Fermilab's Search for SUSY Particles

[touqra]

This is page 4 of the whole article: http://www.nytimes.com/2007/07/24/science/24ferm.html?pagewanted=4&8dpc&_r=1

On this page, it says that D0 is able to find SUSY particle, but till now, to no avail. Is it true that Fermilab is capable of finding some SUSY? I thought we have to wait for LHC. Also, how true is the whole rumour?

 

[Barmecides]

This is page 4 of the whole article: http://www.nytimes.com/2007/07/24/science/24ferm.html?pagewanted=4&8dpc&_r=1

On this page, it says that D0 is able to find SUSY particle, but till now, to no avail. Is it true that Fermilab is capable of finding some SUSY? I thought we have to wait for LHC. Also, how true is the whole rumour?

All big accelerators from the last 15years (like LEP, Tevatron) could/can discover SUSY. But as they haven't observed any stricking excess, they just set low mass limits.
In principle the advantages of LHC wrt Tevatron are both energy and luminosity, but you have to be aware that even LHC cannot reject certainly the existence of SUSY if it does not find anything.

 

[touqra]

All big accelerators from the last 15years (like LEP, Tevatron) could/can discover SUSY. But as they haven't observed any stricking excess, they just set low mass limits.
In principle the advantages of LHC wrt Tevatron are both energy and luminosity, but you have to be aware that even LHC cannot reject certainly the existence of SUSY if it does not find anything.

I don't understand why you can't reject SUSY if it finds nothing. Is it because if SUSY is not found at this energy scale, it may be found in a higher scale ? But if this can be argued for SUSY, so can this be argued for gravitons or extra dimensions or such.

 

[Barmecides]

I don't understand why you can't reject SUSY if it finds nothing. Is it because if SUSY is not found at this energy scale, it may be found in a higher scale ? But if this can be argued for SUSY, so can this be argued for gravitons or extra dimensions or such.

Yes.
The only thing we can reject at LHC is a Standard Model Higgs.

 

[chrisina]

This is just a perfect example of press trying to make science claim something that it doesn't want to claim yet.

 

[Timo]

I don't understand why you can't reject SUSY if it finds nothing. Is it because if SUSY is not found at this energy scale, it may be found in a higher scale ?

Yes. However, one of the main motivations to consider SUSY in the first place is the cancellation of disturbingly large loop-corrections to the unrenormalized mass of the Higgs-boson (known as "hierarchy problem" or "fine-tuning problem"). This cancellation becomes worse the more the masses of the SM particles and the superpartners differ. So with ever-increasing masses of the potential superpartners (driven by increasing lower bounds from collider experiments), SUSY seems to become less attractive - at least as a solution for the fine-tuning problem.

But if this can be argued for SUSY, so can this be argued for gravitons or extra dimensions or such.

I'm not sure if there's a theory predicting massive gravitons (except for exited states in extra-dimensions) - the long range of gravity would probably set very small upper limits on the graviton mass. For curled-up extra-dimensions, there are upper limits on their size at least for some models. In short: There's probably at least some limits for every model (except the mass of particles that don't have any charges and don't interact gravitationally ). The non-excluded parameter-space can still be (relatively) large, though.

 

[Haelfix]

On naturalness and simplicity grounds alone, Tevatron should have already seen many of the popular models of SuSy with natural coupling. In fact, most people think if we are going to see SuSY and a scalar Higgs at all, its got to be very soon in the lifetime of the LHC (long before they go to full luminosity mode). As you push up the mass of the higgs, the bound on the stop mass from the MSSM goes up exponentially. This results in finetuning on a few physical parameters from loop corrections to within the order of a few percent assuming you keep the electroweak symmetry breaking scale stable.

This isn't without historical precedence, in nuclear physics we've seen fine tuning of that order, but start going too far and the whole thing starts getting really nasty and *unprecedented*. What was once a very well motivated physical theory for solving the electroweak hierarchy, becomes rather unmotivated and contrived as it introduces new 'mini' hierarchy problems unless you abandon minimalism.

Then there's the other nagging rhetorical question. Why is nature trying so hard to hide this new physics and making phenemonologists life highly aggravating?

So yea if no SuSy is seen, the primary motivation for the theory in the first place is gone. Then the only people who will still be interested in the theory are GUT modelers (b/c of gauge coupling unification) and quantum gravity people. The rest of us then, will face the full brunt and craziness of the hierarchy problem absent something discovered that we haven't thought off.