even if the LHC luminosity is increased by a factor of ten, e.g. at HL-LHC. The EWRAC values measured at 9, rad/h, however, are diverse. Some samples show up to 3 m -, indicating possible damages in the light response uniformity and thus the energy resolution. Figure 4 shows the expected light output loss as a function of luminosity for PWO crystals at different rapidity predicted in 2 before LHC running [9]. This prediction was made according to the measured relation between light output and radiation induced absorption assuming the average EWRAC values shown in red color in Figure 3. A detailed comparison shows that this prediction agrees well with the data shown in Figure, indicating that radiation damage in PWO crystals observed so far is caused by ionization dose. Additional damage caused by charged hadrons was also studied []. Because of these damages the CMS endcap PWO ECAL is proposed to be replaced by using more radiation hard technologies [], one of which is a LYSO crystal based Shashlik sampling calorimeter [2]. 3. RADATO HARD LYSO/LSO CRYSTALS Because of their high density (7.4 g/cm 3 ), short radiation length (.4 cm), fast (4 ns) and bright (4 times BGO) scintillation, cerium doped lutetium oxyorthosilicate (Lu 2SiO 5:Ce, LSO) [3] and lutetium yttrium oxyorthosilicate (Lu 2( x)y 2xSiO 5:Ce, LYSO) [4, 5] crystals have attracted a broad interest in the high energy physics community pursuing precision electromagnetic calorimeter for future high energy physics experiments [2, 6-9]. Their excellent radiation hardness against gamma-rays [5, 2], neutrons [7] and charged hadrons [] also makes them a preferred material for calorimeters to be operated in a severe radiation environment, such as the HL-LHC. The top plot of Figure 5 shows the photo-luminescence spectra of a LYSO crystal measured before (blue) and after (red) Mrad γ-ray irradiation [2]. To facilitate a comparison, these spectra were normalized to the area between 38 and 46 nm under the spectra. The corresponding relative difference is shown in the bottom plot of Figure 5. The bin by bin average of the absolute difference between the spectra measured before and after the irradiation is found to be.6% in the normalization region, less than the systematic uncertainty for this measurement. This indicates that the γ-ray irradiation does not affect the scintillation mechanism in LYSO crystals. Proc. of SPE Vol T-3 Downloaded From: on 2/4/27 Terms of Use:

5 , SG-LYSO-L normalized area nm average of D before irradiation - after 85 rad /h irradiation.6% (38-46 nm) -2, Wavelength (nm) Figure 5. Photoluminescence of a LYSO crystal before and after Mrad γ-ray irradiation 6 - CP -LYSÓ-L 25x5X2 mm'. : Emission.- Before R: 52.5% 5 EWLT 2 rad: 52.2% - 4 rad: 5.5% - 6 rad: / : V V `ì "t-, - -3 i l l l l l l l i os - CT -LSO -L 25x25x2 mm : Emission.. Before R: 55.3% () 5 U - EWLT 2 rad: 55.% - C - 4 rad: 52.5% - rad: 5. /g - i - -P- - F i 8 - SG -LYS -L 25x25x2 mm3 E : Emission.- Before R: 56.4% rn 5 - EWLT 2 rad: 56.% - 4 rad: 53.8% - i rad: 5.