Of Particular Significance

Tag: cms

[This paragraph was my introductory paragraph from this morning, before the presentation. Details of the presentation follow.] IndependHiggs Day has dawned, warm and hazy.  Yesterday, at the CERN laboratory that hosts the Large Hadron Collider [LHC], all the discussion at lunch, and over afternoon coffee and evening beer, centered on the Higgs particle (here’s my Higgs FAQ, my video clips for non-experts about how the Higgs search is done, and a recent article for non-experts explaining its larger importance;more detailed background on the Higgs is linked from here), and on today’s presentation to update the search for it.  The mood is ebullient and excited; everyone is anticipating a very big step forward, perhaps a definitive one.   Gone is the uncertain mood of December, when CERN preceded its presentations with a warning that the results shown then would not be conclusive — a warning that is notably absent this time.   It’s a party atmosphere, and a media circus; many luminaries are here, invited by the director to witness the event.  The press will fill an entire auditorium all their own; physicists will be spread out over perhaps a dozen auditoriums.  It’s been suggested that CERN should have rented a soccer stadium in Geneva; the small size of the main auditorium at the lab reflects how much smaller particle physics experiments were just 30 years ago.

What I will be watching for in the presentations today is the following (to be updated when I know the answers): Here’s what happened in the presentation today:

[8:50 Professor Higgs has entered the room.]

[9:00 CERN Director General Rolf Heuer very brief opening remarks]

First, CMS (presented by spokesperson Joseph Incandela, from the University of California Santa Barbara): (5.2 inverse fb of data, with 5.6 for muon analyses, improvements on many fronts)

  • Is there a new particle apparent, as a bump in a plot, in the search for a Higgs of mass near 125 GeV/c2 decaying to two photons? Yes!! 4.1 sigma, a bit above standard model expectation though not too much
  • Is there supporting evidence of a bump, at around the same mass as for the photon search, in the search for a Higgs decaying to two lepton/anti-lepton pairs? Yes! 5 or 6 events above background, 3 sigma, a bit below expectation but quite consistent with standard model
  • TOTAL 5 SIGMA!!! LOUD APPLAUSE…
  • Is there supporting evidence for an excess of some sort in the searches for a Higgs decaying (a) to a tau lepton/anti-lepton pair, (b) to a bottom quark/anti-quark pair, and (c) to a lepton, anti-lepton, neutrino and anti-neutrino?   (a) not at all, but very low statistics (b) not incompatible, but still low statistics (c) preliminary technique, yes
  • TOTAL 4.9 sigma, EXPECTED 5.9 sigma ;
  • MASS 125.3 +- 0.6, preliminary
  • Is the 8 TeV collision-energy data from 2012 roughly consistent with what was seen in the 7 TeV data from 2011?  Yes
  • Does the evidence in favor of a new particle support the idea that this is a Higgs particle?  Absolutely!!!!  As I have explained elsewhere, an observation of a signal in both photons and leptons, with even roughly the ratio predicted by the Standard Model, is a very strong argument in favor of the new particle being a Higgs particle.
  • Does evidence in favor of this particle suggest that it is a Higgs, but not a Higgs of the simplest type (i.e., that it is not a Standard Model Higgs)?  No signs of (statistically significant) non-Standard Model behavior

Next, ATLAS (presented by spokesperson Fabiola Gianotti, from CERN): (up to 5.9 inverse fb, and various improvements, some quite important)

