Professor Michio Kaku, of City College (part of the City University of New York), is well-known for his work on string theory in the 1960s and 1970s, and best known today for his outreach efforts through his books and his appearances on radio and television. His most recent appearance was a couple of days ago, in an interview on CBS television, which made its way into this CBS news article about the importance of the Higgs particle.
Unfortunately, what that CBS news article says about “why the Higgs particle matters” is completely wrong. Why? Because it’s based on what Professor Kaku said about the Higgs particle, and what he said is wrong. Worse, he presumably knew that it was wrong. (If he didn’t, that’s also pretty bad.) It seems that Professor Kaku feels it necessary, in order to engage the imagination of the public, to make spectacular distortions of the physics behind the Higgs field and the Higgs particle, even to the point of suggesting the Higgs particle triggered the Big Bang.
In doing this, Professor Kaku sows confusion among journalists and the public, and undermines the efforts of serious particle physicists to explain and convey, both vividly and accurately, the science and the excitement of our time. And on what grounds does he justify this? Doesn’t the taxpaying public deserve the truth? Isn’t the truth already exciting enough? And what will the public think of science if, in this information era, the promulgation of falsehoods and near-falsehoods on national media is unanswered by complaints from other scientists?
I’m so frustrated with Professor Kaku’s unfortunate remarks that rather than write more today, I’ll simply direct you to Sean Carroll’s blog — Sean’s response was much more measured and polite than mine would be if I spoke my mind. For now I’ll just conclude by suggesting that Professor Kaku has some serious explaining to do — to his scientific colleagues, to the science journalist that he misled, and to the public.
(Perhaps you will ask me the same question: “Why DOES the Higgs particle matter?” Here’s my own article from July giving the answer; it’s short and condensed, but it’s not false, as my colleagues will attest! For a longer explanation with more details and fewer shortcuts, you can try Sean Carroll’s book or Lisa Randall’s book, or you can poke around on my website for various related articles; there’s the Higgs FAQ, the story of the Higgs discovery, an article on why the Higgs is not related to gravity, or if you’re really ambitious you can try this set of articles [which requires you first read this set] which is suitable for people who once took a little first-year college physics.)
Since it’s been the main news story of the last week, perhaps it would be useful to do a quick summary of what the CMS and ATLAS experiments at the Large Hadron Collider [LHC] have been saying, over the past fifteen months, about their search for the process in which a Higgs particle is produced and decays to two photons.
Before we start, let me remind you that in statements about how uncertain a measurement is (and all measurements have some level of uncertainty — no knowledge is perfect), a “σ”, or “sigma”, is a statistical quantity called a “standard deviation”; a 5σ discrepancy from expectations is impressive, 3σ intriguing; but anything less than 2σ is very typical, and indicative merely of the usual coming and going of statistical flukes and fluctuations of real data around the truth. Note also that the look-elsewhere effect has to be accounted for; but usually a 5σ discrepancy without the look-elsewhere effect is enough to be convincing. And of course a discrepancy may mean either a discovery or a mistake; that’s why it is important that two experiments, not just one, see a similar discrepancy, since it is unlikely that both experiments would make the same mistake.
Ok: here are the results as they came in over time, all the way back to the inconclusive hints of 15 months ago.
December 2011:
ATLAS (4.9 inverse fb of data at 7 TeV): excess 2.8σ (where 1.4σ would be expected for a SM Higgs); less than 2σ after accounting for “look-elsewhere effect”.
CMS: (4.8 inverse fb of data at 7 TeV): excess just over 2σ (where 1.4σ would be expected for a SM Higgs); much less than 2σ after accounting for “look-elsewhere effect”.
July 2012:
ATLAS: (reanalyzing the 7 TeV data and adding 5.9 inverse fb of data at 8 TeV): signal 4.5σ (where 2.4 was expected for a SM Higgs); 3.6σ after “look-elsewhere effect”; best estimate of size of signal divided by that for a SM Higgs: 1.9 ± 0.5 (about 1.8σ above the SM prediction)
CMS (reanalyzing the 7 TeV data and adding 5.3 inverse fb of data at 8 TeV): signal 4.1σ (where 2.5 was expected for a SM Higgs); 3.2σ after “look-elsewhere effect”; best estimate of size of signal divided by that for a SM Higgs: 1.6 ± 0.4 (about 1.5σ above the SM prediction)
November/December 2012:
ATLAS: (increasing the 8 TeV data to 13.0 inverse fb): signal 6.1σ (3.3 expected for SM Higgs); 5.4σ when look elsewhere is accounted for; best estimate of size of signal divided by that for a SM Higgs: 1.8 ± 0.4 (about 2σ above the SM prediction)
CMS: No update
March 2013:
ATLAS: (taking the full 7 and 8 TeV data sets): 7.4σ (4.1 expected for a SM Higgs); best estimate of size of signal divided by that for a SM Higgs: 1.65 ± 0.30 (slightly more than 2σ above the SM prediction)
CMS: (taking the full 7 and 8 TeV data sets) uses two different methods as a cross-check, one of them complex and (on average) more powerful, the other simpler but (on average) less powerful. For the best estimate of size of signal divided by that for a SM Higgs: one method gives 0.8 ± 0.3 and the other gives 1.1 ± 0.3. Both of these are within 1σ of the SM prediction and within 2σ of the CMS July result.
