Fermi National Laboratory

Tevatron Luminosity--Explanations

Collider Run IIA Integrated Luminosity

Luminosity is a measure of particle interaction, specifically the chance that a proton will collide with an antiproton. The higher the luminosity, the greater the chance of quark production. To achieve high luminosity you place as many particles as possible into as small a space as possible. When the two beams of protons and antiprotons are brought together it's called a squeeze. A good squeeze results in the potential for a higher rate of collisions. There are special quadrupole magnets, called Low Beta magnets, at each of the two experiments, D-zero and the Collider Detector Facility, used for this purpose.

Weekly Integrated Luminosity (nb-1)
Integrated means we're adding up each week's worth of luminosity for display.

The left side of the graph displays the scale as measured by nb-1, or inverse nanobarns. The -1 stands for inverse, which also could be shown as 1/nb. The nanobarn means that we're dealing with very small particles. (See Peak Luminosity for an explanation of exponential numbers.) A nano equals one billionth or 10-9. A barn is a unit for measuring cross sections of particles. 1 barn equals 10-24 square centimeters. (Physicists developed the term "barn" during World War II when they were bouncing neutrons off of uranium nuclei, which they described as being "big as a barn.") Okay, so we're dealing with very small particles, but we're colliding many billions of protons (1012) with somewhat fewer antiprotons (1011). (Remember that since it is an inverse the displayed luminosity is a large positive number.)

Week Number
The bottom of the graph shows the number of weeks we've been collecting data.

Bars and Diamonds
The vertical blue bar shows each week's total luminosity as measured in nb-1. The diamond connected line displays the integrated (totaled from week to week) luminosity in pb-1. A pico equals one trillionth or 10-12. (This change of scale keeps the record on the same graph.)

If there is no weekly bar, the accelerators are off. Since the diamonds show integrated luminosity, the line stays flat during the off periods.

Collider Run IIA Peak Luminosity

Peak Luminosity
The left side of the graph displays the scale in exponential numbers. (An exponent takes what would be a huge number, such as 1,000,000,000, and allows it to be written as 1X109, or one times ten to the ninth power. If it's written as ten to the ninth power, 109, the one is implied. The exponent shows how many times the number should be multiplied by itself, ten times ten times ten and so on. 2.0E30 means 2 times ten to the thirtieth power.)

Relative Store Number
These store numbers keep track of stores that actually have measured luminosity. (They have no relationship to the store numbers mention in the Accelerator Update.)

Peak Luminosity and Peak Luminosity 20X Average
The blue squares show the peak luminosity at the beginning of each store. (The luminosity drops as the particles continue to collide with each other during the life of the store.) The red triangle displays a point representing the last 20 peak values averaged together. (It displays peak luminosity in a format that is easier to follow.)

last modified 4/11/2002   email Fermilab
Security, Privacy, LegalFermi National Accelerator Laboratory