Back in Los Angeles, after my brief action-packed jaunt to Geneva. Higgsteria continues, and I’ll be on NPR’s Science Friday later today to talk about it. That’s 2pm Eastern, 11am Pacific time. Hope to do justice to the palpable air of excitement at CERN and around the world.
After that, I think certain parts of my book are going to need some re-writes…
One thing I don’t want to get lost in all the hubbub. Amidst all the many impressive aspects of the work the physicists and machine-builders did to make the LHC happen and achieve this fantastic discovery, I was very struck by how eager people were to give credit to other people. In their main talks, both Fabiola Gianotti and Joe Incandela went out of their way to give credit to the machine builders, the technicians who worked on their experiments, and the thousands of colleagues within each collaboration who contributed to the result. But that eagerness to share credit went well beyond the official announcements — everyone we talked to was quick to point out how far-reaching and international the project really was. The very quintessence of a group effort.
Unfortunately, at least in the sciences, large groups can’t win the Nobel Prize. There will be much discussion in days to come about who deserves a prize for inventing the theory behind the Higgs; I think it’s complicated, and I’m not going to push for any particular set of people. When it comes to the experiments, the matter is easier: there’s no fair way to give it to anyone, really. There was a lot of Nobel-quality effort, without question, but I can’t see how it’s possible to narrow it down to just three people, which is the strict Nobel rule. What we really need to do is change that rule, but the folks in charge are (probably correctly) very conservative about such things, so I don’t see it happening soon.
So let me throw out one name that should at least be in the conversation: Lyn Evans, “the man who built the LHC.” Evans was in charge of the project for many years, and it was his dedication and ability that brought it to successful completion. He is now officially retired as a CERN staff member, although he’s still working as a member of the CMS collaboration and the leader of the effort to build a linear collider. He didn’t play a central role in the actual experimental effort to find the Higgs, but there’s no person who deserves more credit for enabling the conditions under which it could be found. People who are much more informed about the detailed history of the LHC and the ATLAS/CMS experiments will be in a better position that I to render such judgments, but I think the Nobel committee could do a lot worse.
A couple of us are going to try to live-blog the July 4 Higgs update seminars from CERN. This effort will be subject to the whims of internet connectivity, of course, but we’ll do our best. At the moment we have correspondents on at least three different continents (I [Sean] am at CERN, JoAnne is in Melbourne for ICHEP, and I think John is in California…), so hopefully at least one of us will be able to get through. We’ll just be updating this post, so keep refreshing. You are also welcome to try the CERN webcast.
Seminars proper start at 9am Geneva time (3am Eastern time, midnight Pacific time, 5pm Melbourne time). One from ATLAS, by Fabiola Giannoti, and one from CMS, by Joe Incandela. Then a press conference after. Remember what we’re looking for: how significant is the signal, do the two experiments agree with each other, does the rate agree with the Standard Model prediction, are different channels mutually consistent with each other.
If people ask questions in the comments there is some chance that we will try to answer them.
Has there ever been a scientific discovery (if indeed we will be able to call it that) that has been anticipated so far ahead of time? Can’t think of any off the top of my head. Fasten your seatbelts!
11:38 pm Geneva time (Sean): Preliminary thought #1: There is a “nightmare scenario” that particle physicists have worried about for years. Namely: find exactly the Standard Model Higgs and nothing else at the LHC. I personally assign the nightmare scenario very low probability. Not on the basis of any inside info, just on the basis of physics. We know the Standard Model is not right; there is dark matter, there is dark energy, there is baryogenesis, there are the hierarchy and cosmological constant and strong-CP problems. It can’t be the final answer. Seems to me much more likely that there is interesting physics at the weak scale above and beyond the Higgs, than we just get stuck with a vanilla Standard Model. Beyond this physics-informed prediction, there is the wishful hope that the Higgs itself leads directly to new physics. Most obvious example: in many (most?) models of dark matter as weakly-interacting massive particles, the dominant way that dark matter and ordinary matter interact is through exchange of Higgs bosons. If that’s how nature works, the Higgs is literally a portal from our world to another. This isn’t the end of the show, it’s merely an act break (as we say in the movie biz).
