particles physics


LHC swings back into action


|By Sarah Charley

Protons are colliding once again in the Large Hadron Collider.

This morning at CERN, operators nudged two high-energy beams of protons into a collision course inside the world’s largest and most energetic particle accelerator, the Large Hadron Collider. These first stable beams inside the LHC since the extended winter shutdown usher in another season of particle hunting.

The LHC’s 2017 run is scheduled to last until December 10. The improvements made during the winter break will ensure that scientists can continue to search for new physics and study rare subatomic phenomena. The machine exploits Albert Einstein’s principle that energy and matter are equivalent and enables physicists to transform ordinary protons into the rare massive particles that existed when our universe was still in its infancy.

“Every time the protons collide, it’s like panning for gold,” says Richard Ruiz, a theorist at Durham University. “That’s why we need so much data. It’s very rare that the LHC produces something interesting like a Higgs boson, the subatomic equivalent of a huge gold nugget. We need to find lots of these rare particles so that we can measure their properties and be confident in our results.”

During the LHC’s four-month winter shutdown, engineers replaced one of its main dipole magnets and carried out essential upgrades and maintenance work. Meanwhile, the LHC experiments installed new hardware and revamped their detectors. Over the last several weeks, scientists and engineers have been performing the final checks and preparations for the first “stable beams” collisions.

“There’s no switch for the LHC that instantly turns it on,” says Guy Crockford, an LHC operator. “It’s a long process, and even if it’s all working perfectly, we still need to check and calibrate everything. There’s a lot of power stored in the beam and it can easily damage the machine if we’re not careful.”

In preparation for data-taking, the LHC operations team first did a cold checkout of the circuits and systems without beam and then performed a series of dress rehearsals with only a handful of protons racing around the machine.

“We set up the machine with low intensity beams that are safe enough that we could relax the safety interlocks and make all the necessary tweaks and adjustments,” Crockford says. “We then deliberately made the proton beams unstable to check that all the loose particles were caught cleanly. It’s a long and painstaking process, but we need complete confidence in our settings before ramping up the beam intensity to levels that could easily do damage to the machine.”

The LHC started collisions for physics with only three proton bunches per beam. Over the course of the next month, the operations team will gradually increase the number of proton bunches until they have 2760 per beam. The higher proton intensity greatly increases the rate of collisions, enabling the experiments to collect valuable data at a much faster rate.

“We’re always trying to improve the machine and increase the number of collisions we deliver to the experiments,” Crockford says. “It’s a personal challenge to do a little better every year.”


Nuclear Physics Might Hold The Key To Cracking Open The Standard Model

“Interestingly, this could also lead to a renewed interest in the search for glueballs, which would be the first ever direct evidence of a bound state of gluons in nature! If the exotic QCD predictions of tetraquarks and pentaquarks are borne out in our Universe, it stands to reason that glueballs should be there as well. Perhaps the existence of these composite particles will be verified at the LHC as well, with incredible implications for how our Universe works either way.”

Nuclear physics has, for decades now, been regarded less as a window into fundamental physics and more of a derived science. As we’ve discovered that nuclei, baryons, and mesons are all composite particles made out of quarks, antiquarks, and gluons, though, we’ve realized that there are other possible combinations that nature allows, that should exist. In recent years, we’ve discovered tetraquark and pentaquark states of quarks and antiquarks, and yet there should be even more. QCD, our theory of the strong interactions, predicts that a set of exotic states of bound gluons – known as a glueball – should exist. Finding them, or proving that they don’t exist, might be a way to crack open the Standard Model in an entirely new way.

Nuclear physics might, after all these years, hold the key to going beyond the current limitations of physics.


Physicist Create a Fluid With Negative Mass

Physicists from Washington State university have created a liquid with negative mass meaning that when you push it, instead of accelerating in that direction, it accelerates backwards.

Matter can have a negative mass much the same way that particles can be negatively charged. Newton’s second law of motion (F=ma) tells us that mass will accelerate in the direction of the force so we can deduce that matter with a negative mass would do the opposite and accelerate against the force.

To create the conditions for negative mass, Peter Engels and his team started by cooling rubidium atoms to a Bose-Einstein condensate meaning they reached very near absolute 0. The researchers used lasers to trap the atoms in an area less than 100 microns across and allow high energy particles to escape cooling them further. Then to create negative mass, the physicists applied a second set of lasers to change the way atoms spin back and forth. They then removed the first set of lasers causing the rubidium to rush out and appear to hit some sort of invisible wall; behaving as if it had a negative mass.

What’s great about this is the control we have over the negative mass without any other complications. This gives us a new tool we can use to engineer experiments in astrophysics looking at neutron stars, black holes, dark energy and a lot more.


L: It’s just a particle physics text.

K: So?

L: You’ll find it very dull.

K: But I like it when you read to me.

Listening to sweet/sad music… drawing sweet things.