To understand how consistent the two new CMS results are with each other, you have to consider how the two studies are correlated (since they are selecting events for study from the same pile of data.) Because the two methods select and discard candidate events in two different ways, they don’t include the exact same data. CMS’s simulation studies indicate that about 50 percent of the background events and 80 percent of the signal events are common to the two studies. In the end, the conclusion (see the figure below) is that the two results are consistent at 1.5σ (and at 1.8 if one considers only the 8 TeV data) — in other words, reasonably consistent with one another.
You can also ask how consistent are the new results compared to the old ones from July. When you observe that the uncertainty on the July result was very large (1.6 ± 0.4 times the Standard Model prediction, i.e. a 25% uncertainty at 1σ, 50% uncertainty at 2σ) it should not surprise you that CMS claims that their new results are both consistent with the old ones at below the 2σ level.
Slide from Moriond-QCD conference talk presenting CMS’s results, and looking at the compatibility of the two results with each other (top two lines in the table) and of each of the two new results with the previous published results. Note the conclusion in the last line.
Meanwhile, all of the ATLAS results are closely compatible with each other. This is more what one would naively expect, but not necessarily what actually happens in real data. Of course ATLAS’s results aren’t giving a consistent mass for the new particle yet, whereas CMS’s are doing so… well, this is what happens with real data, folks.
The real issue is whether ATLAS’s measurements and CMS’s measurements of the two photon rate are compatible with each other. Currently they are separated by at least 2σ and maybe as much as 3σ (a very rough estimate), which is not unheard of but is somewhat unusual. Well, whether the cause is an error or a statistical fluke or both, it unfortunately leaves us in a completely ambiguous situation. On the one hand, CMS’s results agree with the Standard Model prediction to within about 1σ. On the other hand, ATLAS’s results are in tension with the Standard Model prediction by a bit more than 2σ. We have no way to know which result is closer to the truth — especially when we recall that the uncertainty in the Standard Model prediction is itself about 20%. If ATLAS and CMS had both closely agreed with the Standard Model we’d be confident that any deviations from the Standard Model are too small to observe; if they both significantly disagreed in the same way, we’d be excited about the possibility that the Standard Model might be about to break down. But with the current results, we don’t know what to think.
So as far as the Higgs particle’s decays to two photons, we’ve gotten as much (or almost as much) information as we’re going to get for the moment; and we have no choice but to accept that the current situation is ambiguous and to wait for more data in 2015. Of course the Standard Model may break down sooner than 2015, for some other reason that the experimenters have yet to uncover in the 2011-2012 data. But the two-photon measurement won’t be the one to crack the armor of this amazing set of equations. (For those who got all excited last July; you were warned that the uncertainties were very large and the excess might well be ephemeral.)
As soon as the discovery of that famous new particle was announced at the Large Hadron Collider [LHC] last year, there were already very good reasons to think it was a Higgs particle of some type. I described them to you back then, as part of my “Higgs Discovery” series. But, as I cautioned, those arguments relied partly on data and partly on theoretical reasoning.
Over the past nine months, with additional data collected through December and analyzed through the present day, it has become more and more convincing that this particle behaves very much like a Higgs particle, along the lines I described following the Edinburgh conference back in January. One by one the doubters have been giving up, and few remain. This is a Higgs particle. That’s my point of view (see last week’s post — you heard it here first), the point of view of most experts I talk to [in a conference I’m currently attending, not one person out of about forty theorists and experimenters has dissented], and now the official point of view of the CERN laboratory which hosts the LHC. (more…)
I’m pleased to say that last night I found comet Pan-STARRS, which is gracing the western sky just after sunset, and so I can recommend now that you all give it a try. Binoculars will definitely make it easier to find, and allow you to see more of it. It looks great! Here are some thoughts on how to find it, appropriate if you’re in a country at roughly the same latitude as the United States. (If you live far to the north or far to the south, you’ll need to get advice from someone who found it in a latitude similar to yours. I don’t believe people in the southern hemisphere can still see it.) (more…)
A quick note: I’ve had a number of questions from commenters about whether the new Higgs-like particle really has spin 0 (as it must if it is truly a Higgs particle) or whether it might have spin 2. Well, spin 2 (with positive parity) is now strongly disfavored, as a result of new results from the ATLAS and CMS experiments at the Large Hadron Collider. CMS has disfavored it at the 98.5-99.9% confidence level (the number depending on assumptions about whether the particle is produced in collisions of gluons or in collisions of a quark and anti-quark) using their data from the particle’s decays to two lepton/anti-lepton pairs. ATLAS has disfavored it at the 95%-99% confidence level (similarly depending on assumptions) using their data from decays of the new particle to a lepton, anti-lepton, neutrino and anti-neutrino. Meanwhile, there is no reason for a spin-2 particle (especially with negative parity) to have the relative decay probabilities that are observed in the data, so the fact that all these probabilities are similar to those of a simple Higgs particle disfavors spin 2 and favors spin 0. And there’s simply no theory of a spin-2 particle (with either parity) that doesn’t have other observable particles rather nearby in mass. No one of these arguments is definitive, but in combination they are pretty convincing.
Meanwhile all the data is consistent with a spin 0 particle with decay probabilities roughly similar to that of a Standard Model Higgs (the simplest type of Higgs particle.)
So let’s stop spending much bandwidth on spin 2: it is disfavored by both ATLAS and CMS — directly by measurement of the particle’s spin, and indirectly via its relative probabilities to decay to various types of particles — and it is disfavored theoretically. The more important measurement is to check whether this apparently spin-0 particle really has positive parity, or whether it has a mix of positive and negative parity.
