Tag: LHC


By Phil Plait | July 4, 2012 3:10 am

Scientists using the Large Hadron Collider in Geneva have announced the discovery of a new subatomic particle to very high confidence that is consistent with what we expect the Higgs particle to look like.


This plot shows the discovery as seen in one of the LHC detectors. Hang tight, and I’ll explain it!

OK, the quick version. The Higgs particle is extremely important, because the Standard Model of particle physics – the basic idea of how all particles behave – predicts it exists and is what (indirectly) gives many other particles mass. In other words, the reason electrons, protons, and neutrons have mass is because of this Higgs beastie. Last year, the Guardian put up a nice article explaining this. A more technical discussion is on Discover Magazine’s Cosmic Variance blog from 2007. Sean Carroll has been live-blogging the announcement, and has lots of good info as well.

This particle is very hard to detect, because it doesn’t live long. Once it forms it decays in a burst of energy and other particles (think of them as shrapnel) extremely rapidly. The only way to make them is to smash other particles together at incredibly high energies, and look at the resulting collisions. If the Higgs exists, then it will decay and give off a characteristic bit of energy. The problem is, lots of things give off that much energy, so you have to see the Higgs signal on top of all that noise.

So, you have to collide particles over and over again, countless times, to build up that tiny signal from the Higgs decay. The more you do it, the bigger the signal gets, and the more confident you can be that the detection is real. I described all this in detail last December, when preliminary results from LHC were announced. I strongly urge you to read that first!

Back now? Good. So last year, an excess signal was seen at an energy around 125 GeV – that’s a unit of energy physicists use, and it also indicates the mass of the particle decaying. Because energy and mass are interchangeable at some level, detecting the energy emitted when a particle decays tells you its mass.

A proton has a mass of about 1 GeV, so this excess found is about 125 times that much. Last year’s results were tantalizing, but the strength of the signal only led to a confidence level of about 90% that it was real. Nice, but not enough to claim a discovery.

Today that all changed. Two different detectors at the LHC both independently found a strong signal between 125 and 126 GeV at about the 5 sigma level – that means they can claim a 99.9999% confidence this signal is real! This means they found a previously undiscovered particle which, as it happens, is within the range of mass the Standard Model predicts for the Higgs particle! That’s what that plot above shows: a bump in the energies detected, and it’s seen so strongly that it can be called a discovery.

That’s huge.

Now technically, that’s all the physicists can say: the particle is definitely there. But is it the Higgs? Well, to be fair, they can’t actually say that. But if it walks like a Higgs, looks like a Higgs, and quacks like a Higgs… yeah.

So there you have it. A new fundamental particle has been found, and if it’s the Higgs – which it really really really looks like it is – is the first step to our truly understanding such basic concepts as mass and gravity in the Universe. It’s technical, and it’s complicated, and it’s the result of a vast amount of time, money, and effort by thousands upon thousands of people… but it’s real.

And it’s only the first step. There’s much work to be done. But oh, what a step. The Universe has once again done something wonderful — let us peek behind the curtain and get a glimpse of its inner workings.

Never forget this either: we humans did this. The discovery of this new particle, and the vast potential it has, was all because we’re curious. This huge machine, the LHC, was built solely because we wanted to find things out, and some people had the vision to fund it and build it. When we wish to explore, when we wish to see what’s over the next hill, wonders unfold before us.

All we have to do is want it enough.

Image credit: CERN

Related Posts:

- Mass effect: Maybe Higgs, maybe not
- Europe: Day 3 — CERN! The LHC!
- Brian Cox calls ‘em like he sees ‘em
- LHC smacks some phrotons (with video I took when I visited the LHC in 2008)

MORE ABOUT: Higgs, LHC, particles

Mass effect: Maybe Higgs, maybe not

By Phil Plait | December 13, 2011 9:29 am

Today, scientists at CERN in Geneva announced their results for their search for the Higgs boson, a subatomic particle that, if it exists, is thought to be responsible for giving other particles mass. It’s no exaggeration to call it a keystone in quantum mechanics, and finding it for sure will be a huge accomplishment for particle physicists.

