AMS Project

7/30/2019 AMS Project

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INDEX:

ABSTRACT

INTRODUCTION (FORMATION OF THE EARLY UNIVERSE) BARYOGENESIS

BIG BANG NUCLEOSYNTHESIS

RECOMBINATION

ELEMENTARY PARTICLES

LARGE HADRON COLLIDER AND THE HIGGS BOSON

CONCLUSION


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ABSTRACT

This project explores the subject of the behavior of atoms and molecules in

the early universe. The chronology of the universe can be subdivided into the

very early universe, which is about 10-32 seconds from the big bang, and the

early universe, when the cosmic inflation ends and the physics is lessspeculative. We will study the Big Bang theory and its effect on the formation

of the first atoms and molecules. We will study the phenomena of

baryogenesis and Big Bang Nucleosynthesis, where the first particles are

formed in the early universe. We will see how the first atoms undergo

recombination to form more complex ones. Finally, we will also look at the

recent discovery of the Higgs boson in the LHC which proves how the first

particles were formed.


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INTRODUCTION

Formation of the universe:

The prevailing scientific model of how the universe came into being and

developed over time using cosmological time parameter of commoving

coordinates is the Big Bang Theory. The instant at which the universe is

thought to have begun rapidly expanding from a singularity is known as the

big bang. The best estimates for this expansion are about 13.77 billion years.

Today, the universe appears to be dominated by dark energy. About 3/4th of

the total mass-energy of the universe is dark energy, while the rest is

dominated by matter (normal and dark.) The radiation in the universe is

mostly the cosmic microwave background and the radiation from stars andgalaxies which are weak. But it was not always this way. The early universe

was radiation dominated. The density of radiation exceeded the density of

matter. In the early universe, matter and anti-matter were being created

equally out of the radiation. This phenomenon is called pair production.

The very earliest universe was extremely hot so that no particles could exist,

and the forces that we see around us today were believed to be merged into

one unified force. Space itself expanded due to the immensity of the

energies involved. Gradually, the immense energies cooled, sufficiently for

forces to allow symmetry breaking, leading finally to the separation of the

strong force from the electroweak force and the first particles. In the secondphase, the universe cooled further the current fundamental forces we know

took their present forms through further symmetry breaking- notably the

breaking of electroweak symmetry- and the full range of complex and

composite particles we see around us today became possible, leading to a

matter dominated universe, the first neutral atoms, and the cosmic

microwave background radiation we can detect today.

The third phase saw a universe whose fundamental particles and forces were

as we know them, and witnessed the emergence of large scale stable

structures, such as stars, quasars, galaxies, etc. Thus, with respect to the

evolution of matter, the first and second phases of development of the earlyuniverse are important. We will now look at the eras in the development of

the universe significant to the formation of atoms and matter in general.

The Planck epoch is an era in the big bang cosmology where the four

fundamental forces we recognize today are unified into one fundamental

force because of the huge extremity in temperature. In the Grand unification


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epoch, the universe expands and cools, and it crosses the transition

temperature at which forces separate from each other. Gravitational forces

separate from the other forces of nature, which are collectively known as the

gauge forces. These forces act through the exchange of quanta of energy

associated with each specific force called bosons. In the electroweak epoch,

the temperature is low enough (1028K) to separate the strong andelectroweak force.

The inflationary epoch, which is particularly interesting for us is a period

when the universe experiences an accelerating expansion because of a

hypothesized Higgs field. The recent discovery of the Higgs boson is a huge

step towards understanding this epoch and through it, the birth of the

universe. All these changes take place within the first 10 -32 seconds after the

big bang. After this, the formation of first atoms takes place through

baryogenesis (birth of the baryons.), nucleosynthesis (synthesis of more

complex nuclei.) and recombination ( formation of electrically neutral

hydrogen atoms.).


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Baryogenesis

In physical cosmology, baryogenesis is the generic term for hypothetical

physical processes that produced an asymmetry between baryons and

antibaryons in the very early universe, resulting in the substantial amounts

of residual matter that make up the universe today.

Baryogenesis theories (the most important being electroweak baryogenesis

and GUT baryogenesis) employ sub-disciplines of physics such as quantum

field theory, and statistical physics, to describe such possible mechanisms.

The fundamental difference between baryogenesis theories is the description

of the interactions between fundamental particles.

The next step after baryogenesis is the much better understood Big Bang

nucleosynthesis, during which light atomic nuclei began to form.

