Of Particular Significance

Tag: particle physics

Garisto’s Reply to Previous Post

Robert Garisto sent me a reply to my previous post; here it is. [A “vev” is shorthand for a non-zero value in the vacuum of space, what I call a “non-zero average value”.]

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Matt – Thanks for your extensive reply to my comment! Of course I agree that a scalar field without a vev can have a hard mass term. And I do agree that how the Higgs boson gets mass is at least somewhat different than how the W does.

Let’s agree to define a Higgs as a scalar field with a vev. Then I think you agree that the mass of the excitation about the vev, the Higgs boson, is not a hard mass term, one obtains it by finding the minimum of the potential as you did above. Now if there are other scalars with vevs, the mass of the Higgs boson we are concentrating on can depend on those too. But isn’t it correct to say that the mass of such a Higgs boson goes to zero in the limit that all of those vevs go to zero? If so, I would say that the Higgs boson mass is provided by the Higgs fields (all scalars with nonzero vevs).

Anyway, the main reason I made the comment is that for the purposes of explaining to the public electroweak symmetry breaking, I think it makes sense to say that the Higgs boson mass comes from the Higgs field, because it is, in the SM, proportional to the vev. It’s also kind of neat, I think.

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We disagree, that’s all there is to it. What Garisto says about the Standard Model is a simple consequence of dimensional analysis, not a fundamental relation that applies widely. And no, it is not correct to say that the mass of a Higgs boson always goes to zero in the limit that all vevs go to zero; there can be first order phase transitions in which, as the parameters change, the Higgs field’s vev jumps from non-zero to zero abruptly, and the mass of the Higgs particle is never zero. So I think to tell the public that the Higgs particle gets its mass from the Higgs field is to confuse them into thinking that the Higgs particle gets its mass the same way the other known particles do — which is false.

But in any case, we agree it’s not that big a deal. The thing which is important for the public to understand is that the Higgs field does not give mass to all massive objects — such as atomic nuclei and black holes. And the thing which it is important for particle physics students to understand is that the Higgs mass is not generically proportional to the vev of the Higgs field.

POSTED BY Matt Strassler

ON October 24, 2012

Colloquia Here and There

This Wednesday I was visiting the University of Massachusetts, in the currently colorful town of Amherst, where I gave a colloquium (an hour-long talk aimed at a physics department’s undergraduate majors, graduate students and faculty who are not themselves experts in particle physics) entitled The Quest for the Higgs Boson. It’s similar to the one I gave two weeks ago at the University of Toronto, which is available on-line now. There’s audio and there are slides, but no video, so I’m afraid you’ll have to figure out on your own how the slides and audio fit together; but I think it should be fairly obvious.

If, however, you’re not a physicist or physics student, but you have been following particle physics a little bit, perhaps by reading this blog or Scientific American articles or books for laypeople by, say, Brian Greene or Lisa Randall, then you might instead want to try listening to this lecture I gave recently, which is also in the form of an audio feed plus slides. It makes far fewer assumptions about what audience members are familiar with. And of course there’s always my [in]famous video clips from my March 2011 public lecture on the Large Hadron Collider; a bit out of date since they were made before the new Higgs-like particle was found, but still basically covering what you need to know.

Please note these presentations are under copyright.

POSTED BY Matt Strassler

ON October 19, 2012

Creating a New Particle from the Annihilation of Two Others

[Long silence should be over for now; personal issues had to take precedence for a little while.]

Back to building up articles on how the Higgs field works! As part of the necessary background, I’ve added another general article on how particles and fields interact with each other to my series on Particles and Fields (with a little math — first-year university level.)

This one explains, among other things, how a small modification of the equations of motion for fields allows two particles of one type to annihilate and create a third one of a different type. Examples of such phenomena include the collision and annihilation of a quark and an antiquark to form a Z particle, or the collision and annihilation of two gluons to form a Higgs particle. Particle decay is often just the time-reversed process.

So this is one of the most important articles, and one of the most sophisticated, to appear on this website so far. Although there are a couple of animations to help you visualize what is going on, to understand the text you will want to have read the other articles in the Particles and Fields series first.

POSTED BY Matt Strassler

ON October 10, 2012

Two Major Steps Forward

Apologies to those who’ve been asking questions: I’ve been away from the website for a few days (family matters) and have not been able to keep up with comments. I will try to catch up over the coming day or two.

But I do have two pieces of good news.

First, I gave a public lecture over the weekend, on-line, called “The Quest for the Higgs”, which I believe many of my readers will find at the right level. Because of some technical difficulties with the sound recording, I didn’t immediately recommend that you listen; but those problems are now fixed and the sound is pretty good. The audio is to be found here at BlogTalkRadio, through the Virtually Speaking Science series; on that website, there’s a link to the slides accompanying the talk, or you can just click here to get them. [Note the slides are under copyright; please ask permission before reproducing or using ideas you find therein.]

Second, the long-awaited final article in the series on Particles and Fields (with a little math) has arrived.

As a bonus, you can then find out what the key technical difference is between bosons and fermions (the consequences of this difference are described, without technicalities, here.)

Next month: a series of articles on How the Higgs Field Works.

