Category Archives: Higgs

Day 2 At CERN

Day 2 of my visit to CERN (host laboratory of the Large Hadron Collider [LHC]) was a pretty typical CERN day for me. Here’s a rough sketch of how it panned out:

  • 1000: after a few chores, arrived at CERN by tram. Worked on my ongoing research project #1. Answered an email about my ongoing research project #2.
  • 1100: attended a one hour talk, much of it historical, by Chris Quigg, one of the famous experts on “quarkonium” (atom-like objects made from a quark or anti-quark, generally referring specifically to charm and bottom quarks). Charmonium (charm quark/antiquark atoms) was discovered 40 years ago this week, in two very different experiments.
  • 1200: Started work on the talk that I am giving on the afternoon of Day 3 to some experimentalists who work at ATLAS. [ATLAS and CMS are the two general-purpose experimental detectors at the LHC; they were used to discover the Higgs particle.] It involves some new insights concerning the search for long-lived particles (hypothesized types of new particles that would typically decay only after having traveled a distance of at least a millimeter, and possibly a meter or more, before they decay to other particles.)
  • 1230: Working lunch with an experimentalist from ATLAS and another theorist, mainly discussing triggering, and other related issues, concerning long-lived particles. Learned a lot about the new opportunities that ATLAS will have starting in 2015.
  • 1400: In an extended discussion with two other theorists, got a partial answer to a subtle question that arose in my research project #2.
  • 1415: Sent an email to my collaborators on research project #2.
  • 1430: Back to work on my talk for Day 3. Reading some relevant papers, drawing some illustrations, etc.
  • 1600: Two-hour conversation over coffee with an experimentalist from CMS, yet again about triggering, regarding long-lived particles, exotic decays of the Higgs particle, and both at once. Learned a lot of important things about CMS’s plans for the near-term and medium-term future, as well as some of the subtle issues with collecting and analyzing data that are likely to arise in 2015, when the LHC begins running again.

[Why triggering, triggering, triggering? Because if you don't collect the data in the first place, you can't analyze it later!  We have to be working on triggering in 2014-2015 before the LHC takes data again in 2015-2018]

  • 1800: An hour to work on the talk again.
  • 1915: Skype conversation with two of my collaborators in research project #1, about a difficult challenge which had been troubling me for over a week. Subtle theoretical issues and heavy duty discussion, but worth it in the end; most of the issues look like they may be resolvable.
  • 2100: Noticed the time and that I hadn’t eaten dinner yet. Went to the CERN cafeteria and ate dinner while answering emails.
  • 2130: More work on the talk for Day 3.
  • 2230: Left CERN. Wrote blog post on the tram to the hotel.
  • 2300: Went back to work in my hotel room.

Day 1 was similarly busy and informative, but had the added feature that I hadn’t slept since the previous day. (I never seem to sleep on overnight flights.) Day 3 is likely to be as busy as Day 2. I’ll be leaving Geneva before dawn on Day 4, heading to a conference.

It’s a hectic schedule, but I’m learning many things!  And if I can help make these huge and crucial experiments more powerful, and give my colleagues a greater chance of a discovery and a reduced chance of missing one, it will all be worth it.

Off to CERN

After a couple of months of hard work on grant writing, career plans and scientific research, I’ve made it back to my blogging keyboard.  I’m on my way to Switzerland for a couple of weeks in Europe, spending much of the time at the CERN laboratory. CERN, of course, is the host of the Large Hadron Collider [LHC], where the Higgs particle was discovered in 2012. I’ll be consulting with my experimentalist and theorist colleagues there… I have many questions for them. And I hope they’ll have many questions for me too, both ones I can answer and others that will force me to go off and think for a while.

You may recall that the LHC was turned off (as planned) in early 2013 for repairs and an upgrade. Run 2 of the LHC will start next year, with protons colliding at an energy of around 13 TeV per collision. This is larger than in Run 1, which saw 7 TeV per collision in 2011 and 8 TeV in 2012.  This increases the probability that a proton-proton collision will make a Higgs particle, which has a mass of 125 GeV/c², by about a factor of 2 ½.  (Don’t try to figure that out in your head; the calculation requires detailed knowledge of what’s inside a proton.) The number of proton-proton collisions per second will also be larger in Run 2 than in Run 1, though not immediately. In fact I would not be surprised if 2015 is mostly spent addressing unexpected challenges. But Run 1 was a classic: a small pilot run in 2010 led to rapid advances in 2011 and performance beyond expectations in 2012. It’s quite common for these machines to underperform at first, because of unforeseen issues, and outperform in the long run, as those issues are solved and human ingenuity has time to play a role. All of which is merely to say that I would view any really useful results in 2015 as a bonus; my focus is on 2016-2018.

