ATLAS Experiment at CERN

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ATLAS Experiment at CERN
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Why Build ATLAS?

• Before the LHC there was LEP (large electron
  positron collider) the experiments at LEP had
  observed the W and Z boson which carry the weak
  force. At the upper end of the LEP energies it
  was hypothesised that the Higgs Boson would be
  observed.
• The Higgs boson is only one particle left in the
  standard model that has yet to be observed.
• It is unknown why fundamental particles have such
  varying masses and it is believed that the
  discovery of the higgs boson could help to answer
  some of these questions.

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Although the higgs boson was the main motivation
for building ATLAS it is also hoped that it will
answer other questions left open by the standard
model such as 1-Why are there three types of
quarks and leptons of each charge? 2-Are there
more types of particles and forces to be
discovered? 3-Are the quarks and leptons really
fundamental, or do they, too, have substructure?
4-What particles form the dark matter in the
universe? 5-How can the gravitational
interactions be included in the standard model?
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Why can ATLAS answer these questions?

• The LHC will provide colliding beams of much
  greater energy than available at LEP. The maximum
  energy of the protons in the beam will be 7TeV.
• From Einsteins famous equation
• it is known that mass and energy are equivalent.
• The higher energy beam means that in a collision
  a more massive particle can be produced. This
  will be needed if the Higgs boson is to be
  observed.
• Higher energy beams may also answer some of the
  questions left from the standard model.

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The ATLAS Detector

• A diagram of the ATLAS detector which is the size
  of a five story building

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The Higgs Boson

• The higgs boson is the last of the particles
  predicted by the standard model yet to be
  detected directly.
• The Higgs is believed to exist in a field which
  is present in all of space. An analogy to both of
  these is given below.

To understand the Higgs mechanism, imagine that a
room full of physicists chattering quietly is
like space filled with the Higgs field ...
... a well-known scientist walks in, creating a
disturbance as he moves across the room and
attracting a cluster of admirers with each step
...
... this increases his resistance to movement, in
other words, he acquires mass, just like a
particle moving through the Higgs field
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... if a rumor crosses the room, ...
... it creates the same kind of clustering, but
this time among the scientists themselves. In
this analogy, these clusters are the Higgs
particles.
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What if the Higgs boson is not Found?

• If the Higgs is not found then there are plenty
  of other things that scientists at ATLAS can
  search for.
• GUTS- Grand Unified Theory, where all the forces
  will act together as one -already started with
  Maxwells theory of electromagnetism.
  
• -electroweak theory by Glashow, Salam, and
  Wienberg.

Other possible searches include looking for
supersymmetry and dark matter.