MATT STRASSLER
Of Particular Significance

Some Weird Twists and Turns

In my last post, I promised you some comments on a couple of other news stories you may have seen.  Promise kept! see below.

But before I go there, I should mention (after questions from readers) an important distinction.  Wednesday’s post was about the simple process by which a Bs meson (a hadron containing a bottom quark and a down[typo] strange anti-quark, or vice versa, along with the usual crowd of gluons and quark/antiquark pairs) decays to a muon and an anti-muon.  The data currently shows nothing out of the ordinary there.  This is not to be confused with another story, loosely related but with crucially different details. There are some apparent discrepancies (as much as 3.7 standard deviations, but only 2.8 after accounting for the look-elsewhere effect) cropping up in details of the intricate process by which a Bd meson (a hadron containing a bottom quark and a down antiquark, or vice versa, plus the usual crowd) decays to a muon, an anti-muon, and a spin-one Kaon (a hadron containing a strange quark and a down anti-quark, or vice versa, plus the usual crowd). The measurements made by the LHCb experiment at the Large Hadron Collider disagree, in some but not all features, with the (technically difficult) predictions made using the Standard Model (the equations used to describe the known particles and forces.)

Don't confuse these two processes! (Top) The process B_s --> muon + anti-muon, covered in Wednesday's post, agrees with Standard Model predictions. (Bottom) The process B_d --> muon + anti-muon + K* is claimed to deviate by nearly 3 standard deviations from the Standard Model, but (as far as I am aware) the prediction and associated claim has not yet been verified by multiple groups of people, nor has the measurement been repeated.
Don’t confuse these two processes! (Top) The process B_s –> muon + anti-muon, covered in Wednesday’s post, agrees with Standard Model predictions. (Bottom) The process B_d –> muon + anti-muon + K* is claimed to deviate by nearly 3 standard deviations from the Standard Model, but (as far as I am aware) the prediction and associated claim has not yet been verified by multiple groups of people, nor has the measurement been repeated.

A few theorists have even gone so far as to claim this discrepancy is clearly a new phenomenon — the end of the Standard Model’s hegemony — and have gotten some press people to write (very poorly and inaccurately) about their claim.  Well, aside from the fact that every year we see several 3 standard deviation discrepancies turn out to be nothing, let’s remember to be cautious when a few scientists try to convince journalists before they’ve convinced their colleagues… (remember this example that went nowhere? …) And in this case we have them serving as judge and jury as well as press office: these same theorists did the calculation which disagrees with the data.  So maybe the Standard Model is wrong, or maybe their calculation is wrong.  In any case, you certainly musn’t believe the news article as currently written, because it has so many misleading statements and overstatements as to be completely beyond repair. [For one thing, it’s a case study in how to misuse the word “prove”.] I’ll try to get you the real story, but I have to study the data and the various Standard Model predictions more carefully first before I can do that with complete confidence.

Ok, back to the promised comments: on twists and turns for neutrinos and for muons…   (more…)

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POSTED BY Matt Strassler

ON August 2, 2013

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A Couple of Rare Events

Did you know that another name for Minneapolis, Minnesota is “Snowmass”?  Just ask a large number of my colleagues, who are in the midst of a once-every-few-years exercise aimed at figuring out what should be the direction of the U.S. particle physics program.  I quote:

  • The American Physical Society’s Division of Particles and Fields is pursuing a long-term planning exercise for the high-energy physics community. Its goal is to develop the community’s long-term physics aspirations. Its narrative will communicate the opportunities for discovery in high-energy physics to the broader scientific community and to the government.

They are doing so in perhaps the worst of times, when political attacks on science are growing, government cuts to science research are severe, budgets to fund the research programs of particle physicists like me have been chopped by jaw-dropping amounts (think 25% or worse, from last year’s budget to this year’s — you can thank the sequester).. and all this at a moment when the data from the Large Hadron Collider and other experiments are not yet able to point us in an obvious direction for our future research program.  Intelligent particle physicists disagree on what to do next, there’s no easy way to come to consensus, and in any case Congress is likely to ignore anything we suggest.  But at least I hear Minneapolis is lovely in July and August!  This is the first Snowmass workshop that I have missed in a very long time, especially embarrassing since my Ph.D. thesis advisor is one of the conveners.  What can I say?  I wish my colleagues well…!