Isn’t it a bit early to be thinking about 2016? No, now is the time to be thinking about 2016 triggering challenges for certain types of difficult-to-observe phenomena. These include exotic, unexpected decays of the Higgs particle, or other hard-to-observe types of Higgs particles that might exist and be lurking in the LHC’s data, or rare decays of the W and Z particle, and more generally, anything that involves a particle whose (rest) mass is in the 100 GeV/c² range, and whose mass-energy is therefore less than a percent of the overall proton-proton collision energy. The higher the collision energy grows, the harder it becomes to study relatively low-energy processes, even though we make more of them. To be able to examine them thoroughly and potentially discover something out of place — something that could reveal a secret worth even more than the Higgs particle itself — we have to become more and more clever, open-minded and vigilant.

Will the Higgs Boson Destroy the Universe???

No.

The Higgs boson is not dangerous and will not destroy the universe.

The Higgs boson is a type of particle, a little ripple in the Higgs field. [See here for the Higgs FAQ.] This lowly particle, if you’re lucky enough to make one (and at the world’s largest particle accelerator, the Large Hadron Collider, only one in a trillion proton-proton collisions actually does so) has a brief life, disintegrating to other particles in less than the time that it takes light to cross from one side of an atom to another. (Recall that light can travel from the Earth to the Moon in under two seconds.) Such a fragile creature is hardly more dangerous than a mayfly.

Anyone who says otherwise probably read Hawking’s book (or read about it in the press) but didn’t understand what he or she was reading, perhaps because he or she had not read the Higgs FAQ.

If you want to worry about something Higgs-related, you can try to worry about the Higgs field, which is “ON” in our universe, though not nearly as “on” as it could be. If someone were to turn the Higgs field OFF, let’s say as a practical joke, that would be a disaster: all ordinary matter across the universe would explode, because the electrons on the outskirts of atoms would lose their mass and fly off into space. This is not something to worry about, however. We know it would require an input of energy and can’t happen spontaneously.  Moreover, the amount of energy required to artificially turn the Higgs field off is immense; to do so even in a small room would require energy comparable to that of a typical supernova, an explosion of a star that can outshine an entire galaxy and releases the vast majority of its energy in unseen neutrinos. No one, fortunately, has a supernova in his or her back pocket. And if someone did, we’d have more immediate problems than worrying about someone wasting a supernova trying to turn off the Higgs field in a basement somewhere.

Now it would also be a disaster if someone could turn the Higgs field WAY UP… more than when your older brother turned up the volume on your stereo or MP3 player and blew out your speakers. In this case atoms would violently collapse, or worse, and things would be just as nasty as if the Higgs field were turned OFF. Should you worry about this? Well, it’s possible this could happen spontaneously, so it’s slightly more plausible. But I do mean slightly. Very slightly. Continue reading

Some Higgs News from the LHCP Conference

Some news on the Higgs particle from the ATLAS and CMS experiments, the two general purpose experiments at the Large Hadron Collider. I just mention a few highlights. Continue reading

Modern Physics: Increasingly Vacuous

One of the concepts that’s playing a big role in contemporary discussions of the laws of nature is the notion of “vacua”, the plural of the word “vacuum”. I’ve just completed an article about what vacua are, and what it means for a universe to have multiple vacua, or for a theory that purports to describe a universe to predict that it has multiple vacua. In case you don’t want to plunge right in to that article, here’s a brief summary of why this is interesting and important.

Outside of physics, most people think of a vacuum as being the absence of air. For physicists thinking about the laws of nature, “vacuum” means space that has been emptied of everything — at least, emptied of everything that can actually be removed. That certainly means removing all particles from it. But even though vacuum implies emptiness, it turns out that empty space isn’t really that empty. There are always fields in that space, fields like the electric and magnetic fields, the electron field, the quark field, the Higgs field. And those fields are always up to something.

