“The Great Question of Life, the Universe and Everything”“The Great Question of Life,

the Universe and Everything”

Dr. Véronique Boisvert

Royal Holloway, University of London

A lot of the following pictures come from: www.particleadventure.org

Every day ParticlesEvery day Particles

All of biology, chemistry and 95% of physics make use of 4 particles!

Quarks and LeptonsQuarks and Leptons

Mesons: quark + anti-quark: K0 (sd)

Baryons: 3 quarks: p (uud), n(udd), (usd)

How do Particles interact?How do Particles interact?

• 4 fundamental forces

Action at a distance?Action at a distance?

• Exchange of particles!

Gravity?Gravity?

• Force carrier: graviton?• Very long range• Einstein: property of space-time (General Relativity)

• Been trying to unify with quantum mechanics for 75 years!

Unification Unification

• Weak is not so weak: at 10-18m same strength as electromagnetic!

The Standard ModelThe Standard Model

• Very successful model• No discrepancy so far

• But incomplete!• Neutrino mass!• Why 3 generations?• Why Universe is mostly

matter?• Where do the mass of

particles come from?

The Higgs bosonThe Higgs boson

• Electroweak symmetry is exact only if W,Z are massless: so symmetry broken?

• Not quite: the physical vacuum is not unique• Higgs field might be responsible?

Re(Higgs Field)

Im(Higgs Field)

Potential Energy

The Higgs field and bosonThe Higgs field and boson

Higgs field mechanism

Higgs boson

CERN © and inspired by David J. Miller at UCL

The Cosmic Pie

How do we know what we know? Method 1

How do we know what we know? Method 1

De Broglie : Wave-Particle Duality

€

λ= h / p

nucleus

nucleon

quark

10-14 m 10-16 m 10-18 m

quark

?

wavelength momentum

Planck’s constant

Einstein : Mass Energy Equivalence

€

E = mc 2

energy speed-of-light

mass

How do we know what we know? Method 2

How do we know what we know? Method 2

• We can take the subtle approach: make precision measurements

• Example: b quark turns into an s quark• Only happens if there is a “loop” of

virtual quarks• Since we don’t observe these quarks

in the loop, all quarks will participate• Rate of this reaction proportional to

mass of the quarks• First (indirect) detection of the top quark!

AcceleratorsAccelerators

• Step 1: Get the particles you want to accelerate

• Step 2: Accelerate them using electromagnetic radiation

AcceleratorsAccelerators

• Linac: can reach 25MeV/m • Would need 40km to

reach 1000GeV!

SLAC

• Cyclotron: uses circular path!• p=0.3Bq• Bq/m• If particle reaches relativistic v: gets out

of phase!

AcceleratorsAccelerators

• Synchrotrons: keep varying the magnetic field and synchronize the accelerating cavities

Tevatron at FNAL (method 1)

PEP-II at SLAC Center of mass E = 10.58GeV

(method 2)

The Large Hadron ColliderThe Large Hadron Collider

World’s biggest ever scientific undertaking!

15 years to build : data taking starts this year!

The Large Hadron Collider

• 9300 magnets along the ring• Magnets are precooled to -193.2°C (80 K)

using 10 080 tons of liquid nitrogen• before they are filled with nearly 60 tons

of liquid helium to bring them down to -271.3°C (1.9 K)• Cooler than outer space!

• Radiofrequency cavities:• Accelerate the beam of particles

• Vacuum chambers:• Beam pipe under high vacuum to

prevent collisions with air

• Magnets:• Dipole, quadrupoles, etc.

Center of Mass EnergyCenter of Mass Energy

• 7 TeV proton beam colliding with 7 TeV proton beam = 14 TeV available

• TeV = Tera (1012) electronVolt• 1 electronvolt

• E of 1 electron under a potential difference of 1 Volt• E=qV = (1.602x10-19C)(1V) = 1.602x10-19J

• So 14TeV = 2.23 x 10-6 J (1J: E released when an apple falls 1m)

• Trick is: we use the energy to make particles!• E=mc2 in SI units: 2.23x10-6J = m (3x108m/s)2

• m = 2.48x10-23 Kg • m of p: 1.67x10-27Kg (938 MeV), m of heaviest particle (top quark):

3.06x10-25Kg (172 GeV)• So 80 times heavier than currently heaviest particle!

