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Tim B.

Particle Adventure Reading: How do we know any of this?

To test theories, physicists put together experiments and use what they already know to find out what they do not know.

Up until 1909 - atoms= mushy, semi- permeable balls, with bits of charge strewn around them.

1909 – Rutherford experiment – Shot positive alpha particles at gold foil. Some of the alpha particles bounced off in different directions. Concluded that there must be small, dense, and positively charged objects, nuclei, in the gold foil

Now almost all particle physics experiments today use the same basic elements that Rutherford did: a beam, a target, and a detector

BaBar Experiment Summary

To find the half life of the KO particle

1. Divide L/V (L=Lenght particle travels, V=velocity of the particle)to get the time the particle takes to decay

2. Find gamma of the particle for special relativity

3. Divide the time calcuated in step 1 by the gamma from step 2 to get the time of decay from the particle's point of view

BaBar Histogram

Excel spreadsheet results

Cosmic Rays

The point of this lab was to show the correlation between solar events and surface radio disturbances.

Solar Winds

5.a. The events in the graph of the whole year appear to be periodic. The rise and fall rapidly and there appears to be a similar distance between each peak. On the graph with the shorter time frame, the events don’t appear to be periodic. The distances between the peaks appear to be quite different.

5.b. The peaks of the year long graph appear to be about the same size, but the peaks in the short term graph do not appear to be the same size.

5.c. on January 21, 2007 there was a sunspot. This event corresponded with a high proton speed and a large He++ to H + ratio. So we can assume that the sunspot causes a peak in the proton speed and He++ to H + ratio.

Radio Waves

January 14

January 23

Because the radio waves travel at the speed of light, they get to earth much faster than the solar winds. This means that the events on the ACE graphs will look similar to the radio wave graph except the bursts on the ACE graph occur after the radio wave bursts. The burst in the radio wave graph seen on January 14 reaches the earth in solar winds on January 21. The burst that the radio waves pick up on January 23 is seen in the solar wind on January 29. Based in this trend in take the solar wind about 7 more days to reach the earth than the radio waves. This trend makes sense because the radio waves travel at the speed of light compared to the 400 Km/Sec that the solar winds travel at.

Will H.

Particle Adventure Reading: Other Points of Interest

There could be more than three physical dimensions that are so small that we cannot perceive them.

Antimatter

Antimatter? What is this, Star Trek?

All types of particles that we know have corresponding antiparticles. Antiparticles appear and act like their corresponding particles, except they have opposite charges. For example, a proton is charged positively while an antiproton is negative. The corresponding particles have the same mass and react the same way to gravity. When matter and antimatter collide, they form pure energy.

Antimatter seems to go against everything we know about the universe. The following is a "bubble chamber." The magnetic field affects the matter and antimatter differently. If you notice the two highlighted curls, the positron particles curl to the right while the electron particles curl to the left. This is antimatter and matter.

The usual symbol for an antiparticle is a bar over the corresponding particle symbol. For example, the "up quark" u has an "up antiquark" designated by , pronounced hUUUUe-bar.

Antimatter is said to be the most expensive substance in existence, with an estimated cost of $300 billion per milligram. That's a lot of antidollars!

History

In 1932, soon after Paul Dirac's prediction of positrons, Carl D. Anderson found that cosmic-ray collisions produced positrons in a cloud chamber, which is a particle detector in which moving electrons (or positrons) leave behind trails as they move through the gas.

Originally, positrons, because of the direction that their paths curled, (as shown in the previous visual) were mistaken for electrons traveling in the opposite direction.

The antiproton and antineutron were found by Emilio Segrè and Owen Chamberlain in 1955 at the UC Berkeley.

Bubble Chamber Lab

Lets Get Quantitative

In the Bubble Chamber momentum appeared to not be conserved by a significant amount. However momentum was conserved. Possible reasons for the appearance are that a neutral particle that we couldn't detect and/or the third particle fell off in the z-direction. The actual numbers were: Momentum started at {-3.788MeV/c, -7.766MeV/c} and ended at {-2.513MeV/c, -4.52MeV/c}.

Nelly K.

Particle Adventure Reading: What is Fundamental?

