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An Extraordinarily Productive Visit to Fermilab

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This has been an exceptional few days, and I’ve had no time to breathe, much less blog. In pre-covid days, visits to the laboratories at CERN or Fermilab were always jam-packed with meetings, both planned and spontaneous, and with professional talks by experts visiting the labs. But many things changed during the pandemic. The vitality … Read more

A Week On Topic at Fermilab

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The blog’s been quiet recently, thanks to a series of unfortunate events, not the least of which were my first (known) Covid-19 infection and an ongoing struggle with a bureaucracy within the government of Massachusetts. But meanwhile there is some good news: it seems I will someday have a book published. More on that another time.

Meanwhile I have also been doing some science. Recent efforts included presenting at a workshop on the potential capabilities of the Future Circular Collider [FCC], a possible successor to the Large Hadron Collider [LHC]. Honestly, my own feeling is that the FCC is an unfortunate distraction from important LHC activities. For my part I remain focused on the latter, and on trying to remind everyone just how much remains to do with the LHC data sets from previous years.

Visiting the LPC at Fermilab

Toward that end, I’ll be at the Fermilab National Accelerator this week, near Chicago. I’ll be visiting their LHC Physics Center [LPC], which is the major US hub for the CMS experiment at the LHC. (CMS is one of the LHC’s two general purpose experiments, the other being ATLAS; these are the experiments that discovered the Higgs particle.)

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At a Workshop on Hidden Particles at the LHC

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Cutting edge particle physics today:

I’ve been spending the week at an inspiring and thought-provoking scientific workshop. (Well, “at” means “via Zoom”, which has been fun since I’m in the US and the workshop is in Zurich; I’ve been up every morning this week before the birds.) The workshop brings together a terrific array of particle theorists and Large Hadron Collider [LHC] experimenters from the ATLAS and CMS experiments, and is aimed at “Semi-Visible Jets”, a phenomenon that could reveal so-far-undiscovered types of particles in a context where they could easily be hiding. [Earlier this week I described why its so easy for new particles to hide from us; the Higgs boson itself hid for almost 25 years.]

After a great set of kick-off talks, including a brand new result on the subject from ATLAS (here’s an earlier one from CMS) we moved into the presentation and discussion stage, and I’ve been learning a lot. The challenges of the subject are truly daunting, not only because the range of possible semi-visible jets is huge, but also because the scientific expertise that has to be gathered in order to design searches for semi-visible jets is exceptionally wide, and often lies at or beyond the cutting edge of research.

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Celebrating the 34th Birthday of the Higgs Boson!

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Ten years ago today, the discovery of the type of particle known as the “Higgs Boson” was announced. [What is this particle and why was its discovery important? Here’s the most recent Higgs FAQ, slightly updated, and a literary article aimed at all audiences high-school and up, which has been widely read.]

But the particle was first produced by human beings in 1988 or 1989, as long as 34 years ago! Why did it take physicists until 2012 to discover that it exists? That’s a big question with big implications.

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Long Live LLPs!

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Particle physics news today… I’ve been spending my mornings this week at the 11th Long-Lived Particle Workshop, a Zoom-based gathering of experts on the subject.  A “long-lived particle” (LLP), in this context, is either a detectable particle that might exist forever, or a particle that, after traveling a macroscopic, measurable distance — something between 0.1 … Read more

A Prediction from String Theory

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(An advanced particle physics topic today…)

There have been various intellectual wars over string theory since before I was a graduate student. (Many people in my generation got caught in the crossfire.) But I’ve always taken the point of view that string theory is first and foremost a tool for understanding the universe, and it should be applied just like any other tool: as best as one can, to the widest variety of situations in which it is applicable. 

And it is a powerful tool, one that most certainly makes experimental predictions… even ones for the Large Hadron Collider (LHC).

These predictions have nothing to do with whether string theory will someday turn out to be the “theory of everything.” (That’s a grandiose term that means something far less grand, namely a “complete set of equations that captures the behavior of spacetime and all its types of particles and fields,” or something like that; it’s certainly not a theory of biology or economics, or even of semiconductors or proteins.)  Such a theory would, presumably, resolve the conceptual divide between quantum physics and general relativity, Einstein’s theory of gravity, and explain a number of other features of the world. But to focus only on this possible application of string theory is to take an unjustifiably narrow view of its value and role.

The issue for today involves the behavior of particles in an unfamiliar context, one which might someday show up (or may already have shown up and been missed) at the LHC or elsewhere. It’s a context that, until 1998 or so, no one had ever thought to ask about, and even if someone had, they’d have been stymied because traditional methods are useless. But then string theory drew our attention to this regime, and showed us that it has unusual features. There are entirely unexpected phenomena that occur there, ones that we can look for in experiments.

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The Importance and Challenges of “Open Data” at the Large Hadron Collider

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A little while back I wrote a short post about some research that some colleagues and I did using “open data” from the Large Hadron Collider [LHC]. We used data made public by the CMS experimental collaboration — about 1% of their current data — to search for a new particle, using a couple of twists (as proposed over 10 years ago) on a standard technique.  (CMS is one of the two general-purpose particle detectors at the LHC; the other is called ATLAS.)  We had two motivations: (1) Even if we didn’t find a new particle, we wanted to prove that our search method was effective; and (2) we wanted to stress-test the CMS Open Data framework, to assure it really does provide all the information needed for a search for something unknown.

Recently I discussed (1), and today I want to address (2): to convey why open data from the LHC is useful but controversial, and why we felt it was important, as theoretical physicists (i.e. people who perform particle physics calculations, but do not build and run the actual experiments), to do something with it that is usually the purview of experimenters.

The Importance of Archiving Data

In many subfields of physics and astronomy, data from experiments is made public as a matter of routine. Usually this occurs after an substantial delay, to allow the experimenters who collected the data to analyze it first for major discoveries. That’s as it should be: the experimenters spent years of their lives proposing, building and testing the experiment, and they deserve an uninterrupted opportunity to investigate its data. To force them to release data immediately would create a terrible disincentive for anyone to do all the hard work!

Data from particle physics colliders, however, has not historically been made public. More worrying, it has rarely been archived in a form that is easy for others to use at a later date. I’m not the right person to tell you the history of this situation, but I can give you a sense for why this still happens today.

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A Broad Search for Fast Hidden Particles

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A few days ago I wrote a quick summary of a project that we just completed (and you may find it helpful to read that post first). In this project, we looked for new particles at the Large Hadron Collider (LHC) in a novel way, in two senses. Today I’m going to explain what we did, why we did it, and what was unconventional about our search strategy.

The first half of this post will be appropriate for any reader who has been following particle physics as a spectator sport, or in some similar vein. In the second half, I’ll add some comments for my expert colleagues that may be useful in understanding and appreciating some of our results.  [If you just want to read the comments for experts, jump here.]

Why did we do this?

Motivation first. Why, as theorists, would we attempt to take on the role of our experimental colleagues — to try on our own to analyze the extremely complex and challenging data from the LHC? We’re by no means experts in data analysis, and we were very slow at it. And on top of that, we only had access to 1% of the data that CMS has collected. Isn’t it obvious that there is no chance whatsoever of finding something new with just 1% of the data, since the experimenters have had years to look through much larger data sets?

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