1 Tianchi Zhao University of Washington Concept of an Active Absorber Calorimeter A Summary of LCRD 2006 Proposal A Calorimeter Based on Scintillator and Cherenkov Radiator Plates Readout by SiPMs Tianchi Zhao University of Washington Adam Para Fermilab March 12, 2006, LCWS06 Bangalore, India

2 Energy Compensation Reference: 1. “Compensating hadron calorimeters with Cerenkov light” Winn, D.R. Worstell, W.A., IEEE Trans. NS Vol 36 (1989) “Hadron Detection with a Dual-Readout Calorimeter” N. Akchurina et al., NIM A 537 (2005) “Cherenkov Compensated Calorimetry”, Yasar Onel et al., 2004 LCRD Proposal Hadron energy E h is given by: E h : Compensated hadron energy E sc : Energy measured by plastic scintillators E ch : Energy measured by cherenkov radiators

3 Basic Idea of Active Absorber Calorimeter In a sampling calorimeter based on active detector (scintillator) + absorber layers, partially replace absorber plates by cherenkov radiator and read out both scintillation light and cherenkov light. Thin plastic scintillator plates: Measure energy of both hadron and EM components of hadron showers as in a standard sampling calorimeter Cherenkov radiator Plastic scintillator Heavy structural layer Thick Cherenkov radiator plates: Measure mostly energies of EM components in hadron showers in an active absorber calorimeter Both readout by WLS fiber and SiPM/MPPC

4 Configuration Example Consider a 40 layer arrangement MaterialLayers T (cm) Layer  Thickness (cm) No. of T Plastic scintillator  0.5 = Lead glass30 30  2 = 60 2 Iron  0.5 = Iron  2.5 = TOTAL mm lead glass 5 mm steel ~1.3 X0 25 mm steel Last 10 layers First 30 layers 5 mm plastic scintillator

5 Options for EM Calorimeter Section 15 mm PbF 2 3 mm scintillator 2 mm tungsten 15 mm PbF 2 3 mm scintillator 2 mm tungsten 20 layers Good EM energy resolution Maintaining energy compensation 1.Any other EM calorimeter considered for ILC 2.A segmented active absorber calorimeter with dual energy readout Example

6 Transverse Segmetation Need Monte Carlo simulation to optimize the choice of segmentation for - EM section - Front part of hadron section - Back part of hadron section Minimum size of plates mainly limited cost considerations  3 cm × 3 cm (?)

7 Number of p.e. measured by using cosmic ray muons Lead glass: 2.4  0.5 p.e. Bicron 408: 27  4 p.e. Ralph Dollan, 2004 Thesis Cherenkov Light Readout by WLS Fiber Groove along 40 mm length White paper wrapped  1 mm BCF-91AWSL fiber One end open XP1911 PMT (Average Q.E. ~ 13% for BCF-91A ) Bicron x 6 x 30 mm 3 P.E. yield of lead glass is about 5% of plastic scintillator Lead glass SF57 10 x 10 x 40 mm 3

8 Cherenkov Light Yield of  1 Charged Particles Forward Cherenkov Radiator Density X0 (cm) (cm) Index of refraction Absorption Edge (nm) SF2 lead glass SF6 lead glass SF57 lead glass PbF 2 crystal UVT acrylic Lead glass was popular calorimeter material in LEP experiments Cast or extruded lead glass has the same light yield as cut/polished crystals Plastic scintillator light yield ~ 10,000 photons/cm Chrenkov light yield: 200 – 300 photons/cm Isotropic

9 Cherenkov Plate Readout by MPPC or SiPM MPPC or SiPMWLS fiber Cherenkov Radiator 2 cm Target: Combined efficiency = η 1 × η 2 × η 3 × η 4  > 1% η 1 : probability of a photon hitting the core of a WLS fiber η 2 : conversion efficiency of WLS fiber η 3 : light trapping efficiency in WLS fiber η 4 : MPPC/SiPM quantum efficiency Cherenkov photon  Photoelectrons

10 Signals from a   1 Charged Particle Number of P.E. = N 0 x η 1 x η 2 x η 3 x η 4 = 400 x 1.6 % = 6.4 Cherenkov light yield: N 0 = 400  ’s in 2cm radiator Light collection efficiency by WLS fiber: η 1 ~ 50% WLS fiber efficiency: η 2 ~ 80% Assume η 3 ~ 10% with mirror at far end of fiber MPPC Q.E.: η 4 ~ 40 % (100 pixel device may be sufficient) MPPC Mirror WLS fiber: high efficiency for blue light; emits green/yellow light to match MPPS WLS fiber Should be able to make reasonable measurements for high energy EM showers

11 Basic structure An Alternative Configuration MaterialLayers T (cm) Layer  Thickness (cm) No. of T Plastic scintillator  0.5 = UVT Lucite  2 = Uranium  0.5 = Iron  2.5 = TOTAL mm lucite 5 mm uranium 25 mm steel Last 10 layersFirst 30 layers 5 mm plastic scintillator

12 Potential Advantages Energy compensation for hadron showers on event by event basis as demonstrated by the DREAM Project, but allowing for fine transverse and longitudinal segmentation Performance should be better than the dual r eadout calorimeter of Dream project since cherenkov radiator in our implementation is 2/3 of total volume!! Energy resolution should be better than a calorimeter based only on scintillator plates and should achieve the “required” jet energy resolution Tighter spatial spread of hadron showers recorded by Cherenkov radiator may help correctly assigning energy clusters in HCal to tracks that produced them, therefore, improving the results of PFA. Very flexible design options for material choices and segmentations

13 Disadvantages Significant cost increase compared to HCal that uses plastic scintillator plates only Density of calorimeter is reduced compared to a design that uses passive absorber only. Using a heavy metal such as uranium or tungsten may solve this problem.