So, did they find it?

Maybe. Then again, maybe not.

Um, what? OK, this’ll take a wee bit of explaining.

Last things first

I said Higgs, Magnum. HIGGS.

First, the conclusion, so at least you have that in mind as you read the rest. There are two experiments running at CERN looking for the Higgs particle. They don’t smash particles together, look around with magnifying glasses and tweezers, and then yell “AHA!” when they find one. Instead, they build up a picture of it after doing gazillions of particle collisions. After a year of runs, both experiments see something that might be Higgs, but they’re not 100% sure. One sees something at about the 94% confidence level, the other at 98%. That’s pretty good, but it’s not enough to be completely sure. It seems likely they’ve found something, but it’s like a fuzzy picture: it looks like Higgs, but it still might be something else.

So why can’t they be sure one way or another?

CSI: Geneva

Basically, what the Large Hadron Collider at CERN does is whip protons around at nearly the speed of light, then smashes them into each other. At that speed they have huge energies, and when they collide that energy gets converted into matter: other particles. Like shrapnel, these new particles explode away from the collision site. Many of these new particles aren’t stable; they decay into yet lower energy particles after incredibly short time intervals. For example, electron and protons are almost certainly stable over long times (like the lifetime of the Universe), but neutrons decay after only a few minutes, turning into a proton, and electron, and a particle called an antineutrino.

So these daughter particles from the proton collisions in LHC decay, and they have daughter particles, and some of those decay, and so on. At the LHC there are two ginormous detectors called ATLAS and CMS. Both of these, in essence, measure the energy of the particles that hit them; like forensics team, they look at the aftermath of the collision and try to work backwards to figure out what happened.

We know to some extent how much energy is expected from these collisions due to all the particles that are currently known, so those can be accounted for. But if there’s some excess of energy, that could very well indicate a new particle. And we have theories as to how much energy the Higgs particle should have. So the energies are measured, calibrated for known particles, and the excesses are examined.

What both experiments found is an excess of energy — a bump in the graph — indicating a particle that has an energy* about 125 times that of a proton — right in the expected range for the Higgs particle. That’s exciting! But what they’re doing is counting up things statistically, so they can’t be 100% sure. The bump in the graph is still fuzzy.

Read More

CATEGORIZED UNDER: Cool stuff, Science, Top Post
MORE ABOUT: ATLAS, CERN, CMS, Higgs, Higgs boson, LHC

Don't cross the LHC stream!

By Phil Plait | September 21, 2010 7:05 am

There are a lot of questions in science that seem simple, but in fact lead to profound concepts. Why is the sky dark at night? Why does gravity pull me down? Why is the Sun hot?

And some questions seem silly and frivolous, but it turns out are really hard to answer, and in fact scientists might disagree on the answer. Case in point: what happens if you put your hand in the beam of the Large Hadron Collider?

So the folks at Sixty Symbols asked this of several scientists, and the first four minutes of this video are the result:

Fantastic! I love how different scientists think of different angles on this, and come up with different answers. Clearly, they hadn’t really thought about this before, so as they realize various aspects of this the answer changes.

It’s complicated! You have to think about the energy of the beam, of course, but also the energy of a given proton as it moves at 99.9999% the speed of light. But that number doesn’t mean anything if the proton doesn’t actually interact with the matter in your hand, so you have to consider the "cross-section" of the atoms in your hand. Think of it this way: if you shoot a gun at a target, you make a hole. But if you shoot a gun at a fishing net, it might pass right through. Most of the area of a fishing net is holes! The nuclei of atoms are very small compared to the atoms themselves, so in a sense most of you is empty space.

And there’s more. Read More

CATEGORIZED UNDER: Cool stuff, Science, Top Post
MORE ABOUT: LHC, protons, Sixty Symbols

LHC smacks some protons!

