Separation of Scintillation and Cerenkov Light in an Optical Calorimeter Heejong Kim on behalf of DREAM collaboration

Dept. of Physics, Texas Tech University

1. Introduction

2. Experimental Setup

3. ResultsDual-Readout Module(DREAM) calorimeter showed thatthe energy resolution of hadronic shower can be improv-ed by measuring the scintillation and the Cerenkov lightsimultaneously to eliminate the effect of the fluctuation of electromagnetic shower fraction (fem). The idea of theDREAM calorimeter can be applied to the optical

calorim-eter, even homogenous calorimeter, if it is possible to separate the light into its scintillation and Cerenkov co-mponents. The scintillation lights are isotropically gene-rated as a molecular de-excitation process while Cere-nkov light has spontaneous process, which has prefer-red angle with respect to the particle direction. Based onthese different characteristics of the lights, 1) the timestructure and 2) the angular distribution of light, two Techniques to separate the lights into two componentswere tested with the DREAM calorimeter.

4. Summary

1 cell = extruded copper rodDimension = 2mm X 2mm X 2m2.5mm hole holds 7 fibers.3 scintillating + 4 quartz(plastics) fiber.Uniform pattern for all rods.

1 tower consists of 270 rods.2 fiber bundles for each tower.Scintillation and quartz fiber bundles.Hamamatsu R580PMT for readout.38 PMTs for 19 towers in total.Honey-comb shape structure.

Fig. 1. Sectional view of a cell

Fig. 2. Front view of DREAM.

DREAM calorimeter•5580 copper rods(1130Kg) and 90km of optical fibers.•Effective radiation length(X0) = 20.10mm.

•Nuclear interaction length(int) = 200mm.

•Moliere radius(M) = 20.35mm.

Newly implemented features for this study •6m long fibers installed in the copper tubes.•Fibers were bent 180 at the center and •both end of fibers inserted into the areas, top and bottom.•The fibers were separated into 3 bunches. (scintillation, Cerenkov and mixed of both)•Lights from 6 fiber bunches were readout 6 PMTs(R580).

Beam test•CERN Super Proton Synchrotron (SPS) H4 in July, 2004.•Pion and electron beam with 40~300GeV energy.

a. Method using the time structure

b. Method using the directionality of lights

•Split PMT signal from Tower 1 and sent to 2 ADCs.•2 ADCs with different gate time by t.•Compared both delay/non-delayed signals. (Fig. 3)•Time structure of lights was measured by varying t.(Fig.4)

• t = 12 ns was chosen as a optimum delay.• How to extract fem or Q/S from mixed signal? (Q/S = ratio of Cerenkov and scintillation lights.)

Sum of Cerenkov & Scintillator signal with 12ns delay • f12 = Sum of the 2 original signals

• Found a correlation of f12 and Q/S. (Fig. 5)

Fig. 3. Fraction of signal vs t. Fig. 4. Time structure of lights.

Fig. 5. f (t = 12ns) vs Q/S from 100GeV ‘jets’.

•Particle beam was steered onto the top (T) area.•Measure the lights from both ends, at the top (forward) and the bottom (backward).•B/F = ratio of light emitted in the backward and forward.•Clear difference was found in B/F ratio between Cerenkov and scintillation light.( Fig. 6)•Scintillation light is generated isotropically and only 20% difference in backward and forward signals.•Cerenkov light in forward direction is ~6 times larger than in backward direction.

Fig. 6. B/F ratio for scintillator (a) and Cerenkov (b) signals generated by 80GeV electron.

•B/F ratio of mixed signal of Cerenkov and scintillation light.•Q/S measured separately.•Correlation of B/F(mixed) and Q/S. (Fig. 7)•Small detector area is a limiting factor in addition to small Cerenkov signal in backward direction.

Fig. 7. Q/S vs B/F ratio for 150GeV ‘jet’.

•Two techniques were studied to separate lights from an optical calorimeter into Cerenkov and scintillation comp- onents.•The time structure and directionality of light were tested methods in this study with DREAM calorimeter.•Both methods showed a correlation between a measured property of signals and Q/S.•Quality of separation was limited by small light yield of Cerenkov.•These techniques can be applied to any optical calorim- eter to improve its performance for hadron.

References for DREAM calorimeter

1. Nucl. Instr. and Meth. A533 (2004) 305.2. Nucl. Instr. and Meth. A536 (2005) 29.3. Nucl. Instr. and Meth. A537 (2005) 537.4. Nucl. Instr. and Meth. A548 (2005) 336.