  • Is there a new particle apparent, as a bump in a plot, in the search for a Higgs of mass near 125 GeV/c2 decaying to two photons?  Yes!! 4.5 sigma , 3.6 sigma with look-elsewhere effect over 110-150 GeV: (cross-section almost twice as big as expected! but only 2 sigma excess); mass about 126.5 GeV
  • Is there supporting evidence of a bump, at around the same mass as for the photon search, in the search for a Higgs decaying to two lepton/anti-lepton pairs?  Yes!! 6 or  7 events above background, 3.4 sigma (2.5 sigma after look-elsewhere over 110-140), cross-section again a bit large, 1.3 +- 0.6 of Standard Model expectation
  • Is there supporting evidence for an excess of some sort in the searches for a Higgs decaying (a) to a tau lepton/anti-lepton pair, (b) to a bottom quark/anti-quark pair, and (c) to a lepton, anti-lepton, neutrino and anti-neutrino? Nothing from 8 TeV collisions shown today
  • TOTAL 5.0 SIGMA!!!!!!  LOUD APPLAUSE…
  • MASS 126.5 GeV (from photons only; leptons are lower; no error bar given, so measurement of mass is not complete) with 1.2 of standard model production rate
  • Is the 8 TeV collision-energy data from 2012 roughly consistent with what was seen in the 7 TeV data from 2011?  Yes
  • Does the evidence in favor of a new particle support the idea that this is a Higgs particle?  Absolutely!!
  • Does evidence in favor of this particle suggest that it is a Higgs, but not a Higgs of the simplest type (i.e., that it is not a Standard Model Higgs)?  No significant deviations from Standard Model though two-photon rate is currently 2 sigma high.  Two sigma is not enough to be excited about.  This is especially since the Standard Model prediction for the overall cross-section is a very tricky calculation; its current precision is estimated at 15%, but perhaps one might worry about that estimate.

Then:

  • Is what CMS observes largely consistent with what ATLAS observes?  Absolutely!!
  • Are there any notable discrepancies between the two experiments that might undermine confidence in their results? None!  The discrepancy of about 1.2 GeV in the masses quoted is not official, since ATLAS does not yet have a final mass measurement with a proper uncertainty estimate.  Even if I take the ATLAS estimate as if it were a mass measurement, if I put a similar uncertainty on it as CMS has quoted, the discrepancy between the two experiments is below 2 sigma, not enough to cause concern at this time, especially given the strength of the signal in each experiment separately.

WOW!!!!  CONGRATULATIONS LHC, ATLAS and CMS !!!

[Heuer celebrates a global success… A standing ovation for all…]

[No one has any questions; the data is so clean and so convincing!]

[Some nice words from the inventors of the idea…]

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POSTED BY Matt Strassler

ON July 4, 2012

Excitement is reaching fever pitch as the presentation at CERN on the Higgs search approaches!  What’s important is that they measure By now the experiments have actually finished their analyses, and the press is reporting (harmless) rumors that both of the big Large Hadron Collider experiments, ATLAS and CMS, are seeing something.  Presumably, assuming the rumors aren’t wrong, what they are observing, using this year’s data, is signs of a Higgs-like particle with a mass of 125 GeV/c2 that are roughly similar to what they reported in December, January and March using last year’s data.  The details will be fascinating to see!

UPDATE: The CDF and DZero experiments at the now-closed Tevatron just updated their Higgs searches, and they find some amount of evidence in favor of a Higgs particle being produced through its interaction with W and Z particles and decaying to bottom quark/anti-quark pairs.  Resonaances has a summary.  This process is interesting because neither this production mechanism nor this decay mode are yet accessible to ATLAS and CMS; they don’t have enough data collected yet.  One should be a bit cautious about such difficult analyses, but taken at face value these measurements are complementary to what ATLAS and CMS can tell us on Wednesday.

What’s all this fuss about?  For the non-technical reader (and/or for your non-technical friends) I’ve written an article trying to put this historic moment in perspective, using language that is as non-technical and unfrightening as I can manage.  If you agree that this is a good article for non-experts, please forward the link to others!

For the reader who wants to follow more details: Let me remind you of the sharpest questions that we’ll be asking on Wednesday, many of which are the same or almost the same as those we asked last December. (You can review my various background articles on the Higgs if you want to understand why these are the right questions):

For both ATLAS and CMS, we will ask: (more…)

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POSTED BY Matt Strassler

ON July 2, 2012

Coming very soon: News on the search for the Higgs particle by CMS and ATLAS, the two big experiments at the Large Hadron Collider [LHC]. Presentations updating the search are expected on July 4th, IndependHiggs Day, at 9:00 am Geneva (Switzerland) time, at the CERN laboratory, which hosts the LHC. The talks, like those of December 13th, 2011, are expected to be technical and intended for experts, though non-experts with some significant amount of background might enjoy directly seeing the data and sharing in the sense of excitement.

