Hunting the Higgs: The Rediscovery of Physics

>> Thursday, April 15, 2010

I had titled the last blog pedal to the metal, but as a tyro impressed by the gargantuan machine and counter intuitive contrasts of scales - I really had no idea. Yes, the CMS logged hundreds of thousands of p-p collisions in a day or two. But they were a bit like Saturday afternoon slow pitch, or in deference to my Mentor in this endeavor - backyard bowling practice - as compared to fast yorkers and googlys at the Cricket World Cup.

Man-on-the-scene Matt LeBourgeios on March 30, 2010

As explained to me by our man-on-the-scene Matt LeBourgeois, the last week or so was only preparation for what Vivek calls "The Rediscovery of Physics". Even though my occasional visits to the LHC status page showed 7TeV beams and what looked to me like a lot of luminosity (they were, and there was), there were a lot of not-so-subtle nuances to what was going on. Last week or so was the beam operators; the people responsible for injecting protons into the 27 kilometer race track and providing focused, stable and energetic beams tuning their instrument to perfection.

The line traces the 27 kilometer track of the LHC on the French - Swiss countryside...

As Matt related, the operators maintain that what they provided in that first week or so was not intense enough for "discovery physics"; that is, really compelling huge numbers of protons to collide - but it was exciting enough for our young Ahab (I'll get to that in a later blog) to whet his appetite.

Actually, it was the opportunity CMS needed to tune its instrument, doing among other things something called timing scans, which has to do with setting the triggers on the CMS. This is the realm where Matt works, where he is one of many monitoring all sorts of different parameters and data involved with timing to make sure things are working, or for working out problems when they arise. In his typically gracious manner he calls himself “just a pawn.” I’ll maintain whatever one does on this job is going to mean something pretty darn important one day. Anyway, as Vivek explained, the CMS is like a 100 million pixel camera. The catch, as Matt pointed out, is that each pixel has its own shutter, here in his own words: "the point of the timing scan is to sync the 100 megapixels of the camera. Instead of thinking of having to hit one camera button to take a snap shot, think of it as each 'pixel' has its own button, and these timing scans ensure that we are hitting all 100 million buttons at once." Whew! I can only assume if that doesn't happen, the resulting "picture" lacks focus.

So CMS now has the shutters timed and the beam operators are really putting the pedal to the metal. The latest from Vivek is " squeezing the beams like hell - so more rapidfire collisions". What? Vivek explained that the beams that collided on March 30 were something like the diameter of a hair, now the operators are tuning the beams to be something much thinner (?!!)- with the same number of protons in the beams. They're focusing and concentrating the beams. Why? Same number, smaller space = greater density = greater luminosity. Vivek has a vivid description of those less focused March 30th beams in this video clip.

Another way to put it is like shooting two shotguns at each other - you get two bunches of shot, each with 10 to the 11th pellets (that's like, oh, a hundred billion pellets in each), flying towards each other in the hope that some of the pellets hit directly head-on with all their momentum going into their mutual deconstruction. The more concentrated the shot pattern, the better the odds of collisions. So when the operators can provide focused, stable beams, then people like Vivek and Matt and their colleagues can really do their work - which is PHYSICS; and the operators can post messages like "enjoy the collisions" and "physics beams" on the LHC status page here. Now I've simplified, and probably to the horror of physicists out there, over-simplified this. Be certain, there are a lot of precise and very specific protocols involving terms like beta-star and picobarns that indicate the level of performance and quantity of data the physicists are getting - very strict parameters that are adhered to, because remember-they're working with things we can't see, have never seen before, and whose existence we can only infer, albeit very precisely and with great certainty, but only through the evidence they leave behind.

So what is that evidence? Well in the energy range - or mass - (remember it ALL boils down to this - E=mc2) in which the LHC will be looking for the next year or so, the signature of a Higgs boson of about the mass of an entire gold atom (which is about 185 GeV!), will be the remains of two W bosons. And that - which Matt and Vivek and a few thousand others will be looking for - will be events that show specific combinations of electrons, muons, or electrons and muons AND their corresponding neutrino counterparts, which show up only as a precise amount of missing energy - something called Missing Transverse Energy. If the event shows all three of those parameters to an exceedingly high degree of certainty, then it will get some interest, and Vivek, Matt and a world of physicists will pore over it. The catch is, one event won't be telling. They need several such events, enough to satisfy something called 5 sigma criterion - I know you all know what that indicates, sorry I'm playing catch up, but for those like me, it is a term describing a statistical certainty to a level of less than one fault in a billion. In other words, there is only less than a 1-in-a-billion chance that they're wrong. So you need a lot of incontrovertible events, and to get several such need thousands, millions and ok I'll hyperbolize, (but I have a feeling it isn't really hyperbole) - probably billions of p-p collisions to get those events. Just to add another twist, as Matt told me the other day, W boson production, without the creation of a Higgs first is almost a hundred times more likely to occur. So there will be a lot of W bosons that show up WITHOUT evidence for Higgs....hence, collisions, collisions, collisions, "squeeze the hell" out of those beams. And then there are the usual gremlins encountered with complex systems. Vivek recently showed me how one such event looked interesting, but one of the parameters was due to an instrumental glitch - so, "close but no cigar" and into the trash with that, collisions, collisions, collisions.

In the meantime, as the operators keep perfecting their craft, "squeezing the hell" out of the beams, with the p-p events occurring at an ever accelerating rate, Vivek and company are happy to do what Vivek describes as "Rediscovering Physics". It isn't just an idle exercise or coincidence of smashing protons. As of the Ides of April Vivek explained that the LHC has “discovered” every major particle revealed in the 20th century, up to about 1983, when Carlo Rubbia discovered the the W and Z bosons. Or that is - it has rediscovered them, and this is important why?

This is a new instrument, a new machine, and as Vivek explained, if you don't see what you already know about with this machine, then you may have a problem with your instrument, and basically, you can't trust the results....So now, working at heretofore unattained energy the LHC has tallied a gamut of fundamental particles, starting with the pi mesons of 1947. Their discovery bolstered the existence of Up and Down quarks. Oh, and the LHC attained this in the first 15 minutes of operation at 7TeV. Then it was the Strange (50's) and Charm quarks of the 70's and on and on. As of this writing they're still in the hunt for the last few particles - variations of the Z boson, a hunt which might end at any moment the way they're smashing zillions of protons (my hyperbole). Even for a naive eye the data is totally convincing, you'll be able see it soon when it is published and when you do, I think you'll agree it's waaaay 5 sigma. And that's a good thing. The LHC is seeing what it is supposed to be seeing - so when new things show up - those electron-neutrino (elnu), muon-neutrino (munu), MTE (Missing Transverse Energy) triptychs of data - Vivek and friends will know it isn't a phantom - but instead, perhaps, the sign of the holy grail, the great white whale, or as it has been called - the god particle.....Bonne Chasse mes amis!


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