> % - -. i ì-'t-- - -r A 8 - SC-LYS-L 25x25x2 mm - : Emission. Before R: 59.9% 5 - EWLT 2 rad: 59.8% - 4 rad: 57.7% - 6 rd -r--r- i 5:( 3 /o l' l i ì- l 8 SPAT -LYSO -L 25x25x2 mm = : Emission_.. Before R: 55.4% 5 - EWLT 2 rad: 55.3% - 4 rad: 54.9% F i.,6.; 53.,ì /4 : Wavelength (nm) Figure 6. LT of 2 cm long LYSO crystals before and after irradiations Figure 6 shows the longitudinal transmittance spectra for five 2 mm long LYSO crystals from different vendors before and after several steps of the γ-ray irradiation with integrated dose of 2, 4 and 6 rad. Also shown in the figure is the corresponding numerical values of the photo-luminescence weighted longitudinal transmittance (EWLT), which is defined as:. () EWLT represents crystal s transparency better than the transmittance at the emission peak since it runs through the entire emission spectrum. This is particularly important for crystals with self-absorption nature, i.e. a part of scintillation is. =SPAT-LYSÓ-L7 Seed end coupling As received = - 4 LYSO SC- A J.8 Ñ. To Ó.9 Z S = (2.8±.5) Average L.O. = 5 p.e./mev 2 rad = W - * * * * * - 6 = (2.4±.5) 6 = (3.±.5) t Average L.O. = 49 p.e./mev A Average L.O. = 4 p.e./mev 6 = (2.6±.5) Average L.O. = 3 p.e./mev rad = V - 6 rad Distance from the end coupled to APD (mm) V -... a) 23 a) Q -92 o Before radiation L.O = Ap+A,(-e(-"" ) Ao A, r rad rad * 7 rad Time (ns) 5 Figure 7. LO and LRU measured by APD for a 28 cm long SPAT LYSO crystal Figure 8. LO and decay kinetics measured by PMT for SC LYSO plate Proc. of SPE Vol T-4 Downloaded From: on 2/4/27 Terms of Use:

6 self-absorbed in the crystal [7]. Consistent damages are observed on the longitudinal transmittance of all LYSO crystal samples. t is noted that the degradation of longitudinal transmittance is small even after 6 rad. Figure 7 shows light output (LO) and light response uniformity (LRU) for a 28 mm long LYSO crystal before and after several steps of the γ-ray irradiations with integrated dose of 2, 4 and 6 rad [2]. About 4% LO loss is observed after Mrad irradiation with LRU maintained. Figure 8 shows LO and decay time for a LYSO plate of mm grown by SC before and after several steps of the γ-ray irradiations with integrated dose of 5, 6 and 7 rad. A LO degradation of 3.4% was observed after Mrad, indicating significant reduction of radiation damage because of short light path. These results as well as the irradiation by 24 GeV protons of up to a fluence of 4 cm -2 [] demonstrate the excellent radiation hardness of LYSO crystals. 4 mm W (2.5 mm) / LYSO (.5 mm) 4x WLS fibers lx Monitoring fiber Figure 9. A schematic showing a LYSO/W Shashlik calorimeter concept consisting of LYSO plates of.5 mm thick and tungsten plates of 2.5 mm thick, 4 WLS fibers and one monitoring fiber. Figure 9 shows a LYSO crystal based Shashlik calorimeter detector concept with four evenly distributed wavelength shifting (WLS) fibers for readout and a monitoring fiber at the center [2]. This detector concept reduces the crystal volume and cost, and improves the radiation hardness of the calorimeter because of the much reduced light path. As shown in Figure 9, the initial design consists of 3 LYSO plates of.5 mm thick and 29 W plates of 2.5 mm thick. Each tower has a depth of 25 X to accommodate electrons and photons with energies up to the TeV range. The sampling fraction was chosen to be around 2% to provide an adequate stochastic term of the energy resolution at a level of %. Because of the high density of both the LSO/LYSO crystals and the absorber materials, the average radiation length (.5 