POSTED BY Matt Strassler

ON September 13, 2012

The Quantum Wave

If you’ve just gotten back from vacation, perhaps after days or weeks seeking the perfect wave, well, what a treat awaits! So much reading to do, about such interesting things. I’m writing a set of articles, intended for the reader who has once-upon-a-time seen beginning physics (what we in the U.S. would call “freshman physics”, or even a good “advanced placement physics” course pre-university) with the goal of explaining what fields and particles are. Five of the seven or eight articles are done; four appeared over the last two weeks, and now there’s a new one:

After this: an article on Fields, and then one on Particles, and maybe one more with some follow-up information. And then, with this set complete, I’ll move on to another series of articles, about how the Higgs field works…

POSTED BY Matt Strassler

ON September 4, 2012

A Little Math; A Lot of Physics

One of my current goals is to explain how the Higgs field works to anyone who’s learned a bit of physics at the beginning-university or advanced pre-university level. As a step toward the goal, I am creating a set of pages that explain how fields work, why quantum mechanics implies that sufficiently simple fields have particles, and which aspect of a field’s behavior determines the masses of its particles. You will find that knowing a little physics and a little math is helpful.

[I’m afraid that most of you who never had a beginning physics class at all will have to be patient. It’s an even greater challenge for me to explain the Higgs field to someone who’s allergic to math, or hasn’t had much math yet; I’m hoping my current efforts will help me see how surmount that challenge. But meanwhile you might like to read my Higgs FAQ and my popular article on Why the Higgs Particle Matters.]

The first step is to remember how a ball on a spring works — one of the first things one learns in any physics class — and then learn a little bit about how quantum mechanics changes the answer — one of the first things one learns in a quantum mechanics class. This is where the concept of a “quantum” first makes its appearance in physics. Those articles are now ready for you to look at. The next step [waves, both without and with quantum mechanics] will follow over the coming week.

Note: I’ve included, for the first time on this website, some animated gifs among the figures. These should animate when you click on them. I know they need improvement; over the next day I’ll be trying to make them faster to load and run. Please be patient and let them load; but do let me know if you can’t make them work at all, and if so, what browser and hardware you’re using. Update: they should be much faster now.

POSTED BY Matt Strassler

ON August 27, 2012

Physics and Curiosity on Mars

The promised follow-up article on the workshop last week in Waterloo, Canada will have to wait til Monday; I had too many scientific activities and chores to take care of today, and I want to make sure the article, which is a bit complicated, is nevertheless clear. But in the meantime, let’s celebrate Martian Curiosity!

First, a big congratulations to the NASA folks! Very impressive, and fantastically cool. I was a huge fan of the Spirit and Opportunity rovers, especially of their 3D photography. Looking at those photos on a big screen, through red/green 3D glasses. brought me to sweeping Martian vistas and deep Martian craters — as vivid and as close as I’ll ever see them. It was amazing stuff, and I look forward to more from the new rover.

Next: some perspective. (more…)

POSTED BY Matt Strassler

ON August 10, 2012

Some Personal Reflections on the Discovery of a Higgs-Like Particle

The intensity of the last few weeks has been almost beyond description, and certainly unmatched in my career as a theoretical physicist. For me, and for many of my colleagues, the end of a decades-long hunt for the Higgs particle comes with a sense almost of disbelief. Did this really just happen? Did the years and years of anticipation, which had become almost a part of our communal culture, a sort of Waiting For Godot, a hope for a Promised Land always out of reach, actually come to an end?

Click here to read the full article.

POSTED BY Matt Strassler

ON August 1, 2012

This Site’s Background Articles on the Higgs

Coming very soon: News on the search for the Higgs particle by CMS and ATLAS, the two big experiments at the Large Hadron Collider [LHC]. Presentations updating the search are expected on July 4th, IndependHiggs Day, at 9:00 am Geneva (Switzerland) time, at the CERN laboratory, which hosts the LHC. The talks, like those of December 13th, 2011, are expected to be technical and intended for experts, though non-experts with some significant amount of background might enjoy directly seeing the data and sharing in the sense of excitement.

The current phase of the search is aimed at either discovering or excluding the simplest type of Higgs particle, known as the Standard Model Higgs. If you are interested in understanding what this particle is and how one looks for it, you can read

To learn more about what the Higgs field and particle are and do, try

Regarding Higgs particles that are more complex than the Standard Model Higgs, and that may be harder to find, you can read

POSTED BY Matt Strassler

ON June 27, 2012

Tying Off Loose Ends

Reminder: New York, Saturday June 16th at 2pm, I’ll be giving a public lecture (click here for details): THE EINSTEIN OBSESSION: SCIENCE, MYTH AND PUBLIC PERCEPTION.

I’ve been doing a little work on my extra dimensions articles, adding one that describes how we know experimentally that the ordinary particles we’re made of (and most of the others we know about) can’t be moving in more than three spatial dimensions — more precisely, that any additional dimensions must be smaller in extent than 1/100th or so of the distance across a proton. The first half of the article is drafted; the second half, on what we know about dimensions in which no known particles can move but which are accessible to gravity and gravitons, will come soon, probably next week. Comments and questions welcome as always.

Meanwhile, following up on Friday’s post about the End of the OPERA Not-Faster-Than-Light Neutrino Story: a paper has appeared by the LVD and OPERA experiments explaining how they worked together to confirm that OPERA’s two known problems (a fiber-optic cable connection and a clock running off-speed) did in fact cause their faulty measurement of neutrino speeds. This information was made public (in large part) back in March and I wrote about it in detail here.

POSTED BY Matt Strassler

ON June 13, 2012

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Tag: particle physics

POSTED BY Matt Strassler

POSTED BY Matt Strassler

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