The current phase of the search is aimed at either discovering or excluding the simplest type of Higgs particle, known as the Standard Model Higgs. If you are interested in understanding what this particle is and how one looks for it, you can read

To learn more about what the Higgs field and particle are and do, try

Regarding Higgs particles that are more complex than the Standard Model Higgs, and that may be harder to find, you can read

 

Picture of POSTED BY Matt Strassler

POSTED BY Matt Strassler

ON June 27, 2012

Ever have the experience of feeling that no one is listening to you, and so, to make yourself heard, you yell really loudly? And then discover that one of the key people you were trying to reach is standing right behind you?

That’s a bit how I feel after my recent post about Tuesday’s article in the New York Times on the search for the Higgs particle at the Large Hadron Collider [LHC]. My readership is minuscule compared to Dennis Overbye’s, so I shouted. But Mr. Overbye, to my surprise, read the post. Clearly I could have made my points more gently, and for the unnecessary stridency of my tone, Mr. Overbye, I apologize.

I also believed the NY Times article contained an error, and said so. Mr. Overbye defended himself in a comment to my post, saying that the phrasing he chose was meant to imply the correct situation without going into too much detail. I accept this was his intent; I do understand that squeezing these complex ideas into very short articles is a huge challenge, one that he and his colleagues often do very effectively.

Still, in this case, the phrasing chosen could easily lead to an unfortunate and problematic misunderstanding in the wider public — negating the otherwise admirable features of the article. And the risk of causing this particular misunderstanding is the hot button issue on this website. I’ll explain why in a moment.

Before I go into detail, let me balance my negative comments, in the interest of fairness. As a commenter noted, Mr. Overbye carefully avoids referring to the Higgs particle (or “Higgs boson”, as most physicists call it [what’s a boson? just a particular type of particle — click here to read more]) as the “God particle”, a term invented purely to sell a book, and detested by most physicists I know. Thank you, Mr. Overbye, for setting a high standard here. And Mr. Overbye successfully evokes the current mood of extremely high excitement in the field — that 2012 is a very, very big year, in which huge questions bothering particle physicists for decades are finally coming to a head.

But what precisely are those questions? And why do I think it matters?

I do think it’s useful to look at why Mr. Overbye’s phrasing could be disturbing to some particle physicists. First off is the notion that the upcoming conference called ICHEP is “the boson’s last stand”.

In disagreeing with this statement, I am not (as some commenters thought) making a statement of theoretical prejudice. This has nothing to do with what I believe about nature, or what anyone else believes. I am making a simple logical point.

What is the “Standard Model”? It is the set of equations used by particle physicists to describe all known particles and forces at the LHC, along with the simplest possible Higgs particle. [Sometimes this is called the Minimal Standard Model.]

What the LHC experimenters are doing right now is an exhaustive search for this `simplest Higgs’. This search is nearing completion. (Caution: completion may not come at ICHEP. The limited data available so far means that ambiguities may still remain, due to statistical flukes. In that case we’ll have no choice but to wait for the end of 2012.) When the search is done, either a Higgs particle will have been found (perhaps a simple one, or perhaps a more complex one uncovered more or less by accident) or the simplest Higgs will have been ruled out.

Suppose indeed the simplest Higgs is definitively excluded by the data. Which of the following conclusions follows logically?

  • The simplest Higgs particle does not exist in nature.
  • The (Minimal) Standard Model is not a complete description of nature.
  • There is no Higgs particle in nature.

The first two conclusions are logically correct, as well as scientifically spectacular. The third would be even more spectacular, but does not follow. But in saying that ICHEP is “the boson’s last stand”, Overbye gives the strong impression that the third conclusion will follow.

What is actually having its last stand, now or soon, is the Standard Model, [or Minimal Standard Model if you prefer that name] and its simplest Higgs. Professor Higgs and the others — Brout, Englert, Guralnik, Hagen and Kibble — will be disappointed if the Higgs doesn’t show up in its simplest form, but will have no reason to give up hope.

