Higgs field

Física de Partículas
Experimental
5a clase
Luis Manuel Montaño Zetina
Departamento de Física Cinvestav
Departamento de Física USON Hermosillo Sonora 5-9
agosto 2013
ALICE @ LHC (i)
Quarks and gluons in ordinary
matter are confined in hadrons.
Theory predicts that in extreme
conditions of temperature and
energy density a phase transition
from ordinary nuclear matter to
Quark Gluon Plasma (QGP) should
occur. In this new state, probably
existed 10-6 s after the Big Bang,
quark and gluons are not anymore
confined.
Experiments at LHC
energy density of nuclei
0.13 GeV/fm 3
energy density in the proton
3
0.44 GeV/fm
Las 4 fuerzas de la naturaleza
Débil
• Decaimiento
Beta
• Fusión pp
Carga
débil
Fuerte
• quarks
Carga
fuerte
Electromagnetismo
• TV, etc
• Imanes
• creación ee
Carga
eléctrica
Gravedad
Sólo atractiva
masa
Fuerza Electromagnética
La fuerza repulsiva que dos electrones aproximándose “sienten”
e-
El fotón es la partícula asociada a la
fuerza electromagnética
e-
Fotón
Weak force: W-,W+,Z0
Decaimiento β
n→peνe
WLa carga eléctrica
se conserva en
Cada vértice.
Interacción Electrodébil
En el modelo estandar las interacciones electromagnética y débil se
combinaron en una teoría unificada llamada electrodébil.
A distancias pequeñas (10-18 m) la intensidad de la interacción
débil es comparable a la electromagnética. Sin embargo, a 30
veces esa distancia (3x10-17 m) esa intensidad de interacción
es 1/10000 veces la intensidad electromagnética. A distancias
típicas del protón (10-15 m) la fuerza es aún menor.
La diferencia observada entre estas dos fuerzas es debida a
la gran diferencia de las masas de W y Z con respecto al
fotón..
Fuerza fuerte: gluones
Gluones interaccionan con quarks
Gluones interaccionan con gluones
Strong interactions
The strong force holds the nuclei together to form hadrons.
The theory of strong interactions is called Quantum
Chromodynamics (QCD). This name is due to the fact that
quarks, besides the electric charge, have a different kind of
charge called “color charge”, which is responsible of the strong
force.
The force carrier particles are
called “gluons”, since they so
tightly “glue” quarks together
Gluons have color charge, quarks have color charge but hadrons
have no net color charge (“color neutral”). For this reason, the
strong force only takes place on the small level of quark
interactions.
Color charge
Color charged particle interact by exchanging gluons. Quarks
constantly change their color charges as they exchange gluons
with other quarks.
There are 3 color charges and 3
corresponding anti-color charges.
Each quark has one of the color
charges and each antiquark has one
of the anticolor charges.
In a baryon a combination of red, green and blue is color neutral. Mesons are
color neutral because they carry combinations as red and antired.
Because gluon emission and absorption always changes color, gluons can be
thought of as carrying a color and an anticolor charge. QCD calculations
predict 8 different kinds of gluons.
Quark confinement
Color-charged particles cannot be found individually.
They are confined in hadrons.
Quarks can combine only in 3-quarks objects
(baryons) and quark-antiquark objects (mesons) which
are color-neutral, particle as ud or uddd cannot exist.
If one of the quarks in a given hadron is pulled
away from its neighbours, the color force field
stretches between that quark and its
neighbours. More and more energy is added to
the color-force field as the quark are pulled
apart.
At some point it’s energetically cheaper to snap into a new quark-antiquark
pair. In so doing energy is conserved because the energy of the color-force
field is converted in the mass of the new quarks.
I. Newton
Gravity
Gravity is one of the fundamental interactions, but the
Standard Model cannot satisfactorily explain it.
This is one of the major unanswered problems in physics today
The particle force carrier for gravity, the graviton, has not
been found
Fortunately, the effects of gravity are extremely tiny in most
particle physics situations compared to the other three
interactions, so theory and experiment can be compared without
including gravity in the calculations. Thus, the Standard Model
works without explaining gravity.