WHAT IS FUNDAMENTAL Protons and neutrons are composed of quarks. Quarks and the electron are fundamental and are less than 10E-18 m in diameter. 99.99999999999% of atom is empty space. STANDARD MODEL THEORY: The fundamental particles are 6 quarks, 6 antiquarks, 6 leptons, 6 antileptons, and force carrier particles When a matter particle and antimatter particle meet, they annihilate into pure energy!

BUBBLE CHAMBER A bubble chamber is filled with protons. Momentum varies with radius: low momentum particles curve about a circle with a small radius and high momentum particles curve about a circle with a large radius Particles leave tracks due to their charges, so there are gaps in the tracks when only neutral particles pass through those areas. However, neutral particles can decay to form charged particles that are detected by a magnetic field. So, charge and momenta can be calculated from the tracks

The Fireworks of Elementary Particle Physics There are two types of quarks: up quarks (charge of +2/3) and down quarks (charge of -1/3) The composite particles that consist of quarks (such as neutron and proton) are called hadrons Protons: 2 up quarks and 1 down quark; neutron: 2 down quarks and 1 up quark.

Electromagnetic residual charge: between neutral atoms, electrons and protons of different atoms

Strong residual charges: charge that holds nucleus together; overcomes repulsive electromagnetic force

Weak interactions are responsible for the decay of massive quarks and leptons into lighter quarks and leptons.

The Generations of Elementary Particles The structure of matter requires only 4 structural units: the up quark, the down quark, the electron, and the neutrino. Neutrino: electrically neutral particle that is essentially massless; by-product of neutron decay; along with electrons, they are called leptons. Leptons: electron, electron neutrino, muon, muon neutrino, tau, tau neutrino Quarks: Up, down, charm, strange, top, bottom Because every particle has an antiparticle, there are antileptons and antiquarks: 24, not 12, particles

FermiLab Accelerators: More powerful than any microscope, a high-energy accelerator allows physicists to study the smallest things human beings have ever seen, for example the quarks inside a proton. By creating tiny fireballs of high density and high temperature, physicists can recreate the conditions of the early universe (one-trillionth of a second after the Big Bang). In 1995, high-energy collisions of the Tevatron (the world's most powerful accelerator) led to the discovery on the top quark --the heaviest fundamental particle (as heavy as gold atom).

Collider Experiments: Physicists can count particles, identify their tracks, measure their energy, record their time of flight and distinguish one particle from another by using particle detectors that can take snapshots of particle collisions every second. By analyzing the stored data from the CDF and Dzero detectors, physicists make discoveries about the fundamental nature of matter and energy.

Technology: High-energy physicists rely on four essential scientific tools: powerful accelerators to create high-energy particle collisions, superconducting magnets with advanced materials and design to guide particle beams, sophisticated particle detectors with superfast readout technology to observe and record particle collisions, innovative computing solutions to store, access and analyze huge quantities of data.

Discoveries at FermiLab: top quark, bottom quark, mass of top quark and W boson, lifetime of charm particles, first direct evidence of tau neutrino, mapping structure of protons and neutrons using neutrino beams, and measurement of magnetic moments of particles containing strange quarks, among others.

Electrons J.J. Thompson believed that cathode rays could be separated from the charge within them. 1897, he measured deflections of cathode rays in magnetic field and electrical field. He discovered corpuscles using cathode rays. In 1903, he created plumb pudding model, in which thousands of tiny, negative corpuscles swarmed inside a cloud of massless, positive charge. Rutherford corrected him. Cathode rays are negatively charged. Electron: best known lepton, stable, APPLICATIONS: electronics, electron microscopes, radiation therapy.

Heavy Leptons: Muon and Tau Before they were discovered, they only knew about the electron. 1936 Carl Anderson discovered muons while studying cosmic radiation. more mass=more energy=unstable. Between 1975 and 1977, Martin Lewis Perl detected the tau lepton using a colliding ring, called SPEAR, and the LBL magnetic detector. Heavy leptons are not found in matter because as soon as they are produced, they decay (into corresponding neutrino and other particles). Muon: radiography. Tau: used in electrical currents.

