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String Theory

String Theory . Why strings?! Gravity cannot be reconciled into the Standard Model We have all but ignored it when discussing particle physics! If these particles are so close together and have mass then surely the effects of gravity do need to be taken into account. String Theory.

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String Theory

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  1. String Theory • Why strings?! • Gravity cannot be reconciled into the Standard Model • We have all but ignored it when discussing particle physics! • If these particles are so close together and have mass then surely the effects of gravity do need to be taken into account.

  2. String Theory • String theory uses the idea that fundamental particles are not “points” at all but behave like very short strings (10-35m long) • Now when the particles interact they don’t need to get so close to do so! • Each fundamental particle is actually an excitation mode of an elementary string • Think back to harmonics!

  3. String Theory • In harmonics there are only certain vibration patterns allowed on a string (to make a known note) • The same applies in string theory. Each fundamental particle is a “note” that can be “played” when the string vibrates in a certain way. • There are only a certain amount of ways for the string to vibrate so there are a set amount of fundamental particles that can exist.

  4. String theory • For this to work, extra dimensions must exist. • We live in the four dimensions of space and time • Bosonic String theory requires 26 dimensions • M- theory requires 11 dimensions • Superstring theory requires 10 dimensions • These are mathematically sound theories but hard to visualise!!

  5. Particle accelerators - Linac

  6. Linac – Key points • Ions are accelerated between the gaps (due to the p.d between the tubes) • They travel at a constant velocity in the tube • Tubes are connected to alternating p.d which reverses the polarity of the tubes when needed • The alternating p.d must be timed to change when needed • This is based on the length of the tube and the velocity of the particles • Each tube is longer than the one before • Ions increase in velocity as they travel through the accelerator

  7. Linac – Advs and Disadvs • Advantages Capable of accelerating particles to higher energies than those achieved in ring-style accelerators Produces a lot of particles Good for anti-matter creation • Disadvantages Expensive Need to be incredibly long. Particles can only be used once SLAC is 3km long The proposed ILC at CERN will be 20 miles long! ($7 Billion)

  8. Particle Accelerators - Cyclotron

  9. Cyclotron- Key Points • Particles move in a circle rather than a straight line • Magnetic field applied at right angles (condition for centripetal motion) • Dees are constantly changing their polarity • Particles are accelerated across the gap • As the particle’s velocity increases their radial path also increase • Time in each dee remains constant

  10. Cyclotron • Magnetic field strength can be equated to the centripetal force to give

  11. Cyclotron- advs and disadvs • Advantages As particles move in a circle rather than straight line the accelerator takes up less space More cost effective/ less power used • Disadvantages Cannot create the high energy particles created in the linac

  12. Particle accelerators- Synchrotron

  13. Synchrotron – Key Points • Same idea as the linac but now the particles move in a circle • Particles can travel around the tube more than once, increasing in energy • Superconducting magnetics apply a field that directs the beam around in a circle • As the beam gets faster the magnetic field required to keep it in a circle must also increase. • The larger the radius of the synchrotron the greater the velocity the particles can reach • Between the magnets the particles are accelerated by the alternating electric field • As the particles get faster and faster the time in any magnet gets shorter and shorter so the alternating p.d frequency must increase • The current supplied to the magnets (to keep the beam travelling in a circle) must also increase at the same time • Hence the name SYNCHROTRON

  14. Bremsstrahlung Radiation • Any accelerating charged particle will emit EM radiation • To travel in a circle the beam must be constantly accelerating • On each bend in the synchrotron, x-ray radiation is released resulting in a loss of energy • This is called braking or Bremsstrahlung radiation

  15. Synchrotron – Advs and Disadvs • Advantages Can be used in collision events. One synchrotron – Two beams in opposite directions (produces more energy than firing at a fixed target) • Disadvantages Production of Bremsstrahlung radiation reduces the energy of the beam, takes more energy to reach required speeds

  16. Why do we need particle accelerators Two reasons • The higher energy the beam of particles in the collision the more massive or energetic the particles will be that we can create. • To see or detect small particles we need diffract the particle beam around the particles. A particle’s de Broglie wavelength (in the beam) needs to be close to the separation of the particles (in the target) to allow the particles to diffract around them and be “seen”

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