Why is this such an important distinction? Because a non-expert reading the phrase “the boson’s last stand” might naturally conclude that if no Higgs particle discovery is announced at ICHEP, it’s all over… that we know there is no Higgs particle in nature, and the search for the Higgs is done. And the natural next question for many people will be: “ok, but then what do we need the LHC for?” And for others, “so you mean to tell me that theorists said for 50 years there’d be a Higgs particle, and we paid for this 9 billion dollar machine, and the Higgs isn’t there?!” Personally, I do not want to see the New York Times creating these sorts of very dangerous misunderstandings, at a time of severe economic crisis. (Anyone who thinks no dangers lurk here should consider the last two decades of history carefully.) And that’s why I reacted so strongly to Mr. Overbye’s article.

According to Mr. Overbye, he was trying to convey this distinction. I realize these things are very hard to do, but, with respect, I think in this case it wasn’t done clearly. And that’s partly because he added the statement that “theorists will have to go back to the drawing boards” — which implies that theorists will all be so astonished and befuddled if the Higgs doesn’t turn up at ICHEP that they’ll all have to go back to square one.

Will the demise of the (Minimal) Standard Model and its simplest Higgs send theorists back to the drawing board? No. Theorists have not been idle over the past decades. They’ve been at the drawing board the whole time; it’s their job not to be satisfied with the conventional wisdom. It’s not the drawing board but the library and the desk drawer and the computer archive to which they will turn. And in those places you will find dozens and dozens of sensible alternatives to the simplest Higgs, many of which are harder to find than the simplest one and will still be worth searching for, well beyond 2012. And you will find numerous papers, by famous and less famous scientists, showing how nature can have a Higgs field but no Higgs particle; this situation (usually omitted by science journalists, because it is admittedly very hard to explain in a few words) always comes with other scientific opportunities for the LHC. [I’ve written about this here, if you want to learn more; see section 6 — the article is out of date in its details but not in its scientific points.] [Experts: by “Higgs field” I specifically mean any effective field whose would-be Nambu-Goldstone bosons provide the longitudinal components of the W and Z particles. You may prefer a different terminology, but I hope you do not disagree with the science. The example I have in mind is technicolor, and its various cousins.]

If late this decade there’s still no Higgs particle and still nothing else unexpected in the LHC data, then you’ll find most of us at the drawing board.

I should note that a few commenters stated their opinion that if the simplest Higgs, or something like it, doesn’t show up in the current search, then they will be sure there is no Higgs particle in nature, because “nobody believes” these alternatives to the simplest Higgs. First, their opinion is one of theoretical prejudice, not logic; and if scientists’ beliefs were always right, experiments would be a lot less important than they are. And second, the point is not that anyone believes a particular alternative; I don’t “believe” in any specific one myself. The point is that there are so many, and so easy to create. It would be foolhardy to dismiss the possibility that nature might hide the Higgs from our initial searches.

Also, there is an unfortunate public perception (partly due to physicists cutting corners in public statements) that theoretical physicists said that “there is a Higgs particle in nature” and that the experimental physicists built the LHC to find it. This is too glib. As I have written in more detail elsewhere, what theorists said (collectively) is that “there is a Higgs field in nature” — a Higgs particle being likely but not a certainty. The LHC was built to help us understand the Higgs field, and was designed to handle both the cases where a Higgs particle would be found early on, and the cases where it would not be found early, or at all. In short: particle physicists have come to this point fully prepared.

And we need the news media to convey this. Having provided several billion dollars for this machine, taxpayers and politicians around the world rightly expect particle physicists to do a first-rate job with the money. We have a reputation to uphold. If the media, directly or indirectly, leads the public to view us unfairly as bewildered, stunned, unprepared, or otherwise incompetent, this would be very damaging. And so I feel that cannot sit idly by if a New York Times article, even unintentionally, could imply to many readers that not finding the Higgs by ICHEP would mean that nobody in the field would have any idea what to do next.

