Introduction to CERN David Barney, CERN

Introduction to CERN ActivitiesIntroduction to CERN Activities

•Intro to particle physics•Accelerators – the LHC•Detectors - CMS

Introduction to CERN David Barney, CERN

From atoms to quarks IFrom atoms to quarks I

Introduction to CERN David Barney, CERN

From atoms to quarks IIFrom atoms to quarks II

Hadrons are made of quarks,e.g.

p = uud0 = uds0

b = udb+ = ud = cc

= bb

Baryons

Mesons

Leptons are fundamentale.g.

electronmuonneutrinos

Introduction to CERN David Barney, CERN

The structure of the ProtonThe structure of the Proton

Proton is not, in fact, simplymade from three quarks (uud)

There are actually 3 “valence”quarks (uud) + a “sea” of gluonsand short-lived quark-antiquarkpairs

Introduction to CERN David Barney, CERN

Matter and Force ParticlesMatter and Force Particles

Gluons (8)

Quarks

MesonsBaryons Nuclei

Graviton ? Bosons (W,Z)

AtomsLightChemistryElectronics

Solar systemGalaxiesBlack holes

Neutron decayBeta radioactivityNeutrino interactionsBurning of the sun

Strong

Photon

Gravitational Weak

The particle drawings are simple artistic representations

Electromagnetic

Tau

Muon

Electron

TauNeutrino

MuonNeutrino

ElectronNeutrino

-1

-1

-1

0

0

0

Bottom

Strange

Down

Top

Charm

Up

2/3

2/3

2/3

-1/3

-1/3

-1/3

each quark: R, B, G 3 colours

QuarksElectric Charge

LeptonsElectric Charge

Introduction to CERN David Barney, CERN

Unanswered questions in Particle Unanswered questions in Particle PhysicsPhysics

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

CERN SiteCERN Site

LHC

CERN Site (Meyrin)CERN Site (Meyrin)

SPS

Introduction to CERN David Barney, CERN

CERN Member StatesCERN Member States

Introduction to CERN David Barney, CERN

CERN UsersCERN Users

Introduction to CERN David Barney, CERN

Beam par t icles

A cceler at ing cavit ies

Defl ect ion magnet s

F ocussing magnet s

Par t icle sour ce

Cir cular acceler at or

wit h colliding beams

Introduction to CERN David Barney, CERN

Types of Particle ColliderTypes of Particle Collider

Electron-Positron Collider (e.g. LEP)

e- e+

Ecollision = Ee- + Ee+ = 2 Ebeam

e.g. in LEP, Ecollision ~ 90 GeV = mZ

i.e. can tune beam energy so thatyou always produce a desired particle!

Electrons are elementary particles, so

Proton-Proton Collider (e.g. LHC)

uu

d

uu

d

Eproton1 = Ed1 + Eu1 + Eu2 + Egluons1

Eproton2 = Ed2 + Eu3 + Eu4 + Egluons2

Collision could be between quarksor gluons, so

0 < Ecollision < (Eproton1 + Eproton2)

i.e. with a single beam energy you can“search” for particles of unknown mass!

Introduction to CERN David Barney, CERN

LHC DetectorsLHC Detectors

B-physicsCP Violation

Heavy IonsQuark-gluon plasma

General-purposeHiggsSUSY??

General-purposeHiggsSUSY

??

Introduction to CERN David Barney, CERN

The two Giants!The two Giants!ATLASA Toroidal LHC ApparatuS

µ

CMSCompact Muon Solenoid

µ

Introduction to CERN David Barney, CERN

Particle Detectors IParticle 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 MeasurementParticle 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 trackerElectronIn CMS

Introduction to CERN David Barney, CERN

Energy Measurement - CalorimetersEnergy 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 detectorsParticle interactions in detectors

Introduction to CERN David Barney, CERN

CMS – Compact Muon SolenoidCMS – Compact Muon Solenoid

Introduction to CERN David Barney, CERN

CMS – Compact Muon SolenoidCMS – Compact Muon Solenoid

Introduction to CERN David Barney, CERN

PuzzlePuzzle

Find 4 straight tracks.

Introduction to CERN David Barney, CERN

AnswerAnswer

Make a “cut” on theTransverse momentumOf the tracks: pT>2 GeV