11:44 pm Geneva time (Sean): Preliminary thought #2: I am a mere theorist, and let me be as legitimately humble as I can be right here. Beyond the details of whatever may or may not be found, the LHC is a gargantuan effort undertaken by literally thousands of people over the course of years and in many cases decades. This moment, we hope, is something of a payoff for their perseverance. My hat is off to the experimentalists and engineers and technicians who really made it happen.
Last September 30, at 3:00 in the afternoon, after a quarter century of operations, the Tevatron collider at Fermilab collided its final proton and antiproton. Since then, physicists from the two big Tevatron experiments CDF and D0 have been analyzing the complete data set, totaling 10 inverse femtobarns, squeezing every last bit of statistical significance in the search for the Higgs boson.
Fourteen years ago I helped lead a study at Fermilab of how much data we would need to collect in “Run 2”, then slated to begin in 2000, in order to observe the Higgs boson. How much data we’d need depended on the mass of the Higgs, because as the mass increases the number of Higgs bosons produced drops, and also the way that the Higgs boson decays changes. We also assumed that we would upgrade the detectors, an assumption that later turned out to be unfilfilled; in 2003 the DOE canceled the $50 million upgrade to the inner silicon tracking detectors. Anyway, our predictions were that to get a golden 5-standard-deviation discovery, it would take on average about 20 inverse femtobarns of collisions. If the Higgs boson was lighter, it would take less data. But could the Tevatron do it?
The early years of Run 2 saw slow progress in bringing up the Tevatron luminosity. Numerous technical problems plagued the machine, but one by one they were conquered and significant data samples began to accumulate. The LHC at CERN, initially slated to start colliding in late 2005, was also delayed due to its own challenges, giving the Tevatron experiments an opportunity to glimpse the Higgs boson. Late in the decade, it began to look like a horse race when in 2008 the LHC suffered a catastrophic failure after its first week of operation. Data were pouring in at the Tevatron, some 5 inverse femtobarns were being analyzed by mid 2009, and it was difficult to predict what would happen.
In late 2009, though, the LHC turned on at low energy, and in early 2010 the machine began colliding at energies three and a half times higher than those at the Tevatron, which were just under 2 TeV (trillion electron volts). That advantage was crucial: more energy means more collision at a given mass for the Higgs bosons, since we are actually colliding the constituents of the protons. But still, by late 2010 the LHC had accumulated only 0.035 inverse fembobarns, far too little to observe the Higgs boson, while the Tevatron was expected to reach 10 inverse femtobarns by the end of summer 2011.
Then the LHC hit the gas, and in 2011 started colliding in earnest, still at 7 TeV, and by summer of last year the LHC experiments had a full inverse femtobarn to analyze, and it became clear that by the end of the year, if the LHC kept going as well, it would amass a sample at least as sensitive, if not more, than the Tevatron experiments would have. And indeed, hints of a signal for the Higgs boson at about 125 GeV began to emerge at the end of the year, with the LHC experiments CMS and ATLAS analyzing nearly five inverse femtobarns.
At the 2012 winter conferences, the CMS and ATLAS experiments showed a dramatically reduced mass window remaining in which the Higgs boson could live, spanning the narrow range from about 115-130 GeV. Due to the peculiarities of the available search channels at the two machines, the lower end of this mass range favored the Tevatron, which is more sensitive to the decays of the Higgs boson to bottom-quark pairs, while the higher end favored the LHC, which is sensitive to the much rarer decays to pairs of photons or Z bosons, both of which give very sharp mass peaks. If the hints of the beast at 125 GeV turned out to be real, then the LHC would win the race for discovery.
And as I said at the outset, the name of the game for the Tevatron was clear: extract as much statistical significance as possible. The analyzers did an amazing job, and today unveiled the final answer: a broad excess in the data, consistent with a 125 GeV Higgs boson decaying to b-quark pairs. Combining both experiments’ data the statistical significance is equivalent to about 2.5 standard deviations at that mass. This is shown in the plot by the fact that the black curve, which shows the probability that the background alone could look at least as signal like as what is observed, dips down to nearly the three-standard-deviation level.
On Wednesday, at CERN, the LHC experiments will reveal the results of combining the large 2011 data sample with an even larger 2012 data sample at a higher energy, 8 TeV. It is obviously a tremendously exciting time – stay tuned!
