why is there mass in our universe ?

08/06/2008AZEDDINE KASMI QuarkNet talk 1

Why is there mass in our universe ? Azeddine Kasmi*

*Lightner-Sams Fellow Physics Department

Southern Methodist University


Some History of Physics.

Particle Physics and the Standard Model.

Coffee Break

The Large Hadron Collider (LHC).

Potential discoveries using the ATLAS detector.


Early Elementary particles pioneers • What is the world made of ?

• and what holds it together ?

The Greek philosopherDemocritus (460 BC – 370 BC) introduced the notion of the atom.

In ancient times, people tried the combination of 4 components: Air, Water, fire, Earth


Classical Physics and Relativity

Gravitation is a natural phenomenon.

allows objects with mass attract each other.

Keeps planets in orbits

Gravity acts immediately

Speed of light is the speed limit

Light does not travel instantly.

James Clerk Maxwell

(1866-1870)

And God said

...and there was light.

Isaac Newton (1643-1727)


Classical Physics and Relativity

3D of space and 1D of time as bound together in a single fabric of space time.

This fabric of space-time is stretched by heavy object.

Curving of that space-time is what we feel as gravity.

Earth stays in orbit because it follows the curvature in the space-time caused by the sun presence.

If Sun

disappears Gravitational disturbance

forms a wave

No change in orbit until the wave reaches

Earth

Mass–Energy Equivalence

Albert Einstein (1915)


Quantum Mechanics 1920’s

W. Heisenberg ( in 1932)

Quantum mechanics :

the study of mechanical systems whose dimensions are close to or below the atomic scale.

Explains why Classical Mechanics failed to explain

• radiation by heated bodies

• stable atoms

•Heisenberg uncertainty principle

It’s impossible to measure simultaneously the position and momentum of a particle. p

xIn QM all what we can do is find the probability of finding a particle in a given state.


No speeding tickets in the quantum world !

The cop says:

Do you have any idea how fast you were going back there ?

Driver answers:

No

Cop:

Crap ! Me neither


Special relativity + Quantum Mechanics = Antimatter

Paul A.M. Dirac (1928)

... to blow up the Vatican, an old “enemy of science and CERN”.

... to blow up the Vatican, an old “enemy of science and CERN”.

Detective story about a secret society which ...Detective story about a secret society which ...

... steals 1 g of antimatter from a place called “CERN” ... steals 1 g of antimatter from a place called “CERN”

What made CERN Popular

Every particle has its antiparticlewith same mass but opposite charge

Particle and its antiparticle annihilates

Movie, May 2009


Reductionism

Most of the particles that were taught to be elementary turned out to have constituents Thomson (1897): Electron discovery

SLAC(1968): Quarks discovery

Chadwick(1932): discovers neutron

Rutherford:Nuclear atom (proton)


The forces in natureType of Force

Strength of

Force

Binding Particle.

Occurs in

Strong Nuclear

~1 Gluons

(no mass)

Holds atomic Nucleus together

Electro-Magnetic

~10-3 Photons

(no mass)

Atomic shell

Weak Nuclear

~10-5 Bosons

Zo , W+, W-

Massive

Radioactivity

Gravity ~10-38 Gravitons (?)

Heavy Bodies Exchanged particle transfers momentum from one interacting particle to another.

Think of forces as interaction

Two particles interact by exchanging a messenger particle.


The Standard Model (SM) of particle physics The SM describes

interactions between the elementary particles that make up all matter.

To date, the SM agrees well with experiment.

Last confirmation Top quark discovery (1995 Fermi Lab)

The building blocks of matter are fermions

Force carriers are bosons


The origin of mass ? The Standard Model proposes:

another field not yet observed. indistinguishable from empty

space. This is known as the Higgs field. All space is filled with this field, and

that by interacting with this field, particles acquire their masses.

The Higgs field has at least one new particle associated with it, the Higgs particle (or Higgs boson).

The ATLAS detector at the LHC will be able to detect this particle if it exists. This would be one of the greatest scientific discoveries ever!