I myself write to explain science, mainly particle physics, to the public, and I know that science journalists everywhere have a very tough job. Mr. Overbye, in his position at the NY Times, can have huge influence on scientific understanding and science policy in the public, and consequently he has responsibilities that make his job even tougher. His contribution to public excitement about the current moment in particle physics is more than welcome. But isn’t there some way, in a few words, also to convey the decades of careful preparation by the particle physics community, not just for the conventional wisdom but also for the broad range of alternatives? And not just for this critical moment, but for the decade of LHC studies that lies ahead?

For even if we see strong evidence of a Higgs-like particle at ICHEP, the correct understanding of that particle — in particular, determining whether it is or isn’t a `simplest Higgs’ — may take many years. And we’re prepared for that.

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POSTED BY Matt Strassler

ON June 25, 2012

[UPDATE: in the comments below, Dennis Overbye (the article’s author) explains what his wording was intended to imply, and that his article contains no error, just wording that was perhaps a little too simple.  I have also replied, with a request for much greater clarity in future, and explaining why I feel this is such an important issue.]

The New York Times has an article about the search for the Higgs particle! (Using the scientific jargon of physicists, it calls this particle the Higgs “boson”. If you want to know what a boson is, click here.)

Although a lot of the article is pretty good (though I can’t vouch for its accuracy in describing what’s going on inside the experiments) it does contain a HUGE conceptual and factual error that is vastly misleading.  [According to the author Dennis Overbye, this is not an error, but phraseology that is perhaps not entirely clear; see his comment below.] Here’s what it says about the Higgs particle:

“The new data will show whether [the hint in the December data] was a fluke or whether they are really on the road to discovering the long-lost [Higgs] boson, physicists say. They are racing to make a deadline to report the results at the International Conference on High Energy Physics, or Ichep, in Melbourne, Australia, starting July 4.

This, all agree, is the boson’s last stand. If the December signal fades, it probably means that the Higgs boson, at least as physicists have envisioned it for the past 40 years, does not exist, and that theorists have to go back to their drawing boards.”

This is misinformation — completely wrong — and in the interest of its readers, I do hope the Times would publish a correction.  [Again, I refer you to Overbye’s comment.]

This is NOT “the boson’s last stand”, and NOBODY agrees that it is the case.  What everyone agrees (with one caveat about heavier Higgs particles that actually haven’t been ruled out yet) is that it is the last stand of the Standard Model Higgs particle.   The Standard Model Higgs particle is only the SIMPLEST possible type of Higgs particle. Read about this form of Higgs particle here, if you like.

Let me say that again.  There is a big difference between ruling out the Standard Model Higgs particle and ruling out all possible forms of the Higgs particle.

Unfortunately, I’ve previously had to criticize the New York Times on precisely this point … back in August 2011.

Not finding the Standard Model Higgs particle — in Phase 1 of the Higgs search — just means that Phase 2 of the Higgs search has to involve a wider set of search strategies.  The two phases of the Higgs search was one of the main topics of my Cosmic Variance guest-post article and of this slightly more detailed article (both articles a bit out of date now as far as the data, but the basic point about the two phases still holds).  And in fact I pointed out in a related article, linking to some scientific lectures I gave on the topic, that it will take ten years to be confident there is no Higgs particle of any type.  I’m not telling you anything radical; ask any theorist in the field who has worked on Higgs physics and they will tell you the same thing.

So to say that “theorists will have to go back to their drawing boards” if the Higgs does not show up by December 2012 is badly mistaken.  There are hundreds of theory papers, going back decades, on versions of the Higgs particle (or particles) that would not show up by December 2012.   Here are some examples of such papers by well-known authors: http://arxiv.org/abs/hep-ph/0009158 ; http://arxiv.org/abs/hep-ph/0608310 ; http://arxiv.org/abs/1012.1316; there are plenty of such papers from the 1990s and even the 1980s.  Heck, I even wrote some myself.

One other minor error, caused by out-of-date information: the discrepancy between the masses of the possible Higgs signal seen at ATLAS and at CMS (which made the statistical combination of the two data sets unstable to small shifts) did indeed shift when the CMS data was reanalyzed in March.  The shift went in the “right direction”, eliminating the discrepancy and increasing confidence in the consistency of the ATLAS and CMS results.  On the other hand, the significance of the signal seen at ATLAS and CMS went down in March, too.  A complicated story; but these details won’t matter in the long run.

