ATLAS is a general purpose detector for the study of pp collisions at 14 TeV center-of-mass energy using the LHC collider at CERN. The collider is the highest energy and luminosity collider in the world. ATLAS, together with CMS, discovered the Higgs boson which led to the 2013 Nobel Prize. We are part of the pixel detector group. The pixel detector is the tracking device closest to the interaction region and is designed to improve the charged particle tracking and identification of b quarks in hadronic jets, critical for the study of the top quarks and Higgs decay to bottom quarks.
The extreme high energy of the LHC allows us to look for physics beyond the Standard Model. Lepton signatures have been used in the past for several major discoveries. The OSU groups therefore concentrate on using leptons as a tool in the searches for new physics, including the use of W and Z reconstructed in the leptonic decay modes. We are currently involved in several analysis projects, including the search for vector boson scattering, lepton flavor violation, exotic multiple-photon decays, and new heavy quarks.
The ATLAS pixel detector consists of four barrel layers and three forward and backward disks. The primary contribution of the OSU group is in the R&D, design, fabrication, and maintenance of the on-detector radiation-hard and high-speed optical communication. We built the fiber optic transceiver boards (opto-board) for the optical links. Each board contains both optical and electrical components, VCSELs, PINs, DORICs, and VDCs. The differential hit signal (LVDS) from the pixel electronics is converted by the VCSEL Driver Chip (VDC) on an opto-board into a single-ended signal appropriate to drive a Vertical Cavity Surface Emitting Laser (VCSEL) and transmitted to the readout system using a fibre. The 40-MHz beam-crossing clock, encoded with the command signal to control the pixel electronics, is transmitted to a PIN diode via a fibre. The signal from the PIN diode is decoded using a Digital Opto-Receiver Integrated Circuit, DORIC. We use VCSEL and PIN diodes that are fabricated in the highly compact array and each array couples to a fibre ribbon inside an optical package (opto-pack). An opto-board contains one 12-channel PIN array opto-pack and two 12-channel VCSEL array opto-packs couple to two 4-channel DORICs and four 4-channel VDCs. OSU responsibilities include the design and testing of the radiation-hard VDC and DORIC, and the design, fabrication, and testing of opto-boards. The research is performed in collaboration with Siegen.
For the so-called high luminosity LHC (HL-LHC) upgrade in 2022, we propose the continue use of the optical arrays for three reasons, compact, efficient, and robust, which we much appreciate after 15 years of experience in using the devices. In collaboration with Siegen, we are designing a 10 Gb/s VCSEL array driver using the 65 nm CMOS process.
OSU has perhaps the best equipped optical electronics lab for high energy physics research in US. The lab includes three automatic wire bonders (K&S 1470 and 8060 and F&K Delvotek G5), two manual wire bonders, wire-bond pull tester, dice probe station with pattern recognition (Cascade Microtech PA200), high speed scope (LeCroy SDA 825Zi-A 25 GHz/80 GS/s), Agilient N4903A 12.5 Gb/s serial bit error rate tester (BERT), optical spectrum analyzer (OSA), optical comparator, precision vision measuring machine, fiber polisher and fusion splicer, high power UV light, precision scale (0.1 mg), high resolution IR camera, one humidity chamber, and three environmental chambers and ovens. The equipment are funded in part by two Major Research Instrumentation (MRI) grants of NSF. The equipment are housed in the clean room and the adjacent staging room of the new physics building.
More technical information is available at Jason Moore and Shane Smith web sites.
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