The Higgs mechanism !

To understand the Higgs mechanism, imagine that a room full of physicists chatting quietly is like space filled with the Higgs field ...

... a well-known scientist walks in, creating a disturbance as he moves across the room and attracting a cluster of admirers with each step ...

... this increases his resistance to movement, in other words, he acquires mass, just like a particle moving through the Higgs field...

It should be probably a Hollywood star as who cares about a scientist !


Spontaneous Symmetry Breaking

There is symmetry

All directions look the same

The symmetry is broken here

As the birds have chosen one direction


Ferromagnet analogy

•At low temperature, the iron atoms will align themselves

•Despite no direction preferred in interaction between atoms

•Therefore, atoms acquire certain energy.

•i.e. must add heat to break the alignment.

•Lowest energy state of universe

•Non zero Higgs field

•Generates mass for W,Z


Spontaneous symmetry breaking illustrated by the horse and the carrot

1 2

43


The Standard Model relies on the process of spontaneous symmetry breaking to generate mass to the elementary particle.

Without it, the elementary particle would indeed remain massless.

When applied to particle physics, it leads to the production of a scalar particle named the Higgs boson.

Conclusion on Spontaneous Symmetry Breaking

Mexican hat potential


What we know so far in the universe The SM is not a complete theory of

fundamental interactions for the following reasons.

The lack of inclusion of gravity.Incomplete description of why

particles have mass.

We are surrounded by:

Dark Matter

or unseen matter.

Dark Energy

•Tends to increase the expansion rate of the universe.

SM


Evidence of what we do not know yet Evidence for Dark Matter

Rotational speeds of galaxies B. Observed

A. Predicted by Newtonian

dynamics

Rotation curve of a typical spiral galaxy

Multiwavelength X-ray image of SN 1572 or Tycho's Nova, the remnant of a Type Ia supernova. (NASA/CXC/Rutgers/J.Warren &

J.Hughes et al.)

Evidence for Dark Energy

•Supernovae

Redshift tells us how fast it receding

Standard candles (object with extreme consistent brightness e.g. Supernova Type la) are used to measure the distance.

•Expansion of the universe accelerates.

http://en.wikipedia.org/wiki/SN_1572

http://en.wikipedia.org/wiki/Tycho_Brahe


Grand Unification theory GUT

1973: Salam and WeinbergUnification of the electromagnetic and weak interactions.W, Z bosons

1864: J.C.Maxwell Unified

Electricity and Magnetism. Electromagnetism


Coffee Break


To test a theory you need an Accelerator, Detector, and

Cafeteria

LHC PROTONS:

99.9999991 per cent of the speed of light

11000 times per second circling the 27 km ring


General view of the LHC and experiments


The Large Hadron Collider (LHC)

One Higgs per Hour 10-4 Hz


ATLAS collaboration

2100 scientists

37 countries (5 continents)

167 universities and labs

http://atlas.ch

100 747 jets (empty) is weight of ATLAS Detector

0.5 ATLAS is half the size of Notre Dame Cathedral

122 kilometers of superconducting wire in magnets

3000 kilometers of ordinary cable in ATLAS

PEOPLE SIZEPhilippe has a good coffee maker ($1.5)


ATLAS detector vs. Foundren science building

Length 46 mHeight 25 mOverall weight 7000 Tons


General Principle for particle detection

Visible particles are measured by the various subdetectors and identified from their characteristic pattern .


ATLAS: The Technical Challenges ATLAS major components

•The Inner Detector

350000 particles/ mm2 s makes the radiation

hardness a top priority.

Transition Radiation Tracker

•The Calorimeters

•The Muon Spectrometer

•Solenoidal and Toroidal Magnets

•Data acquisition and Couputing

80 M rectangular pixels

Central Selenoid: 5 tons coil contains 9 km of superconducting wire cooled by liquid helium, I = 8000 Amps, B = 2

T

Hundreds of thousands of gas-filled straws at high voltage, each with a wire down its axis

TRT


Electromagnetic Calorimeter (EMC)

The calorimeter consists of thin lead plates (about 1.5 mm thick) separated by sensing devices.