Neutron Before the neutron, we thought atom had a positively charged nucleus with protons and electrons. Rutherford theorized neutron's existence in 1920. James Chadwick actually discovered it in 1932 by bombarding hydrogen beryllium, helium, and nitrogen in cloud chamber. Compared the energies of hugely varying recoiling charged particles from different targets (particle must have mass equal to proton). Constituents: Baryons, Strong force (gluons). Neutron decay: outside the nucleus-unstable; caused by the weak force; decays to proton, electron, and antielectron neutrino. Current research: Neutron scattering-penetrative neutron radiation used to study complex solids: inelastic-involves nucleus excitation, elastic does not

X Rays: Electromagnetic Radiation Non ionizing: thermal radiation, radio waves, microwave radiation, visible light. IONIZING: X rays, gamma rays, UV rays. Discovered in 1895 by Wilhelm Rontgen by researching cathode rays in vacuum tube and he accidentally placed cardboard covered in fluorescent mineral near the experiment, and the cardboard glowed in the presence of cathode rays. Showed mysterious x rays could penetrate though body. transparency of material based on thickness. Becquerel's experiment: studied fluorescence, found photographic plates were exposed in presence of some metal ores. current applications: diagnostic x rays, x ray crystallography, astronomy, microscopic analysis, and fluorescence.

Power of Protons Rutherford disclaimed the plum pudding model of the atom by discovering that there was a dense center in atom. He discovered the nucleus. 1918, he shot alpha particles into nitrogen, and he detected hydrogen nuclei, deducing that nitrogen must contain hydrogen nuclei (hydrogen must be contained in all atoms: proton). Proton: 2 up quarks and 1 down quark. Because they are stable and massive, they are used in particle colliders.

Planck's Constant: The Photoelectric Effect Before Planck's discoveries, light was considered a continuous electromagnetic wave, thought strength of light = strength of protons (but it = strength of photons)1900: Max Planck - Measure energy emitted as photons. Greater intensity of light means that more photons hit per second and more electrons are ejected (but does not mean more energy). E = hv (v = frequency). Color of light (frequency) determines its energy.

Unstable Heavy Baryons Baryon: 3 quarks held together by gluons. Different masses. Not all are stable. Protons and neutrons are stable baryons. Unstable heavy baryons: lambda, omega, xi, delta, sigma; over 120 types of baryons. Proton discovered in 1919. Antiproton discovered in 1955. Lambda in 1947. Xi in 1964. Omega in 1964. The big experiment that led to the classification of baryon was the discovery of the antiproton. momentum and magnetism used to isolate antiprotons. Different decay schemes. Current research: Pentaquarks (exotic baryons), avg. lifespan is 10^-20 seconds.

Antimatter 1932: Paul Dirac's prediction of positrons; 1955: antiproton and antineutron. Positron discovered in a bubble chamber (moving in opposite direction from electron). Act exactly like matter, but just have opposite charges. antimatter + matter = pure energy. Possible uses: huge amount of energy, warp drive?, impractical because antimatter costs $300 billion per milligram.

Top Quark Discovered bottom quark in 1977, so predicted existence of top quark. Collided proton and antiproton, and a new particle was released which decayed rapidly--discovered in Fermi Lab in 1995. Top quark: 3rd generation up quark. spin 1/2. charge 2/3. mass: very high (strange that a fundamental particle is so massive-mass of gold nucleus) 170.9 GeV. Decays into W boson and bottom quark. Current Experiment: CDF and DZero: 3 major questions: how does top quark interact with other particles? why is it 100,000 times heavier than lightest quark? what was its role in the early universe?

Higgs Boson Hasn't been discovered yet. Postulated by Peter Higgs in 1864 to explain how electromagnetic and weak forces interact. theorized in 1967 by Weinberg and Salam. Photons and W and Z bosons have such different masses that something seems to be missing. Physical particles moving through Higgs field create distortion in the field, which lends mass to the particle. H = higgs force. If H is large, field is strong. if H is small, field is weak. Assumptions: Higgs field is zero for high energy and nonzero for low energy. Current experiments at FermiLab and CERN.

Up and Down Quarks Postulated by Murray Gel-Mann in 1964. Discovered in 1980 by Jacob and Lanshoff. up quark-lightest charge 2/3. down quark: 2nd lightest charge -1/3. these 2 quarks make up most matter. ALICE: a Large Ion Collider Experiment at CERN, hope that protons and neutrons will melt and free the quarks from their bonds.