El Modelo Estandar
Incluye:
Materia
• 6 quarks
• 6 leptones
Agrupados en 3 generaciones
Fuerzas
• Electrodébil:
− γ (fotón)
- Z0, W±
• Fuerte
- g (gluon)
H= Lo que faltaba, el bosón de Higgs
Teoría exitosa para describir el mundo subatómico
Higgs boson
The Standard Model cannot explain why a particle has
a certain mass.
Physicists have theorized the existence of the
so-called Higgs field, which in theory interacts with
other particles to give them mass. The Higgs field
requires a particle, the Higgs boson. The Higgs boson
has not been observed.
Higgs mechanism (i)
The Higgs mechanism was postulated by British physicist
Peter Higgs in the 1960s. The theory hypothesizes that a sort
of lattice, referred to as the Higgs field, fills the universe.
This is something like an e.m. field, which affects particles
moving in it. It is known that when an electron passes through
a positively charged crystal lattice, its mass can increase as
much as 40 times. The same may be true in the Higgs field: a
particle moving through it creates a little bit of distortion and
lends mass to the particle.
Higgs mechanism (ii)
To understand the
Higgs mechanism,
imagine that a room
full of physicists
chattering 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...
Higgs mechanism (iii)
... if a rumor crosses
the room, ...
... it creates the same
kind of clustering, but
this time among the
scientists themselves.
In this analogy, these
clusters are the Higgs
particles.
Grand Unified Theory
Physicists hope that a Grand Unified Theory will unify the strong, weak,
and electromagnetic interactions. If a Grand Unification of all the
interactions is possible, then all the interactions we observe are all
different aspects of the same, unified interaction.
However, how can this be the case if strong and weak and
electromagnetic interactions are so different in strength and effect?
Current data and theory suggests that these varied forces merge into
one force when the particles being affected are at a high enough energy.
Grand Unified Theory
Más allá del modelo estandar:
unificación de fuerzas
ELECTROMAGNÉTICA
GRAVEDAD
FUERZA
UNIFICADA
FUERTE
DÉBIL
¿Será posible, es necesario?
Beyond the Standard Model
The SM explains the structure and stability of matter, but there
are many unanswered questions:
Why do we observe matter and almost no antimatter?
Why can’t the SM predict a particle’s mass?
Are quarks and leptons actually fundamental?
Why are there 3 generations of quarks and leptons?
How does gravity fit into all of this?
Is the SM wrong?
No, we need to extend the SM with something totally new in
order to explain mass, gravity and other phenomena.
Supersymmetry
Some physicists attempting to unify gravity with the
other fundamental forces have come to a startling
prediction: every fundamental matter particle should
have a massive "shadow" force carrier particle, and
every force carrier should have a massive "shadow"
matter particle.
This relationship between matter particles and force
carriers is called supersymmetry. For example, for
every type of quark there may be a type of particle
called a "squark."
No supersymmetric particle has yet been found, but
experiments are underway at CERN and Fermilab to
detect supersymmetric partner particles.
AMS measures antimatter excess
in space
• Alpha Magnetic Spectrometer, antimatter by
dark matter.
• Positrons’ origin in the anihilation of dark matter
particle in space
• An excess of antimatter within the cosmic ray
flux was seen by PAMELA.
• Supersymmetry says that positrons are
produced when two dark matter particles collide
and anihilate.
• Maybe from pulsars around the galactic plane.
ATRAP makes world’s most precise
measurement of antiproton
magnetic moment
• CERN antiproton decelerator reported new result of
antiproton magnetic moment 680 times more precise
than previous measurements.
• Thanks to ability of trapping antiprotons and use large
magnetic gradient. Used Penning trap (suspended at the
center of an iron ring electrode sandwiched between
cooper electrodes.
• Useful result to understand the matter-antimatter
imbalance of the universe. This tests the SM CPT
theorem, magnetic moment of proton and antiproton are
exactly but opposite: equal in strength but opposite in
direction.
Producción de antihidrógeno
(CERN)