Tuesday, February 15, 2005 ... Deutsch/Español/Related posts from blogosphere

Kenneth Lane on SSC and LHC

Kenneth Lane from Boston University just gave an interesting talk about a topic that you can view as messy and boring: the imperfections of hadron colliders. He described various types of background:

  • real background
  • faked background
  • detector-induced background
There are a lot of effects caused by boring, well-known physics that can fake a signal for new physics. You have to reduce these fakes to at least the level of the real signal - if there's lots of real signal - or far below it if the real signal is rare (i.e., produces only a few events).

He showed the structure of the detectors - such as the huge detector GEM - designed for the Superconducting SuperCollider (SSC) that has been stopped 10+ years ago. That was sad. We could have had a lot of data already. One of the clear lessons from the SSC is that the particle physicists should have voted for the Republicans at that time :-) - although the current correlation between the parties and the physics policies is less clear and might be, in fact, reverted.




Various quantities are measured with various large errors. These machines are not perfect and the Large Hadron Collider (LHC) won't be perfect either. In various directions, the detectors and calorimeters are insensitive because the wires and cooling and similar necessary things must go through somewhere. Moreover, GEM - as tall as a 7-story building and almost twice as long - was divided into two parts exactly in the middle. This is the most interesting point corresponding to zero rapidity where new physics is expected. Nevertheless, they planned that there would be a blind spot exactly at this place. It's like your brain that is divided into two hemispheres exactly in the middle.

Kenneth Lane said that the experimentalists who design these detectors spend a lot of time arguing about technology choices. For example, should they use liquid argon or crystals for an electromagnetic calorimeter? He thinks one of the rules that help them to find the right answer is that, if theorists like Lane have an opinion on the technology, then they are certainly wrong. Comparing the SSC and LHC detectors, Lane thinks the choices may not always matter as much as taste and politics -- there is a lot of money and power involved. However, all these decisions are done by smart people who have very rational, scientific arguments, he added. ;-)

Incidentally, Peter Woit on his educational low-dimensional blog Not Even Wrong tried to distort the image of Kenneth Lane. Peter has even tried to picture Kenneth Lane as a person who is not enthusiastic or even bitter about string theory! :-) In reality, when we were taking the standard visitor's photograph, Kenneth Lane insisted that he should be photographed with Edward Witten, Joe Polchinski, Andrew Strominger, and Cumrun Vafa as all of them celebrate 20 years of superstring theory. In fact, Kenneth Lane is on his way to the 21st Aspen Winter Conference and he wants to have a proof that he also celebrated the 20th anniversary of strings.

Although most of us at Harvard are very realistic and sometimes even frustrated by the relatively slow progress in our field, why should we inhibit the enthusiasm of Kenneth Lane for string theory? The pictures are here and here.

Acknowledgements: I am grateful to K.L. for improvements of this text.

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reader Anonymous said...

Republicans and the death of SSC

http://www.lbl.gov/Science-Articles/Archive/ssc-and-future.html


reader Anonymous said...

Cute story! :)


reader Quantoken said...

Lubos said:
"Kenneth Lane showed that the adult people who design the detectors often argue about irrelevant things. For example, should they use liquid argon or crystals for a detector? One of the rules that help them to find the right answer is that the theorists like Kenneth Lane are always wrong, the experimentalists think. Ultimately, the answers do not really matter - it is pure politics, not science, and a random choice. However, all these decisions are done by smart people who have very rational, scientific arguments, he added. ;-)"

How would you expect a group of theoretical physicists to be able to design a 24 miles circumference particle accelerator? They probably can not hammer a nail straight into a wall. I do not even think experimental physicists would be able to pull this off. Does any experimentalists know how to select and program some of the fastest DSP chips from Motorola and write assembly code to implement the Markov chain statistical model. Or do things like that?

I think it's much more of a engineering technology wonder than the state of art of science. For example, the protons would come in bunches each within a volume of no more than a few micron in diameter and a few centimeter in length. How would they be able to aligh the two jets exactly for collision to happen, when the whole machine is mounted on a rotating earth, which means when the protons circled one round the beam has already been bended a few milimeters away from where they are expected, relative to the machine, due to earth rotation!!!

All those protons would eventually hit something, turn the matters in the environment into radioactive materials. So it is a pretty hostile environment for any enectronic devices to work properly. You know one charged particle hits a key circultry of a CPU processor, and it causes a TTL logic upset which yields the wrong calculation result. Things like that.

We are talking about an extremely complicated process where it starts with one rare collision out of a bizillion in years, and that event transmutates through countless steps of electronic processing and computations, and human logic and communication, before it finally lands as a little drop of fresh ink on a piece of scientific paper published.

How do we know for sure that during this whole chain of extremely complicated processing, an error, be it a software bug, a hardware defect, or an artifact from the environmental noise, or anything, has not been introduced, leading to the wrong conclusion. Or even something intensional injected for political purpose to obtain the designed result?

Quantoken


reader Zelah said...

Here is a detailed discussion of who REALLY killed the SSC!

http://www.physicsforums.com/archive/
t-59324_The_Killing_of_the
_Superconducting_Supercollider.html

Now, I am a European and so was pleased when SSC was killed (made us look good!

But AT BEST, it was a bi partisan effort. Certainly, if you are a particle physicist, voting Rebpublican is no guarantee!

An Amateur Mathematician.


reader TripleIntegral said...

Lubos:

By the way, it looks like the witch hunt on Prof Summers is continuing, as I predicted. I would be interested in your thoughts about how the faculty is thinking.

Would you like a friendly wager that he resigns within the next 3 months?

Regards,

3I