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Explaining the Higgs: on TV last night!

“We knew that we had indeed done something that was very different and very exciting, but we still didn’t expect it to have something to do with physical reality.” -Gerald Guralnik, co-developer of the Higgs mechanism

Might as well make this entire week “Higgs week” here on Starts With A Bang, given how important yesterday’s discovery/announcement was! It isn’t every day, after all, that you see a theoretical physicist on the 7PM news. (Video here.)

Ethan on KGW explaining the Higgs

Image credit:

(So proud of Portland, OR’s local TV station, KGW NewsChannel 8, for being willing to promote science to the whole city and have me on last night!)

Let’s just take a little time today — now that we’ve confidently announced the discovery of the Higgs — to recap what we now know.

Inside matter

Image credit: ETH Zurich, Institute for Particle Physics.

All the matter we know of is made out of quarks and leptons of various types, with the most common being the up-and-down quarks (that bind together to make protons and neutrons) and electrons (that bind with nuclei to make atoms). There are heavier fundamental quarks and leptons that will decay into the light ones with very short lifetimes, but they’re just as fundamental to the Universe as the ones that make us up. All quarks and leptons have an intrinsic angular momentum — known as spin — equal to Planck’s constant (ħ) divided by 2.

Fundamental Forces

Image credit: Fundamental Forces, via

There are also the gauge bosons: the fundamental particles responsible for the fundamental forces. There are the gluons, responsible for the strong force holding atomic nuclei and individual nucleons together, the weak bosons, responsible for radioactive decay and neutrino interactions, and the photon, responsible for electromagnetic interactions, radiation, and light. All of these gauge bosons have a quantum mechanical spin of Planck’s constant (ħ), double the value for quarks and leptons.

Curved spacetime

Image credit: curved spacetime, courtesy of

On the level of individual particles, we do not have a complete understanding of how gravity works. Our best theory for that is Einstein’s general relativity, which treats space-time as a fabric, and where matter and energy are responsible for curving this fabric. The matter and energy in the Universe determine the shape of the fabric, and then the particles in the Universe follow the path determined by that fabric.

Hawking Radiation

Curved spacetime is necessary for understanding quantum effects like Hawking radiation. Image credit:

The shape of the fabric is also important for quantum field theory; all of these particles we know of exist and interact in this curved spacetime, and the shape of this spacetime must be taken into account to get the correct predictions for the behavior of particles in the Universe. That’s our best understanding of gravitation.

And finally, as of yesterdaythere’s the Higgs.

Standard model particles

Image credit: The standard model by Fermilab, modifications by me.

The first and only fundamental particle with no spin. The particle that comes from the mechanism responsible for the masses of all the other fundamental particles, including the Higgs bosonitself. The final piece of the standard model puzzle required to explain the strong, weak, and electromagnetic forces and all of the particles therein.

CERN with detectors CMS and ATLAS

Image credit: © 2012 The School of Physics and Astronomy, The University of Edinburgh.

It took us decades of recreating temperatures and energies here at particle accelerators on Earth not found anyplace else to figure this out. The conditions we create in our most powerful accelerators are not found in the center of the Sun, nor in the central core of the Milky Way galaxy, nor around neutron stars and black holes, nor in the cosmic supernova explosions that give rise to all the heavy elements.

Supernova 1987a

Image credit: SN 1987a by NASA, ESA, P. Challis and R. Kirshner, by the Hubble Space Telescope.

These conditions have not existed* in the Universe, in fact, since the very early stages of the Big Bang, when the Universe was less than a microsecond old!

Quark-Gluon plasma

Image credit: CERN.

But yet, here we are, having successfully accelerated protons up to a record 299,792,450 m/s, just 8 m/s shy of the true speed of light, and collided them with protons moving the same speed in the opposite direction. Do this billions upon billions of times with a giant particle detector around the collision point, and on very rare occasions, you’ll be fortunate enough to create a Higgs boson, whose decay remnants we can detect.

