Of Particular Significance

Category: Higgs

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

The Trigger and the Parking Lot

I told you a few days ago about the workshop I attended recently at the Perimeter Institute (PI), which brought a number of particle theorists together with members of the CMS experiment, one of the two general purpose experiments operating at the Large Hadron Collider [LHC]. I described the four main areas of discussion, and mentioned a fifth issue that underlies them all: triggering. Today I’m going to explain to you one of two big advances in triggering at CMS that have recently been made public, the one called “Data Parking”. And I’ll also describe my small role in Data Parking over the last ten months, which will explain, in retrospect, some of the other articles that have appeared on this site during that period.

[This article is almost entirely about CMS, but CMS’s competitor, ATLAS, has also made public that they have something essentially identical (I think!) to Data Parking, which they call “Delayed Data Streaming”.]

Click here to read the rest of this article.

POSTED BY Matt Strassler

ON August 13, 2012

A Real Workshop

In the field of particle physics, the word “workshop” has a rather broad usage; some workshops are just conferences with a little bit of time for discussion or some other additional feature. But some workshops are about WORK…. typically morning-til-night work. This includes the one I just attended at the Perimeter Institute (PI) in Waterloo, Canada, which brought particle experimentalists from the CMS experiment (one of the two general-purpose experiments at the Large Hadron Collider [LHC] — the other being ATLAS) together with some particle theorists like myself. In fact, it was one of the most productive workshops I’ve ever participated in.

The workshop was organized by the PI’s young theoretical particle physics professors, Philip Schuster and Natalia Toro, along with CMS’s current spokesman Joseph Incandela and physics coordinator Greg Landsberg. (Incandela, professor at the University of California at Santa Barbara, is now famous for giving CMS’s talk July 4th announcing the observation of a Higgs-like particle; ATLAS’s talk was given by Fabiola Gianotti. Landsberg is a senior professor at Brown University.) Other participants included many of the current “conveners” from CMS — typically very experienced and skilled people who’ve been selected to help supervise segments of the research program — and a couple of dozen LHC theorists, mostly under the age of 40, who are experienced in communicating with LHC experimenters about their measurements. (more…)

POSTED BY Matt Strassler

ON August 7, 2012

At a Workshop; and Higgs Papers Are Out

Today finds me in Canada, at the Perimeter Institute in Waterloo, Ontario, where I’ll be for the next few days. I’m attending a workshop on strategies for searching for new phenomena at the Large Hadron Collider (LHC), which is bringing together a couple of dozen theorists like myself with experimentalists in leadership positions at the CMS experiment, one of the experiments at the LHC. More on that later, though I won’t be at liberty to discuss details.

Meanwhile, yesterday ATLAS and CMS, the two general purpose experiments at the LHC, released their pre-publication papers that summarize their observation of a new Higgs-like particle. (Here’s ATLAS’s and here’s CMS’s paper; they’ve been submitted now to the journal Physics Letters, which normally doesn’t publish tomes.) (more…)

POSTED BY Matt Strassler

ON August 2, 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

The First Human-Created Higgs-Like Particle: 1988 or 89, at the Tevatron

Yesterday’s Quiz Question: when was the first Higgs particle produced by humans? (where admittedly “Higgs” should have read “Higgs-like”) got many answers, but not the one I think is correct. Here’s what I believe is the answer.

——

[UPDATE: After this post was written, but before it went live, commenter bobathon got the right answer — at 6:30 Eastern, just under the wire! Well done!]

The first human-produced Higgs particle [more precisely, the Higgs-like particle with a mass of about 125 GeV/c² whose discovery was reported earlier this month, and which I’ll refer to as “`H”– but I’ve told you why I think it is a Higgs of some sort] was almost certainly created in the United States, at the Fermilab National Accelerator Center outside Chicago. Back in 1988 and 1989, Fermilab’s accelerator called the Tevatron created collisions within the then-new CDF experiment, during the often forgotten but very important “Run Zero”. The energy per collision, and the total data collected, were just enough to make it nearly certain that an H particle was created during this run.

