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The Way You Look at the World Will Change… Soon December 2, 2011

Posted by gordonwatts in ATLAS, CERN, CMS, Higgs, physics.

We are coming up on one of those “lucky to be alive to see this” moments. Sometime in the next year we will all know, one way or the other, if the Standard Model Higgs exists. Or it does not exist. How we think fundamental physics will change. I can’t understate the importance of this. And the first strike along this path will occur on December 13th.

If it does not exist that will force us to tear down and rebuild – in some totally unknown way – our model of physics. Our model that we’ve had for 40+ years now. Imagine that – 40 years and now that it finally meets data… poof! Gone. Or, we will find the Higgs, and we’ll have a mass. Knowing the mass will be in itself interesting, and finding the Higgs won’t change the fact that we still need something more than the Standard Model to complete our description of the universe. But now every single beyond-the-standard model theory will have to incorporate not only electrons, muons, quarks, W’s, Z’s, photons, gluons – at their measured masses, but a Higgs too with the appropriate masses we measure!

So, how do I know this is going to happen? Look at this plot that was released during the recent HCP conference (deepzoom version Smile) in Paris.

Ok, this takes a second to explain. First, when we look for the Higgs we do it as a function of its mass – the theory does not predict exactly how massive it will be. Second, the y-axis is the rate at which the Higgs is produced. When we look for it at a certain mass we make a statement “if the Higgs exists at mass 200 GeV/c2, then it must be happening at a rate less than 0.6 or we would have seen it.” I read the 0.6 off the plot by looking at the placement of the solid black line with the square points – the observed upper limit. The rate, the y-axis, is in funny units. Basically, the red line is the rate you’d expect if it was a standard model Higgs. The solid black line with the square points on it is the combined LHC exclusion line. Combined means ATLAS + CMS results. So, anywhere the solid black line dips below the red horizontal line means that we are fairly confident that the Standard Model Higgs doesn’t exist (BTW – even fairly confident has a very specific meaning here: we are 95% confident). The hatched areas are the areas where the Higgs has already been ruled out. Note the hatched areas at low mass (100 GeV or so) – those are from other experiments like LEP.

Now that is done. A fair question is where would we expect to find the Higgs. As it turns out, a Standard Model Higgs will mostly likely occur at low masses – exactly that region between 114 GeV/c2 and 140 GeV/c2. There isn’t a lot of room left for the Higgs to hide there!! These plots are with 2 fb-1 of data. Both experiments now have about 5 fb-1 of data recorded. And everyone wants to know exactly what they see. Heck, while in each experiment we basically know what we see, we desperately want to know what the other experiment sees. The first unveiling will occur at a joint seminar at 2pm on December 13th. I really hope it will be streamed on the web, as I’ll be up in Whistler for my winder ski vacation!

So what should you look for during that seminar (or in the talks that will be uploaded when the seminar is given)? The above plot will be a quick summary of what the status of the experiments. Each experiment will have an individual one. The key thing to look for is where the dashed line and the solid line deviate significantly. The solid line I’ve already explained – that says that for the HIggs of a particular mass if it is there, it must be at a rate less than what is shown. Now, the dashed line is what we expect – given everything was right – and the Higgs didn’t exist at that mass – that is how good we expect to be. So, for example, right around the 280 GeV/C2 level we expect to be able to see a rate of about 0.6, and that is almost exactly what we measure. Now look down around 120-130 GeV/c2. There you’ll notice that the observed line is well above the solid line. How much – well, it is just along the edge of the yellow band – which means 2 sigma. 2 sigma isn’t very much – so this plot has nothing to get very interested yet. But if one of the plots shown over the next year has a more significant excursion, and you see it in both experiments… then you have my permission to get a little excited. The real test will be if we can get to a 5 sigma excursion.

This seminar is the first step in this final chapter of the old realm of particle physics. We are about to start a new chapter. I, for one, can’t wait!

N.B. I’m totally glossing over the fact that if we do find something in the next year that looks like a Higgs, it will take us sometime to make sure it is a Standard Model Higgs, rather than some other type of Higgs! 2nd order effect, as they say. Also, in that last long paragraph, the sigma’s I’m talking about on the plot and the 5 sigma discovery aren’t the same – so I glossed over some real details there too (and this latter one is a detail I sometimes forget, much to my embarrassment at a meeting the other day!).

Update: Matt Strassler posted a great post detailing the ifs/ands/ors behind seeing or not seeing – basically a giant flow-chart. Check it out!


Rumors July 18, 2010

Posted by gordonwatts in Critical Thinking, Gossip, Higgs, Rumors.
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Who doesn’t love a little gossip every now and then? Tommaso, as is usual for his style, started one the other day – that the Tevatron claims to have seen a light standard model Higgs. For whatever the reasons (both positive and negative) this one caught like wildfire. You know its big when it shows up on this site!

But to make this really work – and I mean really work in that rumors provide some sort of science payback – you need a conversation. Someone has to say the rumor (to start it). Then someone else picks it up and perhaps spreads it. But then people want to join in on the conversation. For example – “there is no way that can be true because of x, y, and z”, and then someone else says “ah – but you forgot that x can be zero, and if that happens then y and z don’t matter, and this becomes possible once more! Ha!” And so on.

That part of the rumor and gossip conversation I do consider useful. For one thing, it makes the gossipers smarter. Assembling the set of critical arguments to work out the possibility that a rumor is true or not often takes some pretty deep knowledge of the field. And from this discussion new ideas can come as well. For example, I learned quite a bit by watching the gossip and speculation after the CDF forward muon results (shoot, I can’t find a link for that result!) and DZERO same sign asymmetric muon results were released.

Which brings me to the real reason I’m writing this result. That conversation. Currently I see it on Facebook. Seriously! In my circle of friends there are a bunch of experimentalists and theorists who get into some pretty serious discussions using nothing more than one or two lines of text – or perhaps a paragraph. It is excellent. Facebook does an excellent job of re-creating the water cooler – a bunch of people standing around. Though it is better – even if you have to be busy in a meeting or teaching a class you can skip out and rejoin the conversation and read up on what everyone said! This style of conversation is also very important for someone like me: who is constantly traveling and can’t always drop by an office to catch up on the latest.

Before Facebook this happened mostly in blog comments. It still does, and the quality is quite high there, but it seems like it moves more slowly. How about twitter? I did a search over there, and there is lots of chat. But the quality level is pretty low – it is mostly people riffing of the idea or pointers to articles, etc. Are there other places people discuss this sort of thing, but at a physics level? Or perhaps better ways to use tools like twitter to find good conversation? Where else do these conversations occur in the modern digital world?

Favorite Higgs joke seen on twitter. 🙂

P.S. It is almost impossible for me to participate in this particular rumor/gossip because I am an active member of DZERO, one of the two Tevatron experiments. No matter what I say, I’m screwed. So, best not to say anything. Sorry if you came to this post expecting something else!