Flying Spaghetti Monster, is that you?

Image credit: the CMS detector at CERN, 2009.

And now, at long last, the Higgs boson — the last undetected particle from the standard model — has been discovered. We’ve measured its mass and its spin, but not its width or its lifetime, yet, and there are still a bunch of unanswered questions. But for now, at least, I’m still celebrating the one question we did answer: the Higgs mechanism is correct, the Higgs boson (a fundamental, spinless scalar particle) does exist, it has a mass of 125-126 GeV, and the standard model is now complete!

We’ll take a look at the unanswered questions — and what’s next for physics and the LHC — very soon, but in the meantime, enjoy the continue Higgs-celebration, and if you’ve made it this far, enjoy my appearance on yesterday’s evening news!

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Wed Jul 04 19:37:02 PDT 2012

Hot Box: Explaining the Higgs boson

Theoretical astrophysicist Ehan Siegel explains the big Higgs boson announcement and what it means for the rest of us. view full article

* — Okay, so occasionally there are ultra-high-energy cosmic rays that are energetic enough to produce a particle such as this. But they’re extremely rare and their origin is not understood, so for all intents and purposes, these conditions don’t exist in the Universe today.

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Replies to This Discussion

A myriad Scientific American blogs and articles on the Higgs boson can be found here (some complaining about the hype, and rightly so). And yes, I SO agree we need to cut this crap of the "God particle".  

Beyond Higgs: Deviant decays hint at exotic physics

Continue reading page ||2 |3

Surprise behaviour from the new particle will help test theories that transcend the limits of the standard model of particle physics

Read more: "Higgsteria: Hunting the world's most wanted particle"

Editorial: "Particle discovery is a start, not an end"

A NEWLY glimpsed boson is prompting celebration around the world, but the particle could yet break the model that it is credited with completing. Or so most physicists hope.

Although spotted at last, many properties of the new particle - thought to be the Higgs boson, or at least something similar - have yet to be tested. What's more, the telltale signature it left in the detectors at the Large Hadron Collider (LHC) does not exactly match what is predicted by the standard model of particle physics, the leading explanation for the known particles and the forces that act on them. So it is possible the new particle is something much more exotic, such as a member of a more complete model of the universe that includes the mysterious entities of dark matter and gravity. That would end the standard model's supremacy, but it would also be a cause for even greater celebration than the discovery of the Higgs itself.

"Many of my colleagues and I think that this discovery on Wednesday may mark the beginning of the end of the standard model," says Georg Weiglein of the German Electron Synchotron research centre (DESY) in Hamburg. "Maybe these little deviations from the standard model really build up to a significant deviation. Maybe once we make this more precise with more data we will see that this is not the standard-model Higgs."

Rapturous applause, whistles and cheers filled the auditorium at CERN, near Geneva, Switzerland, as the heads of the twin LHC experiments presented their particle discoveries on 4 July. Joe Incandela of CMS and Fabiola Gianotti of ATLAS both reported seeing excesses of particles that fit the profile of a Higgs, with masses of 125 and 126 gigaelectronvolts (GeV) respectively. (In particle physics energy and mass are interchangeable.)

The Higgs doesn't just complete the standard model, it also has a key role to play in the nature of matter itself, as the fundamental component of the Higgs field. According to the standard model, all particles must pass through this omnipresent entity. Some, like the photon, slip through unhindered - they are massless. Others are slowed down, resulting in mass. "This boson is a very profound thing," says Incandela. "It embodies substance to all these other particles that exist."

Given the rumours, leaks and hype leading up to the announcement - and theknowledge that a discovery was in principle possible given the data...- the particle discovery was not a complete surprise. Remarkably though, ATLAS and CMS both claimed 5 sigma confidence in the result, equivalent to a 5 in 10 million chance that the readings could have been created by background processes in the detector. That exceeded the best of the anticipated outcomes. "I think we have it," concluded Rolf-Dieter Heuer, director general of CERN.

