Pentaquarks: An Exotic Particle Discovered by LHC

CERN announced the discovery of the “pentaquark” — a collection of five quarks bound together to form an exotic state of matter, a particle that has been theorized for some time but other experiments have had a hard time nailing down a true detection.

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The pentaquark is not just any new particle, It represents a way to aggregate quarks, namely the fundamental constituents of ordinary protons and neutrons, in a pattern that has never been observed before in over fifty years of experimental searches. Studying its properties may allow us to understand better how ordinary matter, the protons and neutrons from which we’re all made, is constituted.

Quarks are the subatomic constituents of regular particles, called hadrons. Hadrons come in two varieties, baryons (which contain 3 quarks) and mesons (which contain 2 quarks). Protons and neutrons are baryons where, for example, a proton is composed of 2 “up” quarks and 1 “down” quark; a neutron has 2 “down” quarks and 1 “up” quark.

But in the 1960′s, theorists realized that the Standard Model also allows the formation of 5 quarks in the same particle, known as a pentaquark. But experimental searches for this elusive 5-quark particle kept drawing blanks and any vaguely positive detection was quickly shot down by follow-up experiments.

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Now, a strong signal in the LHCb detector has led to the pentaquark’s discovery. LHCb physicists examined the decay of a baryon known as Lambda b (Λb) into 3 other particles, the J-psi (J/ψ-), a proton and a charged kaon. By using the highly sensitive detector to characterize the masses of these decay products, the physicists were able to see that intermediate states were sometimes involved in their production. They named these intermediate states Pc(4450)+ and Pc(4380)+ and indicate that pentaquarks are at play.

In a nutshell, the physicists noticed a signal emerge from the post-collision noise of particles. This signal, or “excess,” indicated the creation of J/ψ-, protons and kaon in quantities predicted by theories surrounding subatomic decay processes that involve pentaquarks. The decay particles acted as a “fingerprint” of sorts.

“More precisely the states must be formed of two ‘up’ quarks, one ‘down’ quark, one ‘charm’ quark and one ‘anti-charm’ quark.”

Computer model of a baryon and meson bonded to form an alternate form of the 5-quark pentaquark.

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Although their decay signatures have been found, there’s still some ambiguity as to their configuration. Are the quarks all bound together as a 5-quark particle? Or is there a 3-quark particle (baryon) and a 2-quark particle (meson) interacting together to form a 5-quark “molecule”?

“The quarks could be tightly bound,” said Liming Zhang, LHCb physicist from Tsinghua University, “or they could be loosely bound in a sort of meson-baryon molecule, in which the meson and baryon feel a residual strong force similar to the one binding protons and neutrons to form nuclei.”

For now, the pentaquark’s configuration isn’t exactly known, but what is known is that it exists, and the newly-upgraded LHC will continue to examine its signal, revealing more detail behind the nature of this elusive particle.

Source: http://news.discovery.com/  JUL 14, 2015

SOME INTERESTING DISCOVERIES IN PHYSICS

10. Time Stops at the Speed of Light

According to Einstein’s Theory of Special Relativity, the speed of light can never change—it’s always stuck at approximately 300,000,000 meters/second, no matter who’s observing it. This in itself is incredible enough, given that nothing can move faster than light, but it’s still very theoretical. The really cool part of Special Relativity is an idea called time dilation, which states that the faster you go, the slower time passes for you relative to your surroundings. Seriously—if you go take a ride in your car for an hour, you will have aged ever-so-slightly less than if you had just sat at home on the computer. The extra nanoseconds you get out of it might not be worth the price of gas, but hey, it’s an option.

Of course, time can only slow down so much, and the formula works out so that if you’re moving at the speed of light, time isn’t moving at all. Now, before you go out and try some get-immortal-quick scheme, just note that moving at the speed of light isn’t actually possible, unless you happen to be made of light. Technically speaking, moving that fast would require an infinite amount of energy.

