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Higgs boson

27 Apr

I promise I’ll get back to writing real posts some time soon. For now, check out this fun explanation of the Higgs boson by phd comics.


Faster-than-light neutrinos no longer faster than light

22 Feb

The possibly faster-than-light neutrinos that everyone was so excited about may have been the result of a loose cable on an atomic clock. That’s embarrassing.

Symmetry violations and the standard model

28 Nov

The theory that governs the elementary particles (see this post) and the forces that affect them (see this post) is called the Standard Model. The Standard Model calls for some degree of symmetry in the Universe. There should be spacial symmetry called parity and symmetry under charge conjugation, meaning that the laws of physics should stay the same if you put a negative sign in the charge or change the right- or left-handedness of the system. Violations of these symmetries are called C-P violations (C for charge and P for parity).

Part of the symmetry called for by the Standard Model is that particles and antiparticles should have similar decay rates. Recent findings from the LHCb show that this may not be the case for charm quarks and antiquarks. It is an early result, but it is exciting. The LHCb is the part of the LHC that detects mesons, a particle that contains a heavy quark (strange, charm, top or bottom). The “b” stands for “beauty” which is another name for the bottom quark.

We’re particularly interested in the symmetry of particle and antiparticle decay rates, because it pertains to one of the big questions in physics: Why is it that there is so much more matter than antimatter in the Universe? When matter and its corresponding antimatter come into contact, they annihilate one another. So it makes sense that there is an abundance of one and not the other. Eventually one or the other would win out if there are to be large, stable structures, but why did matter win? Is there something fundamentally different about matter that made it win the cosmic fight for dominance in the Universe? This discrepancy between charm quark and antiquark decay rates may shed some light on this question some day.

LHCb announcement here.

The Force(s of nature)

23 Nov

There are four fundamental forces in the Universe (and love is not one of them). They are: gravity, the electromagnetic force, the strong force and the weak force. Gravity and electromagnetism you are probably familiar with. Gravity is actually the weakest of the four forces (which is a good thing for us). The force of gravity is so weak that it is negligible when we’re talking about particles. But gravity does have the furthest range of all the forces.

The electromagnetic force is the second strongest force, and acts with the second longest range. The electromagnetic force is much, much stronger than gravity. The electromagnetic force between our atoms is what keeps us from falling down through the floor straight to the center of the earth.

The strong force is sometimes called the “strong nuclear force” or the “strong nuclear interaction,” and is responsible for holding protons and neutrons together in the nucleus, and quarks together to form hadrons. It is the strongest of the four forces, but acts at very short distances.

The weak force, sometimes called the “weak interaction,” is the weakest force except for gravity, and it acts on a very short range. The weak force is responsible for radioactive decay.

I bet you’re wondering why we call some of these forces “interactions.” Good question! It turns out that at least three (and probably all four) of these forces are actually the result of an exchange of particles. Each fundamental force has a corresponding boson (sometimes called a “gauge boson”) that is the carrier of that force. For the electromagnetic force, it is a photon. When two particles with electromagnetic charge interact, they exchange discreet amounts of energy in the form of photons. The gluon is the carrier particle for the strong force, and the weak force is carried by W and Z bosons. It has not been discovered yet, but we suspect there exists a “graviton” that is the carrier particle for gravity.

The theory about the fundamental forces, their carrier particles, and how they all act on the particles that make up matter, is called the “Standard Model.” It works remarkably well in describing how the world works. There is a strange sort of similarity between the weak and electromagnetic forces that hints at further connections between the fundamental forces. And there is an overall symmetry that is kind of beautiful about the Standard Model. Gravity, however, is the fly in the ointment. Gravity isn’t part of the Standard Model and we don’t understand how it fits in with the other forces. Luckily, gravity is a large-scale force and is negligible at the small scale of the other forces, so its absence isn’t felt too strongly.

So there you have it. We live in a strange world where everything that ever acts on anything else does so by exchanging energy in the form of these crazy little particles.

Elementary particle crash course

22 Nov

We used to think atoms were the smallest things in the universe and that they couldn’t be divided up into smaller parts. Then we learned that protons, neutrons and electrons are what atoms are made up of. Quarks are what protons and neutrons are made up of.

Quarks are elementary particles. There are six different flavors of quark: up, down, charm, strange, top and bottom (hey, we needed to call them something). Quarks have properties like mass, charge and spin. Up and down quarks have the smallest masses of the quarks, and they are the most stable, abundant quarks in the universe. The other, larger mass quarks decay into up and down quarks. We have only observed these other quarks (charm, strange, top and bottom) in high energy collisions. As with most elementary particles, there are antimatter equivalents of quarks called antiquarks. Antimatter isn’t as mysterious as it sounds. Antiquarks have all the same properties of quarks, except that some of the properties are reversed (meaning they have the opposite sign).

