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¿ De qué está hecho el Universo ?
de las partículas elementales a la materia oscura
Carlos Muñoz
Residencia de Estudiantes, Madrid, 6 Noviembre 2014
RESUMEN
1.
Solo entenderemos la composición del Universo si conocemos las
partículas elementales que lo constituyen y las fuerzas que se ejercen
entre ellas
•
Describiremos todas las partículas y las interacciones conocidas
2.
Después especularemos
•
¿Hacen falta más partículas en nuestra lista?
3.
•
Carlos Muñoz
IFT UAM-CSIC
Supersimetría, Supercuerdas, ...
¿De qué está hecha la materia oscura?
¿De qué está hecho el Universo?
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Esta charla, al ser la primera, espero que sirva de introducción a otras
charlas posteriors de este ciclo donde se desarrollarán de forma mucho más
extensa temas que aquí solo se introducen:
Higgs, quarks y gluones, cuerdas, cosmología, etc.
Carlos Muñoz
IFT UAM-CSIC
¿De qué está hecho el Universo?
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The mess at the beginning of the 20th century:
Heat, magnetism, electricity, light, X-rays, ultraviolet rays, …
finalized in 1948 when
Feynman, Schwinger, Tomonaga
showed it was renormalizable
(Nobel Prize in 1965)
QED is a quantum field theory, where
the particles are excitations of the fields
What is the Universe made of?
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Carlos Muñoz
IFT UAM-CSIC
What is the Universe made of?
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Carlos Muñoz
IFT UAM-CSIC
What is the Universe made of?
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Gell-Mann
(Nobel Prize in 1969)
Zweig 1964, proposed quarks
Friedman, Kendall & Taylor
discovered the quarks
in 1967-73 at SLAC
(Nobel Prize in 1990)
Carlos Muñoz
What is the Universe made of?
QCD was finalized in 1973
when Gross & Wilczek, Politzer
proposed asymptotic freedom
(Nobel Prize in 2004)
m = 1/7 mp
What is the Universe made of?
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Carlos Muñoz
IFT UAM-CSIC
What is the Universe made of?
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(+2/3)
(-1)
(-1/3)
Carlos Muñoz
IFT UAM-CSIC
¿De qué está hecho el Universo?
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La emission de neutrinos está asociada a la
desintegración beta. Parecía que este proceso
no conservaba la energía y eso llevó a Pauli a
postular la existencia de una partícula nueva (el
neutrino)
25 años más tarde, Reines lo descubrió
(Nobel Prize in 1995)
la carga está relacionada con el estado de
movimiento y no con el tipo de partícula
(aquellas con espín anti-paralelo a la
dirección del movimiento poseen carga débil)
Glashow, Weinberg, Salam,
proposed the electroweak theory
SU(2)XU(1) in 1960’s
(Nobel Prize in 1979)
‘t Hooft, Veltman,
showed it was renormalizable
thanks to the Higgs mechanism
in early 1970’s
(Nobel Prize in 1999)
Rubia, Van der Meer,
discovered W, Z
in 1983 at CERN
(Nobel Prize in 1984)
Carlos Muñoz
IFT UAM-CSIC
Carlos Muñoz
IFT UAM-CSIC
What is the Universe made of?
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Carlos Muñoz
IFT UAM-CSIC
¿De qué está hecho el Universo?
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~0.00000001
Carlos Muñoz
IFT UAM-CSIC
¿De qué está hecho el Universo?
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Mendeleiev, 1869
~1970’s
~0.00000001
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Mendeleiev, 1869
~1970’s
~0.00000001
H
~125000
And, in addition, the Higgs boson exists!
Glashow, Iliopoulos & Maiani,
predicted in 1970 the quark c
Richter at SLAC, Ting at BNL
discovered it in 1974
(Nobel Prize in 1976)
Kobayashi & Maskawa,
predicted in 1972
a third familiy of quarks
(Nobel Prize in 2008)
b and t discovered in
1977 and 1995 at Fermilab
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The Higgs is not just another elementary particle
It has a huge mass = 125 mp . Only the top quark is heavier
It’s a scalar. The first known elementary particle with spin=0
The Higgs (field) defines the vacuum. Since <0|H|0>=v≠0, we
can imagine the quantum vacuum as a sea full of the Higgs field
(rather like the concept of the ether of one century ago!)
