introduction to cern activities
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Introduction to CERN Activities. Intro to particle physics Accelerators – the LHC Detectors - CMS. From atoms to quarks I. Hadrons are made of quarks, e.g. p = uud L 0 = uds L 0 b = udb p + = ud Y = cc U = bb. Baryons. Mesons. From atoms to quarks II. Leptons are fundamental - PowerPoint PPT PresentationTRANSCRIPT
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
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.
Introduction to CERN David Barney, CERN
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
?
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
The Standard ModelThe Standard Model
Where is Gravity?
Me ~ 0.5 MeVM ~ 0Mt ~ 175,000 MeV!
M = 0MZ ~ 100,000 MeV
Why ?
Introduction to CERN David Barney, CERN
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
Introduction to CERN David Barney, CERN
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 ?
Introduction to CERN David Barney, CERN
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
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
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
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
CERN Accelerator ComplexCERN Accelerator Complex
Introduction to CERN David Barney, CERN
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)
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