The Gluon discovered in 1979 with a positron accelerator. question, why doesn't the nucleus separate apart if protons repel each other? Because, gluons hold quarks together, thus holding protons together (overcomes electromagnetic force). red, green, blue. gluons carry a color and anticolor. quarks found as hadrons. quarks color must change to conserve color. residual strong interaction: keeps nucleus from exploding. NY: testing existence of quark-gluon plasma.

W and Z bosons Bosons were discovered by Carlo Rubbia and van der Meer in CERN's biggest accelerator. they live for about 3E-25 sec. almost 100 times the mass of a proton. W+ and W- bosons are the mediators of the weak nuclear force: cause beta decay. Z bosons are its own antiparticle (has no charge, 0 for all quantum numbers).

Strange Quarks Charge of -1/3. they occur as components of K mesons. 1947: a product of proton collision with a nucleus was found to live for much longer time than expected: the property which caused it to live so long was dubbed "strangeness." conservation of strangeness (of strangeness quantum number = -1) heavier than up and down quarks. although they interact through strong force, it can only decay by conversion to a different quark through weak interaction. Experiments: Armstrong at Jefferson Lab used electron scattering to examine the impact of strange quarks on the shape of the proton. International scientists at Brookhaven used a particle accelerator in 1991. Make Kaon mesons, which are sensitive to the strong force and have equal numbers of quarks and antiquarks. 1947: confirmation of existence of mesons

Bottom Quarks Discovered in 1977 by Leon Lederman in FermiLab. charge -1/3. mass of 5GeV/c^2. avg lifespan 10^-12 sec. 3rd generation quark. B meson, Bc meson, Bs meson, Upsilon meson, and bottom baryons are baryons that contain bottom quark. Current research: BaBar (Stanford) and Belle (Japan) experiments to prove that antiparticle and particle do not decay at same rate (CP violation)

Cosmic Rays Made of nuclei of collider atoms like hydrogen. travel at nearly the speed of light. what kinds: Galactic CRs (accelerated from supernovae), solar energy particles (nuclei and electrons), very high energy cosmic rays (collide with atoms in Earth's atmosphere: create pions to muons, neutrinos, and CRs to electrons and positrons), anomalous cosmic rays (electrically neutral but they ionize), ultrahigh cosmic rays (speculated to come from distant stretches of universe, very powerful). Discovered in 1912 by Victor Hess with electroscope and hot air balloon (the higher up he went, the more the electroscope would go off-radiation must be coming from above). 1930s: electrically charged. They are important in finding the existence of muons and positrons. Modern day cosmic rays: chemical changes, lightning, cloud formations, computer chip, airline cancer, trying to find how so much energy can be squeezed into a single particle (like the proton), astronomical research

Photons Before, they though light energy was just a wave. 1900 Planck said light energy proportional to wave frequency: hv. 1905 Einstein said photoeffect depended not on intensity, but on frequency. E=hv. 1923: Arthur Compton shot x-rays at electrons; the angle changed, so the wavelength and energy changed. light is a collection of particles that obeyed the laws of momentum (but it has no rest mass; since it has high energy, it is never at rest). photons is used in quantum computers (to increase power and speed), molecular distances

Radioactive decay results

The average half life calculated from these results was 13.657 steps. The lowest was 12.667 steps and the highest was 14.525 steps. By using the histogram and the equation, m = Σnibi/N, where m equals mean value, ni equals the frequency, and bi equals the midpoint of each bin, the mean value of the lifetime was found. Since the mean value is a weighted sum (similar to center of mass), the weighting is the number of counts; multiply this value by the midpoint of each bin; sum up these products and divide by the total number of counts. Bin size was 0.25. Mean value = 246.25/18 = 13.681 steps

To calculate standard deviation from the mean, the formula s = SQRT [(Σ(xi - m)2)/N], where m is the mean of N measurements xi. In other words, subtract each measurement from the mean and square the difference. Add the squares, divide by the number of measurements, and take the square root. Standard deviation from mean = 0.502

Vail

Particle Adventure Reading: What Holds the Universe Together?

There are four fundamental interactions between particles that cause all forces.

What is the difference between force and interaction?

A force is the effect on a particle due to the presence of other particles. The interactions of a particle include all the forces that affect it, including decays and annihilations. Particles that carry interactions are called force carrier particles.

How do matter particles interact?

