SFU

Quest for the Higgs Bosonis our understanding of the universe about to change ?

Organized by SFUs Physics Department and VP Research Officeon behalf of the ATLAS Group Bernd StelzerSimon Fraser University

SFU ATLAS GroupSFUBernd Stelzer 2

Faculty Dugan O'Neil, Bernd Stelzer and Mike Vetterli, postdoctoral fellows Jiri Kvita, Michele Petteni and Andres Tanasijczuk, and graduate students Michelle Boudreau, Noel Dawe, Jennifer Godfrey, Jamie Horton, David Shinkaruk, Michel Trottier-McDonald, and Koos van Nieuwkoop.

OutlineSFUBernd Stelzer 3Particle Physics and the Fundamental Building Blocks of Nature

The Large Hadron Collider

The ATLAS and CMS experiments

Particle Physics Successes and Mysteries

What is the Origin of Mass?

Latest results in the search for the Higgs Boson

Conclusions

News Stories What are they about?SFUBernd Stelzer 4

Last December, media was covering stories about hints for elusive Higgs boson at the Large Hadron ColliderOn July 4th, media was headlining stories about the Higgs boson What is this all about?News Stories What are they about?SFUBernd Stelzer 5

Mike Vetterli

Dugan ONeilKnowledge gained in the last CenturySFUBernd Stelzer 6~0110,000~1910110~19401100,000~1970

atomnucleusLHC110?10-13 cm10-8 cm10-12 cm10-17 cmStandard Model SFUBernd Stelzer 77

Weak

The Large Hadron Collider (LHC)SFUBernd Stelzer 8

ATLAS

ppLHCLake GenevaMont BlancThe Large Hadron Collider (LHC)SFUBernd Stelzer 9

LHC protons go fast: 99.999999% of the speed of light make a full turn 11254 times per secondLarge Hadron ColliderSFUBernd Stelzer 10

1eV = 1.6 x 10-19 J

For the LHCMore facts:CERNs LHC pp collider at 8 (7) TeV (design 14 TeV increase in 2014)Beams circulate ~10h travelling more than 10 billion km (to Neptune and back!)

Large Hadron ColliderSFUBernd Stelzer 11Circumference: 26 659 m9593 superconducting magnetsTotal of 1232 Dipole magnets:15m long, 35 tons, 8.4 TOperated at 1.9K (colder than outer space)

First Collision EventsSFUBernd Stelzer 12

Producing Massive ParticlesSFUBernd Stelzer 13Creating massive fundamental particlesEnergyparticle beam

energyparticle beam

energyEaEbmxppmXmX

R. Goscinny, U. UderzoAsterix and the Big Fight

What is a proton?SFUBernd Stelzer 14

Can create particle X with mass mX < 2Ebeam GeV/c2

Collisions at ATLASSFUBernd Stelzer 15

How to Discover new ParticlesSFUBernd Stelzer 16

The mass mZ of the parent particle can be determined from the kinematics of its decay products. E.g. for Z-> we can make use of:

From relativity:

Relativistic kinematicsUnits and NumbersSFUBernd Stelzer 17Mass is measured in electronVolt / c2 where: c = speed of light:

1 eV/c2 = 1.8 x 10-36 kg

melectron = 0.5 MeV/c2 = 1 x10-30 kgmsun = 2 x 1030 kgWe will mostly use the unit GeV=Giga electronVoltDiscover new Particles

SFUBernd Stelzer 18

A history ofresonance discoveriesJ/ DiscoveryNobel Prize 1976 Z Boson DiscoveryNobel Prize 1983Y Discovery 1977Neutral resonances havea long history of discovery+1Particle IdentificationSFUBernd Stelzer 19

Collisions enclosed by layers of different detectors (like an onion):separate particle types measure their energies / momenta

ATLAS and CMS DetectorsSFUBernd Stelzer 20

Weight (tons)Length (m)Height (m)ATLAS7,0004222CMS12,5002115

EiffeltowerEiffeltower100 million electronic channels3000 km of wiresATLAS Tracking DetectorSFUBernd Stelzer 21

CalorimetersSFUBernd Stelzer 22Measure energy and position of electrically charged and neutral particles Electrons and photons (electromagnetic calorimeter)Hadrons: protons, pions, etc, (hadronic calorimeter)e or

TRIUMF: assembly of one of the Canadian components, completed in 2004Muon SystemSFUBernd Stelzer 23

