* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Discovery of Higgs Boson - High Energy Physics
Quantum field theory wikipedia , lookup
Electron configuration wikipedia , lookup
Hydrogen atom wikipedia , lookup
Canonical quantization wikipedia , lookup
Double-slit experiment wikipedia , lookup
Relativistic quantum mechanics wikipedia , lookup
Quantum chromodynamics wikipedia , lookup
Identical particles wikipedia , lookup
Renormalization wikipedia , lookup
Quantum electrodynamics wikipedia , lookup
Theoretical and experimental justification for the Schrödinger equation wikipedia , lookup
Wave–particle duality wikipedia , lookup
Boson sampling wikipedia , lookup
Scalar field theory wikipedia , lookup
History of quantum field theory wikipedia , lookup
Nuclear force wikipedia , lookup
Higgs boson wikipedia , lookup
Technicolor (physics) wikipedia , lookup
Atomic theory wikipedia , lookup
The Discovery of the Higgs boson Matthew Herndon, University of Wisconsin Madison Phys 301: Physics Today M. Herndon, Phys 301 2017 1 The Atom In the early twentieth century atomic physics was well understood The atom had a nucleus with protons and neutrons. An equal number of electrons to the protons orbited the nucleus The keys to understanding this were the electromagnetic(EM) force and the new ideas of quantum mechanics The EM force held the electrons in their orbits Quantum mechanics told us that only certain quantized orbits were allowed Allowed a detailed understanding of the properties of matter M. Herndon, Phys 301 2017 M. Herndon 2 The Periodic Table Different types of quantum orbits M. Herndon, Phys 301 2017 Elements in same column have similar chemical properties 3 We Observed New Physics Already there were some unexplained phenomena One type of atom could convert itself into another type of atom Nuclear beta decay Charge of atom changed and an electron was emitted How could the nucleus exist? Positive protons all bound together in the the atomic nucleus M. Herndon, Phys 301 2017 Needed a new theory 4 The Forces Best way to think about the problem was from the viewpoints of the forces Needed two new forces and at first glance they were not very similar to the familiar electromagnetic and gravitational forces! Couples to: Example Strength in an Atom EM Weak Strong Gravity Particles with Protons, Neutrons Protons and All particles with electric charge and electrons Neutrons mass Attraction Nuclear beta decay Attraction between between protons Not an attractive protons and and electrons force neutrons F = 2.3x10-8N Decays can take thousands of years F = 2.3x102N Only attractive F = 2.3x10-47N How do we understand the Forces? Why so different in in properties? M. Herndon, Phys 301 2017 5 A New Theory Relativistic quantum field theory (QFT): Unification of special relativity(the theory space time) and quantum mechanics(used to understand the atom) Forces described by exchanging particles Electromagnetic force comes about from exchange of photons. electron photons Example :Electromagnetic repulsion via emission of a photon Exchange of many photons allows for a smooth force(EM field) M. Herndon, Phys 301 2017 electron 6 Unification! Maxwell had unified electricity and magnetism Both governed by the same equations with the strengths of the forces quantified using a set of constants related by the speed of light The Standard Model of Particle Physics (proposed 1960) QFTs for EM, Weak and Strong Unified EM and Weak forces - obey a unified set of rules with strengths quantified by single set of constants All three forces appear to have approximately the same strength at very high energies. May also unify. 1eV = 1.6x10-19 J A very successful theory A Key component was missing to fully understand EM-Weak Unification M. Herndon, Phys 301 2017 7 Weak and EM Force: Strength For EM force For weak force Coupling strength: Same as EM force P µ a2/(q2+Mg2)2 P µ a2/(q2+MW2)2 q momentum of the W or Z bosons Mass of the photon is 0, mass of the W and Z bosons is large When the mass of the W boson is large compared to the momentum transfer, q, the probability of a weak interaction is low compared to the EM interaction! Too low to form a field and bound states. At high energy when q was much larger than the mass of the weak bosons the the weak and EM interaction have the same strength The key missing element is to explain the mass of the W and Z bosons M. Herndon, Phys 301 2017 8 The Forces Revisited EM Couples to: Particles with electric charge Attraction Weak Weak charge: quarks and electrons Strong Gravity Color charge: All particles with quarks mass Nuclear beta decay Attraction between No attractive force quarks/nucleons Photon W and Z Boson Gluon Graviton Mass 0 80 and 91 GeV 0 0 Decay time/ Decay time: Decay time: Strength in an 10-18 sec 10-12 sec to F = 2.3x102N F = 2.3x10-47N Atom F = 2.3x10-8N thousands of years Example between protons and electrons Quanta: Force Carrier M. Herndon, Phys 301 2017 Only attractive 9 The SM Higgs Boson SM postulates a mechanism of electroweak symmetry breaking via the Higgs mechanism (proposed 1964) Interaction with the Higgs field results in masses for the W and Z vector bosons A primary reason for the difference EM and Weak interactions Fills in the key missing element of