PhysicsLAB Lab
Mass of the Top Quark

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During class you will be distributed two "top anti-top quark event" data plots recorded at Fermi Lab's D-Zero Detector. You are to carefully analyze each one and you use your results to experimentally calculate the mass of the top quark.
 


Image courtesy of Fermi Lab
 
 
For each event, you are to determine the "center of mass" for each of the four quark jets. Then you are to draw in its momentum vector and measure the exit angle. Next you need to measure the exit angles for the hard (high energy) muon and the soft (low energy) muon.
 
 

Event #1

 
What is the date and event number for this data plot? 

Record the exit angles and magnitude of each of the six recorded energy deposits.
 
Description Momentum Angle
GeV/c 0-360º
Jet #1
Jet #2
Jet #3
Jet #4
Hard Muon
Soft Muon

Remembering that the total momentum before the collision (protons and antiprotons traveling in opposite directions through the beam pipes to the collision area) equaled zero, you now need to complete a scaled vector diagram of your measured momenta to determine the missing momentum of the unrecorded anti-neutrino. On your vector diagram, please outline the anti-neutrino's vector in red.

NOTE: At relativistic speeds, like those in these D-Zero experiements, the concepts of momentum [measured in GeV/c], mass [measured in GeV/c2], and energy [measured in GeV] are so closely related that they can be numerically set equal to each other without changing units. To do this, particle physicists often "normalize c" to equal 1 allowing all three units to become equivalent.
 
What scale did you use to graph your vectors - that is, now many centimeters represented 10 GeV/c2?
 

How long, in centimeters, was your anti-neutrino's vector? 

How much energy, in GeV, did the anti-neutrino carry away from the collision? 

Now that you know the anti-neutrino's momentum, what was the total energy released when the top and anti-top quarks decayed? 

This energy is shared between the top and anti-top quark. If you assume the energy to be equally divided, what is the mass of a top quark? 

If the accepted mass is 174 GeV/c2, what is your percent error? 


Event #2

 
What is the date and event number for your second data plot? 

Record the exit angles and magnitude of each of the six recorded energy deposits.
 
Description Momentum Angle
GeV/c 0-360º
Jet #1
Jet #2
Jet #3
Jet #4
Hard Muon
Soft Muon

Once again, complete a scaled vector diagram of your measured momenta to determine the missing momentum of the unrecorded anti-neutrino. As before, please outline the anti-neutrino's vector in red.
 
What scale did you use to graph your vectors - that is, now many centimeters represented 10 GeV/c? 

How long, in centimeters, was your anti-neutrino's vector? 

How much energy, in GeV, did the anti-neutrino carry away from the collision? 

Now that you know the anti-neutrino's momentum, what was the total energy released when the top and anti-top quarks decayed? 

This energy is shared between the top and anti-top quark. If you assume the energy to be equally divided, what is the mass of a top quark? 

If the accepted mass is 174 GeV/c2, what is your percent error? 


General Overview

 
Compare your two percent errors and elaborate on whether the percent error appears to be related to the magnitude of the missing anti-neutrino's mass.
 

What recommendation can you make to assist future students so that their mass results will be consistently closer to the accepted value of 174 GeV/c2?
 



After submitting your results online, make sure that you turn in your measured data plots and momentum vector diagrams to the one-way box.

 
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