9. Quantum Entanglement

Quantum mechanics, in essence, is the study of physics at a microscopic scale, such as the behavior of subatomic particles. These types of particles are impossibly small, but very important, as they form the building blocks for everything in the universe. Let leave the technical details aside for now (it gets pretty complicated), but you can picture them as tiny, spinning, electrically-charged marbles.

So say we have two electrons (a subatomic particle with a negative charge). Quantum entanglement is a special process that involves pairing up these particles in such a way that they become identical (marbles with the same spin and charge). When this happens, things get weird—because from now on, these electrons stay identical. This means that if you change one of them—say, spin it in the other direction—its twin reacts in exactly the same way instantly. No matter where it is, without you even touching it. The implications of this process are huge—it means that information (in this case, the direction of spin) can essentially be teleported anywhere in the universe.

8. Light is affected by Gravity

But let’s get back to light for a minute, and talk about the Theory of General Relativity this time (also by Einstein). This one involves an idea called light deflection, which is exactly what it sounds like—the path of a beam of light is not entirely straight.

Strange as that sounds, it’s been proved repeatedly (Einstein even got a parade thrown in his honor for properly predicting it). What it means is that, even though light doesn’t have any mass, its path is affected by things that do—such as the sun. So if a beam of light from, say, a far off star passes close enough to the sun, it will actually bend slightly around it. The effect on an observer—such as us—is that we see the star in a different spot of sky than it’s actually located (much like fish in a lake are never in the spot they appear to be). Remember that the next time you look up at the stars—it could all just be a trick of the light.

7. Dark Matter

Thanks to some of the theories we’ve already discussed (plus a whole lot we haven’t), physicists have some pretty accurate ways of measuring the total mass present in the universe. They also have some pretty accurate ways of measuring the total mass we can observe, and here’s the twist—the two numbers don’t match up.

In fact, the amount of total mass in the universe is vastly greater than the total mass we can actually account for. Physicists were forced to come up with an explanation for this, and the leading theory right now involves dark matter—a mysterious substance that emits no light and accounts for approximately 95% of the mass in the universe. While it hasn’t been formally proved to exist (because we can’t see it), dark matter is supported by a ton of evidence, and has to exist in some form or another in order to explain the universe.

6. Our Universe is Rapidly Expanding

Here’s where things get a little trippy, and to understand why, we have to go back to the Big Bang Theory. The Big Bang Theory was an important explanation for the origin of our universe. In the simplest analogy possible, it worked kind of like this: the universe started as an explosion. Debris (planets, stars, etc) was flung around in all directions, driven by the enormous energy of the blast. Because all of this debris is so heavy, and thus affected by the gravity of everything behind it, we would expect this explosion to slow down after a while.

It doesn’t. In fact, the expansion of our universe is actually getting faster over time, which is as crazy as if you threw a baseball that kept getting faster and faster instead of falling back to the ground. This means, in effect, that space is always growing. The only way to explain this is with dark matter, or, more accurately, dark energy, which is the driving force behind this cosmic acceleration. So what in the world is dark energy, you ask? Well, that’s another interesting thing…

5. All Matter is Just Energy

It’s true—matter and energy are just two sides of the same coin. In fact, you’ve known this your whole life, if you’ve ever heard of the formula E = mc^2. The E is for energy, and the m represents mass. The amount of energy contained in a particular amount of mass is determined by the conversion factor c squared, where c represents speed of light.

The explanation for this phenomenon is really quite fascinating, and it has to do with the fact that the mass of an object increases as it approaches the speed of light (even as time is slowing down). For proof (unfortunately), look no further than atomic bombs, which convert very small amounts of matter into very large amounts of energy.

4. Wave-Particle Duality

Speaking of things that are other things…

At first glance, particles (such as an electron) and waves (such as light) couldn’t be more different. One is a solid chunk of matter, and the other is a radiating beam of energy, kind of. It’s apples and oranges. But as it turns out, things like light and electrons can’t really be confined to one state of existence—they act as both particles and waves, depending on who’s looking.