The Standard Model can incorporate baryogenesis, though the amount of net

baryons (and leptons) thus created may not be sufficient to account for thepresent baryon asymmetry; this issue has not yet been determined

decisively.

Baryogenesis within the Standard Model requires the electroweak symmetry

breaking be a first-order phase transition, since otherwise sphalerons wipe

off any baryon asymmetry that happened up to the phase transition, while

later the amount of baryon non-conserving interactions is negligible. [7]

The phase transition domain wall breaks the P-symmetry spontaneously,

allowing for CP-symmetry violating interactions to create C-asymmetry on

both its sides: quarks tend to accumulate on the broken phase side of the

domain wall, while anti-quarks tend to accumulate on its unbroken phase

side. This happens as follows:[5]

Due to CP-symmetry violating electroweak interactions, some amplitudes

involving quarks are not equal to the corresponding amplitudes involving

anti-quarks, but rather have opposite phase (see CKM matrix and Kaon);


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since time reversal takes an amplitude to its complex conjugate, CPT-

symmetry is conserved.

Though some of their amplitudes have opposite phases, both quarks and

anti-quarks have positive energy, and hence acquire the same phase as theymove in space-time. This phase also depends on their mass, which is

identical but depends both on flavor and on the Higgs VEV which changes

along the domain wall. Thus certain sums of amplitudes for quarks have

different absolute values compared to those of anti-quarks. In all, quarks and

anti-quarks may have different reflection and transmission probabilities

through the domain wall, and it turns out that more quarks coming from the

unbroken phase are transmitted compared to anti-quarks.

Thus there is a net baryonic flux through the domain wall. Due to sphaleron

transitions, which are abundant in the unbroken phase, the net anti-baryonic

content of the unbroken phase is wiped off. However, sphalerons are rare

enough in the broken phase as not to wipe off the excess of baryons there. In

total, there is net creation of baryons.

In this scenario, non-perturbative electroweak interactions (i.e. the

sphaleron) are responsible for the B-violation, the perturbative electroweak

Lagrangian is responsible for the CP-violation, and the domain wall is

responsible for the lack of thermal equilibrium; together with the CP-violation

it also creates a C-violation in each of its sides.

Baryon asymmetry parameter:

The challenges to the physics theories are then to explain how to produce

this preference of matter over antimatter, and also the magnitude of this

asymmetry. An important quantifier is the asymmetry parameter,

.

This quantity relates the overall number density difference between baryonsand antibaryons (nB and nB, respectively) and the number density ofcosmic

background radiationphotons n.

According to the Big Bang model, matter decoupled from the cosmic

background radiation (CBR) at a temperature of roughly 3,000 kelvin,

corresponding to an average kinetic energy of 3,000 K / (10.08103 K/eV)

= 0.3 eV. After the decoupling, the total number of CBR photons remains
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constant. Therefore due to space-time expansion, the photon density

decreases. The photon density at equilibrium temperature T per cubic

centimeter, is given by

with kB as the Boltzmann constant, as the Planck constant divided by 2

and c as the speed of light in vacuum. At the current CBR photon

temperature of 2.725 K, this corresponds to a photon density nof around

411 CBR photons per cubic centimeter.

Therefore, the asymmetry parameter , as defined above, is notthe "good"

parameter. Instead, the preferred asymmetry parameter uses

the entropy density s,

because the entropy density of the universe remained reasonably constant

throughout most of its evolution. The entropy density is

with p and as the pressure and density from the energy density tensor T,and g* as the effective number of degrees of freedom for "massless" particles

(inasmuch as mc2 kBT holds) at temperature T,
http://en.wikipedia.org/wiki/Boltzmann_constanthttp://en.wikipedia.org/wiki/Planck_constanthttp://en.wikipedia.org/wiki/Entropyhttp://en.wikipedia.org/wiki/Boltzmann_constanthttp://en.wikipedia.org/wiki/Planck_constanthttp://en.wikipedia.org/wiki/Entropy


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,

for bosons and fermions with g i and gj degrees of freedom at temperatures

Ti and Tj respectively. At the present era, s = 7.04n.


