Transcript TOF Slat
How We Became Experimentalists Suzanne Levine Saba Zuberi Len Zheleznyak REU 2002 Define Problem Draw Conclusions New Questions Arise Develop Method(s) to Investigate the Problem Design and Collect Equipment Needed for the Experiment(s) Analyze Data Collect Data Develop a Method to Collect the Data. (DAQ) Test,Calibrate, and Understand the Equipment. Determine Trends Expected in Data. PHOBOS at RHIC TOF Walls TZeros TZeros Detector Background Information •The detectors being used provide information about the energy and time of arrival of incident particles. - Radiator - Scintillator Produces Cherenkov radiation Atoms are excited when struck when a charged particle in the by charged particles producing medium has a velocity faster scintillation light when they than the speed of light in that decay to their ground state. medium. •When coupled with a PMT the light produced is converted to electrical pulses that can be analyzed electronically. Radiator Bare scintillator with light guides attached What’s the problem? •TZero Counter: [Cherenkov detector] Investigate the timing properties of TZero Counters, varying supply voltage and position of incident particles. The results of our investigation will be used to determine the operating conditions for the next run at RHIC. •TOF (Time Of Flight) Slat: [Scintillation detector] Understand the position properties of TOF scintillator with cosmic rays. The results of the measurements can be compared with the position studies with an electron source. TZero Counter TOF Wall at RHIC Develop a Method of Investigation Example: TOF Slat Setup TOF Slat setup in PHOBOS lab at Rochester TOF Slat PMT PMT to define position PMT • Design a setup with three PMTs to select and define a position of cosmic rays • In order for an event to be recorded, signals must be received by all three PMTs • Study the response of the TOF slat as a function of hit position Collect and Assemble Equipment Scintillator Preparation to Optimize Light Collection: • 4 steps to wrapping a scintillator (i) polish scintillator with toothpaste (ii) wrap in aluminum foil for maximum internal reflection (iii) apply optical grease to open end of scintillator and connect to PMT (iv) wrap electric tape over foil to stop external light from penetrating the scintillator 0 0 1 Electronics LOGIC TIME ANALOG 1 0 1 0 0 1 1 0 1 0 1 0 •Logic - Select the events most likely to be cosmic rays •Time - Measure the time difference between the arrival of the cosmic rays and light reaching the PMTs 0 1 1 1 1 0 0 •Energy - Measure the energy DIGITAL of the charged particle by examing the pulse produced by the PMT 1 0 1 0 0 1 TIME LOGIC DAQ Why do we need a DAQ? A Data Acquisition System (DAQ) will: (i) Allow the user to read the information from the electronics on a PC (ii) Present and store the data in a way which is useful to the user (iii) Write data to files so that it can be analyzed later ANALOG DIGITAL DAQ Collect Data: DAQ Graphical User Interface 19cm QuickTime™ and a Photo - JPEG decompressor are needed to see this picture. Diagram of Setup Analyze Data Example: Determine Position from Pulse Height • L1 = A1e-(x/ ) L2 = A2e-((d-x)/) •Log(L1/ L2) = -(2/)x + [d/ Log (A1/ A2) ] •Attenuation factor for this scintillator is 44 + 7 cm.It was calcuated from the gradient of this graph. Log(L1/ L2) •The charge measured is proportional to the amount of light incident on the PMT QuickTime™ and a GIF decompressor are needed to see this picture. Distance (cm) • Timing resolution improves with increased voltage up to -2700V. Beyond this voltage, no dependence of resolution on voltage is apparent • A requirement was to achieve a timing resolution of under 100 picoseconds; at -2700V the timing peaks exhibit a 55 picosecond resolution Timing Resolution (ps) Analyze Data: Results of TZero Experiments QuickTime™ and a GIF decompressor are needed to see this picture. Voltage (V) [note: suppressed zero] Summary of Results TZERO • We found that the TZero response has little dependence on position • We have verified that the most effective operating voltage is -2700V TOF Slat • We studied position information by both time and the amount of light received by the PMTs. • Both parameters indicate a linear dependence • We have determined the attenuation coefficient to be 44 + 7 cm and the effective velocity of propagation of light in the scintillator to be 10.3 + 0.8cm/ns. Lessons Learned • More of your time is dedicated to isolating and identifying a problem than correcting the problem itself. • You learn the most from your mistakes. • Keep good records. You can never write too much. • Computers can be a dangerous tool; they will always give you an answer, whether it makes sense or not. • You learn a lot by explaining what you did to others.