ATLAS CollaborationSFUBernd Stelzer 243000 Physicists from 38 countries and 174 institutes (150 Canadians from 10 institutes )

The Standard ModelSFUBernd Stelzer 25its the most precise theory there is!Feynman diagrams allow us to calculate any processes with a production rate prediction better than 1-10%Tested and verified in many experiments

What we try to find at the LHCWhat is the Origin of mass?Find the Higgs boson or rule it out.Nature of Dark Matter? Weakly Interacting massive particle must have mass ~0.1-1 TeV to reproduce observed DM density.Grand Unification: Do all forces become one at high energies? Higher gauge groups in GUT inspired models give rise to new particles possibly at the TerascaleWhere did the anti-matter go?broken symmetries of nature in quark flavor and neutrino sectorExplore the unknownsurprises can happen at any timeSFUBernd Stelzer 26

Physics Beyond the Standard ModelSFUBernd Stelzer 27

Many theoretical modelsfor physics Beyond the Standard ModelWhy is the Higgs called the God Particle?SFUBernd Stelzer 28

What is Mass?SFUBernd Stelzer 29Newton, definition #1 of Principia:

the quantity of matter is the measure of the same, arising from its density and its bulk conjointly. I think it means: (m = V)

Merriam-Webster dictionary:

the property of a body that is a measure of its inertia and that is commonly taken as a measure of the amount of material it contains and causes it to have weight in a gravitational field

Generation of Mass in the Standard ModelSFUBernd Stelzer 30According to the Standard Model of particle physics, particles acquired mass during a phase transition when the Universe was ~10-12 seconds old and cooling rapidlyDuring this phase transition, a scalar field (the Higgs field) turns onTemperature (energy) of universe at transition: ~few 100 GeV

The Higgs MechanismSFUBernd Stelzer 31

1964The Higgs MechanismSFUBernd Stelzer 32

The Higgs MechanismSFUBernd Stelzer 33

Higgs field acts as background field (e.g. like a fluid) Heaviest particles interact most strongly with Higgs fieldField slows particles down gives them massWhy do particles have mass?

The Higgs MechanismSFUBernd Stelzer 34

D. Miller / UCLParty:Guests are evenly spreadArrival of celebrity:Guests cluster near celebrity Guests act like Higgs field slowing celebrity down Celebrity moves slower acquires mass

Higgs Field and Higgs Boson particleSFUBernd Stelzer 35In particle physics fields are associated with particles, e.g.electric field photonstrong interaction field gluonIn initial paper Peter Higgs did not identify field with particlehe added that a measurable consequence is the existence of a new bosons (particle) only after journals peer reviewSearching for the HiggsSFUBernd Stelzer 36

Complementary approach taken: Look for Higgs in quantum effects

Need to measure mass of W boson super precisely

Sounds good, but how do we know it's true?

Excite the Higgs field make Higgs particles !!!

Need to collide particles with enough energy to create the Higgs boson: E=mc2

W Boson Mass Precision ConstraintsSFUBernd Stelzer 37

Derive W mass from precisely measured electroweak measurements (Large Electron Positron Collider at CERN, Tevatron at Fermilab)Radiative corrections dominated by top quark and Higgs quantum loops allows constraint on Higgs mass

MHiggs=94+25-22 GeV

The Large Hadron Collider (LHC)SFUBernd Stelzer 38

ATLAS

ppLHCLake GenevaMont BlancSFUBernd Stelzer 392012 Data Taking

ATLAS Control Room

94% good quality data

Delivered luminosity L= 5.6+6.6 fb-1Corresponds to 8x1020 proton-proton interactionsNumber of events = Luminosity x cross sectionCorresponds to ~170 Higgs bosons (in diphoton decay)But need to find them above all the background!Data included in results that were taken less than 2 weeks before!

2012:6.6 fb-1 at 8 TeV20115.6 fb-1 at 7 TeV20100.05 fb-1 at 7 TeVGrid ComputingSFUBernd Stelzer 40

260 sites >140,000 CPU cores >25 PB disk 39 PB tape

100 kIn Canada: Tier-1 center: TRIUMF/SFUTier-2 center: SFU, UVic, Alberta Toronto, McGillSFUBernd Stelzer 41Measuring the Standard ModelInner error: statisticalOuter error: total

Important on their own and as foundation for Higgs searchesMost of these processes are backgrounds to HiggsReconstruction and measurement of challenging processes are good training for Higgs final statesHiggsSFUBernd Stelzer 42Standard Model Higgs Searches at the LHC

Most sensitive channels 120