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Big Bang Nucleosynthesis

For the formation of a heavier isotope of hydrogen known as deuterium (H- In

physical cosmology, Big Bang nucleosynthesis (or primordialnucleosynthesis, abbreviated BBN) refers to the production of nuclei other

than those of the lightest isotope of hydrogen during the early phases of the

universe. Primordial nucleosynthesis is believed by many scientists to have

taken place just a few moments after the Big Bang and is believed to be

responsible 2 or D), the helium isotopes He-3 and He-4, and the lithium

isotopes Li-6 and Li-7. In addition to these stable nuclei some unstable, or

radioactive, isotopes were also produced notably: tritium or H-3; beryllium-7

(Be-7), and beryllium-8 (Be-8). These unstable isotopes either decayed or

fused with other stable nuclei.

There are two important characteristics of Big Bang nucleosynthesis (BBN):

1. The era began at temperatures of around 10 MeV (116 gigakelvin) andended at temperatures below 100 keV (1.16 gigakelvin). Thecorresponding time interval was from a few tenths of a second to up to103 seconds. The rate of cooling in this era can be given by the

equation:

Where t is time in seconds, T is temperature in MeV and g * is theeffective number of particle species. (g* includes contributions of 2from photons, 7/2 from electron-positron pairs and 7/4 from eachneutrino flavor. In the standard model g* is 10.75). This expression also

shows how a different number of neutrino flavors will change the rateof cooling of the early universe.

2. It was widespread, encompassing the entire observable universe. Thekey parameter which allows one to calculate the effects of BBN is the
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number ofphotons per baryon. This parameter corresponds to thetemperature and density of the early universe and allows one todetermine the conditions under which nuclear fusion occurs. From thiswe can derive elemental abundances. Although the baryon per photonratio is important in determining elemental abundances, the precise

value makes little difference to the overall picture. Without majorchanges to the Big Bang theory itself, BBN will result in massabundances of about 75% of H-1, about 25% helium-4, about 0.01% ofdeuterium, trace amounts (on the order of 1010) of lithium andberyllium, and no other heavy elements. (Traces ofboron have beenfound in some old stars, giving rise to the question whether someboron, not really predicted by the theory, might have been produced inthe Big Bang. The question is not presently resolved.) That theobserved abundances in the universe are generally consistent withthese abundance numbers is considered strong evidence for the BigBang theory.

In this field it is customary to quote percentages by mass, so that 25%

helium-4 means that helium-4 atoms account for 25% of the mass, but only

about 8% of the atoms would be helium-4 atoms.

Important Parameters:

The creation of light elements during BBN was dependent on a number of

parameters; among those was the neutron-proton ratio and the baryon-

photon ratio.

Neutron-Proton Ratio:

Neutrons can react with positrons or electron neutrinos to create protons and

other products in one of the following reactions:

n + e+ anti-e + p

n + e p + e
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These reactions continue until expansion of the universe outpaces the

reactions, which occurs at about T = 0.7 MeV and is called the freeze out

temperature. At freeze out, the neutron-proton ratio is about 1/7. Almost all

neutrons that exist after the freeze out combined to create Helium-4, due to

the fact that Helium-4 has the highest binding energy per nucleon among

light elements. This predicts that the mass fraction of Helium-4 should beabout 25%, which is in line with observations. Some deuterium and Helium-3

remained as there was insufficient time and density for them to react and

form Helium-4.

Baryon-Photon Ratio:

The baryon-photon ratio , is a strong indicator of the abundance of light

elements present in the early universe. Baryons can react with lightelements in the following reactions:

(n,p) + 2H (3He, 3H)

(3He, 3H) + (n,p) 4He

It is evident that reactions with baryons during BBN would ultimately result in

Helium-4, and also that the abundance of primordial deuterium is indirectly

related to the baryon density or baryon-photon ratio. That is, the larger the

baryon-photon ratio the more reactions there will be and the more deuterium

will be eventually transformed into Helium-4. This result makes deuterium a

very useful tool in measuring the baryonic change of the universe.

Sequence:

Big Bang nucleosynthesis began a few minutes after the big bang, when the

universe had cooled down sufficiently to allow deuterium nuclei to survive

disruption by high-energy photons. This time is essentially independent of

dark matter content, since the universe was highly radiation dominated until

much later, and this controls the temperature/time relation. The relative

abundances of protons and neutrons follow from simple thermodynamical

arguments, combined with the way that the mean temperature of the

universe changes over time. If the reactions needed to reach the


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thermodynamically favoured equilibrium values are too slow compared to the

temperature change brought about by the expansion, abundances would

have remained at some specific non-equilibrium value. Combining

thermodynamics and the changes brought about by cosmic expansion, one

can calculate the fraction of protons and neutrons based on the temperature

at this point. The answer is that there are about seven protons for everyneutron at the beginning of nucleosynthesis. This fraction is in favour of

protons initially, primarily because their lower mass with respect to the

neutron favors their production. Free neutrons decay to protons with a half-

life of about 15 minutes, but this time-scale is longer than the first first three

minutes of nucleogenesis, during which time a significant fraction of them to

were combined with protons into deuterium.

