1
$\begingroup$

If two accelerators operate at the same energy but different luminosity, is the only advantage of accelerator with a higher luminosity that there will be more events in a given amount of time, thus it can operate for a shorter amount of time to observe same number of events?

Or is there some fundamental advantage in which some processes can only be studied by the accelerator with higher luminosity?

$\endgroup$

2 Answers 2

1
$\begingroup$

In most cases we are looking for a small signal on a large background and the usual signal-to-noise rules apply. If we do $N$ observations we expect the signal strength to be proportional to $N$ while the noise is proportional to $\sqrt{N}$. So the signal to noise ratio is proportional to $\sqrt{N}$. The higher the luminosity the greater the value of $N$ so the better the signal to noise ratio.

$\endgroup$
1
  • $\begingroup$ While it is true that running for a longer time you collect more background from cosmic rays and environment activity, at a high energy experiment most of the background comes from the collisions themselves. $\endgroup$
    – DarioP
    Sep 15, 2015 at 16:05
1
$\begingroup$

You are right saying that the only advantage of the higher lumi accelerator will be to operate for a shorter amount of time. Indeed you can build up the same statistics just running longer at a lower lumi.

But if you contextualize this, you find out important consequences. With physics programmes that already extend over decades, a factor 10 less luminosity means going into centuries!! Then the fixed costs of operating the facility (people, spare parts and maintenance, background power consumption, ...) are a factor 10 higher. Moreover as a machine gets older and older the performances and reliability can easily become an issue. You also have to take into account that physicists, and people in general, are not very happy to work for a lifetime already knowing that they won't be able to see the results of their efforts.

So in the end, if you don't get enough luminosity you just miss the physics.

$\endgroup$
2
  • $\begingroup$ Why does 10 factor less in luminosity mean much much longer time needed to run the exp. to get the same statistics? Isn't the flux ratio about 10, thus effectively time should be about a factor of 10 difference too? $\endgroup$ Sep 16, 2015 at 1:10
  • $\begingroup$ Yes, I think we are saying the same thing: if you multiply the lumi for a cross section and for a time you get the number of events $N$, which is also generically called statistics. $\endgroup$
    – DarioP
    Sep 16, 2015 at 6:40

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.