the SM Can explain the mass of the fermions (quarks and leptons) as well Also expect an observable quanta of the field: Higgs boson à directly testable by searching for the Higgs boson! The primary goal of the LHC Run 1 M. Herndon, Phys 301 2017 10 Searching for the Higgs How do we search for the Higgs Boson? In the SM particles that carry the charge of a given force can interact by absorbing or emitting the force carrier The diagrams (Feynman diagrams) can be converted into Also they can annihilate or pair produce equations to calculate the probability of the process occurring. M. Herndon, Phys 301 2017 11 Searching for the Higgs The “charge” that the Higgs boson interacts with is mass Particles with high mass will interact with higher probability with a Higgs boson W and Z bosons: 80 and 91 GeV - mass of a krypton atom The top quark: 172.6 GeV - mass of a gold atom However, the LHC collides protons made of quarks and gluon Some thought needed to understand the best way to make Higgs bosons M. Herndon, Phys 301 2017 12 Searching for the Higgs Also look for decay to massive particles M. Herndon, Phys 301 2017 13 Searching for the Higgs Those decays should be to particles that are easy to detect: i.e. uniquely identify and measure the momentum of M. Herndon, Phys 301 2017 14 Need Every Advantage LHC collision rates LHC collides protons every 50 ps 20 proton-proton interactions each time Probability of a Higgs interaction 11 orders of magnitude less. 1/100000000000 collisions produces a Higgs boson ~1 Higgs every 10 minutes 100-1000 less, easily detected Higgs M. Herndon, Phys 301 2017 15 Plan of action Calculate the probability of Higgs production and decay expected in proton-proton collisions A decade of work by dozens of theorists Build a collider to collide the protons at high energy and high enough rate A decade of work by hundreds of collider physicists Build experiments that can detect the Higgs boson A decade of work by thousands of experimental physicists Apply our best ideas to achieve the above All built on decades of experience from previous experiments. M. Herndon, Phys 301 2017 16 SM Higgs Production and Decay Take advantage of large gg ® H production cross section Had to calculate as a function of mass as Higgs mass was not predicted Alternative production mechanisms Primarily VBF: qq ® Hqq Decay modes: H ® gg, H ® ZZ, Sensitive since they are well reconstructed M. Herndon, Phys 301 2017 17 The Large Hadron Collider 14 TeV proton-proton collider (now 8 TeV) 27 Km tunnel 100m underground 109 collisions/second M. Herndon, Phys 301 2017 18 The CMS Detector Detector designed to measure all the SM particles Tracker Electromagnetic Calorimeter Hadronic Calorimeter Solenoid M. Herndon, Phys 301 2017 Muon System 19 Particle Detection in CMS Particle Detection M. Herndon, Phys 301 2017 20 LHC Collision M. Herndon, Phys 301 2017 LHC Collision 21 Higgs Sensitivity q As of 2012 the Higgs boson not yet been found but the mass was constrained to the range mH: 115-130 GeV q UW UW Plot shows convolution of production, decay and detector capabilities q Strong sensitivity to 5 decay modes led by γγ and ZZ (below 1 means sensitivity to SM Higgs production) M. Herndon, Phys 301 2017 22 Multiboson Physics UW UW UW UW UW Some preparation: Other SM processes with decays to bosons. M. Herndon, Phys 301 2017 23 Final Higgs Search Once you have your best calculations, collider, detector and have applied all your ideas the final analysis in essence consists of looking for events with two photons or two Z bosons where the combined mass of the two bosons adds up to a consistent mass. M. Herndon, Phys 301 2017 M. Herndon 24 LHC Higgs Event: gg M. Herndon, Phys 301 2017 25 LHC Higgs Event: ZZ ® µµee M. Herndon, Phys 301 2017 26 26 Higgs Searches Events / 3 GeV CMS Preliminary s = 7 TeV, L = 5.05 fb-1 ; s = 8 TeV, L = 5.26 fb-1 12 Data 7 TeV 4e, 4µ , 2e2µ 8 TeV 4e, 4µ , 2e2µ Z+X 10 UW 8 Zγ *,ZZ mH=126 GeV 6 4 2 0 m4l [GeV] 80 100 120 140 160 180 m4l [GeV] γγ: 4.0σ M. Herndon, Phys 301 2017 ZZ 3.2σ 27 1 1σ 2σ -1 10 10-2 10-3 10-4 10-5 10-6 10-7 10-8 10-9 10-10 10-11 10-12 3σ Combined obs. Exp. for SM Higgs H → γγ H → ZZ UW CMS Preliminary H → ZZ + γ γ s = 7 TeV, L = 5.1 fb-1 s = 8 TeV, L = 5.3 fb-1 6 5 4σ 4 5σ 3 6σ Combined H → γ γ (inc.) H → γ γ (VBF) CMS Preliminary H → ZZ + γ γ s = 7 TeV, L = 5.0 fb-1 s = 8 TeV, L = 5.2 fb-1 H → ZZ 2 1 7σ 116 118 120 122 124 126 128 130 Higgs boson mass (GeV) σ/σSM Local p-value Higgs Observation! 0 123 124 125 126 127 128 129 Higgs Boson Mass (GeV) mH=125.3±0.6(stat+sys ) experiment as well Simultaneously observed by ATLAS Combined 5.0σ! M. Herndon, Phys 301 2017 28 Higgs Properties Couples proportional to mass M. Herndon, Phys 301 2017 29 Conclusions LHC has observed a Higgs boson with mass ~125 GeV! Observed at the gold standard of statistical significance. Simultaneous observation by independent experiments providing both discovery and proof of reproducibility. Now observed with the event rates expected for both W and Z interactions with the Higgs. All properties very consistent with SM expectation. The last piece of the SM confirmed! A beginning, not an end, for the LHC story More mysteries to solve. Dark matter, unification of the forces …. M. Herndon, Phys 301 2017 30