cm) and Moliere radius (.3 cm) are much smaller as compared to commonly used crystal scintillators. This detector concept thus also provides a very compact calorimeter to mitigate the pile-up effect expected at the HL-LHC. Figure shows a photograph of LYSO/W Shashlik tower with four Y- WLS fibers coupled to a readout PMT. A beam test for a LYSO/W Shashlik matrix consisting of sixteen towers is being carried out at Fermilab. Coupled to PMT LYSO Plates (4x4x.5 mm) W Plates (4x4x2.5 mm) 4 Y - WLS fibers Figure. A photo showing a LYSO/W Shashlik tower with four WLS fibers inserted Proc. of SPE Vol T-5 Downloaded From: on 2/4/27 Terms of Use:

7 Figure shows a set-up used to measure longitudinal response uniformity for the LYSO/W Shashlik detector concept. A mm 3 LYSO plate was moved along four Y- WLS fibers at five points of 2 cm apart. The LO was measured by using a γ-ray source shooting to the LYSO plate. Figure 2 shows the measured result and the corresponding fit for two straight lines using first and last three points. The corresponding slope of the fit is.2%/x at the front, which is less than.3%/x required to maintain good energy resolution [22]. The slope at the back is.7%/x, which is close to the optimum of 8% rise required in the last X....,, L BaF2.5. 4x4x.5 mm3 LYSO plate, 4 cm WLS fiber PMT:R259, HV= -27 V Coupling: Air gap Al mirror 4x4x.5mm3 Fiber mount LYSO plate wrapped with Tyvek Figure. A setup used to measure the longitudinal uniformity for a LYSO/W Shashlik tower Table 2 Basic Properties of Fast Crystal Scintillators }.5 a, (Q i= Z Average LY = 27.7 p.e. /MeV (2 ns) RMS = 3.2% Front Slope = (.2±.3)%/X Back Slope = (.7 ±.3) % /X Distance from Al mirror (cm) Figure 2. The longitudinal response uniformity of a LYSO/W Shashlik tower 2.6.d Yfiznea (fm3\8) $niflsm fnioq (DO) noiisibsa rlipnsj (ma) e73om zuibsa (rn3) noifas7sfnl rugnej (ma) S sulsv Xb\3b (rno\vsm) noia2im3 b>lssg (mn) svit369la dxsbnl svifslsa fr8ij tiblsiy J. cemitysasa (2n) Tb\(YJ)b b J \\) ( \2J 2YJ 4.V 2S Al.]: CO.S e.os 8.Aa 22.e OSA S8. A S.- 2a 2et 8E. ES.S SSE e.v OEA 28. 2A ET 4.- 2Y 44.4 o8et.e ces e.cs E.EE 32.3 SA 8. ac oa E.- qot :snil wolz,tnsnogmod mottod :snil test.tnsnogmod ta snit rit$nslsv6w srltio noizzims.mumix6m.3 svitslsa trl$i blsiyr bssilsmion of silt trl$il blsiyr.b to moo? siutsisgmst OS) (J.# gninstfio2 tnioq 2J OE ire. a,js8 8., 2a e.o }e' ' 8eD #M 2E e_t tolloc2 AS &sj,i a2e e Ad 3if2s9 iotsllifnl2 )8) (AA O noc A2.SA e _ SO oua s ts s oula.m 2o4's.2i(.2e C (Se@r) 8e2-OeS i, mtri.7rolool2toubo7qlriailpnelq(.oamerio-iriostirl.wwwll:giirl.s.w awobso7a te 333.s.2/,5T.A,2,CC.JOV E.OV (85) r ree aeerpnsilnerio ij te s bilo2 ssss2,ttummo emulov,aar asuaal a-a ,(72) lvop.ldl.7otsllitnioall:qttri E xgas.7otsllitnio2-oitasl9lmoo.nisdop-tnisa.a7otoeteb.wwwll:gttri. JMTHasit7ego797selouVloimotA82vop.dl.pbgl:gttri rs23oaq mtri.8 2E 8. Proc. of SPE Vol T-6 Downloaded From: on 2/4/27 Terms of Use:

8 4. ALTERATVE FAST CRYSTALS The high cost of LYSO crystals caused by high Lu 2O 3 price, however, may limit their use in future HEP experiments. Table 2 lists basic optical scintillation properties for alternative fast crystal detectors with scintillation decay time ranged from sub-nanosecond to a few tens nanosecond, and compared to plastic scintillator. Among the fast crystals listed in Table 2 mass-production cost of barium fluoride (BaF 2) and pure Cs crystals is significantly lower than others because of their low raw material cost and low melting point. At this point BaF 2 is baselined for the Mu2e experiment with pure Cs as an alternative option [23]. For applications in severe radiation environment, such as HL-LHC, one of the crucial issues for their application is radiation hardness. nvestigation of radiation hardness for alternative fast crystals would provide important input for future HEP experiments at the energy and intensity frontiers. On the other hand, costeffective fast scintillating glass and ceramics may also be considered and developed. 4. Radiation hardness of large size BaF2 crystals SC22 ()...= 22nm) Q SC22 ()...= 3nm) A S32 (a.= 22nm) Q S32 ()Lem= 3nm) BGR22 ()..= 22nm) BGR22 ().p= 3nm) ', E 3 Y Q 2.5 O (/) 2 * SC-ref (Xem= 22nm) ßt SC-ref (Xem= 3nm) S32 (),.em= 22nm) - S32 (a.em= 3nm) SC22 (iem= 22nm) - O SC22 ()`em= 3nm) BaF2.8 W.5,-- CD AL SC22 ().om= 22nm)' Q SC22 ().m= 3nm) S32 (xer= 22nm) Q S32 (x,n= 3nm) BGR22 ().em= 22nm) BGR22 (). 3nm) ' ntegrated Dose (rad) Q ntegrated Dose (rad) Figure 3. ormalized EWLT and LO as a function of integrated dose for 3 BaF2 crystals Figure 4. RAC as a function of integrated dose for three long BaF2 crystals Figure 3 shows normalized emission weighted longitudinal transmittance (EWLT, top) and light output (LO, bottom) as a function of integrated γ-ray dose for three 25 mm long BaF 2 crystals. While SC22 and BGR22 were grown by SC and BGR respectively in 22, the crystal S32 was grown by SC twenty years ago during nineties for the SSC. The result shows that SC22 is more radiation hard than other samples, indicating an improvement of crystal quality. t was also found that the slow component (3 nm) of all crystals is more radiation hard than the fast component (22 nm). BaF 2 crystals also show stable damage after krad, indicating limited defect density in these crystals which was fully exhausted after krad. This promises a stable BaF 2 crystal calorimeter in a severe radiation environment. Figure 4 shows radiation induced absorption coefficient (RAC) as a function of integrated dose for three BaF 2 crystals, indicating that RAC of mass produced BaF 2 may be controlled to less than.6 m - for the fast component. ote, RAC is independent of sample size, so can be compared to other crystals. Proc. of SPE Vol T-7 Downloaded From: on 2/4/27 Terms of Use:

9 4.2 Radiation hardness of large size pure Cs crystals Figure 5 shows normalized EWLT and LO as a function of integrated γ-ray dose for large size Cs crystals. SC23 (3 cm long) and SC2 were grown by SC in 23 and 2 respectively. The crystals Cs-3 (2 cm long) and Cs-4 (9 cm long) were grown by Kharkov with data published in ucl. ns. Meth. A 326 (993) Consistent radiation damage between these crystals is observed. Figure 5 also shows that radiation damage in Cs is small below krad, but degrades continuously with no sign of saturation at high dose, indicating high defect density in the crystals. Figure 6 shows RAC as a function of integrated dose, which is longer than 3 m - after Mrad Csl SC23 (Xa= 3nm) Cs! SC2 (x..= 3nm) Cs-3 Ref (k..