A little more on Quantum Entanglement and Teleportation

Fundamental particles all have a quantum state called spin. Quantum entanglement means that if one particle has a spin of up, then its partner will have a spin of down and any change in the quantum state of one particle will alter the spin of the other.

Everything in the universe is made up of the fundamental quantum bits and that allows us to view everything as a collection of information stored in qubits. We are not entirely sure how quantum teleportation works but it could be some sort quantum tunnel that opens allowing the quit to bypass spacetime. Multiple experiments have been done demonstrating that the electronic state of an atom can be transferred from one place to another instantaneously.

Why space dust emits radio waves upon crashing into a spacecraft

When spacecraft and satellites travel through space they encounter tiny, fast moving particles of space dust and debris. If the particle travels fast enough, its impact appears to create electromagnetic radiation (in the form of radio waves) that can damage or even disable the craft’s electronic systems.

A new study published this week in the journal Physics of Plasmas, from AIP Publishing, uses computer simulations to show that the cloud of plasma generated from the particle’s impact is responsible for creating the damaging electromagnetic pulse. They show that as the plasma expands into the surrounding vacuum, the ions and electrons travel at different speeds and separate in a way that creates radio frequency emissions.

Keep reading


Heisenberg’s Astrophysics Prediction Finally Confirmed After 80 Years

“Heisenberg and Euler made this prediction all the way back in 1936, and it’s gone completely untested until now. Thanks to this pulsar, we have confirmation that light polarized in the same direction as the magnetic field has its propagation affected by quantum physics, in exact agreement with the predictions from quantum electrodynamics. A theoretical prediction from 80 years ago adds another feather in the cap of Heisenberg, who can now posthumously add “astrophysicist” to his resume.”

Empty space, according to quantum mechanics, isn’t exactly empty. Take away all the matter, radiation and anything else you can have populating your space, and you’ll still have some amount of energy in there: the zero-point energy of the Universe. One consequence of quantum electrodynamics is that this sea of virtual particles is always present, and a strong magnetic field can lead to some really bizarre behavior. Known as vacuum birefringence, it was theorized by Werner Heisenberg and Hans Euler more than 80 years ago, as these electron/positron pairs get yanked along the magnetic field lines. In theory, this should polarize the light from photons passing through fields that are strong enough, but we’ve never been able to observe it. Until now. Thanks to the VLT and light from a neutron star, the prediction is confirmed for the very first time.

Come learn the incredible science 80 years in the making, and how we’re poised to learn even more about this fascinating property of light and empty space moving forward!


Excitation of atom by photon

Electron excitation is the transfer of a bound electron to a more energetic, but still bound state. This can be done by photoexcitation (PE), where the electron absorbs a photon and gains all its energy or by electrical excitation (EE), where the electron receives energy from another, energetic electron.

When an excited electron falls back to a state of lower energy, it undergoes electron relaxation. This is accompanied by the emission of a photon (radiative relaxation) or by a transfer of energy to another particle. The energy released is equal to the difference in energy levels between the electron energy states.


Superfluid Helium

It was previously thought that superfluid Helium would flow continuously without losing kinetic energy. Mathematicians at Newcastle University demonstrated that this is only the case on a surface completely smooth down to the scale of nanometers; and no surface is that smooth.

When a regular fluid like water is passing over a surface, friction creates a boundary layer that ‘sticks’ to surfaces. Just like a regular fluid, when superfluid Helium passes over a rough surface there is a boundary layer created. However the cause is very different. As superfluid Helium flows past a rough surface, mini tornados are created which tangle up and stick together creating a slow-moving boundary layer between the free-moving fluid and the surface. This lack of viscosity is one of the key features that define what a superfluid is and now we know why it still loses kinetic energy when passing over a rough surface.

Now we can use this information to help our efforts on applications of superfluids in precision measurement devices such as gyroscopes (I think this was on the Big Bang theory where they make a gyroscope using superfluid Helium that can maintain angular momentum indefinitely because it would flow across a smooth surface without losing kinetic energy) and as coolants.


Ask Ethan: What’s The Difference Between A Fermion And A Boson?

“Could you explain the difference between fermions and bosons? What differs from an integer spin and a half-integer spin?”

On the surface, it shouldn’t appear to make all that much difference to the Universe whether a particle has a spin in half-integer intervals (±1/2, ±3/2, ±5/2) or in integer intervals (0, ±1, ±2). The former is what defines fermions, while the latter defines bosons. This hardly seems like an important distinction, since intrinsic angular momentum is such a nebulous property to our intuitions, unlike, say, mass or electric charge. Yet this simple, minor difference carries with it two incredible consequences: one for the existence of distinct particles for antimatter and one for the Pauli exclusion principle, that are required for matter as we know it to be. Without these differences, and without these rules, it’s simply a matter of fact that the atoms, molecules and living things we see today wouldn’t be possible to create.

What’s the difference between fermions and bosons? A little difference goes a long way! Find out on this edition of Ask Ethan. (And thanks to the anonymous tumblr question that inspired it!)