One feature of BBN is that the physical laws and constants that govern the

behavior of matter at these energies are very well understood, and henceBBN lacks some of the speculative uncertainties that characterize earlier

periods in the life of the universe. Another feature is that the process of

nucleosynthesis is determined by conditions at the start of this phase of the

life of the universe, making what happens before irrelevant.

As the universe expands, it cools. Free neutrons and protons are less stable

than helium nuclei, and the protons and neutrons have a strong tendency to

form helium-4. However, forming helium-4 requires the intermediate step of

forming deuterium. Before nucleosynthesis began, the temperature was highenough for many photons to have energy greater than the binding energy of

deuterium; therefore any deuterium that is formed was immediately

destroyed (a situation known as the deuterium bottleneck). Hence, the

formation of helium-4 is delayed until the universe became cool enough to

form deuterium (at about T = 0.1 MeV), and for it to remain; after which

there was a sudden burst of element formation. However, very shortly

thereafter, at twenty minutes after the Big Bang, the universe became too

cool for any further nuclear fusion and nucleosynthesis to occur. At this point,

the elemental abundances were nearly fixed, and only change was the result

of the radioactive decay of some products of BBN (such as tritium).


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Recombination

In cosmology, recombination refers to the epoch at which charged electrons

and protons first became bound to form electrically neutral hydrogen atoms.

After the Big Bang, the universe was a hot, dense plasma of photons,

electrons, and protons. This plasma was effectively opaque to

electromagnetic radiation, as the distance each photon could travel before

encountering a charged particle was very short. As the universe expanded, it

also cooled. Eventually, the universe cooled to the point that the formation of

neutral hydrogen was energetically favored, and the fraction of free electrons

and protons as compared to neutral hydrogen decreased to about 1 part in

10,000.

Shortly after, photons decoupled from matter in the universe, which leads to

recombination sometimes being called photon decoupling, although

recombination and photon decoupling are distinct events. Once photons

decoupled from matter, they traveled freely through the universe withoutinteracting with matter, and constitute what we observe today as cosmic

microwave background radiation. Recombination occurred when the universe

was roughly 378,000 years old, or at a redshift of z = 1,100.


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Derivation of recombination epoch:

It is possible to find a rough estimate of the redshift of the recombinationepoch, starting by considering that during the era preceding recombination,

the photons were primarily coupled to matter through the reaction

This reaction requires that the photon () have an energy of at least13.6 electron volts. As long as photons are coupled to matter, this reactionwill be in statistical equilibrium, and so the Saha equation can be applied todetermine the equilibrium values of the constituents. This results in theequation

where n represents the number density of the subscripted particle, me isthe mass of the electron, kB is Boltzmann's constant, Tis thetemperature, is the reduced Planck's constant, and Q is the bindingenergy of hydrogen.[2] Noting that charge neutrality requires ne = np, andthen defining the fractional ionization as

the Saha equation can be rewritten as

The final step is to put this equation in terms of the number density ofphotons, which is related to the number density of baryons through thebaryon-to-photon ratio . The reason for this is that the baryon-to-photonratio can be measured, and the number density of photons is given by
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where c is the speed of light. Then

Solving this equation for a 50 percent ionization yields a recombinationtemperature of roughly 4,000 K. This, in turn, gives the redshift asapproximatelyz= 1,500, as the temperature of the radiation in the universeis given by Tr = 2.728 (1 + z). In units ofelectronvolts, this temperature isroughly 0.3 eV. This is nearly two orders of magnitude lower than the bindingenergy ofhydrogen, which may seem strange, as equilibrium often occurswhen the energy scales of two phenomena are roughly equal. The reason forthe difference is because photons greatly outnumber baryons; the baryon-to-photon ratio is approximately 109. If there are roughly the same number ofphotons with an energy greater than the binding energy of hydrogen as thereare hydrogen atoms, then the gas will remain ionized. There will be somephotons in the Wien region of the black body spectrum with an energygreater than kT, and the number of photons with an energy greater than

13.6 eV does not drop below the number of hydrogen atoms until thetemperature is roughly 4000K or 0.3 eV. A different statement of this is thatrecombination was delayed due to the high entropy of the universe. Thisderivation relied on the assumptions ofthermodynamic equilibrium andrecombination directly to the ground state of hydrogen, each of whichsimplifies the calculation but also modifies the result. Recombination to anexcited state of hydrogen means that recombination proceeds more slowlythan that predicted with the Saha equation. A more careful treatment of thephysics of recombination yields a value closer toz= 1,100.