Of course, all of this may be moot, if more evidence for the Higgs shows up at the ICHEP conference in July.  But please, NY Times, get your facts straight on this very important point, which lies at the heart of the LHC program!  No discovery of the Higgs particle in 2012 absolutely will not mean that we know there is no Higgs particle at all.   It just means we would give up on the simplest version of the Higgs (which would be great news!), and that the Higgs search would move on to Phase 2.

Simplified diagram of how the Higgs search proceeds at the LHC; 2012 will be the transition point between Phase 1 and possible branches of Phase 2.
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POSTED BY Matt Strassler

ON June 21, 2012

The rumors about the Higgs particle at the Large Hadron Collider [LHC] have begun again, and since that’s all anyone is going to want to talk about until we actually get the news for real, at the ICHEP conference in Melbourne in a couple of weeks, we may as well get started.

[This is especially true since we learned last year that some well-known non-particle-physicist bloggers have information pipelines directly into the experiments.  It is perhaps inevitable that there are scientists who see it in their best interest to subvert the scientific process.]

The current hot rumor is that the LHC experiments ATLAS and CMS have seen, in the new 2012 data, very roughly what they saw last December in the 2011 data, at least as far as the signal from a Higgs decaying to two photons (particles of light) in the mass range of 125 GeV/c2.  Note I am just repeating what I have seen on other blogs; as a matter of policy, I do not report secret information on this website, and I make no comment on the validity of any rumors.

Suppose this were true; what would it mean?  Well, it’s pointless to try to speculate about exactly how many standard deviations you would obtain by combining data in various ways — if I tried, the only thing I could guarantee you was that I’d get it wrong.  So rather than kick arbitrary numbers around based on guesswork, let’s talk about the larger picture.

There are two ways to think about the 2011 and 2012 data. One is to think about them as data sets you should combine together to extract the maximum information.  That’s what you would ideally do if you had access to all of the data and knew all the subtleties about how to do this.  It is not going to be that easy. Among many issues, one is that the data are taken at different energies, 8 TeV per proton-proton collision this year versus 7 TeV last year.  So in combining them you are making a theoretical assumption about how the production rate for Higgs particles changes as you change the energy from 7 TeV to 8 TeV.  That’s something you may or may not want to do, and at best it makes things rather complicated when you try to interpret the result.

Another way to think about it, as I discussed last week — and I think this will turn out to be more useful as a rule of thumb — is that last year’s data was good for excluding the Standard Model Higgs particle over much of the range for its mass that was available before 2011.  From a range of 115 to 800 GeV/c2 we’re now down, after 2011, to a range of something like 120 to 128  (where we can argue about the edges, but it doesn’t matter very much) or above 600.  The hints we saw last year at around 125 GeV/c2 (see also here, here and here) were very interesting and suggestive, but weren’t convincing, in part because with such a large range of possibilities to explore, the possibility of such hints appearing by random chance was not that low.  That’s due to the so-called “look-elsewhere effect”.  One could only obtain high significance by combining lots of different low-significance measurements together, a technique which can be very problematic, especially when some of these measurements are very difficult.

Now we come to 2012.  The LHC experiments ATLAS and CMS have just about the same number of collisions so far in 2012 as they had in all of 2011; and since the energy is a bit higher, the production rate for Higgs particles should be a bit higher (by several tens of percent.)  So what we’re going to see in the current 2012 data is a bit like a do-over of 2011… except that now the range of possible Higgs masses that needs to be explored is much smaller.  The smaller range means that if the same hints were seen in the same place as they were seen in 2011, the probability of this happening in the search region by random chance would be much lower than in 2011.  More precisely, this means the difference between the naive significance of any excess in the data, and the significance after accounting for the look-elsewhere effect, will not be very important.  Look-elsewhere was a big effect in 2011; but after the 2011 results, it will not be a big effect in 2012.  Thus (roughly) if you view the 2011 data as needed to narrow down the search region to a small window, you can roughly take the significance of any reported 2012 excess almost at face value.