Run Zero, though short, was important because it allowed CDF to prove that precision mass measurements were possible at a proton collider. They made a measurement of the Z particle’s mass that almost rivaled the one made simultaneously at the SLC electron-positron collider. This surprised nearly everyone. [Unfortunately I was out of town and missed the scene of disbelief, back in 1989, when CDF dropped this bombshell during a conference at SLAC, the SLC’s host laboratory.] Nowadays we take it for granted that the best measurement of the W particle’s mass comes from the Tevatron experiments, and that the Large Hadron Collider [LHC] experiments will measure the H particle’s mass to better than half a percent — but up until Run Zero it was widely assumed to be impossible to make measurements of such quality in the messy environment of collisions that involve protons.

Anyway, it is truly astonishing that we have to go back to 1988-1989 for the first artificially produced Higgs(-like) particle!! I was a first-year graduate student, and had just learned what Higgs particles were; precision measurements of the Z particle were just getting started, and the top quark hadn’t been found yet. It took 23 years to make enough of these Higgs(-like) particles to convince ourselves that they were there, using the power of the CERN laboratory’s Large Hadron Collider [LHC]!

[Perhaps this remarkable history will help you understand why I keep saying that although the LHC experiments haven’t yet found something unexpected in their data, that absolutely doesn’t mean that nothing unexpected is there. What’s new just may be hard to see, waiting to be noticed with more sophisticated methods and/or more data.] (more…)

POSTED BY Matt Strassler

ON July 27, 2012

Quick Higgs Quiz: The First One

Ok, testing you to see if you’re on your toes: when was the first Higgs particle produced by humans? We can’t know the exact date, but make your best estimate. 🙂

[Hint: how many Higgs particles will be produced at the Large Hadron Collider in 2012?]

POSTED BY Matt Strassler

ON July 26, 2012

Heading Home

The time’s come for me to return home to the United States. It is almost impossible to convey the intensity of the last few weeks. I’m excited, exhilarated and exhausted.

Even in more normal times, a visit to the CERN laboratory that built and operates the Large Hadron Collider [LHC] always wipes me out. When I’m there, several times a day I run into physicists I know who work on the LHC experiments, and so I’m constantly getting into impromptu conversations, both about the most recent scientific results and about planning how to investigate the data in future. And then there are lots of theoretical physicists of all stripes to talk to and learn from, including not only CERN faculty but also many, many visitors from all around the world.

This visit, of course, was unique. Not only did was there the historic presentation July 4th that convinced the particle physics community that a new particle, most likely a type of Higgs particle, has been found, it was followed (as was anticipated) by days and days of incessant discussions about interpreting the data that demonstrated the particle’s presence, and about future strategies to learn more about it. Then there was a five-day workshop at CERN (over a weekend!) concerning not only the Higgs search but also all of the other new results (of which there are many, though not as newsworthy) that the LHC experiments have produced. [For that workshop, I was asked to put together a presentation on a subject on which I don’t feel entirely an expert, which was an interesting but rather stressful experience.] And finally there was a three-day Higgs Hunting Workshop on the outskirts of Paris, entirely focused on the Higgs, where we saw some new Higgs data presented by the ATLAS experiment, a full review of all the previously presented Higgs data from all the relevant experiments, lots of theoretical talks about how to calculate the properties of the simplest type of Higgs particle with very high precision, discussions of the implications of the current data for whether the new particle might be a Higgs of a more complicated type, and also presentations reviewing the history of the Higgs search and looking forward into the near-term and long-term future. All Higgs All The Time! [Yet again, I had to prepare a presentation that I found very stressful, and struggled with until almost the last moment. Between my departure from Geneva Tuesday afternoon until the Higgs Hunting Workshop ended late Friday afternoon, I don’t think I took a break except for meals.]

So I think you can understand why I’ve been a little slow to post and why I’m a little slow to answer your questions and comments just now. I expect to be ready to start answering questions and putting more pedagogical stuff up on the site over the coming week. In fact, for those of you who’ve had a bit of a freshman physics course, I’ve figured out how to explain how the Higgs field does its thing, namely, how it gives mass to other particles. Maybe as I put that explanation together I’ll figure out how to explain it even for those of you who haven’t had freshman physics, though that will be a lot trickier.