Impact:

Prior to recombination, photons were not able to freely travel through theuniverse, as they constantly scattered off the free electrons and protons. Thisscattering causes a loss of information, and "there is therefore a photonbarrier at a redshift" near that of recombination that prevents us from usingphotons directly to learn about the universe at larger redshifts. Once
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recombination had occurred, however, the mean free path of photons greatlyincreased due to the lower number of free electrons. Shortly afterrecombination, the photon mean free path became larger than the Hubblelength, and photons traveled freely without interacting with matter. For thisreason, recombination is closely associated with the last scattering surface,

which is the name for the last time at which the photons in the cosmicmicrowave background interacted with matter. However, these two eventsare distinct, and in a universe with different values for the baryon-to-photonratio and matter density, recombination and photon decoupling need nothave occurred at the same epoch.

Elementary Particles

Elementary particles are particles which are known not to have any

substructure. This means that they form the basis of observable matter, inthe form of building blocks. The ancients believed that atoms were the basic

elementary particles in nature, a theory which was discarded after we were

able to study the substructure of atoms. In the study of the formation of the

first atoms, it is very important for us to understand the basics of these

elementary particles, since it is their combination and recombination that

formed the first atoms and molecules.


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The standard model of particle physics includes in the elementary particles

the fermions (quarks, leptons and their antiparticles.) and the bosons

(including the gauge bosons and the Higgs boson.) Bosons are essentially

force carriers, or particles that give rise to forces through their exchange.

These are bundles of energy, or quanta, of a particular kind of field. For

example, for the electromagnetic field, we have photons.

Corresponding to most kind of particles, there are antiparticles with the same

mass with opposite electric charge. For example, there is an anti-electron, or

a positron, corresponding to an electron. The laws of nature are very nearly

symmetrical when it comes to particles and antiparticles. This leads to the

question that why, when the matter in the universe was formed, most of it

consisted of matter and not equally divided between matter and

antiparticles. This question was atleast partially resolved through the

discovery of Charge Parity symmetry violation. The Charge Parity symmetry

states that if a particle was swapped with its antiparticle (C symmetry), and

then the Parity was inverted, the laws of physics would stay the same. The

violation of the CP symmetry was discovered in 1964 in the decays of neutral

kaons (or K mesons).

Thus, the elementary particles we know as of now, consist of bosons and

fermions. Bosons being the primary force carriers while fermions, consisting

of quarks and leptons conjoining in various combinations to form a multitude

of observable particles.

The Standard Model of particle physics contains 12 flavors of

elementary fermions, plus their corresponding antiparticles, as well as

elementary bosons that mediate the forces and the Higgs boson, which was

reported on July 4, 2012, as having been likely detected by the two main

experiments at the LHC (ATLAS and CMS). However, the Standard Model is

widely considered to be a provisional theory rather than a truly fundamental
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one, since it is not known if it is compatible with Einstein's general relativity.

There may be hypothetical elementary particles not described by the

Standard Model, such as the graviton, the particle that would carry

the gravitational force, and sparticles, supersymmetric partners of the

ordinary particles.

The 12 fundamental fermionic flavours are divided into three generations offour particles each. Six of the particles are quarks. The remaining sixare leptons, three of which areneutrinos, and the remaining three of whichhave an electric charge of 1: the electron and its two cousins,the muon and the tau.

Isolated quarks and antiquarks have never been detected, a fact explainedby confinement. Every quark carries one of three color-charges of the stronginteraction; antiquarks similarly carry anticolor. Color-charged particlesinteract via gluon exchange in the same way that charged particles interactvia photon exchange. However, gluons are themselves color-charged,

resulting in an amplification of the strong force as color-charged particles areseparated. Unlike the electromagnetic force, which diminishes as chargedparticles separate, color-charged particles feel increasing force.

