First collisions at the LHC with unprecedented Energy! (Ask a particle physisicist)

[Pyrrho]

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What, do you think physicists sit around drinking wine all day mucking around on forums!

Well, now that you mention it...

[Alex K]

Why do they need to see multiple higgs bosons?  Last time they found it, I thought this time they would look for different particles

Ah, now we get to the proverbial meat of particle physics.

It's all a matter of statistics. A discovery of a particle is usually announced when the scattering events stick out from the so-called background events (those that look the same, but are from non-higgs events) by 5 standard deviations. For this, roughly a 100000 higgs bosons needed to be made. 

As soon as you have that, you can say with good confidence that you have found a new particle, but at the discovery threshold (i.e. the data they had analyzed in july 2012), you have only a very rough idea about its properties. In order to really tell how closely this guy rsembles the simplest version of the higgs boson that theorists have predicted 45 years ago, or whether it is part of a more elaborate scheme, you have to have precision measurements of its properties:

- what is its mass as measured from the different decay products
- how often does it decay to photons, to b quarks, to leptons and Z bosons, to W bosons, 
- how often is it produced in conjunction with a Z boson, with quark pairs and more, with top quarks, from gluons
- what are the angular and energy distributions of the particles coming out of these processes

For *all of these* except the higgs particle mass, the Standard Model gives a hard prediction. Every one of these measurements could be the place where one finds the crucial deviation to shoot down the theory and discover something new.

The more statistics you have, the more precise all these measurements get.

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What, do you think physicists sit around drinking wine all day mucking around on forums!

Well, now that you mention it...

Coffee is the key

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Maybe they want to make sure that they found what they think they found.

Yes, exactly. But they would love it even more if they found out thst they have discovered something, but *not* quite what they though they had.

It would be good to have another large particle accelerator to double-check things.  If they did, and they could not replicate the results, maybe they would dig into this one and find out that they had a speck of dirt somewhere in their equipment that is causing erroneous readings.

This gives me a question for Alex.  How do they know if the thing works properly, if there is only one of this size and they have nothing with which to compare things?

Excellent question.

While it is true that they only have one particle accelerator, that is not such a big problem. The accelerator only provides two high powered proton beams coming out of the wall for the experiments. As long as this beam is properly focused, that's good enough.

The crucial feature is that they have two experiments connected to this beam, ATLAS and CMS, which each have their own collisions at opposite ends of the ring, are constructed quite differently, but do exactly the same thing.

They are run be two different teams of 4000 people each, they have perpendicular magnetic geometry (one a Toroidal one where the magnetic field circles around the beam, and a solenoid where it goes in the direction of the beams), they use different detector technologies and independent analysis methods. Ideally they shouldn't even talk to each other about what they found before publishing, but of course you can't stop gossip. Either way, both have seen the new particle in their data with high significance, with compatible properties within the error bars.

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[Alex K]

Why do they need to see multiple higgs bosons?  Last time they found it, I thought this time they would look for different particles

Oh, and I forgot to say - of course they don't just run the experiments for that one search. There are dozens of different analysis groups working in parallel and combing through the data using different filters, looking for different types of effects. Even just for the higgs, the people doing the search for higgs bosons decaying to photons are completely different ones from those who do the search for the higgs decaying to four muons or whatever.In the end, each publication needs to get approved by all 4000 collaboration members before it is even sent to a journal, which is a MAJOR pain in the ass. Imagine answering and addressing thousands of emails with comments and criticism from colleagues who are also your academic rivals or could be your next boss. The internal peer review process within each experiment is daunting.

[Pyrrho]

Sciencey things just don't have the excitement they used to have.  Looking at data and doing statistical analyses just isn't the same as:




Trinity test (first atomic bomb test).






Both of the above are from Apollo 11, the first landing on the moon.



Your little toy doesn't seem to have the same destructive capabilities of things in the past.  How many people have been killed with the LHC?  If it could vaporize a city, then you would have something!

That is probably why we Americans changed our minds about our own little toy, as what is the point if there is not a lot of fire and explosions going on?  Advancing knowledge, you say?  Pfffffft.  When you figure out how to use that knowledge to blow something up, then give us a call.

[Alex K]

That's not really a good excuse. The way the SSC costs skyrocketed, adding fancy explosion special effects on top of it would have only cost marginally more.

[Pyrrho]

That's not really a good excuse. The way the SSC costs skyrocketed, adding fancy explosion special effects on top of it would have only cost marginally more.

We don't want added special effects!  We want something real, with fire and/or explosions being an essential part.  If you look at the massive fire coming out of a Saturn V rocket, that isn't just for looks, that is essential to it working.  And with the atom bomb, the explosion itself is the point.  (Which makes it a perfect example of the kind of project we want.)

We don't want some sissy thing that doesn't involve anything real, but has added effects to look like something.  If we wanted that, we would just look at an action film coming out of Hollywood.

So, we need to come up with a particle accelerator that involves some real fire and explosions on a grand scale, or we need to be spending our money on something else that does.  Now, a big laser beam that can vaporize a city, that would be something we could appreciate.

Maybe we should rethink the design of a particle accelerator and make it so it can be aimed at things, so it could be used as some form of weapon.  Then we might be willing to spend the money for it.  But somehow I doubt it would ever be practical for that purpose.

Really, how many people have been killed by the LHC?  How can it be used to destroy things?  If you can't even claim one death from it after all these years, how can you say it was money well spent?

[FatAndFaithless]

Are there any practical applications of this new information that scientists are considering/hypothesizing about? Or is it still in the 'holy shit look at this' phase?

[Anomalocaris]

Sciencey things just don't have the excitement they used to have.  Looking at data and doing statistical analyses just isn't the same as:




Trinity test (first atomic bomb test).






Both of the above are from Apollo 11, the first landing on the moon.



Your little toy doesn't seem to have the same destructive capabilities of things in the past.  How many people have been killed with the LHC?  If it could vaporize a city, then you would have something!

That is probably why we Americans changed our minds about our own little toy, as what is the point if there is not a lot of fire and explosions going on?  Advancing knowledge, you say?  Pfffffft.  When you figure out how to use that knowledge to blow something up, then give us a call.

How about this, LHC so dwarves the trinity test that if the trinity atomic bomb were to detonate in the center of accelerator donut,  the entire donut would be well outside of danger zone.

LHC is so vast that it would take SATURN 5 Rockets a full minute, and 600 tons of fuel, or a quarter of its entire fuel load, to climb a distance equal to the diameter of the LHC.

If you put LHC in Washington state it would completely encircle Mt. St. Helens. 

LHC is a god damned megamachine of a dimension so gargantuan you can not only see it from space, but even from low earth orbit it would look almost as big as your palm held at the end of your extended arm.

Of course SSC would have been much more impressive still, but c'est la vie.

[Alex K]

Are there any practical applications of this new information that scientists are considering/hypothesizing about?  Or is it still in the 'holy shit look at this' phase?

The current research, definitely in the holy shit phase for the time being. Particle physics from 70 years ago now has practical applications, in particular in medicine. The immediate practical applications of LHC physics only come from the huge hightech know-how that was gained building it. The most famous collateral benefit from cern is the WWW.

[Pyrrho]

The current research, definitely in the holy shit phase for the time being. Particle physics from 70 years ago now has practical applications, in particular in medicine. The immediate practical applications of LHC physics only come from the huge hightech know-how that was gained building it. The most famous collateral benefit from cern is the WWW.

So you are saying that because of LHC, the great benefit is that people throughout much of the world now have easy access to porn.