* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Higgs colloquium - High Energy Physics
Relativistic quantum mechanics wikipedia , lookup
Double-slit experiment wikipedia , lookup
Scalar field theory wikipedia , lookup
Nuclear structure wikipedia , lookup
History of quantum field theory wikipedia , lookup
Identical particles wikipedia , lookup
Strangeness production wikipedia , lookup
Theory of everything wikipedia , lookup
Introduction to quantum mechanics wikipedia , lookup
Quantum chromodynamics wikipedia , lookup
Renormalization wikipedia , lookup
Quantum electrodynamics wikipedia , lookup
ALICE experiment wikipedia , lookup
Weakly-interacting massive particles wikipedia , lookup
Nuclear force wikipedia , lookup
Theoretical and experimental justification for the Schrödinger equation wikipedia , lookup
Supersymmetry wikipedia , lookup
Electron scattering wikipedia , lookup
Large Hadron Collider wikipedia , lookup
Atomic nucleus wikipedia , lookup
Technicolor (physics) wikipedia , lookup
ATLAS experiment wikipedia , lookup
Future Circular Collider wikipedia , lookup
Compact Muon Solenoid wikipedia , lookup
Higgs boson wikipedia , lookup
Grand Unified Theory wikipedia , lookup
Mathematical formulation of the Standard Model wikipedia , lookup
Elementary particle wikipedia , lookup
Minimal Supersymmetric Standard Model wikipedia , lookup
Higgs mechanism wikipedia , lookup
Searches for the SM Higgs Boson ggs Forces of Nature Unification of the Forces and the Higgs Particle Searching for the Higgs/Higgs Searches Results Matthew Herndon, Dec 2008 BEACH 04 University of Wisconsin University of Massachusetts Amherst Physics Colloquium J. Piedra 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 detailed understanding of the properties of matter M. Herndon 2 The Periodic Table Different types of quantum orbits Elements in same column have similar chemical properties M. Herndon 3 We Observed New Physics Already there were some clear problems One type of atom could convert itself into another type of atom Nuclear beta decay Charge of atom changed and electron emitted How could the nucleus exist? Positive protons all bound together in the the atomic nucleus Needed a new theory M. Herndon 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 between protons and electrons Nuclear beta decay and nuclear fission Holds protons and neutrons together the nucleas Only attractive F = 2.3x10-8N Decays can take thousands of years F = 2.3x102N F = 2.3x10-47N How do we understand the Forces? Fundamental differences in strengths! M. Herndon 5 How Do the Forces Work Relativistic quantum field theory (QFT): Quantum electrodynamics(QED) Unification of relativity(the theory space time and gravity) and quantum mechanics(the theory of atoms as described by the EM Force) Description of the particles and the forces at one time Allowed for a possible unification of the forces - description by one theory Electromagnetic force comes about from exchange of photons. Electromagnetic repulsion via emission of a photon Exchange of many photons allows for a smooth force(EM field) electron photon electron For a very quick interaction we can see individual photon exchanges Particle Annihilation or Creation The new QED EM Theory has one very interesting additional feature Can rotate diagrams in any direction ??? electron photon ??? photon electron electron electron Time goes from left to right. What is an electron going backward in time? Antiparticles! Antielectron or positron. This is going to be a useful way to make new particles. Also learned from studying EM force that the proton and neutron were made of smaller particles. up and down quarks. p=uud, n=udd 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 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 1eV = 1.6x10-19 J So far just a theory - though a successful one Still working to fully understand EW=EM+Weak Unification M. Herndon 8 Electroweak Symmetry Breaking Consider the Electromagnetic and the Weak Forces SM says that they are two aspects of one force and governed by the same rules They should be the same strength, but EM always active, weak decays can take thousands of years! Coupling probabilities at low energy: EM: ~2, Weak: ~2/(MW,Z)4 Fundamental difference in the coupling strengths at low energy, but apparently governed by the same constant Difference due to the massive nature and short lifetime of the W and Z bosons. At high energy the strengths become the same. We say the forces are symmetric SM postulates a mechanism of electroweak symmetry breaking via the Higgs mechanism Predicts a field, the Higgs field, and an associated particle, the Higgs boson. Introduces terms where particles interact with themselves: self energy or mass Directly testable by searching for the Higgs boson A primary goal of the Tevatron and LHC Weak and EM Force: Strength For EM force For weak force P 2/(q2+M2)2 P 2/(q2+MW2)2 Coupling strength: Same as EM force 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! 