Obligatory Exercises II
11.05.2012 to be delivered 21.05.2012 @ 12:15 Farid Ould-­‐Saada 5/10/12
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The top quark decays into a W boson and and a b-­‐quark.   Justify this. (Consider the CKM mass matrix).   Feynman graph of decay and interaction at work? 
Assuming the top width to be ~1.5 GeV   Estimate the lifetime of the top quark 
If QCD color interactions can be characterized by the fly-­‐by time of 2 hadrons (time needed to exchange gluons)   What is the ratio of lifetime to interaction time for top quarks?   Compare to the properties of b-­‐quarks and draw conclusions. 
Top-­‐pair production in hadron colliders proceed through p + p →t + t + X ;
p + p →t + t + X
where X stands for any other hadrons ensuring necessary conservation of various quantum numbers   Draw possible Feynman diagrams   Compare p-­‐p and p-­‐antip €
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Because of the rapid fall-­‐off in parton distribution functions f(x) with increasing x, where x is the fraction of the hadron momentum carried by the interacting parton, the peak of the production cross section occurs essentially at threshold   What is the typical momentum of the b-­‐quark?   What are the typical x values of the colliding partons that can produce top-­‐
pairs at the Tevatron and at the LHC Tevatron :
LHC :
▪  Hint: show that the center of mass energies of the hadron-­‐hadron and parton-­‐parton systems are related by ▪  s = 2TeV
s = 7TeV ; 14TeV
sˆ =€x a x b s
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What could be the signature of top-­‐pair production at the LHC?   Comment the ATLAS event display below   (think of which particles are detected by ATLAS) €found to be heavier than expected when B-­‐Bbar The top quark was mixing was first observed in the 198os.   How come? 5/10/12
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https://twiki.cern.ch/twiki/bin/view/AtlasPublic/EventDisplayPublicResults#Top_events
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Consider the ground states of the following nuclei: 23 Na; 37 Cl; 41 Ca 11
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  What are the expectations for spin, parity and magnetic moment on the basis of the single-­‐particle shell model?   Compare to the experimental values. Make use of the energy-­‐levels of Figure 7.4 as well as appendix E.3 
The ground state of 13756Ba has spin-­‐parity JP=3/2+.The first excited states have JP=1/2+ and JP=11/2-­‐.   According to the shell model, what assignments would be expected for these states?   Make a thorough discussion. 5/10/12
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Read Section 8.4 (pp. 278-­‐293)   Summarize (max 2 pages, including figures) one of the 2 sub-­‐sections 
www.howstuffworks.com
  Medical imaging using ionizing radiation (8.4.2) OR   Magnetic resonance imaging (8.4.3) 5/10/12
http://photosmedical.blogspot.com/
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