Discussion quickly moved to what exactly "it" was. The Higgs hasn't been glimpsed directly - but via its decay into a plethora of other particles more easily picked up by the LHC detectors.

The standard model predicts the rate at which a Higgs of a given mass should decay into these particles. But the reported rates for the new particle do not exactly match what is predicted for a mass of about 125 GeV (see diagram). The anomalies could disappear, producing a standard-model Higgs - or they could grow. Most physicists are hoping for the latter.

Read the whole article here. You'll need to register for login, but it is free. 

Higgs-spotting is much easier in Flatland

25 July 2012 by Lisa Grossman

CALL them the alternative Higgs hunters. A group of researchers has glimpsed a simulated version of the elusive particle in the behaviour of a handful of atoms on a lab bench.

In marked contrast to the high-energy collisions of the Large Hadron Collider (LHC) at CERN near Geneva, Switzerland, where the real Higgs boson was made, the atoms in the new work were arranged in an ultracold, flat array. The work suggests that something like the Higgs mechanism, which is thought to have given mass to elementary particles in the hot, early universe, operates in a range of physical situations. Similar physics could even be at play in the alternate universes that pop up in some versions of string theory, if they turn out to exist.

"It says a lot about the unity of physics, and how this is a deep and fundamental concept that appears in many different physical situations," says Subir Sachdev of Harvard University, who studies ultracold systems but was not involved in the new work.

The Higgs boson that appears in the standard model of particle physics is the calling card of the omnipresent Higgs field. The field cannot be observed, but high-energy protons smashing into each other inside the LHC can "shake" the field and produce Higgs bosons.

Thanks to the wave-particle duality of quantum mechanics, Higgs bosons can also be thought of as waves that appear in the Higgs field when it is shaken. This idea allowed a team led by Immanuel Bloch of the Max-Planck Institute of Quantum Optics in Munich, Germany, to test whether the Higgs mechanism could be at play in a cold, two-dimensional system.

The rest is HERE.

Take That Hepatitis C!
Submitted by: Unknown (via Gizmag)
Adorable Physics

Aaaah! The Hugs Bison! At last!

“If you’re a reporter, the easiest thing in the world is to get a story. The hardest thing is to verify. The old sins were about getting something wrong, that was a cardinal sin. The new sin is to be boring.” -David Halberstam

It was only a few months ago that both collaborations at the Large Hadron Collider in CERN — CMS and ATLAS — announced the discovery of a new particle at about 125-126 GeV of energy: something that looked an awful lot like what the Standard Model predicted the Higgs Boson should be.

Image credit: the CMS detector at CERN, 2009.

Image credit: the CMS detector at CERN, 2009.

This was the result of decades of investing, thousands of people’s tireless efforts, and unprecedented international collaboration. But in many ways, this was also only the beginning. Yes, by combining all of the data, we were able to tell that there was a new particle there of a certain mass, that it’s a boson (as opposed to a fermion), and that it has many properties consistent with a Higgs Boson.

Image credit: Fermilab, with slight modifications by me.

Image credit: Fermilab, with slight modifications by me.

But there were also some important questions that needed to be asked, that we weren’t ready to answer yet.

Image credit: CERN, ATLAS and CMS Collaborations, via

Image credit: CERN, ATLAS and CMS Collaborations, via

1.) Does this particle, in fact, behave and decay the way the Standard Model’s lone Higgs Boson is expected to?

When the discovery was first announced, only a few decay channels had been measured. A number of them were suspiciously silent — although that could have been just due to low statistics — while one of them (the two-photon channel) had almost triple the expected signal. This could have meant that this particle wasn’t the Standard Model Higgs, but was instead a different type of particle. This is akin to if you flipped a coin ten times, and it came up heads eight times, you might start to worry that your coin was biased against tails, or unfair in some way.

Image credit: © 2013 The School of Physics and Astronomy, The University of Edinburgh.

Image credit: © 2013 The School of Physics and Astronomy, The University of Edinburgh.

