I’ve done some work today on writing the first parts of a section on Extra Dimensions of Space, a very important but very large topic. It will probably be months before the whole thing is fleshed out, but some of you may be curious to read along as it takes shape. In particular, you can’t understand extra dimensions of space if you don’t understand dimensions properly, so I’m starting from the point of view that I need to explain how I and many other physicists think about dimensions in general, and spatial dimensions in particular. Right now, of several planned sub-articles, only one (on one-dimensional worlds) exists so far, but even that article is pretty thick with material, and perhaps interesting for many readers.
Author: Matt Strassler
Did you know that most of the information produced in the proton-proton collisions at the Large Hadron Collider (LHC) is dumped irretrievably in the metaphorical trash bin — sent ingloriously into oblivion — yes, discarded permanently — as quickly as it comes in? By “most,” I don’t mean 75%. I don’t mean 95%. I mean 99.999% to 99.9999% of all the data at the Large Hadron Collider is erased within a second of its being collected.
It sounds crazy; how can a scientific experiment simply ignore the vast majority of its data?! Well, it’s not as insane as if first appears. Nor is it unprecedented; previous generations of hadron colliders have done something similar. And finally, it is absolutely necessary. In this article I’ll tell you why.
POSTED BY Matt Strassler
ON November 4, 2011
Matt Strassler 11/1/11. No rest for the weary: yet another discrepancy. This one is somewhat different from the small multi-lepton excess at CMS of a couple of weeks ago (tenuous, but in a very interesting and plausible place) and from the OPERA faster-than-light neutrino claim (not so tenuous, but not so plausible either). Now we have a discrepancy involving collisions that produce two low-energy photons [particles of light]. The effect is seen in four experiments, not one: both ATLAS and CMS at the Large Hadron Collider (LHC), and also CDF and DZero at the Tevatron collider. It’s too large to be a statistical fluke (the excess is not small and it shows up in four experiments). Nor does it look like an experimental mistake (since it shows up in four experiments). Might it be a sign of a new phenomenon not predicted by the Standard Model (the equations that describe the known particles and forces, plus the simplest possible Higgs particle)? Maybe… Can’t rule it out, though there’s not enough information in the experiments’ public documents for a serious evaluation of that possibility. But in any case, my preliminary impression is that it’s most likely something else: either a problem with the theoretical calculation of what the Standard Model predicts, or a problem with the way this theoretical calculation was used by the experiments.
Now why would I come to that conclusion? To read more, click here.
POSTED BY Matt Strassler
ON November 2, 2011
I’m hoping to focus this week on updating and improving some of the background articles on the website, rather than updating the latest news (unless something really crucial happens.) I’ve just put up an improved version of my article on one of the most important aspects of the physics of the Large Hadron Collider, and indeed of any modern high-energy particle collider: jets, the experimental manifestation of high-energy quarks, anti-quarks, and gluons. The article, which explains why a high-energy quark created in a particle collision is measured as a spray (or “jet”) of hadrons, now has figures and an accompanying text that should make it much clearer. Comments welcome, as always.
POSTED BY Matt Strassler
ON October 31, 2011
Shoichi Sakata would have been 100 years old this year, and a conference celebrating his achievements in high-energy physics and beyond is underway here in Nagoya. The university president made brief introductory remarks, describing how, right after the war, Sakata introduced a democratically-inspired culture into the physics department, insisting on the right of young researchers to choose their own research paths independent of senior faculty, and permanently impacting the culture of physics (and beyond) at Nagoya University. There followed a talk reviewing Sakata’s most important work, including central contributions to the understanding of the muon, many of the hadrons, and the first two neutrinos. Unfortunately for Sakata, English publication of one of his most important papers (correctly identifying the muon as a decay product of an electrically-charged pion) was delayed by the war; another of his ideas (concerning the nature of hadrons) inspired many important developments, but was not itself correct; and a third idea (suggesting two neutrinos, which could oscillate one into the other) arrived just a bit too late to predict an experimental result. On top of this, he died young, before he was 60. Consequently, outside Japan he is not so widely known today. But here he casts a long shadow. Indeed, Professor Maskawa’s brief address at the opening of the Inaugural Conference of the Kobayashi-Maskawa Institute (earlier this week) was entirely devoted to lauding his mentor.