Meanwhile, I’d like to comment briefly on a few particle physics stories that you’ve perhaps seen in the press over recent days. I’ll cover one of them today — a measurement of a rare process which has now been officially “discovered”, though evidence for it was quite strong already last fall — and address a couple of others later in the week.  After that I’ll tell you about a couple of other stories that haven’t made the popular press… (more…)

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POSTED BY Matt Strassler

ON July 31, 2013

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A Short Break

Personal and professional activities require me to take a short break from posting.  But I hope, whether you’re a novice with no knowledge of physics, or you’re a current, former, or soon-to-be scientist or engineer, or you’re somewhere between, that you can find plenty of articles of interest to you on this site.  A couple of reminders and pointers:

* If you haven’t yet seen my one-hour talk for a general audience, “The Quest for the Higgs Boson”, intended to explain accurately what the Higgs field and particle are all about, while avoiding the most common misleading short-cuts, it’s available now, along with a 20-minute question and answer session.

* If you want a slightly more technical and written discussion of the Higgs field and particle, complete with animated images, and suitable for people who may once have had a semester or two of university physics and math, try this series of articles first, and then go to this series.

* If you’d like to better understand the language of “matter”, “mass”, and “energy” that is everywhere in popular explanations of science, but eternally confusing because of how different authors choose to talk about these subjects, you might find some useful tips in these articles: #1, #2, #3, #4.

* If you need a reminder about what “ordinary matter” (i.e. things like pickles, people and planets) is made of, try this series, which goes all the way from molecules down to quarks.

* If you’re curious about what “particle/anti-particle annihilation” does and doesn’t mean, try this article.

* And here are the types of particles and forces of nature that we know about, and (for the moderately advanced reader) here’s how they’d be rearranged if the Higgs field were turned off.

Hopefully there’s something on that list that interests you, and many links within those articles to other things that may even interest you more.  Have fun exploring!  And stay tuned; I’ll be writing more in the near future…

Picture of POSTED BY Matt Strassler

POSTED BY Matt Strassler

ON July 15, 2013

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Mass-ive Source of Confusion

One of the challenges for a person trying to explain physics to the non-expert — and for non-experts themselves — is that scientific language and concepts are often frustratingly confusing. Often two words are used for the same thing, sometimes words are used that are fundamentally misleading, and often a single word is used for two very different but related concepts. You’d think we’d clear this stuff up, but no one has organized a committee dedicated to streamlining and refining our terminology.

A deeply unfortunate case, the subject of today’s post, is the word “mass”. Mass was confusing before Einstein, and then Einstein came along and (accidentally) left the word mass with two different definitions… both of which you’ll see in first-year university textbooks. (Indeed, this confusion even extended to physicists more broadly, causing the famous particle physicist Lev Okun to make this issue into a cause celebre…) And it all has to do with how you interpret E = mc² — the only equation everybody knows — which relates the energy stored in an object to the mass of the object times the square of the universal speed limit c, also known as “the speed of light”.

Here are the two possible interpretations of this equation. Modern particle physicists (including me) only use the first interpretation. The purpose of this post is to alert you to this fact, and to point you to an article where I explain more carefully why we do it this way. (more…)

Picture of POSTED BY Matt Strassler

POSTED BY Matt Strassler

ON July 11, 2013

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Floating in Space … But Why?

Have you perhaps wanted to go into space someday, so you could float around and do somersaults like the astronauts you see on TV? You know, out in space, where everything floats, because … because …

…

because there’s no gravity in outer space???

  • Hmm… If there were no gravity in space, what would keep the Earth orbiting the Sun? Or the Moon orbiting the Earth?

umm… because…

Picture of POSTED BY Matt Strassler

POSTED BY Matt Strassler

ON July 8, 2013

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Happy IndependHiggs Day!

July 4th will never be the same.  As a child growing up in the United States, it meant flags, humidity, Sousa marches, democracy, and fireworks.  Now it means something else: Switzerland, laboratories, technical wizardry, Higgs particles and — fireworks!

ATLASH2e2mu

Yes, this picture is a representation of the data taken by the ATLAS experiment during a 2012 proton-proton collision at the Large Hadron Collider [LHC], in which (probably) a Higgs particle was created and swiftly decayed to (i.e. was transformed into) a muon, an antimuon, an electron and an anti-electron [“positron”]. Also flying about are many proton-like particles, called hadrons, the debris always seen in a proton-proton collision.  Boom!  (Admittedly a very quiet boom!)

2012 was a remarkable year that we’ll never forget, and its July 4th, when the Higgs particle’s discovery was announced, was unique.   [And if you’re still confused about what the excitement is all about, or want to learn more, click here for some of my writing and speaking about it all.]

But as we wait for the LHC to start running again in 2015, analysis of the 2011-2012 data continues.  People are working very hard, even on July 4th :-), and the possibility of other discoveries in that data is real!  So stay tuned as more results emerge over the summer and fall and into 2014.

Picture of POSTED BY Matt Strassler

POSTED BY Matt Strassler

ON July 4, 2013

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