How can two objects affect one another without touching? What we normally think of as forces are actually the effects of force carrier particles on matter particles. A matter particle affected by that particular force absorbs or produces that force’s carrier particle. For instance, electrons and protons have electric charge, so they can produce and absorb the photon, which carries electromagnetic charge. Neutrinos have no electric charge, so they cannot absorb or produce photons. If a particle absorbs or produces a force carrier particle, the particle itself is affected.

What is the electromagnetic force?

Electromagnetic force causes like-charged things to repel and oppositely-charged things to attract. Friction and magnetism are caused by the electromagnetic force. For instance, the force that keeps you from falling through the floor is the electromagnetic force that causes the atoms in your feet and the floor to resist displacement. The carrier particle of the electromagnetic force is the photon. Photons of different energies span the electromagnetic spectrum of x-rays, visible light, radio waves, and so forth. Photons have zero mass and always travel at the speed of light, even in a vacuum.

How do atoms form molecules?

Charged parts of one atom interact with the charged parts of another atom to bind them together, an effect called the residual electromagnetic force.

What binds the nucleus together?

Why doesn’t the repulsion force of protons cause the nucleus to blow apart? Quarks have electromagnetic charge and an unrelated charge called color charge. The force between color-charged particles is very strong, so it is called “strong.” In short, they don't call it the strong force for nothing. The strong force between the quarks in one proton and the quarks in another proton is strong enough to overwhelm the repulsive electromagnetic force. This is called the residual strong interaction, and it is what "glues" the nucleus together. Carrier particles: gluons

What are quarks and leptons?

There are six kinds of quarks and six kinds of leptons. But all the stable matter of the universe appears to be made of the two least-massive quarks (up quark and down quark), the least-massive charged lepton (the electron), and the neutrinos.

What are weak interactions?

Weak interactions are responsible for the decay of massive quarks and leptons into lighter quarks and leptons. When fundamental particles decay, the particle vanishes and is replaced by two or more different particles. Although the total of mass and energy is conserved, some of the original particle's mass is converted into kinetic energy, and the resulting particles always have less mass than the original particle that decayed.

The only matter around us that is stable is made up of the smallest quarks and leptons, which cannot decay any further. When a quark or lepton changes type due to the weak interaction, it is said to change flavor.

The carrier particles of the weak interactions are the W+, W-, and the Z particles. The W's are electrically charged and the Z is neutral. The Standard Model has united electromagnetic interactions and weak interactions into one unified interaction called electroweak. The weak and electromagnetic forces have essentially equal strengths. This is because the strengths of each interaction depend strongly on both the mass of the force carrier and the distance of the interaction. The difference between their observed strengths is due to the huge difference in mass between the W and Z particles, which are very massive, and the photon, which has no mass as far as we know.

How does gravity factor in to the situation?

Gravity is one of the fundamental interactions, but the gravity force carrier particle has not been found. Such a particle, however, is predicted to exist and may someday be found: the graviton. 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.

What is quantum physics?

One of the surprises of modern science is that atoms and sub-atomic particles do not behave like anything we see in the everyday world. They are not small balls that bounce around; they have wave properties. The Standard Model theory can mathematically describe all the characteristics and interactions that we see for these particles, but our everyday intuition will not help us on that tiny scale. Physicists use the word "quantum," which means "broken into increments or parcels," to describe the physics of very small particles.

How do we define particles?

We can use these quantum particle properties to categorize the particles we find.

Electric charge: Quarks may have 2/3 or 1/3 electron charges, but they only form composite particles with integer electric charge. All particles other than quarks have integer multiples of the electron's charge.

Color charge: A quark carries one of three color charges and a gluon carries one of eight color-anticolor charges. All other particles are color neutral.

Flavor: Flavor distinguishes quarks (and leptons) from one another.

Spin: Large objects like planets or marbles may have angular momentum and a magnetic field because they spin. Since particles also to appear have their own angular momentum and tiny magnetic moments, physicists called this particle property spin. This is a misleading term since particles are not actually "spinning."

What is the Pauli Exclusion Principle?

At one time, the predominant school of thought followed the Pauli Principle that no two particles in the same quantum state could exist in the same place at the same time. But it has been since discovered that a certain group of particles do not obey this principle. Particles that do obey the Pauli Exclusion Principle are called fermions, and those that do not are called bosons.