The lead plates are immersed in a bath of liquid argon.

The liquid argon gaps (about 4 mm) between plates are subjected to a large electric field.


How does the EMC work ?

When the electron shower gets into the argon, it makes a trail of electron-ion pairs along its path.

The electric field causes the electrons (from the Argon) to drift to the positive side.

This produces an electric current in an external circuit connected to the calorimeter. When a High energy photons or

electrons traverse the lead, they produce an electron shower.


Muons detections Muons are the only charged particle that can travel through all of the calorimeter material and reach the outer layer.

much less affected by the electric forces of the atomic nuclei that they encounter (200 times more massive than electrons).

Do not produce same kind of electromagnetic shower of electrons.Energy loss via electron-ion pairs along their path. in case of steel or copper, 1 MeV per millimeter of path.

Example a muon of 5 GeV penetrate about 5 meters of steel.

Thus energetic particles seen outside the hadron calorimeter are guaranteed to be muons.

Monitored Drift TubesGas-filled 3 cm tube


Selection of events Trigger System

Level1Trigger decision less than 2s larger than interaction rate of 25 nsOf 40 M bunch crossings per seconds, less than 100000 pass Level-1Level2Analyses in greater detail specific regions of interest identified by Level 1. Less than 1000 events per second pass Level2Level3Less than 100 events per second are left after Level3.

These events are passed on to a data storage system for offline analysis

Interaction rate: ~ 109 events/sCan record ~ 200 events/s (event size 1 MB)


Concorde (15 Km)

Balloon(30 km)

CD stack with1 year LHC data!(~ 20 Km)

LHC will be completed in 2008 and run for the next 10-15 years

Experiments will produce about 15 Millions Gigabytes per year of data (about 20 million CDs!)

LHC data analysis requires a computing power equivalent to around 100000 of today’s fastest PC processors

Requires many cooperating computer centers, as CERN can only provide the 20% of the capacity.

SMU is part of the grid

Mont Blanc (4.8 km)

The Grid


What’s an event ? The occasion of two elementary particles colliding (or a single particle decaying)

Higgs ZZ* 2e + 2 + jet

After some cuts

This is NOT Higgs and yet it repeats every 25 ns ! 40M/s

It’s just a junk

10-9 of that is a Higgs


Data Analysis and statistics

The situation is similar to searching for a needle in a stack of hay

H1

H1

H1

Fortunately, the characteristics of signal (Higgs) event are different from those of a background.


Missing Energy in case of WZ

WZ 3e +

e-

e-e-

No net momentum into reaction

But summing 3e gives net momentum out

Vector Addition

Neutrino momentum would the missing Energy

Conservation of Momentum.

Thus, a huge missing Energy will characterize the background event.So, the missing Energy can be used as a veto


What’s the plan

Understand ZZ, ttbar, (SM)

Higgs searches


Higgs production


Higgs decay to a 4 leptons channel

Z

ZL+

L+

L-

L-

Unfornately, The ATLAS detector is not perfect.

Thus, a substantial leptons identification problems will occur in the 4 leptons channel

@SMU we have a group that looks at events with 3 identified leptons and try to find the 4th leptons somewhere on the Detector to increase the efficiency


Higgs 4leptons and background

The signal (H) will follow a Gaussian distribution and will be seen as a bump.

However, the background will be as flat distribution.

Note that the discovery of ZZ dibosons was made on July 25th 2008 by Fermi Lab. (only 3 events)

The Standard Model has a limit on the Higgs mass up to 1000 GeV

Experiments have ruled out low masses up to 114 GeV.

My focus is on Higgs mass within the range 130 GeV -180 GeV


Higgs in case of a lost electron

H 21e + X

Here the non identified electron was recovered via the jet algorithm


The complete picture of the standard Model

with the Higgs

THANK YOU THE END ! Wanted

why is there mass in our universe ?

Documents

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