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 However it’s only a theory. Have to find the Higgs boson! 30 years of searching and no luck yet! M. Herndon 10 The Forces Revisited EM Couples to: Example Quanta: Force Carrier Mass Strength in an Atom Particles with electric charge Weak Weak charge: quarks and electrons Strong Gravity Color charge: All particles with quarks mass Attraction between protons and electrons Nuclear beta decay and nuclear fission Holds nucleons, quarks together in the nucleus Only attractive Photon W and Z Boson Gluon Graviton 0 80 and 91 GeV 0 0 Decay time: Decay time: 10-18 sec 10-12 sec to F = 2.3x102N F = 2.3x10-47N F = 2.3x10-8N thousands of years M. Herndon 11 The Standard Model What is the Standard Model? Explains the hundreds of common particles: atoms - protons, neutrons and electrons Explains the interactions between them Basic building blocks 6 quarks: up, down… 6 leptons: electrons… Bosons: force carrier particles All common matter particles are composites of the quarks and leptons and interact by exchange of the bosons Only observing the Higgs Boson is left to complete the experimental program associated with the SM 12 Searching for the Higgs How do we search for the Higgs Boson Use the idea of particle anti-particle annihilation positron Higgs Boson electron Annihilate high energy electrons and positrons or high energy quarks and anti-quarks inside of protons and anti-protons Problem: The probability or strength of Higgs interactions is proportional to the mass of the particle. Electrons and u and d quarks are very light! M. Herndon 13 Searching for the Higgs: Production The Higgs will couple best to the most massive particles and the W and Z t W and Z bosons: 80 and 91 GeV The top quark: 172.6 GeV: Gold atom We need to produce Higgs using interactions with those particles! _ t 10 orders of magnitude smaller cross section than total inelastic cs M. Herndon 14 Searching for the Higgs: Decay We need decays of the Higgs involving massive particles Higgs particle is probably not massive enough to decay to top quarks So we look for the interactions involving the W and Z and the next most massive particle, the b quark, 4.5GeV M. Herndon 15 Higgs Search at LEP Searched for the Higgs using an electron positron collider Achieved an energy of 209GeV which allowed it to search for Higgs particle up to a mass of ~115GeV Final Result mH > 114.4 GeV M. Herndon 16 Indirect Higgs Search Measuring the mass of the most massive quarks and boson should allow you to calculate the Higgs mass. Current Result mH < 160 GeV M. Herndon 17 Tevatron Higgs Search The search for Higgs continues of the Tevatron Accelerator 1.96TeV proton anti-proton accelerator Enough energy to produce the Higgs. However, the rate is expected to be very small - 3fb-1 of data per experiment Two experiments designed to find the Higgs: CDF and DØ Wisconsin participates in the Higgs search at the CDF experiment The stage is set. We can produce the Higgs We know where to look The Higgs boson mass is between 114.4 and ~160GeV M. Herndon 18 The CDF Detector CDF Tracker Silicon detector: 1 million channel solid state device! 96 layer drift chamber Detector designed to measure all the SM particles Dedicated systems for finding different types of particles Electrons and muons Measurement of the energy of quarks(jets) And if any energy is missing Higgs analysis uses most of the capabilities of the CDF detector M. Herndon 19 The Real CDF Detector Wisconsin Colloquium M. Herndon 20 Searching for the Higgs: Low Mass At Higgs masses well below 160GeV we search for Higgs decays to b quarks. b hadrons are long lived. Low efficiency to tag long lifetime. Many different searches. Associated production with a vector boson, VH: Leptonic decays W and Z are distinctive M. Herndon 21 Higgs Search: WHlbb Example: CDF WHlbb - signature: high pT lepton, MET and b jets Key issues: Maximizing lepton acceptance and b tagging efficiency Backgrounds: W+bb, W+qq(mistagged), single top, Non W(QCD) Single top: yesterdays new physics signal is today’s background Innovations: acceptance from isolated/forward tracks. Multiple or NN b tagging methods. Multivariate