All particles interact with the Higgs field, getting their unique masses.
Englert & Brout,
proposed this mechanism in 1964.
Higgs also the particle associated
(Nobel Prize in 2013)
Almost 50 years later, LHC discovered it
Carlos Muñoz
IFT UAM-CSIC
¿De qué está hecho el Universo?
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Besides, the standard model provides
the fundaments of the early Universe cosmology
Carlos Muñoz
IFT UAM-CSIC
¿De qué está hecho el Universo?
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SPECULATION:
Do other particles exist still undetected ?
History
Symmetries are crucial in physics
The laws of modern physics are invariant under certain symmetries:
 Lorentz transformations [special relativity]
 Local gauge transformations [SU(3)CxSU(2)LxU(1)Y]
Supersymmetry (SUSY) was proposed in the early 1970’s:
Golfand, Likhtman, 1971
Volkov, Akulov, 1972
Wess, Zumino, 1974
Carlos Muñoz
IFT UAM-CSIC
¿De qué está hecho el Universo?
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 An invariance of the theory under
interchange of fermions and bosons
L (bosons, fermions)
Boson
Fermion
Fermion
Boson
L (fermions, bosons) = L (bosons, fermions)
But known bosons and fermions
are not married up in this fashion
Quarks (u,d)
Electron
Neutrino
Gluons
W, Z
Photon
Instead, every known particle should have a (super) partner
The spectrum of elementary particles is doubled !
Quarks
Electron
Neutrino
Carlos Muñoz
IFT UAM-CSIC
Squarks
Selectron
Sneutrino
Gluons
Photon
W, Z
¿De qué está hecho el Universo?
Fayet, 1976
With masses  1000 mp
Gluino
Photino
Wino, Zino
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~0.00000001
spin 0 particle
H
~125000
Carlos Muñoz
IFT UAM-CSIC
¿De qué está hecho el Universo?
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~0.00000001
spin 0 particles
Hu , Hd
~125000
~ ~
Hu , Hd
spin 1/2 particle
Carlos Muñoz
IFT UAM-CSIC
¿De qué está hecho el Universo?
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.
msusy
(  100
Carlos Muñoz
IFT UAM-CSIC
mp )
(
¿De qué está hecho el Universo?

1000 mp
1000 mp )
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LEP
LHC
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¿De qué está hecho el Universo?
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E.g., in 2012 with a luminosity of 20 fb-1 and a QCD jet production cross section
of 106 pb, 2x1010 events of this kind were produced.
These are just background events, but they have to be analyzed!!
in order to find the new physics
But no more than 2x106 events of this kind can be
produced!!
Detection of the Higgs
In spite of the huge backgrounds,
ATLAS and CMS detectors at the
LHC were able to observe the
Higgs in 2012.
 (gg
H)  10 pb
H
 clean decay
already ~ 1 million Higgses produced at LHC
…perhaps it is one of the Higgses also predicted by
models beyond the standard model…
Carlos Muñoz
IFT UAM-CSIC
¿De qué está hecho el Universo?
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Englert, Higgs, Nobel Prize in 2013
Be prepared for more Nobel Prizes thanks to the LHC
Particle physics is living a historical moment:
-Years before the LHC, too early to test any model or theory
-Years later, too late, the unknown will already be known
Carlos Muñoz
IFT UAM-CSIC
¿De qué está hecho el Universo?
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MORE SPECULATIONS: What about gravity?
Carlos Muñoz
IFT UAM-CSIC
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Schwarz, Scherk, 1974
Green, Schwarz, 1984
Might be finite
Carlos Muñoz
IFT UAM-CSIC
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Carlos Muñoz
Metaphysics
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All this zoo is unified
in an unique fundamental object
~0.00000001
spin 0 particles
Hu , Hd
~125000
~ ~
Hu , Hd
spin 1/2 particle
Carlos Muñoz
IFT UAM-CSIC
¿De qué está hecho el Universo?
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Carlos Muñoz
IFT UAM-CSIC
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Summarizing: Apart from speculations,
everything in the Universe is made of quarks and leptons,
exchanging photons, W, Z, gluons (also gravitons?) in the Higgs vacuum
EVERYTHING ?