So suppose we did see hints in the 2012 data that roughly resemble those in the 2011 data?  Then I think you’ll see most everyone agree that the evidence for something real in the data is pretty strong.  Of course we’ll need to see this in both the ATLAS and CMS experiments to have full confidence, but let’s assume that’s the case.  What would be next?

  • First, is what’s being seen in the data a Higgs particle at all?  Could it be something else?
  • Second, if it is a Higgs particle, is it the simplest possible type of Higgs particle — the Standard Model Higgs particle — or is it something more complicated?

I’ve described in some detail previously the strategy used to answer these questions, so I refer you to that article.

Generally, I suspect that the July 2012 data won’t be enough (even if you did try to combine it with the 2011 data) to shed clear light on these questions.  But the strong theoretical prejudice on the first question will clearly be that “what’s being seen is a Higgs particle of some type”; after all, the theory of the weak nuclear force requires there be something Higgs-like somewhere, and the Higgs in this mass range was predicted to show up first as a bump in the two-photon search.  I don’t think you’ll find many people who will think it likely that it’s not a Higgs particle, though due diligence will of course be needed to make sure.

The theoretical prejudice on the second question is much weaker, however; we really have no idea whether the Higgs is of Standard Model type or not.  But it seems likely we’ll need the full year’s data set before we start making much progress on this crucial issue (though surprises are possible, if the Higgs is sufficiently different from a Standard Model-type Higgs).  And indeed, even if the Higgs looks somewhat Standard-Model-Higgs-like by the end of the year, our knowledge will still be vague; through Phase 2 of the Higgs search, we’ll be continuing to address the issue for the rest of the decade, making more and more precise measurements of the properties of the Higgs, looking for any deviation from the Standard Model’s predictions.

All of this assumes the rumors are correct.  IF it is true that ATLAS and CMS see something of roughly the same size as last year, in exactly the same place in their plots, then that would mean that evidence for the existence of some type of Higgs particle in the 125 GeV/c2 range had firmed up considerably.  And that would be Very Big News.  Well — we’ll find out soon enough.

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POSTED BY Matt Strassler

ON June 18, 2012

Over the weekend, the Large Hadron Collider [LHC] passed a significant milestone: the amount of data collected so far in 2012 now exceeds the amount of data collected in 2011.  (The LHC is also running very efficiently right now.)  As you may recall, the data is being taken at a slightly higher energy than last year — 8 TeV instead of 7 TeV for each proton-proton collision — and among the benefits of this change are slightly higher probabilities of making Higgs particles.  In short, more Higgs particles (assuming they exist) have now been made this year than last, and if last year’s preliminary evidence of a Standard Model (or Standard-Model-like) Higgs particle [the simplest possible type of Higgs particle] with a mass of about 125 GeV/c2 turns out not to be a mirage, then the number of Higgs particles produced so far this year is about 100,000 for the CMS experiment and a similar number for the ATLAS experiment.  Most of these Higgs particles decay in ways that make them indistinguishable from other processes, but the dozens that decay to two photons and the handful that decay to two lepton/anti-lepton pairs will be the most important in this year’s search.

When will we see results from the new data on the search for the Higgs particle?  (Remember we’re still at the end of Phase 1 of this search, in which the goal is to find or exclude the Standard Model Higgs particle.) (more…)

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POSTED BY Matt Strassler

ON June 11, 2012

For those of you curious about why posts have been a little sparse this month and have been wondering what I’ve been up to, here’s the latest on what has been an on-going story.

The Large Hadron Collider [LHC] is producing lots of new data, and the search for the Higgs particle continues at the ATLAS and CMS experiments. We’re still within Phase 1 of the search for the Higgs particle (I’ve described the two main phases here and in more detail here) in which the experiments are trying to discover unequivocally, or exclude unequivocally, the simplest possible form of the Higgs particle, which is called the Standard Model Higgs. Phase 1 is well along the way, the experimenters having excluded a Standard Model Higgs particle at any mass except a small range around 125 GeV/c2. Within that range there are hints that a Higgs particle might be showing up (see here, here, here and here). Some would say the evidence is significant and are quite convinced already, while others (quite a few of the experimentalists, and a few cautious theorists such as myself) would say the hints are not yet especially significant and are willing to let more data settle the issue. But everyone agrees there’s a very high chance the issue will be settled in 2012.