discriminants: example - Matrix Element Method (probability of any decay configuration based on the SM calculation compared between signal and background) Factor of 1.5 improvement in the expected limits in the last year from innovations Results at mH = 115GeV: 95%CL Limits/SM Analysis Lum (fb-1) Higgs Events Exp. Limit Obs. Limit CDF NN+ME+BDT 2.7 8.4 4.8 5.8 DØ NN 1.7 7.5 8.5 9.3 Worlds most sensitive low mass Higgs search - Still a long way to go! Low Mass Higgs Searches We gain our full sensitivity by searching for the Higgs in every viable production and decay mode Analysis Lum (fb-1) Higgs Events Exp. Limit Obs. Limit CDF NN: ZHllbb 2.7 2.2 9.9 7.1 DØ NN,BDT 2.3 2.0 12.3 11.0 CDF NN: VHMETbb 2.1 7.6 5.5 6.6 DØ BDT 2.1 3.7 8.4 7.5 CDF Comb: WHlbb 2.7 8.4 4.8 5.8 DØ NN 1.7 7.5 8.5 9.3 Analysis: Limits Exp. Limit obs. Limit CDF WHWWW 33 31 DØ WHWWW 20 26 CDF VHqqbb 37 37 CDF H 25 31 With all analysis combined we have a sensitivity of about ~2.4xSM at low mass. DØ WHbb 42 35 DØ H 23 31 A new round of DØ analysis, 2x data and 1.5x improvements will bring us to SM sensitivity. DØ ttH 45 64 Searching for the Higgs: High Mass At Higgs masses around 160GeV we search for Higgs decays to W bosons. Leptonic W decay - Uses the excellent charged lepton fining ability of our detectors Also a primary channel for the LHC M. Herndon 24 Higgs Search: HWW HWWll - signature: Two high pT leptons and MET Key issue: Maximizing lepton acceptance Primary backgrounds: WW and top in di-lepton decay channel Innovations: CDF/DØ : Inclusion of acceptance from VH and VBF CDF : Combination of ME and NN approaches W+ H W+ W- W- e- μ+ ν ν Spin correlation: Charged leptons go in the same direction SM Higgs Search: HWW Most sensitive Higgs search channel at the Tevatron Both experiments Approaching SM sensitivity! Let’s Combine the Results. Results at mH = 165GeV : 95%CL Limits/SM Analysis Lum (fb-1) Higgs Events Exp. Limit Obs. Limit CDF ME+NN 3.0 17.2 1.6 1.6 DØ NN 3.0 15.6 1.9 2.0 SM Higgs Combination High mass only Exp. 1.2 @ 165, 1.4 @ 170 GeV Obs. 1.0 @ 170 GeV SM Higgs Combination Result verified using two independent methods(Bayesian/CLs) 95%CL Limits/SM M Higgs(GeV) 160 165 170 175 Method 1: Exp 1.3 1.2 1.4 1.7 Method 1: Obs 1.4 1.2 1.0 1.3 Method 2: Exp 1.2 1.1 1.3 1.7 Method 2: Obs 1.3 1.1 0.95 1.2 SM Higgs Excluded: mH = 170 GeV We exclude at 95% C.L. the production of a SM Higgs boson of 170 GeV Projections Goals for increased sensitivity achieved Goals set after 2007 Lepton Photon conference First stage target was sensitivity for possible exclusion Second stage goals still in progress Expect large exclusion, or evidence, with full Tevatron dataset and further improvements. Run II Preliminary Discovery Discovery projections: chance of 3 or 5 discovery Two factors of 1.5 improvements examined relative to summer Lepton Photon 2007 analyses. First 1.5 factor achieved for summer ICHEP 2008 analysis Resulted in exclusion at mH = 170 GeV. Conclusions Finding the Higgs Boson would add fundamental information to our understanding of the forces of nature Without the Higgs boson we don’t understand the nature of the weak force: Why it is so much weaker than the electromagnetic force? The Higgs boson search is in its most exciting era ever The Tevatron experiments have achieved sensitivity to the SM Higgs boson production cross section at high mass We exclude at 95%C.L. the production of a SM Higgs boson of 170 GeV Expect large exclusion, or evidence, with full Tevatron data set and improvements SM Higgs Excluded: mH = 170 GeV M. Herndon 31 Backup SM Higgs Combined Limits Limits calculating and combination Using Bayesian and CLs methodologies. Incorporate systematic uncertainties using pseudo-experiments (shape and rate included) (correlations taken into account between experiments) Backgrounds can be constrained in the fit Winter conferences combination April: hep-ex/0804.3423 HWW Systematic Uncertainties Shape systematic evaluated for Scale variations, ISR, gluon pdf, Pythia vs. NL0 kinematics, jet energy scale: for signal and backgrounds. Included in limit setting if significant. Systematic treatment developed in collaboratively between CDF and DØ LHC Prospects: SM Higgs LHC experiments have the potential to observe a SM Higgs at 5 over a large region of mass Observation: ggH, VBF H, HWWll, and HZZ4l Possibility of measurement in multiple channels Measurement of Higgs properties Yukawa coupling to top in ttH Quantum numbers in diffractive production All key channels explored Exclusion at 95% CL CMS ATLAS preliminary Example HEP Detector 36