The ATLAS Experiment and the CERN Large Hadron Collider. HEP101-6 March 12, 2012

Transcription

1 The ATLAS Experiment and the CERN Large Hadron Collider HEP101-6 March 12, 2012 Al Goshaw Duke University 1

2 HEP 101 to date Jan. 23: Overview of CERN and the LHC Feb. 6: Review of elementary particles and forces Feb. 13: Basics of particle detectors Feb. 20: Particle production at the LHC and relativistic mechanics Feb. 27: Overview of heavy ion collisions at the LHC March 12: TODAY Recent news about the Higgs boson search; work out some example assigned problems. March 19: NEXT Physics beyond the Standard Model (this will be given by Ashutosh Kotwal at 6:00pm) 2

3 HEP 101 and summer plans Some goals for summer students Do some reading about the basics of HEP research and elementary particle physics. Make presentations the HEP group about what you learn. Write a report at the end of the summer on what you accomplished. The word processing program of choice is latex. This is worthwhile for you to learn for many applications. Learn to access data from the ATLAS detector, and to make simple analyses to study the detector performance and the characteristics of particle production. Learn simple statistical analysis tools. Exercise some theory calculations that make SM predictions. Learn about construction od a simple particle detector. 3

4 Some comments about the Higgs boson The force-field bosons (photon, W, Z and gluons) interact selectively with particles depending on the type of charge they carry. gluons The Higgs field also interacts with the particles of the Standard Model, but in a unique way. It couples to any particle with a strength that depends on the particle s mass. Or conversely we can say the particle s mass is determined by the strength of its coupling to the Higgs field. 4

5 Some comments about the Higgs boson The term Higgs boson is in honor of Peter Higgs who first introduced this field into the Standard Model (pioneering work done at UNC in the 1960 s). The Higgs Mechanism is the mathematical method for generating mass terms in the field equations (Lagrangians) that start out with zero mass particles. This is done in a manner that breaks the underlying symmetries (electroweak symmetry breaking), producing a theory that: preserves the beautiful predictions of the SU c (3)xSU L (2)xU Y (1) dynamics explains the massive particles we observe in Nature and is still a renormalizable field theory (that is it allows calculations of physical observables.) 5

6 Some recent News: the Higgs boson search The search for the Higgs boson has been going ever since it was proposed, but only recently has the energy and sensitivity of experiments reached the level of an expected observation. The Higgs boson has many production proceses and decay modes which can be used in searches. These differ at the LHC and the Tevatron which makes the searches complmentary. 6

7 Some recent News (ATLAS): the Higgs boson search There is no Higgs boson with mass M H c 2 between 129 to 529 GeV. This assumes that the Higgs boson couples to particles as described by the Standard Model. 7

8 Some recent News (ATLAS): the Higgs boson search There is a hint of a Higgs boson signal at M H c 2 ~ 125 GeV using the decay modes: H -> γ γ and Z Z* 8

9 What about Higgs boson searches at CMS Another hint of a Higgs boson signal at M H c 2 ~ 125 GeV using the decay modes: H -> γ γ and Z Z* 9

10 What about searches at Fermilab? There is a hint of a Higgs boson signal at M H c 2 ~ 120 GeV using various decay mode dominated by H -> b b 10

11 What about other new physics at the LHC? No hints of any other new physics beyond the particles included in the Standard Model. 11

12 Recap: Relativistic Kinematics p = γ β m c E 2 = (pc) 2 + (mc 2 ) 2 E = γ m c 2 Four momentum P µ = (E/c, p ) X µ = (tc, r ) etc. Scalar product P 2 = P µ P µ = (E/c) 2 ( p ) 2 = (mc) 2 etc. Any 4-vector V in O has a value V when measured in O. V µ = L µ ν Vν where the L µ ν is a Lorentz transformation between inertial reference frames. The square of a 4-vector is a Lorentz invariant in the sense it does not change when the four vector is transformed between inertial reference frames : V µ V µ = V µ V µ 12 12

13 Recap: Relativistic Kinematics A simple example of L µ ν is a boost along one axis (say the z axis). Let β o = v o /c and γ o = 1/ 1 - β o 2 Any 4-vector V in O has a value V when measured in O. V µ = L µ ν Vν where the L µ ν are the elements of a boost matrix. p x = p x p y = p y p z = γ o (p z - β o E/c ) E /c = γ o (E/c - β o p z ) L µ ν = γ o 0 0 -β o γ ο β o γ o 0 0 γ o 13 13

14 Solution to exercises 1. Calculation of a particle s kinetic energy given its measured momentum. 2. Calculation of a particle s mass given a measurement of the momentum of its decay products. 3. Comparison of the center-of-momentum energy of a colliding beam and fixed target experiments. What you need for the above calculations is simple relativistic mechanics and the conservation of energy and momentum. 14