One of the great enigmas still unsolved is
the existence of dark matter
Carlos Muñoz
IFT UAM-CSIC
Materia Oscura
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giant galaxy cluster CL0025+1654,
about 1000 Mpc away
The analysis reveals that the cluster's dark matter (shown in blue) is not
evenly distributed, but follows the clumps of luminous matter closely
A SOLUTION
To assume that there is non-luminous matter
Zwicky, 1933
in and around the Galaxies
It has gravitational interaction
but no electromagnetic interaction
This hypothesis is not so odd if we remember that the existence of Neptune
was suggested on the basis of the irregular motion of Uranus
Carlos Muñoz
Materia Oscura
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85% of the matter in the Universe is dark
As often remarked, this implies
another Copernican revolution:
We are not the center of the Universe
+
We are not made of what most of the Universe is made of !
Carlos Muñoz
IFT UAM-CSIC
Materia Oscura
76
BUT…also Dark Energy !!
Perlmutter, Schmidt, Ries,
discovered in 1998 the accelerating
expansión of the Universe
(Nobel Prize in 2011)
Carlos Muñoz
IFT UAM-CSIC
Materia Oscura
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Thus to decipher the nature of the dark matter
is one of the great enigmas still unsolved
PARTICLE CANDIDATES
We need a new particle with the following properties:
 Stable or long-lived
Produced after the Big Bang and still present today
 Neutral
Otherwise it would bind to nuclei and would be excluded
from unsuccessful searches for exotic heavy isotopes
 Reproduce the observed amount of dark matter
Within the Standard Model of particle physics there are no candidates
This is a clear indication that we need to go
beyond the standard model of particle physics
i.e. we need to speculate
Carlos Muñoz
IFT UAM-CSIC
Materia Oscura
56
Could this new particle be a supersymmetric particle?
photino, sneutrino, gravitino
Let us then assume that this kind of particles exist
and that any of them is the dark matter
the question now is:
Can we detect it in experiments ?
Carlos Muñoz
IFT UAM-CSIC
Materia Oscura
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DETECTION
The LHC could detect a new kind of particle
…but how can we be sure it is stable on cosmological scales?
A complete confirmation can only arise from experiments
where the particle is detected as part of the galactic halo
Carlos Muñoz
IFT UAM-CSIC
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DETECTION
Since the detection will be on the Earth or on satellites, we only need
to know the properties of the Galactic halo near the Earth
For m ~ 100 mp these imply
J ~ 100,000 particles/cm2 s,
and therefore direct detection through elastic
scattering with nuclei in a detector is possible
Goodman, Witten, 85
Wasserman, 86
View of some detectors
in the copper box in
progress of installation
experiment: Installing the detectors
inside the copper box and shield
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Materia Oscura
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INDIRECT DETECTION
 Annihilation of dark matter particles
in the galactic halo will produce
gamma rays, antimatter, neutrinos
and these can be measured
in space–based detectors:
Fermi (gammas), PAMELA, AMS (antimatter)
or Cherenkov telescopes
MAGIC, HESS, VERITAS,
CANGAROO (gammas)
Carlos Muñoz
IFT UAM-CSIC
Materia Oscura
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Dark matter can accumulate in the Sun or the Earth. Its annihilation will
produce neutrinos which can be detected in neutrino telescopes, specially
through the muons produced by their interactions in the rock
Under-ice
experiments
(IceCube with
a size 106 m2 )
Underwater experiments
(ANTARES with a size of 104
m2. In the future KM3NeT
with a size of 106 m2 )
CONCLUSIONS
The standard model of particle physics “almost” answers the question:
What is the Universe made of?
However, one of the great enigmas still unsolved is the existence of
dark matter
Within the standard model there are no possible candidates, thus we
need to assume the existence of new particles
Supersymmetry, that predicts that every known particle should have a
partner, has candidates for dark matter, which could be tested in the LHC
and in direct and indirect detection experiments
Supersymmetry is not sufficient to unify gravity with the other
interactions in Nature, but perhaps string theory allow us to achive this
goal
Carlos Muñoz
IFT UAM-CSIC
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