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Measuring the B-meson’s brief but eventful life

Measuring the B-meson’s brief but eventful life. Tim Adye Rutherford Appleton Laboratory Particle Physics Masterclass 15-17 th March 2006. The BaBar Detector at SLAC. Linear Accelerator. 336 Million BB recorded since starting in May 1999. 2.2km ring. BaBar. The BaBar Collaboration.

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Measuring the B-meson’s brief but eventful life

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  1. Measuring the B-meson’s brief but eventful life Tim Adye Rutherford Appleton Laboratory Particle Physics Masterclass 15-17th March 2006

  2. The BaBar Detector at SLAC Linear Accelerator 336 Million BB recorded since starting in May 1999 2.2km ring BaBar

  3. The BaBar Collaboration 10 Countries 77 Institutions 593 Physicists BaBar B-meson lifetime

  4. B-meson production and decay Second B decays First B decays e+ Measure the decay length to calculate the B lifetime t t1 t2 e ̶ BaBar B-meson lifetime

  5. lower energy high energy

  6. BaBar Detector Elements (side view) Muon Detector Electro- magnet Tracking Detailed Tracking Particle Identification Electron & Photon Detector

  7. Event Display Instructions Event number Move between events Particle momentum and type B and B decay to pions, kaons, etc. Their trajectories are extrapolated from the outer detector into the centre and are shown as red and yellow “tracks”: red for one B (or B) and yellow for the other. A track is just an extrapolation of the particle’s path, so is extended past its production point. The final part of the extrapolation is shown with a narrower line to indicate this. Rotate about horizontal axis “Beamspot” where most e+e- collisions take place. This is about 1cm long Click-move-release mouse to measure These white lines are part of the outer detector that overlap our display. They can be ignored at this scale. Reset size Zoom Out Move Up Side view Move Horizontally Reset view Zoom In Centre Move Down

  8. Tips for Finding and Measuring B-meson decays - 1 • B-mesons are created and decay along BaBar’scentral axis • Look for your decay points along, or a little to the left or right of, the “beamspot” (horizontal blue line at the centre) • The B-mesons travelled along this same axis • Some tracks may not give a good extrapolation • could be from the decay of longer-lived particles, or due to scattering • You can ignore tracks that don’t help you form a decay point • even “good” tracks can’t be measured perfectly • Try rotating the event for a better view • use the slider on the right BaBar B-meson lifetime

  9. Tips for Finding and Measuring B-meson decays - 2 • Make sure you use an appropriate magnification • Scale=512 to 1448 is best • you may still want to briefly zoom out to see where you are • Many B-mesons will decay too quickly for you to see any separation • Note these down as zero decay distance • These will still contribute to the average • Don’t panic! • The concepts, data, and display take some getting used to. Take your time on your first few events. • Ask a demonstrator if you have problems. BaBar B-meson lifetime

  10. Finding and Measuring B-meson decays - Summary • B-mesons are created and decay along the central axis • Ignore tracks that don’t help you form a decay point • Try rotating the event for a better view • Zoom factor scale=512 to 1448 is best • If you don’t see any separation D=0 • Don’tPanic – ask for help! BaBar B-meson lifetime

  11. More Information • Particle Physics: http://hepwww.rl.ac.uk/pust/ • and follow the links • BaBar: http://www-public.slac.stanford.edu/babar/ • Includes “live” display of new events BaBar B-meson lifetime

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