Transcript Higgs - SMU Physics

Why is there mass in our universe
?Azeddine Kasmi*
*Lightner-Sams Fellow
Physics Department
Southern Methodist University
AZEDDINE KASMI
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 Some History of Physics.
 Particle Physics and the Standard Model.
Coffee Break
 The Large Hadron Collider (LHC).
 Potential discoveries using the ATLAS detector.
AZEDDINE KASMI
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Early Elementary particles pioneers
• What is the world made of ?
• and what holds it together ?
In ancient times, people tried the
combination of 4 components:
Air, Water, fire, Earth
The Greek philosopher
Democritus (460 BC – 370 BC)
introduced the notion of the atom.
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Classical Physics and Relativity
Gravitation is a natural phenomenon.
 allows objects with mass attract each other.
Keeps planets in orbits
Gravity acts immediately
Isaac Newton (1643-1727)
Speed of light is the speed limit
And God said
Light does not travel instantly.
James Clerk Maxwell
(1866-1870)
...and there was light.
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Classical Physics and Relativity
Mass–Energy Equivalence
 3D of space and 1D of time as bound together in a
single fabric of space time.
Albert Einstein (1915)
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
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Quantum Mechanics 1920’s
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
W. Heisenberg (
in 1932)
•Heisenberg uncertainty principle
It’s impossible to measure simultaneously the
position and momentum of a particle.
In QM all what we can do is find the probability
of finding a particle in a given state.
AZEDDINE KASMI
Dp
Dx
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The cop says:
Do you have any
idea how fast you
were going back
there ?
Driver answers:
No
Cop:
Crap ! Me
neither
No speeding tickets in the quantum world !
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Special relativity + Quantum Mechanics =
Antimatter
What made
CERN
Popular
Paul A.M. Dirac
(1928)
Movie, May 2009
Detective story about a
secret society which ...
Every particle has its antiparticle
with same mass but opposite charge
Particle and its antiparticle annihilates
... steals 1 g of antimatter
from a place called “CERN”
... to blow up the Vatican, an
old “enemy of science and
CERN”.
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Reductionism
SLAC(1968):
Quarks
discovery
Chadwick(1932):
discovers neutron
Most of the particles that
were taught to be elementary
turned out to have
constituents
Rutherford:
Nuclear atom
(proton)
Thomson (1897): Electron discovery
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The forces in nature
Type of
Force
Strong
Nuclear
Strength of
Force
~1
Binding
Particle.
Occurs in
Gluons
Holds atomic
Nucleus together
(no mass)
ElectroMagnetic
~10-3
Weak
Nuclear
~10-5
Photons
Think of forces as interaction
Two particles interact by
exchanging a messenger
particle.
Atomic shell
(no mass)
Bosons
Radioactivity
Zo , W+, WMassive
Gravity
~10-38
Gravitons (?)
Heavy Bodies
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Exchanged particle transfers
momentum from one interacting
particle to another.
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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
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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!
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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 !
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Spontaneous Symmetry Breaking
There is symmetry
All directions look the same
The symmetry is broken here
As the birds have chosen one direction
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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
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Spontaneous symmetry breaking illustrated by the horse and the carrot
1
2
3
4
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Conclusion on Spontaneous Symmetry
Breaking
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.
Mexican hat potential
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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
SM
•Tends to increase the expansion
rate of the universe.
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Evidence of what we do not know yet
Rotation curve of a typical spiral galaxy
Evidence for Dark Matter
B. Observed
Rotational speeds of galaxies
A. Predicted by Newtonian dynamics
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.
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.)
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Grand Unification theory GUT
1864: J.C.Maxwell Unified
Electricity and Magnetism
.
Electromagnetism
1973: Salam and Weinberg
Unification of the electromagnetic
and weak interactions.
W, Z bosons
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Coffee Break
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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
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General view of the LHC and
experiments
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The Large Hadron Collider (LHC)
One Higgs per
Hour 10-4 Hz
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ATLAS collaboration
http://atlas.ch
PEOPLE
2100
scientists
37
countries (5 continents)
167
universities and labs
SIZE
Philippe has a good coffee maker ($1.5)
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
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ATLAS detector vs. Foundren science
building
Length
Height
Overall weight
46 m
25 m
7000 Tons
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General Principle for particle detection
Visible particles are measured by the various subdetectors and
identified from their characteristic pattern .
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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
80 M rectangular
pixels
•The Muon Spectrometer
•Solenoidal and Toroidal Magnets
•Data acquisition and Couputing
TRT
Hundreds of
thousands of
gas-filled
straws at high
voltage, each
with a wire
down its axis
Central Selenoid: 5 tons coil contains 9
km of superconducting wire cooled by
liquid helium, I = 8000 Amps, B = 2 T
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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.
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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.
AZEDDINE KASMI
When a High energy photons or
electrons traverse the lead, they
produce an electron shower.
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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.
Monitored Drift Tubes
Gas-filled 3 cm tube
Thus energetic particles seen outside the hadron
calorimeter are guaranteed to be muons.
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Selection of events
Interaction rate:
Can record
Trigger System
Level1
Trigger decision  less than 2ms
larger than interaction rate of 25 ns
Of 40 M bunch crossings per seconds, less
than 100000 pass Level-1
~ 109 events/s
~ 200 events/s
(event size 1 MB)
Level2
Analyses in greater detail specific regions
of interest identified by Level 1. Less than
1000 events per second pass Level2
Level3
Less than 100 events per second are left
after Level3.
These events are passed on to a data
storage system for offline analysis
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The Grid
Balloon
(30 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!)
CD stack with
1 year LHC data!
(~ 20 Km)
Concorde
(15 Km)

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
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Mont Blanc
(4.8 km)
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What’s an event ?
The occasion of two elementary particles colliding (or a single particle
decaying)
This is NOT Higgs and yet it
repeats every 25 ns ! 40M/s
Higgs  ZZ*  2e + 2m + jet
After some cuts
It’s just a junk
10-9 of that is a Higgs
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Data Analysis and
statistics
H1
H1
H1
The situation is similar to searching for a needle in a stack of hay
Fortunately, the characteristics of signal (Higgs) event are different from
those of a background.
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Missing Energy in case of WZ
n
No net momentum into reaction
e-
But summing 3e gives net momentum out
Vector Addition
Neutrino momentum would the missing Energy
e-
Conservation of Momentum.
WZ  3e + n
Thus, a huge missing Energy will characterize
the background event.
So, the missing Energy can be used as a veto
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What’s the plan
 Understand ZZ, ttbar, (SM)
 Higgs searches
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Higgs production
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Higgs decay to a 4 leptons
channel
L+
Z
L-
Z
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
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Higgs 4leptons and background
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
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)
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Higgs in case of a lost
electron
H  2m1e + X
Here the non identified electron was recovered via the jet algorithm
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The complete picture of the standard Model with the
Higgs
THANK YOU
THE END !
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