STANDARD MODEL & BEYOND SM

1. STANDARD MODEL OF PARTICLE
PHYSICS
BY:
UPVITA PANDEY

2. OUTLINE
• INTRODUCTION
• HISTORICAL BACKGROUND
• WHAT IS STANDARD MODEL OF PHYSICS ?
• PARTICLE CONTENT
• FUNDAMENTAL FORCES
• TESTS AND PREDICTIONS
• LIMITATIONS OF SM
• CHALLENGES
• THEORETICAL PROBLEMS
• BEYOND SM

3. INTRODUCTION
• In particle physics, an elementary particle is a particle
whose substructure is unknown, thus it is unknown whether it
is composed of other particles.
• Known elementary particles include the fundamental
fermions(quarks, leptons, antiquarks and antileptons), which
generally are "matter particles" and “antimatterparticles",
• As well as the fundamental bosons (gauge bosons and Higgs
bosons), which generally are "force particles" that mediate
interactions among fermions.

4. Ancient times People think that earth, air, fire, and water are the fundamental elements.
1802 Dalton’s Atomic theory began forming.
1897 J. J. Thompson discovered the electron.
1911 Rutherford discovered positive nucleus.
1930 Pauli invented the neutrino particle.
1932 James Chadwick discovered the neutron.
1937 The muon was discovered by J. C. Street and E. C. Stevenson.
1956 First discovery of the neutrino by an experiment: the electron neutrino.
1962 Discovery of an other type of neutrino: the muon neutrino.
1969 Friedman, Kendall, and Taylor found the first evidence of quarks.
1974 The charmed quark was observed.
1976 The tau lepton was discovered at SPEAR.
1977 Experimenters found proof of the bottom quark.
1983 Carlo Rubbia and Simon Van der Meer discovered the W and Z bosons.
1991 LEP experiments show that there are only three light neutrinos.
1995 The top quark was found at Fermilab.
1998 Neutrino oscillations may have been seen in LSND and Super-Kamiokande.
2000 The tau neutrino was observed at Fermilab.
2003 A Five-Quark State has been discovered.
2013 Discovery of Higgs Boson.

5. HISTORICAL BACKGROUND
• The first step towards the Standard Model was Sheldon Glashow’s
discovery in 1961 of a way to combine the electromagnetic and weak
interactions.
• In 1967 Steven Weinberg and Abdus Salam incorporated the Higgs
mechanism into Glashow’s electroweak theory, giving it a modern form.
• The Higgs mechanism is believed to give rise to the masses of all
the elementary particles in the Standard Model. This includes the masses
of the W and Z bosons, and the masses of the fermions, i.e.
the quarks and leptons.
• After the neutral weak currents caused by Z boson exchange were
discovered at CERN in 1973, the electroweak theory became widely
accepted and Glashow, Salam, and Weinberg shared the 1979 Nobel Prize
in Physics for discovering it.
• The W and Z bosons were discovered experimentally in 1981, and their
masses were found to be as the Standard Model predicted.

6. WHAT IS STANDARD
MODEL ?
The Standard Model
explains how the basic
building blocks of matter
interact, governed by four
fundamental forces and
classifies all the subatomic
particles known. Because
of its success in explaining
a wide variety of
experimental results, the
Standard Model is
sometimes regarded as a
"theory of almost
everything".

7. PARTICLE CONTENT
The Standard Model includes members of several classes of elementary
particles (fermions, gauge bosons, and the Higgs boson), which in turn can
be distinguished by other characteristics, such as color charge.
FERMIONS GAUGE BOSONS HIGGS BOSON

8. FERMIONS
Fermions are divided into two groups of six, Those that must bind together
are called Quarks and those that can exist independently are called Leptons.
QUARKS
 Six quarks (up, down, charm,
strange, top, bottom).
 they carry color charge.
 they carry electric charge and
weak isospin.
LEPTONS
 Six leptons (electron, electron
neutrino, muon, muon neutrino,
tau, tau neutrino)
 do not carry colour charge
 three neutrinos do not carry
electric charge
Fermions obey the pauli exclusion principle. They are characterized by
Fermi-Dirac statistics. They have half integer spin.