However, color-charged particles may combine to form colorneutral composite particles called hadrons. A quark may pair up with anantiquark: the quark has a color and the antiquark has the correspondinganticolor. The color and anticolor cancel out, forming a color neutral meson.Alternatively, three quarks can exist together, one quark being "red",another "blue", another "green". These three colored quarks together form acolor-neutral baryon. Symmetrically, three antiquarks with the colors

"antired", "antiblue" and "antigreen" can form a color-neutral antibaryon.Quarks also carry fractional electric charges, but, since they are confinedwithin hadrons whose charges are all integral, fractional charges have neverbeen isolated. Note that quarks have electric charges of either +2/3 or 1/3,whereas antiquarks have corresponding electric charges of either 2/3 or+1/3.

Evidence for the existence of quarks comes from deep inelastic scattering:firing electrons at nuclei to determine the distribution of chargewithin nucleons (which are baryons). If the charge is uniform, the electricfield around the proton should be uniform and the electron should scatterelastically. Low-energy electrons do scatter in this way, but, above a

particular energy, the protons deflect some electrons through large angles.The recoiling electron has much less energy and ajet of particles is emitted.This inelastic scattering suggests that the charge in the proton is not uniformbut split among smaller charged particles: quarks.

In the Standard Model, vector (spin-1) bosons (gluons, photons, and the W

and Z bosons) mediate forces, whereas the Higgs boson (spin-0) is

responsible for the intrinsic mass of particles. Bosons differ from fermions in
http://en.wikipedia.org/wiki/Albert_Einsteinhttp://en.wikipedia.org/wiki/General_relativityhttp://en.wikipedia.org/wiki/Gravitonhttp://en.wikipedia.org/wiki/Gravityhttp://en.wikipedia.org/wiki/Superpartnerhttp://en.wikipedia.org/wiki/Supersymmetryhttp://en.wikipedia.org/wiki/Generation_(particle_physics)http://en.wikipedia.org/wiki/Quarkshttp://en.wikipedia.org/wiki/Leptonshttp://en.wikipedia.org/wiki/Neutrinohttp://en.wikipedia.org/wiki/Muonhttp://en.wikipedia.org/wiki/Tau_(particle)http://en.wikipedia.org/wiki/Colour_confinementhttp://en.wikipedia.org/wiki/Color-chargehttp://en.wikipedia.org/wiki/Strong_interactionhttp://en.wikipedia.org/wiki/Strong_interactionhttp://en.wikipedia.org/wiki/Gluonhttp://en.wikipedia.org/wiki/Photonhttp://en.wikipedia.org/wiki/Electromagnetismhttp://en.wikipedia.org/wiki/Composite_particlehttp://en.wikipedia.org/wiki/Hadronhttp://en.wikipedia.org/wiki/Mesonhttp://en.wikipedia.org/wiki/Baryonhttp://en.wikipedia.org/wiki/Antibaryonhttp://en.wikipedia.org/wiki/Electric_chargehttp://en.wikipedia.org/wiki/Deep_inelastic_scatteringhttp://en.wikipedia.org/wiki/Electronhttp://en.wikipedia.org/wiki/Atomic_nucleushttp://en.wikipedia.org/wiki/Nucleonhttp://en.wikipedia.org/wiki/Electric_fieldhttp://en.wikipedia.org/wiki/Electric_fieldhttp://en.wikipedia.org/wiki/Jet_(particle_physics)http://en.wikipedia.org/wiki/Spin_(physics)http://en.wikipedia.org/wiki/Gluonhttp://en.wikipedia.org/wiki/Photonhttp://en.wikipedia.org/wiki/W_and_Z_bosonshttp://en.wikipedia.org/wiki/W_and_Z_bosonshttp://en.wikipedia.org/wiki/Higgs_bosonhttp://en.wikipedia.org/wiki/Masshttp://en.wikipedia.org/wiki/Albert_Einsteinhttp://en.wikipedia.org/wiki/General_relativityhttp://en.wikipedia.org/wiki/Gravitonhttp://en.wikipedia.org/wiki/Gravityhttp://en.wikipedia.org/wiki/Superpartnerhttp://en.wikipedia.org/wiki/Supersymmetryhttp://en.wikipedia.org/wiki/Generation_(particle_physics)http://en.wikipedia.org/wiki/Quarkshttp://en.wikipedia.org/wiki/Leptonshttp://en.wikipedia.org/wiki/Neutrinohttp://en.wikipedia.org/wiki/Muonhttp://en.wikipedia.org/wiki/Tau_(particle)http://en.wikipedia.org/wiki/Colour_confinementhttp://en.wikipedia.org/wiki/Color-chargehttp://en.wikipedia.org/wiki/Strong_interactionhttp://en.wikipedia.org/wiki/Strong_interactionhttp://en.wikipedia.org/wiki/Gluonhttp://en.wikipedia.org/wiki/Photonhttp://en.wikipedia.org/wiki/Electromagnetismhttp://en.wikipedia.org/wiki/Composite_particlehttp://en.wikipedia.org/wiki/Hadronhttp://en.wikipedia.org/wiki/Mesonhttp://en.wikipedia.org/wiki/Baryonhttp://en.wikipedia.org/wiki/Antibaryonhttp://en.wikipedia.org/wiki/Electric_chargehttp://en.wikipedia.org/wiki/Deep_inelastic_scatteringhttp://en.wikipedia.org/wiki/Electronhttp://en.wikipedia.org/wiki/Atomic_nucleushttp://en.wikipedia.org/wiki/Nucleonhttp://en.wikipedia.org/wiki/Electric_fieldhttp://en.wikipedia.org/wiki/Electric_fieldhttp://en.wikipedia.org/wiki/Jet_(particle_physics)http://en.wikipedia.org/wiki/Spin_(physics)http://en.wikipedia.org/wiki/Gluonhttp://en.wikipedia.org/wiki/Photonhttp://en.wikipedia.org/wiki/W_and_Z_bosonshttp://en.wikipedia.org/wiki/W_and_Z_bosonshttp://en.wikipedia.org/wiki/Higgs_bosonhttp://en.wikipedia.org/wiki/Mass