Lab: On-Screen Particle Physics

2. The event is multicolored. When the track changes color, a new particle is formed. a. Neutral to negative curved red, straighter blue to yellow indicates larger momentum. b. Large neutral to positive large curved red, negative slightly curved blue to more curved yellow. c. Neutral to positive curved red and negative slightly curved blue to more curved yellow. d. Initial particle to two neutrals. One neutral to curved positive yellow and negative curved red. Second neutral splits into two oppositely charged particles with very short tracks.

3. R = (a^2 + b^2) / 2a = ((111.9 cm)^2 + (254.6 cm)^2) / (2 ∙ 111.9 cm) = 345.589 cm

4.

Pt = 0.3 ∙ B ∙ R = 0.3 ∙ 0.5 kG ∙ 345.589 cm = 51.838 MeV Pz = (0.3 ∙ B ∙ L) / 2π = (0.3 ∙ 0.5 kG ∙ 200 cm) / 2π = 4.775 MeV The particle has a negative charge. M0 = (p^2 - k^2) / 2k P = sqrt(Pt^2 + Pz^2) = sqrt(51.838^2 + 4.775^2) = 52.057 MeV M0 = ((52.057 kG ∙ cm)^2 - (30 MeV)^2) / (2 ∙ 30 Mev) = 30.166 MeV/c^2

5.

R = (a^2 + b^2) / 2a = ((135.9 cm)^2 + (227.5 cm)^2) / (2 ∙ 135.9 cm) = 258.37 cm Pt = 0.3 ∙ B ∙ R = 0.3 ∙ 0.8 kG ∙ 258.37 cm = 62.008 MeV Pz = (0.3 ∙ B ∙ L)/ 2π = (0.3 ∙ 0.8 kG ∙ 17.5 cm) / 2π = 0.668 MeV

6.

The type 1 and type 2 injected particles are not identical. As the axis rotates, the event decay can be witnessed from various different perspectives at a range of angles. In the type 2 event, the red positive particle changes into positive yellow. This event shows a positive charge, which differentiates it from type 1. Additionally, though it is a subtle difference, the type 2 event curves around a tighter radius than its counterpart.

7.

The injected particle is a short-lived neutral particle. Before two oppositely charged tracks are formed, the remaining empty space at the edge of bubble chamber is extremely short.

Blue: negative pt = 0.3(1.0 kG)(r)

r = (a^2 + b^2)/2a= 284.748

pt = 85.424 MeV/c

pz = 0.3Bl/2PI= 12.653 MeV

p = SQRT (85.424^2 + 12.653^2)= 86.356 MeV

M0 = (p^2 - k^2)/2k

M0 = -242.543 MeV/c^2

Red: positive pt = 0.3(1.0 kG)(r)

r = (a^2 + b^2)/2a = 2838.325 cm

pt = 851.498 MeV

pz= 0.3Bl/2PI= 0.716 MeV

p = SQRT (851.498^2 + 0.716^2)= = 851.498 MeV

M0 = (p^2 - k^2)/2k

M0 = 475.049 MeV/c^2

Because the M0 values are different, the pair does not split energy evenly. The total rest mass cannot be determined because one rest mass quantity was negative, which indicates the presence of undetectable neutral particles. To find the lifetime, use the following equation:

Once the value of v is determined, divide the distance that the original neutral particle traveled, .275 m, by v to get the lifetime in seconds.

8.

Because we don’t have a lifetime, we cannot compare the value to the meson and baryon tables.

Hannah S.

Particle Adventure Reading: What is the world made of?

For every kind of matter there is an antimatter/antiparticle. Antimatter act the same as their corresponding matter, but have opposite charges. Gravity effects antimatter and matter the same way b/c gravity is not charged. When anti and matter meet they become pure energy. Electrons and Positrons come from photons splitting (they curl in different ways). Types of Quarks: Ups, Charms, and Tops charge:(2/3), Downs Stranges, and Bottoms charge: (-1/3). Quarks never exist alone, but they exist in groups called hadrons. Baryons: three quarks, Mesons: One quark, one antiquark. There are three charged and three uncharged Leptons. Charged: Electrons, muons, taus. Uncharged: neutrinos. Leptons decay into other smaller other leptons or quarks. lepton families: the electron and its neutrino, the muon and its neutrino, and the tau and its neutrino. Neutrino's tiny mass but huge numbers may contribute to total mass of the universe and affect its expansion.