No, seriously it sounds ridiculous (and it’ll sound even crazier when we get to Number 1), but there’s concrete evidence that proves light is a wave, and other concrete evidence that proves light is a particle (ditto for electrons). It’s just both at the same time. Not some sort of intermediary state between the two, mind you—physically both, in the sense that it can be either.

3. All Objects Fall at the Same Speed

You would be forgiven for assuming that heavier objects fall faster than lighter ones—it sounds like common sense, and besides, you know for a fact that a bowling ball drops more quickly than a feather. And this is true, but it has nothing to do with gravity—the only reason this occurs is because the earth’s atmosphere provides resistance. In reality, as Galileo first realized about 400 years ago, gravity works the same on all objects, regardless of their mass. What this means is that if you repeated the feather/bowling ball experiment on the moon (which has no atmosphere), they would hit the ground at the exact same time.

2. Quantum Foam

The thing about empty space, you’d think, is that it’s empty. That sounds like a pretty safe assumption—it’s in the name, after all. But the universe, it happens, is too restless to put up with that, which is why particles are constantly popping into and out of existence all over the place. They’re called virtual particles, but make no mistake—they’re real, and proven. They exist for only a fraction of a second, which is long enough to break some fundamental laws of physics but quick enough that this doesn’t actually matter (like if you stole something from a store, but put it back on the shelf half a second later). Scientists have called this phenomenon ‘quantum foam,’ because apparently it reminded them of the shifting bubbles in the head of a soft drink.

1. The Double Slit Experiment

So remember a few entries ago, we discussed everything was both a wave and a particle at the same time. But here’s the other thing—you know from experience that things have definite forms—an apple in your hand is an apple, not some weird apple-wave thing. So what, then, causes something to definitively become a particle or a wave?

The double slit experiment is the most motivating thing and it works like this—scientists set up a screen with two slits in front of a wall, and shot a beam of light through the slits so they could see where it hit on the wall. Traditionally, with light being a wave, it would exhibit something called a diffraction pattern, and you would see a band of light spread across the wall. That’s the default—if you set up the experiment right now, that’s what you would see.

But that’s not how particles would react to a double slit—they would just go straight through to create two lines on the wall that match up with the slits. And if light is a particle, why doesn’t it exhibit this property instead of a diffraction pattern? The answer is that it does—but only if we want it to see as a wave, light travels through both slits at the same time, but as a particle, it can only travel through one. So if we want it to act like a particle, all we have to do is set up a tool to measure exactly which slit each bit of light (called a photon) goes through.

Think of it like a camera—if it takes a picture of each photon as it passes through a single slit, then that photon can’t have passed through both slits, and thus it can’t be a wave. As a result, the interference pattern on the wall won’t appear—the two lines will instead. Light will have acted as a particle merely because we put a camera in front of it. We physically change the outcome just by measuring it.

SOURCE: listverse.com

CATCHING A BULLET

The following curious incident was reported during the First World War. One French pilot, while flying at an altitude of 2 kilometers, saw what he took to be a fly near his face. Trapping it with his hands, he was astonished to find that he had caught a German bullet! How like the tall stories told by Baron Munchausen of legendary fame, who claimed he had caught cannon balls with bare hands! But there is nothing incredible in the bullet-catching story.

A bullet does not fly everlastingly with its initial velocity of 800-900 m/sec. Air resistance causes it to slow down gradually to a mere 40 m/sec towards the end of its journey. Since aircraft fly with a similar speed, we can easily have a situation when bullet and plane will be flying with the same speed, in which case the bullet, in its relation to the plane and its pilot, will be stationary or barely moving. The pilot can easily catch it with his hand, especially if gloved, because a bullet heats up considerably while whizzing through the air.

Source: Physics for Entertainment by Y. Perelman.