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 Leptons are fundamental e.g. electron muon neutrinos Hadrons are made of quarks, e.g. p = uud L0 = uds L0b = udb p+ = ud Y = cc U = bb Baryons Mesons 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 Neutrino -1 Bottom Strange Down Top Charm Up 2/3 -1/3 each quark: R , B G 3 colours Electric Charge Leptons Introduction to CERN David Barney, CERN

Characteristics of the 4 forces What characterizes a force ? Strength, range and source charge of the field. Interaction Exchanged Range Relative Examples quantum (m) Strength in nature (source ch) Strong gluon 10-15 1 proton (quarks) colour Electromagnetic photon <10-2 atoms electric Weak W, Z <10-17 10-5 radioactivity hypercharge Gravity graviton ? 10-38 solar system mass Ratio of electrical to gravitational force between two protons is ~ 1038 !! Can such different forces have the same origin ?? 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 Me ~ 0.5 MeV Mn ~ 0 Mt ~ 175,000 MeV! Mg = 0 MZ ~ 100,000 MeV Why ? Where is Gravity? 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 SPS CERN Site (Meyrin) 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) Proton-Proton Collider (e.g. LHC) u d u d e- e+ Electrons are elementary particles, so Eproton1 = Ed1 + Eu1 + Eu2 + Egluons1 Eproton2 = Ed2 + Eu3 + Eu4 + Egluons2 Collision could be between quarks or gluons, so 0 < Ecollision < (Eproton1 + Eproton2) Ecollision = Ee- + Ee+ = 2 Ebeam e.g. in LEP, Ecollision ~ 90 GeV = mZ i.e. can tune beam energy so that you always produce a desired particle! 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 7x1012 eV Beam Energy 1034 cm-2 s-1 Luminosity 2835 Bunches/Beam 1011 Protons/Bunch 7.5 m (25 ns) 7 TeV Proton Proton colliding beams Bunch Crossing 4x107 Hz Proton Collisions 109 Hz n e - e Parton Collisions µ + q c - µ - 1 Z q ~ q New Particle Production 105 Hz p H g ~ p p p (Higgs, SUSY, ....) ~ Z q + µ + m q c ~ - µ - 2 m c ~ 1 Introduction to CERN David Barney, CERN

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

The two Giants! Introduction to CERN David Barney, CERN

Cannot directly “see” the collisions/decays 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: pT>2 GeV Introduction to CERN David Barney, CERN