First, all of the fields are subject to “quantum fluctuations” — a sort of unstoppable jitter that nothing in our quantum world can avoid.  [Sometimes these fluctuations are referred to as “virtual particles”; but despite the name, those aren’t particles.  Real particles are well-behaved, long-lived ripples in those fields; fluctuations are much more random.] These fluctuations are always present, in any form of empty space.

Second, and more important for our current discussion, some of the fields may have average values that aren’t zero. [In our own familiar form of empty space, the Higgs field has a non-zero average value, one that causes many of the known elementary particles to acquire a mass (i.e. a rest mass).] And it’s because of this that the notion of vacuum can have a plural: forms of empty space can differ, even for a single universe, if the fields of that universe can take different possible average values in empty space. If a given universe can have more than one form of empty space, we say that “it has more than one vacuum”.

There are reasons to think our own universe might have more than one form of vacuum — more than just the one we’re familiar with. It is possible that the Standard Model (the equations used to describe all of the known elementary particles, and all the known forces except gravity) is a good description of our world, even up to much higher energies than our current particle physics experiments can probe. Physicists can predict, using those equations, how many forms of empty space our world would have. And their calculations show that our world would have (at least) two vacua: the one we know, along with a second, exotic one, with a much larger average value for the Higgs field. (Remember, this prediction is based on the assumption that the Standard Model’s equations apply in the first place.)  An electron in empty space would have a much larger mass than the electrons we know and love (and need!)

The future of the universe, and our understanding of how the universe came to be, might crucially depend on this second, exotic vacuum. Today’s article sets the stage for future articles, which will provide an explanation of why the vacua of the universe play such a central role in our understanding of nature at its most elemental.

In Memoriam: Gerry Guralnik

For those who haven’t heard: Professor Gerry Guralnik died. Here’s the New York Times obituary, which contains a few physics imperfections (though the most serious mistake in an earlier version was corrected, thankfully), but hopefully avoids any errors about Guralnik’s life.  Here’s another press release, from Brown University.

Guralnik, with Tom Kibble and Carl Hagen, wrote one of the four 1964 papers which represent the birth of the idea of the “Higgs” field, now understood as the source of mass for the known elementary particles — an idea that was confirmed by the discovery of a type of “Higgs” particle in 2012 at the Large Hadron Collider.  (I find it sad that the obituary is sullied with a headline that contains the words “God Particle” — a term that no physicist involved in the relevant research ever used, and which was invented in the 1990s, not as science or even as religion, but for $$$… by someone who was trying to sell his book.) The other three papers — the first by Robert Brout and Francois Englert, and the second and third by Peter Higgs, were rewarded with a Nobel Prize in 2013; it was given just to Englert and Higgs, Brout having died too early, in 2011.  Though Guralnik, Hagen and Kibble won many other prizes, they were not awarded a Nobel for their work, a decision that will remain forever controversial.

But at least Guralnik lived long enough to learn, as Brout sadly did not, that his ideas were realized in nature, and to see the consequences of these ideas in real data. In the end, that’s the real prize, and one that no human can award.

A Week in Canada

It’s been a quiet couple of weeks on the blog, something which often indicates that it’s been anything but quiet off the blog. Such was indeed the case recently.

For one thing, I was in Canada last week. I had been kindly invited to give two talks at the University of Western Ontario, one of Canada’s leading universities for science. One of the talks, the annual Nerenberg lecture (in memory of Professor Morton Nerenberg) is intended for the general public, so I presented a lecture on The 2013 Nobel Prize: The 50-Year Quest for the Higgs Boson. While I have given a talk on this subject before (an older version is on-line) I felt some revisions would be useful. The other talk was for members of the applied mathematics department, which hosts a diverse group of academics. Unlike a typical colloquium for a physics department, where I can assume that the vast majority of the audience has had university-level quantum mechanics, this talk required me to adjust my presentation for a much broader scientific audience than usual.  I followed, to an extent, my website’s series on Fields and Particles and on How the Higgs Field Works, both of which require first-year university math and physics, but nothing more. Preparation of the two talks, along with travel, occupied most of my free time over recent days, so I haven’t been able to write, or even respond to readers’ questions, unfortunately.