By Phil Plait | March 30, 2010 10:30 am

After more than a decade of triumph, setbacks, and much sturm and drang, the Large Hadron Collider made history last night by taking two beams of protons and smashing them head on at just a whisper under the speed of light.


The LHC is the world’s largest physics experiment, and is attempting to recreate conditions in the Universe when it was only a fraction of a second old. At that point, pressures and temperatures were so high that the laws of physics were somewhat different than we’re used to. These conditions are extremely difficult to duplicate, which is why it’s taken so long to get the LHC running. The collider uses extremely powerful magnets to guide and accelerate two beams of protons to nearly the speed of light. They go around the collider in opposite directions, then are tweaked to smack into each other. The huge energies of the collision create particles and conditions that can be detected and used to test theories of how the Universe behaves.

There were some minor glitches before the protons could be injected into the main collider last night, but once things got going, the beams were sent at each other at full power. The energies were ramped up to 3 TeV, or three trillion electron volts (a unit of energy).

Now, 3 TeV is not much energy in human terms. It’s roughly the amount of energy of a single mosquito in flight. But for a single proton, 3 TeV is huge, vast, incredible, brobdingnagian, ginormous! When the two proton beams are at full power, they contain the same kinetic energy as a battleship moving at several kph! So we’re talking about powerful events, indeed.

I visited CERN and the LHC a couple of years ago, and wrote up my thoughts. I was of the opinion then, and still am now, that this will be a revolution in physics.

I made a video of that tour, too.

My congratulations to the hordes of people who made this moment possible. It has been a long, difficult journey indeed, but now the real voyage is underway. May the wild physics rumpus begin!

CATEGORIZED UNDER: Cool stuff, Science

Get your mass handed to you

By Phil Plait | December 26, 2009 12:00 pm

If you want to lose weight, then you should avoid this Ebay auction, where someone has a Higgs boson up for bids.


The Higgs boson, for those not up on their Standard Model of Particle Physics, is the subatomic particle that is theoretically responsible for giving all the other little particles their mass, and its detection is one of the main goals of the Large Hadron Collider. Come to think of it, the folks at CERN could’ve saved a lot of cash had they simply bid here instead of building a bazillion dollar machine to look for the Higgs. But then how would Brian Cox find work?

And I love that graphic. 10? That’s a big number. You’d think magnifying the Higgs by that amount would make it look bigger.

Anyway, read the whole thing, because it’s pretty funny. Of course, this is a joke, and Ebay will no doubt take it down soon, so look before it’s gone and you’re doomed to travel the Universe forever with your mass kicked.

Tip o’ the spin 1/2 lepton to BABloggee Martin Kielty.


LHC update: it's now all-powerful

By Phil Plait | December 1, 2009 7:24 am

bigpicture_cmsOops! Sorry. I mean "most" powerful. Particle accelerator, that is. On November 30, 2009, it accelerated two beams of protons moving in opposite directions each to an energy of 1.18 TeV – that’s trillion electron volts, well above the previous record of 0.98 TeV. When it’s all ready to go, the LHC will get those beams up to 7 TeV, high enough — we hope — to start doing some serious science, and giving investigators a chance to see how the Universe ticks.

For those who are curious, an energy of 1.18 TeV is about 1.9 ergs, which seems like a ridiculously small energy. An erg is very roughly the amount of kinetic energy a falling raindrop has… but a raindrop has a lot of protons in it. In the case of the LHC, each proton in the beams will have that much energy!

Putting it another way, the speed of the protons moving in the beams when they are juiced up to 7 TeV is 99.999999% of the speed of light. They could travel to the Moon in just over one second. It took the Apollo astronauts more than three days to cover the same distance. The total energy in the beams, as my friend Brian Cox points out, is equivalent to a battleship moving at several miles per hour.

And that’s just before the protons smash together. The collisions will be epic.

So this is yet another milestone on the way to real and cutting-edge science, which is slated to begin in early 2010. Stay tuned!