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the fact that multiple bosons can occupy the same quantum state(Pauli

exclusion principle). Also, Bosons can be either elementary, like photons, or a

combination, like mesons. The spin of bosons are integers instead of half

integers.
http://en.wikipedia.org/wiki/Mesonhttp://en.wikipedia.org/wiki/Meson


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Large Hadron Collider and the Higgs Boson

Large Hadron Collider, or the LHC is the worlds largest high energy particle

accelerator. It is built by the European Organization for Nuclear Research andspans a circumference of 27km, going as deep as 175 meters underground.

The LHC came under limelight last year with the discovery of the so called

God Particle, or the Higgs boson. The discovery was made in the ATLAS (A

large toroidal LHC apparatus) and corroborated by the CMS (Compact Muon

Solenoid)

The protons are accelerated in opposite directions in the Large Hadron

Collider, an underground accelerator ring 27 kilometres in circumference at

the CERN Laboratory in Geneva, Switzerland. Crashing together in the center

of ATLAS, the particles will produce tiny fireballs of primordial energy. LHC

recreates the conditions at the birth of the Universe -- 30 million times asecond. Relics of the early Universe not seen since the Universe cooled after

the Big Bang 14 billion years ago will spring fleetingly to life again. The LHC

is in effect a Big Bang Machine. ATLAS is a particle physics experiment at the

Large Hadron Collider at CERN. The ATLAS detector is searching for new

discoveries in the head-on collisions of protons of extraordinarily high energy.

ATLAS will learn about the basic forces that have shaped our Universe since

the beginning of time and that will determine its fate. Among the possible

unknowns are the origin of mass, extra dimensions of space, microscopic

black holes, and evidence for dark matter candidates in the Universe. ATLAS

is about 45 meters long, more than 25 meters high, and weighs about 7,000tons. It is about half as big as the Notre Dame Cathedral in Paris and weighs

the same as the Eiffel Tower or a hundred 747 jets.

Many particles produced in proton-proton collisions at the LHC are unstable

and decay almost instantaneously into other particles, which may

themselves decay further. Just as a vending machine might return the same

amount of change using different combinations of coins, a particle can decay

into different combinations of other particles. These sets of secondary

particles represent different decay channels. Detectors such as ATLAS and

CMS may not observe the original particles at all, but rather the detectable

collection of secondary particles from their decays that exists long enough tobe detected. This detectable collection of particle species is called the final

state. The Higgs particle, for example, is unstable and has many decay

channels, each having a certain probability to occur called the branching

ratio or branching fraction. The sum of all branching ratios is equal to 1. The

branching ratios of the Higgs boson depend on the mass of the Higgs boson

and are precisely predicted in the SM. For example, for a SM Higgs boson (H)


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of mass 125 GeV, the discovery decay channels HWW, HZZ, and H

have branching ratios ofB(HWW) = 0.14,B(HZZ) = 0.016, and B(H) =

0.0023. Other channels studied include decays to and +, which have

branching ratios and B(H+) = 0.064.