I also dropped in at Canada’s Perimeter Institute on Friday, when it was hosting a small but intense one-day workshop on the recent potentially huge discovery by the BICEP2 experiment of what appears to be a signature of gravitational waves from the early universe. This offered me an opportunity to hear some of the world’s leading experts talking about the recent measurement and its potential implications (if it is correct, and if the simplest interpretation of it is correct). Alternative explanations of the experiment’s results were also mentioned. Also, there was a lot of discussion about the future, both the short-term and the long-term. Quite a few measurements will be made in the next six to twelve months that will shed further light on the BICEP2 measurement, and on its moderate conflict with the simplest interpretation of certain data from the Planck satellite.  Further down the line, a very important step will be to reduce the amount of B-mode polarization that arises from the gravitational lensing of E-mode polarization, a method called “delensing”; this will make it easier to observe the B-mode polarization from gravitational waves (which is what we’re interested in) even at rather small angular scales (high “multipoles”).   Looking much further ahead, we will be hearing a lot of discussion about huge new space-based gravitational wave detectors such as BBO [Big Bang Observatory].  (Actually the individual detectors are quite small, but they are spaced at great distances.) These can potentially measure gravitational waves whose wavelength is comparable to the size of the Earth’s orbit or even larger, which is still much smaller than those apparently detected by BICEP2 in the polarization of the cosmic microwave background. Anyway, assuming what BICEP2 has really done is discover gravitational waves from the very early universe, this subject now a very exciting future and there is lots to do, to discuss and to plan.

I wish I could promise to provide a blog post summarizing carefully what I learned at the conference. But unfortunately, that brings me to the other reason blogging has been slow. While I was away, I learned that the funding situation for science in the United States is even worse than I expected. Suffice it to say that this presents a crisis that will interfere with blogging work, at least for a while.

Which Parts of the Big Bang Theory are Reliable, and Why?

Familiar throughout our international culture, the “Big Bang” is well-known as the theory that scientists use to describe and explain the history of the universe. But the theory is not a single conceptual unit, and there are parts that are more reliable than others.

It’s important to understand that the theory — a set of equations describing how the universe (more precisely, the observable patch of our universe, which may be a tiny fraction of the universe) changes over time, and leading to sometimes precise predictions for what should, if the theory is right, be observed by humans in the sky — actually consists of different periods, some of which are far more speculative than others.  In the more speculative early periods, we must use equations in which we have limited confidence at best; moreover, data relevant to these periods, from observations of the cosmos and from particle physics experiments, is slim to none. In more recent periods, our confidence is very, very strong.

In my “History of the Universe” article [see also my related articles on cosmic inflation, on the Hot Big Bang, and on the pre-inflation period; also a comment that the Big Bang is an expansion, not an explosion!], the following figure appears, though without the colored zones, which I’ve added for this post. The colored zones emphasize what we know, what we suspect, and what we don’t know at all.

History of the Universe, taken from my article with the same title, with added color-coded measures of how confident we can be in its accuracy.  In each colored zone, the degree of confidence and the observational/experimental source of that confidence is indicated. Three different possible starting points for the "Big Bang" are noted at the bottom; different scientists may mean different things by the term.

History of the Universe, taken from my article with the same title, with added color-coded measures of how confident we can be in our understanding. In each colored zone, the degree of confidence and the observational/experimental source of that confidence is indicated. Three different possible starting points for the “Big Bang” are noted at the bottom; note that individual scientists may mean different things by the term.

Notice that in the figure, I don’t measure time from the start of the universe.  That’s because I don’t know how or when the universe started (and in particular, the notion that it started from a singularity, or worse, an exploding “cosmic egg”, is simply an over-extrapolation to the past and a misunderstanding of what the theory actually says.) Instead I measure time from the start of the Hot Big Bang in the observable patch of the universe.  I also don’t even know precisely when the Hot Big Bang started, but the uncertainty on that initial time (relative to other events) is less than one second — so all the times I’ll mention, which are much longer than that, aren’t affected by this uncertainty.

I’ll now take you through the different confidence zones of the Big Bang, from the latest to the earliest, as indicated in the figure above.

Continue reading