Braidwood Prototype Detector a Proposal Hans Jostlein 1052005

Braidwood Prototype Detector - a Proposal Hans Jostlein, 1/05/2005 1

This is about Two Things 1. Proposal to build a Calibration Test Bed 2. Proposal for a particular Calibration System Hans Jostlein, 1/05/2005 2

Motivation As is typical for a reactor neutrino experiment, we are reasonably confident of the counting statistics we can achieve in the Braidwood experiment. What sets us apart from other reactor neutrino experiments is, we think, exquisite control of systematic errors. The systematic errors have two major components: backgrounds and acceptance Hans Jostlein, 1/05/2005 3

This is about Calibration I will not address backgrounds here. Acceptance has several major components. One of them is stability of cuts and event selection, which requires well understood response and calibration. This note is about calibration systems. Hans Jostlein, 1/05/2005 4

A Calibration Test Bed It will require a large amount of work. Most of the work will be directly applicable to the real experiment. Most of the hardware can be either “found” or is prototype hardware for the real experiment. Hans Jostlein, 1/05/2005 5

Purpose of the Test Check calibration system performance for the large detector Provide a test bed for various calibration ideas. Provide a test bed to validate the simulation software. Hans Jostlein, 1/05/2005 6

Scope of the Test Tank with 2 zones (inner plexiglass, outer stainless, with black walls? ) Sufficient number of phototubes (maybe two dozen 2” PMT’s) Sufficient number of light sources, individually pulsable Radioactive source as absolute light standard? PIN diodes as standards ? Single light source (LED or laser) with fibers to each PMT for common calibration ? Readout of all PMT’s with external trigger and also self-triggered Can we use a prototype Braidwood readout system ? Hans Jostlein, 1/05/2005 7

Software Needs ---DAQ software ---Simulations ---Analysis software These are a crucial part of this, and require a major effort. Hans Jostlein, 1/05/2005 8

Part II: A Calibration Proposal Goal: Provide a simple and robust calibration system that: -runs without mechanical motion -runs without an operator -does not upset the detector -measures all gains -measures all light transmission parameters -takes only seconds to run Hans Jostlein, 1/05/2005 9

Thousand Points of Light Also known as “Light Tomography”. Install many light sources (e. g LED’s). Maybe one at each PMT location. The response to each PMT to each light source is one data point. Take calibration data, one light source at a time, while recording all PMT’s. This measures light transmission over many pathways through the detector. Hans Jostlein, 1/05/2005 10

Analysis of TPL Data The simulation package predicts light response for each light-PMT combination. Response depends on absorption, refraction, reflection, PMT response is strictly proportional to light intensity (at the low levels used here). Set up system of linear equations, relating PMT response to light intensity, with coefficients due to geometry, absorption, and reflection from simulation, as well as light intensity of each source and calibration constant of each PMT channel. Hans Jostlein, 1/05/2005 11

Solve the Equations Invert matrix to solve the system of linear equations for all parameters. Number of data points is ( # lights) * (# PMT’s) Number of parameters is (# lights) + (# PMT’s) + (oil parameters) Hans Jostlein, 1/05/2005 12

A Technical Detail Absorption is not linear in path length. We can write the absorption for each path as a Chebychev polynomial , and the absorption will be linear in the coefficients Hans Jostlein, 1/05/2005 13

What Results do we Expect ? After a lot of work, the measure of success or failure is this: Run the measurement and analysis using one calibration system (e. g. the TPL system). Look at all residuals; they should make sense. Hans Jostlein, 1/05/2005 14

More Results Verify independently to what degree of accuracy it describes the detector system: This requires, in essence, a duplicate system. In the simplest fashion, place a source or light pulser with uniform angular emission in the center (for symmetry) and check that all PMT’s respond to light in the exact same way. Hans Jostlein, 1/05/2005 15

Yet More Results If there is no good symmetry point, or just for good practice, run the simulation one more time for the test light, using the best fit parameters obtained by the earlier calibration process. Despair or rejoice. Hans Jostlein, 1/05/2005 16

Ancillary Task Develop a stable, pulsable, light source with precisely uniform (or cos theta) angular light emission pattern. Hans Jostlein, 1/05/2005 17

Conceptual Design This is a crude draft. More understanding and work is needed. The design is based on an existing tank at Fermilab. Everything would mount off the top plate (after cutting it off). We have the PMT’s. Hans Jostlein, 1/05/2005 18

C o n c e p t u Hans Jostlein, 1/05/2005 19