The KNU-WCU Scintillator Laboratory The WCU Collider Physics Research Group in Kyungpook National University Jets from more massive particles decay 1.Introduction The KNU-WCU Scintillator Laboratory is mainly studying the finely segmented calorimeter with plastic scintillator strips, which is the world’s first trial for future high energy collider experiments. Moreover the laboratory is capable to study any other scintillation detectors in other fields which need finer segmentation, like the medical PET system. In the future collider experiments, observation of the Higgs boson and several new physics like Supersymmetric (SUSY) particles are expected. Many of those massive particles w ill emerge into highly collimated multi-jet final states. Therefore one of the major key for the new calorimeters the 3-dimensional spacial resolu- tion with fine granularity. Also as described later, fine segmentation plays an important role for the improvement of the jet energy resolution using Particle Flow Algorithm (PFA). Other requirement to the calorimeter comes from the search for massive invisible particles (like neutralino in the SUSY model) which are supposed to be the dark matter candidates. In those analyses missing energy resolution is also very crucial. In total, We are aiming to establish the new-type calorimeter which achieves both the excellent spatial and energy resolutions using the plastic scintillator strips. E jet = p e + p  + p charged hadron + E  + E neutral hadron [ tracks only] [calorimeter only] 2. The Plastic Scintillator Strip Calorimeter for the ILC As a first target, we focus on the development of calorimeter for the International Linear Collider (ILC) experiment. The ILC is the e + e - collider which can achieve center-of-mass energy of GeV. In order to fully utilize the low background environment of the e + e - collision, the collider detector must have the ability of the precise measurement, espe- cially for jet energies from the decay of massive particles. At the ILC, PFA is proposed for significant improvement of the jet energy resolution. The idea of the PFA is jet particle separation into charged and neutral particles, and opti- mize those measurement method as follows: charged particles (~65% of a jet ) are measured its momenta by tracker with great accuracy, neutral particles ( , K L 0 ) are measured its energies at the calorimeter. Then the total jet energy can be measured as : Using the PFA, jet energy resolution for Z 0  j j events is remarkably improved from to 30%. To realize the PFA, finely segmented calorimeter with the 3-dime- nsional position resolution is indispensable to separate each particle in a jet by the calori- meter signal. The plastic scintillator strip calorimeter (shown in the figure above) is a sandwich calorimet- er with tungsten absorber and layer of the scintillator-strips which are alignend orthogonally in alternate layers. By taking the crossing region of the vertical and horizontal strips, segm- entation of 0.5 x 0.5 – 1 x 1 cm 2 can be achieved. Since the number of calorimeter cells will be huge (~10M channels), reducing production cost is also the big issue. Considering those challenging requirements, the plastic scinti-llator strip calorimeter is feasible for the ILC electromagnetic calorimeter (ECAL) with its very fine spatial resolution and good energy resolution while keeping the low production cost. Plastic Scintillator strip Multi-Pixel Photon Counter (MPPC) Absolute amount of light Response uniformity Mechanical stability Production cost Wavelength Shifting Fiber (Y11) for signal readout High absorption and re-emission efficiency 4.5 x 1 x 0.3 cm Extruded scintillator Extruder and die Finer segmentation DOI information PET detector Photo-sensor & scintillator MPPC Collimated β - ray Automated 2-D scanning system β -ray Source 4. Future Prospects As the 2 nd stage plan, we will perform more systematic measurements of the scintillator stri ps with many different configurations (e.g. covering materials/paints, arrangement of photo -sensor and WLS fibers) for further improvement of the calorimeter performance. The impr- oved strips will be used for next scintillator-ECAL prototype which is planned to be built and tested in the worldwide collaboration. Another project is the optical simulation of scintillation signal transmission. By comparing results of the simulation and the measurement, we can develop the reliable optical simulati on software which will be quite useful for design of any scintillation detectors. For further project, study of the finely segmented radiation detectors for a medical system like Positron Emission Tomography are also in our scope. 3. Study of the Plastic Scintillator Strips At the KNU-WCU scintillator laboratory, we are generating and testing several types of pla- stic scintillator strips as the main element of the finely segmented calorimeter. Current stru- cture of the scintillator strip is shown in the figure below together with the important points on those performance. For the first test, the scintillator strips with several different dimensions, covering materials, readout schemes are produced as listed below. The plastic scintillator production has been done with the regular extrusion method to reduce the production cost. 45 x 10 x 3 mm with WLS fiber, silver film cover 45 x 5 x 3 mm with WLS fiber, silver film cover 45 x 5 x 3 mm, no fiber, silver film cover 45 x 5 x 2 mm, no fiber silver film cover 45 x 10 x 3 mm, with WLS fiber white paint cover 45 x 10 x 3 mm with WLS fiber, silver film cover 45 x 5 x 3 mm, no fiber, silver film cover To evaluate the performance of those strips, precise 2-dimensional scanning system with collimated  -ray has been set up at the scintillator laboratory. This system automatically scans the entire area of the scintillator, and measures the response from the scintillator to t he  -ray at each point. Temperature of the whole system is well controlled by the thermost atic chamber. Figures shown below are some results of the first stage measurement. Large and uniform scintillation signal over entire strip is desirable. Those results already show an interesting behavior. The strip without readout fiber and narrower width (right-side) shows better resp- onse uniformity than the left-side strip while overall amount of the signal are almost the sa- me level. In this way, we are exploring possibility to improve the performance of plastic sci- ntillator performance. The Scintillator-strip ECAL in the ILC collider detector The ILC collider detector (ILD) Jet particles separation In the calorimeter 3 GeV e - e-e- 18 cm 72 strips x 30 layers To realize this challenging calorimeter, we are paying much efforts with a world-wide colla- boration. Construction of the calorimeter prototype has been already started since 2006, and tests of the prototype using high energy particle beams have been performed in Pictures above show the structure of the calorimeter prototype together with an eve- nt display at the beam test to demonstrate the particles separation. Since the KNU group was reformed as the KNU-WCU team, we took the main role of the prototype beam test and its data analysis with more man-power and resources. The development of the plastic scintillator strip calorimeter is still extensively ongoing, and the KNU-WCU team is at the leading position of this project. Especially our main task is improvement of the plastic scinti -llator strip, which is the primary part of the calorimeter.