introduction to cern activities

Introduction to CERN David Barney, CERN

Introduction to CERN ActivitiesIntroduction to CERN Activities

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


From atoms to quarks IFrom atoms to quarks I


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


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


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


Characteristics of the 4 forcesCharacteristics of the 4 forces

Ratio of electrical to gravitational force between two protons is ~ 1038 !!Can such different forces have the same origin ??

Interaction Exchanged Range Relative Examplesquantum (m) Strength in nature(source ch)

Strong gluon 10-15 1 proton (quarks)colour

Electromagnetic photon <10-2atoms electric

Weak W, Z <10-17 10-5 radioactivityhypercharge

Gravity graviton ? 10-38 solar systemmass

What characterizes a force ? Strength, range and source charge of the field.


Unification of fundamental forcesUnification of fundamental forces

Quantum Gravity

Super Unification

Grand Unification

Electroweak Model

QED

Weak Force

Nuclear Force

Electricity

Magnetism

Maxwell

Short range

Fermi

QCD

Long range

Short range

Terrestrial Gravity

Celestial Gravity

Einstein, NewtonGalilei

Kepler

Long range

?

Universal Gravitation

Electro magnetism

Weak TheoryStandard

model

Theories: STRINGS? RELATIVISTIC/QUANTUM CLASSICAL

SU

SY

?


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 ?


The Standard ModelThe Standard Model

Where is Gravity?

Me ~ 0.5 MeVM ~ 0Mt ~ 175,000 MeV!

M = 0MZ ~ 100,000 MeV

Why ?


Mathematical consistency of the SMMathematical consistency of the SM

WL

WL

WL

ZL

ZL

time

At energies > 1 TeV the probability of scattering of one W boson off of another becomes greater than 1

SM gives nonsense !

WL

WL

ZL

H A popular solution is to introduce a Higgs exchange to cancel bad high energy behaviour


What is wrong with the SM?What is wrong with the SM?

• SM contains too many apparently arbitrary features • SM has an unproven element - not some minor detail but a central element - namely mechanism to generate observed masses of the known particles a popular solution is to invoke the Higgs mechanism • SM gives nonsense at high energies. At centre of mass energies > 1000 GeV the probability of W

LW

L scattering

becomes greater than 1! a popular solution is to introduce a Higgs exchange to cancel the bad high energy behaviour • SM is logically incomplete - does not incorporate gravity - build TOE is superstring theory the TOE ?


Origin of mass and the Higgs Origin of mass and the Higgs mechanismmechanism

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


CERN SiteCERN Site

LHC

CERN Site (Meyrin)CERN Site (Meyrin)

SPS


CERN Member StatesCERN Member States


CERN UsersCERN Users


Particle ColliderParticle Collider

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


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!


CERN Accelerator ComplexCERN Accelerator Complex


Collisions at the Large Hadron ColliderCollisions at the Large Hadron Collider

Bunch Crossing 4x107 Hz

7x1012 eV Beam Energy 1034 cm-2 s-1 Luminosity 2835 Bunches/Beam 1011 Protons/Bunch

7 TeV Proton Proton colliding beams

Proton Collisions 109 Hz

Parton Collisions

New Particle Production 105 Hz (Higgs, SUSY, ....)

p pH

µ+

µ-

µ+

µ-

Z

Zp p

e- e

q

q

q

q

1

-

g~

~

20~

q~

1 0~

7.5 m (25 ns)


LHC DetectorsLHC Detectors

B-physicsCP Violation

Heavy IonsQuark-gluon plasma

General-purposeHiggsSUSY??

General-purposeHiggsSUSY

??


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

µ

CMSCompact Muon Solenoid

µ


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


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


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


Particle interactions in detectorsParticle interactions in detectors


CMS – Compact Muon SolenoidCMS – Compact Muon Solenoid


PuzzlePuzzle

Find 4 straight tracks.


AnswerAnswer

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

introduction to cern activities

Documents

particles fundamental

particles of unknown

origin of mass

particle physicsaccelerators

desired particle

quantum field

elementary particles

highlifetimes of particles