Particle + Physics at ATLAS and the Large Hadron Coillder

Particle + Physics at ATLAS and the Large Hadron Coillder Discovering the elementary particles of the Universe Kate Shaw The International Centre for Theoretical Physics

+ Overview Introduction to Particle Physics ATLAS and the LHC The Higgs Boson Discovery What are we going to discover next?

+ Introduction to Particle Physics What do we study in particle physics? Elementary particles in the universe Where particles are thought of as excitations of quantum fields Elementary forces in the universe

+ Introduction to Particle Physics The atom Atom Electron Proton Neutron Quarks

+ The Standard Model of Particle Physics Quarks and Leptons Matter particles Fermions -spin ½ particles Force carriers Mediate the forces Bosons spin integer particles (0, 1, )

+ Introduction to Particle Physics The Standard Model

+ The Standard Model of Particle Physics Elementary forces of nature Strong Force Responsible for holding hadrons (e.g. protons and neutrons) together Gluon (g) is the force carrier Only quarks feel the strong force Electromagnetism Responsible for practically all the phenomena encountered in daily life Photon (l) is the force carrier Occurs between all electrically charged particles (quarks and charged leptons e,µ,τ)

+ The Standard Model of Particle Physics Elementary forces of nature Weak Force Occurs between all matter particles (all quarks & leptons) W +, W - and Z 0 are the force carriers Responsible for radioactive decay of subatomic particles, and initiates hydrogen fusion in stars Gravity Occurs between all matter No explanation for gravity in particle physics! Hypothetical particle that could mediate the force is called the Graviton

+ The Standard Model of Particle Physics Higgs Boson July 2012 the experiments at the LHC finally found our missing part of the Standard Model This particle gives mass to all other fundamental particles Now the Standard Model can be thought as a complete theory

+ The Standard Model of Particle Physics Higgs Boson On the 8 th October 2013 the Nobel Prize for Physics was awarded to Francois Englert and Peter Higgs for their contribution to the development of the theory that predicted the Higgs boson

+ The Standard Model of Particle Physics So, are we all done in particle physics now?

+ Physics Beyond the Standard Model No! Many mysteries remain

+ Physics Beyond the Standard Model Neutrino Oscillations Matter Antimatter Asymmetry Grand Unified Theory Extra Dimensions Supersymmetry Three generations Graviton Mini Black Holes Dark Matter String Theory Dark Energy

+ Discovering the Higgs Boson How do we search for and find any particle? E = mc 2

+ Discovering the Higgs Boson E = mc 2 By colliding particles together at high energies, the energy can be converted into the mass of a new particle

+ Discovering the Higgs Boson

+ Particle Physics The Large Hadron Collider (LHC) is 27km in circumference and 100 m underground. It accelerates beams of Protons (Hadrons) near to the speed of light and collides them at vast energies in the center of particle detectors

+ Discovering the Higgs Boson The LHC has had 2 main runs 2011: proton-proton collisions at 7 TeV ~ 5fb -1 data collected 2012: proton-proton collisions at 8 TeV ~ 21 fb -1 data collected Now shut for upgrade Will run again in 2015 at a centre of mass energy of up to 14 TeV!

+ Discovering the Higgs Boson

+ Particle Physics 46m long, 25m diameter 100 million electronic channels to read-out data. Weighs 7000 tonnes - as much as the Eiffel tower. Approx 3000 km of cables. General purpose detector - designed to be able to discover any new physics at the LHC

+ Discovering the Higgs Boson The ATLAS Detector

+ Discovering the Higgs Boson The ATLAS Detector Muon spectrometer: tracks muons Calorimeters: measures the energy of the particles Inner detetector: tracks the paths of charged particles

+ Discovering the Higgs What is the Higgs? The Higgs was the missing part of the Standard Model. It gives mass to all the other elementary particles.

+ Discovering the Higgs What is the Higgs? Imagine the Higgs as a field of snow... Some particles (like the electron) skate across the top of the snow and barely feel it. We observe these particles as having a very small mass.

+ Discovering the Higgs What is the Higgs? Other particles move through the snow as though they re wearing heavy boots and move very slowly. Particles like this are observed to be very heavy (like the top quark).

+ Discovering the Higgs What is the Higgs?