Update: There’s a slightly expanded version of this post on the NOVA website, where I fill in some background on what the Higgs is and why we care.
Greetings from Geneva, where I’m visiting CERN to attend the much-anticipated Higgs update seminars on Wednesday, July 4. We’re all wondering whether they will say the magic words “We’ve discovered the Higgs,” but there’s more detailed information to watch out for. Hoping for some good book fodder, at the very least. (I personally am not hunting for Higgses, any more than someone who eats at a seafood restaurant has “gone fishing,” but you know what I mean.) Remember Higgs 101, and why we need it.
If at all possible, I’ll try to live-blog here at CV during the seminars. They will start at 9am Geneva time, a slot chosen to enable a simulcast in Melbourne for people attending the ICHEP Conference. For folks in the U.S., not so convenient: it’s 3am Eastern time, Midnight (July 3/4) Pacific time. Here is the seminar announcement, and of course CERN will have a live webcast. Or try to, anyway; last time something like this was arranged, back in December, the live feed collapsed pretty quickly under the load. I’m sure I won’t be the only one live-blogging: here’s Aidan Randle-Conde and Tommaso Dorigo.
So what are we looking for? Read More
I’m going to hop on a plane to Geneva. Have to see a man about a boson.
Here’s something to tide you over. A bit of friendly international-competition humor. [NSFW captions.]
“I should have gone into string theory!”
Accordingly, the alleged injury, destruction of the earth, is in no way attributable to the U.S. government’s failure to draft an environmental impact statement.
Of course, maybe we’re just lucky enough to live in the branch of the wave function where the disaster didn’t happen?
That is to say, CERN is going to share with us what the most recent LHC data are saying about the Higgs (and whatever else might have popped up, I guess) in a seminar on July 4th at CERN itself, just before the ICHEP conference in Melbourne. Excerpt from the press release:
If and when a new particle is discovered, ATLAS and CMS will need time to ascertain whether it is the long sought Higgs boson, the last missing ingredient of the Standard Model of particle physics, or whether it is a more exotic form of the boson that could open the door to new physics.
“It’s a bit like spotting a familiar face from afar,” said CERN Director General Rolf Heuer, “sometimes you need closer inspection to find out whether it’s really your best friend, or actually your best friend’s twin.”
There’s been a lot of talking back and forth about the ethics of trafficking in rumors, and I don’t mean the jokey kind. Personally I think it’s pretty simple: if a collaboration of thousands of physicists wants to keep their results quiet until they are ready to announce them, that’s completely their right. I’m not going to pass along anonymous tips — if the tippers didn’t understand that they were doing something wrong, they wouldn’t stay anonymous. The rumors aren’t part of keeping the public informed; there’s plenty of time for that once the actual results are released.
Which will happen very soon! Whatever the answers may be, it’s a great accomplishment for the LHC folks to have come this far.
The Large Hadron Collider has been humming along this year, collecting about 5 inverse femtobarns of data, similar to what they had all last year, at a slightly higher energy (8 TeV vs. 7 TeV). Of course last year we were treated to tantalizing hints of a Higgs boson with a mass of about 125 GeV, so it’s natural to ask whether that evidence has been continuing to accumulate. Answers should be forthcoming early in July at the International Conference on High Energy Physics in Melbourne, where talks are scheduled from both CMS and ATLAS.
I believe, given the short time available, that each collaboration can update us on the results from this year’s run thus far, but it will probably take longer to combine the results from the two experiments, as well as combining with last year’s data. (Combining results sounds straightforward, but is actually extremely subtle, due to separate kinds of systematic effects for the different experiments, or even the same experiment at different energies.) Presumably that means that we can accumulate new evidence for the Higgs, but it would be surprising if they were actually able to announce a discovery. I’m also told that the analysis of this year’s data thus far has been “blind” — i.e., they add a secret offset to the real data so that all of the reduction and background subtraction can be carried out without bias, and only then do they “open the box” and see what the actual data are saying. If this is true, literally nobody in the world knows right now what the LHC has actually been seeing, as far as the Higgs is concerned. But we’ll find out before too long.
On local TV last night, I somehow got reporter Dave Malkoff to take a stab at explaining quantum field theory: the world is made of fields, but we only notice the ripples within them, which we see as particles. Something about Angelina Jolie in there at the end as well.