9. GAUGE
BOSONS
•Gauge Bosons are of four
types and are classified on
the basis of force they
interact with-
Photon- Electromagnetic
Force
Gluon- Strong Force
W and Z boson- Weak Force
•They have integral spins and
the spin of photon, gluon, W
and Z boson is 1.

10. HIGGS BOSON
 The Higgs particle is a massive scalar elementary particle theorized by Robert
Brout, Francois Englert, Peter Higgs, Gerald Guralnik, C. R. Hagen, and Tom
Kibble in 1964 and is a key building block in the Standard Model
 It has no intrinsic spin, and for that reason is classified as a boson.
 Because the Higgs boson is a very massive particle and also decays almost
immediately when created, only a very high-energy particle accelerator can
observe and record it.
 On 14 March 2013 the Higgs Boson was tentatively confirmed to exist.
 On December 10, 2013, two of them, Peter Higgs and François Englert, were
awarded the Nobel Prize in Physics for their work and prediction.

11. WHAT ARE
FUNDAMENTAL
FORCES ?
The Standard Model
classified all four
fundamental forces in
nature. In the Standard
Model, a force is described
as an exchange
of bosons between the
objects affected, such as
a photon for the
electromagnetic force and
a gluon for the strong
interaction. Those particles
are called force carriers.

13. TESTS AND PREDICTIONS
• The Standard Model (SM) predicted the existence of the W and Z
bosons, gluon, and the top and charm quarks before these particles were
observed.
QUANTITY MEASURED (GeV) SM PREDICTION (GeV)
Mass of W boson 80.387 ± 0.019 80.390 ± 0.018
Mass of Z boson 91.1876 ± 0.0021 91.1874 ± 0.0021
• The SM also makes several predictions about the decay of Z bosons,
which have been experimentally confirmed by the Large Electron- Positron
Collider at CERN.

14. LIMITATIONS
• The model does not incorporate the full theory of gravitation, as described
by general relativity or account for the accelerating expansion of the
universe.
• The model does not contain any viable dark matter particle that possesses
all of the required properties deduced from observational cosmology.
• It also does not incorporate neutrino oscillations (and their non-zero
masses).

15. CHALLENGES
• GRAVITY - The standard model does not explain gravity. The approach of
simply adding a "graviton" to the Standard Model does not recreate what is
observed experimentally without other modifications. Moreover, instead, the
Standard Model is widely considered to be incompatible with the most
successful theory of gravity to date, general relativity.
• DARK MATTER AND DARK ENERGY - Cosmological observations tell us
the standard model explains about 5% of the energy present in the universe.
About 26% should be dark matter, which would behave just like other matter,
but which only interacts weakly (if at all) with the Standard Model fields. Yet,
the Standard Model does not supply any fundamental particles that are good
dark matter candidates. The rest (69%) should be dark energy, a constant
energy density for the vacuum. Attempts to explain dark energy in terms of
vacuum energy of the standard model lead to a mismatch of 120 orders of
magnitude.

16. •MATTER-ANTIMATTER ASYMMETRY - The universe is made out of
mostly matter. However, the standard model predicts that matter and
antimatter should have been created in (almost) equal amounts if the initial
conditions of the universe did not involve disproportionate matter relative to
antimatter. Yet, no mechanism sufficient to explain this asymmetry exists in
the Standard Model.
•MUONIC HYDROGEN - Standard Model makes precise theoretical
predictions regarding the atomic radius size of ordinary hydrogen (a proton-
electron system) and that of muonic hydrogen (a proton-muon system in
which a muon is a "heavy" variant of an electron). However, the measured
atomic radius of muonic hydrogen differs significantly from that of the radius
predicted by the Standard Model.

