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

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

3. 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

4. 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

5. 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

6. 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 proton (quarks)
colour
Electromagnetic photon <10-2 atoms
electric
Weak W, Z < radioactivity
hypercharge
Gravity graviton ? 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

7. Unification of fundamental forces
Introduction to CERN
David Barney, CERN

8. 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

9. 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

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

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

12. 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

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

14. CERN Member States
Introduction to CERN
David Barney, CERN

15. CERN Users
Introduction to CERN
David Barney, CERN

16. Particle Collider
Introduction to CERN
David Barney, CERN

17. 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

18. CERN Accelerator Complex
Introduction to CERN
David Barney, CERN

19. 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 + q c - - 1 Z q ~ q
New Particle Production
105 Hz p H g ~ p p p
(Higgs, SUSY, ....) ~ Z q + + m q c ~ - - 2 m c ~ 1
Introduction to CERN
David Barney, CERN

20. 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

21. The two Giants!
Introduction to CERN
David Barney, CERN

22. 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

23. 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

24. 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

25. Particle interactions in detectors
Introduction to CERN
David Barney, CERN

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

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

28. Puzzle
Introduction to CERN
David Barney, CERN

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