Lepton vs hadron collidersLepton vs hadron colliders

• Why 14TeV?• Since colliding protons

with protons• Not all the proton E

available in the quark or gluon collision

• With 14 TeV about 1-2 TeV will be available for new particles

proton proton

Example of an eventExample of an event

Black hole simulated event

Weight: 7000 t 44 m

22 m

~108 channels (~2 MB/event)

DetectorsDetectors

• Inelastic collisions with the atomic electrons of the material

• ionization

energy loss (Bethe-Bloch equation)

•Elastic collisions with the nuclei of the material

• displacement of the atom

• change of trajectory

• also Bremstrahlung

• deflection of e+/e- because of electric field from nucleus acceleration change radiation

Particles Interactions with matter

Particles Interactions with matter

Charged Particles (p+, ±, …)

e+/e- ()

• Low Energy:

• elastic and inelastic collision, capture, fission

• Higher Energy (relevant to HEP):

• high energy hadron shower production

Photons (X, , …)

Neutral Particles (n, 0, KS/L,…)

ATLAS detectorsATLAS detectors

DetectorsDetectors

• ATLAS Silicon Pixel Detector• Closest to the beam pipe• Charged tracks ionize the silicon• Each pixel is 50 x 300 • 140million of them!

• ATLAS Electromagnetic Calorimeter•Measures energy of photons and electrons•Layers of Lead: incoming particles make showers of secondary particles•Sensing material: liquid argon gets ionized by shower of particle•Amount of charge collected proportional to E of incoming particle

DetectorsDetectors

Animation of ATLAS installation

Webcam in ATLAS cavern

DetectorsDetectors

• When the LHC turns on there will be a rate of 40 million events per second!

• Most of these are uninteresting events, we want to keep about 100 events per second• The Trigger:

• Use signatures of interesting events to decide whether to keep the event or not

• Use both hardware and software algorithms

40 MHz

75 kHz

~1 kHz

~100 Hz

~1 sec

~10 ms

2.5 s

Rate Latency

Reconstructing the eventsReconstructing the events

• Even interesting events are very busy:• ~ 100 particles per event• Most of them are not

related with the interesting part of the event

• Need sophisticated software

• to reconstruct the event• to extract the physics

out of the event

The Computing ChallengeThe Computing Challenge

10 million Gbytes of data per year100,000 PCs needed to analyse it!

How would you do an analysis?How would you do an analysis?

• Step 1: Pick a topic!• Which mystery do you want to elucidate?• Is the time scale of the experiment

appropriate?• How “crowded” is this topic?

How would you do an analysis?How would you do an analysis?

• Step 2: Design the selection of the events of interest• Use Monte Carlo simulations• The selection will be done by

computing algorithms (C++)• You need to optimize:

• Want as many signal events as possible (reduce statistical uncertainties!)

• Want as low backgrounds as possible (reduce systematic uncertainties!)

How would you do an analysis?How would you do an analysis?

• Step 3: run on the data• “counting” experiment:

• count number of signal events• Count signal events that look like this vs look like that

• “fitting” experiment: fit a distribution to get number of events or a parameter: a mass for example

€

MH = mγγ = 2Eγ 1Eγ 2

(1− cosθγ 1γ 2)

Now you try it: http://lppp.lancs.ac.uk/higgs/index.html

What will we find???What will we find???Supersymmetry? Extra Spatial Dimensions ?

Mini black holes?

?

The unexpected ?

ATLAS the CollaborationATLAS the Collaboration

• Make use of virtual tools to communicate• WWW was invented at

CERN!

• 37 countries• 1850 physicists• Many languages!

Particle Physics @ RHULParticle Physics @ RHUL

• Very strong and established group• Was involved on ALEPH• Ramping down on BaBar

• Looking toward the future• Well established group on ATLAS

• Built part of the Data Acquisition System• Designed and implemented significant parts of the High Level

Trigger• Currently: 4 faculty, 6 RA/Engineer, 8 PhD• Covering all interesting physics: Higgs, SUSY, Exotics, Top

quark

• Linear Collider Work : Part of John Adams Institute• 4 faculty, 4 RA, 4 PhD• Beam monitoring as well as detector R&D

ConclusionConclusion

Exciting times ahead!!!