17. THEORETICAL PROBLEMS
Some features of the standard model are added in an ad hoc way. These are not
problems per se, but they imply a lack of understanding.
• Number of parameters — Standard model depends on 19 numerical
parameters. Their values are known from experiment, but the origin of the
values is unknown. Some theorists have tried to find relations between
different parameters, for example, between the masses of particles in
different generations.
• Quantum triviality - Suggests that it may not be possible to create a
consistent quantum field theory involving elementary scalar Higgs
particles.
• Strong CP problem - Theoretically it can be argued that the standard model
should contain a term that breaks CP symmetry, relating matter to
antimatter, in the strong interaction sector. Experimentally, however, no
such violation has been found, implying that the coefficient of this term is
very close to zero. This fine tuning is also considered unnatural.

18. BEYOND STANDARD MODEL
While the Standard Model goes a long way towards explaining the "whys"
of physical interactions, there are still many mysteries yet to be solved.
Due to these shortcomings of the standard model, a need for theories beyond
the standard model arose. These theories attempt to resolve the
shortcomings of standard model.

19. GRAND UNIFICATION
• The standard model has three gauge symmetries; the colour SU(3), the weak
isospin SU(2), and the hypercharge U(1) symmetry, corresponding to the three
fundamental forces.
• Due to renormalization the coupling constants of each of these symmetries vary
with the energy at which they are measured. Around 10^16 GeV these
couplings become approximately equal.
• This has led to speculation that above this energy the three gauge symmetries
of the standard model are unified in one single gauge symmetry with a simple
gauge group, and just one coupling constant. Below this energy the symmetry
is spontaneously broken to the standard model symmetries.
• Theories that unify the standard model symmetries in this way are called Grand
Unified Theories (or GUTs), and the energy scale at which the unified
symmetry is broken is called the GUT scale.

20. SUPERSYMMETRY
Supersymmetry extends the Standard Model by adding another class of
symmetries to the Lagrangian. These symmetries exchange fermionic
particles with bosonic ones. Such a symmetry predicts the existence
of supersymmetric particles, abbreviated as sparticles, which include
the sleptons, squarks, neutralinos, and charginos. Each particle in the
Standard Model would have a superpartner whose spin differs by 1/2 from
the ordinary particle. Due to the breaking of supersymmetry, the sparticles
are much heavier than their ordinary counterparts; they are so heavy that
existing particle colliders would not be powerful enough to produce them.
However, some physicists believe that sparticles will be detected by
the Large Hadron Collider at CERN.

21. STRING THEORY
• String theory is a theoretical framework in which the point-like
particles of particle physics are replaced by one-dimensional
objects called strings. String theory describes how these strings
propagate through space and interact with each other.
• On distance scales larger than the string scale, a string looks just
like an ordinary particle, with its mass, charge, and other
properties determined by the vibrational state of the string.
• In string theory, one of the vibrational states of the string
corresponds to the graviton, a quantum mechanical particle that
carries gravitational force. Thus string theory is a theory of
quantum gravity.

22. TECHNICOLOR
Technicolor theories try to modify the Standard Model in a minimal way by
introducing a new QCD-like interaction. This means one adds a new theory
of so-called Techniquarks, interacting via so called Technigluons. The main
idea is that the Higgs-Boson is not an elementary particle but a bound state
of these objects.

23. PREON THEORY
According to preon theory there are one or more orders of particles more
fundamental than those (or most of those) found in the Standard Model.
The most fundamental of these are normally called preons, which is derived
from "pre-quarks". In essence, preon theory tries to do for the Standard
Model what the Standard Model did for the particle zoo that came before it.
Most models assume that almost everything in the Standard Model can be
explained in terms of three to half a dozen more fundamental particles and
the rules that govern their interactions. Interest in preons has waned since
the simplest models were experimentally ruled out in the 1980s.

24. ACCELERON THEORY
• Accelerons are the hypothetical subatomic particles that integrally link the
newfound mass of the neutrino and to the dark energy conjectured to be
accelerating the expansion of the universe.
• In theory, neutrinos are influenced by a new force resulting from their
interactions with accelerons. Dark energy results as the universe tries to
pull neutrinos apart.