Quarks combine to form hadrons, which are held together by the strong force (insert Star Wars reference here). Hadrons made up of three quarks are called baryons, and hadrons made out of one quark and one antiquark are called mesons. Protons and neutrons are both baryons. A proton is made up of two up quarks and one down quark. A neutron is two down and one up.

Leptons are another type of elementary particle. Electrons, muons and tau particles, along with their corresponding neutrinos, make up the six types of leptons. Together, leptons and quarks are the building blocks for all matter, and what we usually think of when we say “elementary particles.”

Phew. So now you know exactly what a hadron is. It’s time to talk LHC. The Large Hadron Collider is a big machine that collides hadrons (either protons or lead ions), and the world’s largest at that. At full power, protons race around the enormous circular pathway at 99.9999991% of the speed of light. Two of these beams travel in opposite directions around the path and then collide. These high energy collisions are the only place to look for some of these elementary particles, as well as some elementary particles that are predicted to exist but we haven’t found yet (*cough* Higgs boson). These collisions are also the only way to get a glimpse at the kind of conditions that existed in our Universe during those first critical moments of the big bang.

More LHC fun facts here.

Einstein ain’t gonna be happy about this

23 Sep

Nothing can travel faster than the speed of light, c. In fact, nothing with mass can even reach the speed of light. It is the “universal speed limit.” We’ve been saying it for decades. It is one of the main tenets of relativity, a theory which has had a lot of evidence to support it and has not yet been truly called into question. Well, the speed of light as a universal speed limit is being called into question now.

First of all, you need to know about neutrinos. Neutrinos are electrically neutral subatomic particles. They are weakly interacting, which means that they can go through matter without hitting or interacting with anything. In fact, a cascade of neutrinos is raining down on you right now from the cosmos, through the atmosphere, through buildings, through you. Neutrinos were first observed in 1970 at Argonne National Laboratory (See photo at right of the world’s first neutrino observation. A neutrino collides with a proton and creates the three particle paths shown: a proton [short path], a mu-mason [long path] and a pi-mason). We call neutrinos “massless” because they were originally thought to be so, but the truth is that they have been proven to have some mass (because they undergo flavor oscillations–yes, that’s a thing), though very little.

A group of scientists called the OPERA collaboration have taken measurements indicating faster-than-light travel of neutrinos. It has scientists all atwitter. I, for one, can’t stop thinking about the possible implications of such a result. Of course, we all need to take a deep breath because much is yet to be seen. The OPERA scientists themselves are, wisely, being extremely cautious. Particle physics experiments are extremely complicated. This experiment involves using a proton beam at CERN to create the neutrinos and sending them hundreds of miles to an underground detector at Gran Sasso Laboratory. There are many data-altering factors to account for. That isn’t to say that scientists are being in any way careless. They have certainly been very meticulous in their experiment, collaborated with many scientists, reproduced the results in several experiments over three years and used a very large statistical data set. These neutrinos are much higher energy than the ones we study from supernovae, which might explain why we haven’t encountered this phenomenon before… except that there was no energy dependence in their results. There is another team of scientists that claims to have produced greater-than-c velocity measurements for neutrinos, but that they didn’t take the results seriously because they seemed so improbable.

There are many doubts. But it is clear that the OPERA scientists have put a lot of thought and effort into discovering any glitch that could be affecting their results, which is the right thing to do in any experiment, much more so one with results as paradigm-shifting as these. The fact that they feel confident enough to announce it and put a paper out is enough to get everyone thinking. There will be much research done in the future to corroborate or dispute these findings. Only time and billions of dollars of research will tell.

If the findings turn out to be sound, the next step will be discovering theory to explain why neutrinos can travel faster than the speed of light. The only thing I can even think of is that the neutrinos somehow shortcut through extra-planar dimensions, which may not be as far-fetched as it sounds. Mother nature is pretty crazy sometimes.

Watch the webcast presenting the results.

Half-life longer than the universe is old

19 Sep

Unstable elements spontaneously decay, or break down, into other elements. Matter-energy is always conserved, meaning that if what you have left after the decay has a total mass that is less than the mass you started with, then energy has to be released in some other form. But there it is–systems like to be in the lowest-energy state available to them, and that means that particles decay.

The word today is two-neutrino double-beta decay (2nubb). It is a very rare form of particle decay. It is when two neutrons decay into two protons, two electrons, and two antineutrinos (the anti-matter form of a massless particle called a neutrino).

Scientists recently observed this process in Xenon-136, a radioactive isotope of the element Xenon (Xe fluorescence shown above). To be an isotope of Xenon means that it has the same number of protons as Xenon, but a differing number of neutrons. According to their measurements, the half-life of 2nubb decay is 2.11 x 1021 years. That means that it will take 2.11 x 1021 years for half of a sample to undergo this decay. That is 100 billion times longer than the universe has existed (13.75 billion years). This is probably the slowest process ever detected. Pretty cool.

Read more here.