DREAM Collaboration : Recent Results on Dual Readout Calorimetry . F.Lacava

1. DREAM Collaboration: RecentResults on DualReadoutCalorimetry . F.Lacava for the DREAM Collaboration Cagliari – Cosenza – Iowa State – Pavia – Pisa – Roma I – Texas Tech. EPS Conference 2011

2. The DualReadoutMethod The DREAM calorimeter • In hadroniccalorimeters the fluctuationsof the e.m.showerfraction (fem) dominate • the energyresolutionforhadrons and jets. • In non compensatingcalorimeters (i.e. where e/h ≠ 1) itispossibleto eliminate this • effectbymeasuringfemeventbyevent. • Thiswasachieved in 2003 in the DREAM Calorimeterwithtwoactive media: • - the signalSfromScintillatingfiberstomeasuredE/dxfromallchargedparticles, • - the signalQ fromclearfibers (quartz or plastic) forCherenkov light mostlyfrom • the e.m.componentof the showers. • Copper – Scintillating and Quartz (clear) fibers • 19 hexagonaltowers, • eachtower: 270 hollowcopperrods, • 2 m (10 λInt) in depth , radius ≈ 16 cm ( < 1 λInt).

3. If R = 1 fore.m.shower , the responseof the active media foranhadronicshoweris: • where e/h is 1.3 forScintill. and 4.7 forclearfibers • From the ratioof the signals in the quartz (clear) fibers Q and in scintillatingfibers S : • femismeasured and the energyiscorrected. • Resolutionislimitedby the smallCherenkovphotonyield (9-18 per depositedGeV ). “Jets” 200 GeV (pions interacting in a target)

4. DualReadout in crystals • In last yearsextensivestudieswereperformedtoextend the DualReadout in crystals • used in homogeneouscalorimeters . In thesecrystals a fractionof the light yieldis due • toCherenkovemission (1% in BGO, up to 15% in PWO). • The peculiarfeaturesof the Cherenkov light can • beexploitedto separate the twotypesof light: • directionality : cos θ = 1/βn • timing : Cherenkov light isprompt (fewns) while • scintillation light hasdecaycostant. • Spectralproperties: 1/λ²distribution • One more tool: polarizationof the Cherenkov light. PbWO4 Yellow filter long decaytail UV filter prompt light PbWO4 BGO (Signalsafteran UV filter)

5. Polarization in dualread out • Cherenkov light isemittedbymoleculesthat are excited and polarizedby a • superluminal particlecrossing the medium. • The moleculesemitcoherentradiation at an angle θC =arcos (1/βn) with • respectto the particledirectonand with the polarizationvectorperpendicularto • the conewhosecentralaxisis the particletrack. • Then the Cherenkovcomponent can beseparatedfrom the scintillation • light by a polarizerin frontofthe PMT. • Thiswasdoneby the DREAM Collaboration in the 2010 test beam. • (see NIM A 638 (2011) 47-54.

6. Side Top view Edge Mostlyhorizontal polarization • 180 GeV/c pionbeamcrossing a BSO crystal at 30°, • UV filterfollowedby a polarizerto separate the Cherenkov light. Cherenkov Scintillation θ

7. BSO vs BGOcrystals • High density scintillatingcrystals are usedasexcellente.m.calorimeters • buttheyhavepoor performance for detection ofhadrons and jets • (verylarge e/h ratio). • The possibilityto separate the Scintillation/Cherenkovcomponents in • crystalsdemonstratedby the DREAM Collab. allowstoextend • the dual-readoutalso in e.m.crystalscalorimeters. • Extensivestudieshavebeenperformed in the pastby the DREAM • Collaboration on PWO and BGO crystals (see NIMA) . • A recent test beamcomparedtwocrystalsof BSO (BismuthSilicate) and • BGO (BismuthGermanate) ofequaldimensions ( 2.2 x 2.2 x 18 cm³). Now on NIM A 640 (2011) 91-98

8. Averagesignals UV filter • Crystals on a rotating • platform, • UV filter (UG11/U330) • forCherenkov PMT • Yellow filter • forScintillation PMT Cherenkov PMT θ Yellow filter 180 GeVpions Scintillation PMT • Fasterscintillation in BSO ( Scint. yield BGO / BSO ≈ 4), • Sameattenuantionlength (Cher. and Scint.) ≈ 34 cm , • AbsorptionforCherenkov (1/λ²) smaller in BSO , • Cherenkovyield BSO / BGO ≈ 5 with UV330 , lesswith UG11. Time (ns) Deposited Energy (GeV) C/S UG11 filter

9. BGO Matrix (1) • Often in presentexperiments the e.m. • calorimeterisrealizedwithcrystals and an • hadroniccalorimeterisbehind. • Since the dualread out wasproventobe • possible in crystals, the DREAM Collaboration • has tested a full size BGO Calorimeter • backed by the original DREAM calorimeter. • The e.m. section was a matrix of 100 BGO • crystals, 24 cm long and tapered (2.4 x 2.4 • cm² – 3,2 x 3.2 cm²) from L3 experiment. • A first test performed in 2009 , • see NIMA 610 (2009), 488-501. • In the 2010 test beam 16 PMTs with UG11 • filters (scintillation strongly attenuated).