A quantity proportional to the probability for a specified reaction (such as the

creation of a new particle) to occur; for example, when the two proton beams

collide as in the LHC. The name reflects the origin of the concept in classical

mechanics (geometrical cross-sectional area of an object, which could be hit

by a beam), but in particle physics the probabilities are determined from

quantum mechanics. At the LHC, cross sections are typically expressed in

nanobarns (nb), picobarns (pb), and femtobarns (fb). One barn corresponds

to a cross-sectional area of 1028 m2. For example, the cross section for the

production of a SM Higgs boson of mass 125 GeV at the LHC in proton-proton

collisions at the center-of-mass energy of 7 TeV is about 15 pb: (ppH) = 15

pb = 15,000 fb. At the center-of-mass energy of 8 TeV, the cross section is

about 25% higher.

Instantaneous luminosity gives a measure of the rate of collisions

occurring in a particle collider, based on how intense the circulating beams of

particles are and how squeezed in space they are at the point of collision.

Although it does not mean that all those particles will collide, squeezing

more particles into a narrower space makes it more likely that they will.

Instantaneous luminosity is measured in units of cm2 s1. Integrated

luminosity is obtained by summing the product of a given time interval with

the instantaneous luminosity in that interval, over time: L = dt. Integratedluminosity L is often measured in a unit called inverse femtobarn (fb1 =

1039 cm2), which is equivalent to about 100 trillion (1014) proton-proton

collisions at the LHC. The number of events (N) produced in these collisions

for a given process is calculated as the product of the cross section for that

process multiplied by the integrated luminosity L (N = L). For example, for

a proton-proton collision run at 7 TeV resulting in an integrated luminosity

ofL = 1 fb1, the average number of SM Higgs bosons produced in the

process ppH followed by the decay H is N(H) = L (ppH)

B(H) = 1 fb1 15,000 fb 0.0023 = 34.5 (a dimensionless quantity

since fb1 cancels with fb). In a real experiment, the number of observed

events will fluctuate around the average value of 34.5, according to Poisson

statistics.

The impact of the Higgs Boson discovery is far reaching and epoch making.

The Higgs field is a giant vat of molasses spread throughout the universe.

Most of the known types of particles that travel through it stick to the

molasses, which slows them down and makes them heavier. The Higgs boson


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is a particle that helps transmit the mass-giving Higgs force field, similar to

the way a photon transmits the electromagnetic field. Without the Higgs

boson, or something like it, giving mass to the basic building blocks of

matter, electrons would zip about at the speed of light. They would not form

unions with protons or other would-be nuclei to make atoms. Thus, we would

not exist, if not for the Higgs boson.

The Big Bang sent massless particles and radiation energy zooming

throughout the universe. It has been theorized that fractions of a second

later, part of the radiation energy congealed into the Higgs field. When the

universe began to cool, particles acquired mass from the Higgs field, slowed

down and began to bunch up to form composite particles and eventually

atoms. Thus, the discovery and confirmation of the existence of the Higgs

boson, is the confirmation of this theory, which tells us that the physics we

are working on right now is in the right direction.

Conclusion

The first atoms and molecules formed in the early universe were a direct

result of the formation of elementary particles and the interaction of theforces between them. The early universe formed through the Big Bang and

cooled down to a temperature conducive to the formation of elementary

particles and the separation of forces in a matter of a fraction of a second.

The elementary particles and the subsequent basic hydrogen atom were

born through the processes of baryogenesis and big bang nucleosynthesis.

Further complex atoms were formed through the recombination of these

atoms.

We also studied the importance of the recent developments in physics due to

the discovery of the Higgs boson because the formation of Higgs boson in

laboratory conditions is the answer to the question- how were the first

particles formed. This answer helps in solving one of the most important

riddles in nuclear physics about the formation of matter.

Thus, we studied the intricacies involved in the formation of the first atoms

and molecules in the early universe.


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AMS Project

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Transcript of AMS Project