You’ve got to remember that over at the LHC, they’re colliding millions of particles together every second, in bunches just nanoseconds apart. You’ve got to very quickly sift through your data and throw away the 99.999% of it that’s uninteresting (i.e., where no rare particles are created) and then record-and-analyze everything that you kept. The Standard Model, regardless of the Higgs, produces a mountain’s worth of data. (Literally; if you wrote all the data that the LHChasn’t thrown away to CD-R and stacked it, you’d have hit the International Space Station by now.) And you’ve got to find — among that mountain — the few rare gems where a Higgs boson, for just 10-25 seconds, was created.

Image credit: CMS group / Imperial College London; minor edits by me.

Image credit: CMS group / Imperial College London; minor edits by me.

And now the data’s come in. And what we found is that those rarer decay channels are seeing decay rates consistent with Standard Model predictions, and that the two-photon channel is now much closer to what’s predicted. In other words, now that we’ve flipped the coin 100 times, the fact that we have 58 heads doesn’t seem so remarkable anymore.

Image credit: CERN / ATLAS collaboration.

Image credit: CERN / ATLAS collaboration.

So score one for “Standard Model Higgs.”

Image credit: Aidan Randle-Conde of

Image credit: Aidan Randle-Conde of

2.) What is the spin of this particle?

All particles have an intrinsic amount of angular momentum, which physicists refer to as spin. There are fermions, which have a spin in half-integer increments (e.g., ±1/2, ±3/2, ±5/2, etc.) and bosons, which have spins in integer increments (e.g., 0, ±1, ±2, etc.). Because photons are spin-1 and we knew the particle the LHC found could decay into two of those, we knew that it was therefore either spin-0 (because 1-1=0) or spin-2 (because 1+1=2), but couldn’t be either a fermion (because there’s no real way to combine 1 with 1 to get a half-integer) or a spin-1 boson (or higher).

Image credit: CERN / ATLAS collaboration.

Image credit: CERN / ATLAS collaboration.

But there are certain, rare decays that would tell the difference. For example, a spin-o boson could decay into two τ-particles (which are spin-1/2), because (1/2-1/2=0), but a spin-2 boson couldn’t. More subtly, there are some sophisticated differences in distribution that will show up in the two-photon channel and the four-lepton channels if the progenitor particle was spin-o or spin-2. The new data show both evidence that this new particle decays into two leptons — consistent with spin-0 — and also that the two-photon and four-lepton channels favor spin-0 over spin-2.

Image credit: CERN / ATLAS collaboration.

Image credit: CERN / ATLAS collaboration.

So, score two for “Standard Model Higgs.” And finally…

Image credit: Mary Bishai of Fermilab.

Image credit: Mary Bishai of Fermilab.

3.) What is the parity of this particle?

This is perhaps the most challenging of all. Parity is a scientist’s way of asking the world if the laws it obeys are the same as a mirror’s reflection, like the letter “O”, or flipped when you reflect it in a mirror, like the letter “E”.

Image credit: © Futility Closet 2012.

Image credit: © Futility Closet 2012.

For the Higgs boson, it’s supposed to behave like the letter “O”, which means it should have positive parity, as opposed to the “E”, which would be negative parity. This is too difficult to test by directly measuring the Higgs boson, as it doesn’t live long enough. But what we can do is look at the decay products; if there are four (or more) particles that wind up coming out, by measuring the angles the four particles come off at relative to one another, we can figure out whether it’s positive parity (like the letter “X”) or negative (like the letter “K”).

Image credit: Sara Bolognesi et al., 2012.

Image credit: Sara Bolognesi et al., 2012.

Well, the data has come in, and pretty definitively, ATLAS has concluded that this new particle has positive parity, just like the Standard Model’s Higgs Boson should.

And so that makes the Standard Model Higgs three-for-three on the prediction front. So finally…

Image credit: DESY in Hamburg.

Image credit: DESY in Hamburg.

4.) What does this mean for the possibility of extra particles beyond the Standard Model?

