Presentation on theme: "The God particle at last?"— Presentation transcript:
1 The God particle at last? Science Week, Nov 15th, 2012Cormac O’RaifeartaighWaterford Institute of Technology
2 CERN July 4th 2012 (ATLAS and CMS ) “A new particle of mass 125 GeV ”
3 Why is the Higgs particle important? Fundamental structure of matterKey particle in theory of matterOutstanding particleThe forces of natureInteraction of particles and forcesRole of Higgs field in unified field theoryIII. Study of early universeHighest energy density since first instantsInfo on origin of universe‘God particle’
4 Overview Particle physics and the Standard Model What, why, how I The Higgs bosonParticle physics and the Standard ModelII The Large Hadron ColliderWhat, why, howIII The discoveryA new particle at the LHCIV The futurePhysics beyond the Standard Model
5 I Early particle physics (1900-1912) Discovery of the atom (1908)Einstein-Perrin (expected)Discovery of the nucleus (1911)Rutherford Backscattering (surprise)Positive, tiny coreFly in the cathedralNegative electrons outsideFundamental particles (1895)Brownian motionWhat holds electrons in place?What holds nucleus together?What causes radioactivity?
6 Atoms and chemistry Discovery of the proton (1918) Particles of +ve charge inside nucleusExplains periodic tableAtoms of different elements havedifferent number of protons in nucleusNumber protons = number electrons (Z)Determines chemical propertiesDiscovery of the neutron (1932)Uncharged particle in nucleusExplains atomic masses and isotopesWhat holds nucleus together?
7 Strong nuclear force (1934) New force >> electromagneticIndependent of electric charge (p+, n)Extremely short rangeQuantum theoryNew particle associated with forceActs on protons and neutronsHideki YukawaYukawa pion π-, π0, π+Discovered 1947 (cosmic rays)
8 Weak nuclear force (1934) Radioactive decay of nucleus Changes number of protons in nucNeutrons changing to protons?Beta decay of the neutronn → p+ + e- + νNew particle: neutrinoDiscovered 1956Fermi’s theory of the weak forceFour interacting particlesEnrico Fermi
9 Four forces of nature (1930s) Force of gravityLong rangeHolds cosmos togetherElectromagnetic forceElectricity + magnetismHolds atoms togetherStrong nuclear forceHolds nucleus togetherWeak nuclear forceResponsible for radioactivity (Fermi)The atom
11 Walton: accelerator physics Cockcroft and Walton: linear acceleratorProtons used to split the nucleus (1932)1H1 + 3Li6.9 → 2He4 + 2He4Verified mass-energy (E= mc2)New way of creating particles?Cavendish lab, CambridgeNobel prize (1956)11
12 High-energy physics Accelerate charged particles to high velocity High voltageCollisionsHigh energy densityNew particles ; strange particlesNot ‘inside’ original particlesE = mc2m = E/c2
14 Anti-particles Dirac equation for the electron Twin solutions Negative energy values?Particles of opposite charge (1928)Anti-electrons (detected 1932)Anti-particles for all particlesEnergy creates matter and anti-matterWhy is the universe made of matter?Paul A.M. DiracE= mc2
15 New model: quarks (1964) Prediction of - Too many particles Protons not fundamentalMade up of smaller particlesNew fundamental particlesQuarks (fractional charge)Hadrons: particles containing quarksBaryons (3 quarks) mesons (2 quarks)Prediction of -Gell-Mann, Zweig
16 Finding quarks Stanford/MIT 1969 Scattering experiments (similar to RBS)Three centres of mass inside protonStrong force = inter-quark force!Defining property = colourTracks not observed in collisionsQuark confinementThe energy required to produce a separation far exceeds the pair production energy of a quark-antiquark pair
17 Six quarks (1970s –1990s) 30 years experiments Six different quarks (u,d,s,c,b,t)Six corresponding leptons(e, μ, τ, υe, υμ, υτ)Gen I: all of ordinary matterGen II, III redundant?New periodic table