+ Discovering the Higgs How do we detect the Higgs? Well We can t actually detect the Higgs in our ATLAS detector The Higgs is massive (very big) (126 GeV) and has a very short lifetime Which means as soon as it is created, it decays into other particles

+ Discovering the Higgs How do we detect the Higgs? The Higgs decays into: Higgs to tau-antitau Tau lepton Higgs to two photons photon Higgs Anitau lepton Higgs photon

+ Discovering the Higgs How do we detect the Higgs? The Higgs decays into: and two Z-bosons (each Z decays to two electrons or two muons.

+ Discovering the Higgs How do we detect the Higgs? Mass ~ 126 GeV Tau-antitau Two photons ZZ (which decay to four leptons (ee, mm)

+ Discovering the Higgs Why did it take so long to find the Higgs? 1. It s very rare we only produce one Higgs boson for every 10,000,000 other events at the LHC.

+ Discovering the Higgs Why did it take so long to find the Higgs? 2. The Higgs decays to other particles before we can detect it directly and there are lots of other interactions which look very similar For example, how do you tell the difference between a Higgs boson which has decayed to a tau lepton and an antitau

+ Discovering the Higgs Why did it take so long to find the Higgs? 2. The Higgs decays to other particles before we can detect it directly and there are lots of other interactions which look very similar and a Z-boson which has decayed to a tau and an antitau

+ Discovering the Higgs Answer: When a heavier particle decays, the particles it decays to will have more energy than if they had come from a lighter particle (remember that E = mc 2 ).

+ Discovering the Higgs We know what the distribution should like for the Z-boson interactions

+ Discovering the Higgs and we know how the distribution should look if the Higgs is there too

+ Discovering the Higgs so we look at all the data, work out the mass/energy of every tau pair we can find and then see if it looks like there s only the Z-decays there + + + + + + + + + + + + ++++++

+ Discovering the Higgs or if we can also see something extra (the Higgs?)! + + + + + + + + ++ + + + + +++ +

+ Discovering the Higgs How it looks in reality

+ Discovering the Higgs

+ Discovering the Higgs Boson 2013 Noble Prize for Physics awarded jointly to Higgs and Englert "for the theoretical discovery of a mechanism that contributes to our understanding of the origin of mass of subatomic particles, and which recently was confirmed through the discovery of the predicted fundamental particle, by the ATLAS and CMS experiments at CERN's Large Hadron Collider"

+ Physics Beyond the Standard Model Matter Antimatter Asymmetry The Universe we see seems to be dominantly made from matter (not antimatter) However the Standard Model predicts that they should have been created in equal amounts which would have annihilated each other as the Universe cooled

+ Physics Beyond the Standard Model Dark Energy and Dark Matter Cosmological observations have shown that the Standard Model explains only ~4% of the energy of our Universe!

+ Physics Beyond the Standard Model Dark Energy The rate of expansion of the Universe is much higher than it should be given the amount of matter and energy the Universe we know about Dark energy could be the key

+ Physics Beyond the Standard Model Dark Matter By studying Galaxy motion Cosmologists have estimated there should be ~23% of matter in the Universe that we cant see meaning that it does not interact electromagnetically (give off light) Thus it feels the gravitation force and weak force only (weakly interacting)

+ Physics Beyond the Standard Model Dark Matter We are looking for Dark Matter in lots of underground experiments And hoping to find it at the LHC It could be a Supersymmetric particle!

+ Physics Beyond the Standard Model Supersymmetry Supersymmetry proposes that every fundamental particle, has a supersymmetric partner with the same properties except its SPIN

+ Physics Beyond the Standard Model Extra Dimensions There maybe more than three dimensions in the universe, but these extra dimensions are curled up so tightly that we can t see them normally.

+ Physics Beyond the Standard Model Extra dimensions could mean that string theory is correct and that we can unify the theories of quantum mechanics, relativity and gravity.

+ Physics Beyond the Standard Model We may also be able to create microscopic (quantum) black holes which flash in and out of existence.

+ Finding New Particles Colliding Particles E = mc 2 By using particle accelerators to collide particles together at high energies we can study the elementary particles and forces of our universe

+ The ATLAS Collaboration

+ Our ATLAS Udine ICTP Group

+ THANK YOU!