主讲人 (Lecturer)：Dr. Armen Apyan, Northwestern University, USA 

　　主持人 (Chair)：Prof. Jingyu Tang, IHEP 

　　讲座题目 (Theme)：Polarized positron production for future high energy e+e linear colliders 

　　内容摘要 (Abstract)： 

　　Future high energy e+e linear colliders require high intensity positron beams with low emittances and a high degree of longitudinal polarization. Low emittance is essential to attain high luminosity, while the beam polarization expands the physics capabilities of the machine. The electron (and positron) beam may be polarized, allowing selective suppression of backgrounds, enhancement of the effective luminosity etc. However, although the polarization of positron beams is very useful, the technical progress to produce intense polarized positron sources has been rather slow, and significant R&D is needed. A few methods to produce polarized positrons are being considered by the linear collider community. Converting circularly polarized gamma rays create electron-positron pairs. The main concept is to produce circularly polarized photons, followed by the collection of longitudinally polarized positrons produce in a target that acts a converter. Each of the methods has their own problems connected with their cost and/or technical complexity. 

　　演讲人简介 (Lecturer’s short bio): 

　　I am working at Physics department at Northwestern University, Evanston, Illinois, US. I have received my PhD in 2001 in Physics of Nuclei and Elementary Particles at Yerevan Physics Institute, Armenia. I have an extensive experience with Monte Carlo methods, scientific computing and programming. I have experience using GEANT4, G4BeamLine, MARS15, FLUKA, BDSIM, Guinea Pig, CAIN simulation packages and ROOT data analysis package. I have many years of experience working on the subject of interaction of charged particles and photons with matter. 

　　During the last four years I was on academic leave from Northwestern in order to work at CERN. I worked on the design of the CLIC post collision line using Monte Carlo simulations of the various components. My work included not only the design of the beam dump, but also the design and integration of a luminosity monitoring system based on the detection of beamstrahlung photons generated at the interaction point. I was a member of the CLIC Machine- Detector Interface and Beam Instrumentation working groups. 

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