How We Became Experimentalists Suzanne Levine Saba Zuberi Len Zheleznyak REU 2002

DefineProblem Develop Method(s) to Investigate the Problem Design and Collect Equipment Needed for the Experiment(s) Test,Calibrate, and Understand the Equipment. Determine Trends Expected in Data. Develop a Method to Collect the Data. (DAQ) Collect Data Analyze Data Draw Conclusions New Questions Arise

PHOBOS at RHIC TOF Walls TZeros

Detector Background Information - Radiator - Radiator Produces Cherenkov radiation when a charged particle in the medium has a velocity faster than the speed of light in that medium. - Scintillator - Scintillator Atoms are excited when struck by charged particles producing scintillation light when they decay to their ground state. Bare scintillator with light guides attached The detectors being used provide information about the energy and time of arrival of incident particles. When coupled with a PMT the light produced is converted to electrical pulses that can be analyzed electronically. Radiator

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. TOF Wall at RHIC TZero Counter

Develop a Method of Investigation Example: TOF Slat Setup 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 TOF Slat setup in PHOBOS lab at Rochester TOF Slat PMT to define 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

Electronics LogicLogic - Select the events most likely to be cosmic rays TimeTime - Measure the time difference between the arrival of the cosmic rays and light reaching the PMTs EnergyEnergy - Measure the energy of the charged particle by examing the pulse produced by the PMT DAQ TIMELOGIC TIMELOGIC ANALOG DIGITAL

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 DAQ DIGITAL

Collect Data: DAQ Graphical User Interface 19cm Diagram of Setup

Analyze Data Example: Determine Position from Pulse Height The charge measured is proportional to the amount of light incident on the PMT L 1 = A 1 e -(x/ ) L 2 = A 2 e -((d-x)/ ) Log(L 1 / L 2 ) = -(2/ )x + [d/  Log (A 1 / A 2 ) ] Attenuation factor for this scintillator is cm.It was calcuated from the gradient of this graph. Distance (cm) Log(L 1 / L 2 )

Analyze Data: Results of TZero Experiments 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 Voltage (V) Timing Resolution (ps) [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 cm and the effective velocity of propagation of light in the scintillator to be cm/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.