Introduction to CERN David Barney, CERN Introduction to CERN Activities Intro to particle physics Accelerators – the LHC Detectors - CMS

Introduction to CERN David Barney, CERN From atoms to quarks I

Introduction to CERN David Barney, CERN From atoms to quarks II Hadrons are made of quarks, e.g. p = uud  0 = uds  0 b = udb  + = ud  = cc  = bb Baryons Mesons Leptons are fundamental e.g. electron muon neutrinos

Introduction to CERN David Barney, CERN The structure of the Proton Proton is not, in fact, simply made from three quarks (uud) There are actually 3 “valence” quarks (uud) + a “sea” of gluons and short-lived quark-antiquark pairs

Introduction to CERN David Barney, CERN Matter and Force Particles Gluons (8) Quarks Mesons Baryons Nuclei Graviton ? Bosons (W,Z) Atoms Light Chemistry Electronics Solar system Galaxies Black holes Neutron decay Beta radioactivity Neutrino interactions Burning of the sun Strong Photon Gravitational Weak The particle drawings are simple artistic representations Electromagnetic Tau Muon Electron Tau Neutrino Muon Neutrino Electron Neutrino Bottom Strange Down Top Charm Up 2/3 -1/3 each quark: R, B, G 3 colours Quarks Electric Charge Leptons Electric Charge

Introduction to CERN David Barney, CERN Characteristics of the 4 forces Ratio of electrical to gravitational force between two protons is ~ !! Can such different forces have the same origin ?? Interaction Exchanged Range Relative Examples quantum(m)Strengthin nature (source ch) Stronggluon proton (quarks) colour Electromagneticphoton<10 -2 atoms electric WeakW, Z< radioactivity hypercharge Gravitygraviton ? solar system mass What characterizes a force ? Strength, range and source charge of the field.

Introduction to CERN David Barney, CERN Unification of fundamental forces

Introduction to CERN David Barney, CERN Unanswered questions in Particle Physics a. Can gravity be included in a theory with the other three interactions ? b. What is the origin of mass?  LHC c. How many space-time dimensions do we live in ? d. Are the particles fundamental or do they possess structure ? e. Why is the charge on the electron equal and opposite to that on the proton? f. Why are there three generations of quark and lepton ? g. Why is there overwhelmingly more matter than anti-matter in the Universe ? h. Are protons unstable ? i. What is the nature of the dark matter that pervades our galaxy ? j. Are there new states of matter at exceedingly high density and temperature? k. Do the neutrinos have mass, and if so why are they so light ?

Introduction to CERN David Barney, CERN The Standard Model Where is Gravity? M e ~ 0.5 MeV M ~ 0 M t ~ 175,000 MeV! M  = 0 M Z ~ 100,000 MeV Why ?

Introduction to CERN David Barney, CERN Mathematical consistency of the SM

Introduction to CERN David Barney, CERN What is wrong with the SM?

Introduction to CERN David Barney, CERN Origin of mass and the Higgs mechanism Simplest theory – all particles are massless !! A field pervades the universe Particles interacting with this field acquire mass – stronger the interaction larger the mass The field is a quantum field – the quantum is the Higgs boson Finding the Higgs establishes the presence of the field

Introduction to CERN David Barney, CERN CERN Site LHC CERN Site (Meyrin) SPS

Introduction to CERN David Barney, CERN CERN Member States

Introduction to CERN David Barney, CERN CERN Users

Introduction to CERN David Barney, CERN Particle Collider

Introduction to CERN David Barney, CERN Types of Particle Collider Electron-Positron Collider (e.g. LEP) e-e- e+e+ E collision = E e- + E e+ = 2 E beam e.g. in LEP, E collision ~ 90 GeV = m Z i.e. can tune beam energy so that you always produce a desired particle! Electrons are elementary particles, so Proton-Proton Collider (e.g. LHC) u u d u u d E proton1 = E d1 + E u1 + E u2 + E gluons1 E proton2 = E d2 + E u3 + E u4 + E gluons2 Collision could be between quarks or gluons, so 0 < E collision < (E proton1 + E proton2 ) i.e. with a single beam energy you can “search” for particles of unknown mass!

Introduction to CERN David Barney, CERN CERN Accelerator Complex

Introduction to CERN David Barney, CERN Collisions at the Large Hadron Collider Bunch Crossing 4x10 7 Hz 7x10 12 eV Beam Energy cm -2 s -1 Luminosity 2835Bunches/Beam Protons/Bunch 7 TeV Proton colliding beams Proton Collisions 10 9 Hz Parton Collisions New Particle Production 10 5 Hz (Higgs, SUSY,....) p p H µ + µ - µ + µ - Z Z pp e - e     q q q q  1 - g ~ ~  2 0 ~ q ~  1 0 ~ 7.5 m (25 ns)

Introduction to CERN David Barney, CERN LHC Detectors B-physics CP Violation Heavy Ions Quark-gluon plasma General-purpose Higgs SUSY ?? General-purpose Higgs SUSY ??

Introduction to CERN David Barney, CERN The two Giants!

Introduction to CERN David Barney, CERN Particle Detectors I Cannot directly “see” the collisions/decays –Interaction rate is too high –Lifetimes of particles of interest are too small Even moving at the speed of light, some particles (e.g. Higgs) may only travel a few mm (or less) Must infer what happened by observing long-lived particles –Need to identify the visible long-lived particles Measure their momenta Energy (speed) –Infer the presence of neutrinos and other invisible particles Conservation laws – measure missing energy

Introduction to CERN David Barney, CERN Particle Momentum Measurement Electrically charged particles moving in a magnetic field curve Radius of curvature is related to the particle momentum –R = p/0.3B Should not disturb the passage of the particles Low-mass detectors sensitive to the passage of charged particles Many layers – join the dots! E.g. CMS silicon tracker Electron In CMS

Introduction to CERN David Barney, CERN Energy Measurement - Calorimeters Idea is to “stop” the particles and measure energy deposit Particles stop via energy loss processes that produce a “shower” of many charged and neutral particles – pair-production, bremstrahlung etc. Detector can be to measure either hadrons or electrons/photons Two main types of calorimeter: –Homogeneous: shower medium is also used to produce the “signal” that is measured – e.g. CMS electromagnetic calorimeter –Sampling: the shower develops in one medium, whilst another is used to produce a signal proportional to the incident particle energy – e.g. CMS Hadron Calorimeter

Introduction to CERN David Barney, CERN Particle interactions in detectors

Introduction to CERN David Barney, CERN CMS – Compact Muon Solenoid

Introduction to CERN David Barney, CERN CMS – Compact Muon Solenoid

Introduction to CERN David Barney, CERN Puzzle

Introduction to CERN David Barney, CERN Answer Make a “cut” on the Transverse momentum Of the tracks: p T >2 GeV