Tucked in among today’s talks, another ceremony, this one to unveil a memorial stone outside the Kobayashi-Maskawa Institute, in Sakata’s honor.
Unfortunately I cannot stay for the last day of the conference. An amusing feature of my journey home: I depart Tokyo at 5 pm on October 28th and arrive in New York City at 5 pm on October 28th.
POSTED BY Matt Strassler
ON October 27, 2011
The Nagoya (Japan) conference in celebration of the Inauguration of the Kobayashi-Maskawa Institute has come to a close this morning. There was a pleasant little ceremony yesterday in which Kobayashi and Maskawa took up shovels to place dirt around a newly-planted tiny apple tree outside the institute — an apple tree descended directly from “Newton’s apple tree” at Trinity College, Cambridge (you know the one, the tree whose apple is said to have inspired Newton’s theory of gravity — as though he’d never seen a dropped fork before.)
Meanwhile, back indoors there were numerous talks on a wide variety of research topics. Several of these addressed Japan’s broad experimental particle physics program, which covers neutrinos, bottom quarks, dark matter, cosmic rays, and the development of new experimental devices. Here are a few tidbits I heard about yesterday.
First, the one you all want to know: there was some very good news from the OPERA experiment (the one with the speedy neutrinos,) in which Nagoya is a participant. (more…)
POSTED BY Matt Strassler
ON October 26, 2011
I’ve already mentioned in some earlier posts that the international nature of high-energy physics is one of its great pleasures. And occasionally the opportunity for travel arises in the context more of celebration than of pure work. In 2008, Professors Makoto Kobayashi and Toshihide Maskawa won the Nobel Prize, (sharing it with Yoichiro Nambu, who was awarded for a separate topic.) The award was for work they did together in 1973 predicting [more or less] the existence of the “third generation” of quarks (the top and bottom quarks — the first two generations being (1) the up and down and (2) the charm and strange quarks.) (You can read about the known quarks here.) (more…)
POSTED BY Matt Strassler
ON October 25, 2011
The most important thing that happened this week in Berkeley, California was definitely not the news of a small and probably ephemeral excess of multi-lepton events at the Large Hadron Collider‘s CMS experiment — and probably not even the disconcerting earthquakes on (near?) the strained Hayward fault — it was the (public but not yet peer-reviewed) report from the Berkeley Earth Team, a group of mostly non-climate scientists [mostly from physics] who went back to analyze and check the data that climate scientists have been studying for years. Go look at their website; it’s for you.
My understanding is that the scientific director, Richard Muller, organized the team because he was highly skeptical that climate scientists were treating their data properly. His agenda seems to have been largely scientific rather than political. Though I did not share his point of view, I found it understandable. In my field we have often seen data mis-analyzed, even though high-energy physics is a largely apolitical domain. It is not easy, even with full scientific integrity, to avoid all sources of bias. With something that has enormous policy implications, such as climate change, there was some concern among serious scientists that error and/or group-think bias could set in within even a large community. The idea of having a largely independent review by scientifically experienced non-experts was a good one.
Well, in science, when you see vocal skeptics starting to come around to the point of view of those they previously criticized, you know the climate is changing.
I doubt we’ll ever have a more independent review than the Berkeley Earth Team has just given us. I don’t know all the scientists on the team, but I am confident at least that Saul Perlmutter (who just won the Nobel Prize) is of the highest integrity. The team included only scientists who had not taken a public position on climate change, and their funding sources are very broad-based. Moreover, unlike climate scientists, who could be subjected to the accusation of letting a vested interest in obtaining funding bias their science toward a prevailing viewpoint, some members of this team had to give up time from their own personal research, thereby reducing their funding opportunities, in order to participate in this endeavor. None of them has much obviously to gain — no probability of scientific recognition, prizes, funding, or even thanks — especially Muller, who in confirming what he expected the team would likely refute has burned plenty of bridges in the interest of honesty.
I’m definitely not qualified to comment on the details of climate science, and I haven’t read the report. All I have to go on right now is the two-page summary of the results reported here:
http://berkeleyearth.org/Resources/Berkeley_Earth_Summary_20_Oct
which I highly recommend you personally read. It has subtleties and details that the press is not capturing.
