The cross section of top anti-top production at the Tevatron
is 7 pb. The dominant production mechanism is quark and
anti-quark fusion.
Typical "b" quarks produced in top decays have momenta
of 50 GeV.
The total width of Top quark is ~1 GeV.
About 90% of time, CDF and D0 experiments are ready to take
data (10% of dead time due to detector calibrations, detector
mal-fuction, data aquisition system errors, etc.)
CDF and D0 experiments can trigger on electrons and muons with
high momentum: when top quark or anti-top quark decays into
electrons (muons), about 80% (70%) of them will pass the
triggers and events passing the triggers will be recorded.
By 2004, the Tevatron accelerator will deliver 2 fb-1 to
both CDF and D0 experiments.
Questions :
Draw Feynman diagram of the dominant top anti-top
production.
How many top anti-top events will the Tevatron Run II
produce by 2004 ?
How many of them will be recorded (total sum of two
experiments) ? Do not forget
Top branching ratios
Livetime of experiments
Triggers
Divide the total number of events into
events with no leptons
events with one lepton which is an electron
events with one lepton which is a muon
events with two leptons (either electron or
muon)
b-quark identification
Sketch the number of b-quarks (y-axis)
as a function of decay length (x-axis). Do not
forget units of x and y-axis. Decay length =
distance
between the production point and the decay point.
Replace b-quarks with c-quarks in the previous
question and sketch the number of c-quarks (y-axis)
as a function of decay length (x-axis) on top of the
previous plot.
If you want to separate events with b-quarks from
those with c-quarks, what decay length cut would
you make ? (note that the previous plots assume
perfect detector resolutions).
What is the top quark lifetime (units in second) ?
If typical momenta of top quarks are ~60 GeV, what is
the average decay length ?
(quarks are hadronized at ~1fm which is much larger than
the top decay length. Thus top quarks will decay to
W and b-quark before hadronized. W's and leptons from W
decays will carry information of the spin of top quarks.
We expect to measure top properties including spin
at the Tevaton Run II.)