10. BGO Matrix (2) • Both Scintillation and Cherenkov signals in the • same PMT read out: signal from scintillation • extracted by a fit on the tail of the signal, • Cherenkov = total – scintillation. • Preliminary results for 100 GeVe.m. shower. • Scintillation- Cherenkovyields = 67 - 8 ph.e./GeV • Work on the extension of the dual readout to • both e.m. and hadronic sections isin progress. Total Onlyscintillator OnlyCherenkov

11. PWO Matrix • Seven PWO4crystals • doped: 0.3% Molybdenumalready • characterized NIM A621, 212-221. • Eachcrystal: (3 x 3 x 20 cm³) • Both: wavelenght and timing • analysis. Cherenkov side UV 330 filters Scintillation side Yellow filters beam 4 5 Scintillation Cherenkov 1 2 3 σ = 1,2 % σ = 5,0 % 8 9 100 GeVelectrons(work in progress)

12. DualReadoutwithTiles • DualReadout can bealsoimplemented in a tilesamplingcalorimeter. • A test of a smallprototype 9 x 9 cm²wasperformed in the 2010 test beam. • Twosamplings: 4 x (4mm Lead + 4 mm Quartz + 7mm Scint), for a total of6 R.L. • Separate read out ofCherenkov and scintillation light in eachsampling. Photonis XP 2970 pm S2 4 mm Lead 4 mm Quartz 7 mm Scint. S1 1 phel beam C2 2 phel Hamamatsu R8900 pm C1 • Chargedistribution in C1 PMT for 180 GeV/c muon • Fitof a poissonianfor the Npheconvoluted • with a gaussianwithσ² = a + b ·Nphe . • In bothmodules: Nphe = 1.3 fornormalbeam , • 1.6 for 12° tilted detector. • Averagesignalfor 1 phe = PMT gain. 3 phel IntegratedCharge (unit: 10⁵e )

13. 80 GeVelectrons in Quartz – Scint. Tiles Ctot vs Scinttot IntegratedCharge(a.u.) • From a Geant4 simulation: 1.7 GeV / 11.3 GeVdeposited in module 1 / 2. • Fromaveragesignals in C1 and C2 and PMT gains : • 58 Nphe/ GeV in module 1 , 47 Nphe / GeV in module 2 • ComparablewithCherenkovcrystalyield.

14. The New DreamCalorimeter • The DREAM Collaborationisnowpreparing a newprototypeof DREAM like • calorimeterwithbetterperformances. • Twooptions: copper or lead( as the moduletested in 2010), • Extensivestudiesperformedforclearfiberstohave the largestCherenkov light yield, • Samplingfraction : 5% (was 2.6% in the DREAM calorimeter), • Quantum efficiency ~ 50% larger, • Expected 90 Cherenkovphe /GeV , was 18 in DREAM • 1 module: 92 fibers per layer, 46 fiberlayersofeachtype (scintillating/clear) • Dimensionsof the module: 92 x 92 mm², 2,5 m in length • Divided in 4 towersreadoutforCherenkov and Scintillationsignals. • Forcopper : X0 = 2.31 cm , RM = 2,33 cm , λInt = 22.5 cm • Forlead : X0 = 0.92 cm , RM = 2,33 cm , λInt = 25 cm L =92 mm 21 modules : Req = 23.8 cm 16 modules + 12 halfmodules: Req = 24,35 cm

15. Test of the first NewDreammodule in the 2010 test beam (Pbabsorber) Constantdelay = 2,4 nsfrom Scintillationde-excitation • 2.03·1010 cm/s • 2.05·1010 cm/s Beam impact pointfrom PMT (cm) θ = 51° Delay

16. A newleadmodulebuilt in Pavia and nextweek in the test beam A coppermodule in preaparationin Pisa willbereadyforOctober test beam.

17. Conclusions • After the pioneeringtestsof the first DREAM calorimeter, • the DREAM Collaborationhasextensivelystudied the • DualReadout in crystals. • The separationofCherenkov and Scintillation light can beachievedwith • severaltechniquesbased on the peculiarfeaturesof the Cherenkov • radiation. • Dualread-oute.m.calorimeterscomposedwithcrystalshavebeen • testedalsofollowedbyanhadroniccalorimeter (DREAM). • Dualread-out can beusedalso in tilecalorimeters. • The DREAM Collaborationisnowpreparing and testing a newfiber • DualReadoutcalorimeterlargerthan the DREAM calorimeter.