But right now I’m still winding down, and trying to clear my brain. Much work lies ahead of us in particle physics — for the LHC is still in its early stages, and we need many years of study of the new particle before it will teach us what we need to know about the Higgs field(s).

POSTED BY Matt Strassler

ON July 23, 2012

New Higgs Result From the ATLAS Experiment

[2:40 Paris time: UPDATED ]

The ATLAS experiment (in a talk by Olivier Arnaez at the Higgs Hunting workshop in Orsay, France that I’m attending) has made public its search for Higgs particles decaying through real and virtual W particles to a lepton (electron or muon), anti-lepton, neutrino and anti-neutrino. [CMS made its result for this search public on July 4th at the big presentations at which discovery of the Higgs-like particle was announced.] The importance of this search is now no longer to tell whether the Higgs-like particle exists — we are confident that it does — but to try to measure how often these particles are produced and then decay in this particular way.

This is a very difficult measurement, with a small signal and a complex and large background, and it only allows a measurement of a rate of the process; the mass of the particle producing an observed excess cannot be determined to better than 30-50%, because the neutrino and anti-neutrino are not observed, and the lepton and anti-lepton are not enough to figure out the mass of the parent particle. Meanwhile, small amounts of data can play tricks. After last summer’s data, ATLAS saw a sign of something. By March, with the full 2011 data, they said they didn’t. Now, including 2012 data, they see it — in fact, they see slightly more than expected for the simplest possible type of Higgs particle (“the Standard Model Higgs) of mass 125 GeV/c².

More details to follow shortly, but the news is:

ATLAS observes in 2012 data a 3.1 sigma deviation from the no-Higgs hypothesis
Combined with 2011 data (which showed almost no excess) there is now a 2.8 sigma deviation from the no-Higgs hypothesis
the excess looks like a Higgs particle; it is quite consistent in its transverse-mass distribution with the hypothesis of a Higgs-like particle at a mass of 125 GeV/c²
the fit to the signal is 1.4+-0.5 times larger than the Standard Model prediction for a Higgs particle of mass of 125 GeV/c² (though one should not forget that this measurement isn’t good for telling us the mass; just by itself, it would also be consistent with a lighter Higgs particle produced with an expected rate or a heavier Higgs particle with a much lower than expected rate.)
this in turn is in good agreement with what ATLAS observes in the two-photon and four-lepton searches, both of which are a bit higher than the prediction for the simplest Higgs with mass of 125 GeV/c²
this also is consistent specifically with the prediction, which holds for most expected types of Higgs particles, that the ratio of the strengths of the interaction of the new particle with W and Z particles is equal to the ratio of the masses of the W and Z.

These results are also roughly consistent, within the uncertainties, with those from CMS, which sees a slightly smaller production rate than expected, something like 0.6 +- 0.4 (don’t quote me, I’m reading it off a plot) times what is predicted for a simplest Higgs of mass 125 GeV/c².

NOTE ADDED: Did I mention this is a difficult measurement? The excess in the 2012 data looks a lot like a Higgs particle signal, but a mis-estimated background would look pretty similar (though admittedly it would have to be a big mis-estimate — but then again, the signal in 2012 is itself more than twice as big as expected), and so we’re reliant on the estimates of the systematic uncertainties on the backgrounds given by the experimenters. There are differences between the 2011 and 2012 analysis techniques (improvements, surely) that I don’t understand yet. So… an impressive result, but my own view of it is still a little murky. I’m glad this excess wasn’t essential for the claim of Higgs particle discovery.

POSTED BY Matt Strassler

ON July 18, 2012

Buy The Book

Reading My Book?

Got a question? Ask it here.

Media Inquiries

For media inquiries, click here.

Category: Higgs

POSTED BY Matt Strassler

POSTED BY Matt Strassler

POSTED BY Matt Strassler

POSTED BY Matt Strassler

POSTED BY Matt Strassler

POSTED BY Matt Strassler

POSTED BY Matt Strassler

POSTED BY Matt Strassler

POSTED BY Matt Strassler

POSTED BY Matt Strassler

Recent Posts

Buy The Book

Reading My Book?

Media Inquiries

Order Waves In An Impossible Sea