= 3nm).4.2 Cs! SC23 5x5x3 mm3 - Cs! SC2 4x5 mm Cs! SC23 5x5x3 mm3.2 - Cs! SC2 44x5 mm3 - Cs-3 4x4x2 mm3 (Ref) - O Cs-4 5x5x9 mm3 (Ref) 3 3 Ó los 6 lo' ntegrated Dose (rad) Figure 5. ormalized EWLT and LO as a function of integrated dose for 3 Cs crystals ntegrated Dose (rad) Figure 6. RAC as a function of integrated dose for three Cs crystals 5 4 LYSO (k.,= 42nm) YSO GSO O BaF2 Csl (kern= 42nm) (i.o,,,= 43nm) (ñ..= 22nm) (a,,,,= 3nm) rc).6 3 ) E.4 O Z _ BaFzSC22 (Xem 22nm) 25x25x25 mm3 Cs SC23 5x5x3 mm A LYSO CP 25x25x2 mm3 4 5 m 2 m io ntegrated Dose (rad) 6 o 2 3 ; 5 6 ntegrated Dose (rad) 7 Figure 7. ormalized EWLT and LO as a function of dose for BaF 2, Cs and LYSO Figure 8. RAC as a function of integrated dose for crystals with dose rate independent damage Proc. of SPE Vol T-8 Downloaded From: on 2/4/27 Terms of Use:

10 i 4.3 Comparison of radiation hardness between BaF2, pure Cs and LYSO Figure 7 and 8 show normalized EWLT, LO and RAC as a function of integrated dose for crystals with dose rate independent radiation damage, i.e. BaF 2, pure Cs and LYSO. Because of no recovery these crystals promise a more stable calorimeter than that with dose rate dependent radiation damage, such as PWO. LYSO crystals show clearly the best radiation hardness. Among two crystals of low cost, the radiation hardness of BaF 2 is good at high dose and that of Cs is good at low dose. 4.4 Time resolution of crystal scintillation Crystal time resolution is important for many applications. t depends on the signal to noise ratio for the rise time measurement. While scintillation light is known to have very different decay time for various crystals, the intrinsic rising time of most crystals is as fast as tens ps [24]. Figure 9 shows the rising time measured by using a Hamamatsu R259 PMT for ten crystal samples of.5x size. The fast rise time of about.5 ns observed for BaF 2, LYSO, CeF 3 and BGO is dominated by the PMT rise time.3 ns (25 V) and the rise time of.4 ns of the Agilent MSO9254A (2.5 GHz) DSO. The measured rise time values are also reduced for the same crystal with black wrapping, indicating effect of the light propagation in the crystal [25]. u 3-2 Time pik Line pick -off Time pick-off Time pick -off Time pick -off OD BaF2.5Xo cube -Tyvek wrapping. t,= ns -Black wrappng, t,= ns i i 5 Turne (ns) i LYSO:Ce.5Xo cube -Tyvek wrapping, t,= ns -Black wrapping, t,=.8 32 ns CeF3.5Xo cube -Tyvek wrappng, t,= ns -Black wrapping. t,= ns ililltlitlitil BGO.5X cube -Tyvek wrapping, t,= ns -Black wrapping, t,=.8 32 ns i i i i Time (ns) Turne (ns) Time (ns) me pick-off _ Ze pick-off Csl.5; sample -Tyvek window. tp 2. ±.2 m - Black window, t,= ns.7ì : 5 Turne (ns) me pick-off Time pick-off " Time pick-off `Y{J"//_ WBr:Ce.5Xo sample --Tyvek window. t,= ns --Black window. l,=2.93.3ns.... A.. 5 Time (ns)... LaC:Ce _.5Xo sample _-Tyvek window, t,= ns --Black windpw ns Time (ns) d(t) CS(n) " - ' Csl(a) -.5Xo sample..5xo sample. -5Xc sample - Tyvek window t,= 8.8 :.5 ns Tyvekwindow t,= 38 3 ns - Tyvek window t,= 38 3 res -Black window 4=8.33.5ns - -Blackwndowt,=353ns _Blackwindow t,=353ns Time (ns) Time (ns) Time (ns) Figure 9. Scintillation rising time measured for ten crystal samples of.5 X Table 3 Figure of Merit for Time Resolution for Various Crystal Scintillators cans! mn laz 2. re 669An6fA (x3 V'(de) P(ux) o (el. i, cm) 9 f (b'.'\w6a' X633248) f!u Jul (6'6'W6A' Xb3324B) f!u. lux (b'6'w6a' ) laryo'uz (qporouz\wba) d 749 T wo 73e'e 2:C9'C ' 7' f2ova2:c '4 C6k' '3 7 3 SO8 e'8 Se 8 S '3 3'2 bm SO CO 9'S '4 '4 f9bl':c TWO S59" f9cl':cg e SO 2 49'39 2'3 es'2 9: 32 3e4, 74'2 Czl ' 3 53 P 737 Y9 we Cz: e2 5 S93 ' C+G e '2 Proc. of SPE Vol T-9 Downloaded From: on 2/4/27 Terms of Use:

11 Table 3 lists the values of the figure of merit for time resolution for various crystal detectors, which is defined as the light output in the st, or the st., ns [25]. t is clear that the best crystal scintillators for ultra-fast timing are BaF 2, LSO:Ca,Ce and LSO/LYSO:Ce. LaBr 3 is a material with high potential theoretically, but suffers from scattering centers in the crystal as well as its intrinsic hygroscopicity. 5. CRYSTALS FOR THE HHCAL DETECTOR COCEPT Aiming at the best jet-mass resolution cost-effective inorganic crystal scintillators are being developed for a homogeneous hadron calorimeter (HHCAL) detector concept with dual readout of both Cherenkov and scintillation light for future high energy lepton colliders [2]. Because of the unprecedented volume (7 to m 3 ) foreseen for the HHCAL detector concept cost-effectiveness is the most important requirement [3]. n addition, the material must be dense to reduce the calorimeter volume, UV transparent for effective collection of the Cherenkov light, and allow for a clear discrimination between the Cherenkov and scintillation light. The preferred scintillation light is thus at a longer wavelength, and not necessarily bright nor fast. norganic crystals being investigated are doped lead fluoride (PbF 2) [3, 26], lead chloride fluoride (PbFCl) [27-29] and bismuth silicate (Bi 4Si 3O 2 or BSO) [3-32]. CBT7 ' PbF Mo T i. L y xp'' A.. 28 ir. 3 ms '3F. A 'OCF.2.2 o o Light Output (p.e. /MeV) ö Time ns Time ms \n.a.-_ C Time (ms 2 os Ç PbF'.EU.AOxiF A.. i.8.52ns 'r.f D PbF.Sm -Ae.Fi., A. t..2ms CCF. PbFTb o e`.ae A. :.495ms t'df.8 r- 2 Time (ms Time ( ms ) Tima ( ms ) Figure 2. Decay kinetics of doped PbF 2 exited by UV light Figure 2. Decay kinetics of a PbFCl sample excited by γ-rays Figure 2 shows UV light excited decay kinetics of doped PbF 2 samples [26]. The decay time of rare earth doped PbF 2 crystals is several milliseconds which is too long to be used for HHCAL. Figure 2 shows decay kinetics of PbFCl crystal excited by gamma rays. ts 24 ns decay time is appropriate for the HHCAL application. Because the layer structure, however, PbFCl crystal of large size is hard to grow. Because of its low UV cut-off wavelength (3 nm) and low raw material cost (<5% of BGO), BSO crystals are under development at Shanghai nstitute of Ceramics (SC). Figure 22 shows longitudinal transmittance (LT) and photoluminescence (PL) spectra for a 5 mm long BSO crystal. Figure 23 shows relative light output of the BSO crystal comparing to BGO crystal. The LO of BSO with ns decay time is approximately 2% of BGO crystal. See reference [33] for recent development for this crystal. Proc. of SPE Vol T- Downloaded From: on 2/4/27 Terms of Use:

12 7 >, 8 f 6 BSO-8 ( 22 X 5 mm) 6 - em: 48 nm ex: 294 nm ' 'B'Gd ('7 mm dubéj ' ' Source: Cs PetGa. = 53 ch, et peak =55th R, L.O. % L co >` 4 ) ++ C 2 BSO-8 Middl R.L.O.=.7% Wavelength (nm Figure 22. LT and PL of BSO crystal Figure 23. Relative LO of BSO crystal 6. SUMMARY Bright, fast and radiation hard LYSO/LSO crystals may be used for a total absorption ECAL. LYSO/W Shashlik calorimeter is one of two options for the CMS FCAL upgrade technical report for the proposed HL-LHC. Crystal calorimeters with more than ten times faster rate/timing capability require very fast crystals, e.g. sub-ns decay time of the BaF 2 fast scintillation component. Crystals (PbF 2, PbFCl and BSO) may provide a foundation for a homogeneous hadron calorimeter with dual readout for both Cherenkov and scintillation light to achieve unprecedented jet mass resolution for future lepton colliders. ACKOWLEDGEMETS This work was supported in part by the US Department of Energy Grant DE-SC925.. RRFERECES [] Zhu R Y, 22, Physics Procedia 37, 372. [2] Driutti A, Para A, Pauletta G, Briones R, and Wenzel H, 2, J. Phys.: Conf. Ser. (Beijing, China), [3] Mao R H, Zhang L Y, and Zhu R Y, 22, EEE Trans. ucl. Sci., 59, [4] Chatrchyan S, Khachatryan V, Sirunyan A M, Tumasyan A, Adam W, Aguilo E, et al., 22, Physics Letters B, 76, 3 [5] Zhu R Y, 24, EEE Trans. ucl. Sci., 5, 56 [6] T. T. de. Fatis on behalf of the CMS Collaboration, 22, J. Phys.: Conf. Ser.(Sanat Fe, USA), 44, 22 [7] Zhu R Y, 998, ucl nstrum Meth A, 43, 297 [8] Mao R H, Zhang L Y, and Zhu R Y, 24, EEE Trans. ucl. Sci., 5, 777 [9] Zhu R Y, [] Dissertori G, Luckey D, essi-tedaldi F, Pauss F, Quittnat M, Wallny R, et al., 24, ucl nstrum Meth A, 745, [] Biino C, in these Proceedings. [2] Zhang L Y, Mao R H, Yang F, and Zhu R Y, 24, EEE Trans. ucl. Sci., 6, 483 Proc. of SPE Vol T- Downloaded From: on 2/4/27 Terms of Use:

13 [3] Melcher C L and Schweitzer J S, 992, EEE Trans. ucl. Sci., 39, 52 [4] Kimble T, Chou M, and Chai B H T, 22, Proc. EEE uclear Science Symp. Conf., vol 3 (orfolk, Virginia, USA), p 434. [5] Cooke D W, McClellan K J, Bennett B L, Roper J M, Whittaker M T, Muenchausen R E, et al., 2, J Appl Phys, 88, 736. [6] Chen J M, Mao R H, Zhang L Y, and Zhu R Y, 27, EEE Trans. ucl. Sci., 54, 78. [7] Chen J M, Zhang L Y, and Zhu R Y, 25, EEE Trans. ucl. Sci., 52, 333. [8] Eigen G, Zhou Z, Chao D, Cheng C H, Echenard B, Flood K T, et al., 23, ucl nstrum Meth A, 78, 7. [9] Pezzullo G, Budagov J, Carosi R, Cervelli F, Cheng C, Cordelli M, et al., 24, J nstrum, 9, C38. [2] Chen J M, Mao R H, Zhang L Y, and Zhu R Y, 27, EEE Trans. ucl. Sci., 54, 39. [2] Mao R H, Zhang L Y, and Zhu R Y, 22, EEE Trans. ucl. Sci., 59, [22] Graham G and Seez C, CMS ote [23] Pezzullo G, in these Proceedings. [24] Derenzo S E, Weber M J, Moses W W, and Dujardin C, 2, EEE Trans. ucl. Sci., 47, 86. [25] Zhu R Y, [26] Mao R H, Zhang L Y, and Zhu R Y, 2, EEE Trans. ucl. Sci., 57, 384. [27] Yang F, Zhang G Q, Ren G H, Mao R H, Zhang L Y, and Zhu R Y, 24, EEE Trans. ucl. Sci., 6, 489. [28] Zhang G Q, Yang F, Wu Y T, Sun D D, Shang S S, and Ren G H, 24, J norg Mater, 29, 62. [29] Chen J M, Shen D Z, Ren G H, Mao R H, and Yin Z W, 24, J Phys D Appl Phys, 37, 938. [3] Fei Y T, Fan S J, Sun R Y, Xu J Y, and shii M, 2, Prog Cryst Growth Ch, 4, 89. [3] Barysevich A, Dormenev V, Fedorov A, Glaser M, Kobayashi M, Korjik M, et al., 23, ucl nstrum Meth A, 7, 23. [32] shii M, Harada K, Senguttuvan, Kobayashi M, and Yamaga, 999, J Cryst Growth, 25, 9. [33] Yang F, Yuan H, Zhang L and Zhu R Y, in these Proceedings. Proc. of SPE Vol T-2 Downloaded From: on 2/4/27 Terms of Use: