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Slide 1Slide 2Slide 3Slide 4Slide 5Slide 6Slide 7Slide 8Slide 9Slide 10Slide 11Slide 12Slide 13Slide 14Slide 15Slide 16Slide 17Slide 18Slide 19Slide 20Slide 21Slide 22Slide 23Slide 24Slide 25Slide 26Slide 278.882 LHC PhysicsExperimental Methods and MeasurementsHigh Energy Physics Overview[Lecture 16, April 6, 2009]C.Paus, LHC Physics: High Energy Physics Overview 2Organization Next lecture: Michael Betancourt●Baysians versus Frequentists: lesson on statistics●I will be on a plane at that time: so be nice to Michael Project 2●due April 9 (Wednesday)●check web page for instructions, in particular triggersProject 3●B lifetime is coming up....Final Conference Project●planning for ? May 20 at 13:00am in the Kolker Room ?●program should be fixed pretty quicklyC.Paus, LHC Physics: High Energy Physics Overview 3Lecture Outline High Energy Physics overview●overview of the program●B physics, LHCb experiment●cross sections, production fractions, branching ratios●lifetimes and lifetime ratios●CP asymmetries, mixing and lifetime differences●QCD and Electroweak●top physics●Standard Model Higgs●SUSY●extra dimensionsC.Paus, LHC Physics: High Energy Physics Overview 4HEP Program Overview Precursor: Planck mass, mP●Schwarzschild radius: rS ; characteristic radius for which a particle would just turn into a black whole if all its mass was inside that radius●Compton length: λ ; intrinsic position uncertainty for the position measurement of a particle due to its wave character as defined by QM●Planck mass: particle has rS = λ/π Mass of a flea is about 5000 x mPC.Paus, LHC Physics: High Energy Physics Overview 5HEP Program Overview Precursor: Charge Conjugation, C●replacing a particle with its own antiparticle is called charge conjugation: operator in QM Precursor: Parity Inversion, P●inverting the spacial coordinates is called the parity operation and is a QM operator Precursor: CP●combining charge conjugation and parity inversion is called the CP operation E&M and QED completely symmetric under C and P Weak force●violates C and P maximally●CP also violated, less obvious (1964, K0, Cronin, Fitch)C.Paus, LHC Physics: High Energy Physics Overview 6HEP Program Overview Big questions in High Energy Physics●the matter problem●where does matter originate from? which mechanism?●what is the large amount of dark matter in the universe?●(what is the even larger amount of dark energy?)●matter anti-matter asymmetry and CP violation●why is there so much matter and so little anti-matter?●big bang should have produced them in equal amounts●CP operation has to be asymmetric (violates symmetry)●Standard Model CP violation cannot explain observed asymmetry●could explain existence of just one galaxy but not the universe●there must be something else, CP violating, generating the restC.Paus, LHC Physics: High Energy Physics Overview 7HEP Program Overview Big questions in High Energy Physics, continued●Hierarchy problem(s)●general idea: fundamental parameters are much smaller/bigger than parameters measured in the experiment●why is the weak force 1032 times stronger than gravity?●or otherwise put: why is the Higgs mass that much smaller then the Planck mass? to explain this in a natural fashion new physics should appear in vicinity of the Higgs boson (what ever that means)C.Paus, LHC Physics: High Energy Physics Overview 8LHCb Experiment and B PhysicsC.Paus, LHC Physics: High Energy Physics Overview 9LHCb Experiment and B PhysicsC.Paus, LHC Physics: High Energy Physics Overview 10LHCb Experiment and B PhysicsC.Paus, LHC Physics: High Energy Physics Overview 11LHCb Experiment and B PhysicsMeasure triangle in all possible independent ways and confirm its closureC.Paus, LHC Physics: High Energy Physics Overview 12LHCb Experiment and B PhysicsIn the Standard Model we expect:Beyond the Standard Model there could be:Mixing frequency different: unitarity triangle not closed!C.Paus, LHC Physics: High Energy Physics Overview 13Atlas&CMS: High pT Physics Standard Model: Electroweak - Parameters●masses: fermion masses (12), boson masses (4)●couplings(4): αQED, αQCD, gW, ν0●4 quark and 4 leptonic mixing parameters Standard Model●Classical Mechanics is ultimately described by a Lagrangian and the Hamilton Principle●Classical Field theory adds the field to CM and the Lagrangian density●Quantum Mechanics adds uncertainty principles and Operators●SM is a Quantum Field Theory (quantize classical field)●in particular needed to explain particle reactionsC.Paus, LHC Physics: High Energy Physics Overview 14Generation of Mass with Higgs Boson A gauge invariant Lagrangian cannot support simple by hand introduced mass terms because they destroy the gauge invariance Introducing an additional scalar field modifies the derivative and thus the gauge transformation Additional terms appear now in the Lagrangian which have the form of mass terms Vacuum expectation value non zero, particle move through a field which gives them massC.Paus, LHC Physics: High Energy Physics Overview 15A Popular Explanation [CERN] Empty space is like a room full of chattering scientists A highly regarded scientist arrives.... (she represents a particle) While moving through the room people gather around her producing resistance against her motion here interpreted as massC.Paus, LHC Physics: High Energy Physics Overview 16A Popular Explanation [CERN] A rumor is created and crosses the room. The people in the room create a clustering just by themselves which is interpreted as the Higgs boson.C.Paus, LHC Physics: High Energy Physics Overview 17Goal of Electroweak Physics Measure electroweak reactions to constrain Standard Model●direct measure of SM parameters mt, mW, ....●measurements: Oi(mW, mZ, mt, mH,....)●example: cross section, asymmetries, polarizationsC.Paus, LHC Physics: High Energy Physics Overview 18Interpreting Electroweak Results in SM All essential world EW measurements compared to the predicted value Some of the measurements are very high level, combining very many individual measurementsC.Paus, LHC Physics: High Energy Physics Overview 19Interpreting Electroweak Results in SM The one free unknown is obviously the most important goal Higgs mass enters as a logarithm into the electroweak corrections Either Higgs is found or SM is shown to be wrongC.Paus, LHC Physics: High Energy Physics Overview 20Interpreting Electroweak Results in SM Indirect


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MIT 8 882 - High Energy Physics

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