CATEGORIZED UNDER: Cool stuff, Science
MORE ABOUT: LHC, protons

LHC sees its first collisions!

By Phil Plait | November 23, 2009 3:13 pm

Edited to add: My Hive Overmind compatriots at Cosmic Variance have more details.]

lhc_1stcollision_atlasHey, is the Earth still here? Because the Large Hadron Collider saw its first proton collisions today!

OK, it wasn’t at full power, and this is just a preliminary test, but still: It works!

In the graphic above (click to get the whole thing, plus others) shows the particles detected in the ATLAS experiment, one of the two big detectors on the LHC. The paths of the particles are shown, and they all trace back to one spot (or close enough), indicating they all emerged from the same patch of space inside the collider, just as you’d expect if they were the products of a subatomic collision.

There’s still a long way to go, but this was a very important step along the way. Congrats to everyone at CERN!

CATEGORIZED UNDER: Cool stuff, Science

The Big Picture on LHC

By Phil Plait | November 23, 2009 7:35 am

bigpicture_cmsSpeaking of the LHC, the Boston Globe’s terrific feature The Big Picture has a slew of gorgeous pictures of the Large Hadron Collider up on the site.

These images, as beautiful and hi-res as they are, still cannot convey the awesome size and scale of the LHC. It’s been a year and a half since I stood there, 100 meters below of the surface of the Earth, gawking slack-jawed at ATLAS, CMS, and the other magnificent machinery, and it almost seems like a dream to me. But then I shake out of it and remember: this is what we do, and it’s real.

Secrets of the Universe? We humans figure that stuff out over coffee. What’s next?

CATEGORIZED UNDER: Cool stuff, Pretty pictures, Science

LHC: Beams back in business!

By Phil Plait | November 21, 2009 3:01 pm

Yesterday, the Large Hadron Collider once again had a beam of protons whizzing around its 27 km-long circumference!

After a series of setbacks — some devastating, holding up the world’s largest scientific experiment for many months — this milestone achieved shows that the collider is heading back to full operations, which should get started again next year. There will be press conference about this on Monday November 23rd at 1:00 p.m. GMT, which will be webcast live.

And if you’re wondering what the crew at CERN think of this latest news, then take a look at this picture of them looking at the results of the start up:


That picture makes me smile. Those unemotional, cold, calculating scientists. Why can’t they ever reveal their true feelings?

CATEGORIZED UNDER: Cool stuff, Science

Cox on Colbert

By Phil Plait | October 29, 2009 12:20 pm

As promised, Brian Cox was on The Colbert Report last night, and hit it out of the park. The whole show was better than average (which is saying a lot) but Brian truly rocked!

If you missed it (and live in the States) the whole episode is online (Brian’s segment is about 13:50 into the episode). Comedy Central won’t allow embedding the whole show (sigh), and Brian’s segment isn’t separated out on the CC site, but right before he was on Colbert ragged on physics and the LHC:

<td style='padding:2px 1px 0px 5px;' colspan='2'Big Bang Theory
The Colbert Report Mon – Thurs 11:30pm / 10:30c
Colbert Report Full Episodes Political Humor Religion

In the full segment, they talk about Brian’s book Why E=mc2, which was excellent. I’ll try to write a review of it as soon as I can. In the meantime, I do have to praise Colbert for his insight; as Brian points out he was correct in his ideas! I was cheering along with the segment. It still cracks me up that the smartest and most insightful commentary on TV is not from any of the "real" news stations, but from satirical shows like Colbert and The Daily Show. They have better science coverage than CNN, MSNBC and anyone else combined.


Discover's Newsletter

Sign up to get the latest science news delivered weekly right to your inbox!


See More

Collapse bottom bar

Login to your Account

E-mail address:
Remember me
Forgot your password?
No problem. Click here to have it e-mailed to you.

Not Registered Yet?

Register now for FREE. Registration only takes a few minutes to complete. Register now »