At that point, the Higgs search will move toward Phase 2. In fact, in some sense it is already in transition, because either there is a Standard Model Higgs particle with a mass near 125 GeV/c2, or the Higgs particle, if it exists, must be more exotic and complicated — two possibilities on which we can focus our planning.

One of the most important questions that will be asked (and is already being asked) is whether the particle that is showing up in the 2011 data (if it is really there in the first place) is a Standard Model Higgs or a look-alike Higgs particle that is actually more complicated in some way. (more…)

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POSTED BY Matt Strassler

ON May 30, 2012

The final panel discussion at the Maryland SEARCH workshop — six theoretical particle physicists talking about the 2011 experimental results from the Large Hadron Collider [LHC] and looking ahead to the 2012 data — has finally been posted online, along with the rest of the presentations at the workshop. I wrote about the workshop, which took place in mid-March, here and here.  In the latter post, I wrote:

The workshop concluded with a panel discussion — the only point during the entire workshop when theorists were formally asked to say something. The panel consisted of Michael Peskin (senior statesman [and my Ph.D. advisor] famous for many reasons, including fundamental work on the implications of highly precise measurements ), Nima Arkani-Hamed (junior statesman, and famous for helping develop several revolutionary new ways of approaching the hierarchy problem),  Riccardo Rattazzi (also famous for conceptual advances in dealing with the hierarchy problem), Gavin Salam (famous for his work advancing the applications of the theory of quarks and gluons, including revolutionary methods for dealing with jets), and myself (famous for talking too much… though come to think of it, that was true of the whole panel, except Gavin.) And Raman Sundrum, one of the organizers (and famous for his collaboration with Lisa Randall in introducing “warped” extra dimensions, and also anomaly-mediated supersymmetry breaking [which was competitive with a paper by Rattazzi and his colleagues]) informally participated too. (more…)

Picture of POSTED BY Matt Strassler

POSTED BY Matt Strassler

ON May 4, 2012

My talk for the general public about the Large Hadron Collider [LHC] and the search for the Higgs particle, given online as part of the series of talks put on by MICA (Meta Institute for Computational Astrophysics) at Caltech, is now posted.  The pdf of the slides, and the audio, are available here:

http://www.mica-vw.org/wiki/index.php/A_Ring_Of_Truth_-_Seeking_Answers_to_Big_Questions_at_the_Large_Hadron_Collider

And I recommend you take a look at their other talks also; it’s a great list.

http://www.mica-vw.org/wiki/index.php/Popular_Talks

What is MICA?  Here’s what they say at their website.

Meta Institute for Computational Astrophysics

  • The Meta Institute for Computational Astrophysics (MICA) is a professional scientific and educational, non-profit organization based in virtual worlds [VWs]. We are currently using Second Life (SL), and the Intel’s OpenSim-based world ScienceSim, and may expand to other venues as the VWs evolve.

You will sense, if you listen to the talk, that the virtual world is still a little buggy, there are some amusing moments!  But on the whole, the virtual world offers many new opportunities for bringing together large but dispersed communities of people with common interests.

Since particle physicists are dispersed across the globe, in professional settings we use video and audio conferencing all the time.  In fact, in just a few minutes after posting this, I’m going to listen to and watch a presentation at a conference at the CERN Laboratory (which houses the LHC) from the comfort of my office.  I’ve attended conferences in Geneva while in Ontario, and attended conferences in India while in New York.  I’ve even given a talk to a conference in Europe while I was just outside one of our National Parks in California!  (You can either view this as letting work intrude into a vacation, or not allowing work to prevent a vacation; up to you.)  And any experimentalist at the LHC probably attends at least one virtual meeting each day.  So for our especially international and collaborative community, virtual experiences have been the norm for quite a while.

Picture of POSTED BY Matt Strassler

POSTED BY Matt Strassler

ON May 2, 2012

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