Diana Jaunzeikare ‘11 and Anna B oehle ‘11 with Piotr Decowski

1. shutter PMT PMT Signal 200 ns 1 kHz LED Optical filter HV PMT gain vs High Voltage measured at two light attenuations Spectrum of pulses from PMT: dimmer light Distribution of number of photoelectrons emitted from photomultiplier cathode in 200ns time window. Upper panel shows attenuation 1000 times, lower panel 100 times. Attenuation 1000 Attenuation 100 Filter wheel Source of light and a shutter Light diffuser Photomultiplier Setup for Precise Determination of Photomultiplier Linearity and Sensitivity to Single Photons (sponsored by the NSF RUI grant “Parity Violation in Electron Scattering at the Jlab”) Diana Jaunzeikare ‘11 and Anna Boehle ‘11 with Piotr Decowski Introduction This project is related to the PREx experiment planned at the Thomas Jefferson National Accelerator Facility in Virginia (JLab). The purpose of PREx is to precisely measure the thickness of the “neutron skin” (the difference between the radii of neutron and proton distributions) in the 208Pb nucleus (which contains 126 neutrons and only 82 protons). The aimed unprecedented precision of this measurement (R = Rn-Rp determined with accuracy ~1%) will eliminate uncertainties in nuclear interaction models. The measurement will be done using scattering of longitudinally polarized high energy electrons from lead target, and extracting the weak interactions sensitive mainly to neutrons from asymmetry of these scattered electrons (difference between flux of electrons with spins oriented along their motion and flux of electrons oriented in the opposite direction). Detectors for electron flux measurement were designed and constructed at Smith College in collaboration with UMass. An important part of these detectors are the sensitive photomultipliers that register photons produced by electrons as they pass through the detector. The purpose of the setup discussed in this poster is to investigate photomultiplier properties by studying their response to single photons. Spectrum of pulses from PMT: brighter light Composite fit (logarithmic scale) Composite fit (linear scale) Setup of equipment Contribution of individual numbers of photoelectrons to composite fit 1 photoelectron 2 photoelectrons 3 photoelectrons Filter wheel control The control panel of a program written in LabVIEW7 for controlling filter wheel motion. It allows computer to rotate the different installed filters to predefined position remotely. 1 photoelectron 2 photoelectrons Conclusions The photomultiplier testing bench set up at Smith College proved to be able to deliver good data on photomultiplier response to single photoelectrons. The data provided a precise measurement of photomultiplier gain and resolution.