Nevertheless, it seems to me at this early stage that the report’s main result — that where it has so far come to conclusions, it agrees with what many climate scientists have long been saying — represents a success story for science, one worth noting. It confirms yet again that preconceptions and funding sources do not automatically determine scientific results. And it confirms also that it is possible, over time, to obtain consensus about nature — that even while the US Congress witnesses ideology placed before the nation’s best interest, the collective scientific process still manages to put the integrity of science first, and a scientist’s pride second.
POSTED BY Matt Strassler
ON October 24, 2011
For those of you wondering about this new and interesting hint of a possible (but still very doubtful) new physical phenomenon in the data from the CMS experiment at the Large Hadron Collider (LHC), here’s the summary of the situation. [UPDATE: 10/22/11 very slightly reworded and reordered for clarity and proper emphasis]
- Proton-proton collisions that produce three or more charged leptons and/or anti-leptons (“multi-leptons” for short) have long been seen as an excellent but very tricky place to look for new physics. I have written an explanatory article as to why they are so good (to the point of being sometimes called “golden”), but also why they are tricky; there’s some fool’s gold in there.
- On Wednesday and Thursday the CMS experiment gave two presentations (here are my detailed comments, showing some tables and plots, on talks #1 and on #2) at a workshop in Berkeley, CA, giving two perspectives on a single set of multi-lepton events, obtained from data collected through August. They finds a small excess — more events than expected — but too small for CMS to claim to have seen anything significant. [And Nota Bene: CMS has made no claims there is an excess, because the evidence is very weak by the stringent standards used (for good reason) in particle physics.]
- Indeed, it must be remembered that small excesses of this type occur regularly in science, just from statistical fluctuations or from errors by experimentalists or theorists (remember the Higgs hints from earlier in the year, which were stronger, but have so far gone unconfirmed.) And the excess seen here does not look particularly different from a statistical fluctuation. So we should not be surprised if this hint goes away with more data from CMS, or when ATLAS reports their own studies.
- But the excess is still large enough to intrigue theoretical particle physicists and motivate some consideration of what new physics, if any, might cause such an excess, and how to look for it more efficiently.
- Two moderate earthquakes occurred in Berkeley, before and after the second talk. Draw your own conclusions. [joke…!]
- Some of the plots shown at the second talk suggest that any such excess would most likely have to come from rather lightweight particles (well below 500 GeV) that do not carry the strong nuclear force. (The reasoning is explained in my post following the second talk.) The logic is not airtight, but a number of other simple possibilities clearly wouldn’t fit the data at all.
- Supersymmetry theorists will be quick to point out that supersymmetry has particles of the right type (charginos and neutralinos) and many variants of supersymmetry predict such a signal, though typically a bit smaller. (You can read about how supersymmetry does that here; note especially Figure 2.)
- However, many other classes of models of new physics can have light-weight particles with no strong forces, and associated multi-lepton events; such events are very generic and do not depend on anything special to supersymmetry.
- So far I am aware of nothing in the data that would point toward or away from any one of these classes of models, so one cannot draw any conclusions.
- We will know a lot more by March, when analysis of about 2.5 times the current data set will be possible.
POSTED BY Matt Strassler
ON October 21, 2011
So now the second shoe drops, and the earth shakes a bit (3.9 earthquake just outside Berkeley prior to this talk.) Yesterday we had the first report from the CMS experiment’s search for multi-lepton events at the LHC (Large Hadron Collider). (See yesterday’s post.) The emphasis yesterday was on events that show evidence of substantial momentum and energy carried off by undetectable particles such as neutrinos (such evidence involves an imbalance of momentum among the detectable particles, or `missing energy’ as it is often [misleadingly] called). Today the emphasis is on events with large overall energy (not exactly true but close enough for the moment), including both the energy of detectable particles (the leptons and any jets from quarks or gluons) and the evident energy of anything undetectable. One could already tell from yesterday’s table of event rates that today’s talk at the Berkeley supersymmetry workshop would be worth paying attention to. (more…)
POSTED BY Matt Strassler
ON October 20, 2011
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