As you likely well know, there’s been a lot of excitement over the possibility that yes, there’s the Higgs Boson, but that there could be many more particles that the LHC will discover! For instance, if Supersymmetry is correct, there should be superparticles (partner particles to each of the Standard Model ones), as well as multiple Higgs Bosons.

Image credit: Paolo Lodone, Int.J.Mod.Phys. A27 (2012) 1230010.

Image credit: Paolo Lodone, Int.J.Mod.Phys. A27 (2012) 1230010.

So far, no evidence of these has shown up. But what about hints? Those of you who’ve been keeping your ear to the rumor mill may have heard Joe Lykken say the following:

“If you use all the physics that we know now and you do what you think is a straightforward calculation, it’s bad news… [t]his calculation tells you that many tens of billions of years from now, there’ll be a catastrophe… [i]t may be that the universe we live in is inherently unstable and at some point billions of years from now it’s all going to get wiped out.”

What Lykken is referring to is that, if you know how all the particles of the Standard Model interact, and you know the masses of all of those particles, you can determine whether the Universe is stable all the way up to arbitrary energies, or whether there’s an inherent instability, and the Universe is only quasi-stable, up to some finite energy. If there’s an instability, that means that either the Universe is in a quasi-stable state that it won’t stay in forever, or there are new particles before we reach that cutoff energy.

Image credit: Tona Kunz, for D0 and CDF collaborations / Fermilab.

Image credit: Tona Kunz, for D0 and CDF collaborations / Fermilab.

There are three Standard Model particles whose masses still have a fair bit of uncertainty: theHiggs, the top quark, and the W-boson. Accepting them at their best-measured values right now means that the Universe is stable up to about 1011 GeV, or a factor of 10 million higher than the LHC can reach. I don’t know what “straightforward” calculation Lykken is referring to, but the calculations I’ve seen indicate the Universe will remain quasi-stable not for tens-of-billions of years, but quadrillions, at least, even if there are no new particles.

Image credit: From Phys. Lett. B's paper by Mikhail Shaposhnikov & Christof Wetterich.

Image credit: From Phys. Lett. B’s paper by Mikhail Shaposhnikov & Christof Wetterich.

But if we include the present uncertainties in those particle masses, and accept that maybe the top quark is off by about 1.7% than the accepted best-measurement right now (less than a 2-σ uncertainty away from the central value), then the Universe is stable up to arbitrarily highenergies, and will remain stable, forever. With no new particles. So while what Lykken said — with some caveats — is definitely within the realm of possibility, there’s no experimental or observational evidence to indicate that it’s at all likely. The Standard Model is what we’ve got, and until the experiments show otherwise, there’s no reason to believe that, other than something to explain neutrino masses (and possibly a lack of strong-CP violation), there’s anything else out there.

Image credit: original source unknown, retrieved from Akhtar Mahmood of Bellarmine University, mods by me.

Image credit: original source unknown, retrieved from Akhtar Mahmood of Bellarmine University, mods by me.

Of course, the LHC is undergoing an upgrade, and will resume the search for new, exotic particles at even higher energies in a couple of years! But for right now, if we’re following the data, the smart money is that the Standard Model is right, this is the boring Standard Model’s Higgs Boson, and it would be a huge surprise if the LHC found anything else. But we’ve been surprised before, and that’s why we look!

And for those of you who missed it last night, I had the opportunity to tell the world — on Live TV— about the new findings!

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Thu Mar 14 19:39:21 PDT 2013

Hot Box: Pi Day with @StartsWithABang

Astrophysicist Ethan Siegel is our guest on Pi Day. We talk about the Higgs-Boson confirmation, interstellar discoveries and his memorization of the longest number known to man. view full article

Seriously, how often do you get to explain quantum spin addition on broadcast television?! Thanks to my local news team at KGW, you can go see it anytime. (And click here for a behind-the-scenes peek!) We’re one step closer to understanding, at a fundamental level, what makes up all the normal matter in our Universe.


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