Bubble Chamber Lab

How do we see subatomic particles?

1. The tracks are curved, not straight.

2. Yes there is different curvature and this may represent the size, charge, or momentum of the particles. Oppositely charged particles curve in opposite directions, particles with low momentum curve with a small radius, and particles with high momentum curve with a large radius.

3. The particles don't leave a trail if it is not charged.

4. The track fades out if the a charged particle decays to produce a neutral particle, loses so much energy it stops, or is traveling on the z-plane.

5. Two tracks spontaneously appear when a neutral particle breaks into two equal and oppositely charged particles.

6. The corkscrews represent either a collision of two particles or the breaking off of a particle. The tighter the corkscrew the slower the particle is moving and the lower the momentum.

7. Yes, there is evidence of collisions: the corkscrews, the disappearances of tracks, and the opposite curved tracks due to negative charge (since the chamber is initially filled only with positive protons).

Curving Tracks

The external force of a bubble chamber is a magnetic field. Positive particles curve counterclockwise. Negative particles curve clockwise. Less curving means more momentum (p=.3Br).

Isaac Z.

Particle Adventure Reading: How do we experiment with tiny particles?

All particles behave like waves. If you increase the speed of a particle, you decrease the wavelength. Particle accelerators work by accelerating particle using magnetic fields (read Coulombs Force). To obtain particles to be used for acceleration, we can ionize hydrogen for protons, we can heat metal for electrons (same principle that allows old monitors and old TVs to work). To gain antiparticles, you fire an energetic particle at a target, then an antiparticle/particle pair is created. You can then separate the pair with a magnetic field (They have opposite charges, remember?). Here is an animation that is the easiest way to understand a particle accelerator:

Types of Collisions There are two ways to collide particles with an accelerator. You can shot the particles at a fixed target or you can cross two particle beams to create collisions between particles.

Types of Accelerators Linear Accelerators feed particles in one end and accelerate them out the other. Synchrotrons are built in a circle instead of a line.

Fixed Target Elements One target of particle accelerators is a fixed element. Instead of another beam of particles, the fixed element is placed in the path of the accelerated particle beam. Fixed elements can be solids, liquids, or gases, but they must be stationary. Advantage: controlled environment, for precision experiments, and for searches for and studies of rare phenomena. Rutherford's Gold Foil experiment is an example of a fixed target experiment. He accelerated alpha particles at the gold foil and monitored the foil.

Particle Beam Elements

Particle beam experiments are more interesting because they produce more massive particles. These experiments involve two accelerated beams. Since, there is much more momentum involved, there is much more mass/energy involved in the collisions. Remember, velocities don't add normally, so use the velocity composition formula instead.

Linear Accelerators vs. Circular Accelerators Linear Accelerators are used for fixed target experiments or as extraction paths for circular accelerators when the circular accelerator is being use for a fixed target experiment.

Fermilab's circular accelerator.

BaBar Experiment Summary

We learned that to compute the half life of a neutrally charged unstable particle, you need the length of the track of the particle and the speed of the particle. If you are given neither, you can calculate the momentum of the particle by adding up the momenta of all the visible particles and performing some additional momentum calculations (which I won't go into here). Once you have the speed of the particle, you can calculate its gamma factor. You will also be able to calculate the time in the inertial reference frame using the velocity of the particle. Once you have the gamma factor and the time in an inertial reference frame, you can calculate the dilated time as experienced by the particle. It is this dilated time that represents the half life of the particle. To get a good feel for the actual half life of the particle, you should calculate this time for several different experiments and calculate a histogram.

Z Boson Experiment Summary

In the Z Boson experiment, the components of the particles' momentum were calculated using the angle of the track of the particle and the vector of momentum. Pt cos @ = Px, and Pt sin @ = Py. Once the components of momentum were calculated for both particles, the vectors were added and the "missing" momentum was calculated (negative sum of the components). Then the magnitudes of both particles and the missing particles were calculated. These magnitudes were added together to get the total momentum, which equaled the total energy and mass of the Z boson. The values were compiled into a histogram. Once a 6th order fit was created, there were two peaks in the 88 GeV range. This suggests that the Z Boson has a mass in the 88 GeV range. Excel spreadsheet results

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