Transcript Bubble Chamber Work Group Presentation

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Targets of our work group
Simple lessons with BC photographs
History of BC
Overview of 50-minutes lesson
FAQs
• To create simple lesson with BC photographs
• To update webpage on history of BC
• To create 50 minutes modular lesson for teaching BC
concepts
• To create webpage of frequently-asked questions (FAQs)
• You can make your own cloud chamber and see tracks of
particles produced by cosmic rays
• Click here for instructions
• When a charged particle goes through a superheated
liquid, it ionises atoms along its path and makes the
liquid boil, creating a trail of bubbles
• Click here for a simulation of bubble formation
A plane in the sky causes water
vapour in the air to condense
Charged particle in BC causes
superheated liquid to boil
• The different coloured
tracks are produced by
different charged
particles
Kp
B
– Bright Green kaon K– Red electron e– Blue proton p
• Why are tracks curve?
Click here for discussion
A
e
• A particle of charge q travelling through a magnetic field
B with a velocity v experiences a force, given by
F  q(v  B )
• We use the formula for the Lorentz force to calculate
the value and direction of the force exerted on charged
particles by the magnetic field
• The thumb points in the
direction of the force F
• First finger points in the
direction of the magnetic
field B
• Second finger points in
the direction of motion
of the positive charge v
• In principle, the
momentum of a charged
particle is obtained using
the formula
p  B  q   r
v
B
+
-
F
F
v
• Spiralling tracks are common in BC
photographs, caused by e- or e+
• An e- loses energy at a considerable
rate as it travels through BC liquid
• All other charged particles, unless
they collide with a nucleus, slow
down very gradually – get more
curved – as they lose energy by
ionisation
• e- are able to lose energy
more quickly by another
process in which all
accelerated charges radiate
• Click here for more
information
Dark tracks belong to a slow particle
Spiralling tracks are e- because of
their very small mass
Particles with large
momenta are less curved
Particles with small
momenta are more
curved
• All physical laws must be fulfilled in every BC event
– Momentum conservation
– Charge conservation
– Energy conservation
– Behaviour of moving charged particles in magnetic field
– Other physics laws
• The primary (orange) beam has
–ve charge while one of the two
secondary beams has –ve
charge (green) and the other
+ve charge (bright green)
• We also know that the two
outgoing tracks have low
momentum because they curve
significantly in B-field
• What is the direction of the
momentum of the primary
beam?
• Estimate the momenta of the
secondary tracks
• What is the total momentum
after interaction?
• Clearly the total
momentum of the
outgoing charged
particles does not equal
to the momentum of the
beam particle
• Draw an arrow to show
the “missing” momentum
• Click here for more info
• In all BC photographs, the charge of the particle can be
only +e or -e
• Sign of particles can be determined by the direction of
the track’s curvature
• Click here to find this
• The primary beam is K• What are the charges of
secondary particles?
[Hint: the red spiral is
produced by an electron]
• Green is negative and
bright green is positive
• If this event do not
involve other particle,
total charge before
interaction (-e) is not
equal to the total charge
after it (0)
• But the collision involves
a proton (+e), so the total
charge is conserved
• Here is another picture
that could be used for a
similar exercise
• Improve and publish a webpage on history of BC
– Birth and evolution of BC and its main discoveries
– Important photographs
– 2 articles on history of BC and personal experience
• PowerPoint on history of BC
Cloud chamber
Anderson (1932), positron (e+)
Nuclear Emulsion
Powell (1947), pion p+
• It’s faster to reactivate than cloub chambers
• The expansion of BC can coincide with the accelerator
cycle
• BC were very small initially; only a few cubic centimetre
of liquid
• Big European Bubble Chamber (BEBC) in 70’s has a
diameter of 3.7 m
• 1956. Discovery of S0 in a propane BC
• 1964. Discovery of - which gives acceptance of GellMann theory of ordering all subatomic particle “eightfold way”
• 1973. Neutral current discovered at CERN’s 25-ton
Gargamelle
• 1975. Discovery of “charmed” baryon in 7-foot
Brookhaven
• Research on earlier particle detectors – cloud chamber
& nuclear emulsions
• Design a PowerPoint presentation using the contents of
the webpage
• Short biographies of the people who developed the BC
• Lesson 1 – “Introduction to BC and Basic Feature of the
Interactions”
– Photographs, Worksheet 1
• Lesson 2 – “Identifying the Particles and Conservation of
momentum & Charge”
• Lesson 3 – “Particle Interactions – Collisions & Decays”
• Lesson 4 – “Principle of determination of momentum”
• Lesson 5 – “Principle of determination of energy”
• Lesson 6 – “More complex BC photographs”
What does LHC stand for?
• Large Hadron Collider. Click here for further detail.
What are antiparticles?
• To every particle that has a non-zero value of some
quantity such as electric charge, it is possible to create
another particle with the opposite value – this is the
antiparticle of the original one. For an example, click
here.
• Profile of Jonni Fulcher
• An example of a collision
• Jonni Fulcher Stunts
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