01 | 02 | 03 | 04 | 05 | 06 | 07 | 08 | 09 | 10

Measurements and Data Processing

The aim of the bubble chamber picture data processing system is to produce well-measured values for the energy E and momentum (px, py, pz) of each particle produced in a collision.

The details are very complicated technically, so here we will limit ourselves to listing some of the key ideas:

By means of a computer controlled device, the coordinates of vertices and points on tracks are measured on three views and stored.
Using the accurately-known positions of 'fiducial' crosses scratched onto the bubble chamber windows, the measured coordinates are used to calculate the curves along which the particles have travelled.
Having made corrections to allow for the fact that the particles are slowing down, the curves are used to calculate the momenta of the particles as they leave the collision point. (Due to measurement errors, or due to the fact that neutral particles may have escaped, it is not always possible to do this in a unique way.)
For our event the following assignments were made:

	px(MeV/c)	py(MeV/c)	pz(MeV/c)	E (MeV)
	8213.4	-248.3	15.2	8232.0
	0.0	0.0	0.0	938.3
Total	8213.4	-248.3	15.2	9170.3	initial state

	1481.8	27.8	224.0	1578.1
	149.7	-11.3	38.8	208.6
	37.9	-122.2	-22.7	190.7
	1508.6	128.5	-70.5	1782.6
	3545.6	-162.9	-245.0	3592.4
Total	6723.6	-140.1	-75.4	7352.4	final state

A brief inspection of these figures shows that there is less energy and momentum in the final state, showing that at least one neutral particle has escaped.

Exercise. What can you say about what is missing? (Click here to find out)

The purpose of the data processing is to provide as full a record as possible of all the interactions found in an experiment - which typically might have tens or even hundreds of thousands of interactions.

These are then analyzed by programs written by physicists to compare the results of the experiment with current theoretical ideas.

< step back | next step >