18 Bosons and the Standard Model Bosons: particles associated with forcesSatyendra Nath BoseElectromagnetic force mediated by photonsStrong force mediated by gluonsWeak force mediated by W and Z bosonsProblems constructing theory of weak forceEm + w: single interaction above 100 GeVQuantum field causes symmetry breakingSeparates em, weak interactionsEndows W, Z bosons with massCalled the Higgs field
19 The Standard Model (1970-90s) Strong force = quark force (QCD)EM + weak force = electroweak forceHiggs field causes e-w symmetry breakingGives particle massesMatter particles: fermions (1/2 integer spin)‘Force’ particles: bosons (integer spin)Experimental testsTop, bottom , charm, strange quarksLeptonsW+-,Z0 bosonsHiggs boson outstanding
20 The Higgs field Electro-weak symmetry breaking Peter Higgs Mediated by scalar fieldHiggs fieldGenerates mass for W, Z bosonsW and Z bosons (CERN, 1983)Kibble, Guralnik, Hagen, Englert, BroutGenerates mass for all massive particlesAssociated particle : scalar bosonHiggs bosonParticle masses not specified
21 The Higgs field Particles acquire mass by interaction with the field Some particles don’t interact (massless)Photons travel at the speed of lightHeaviest particles interact mostTop quarksSelf-interaction = Higgs bosonMass not specified by SM
22 II The Large Hadron Collider Particle accelerator (8TeV)High-energy collisions (1012/s)Huge energy densityCreate new particlesm= E/c2Detect particle decaysFour particle detectorsE = mc2
23 How Two proton beams E = (4 + 4) TeV v = speed of light 1012 collisions/secUltra high vacuumLow temp: 1.6 KSuperconducting magnetsLEP tunnel: 27 kmLuminosity: 5.8 fb-1
24 Around the ring at the LHC Nine acceleratorsCumulative accelerationVelocity increase?K.E = 1/2mv2Mass increase x1000
27 III A Higgs at the LHC? Search for excess events Mass not specified? Close windows of possibilityGeV (1999)Set by mass of top quark, Z bosonSearch…running out of space!
28 Higgs production in LHC collisions 1 in a billion collisions
29 Detect Higgs by decay products Most particles interact with HiggsVariety of decay channelsMassive particles more likelyDifficult to detect from backgroundNeedle in a haystackNeedle in haystack of needlesHigh luminosity requiredRef: hep-ph/29
30 Analysis: GRID Huge number of collisions Data analysis World Wide Web (1992)Platform for sharing dataGRID (2012)Distributed computingWorld-wide networkHuge increase in computing power
31 Higgs search at LHC (2011)Excess events at 125 GeV in ATLAS and CMS detectorsHigher luminosity required 4.8 fb-1
32 April-July 2012: 8 TeV, 5.8 fb-1 Measure decay products of Z bosons Measure energy of photons emitted
36 Results summary Higgs boson? New particle Mass 126 +/- 0.5 GeV Zero chargeInteger spin (zero?)Scalar boson6 sigma signal (August, 2012)Higgs boson?
37 IV Next at the LHC Characterization of new boson Branching ratios, spinDeviations from theory?SupersymmetryNumerous Higgs?Other supersymmetric particlesImplications for unificationCosmologyDark matter particles?Dark energy?Higher dimensions?
38 Supersymmetry Success of electro-weak unification Extend program to all interactions?Theory of everythingNo-go theorems (1960s)Relation between bosons and fermions?Supersymmetry (1970s)New families of particlesBroken symmetry – particles not seenHeavy particles (LHC?)
40 Cosmology at the LHC Snapshot of early universe Highest energy density since BBDark matter particles?Neutralinos (SUSY)Dark energy ?Scalar fieldHigher dimensions?Kaluza Klein particlesString theory?T = 1019 K, t = 1x10-12 s, V = football
41 Summary (2012) New particle detected at LHC Mass 126 +/- 0.5 GeV Zero charge, integer spin (zero?)Consistent with Higgs bosonConfirmation of e-w unificationParticle theory right so farEn route to a theory of everything ?Slides on Antimatter
42 Epilogue: CERN and Ireland European Centre for Particle ResearchWorld leader20 member states10 associate states80 nations, 500 univ.Ireland not a memberNo particle physics in Ireland…..almost