Sweet SUSY at LHC

hangin’ out at KITP sneaking into the LHC workshop talks,
sort of liveblog of the constraints on supersymmetry from preliminary LHC results.

today’s seminar is Reece: on Assessing SUSY After 1 fb-1 (blackboard talk, but audio/video will be up on the website soon) on constraints on supersymmetry from current LHC data, good turnout, serious punditry in the audience

basically: should LHC have seen superpartners by now, or ought it to see it real soon now?

I like this – he kicks off with quoting physics blogs on why lack of susy detection is heading physics into a crisis, then he reassures us…

not worried about SUSY CDM or lack of direct detection, yet, in CDM experiments
also whether particle proliferation causing problems for cosmology

this is going to be fun – going beyond vanilla SUSY

bottom line is that with current data, a lot of the “natural” supersymmetry parameter space is starting to close up – so either sparticles are hiding in some unexplored corner of parameter space, or there is some fine tuning, or supersymmetry is not “simple’ in some natural sense.
ie you can get out of tight corners by adding parameters, which will go a long way.

eg the “stop squark” – the super partner to the top quark, is having its plausible mass range squeezed.

(I think we knew this endeavour was doomed many years ago, when the nomenclature turned out so awkward and never improved to something snappier…)

Look! Iconic image of real data!
Yes, it is a candidate Higgs decay event, or random background!
(click to embiggen)

getting some constraints on gluino decays, getting close to TeV mass constraints from current femtobarn cross-section, making some friendly assumptions about kinematics of other spartners.

so, the LHC really is working, in the sense that parameters are being squeezed and models ruled out, which is progress.
Maybe someone will win the gold and a blip will be found at some particular energy, only way to know is to look.

bino, higgsino, neutralino, and now someone wants sleptons… how to selectron them all.
seriously, since none of the masses are known, any or all can come in somewhere in the cross-sections, and each changes the constraints inferred from the data.
argh, here comes the gravitino…

nope, they haven’t found any, in case you’re wondering, or do I mean wandering?

I think one thing we’ve learned is that free hand blackboard presentations are not optimal for presenting results of parametric modeling of constraints on multichannel processes.

remind me: is it a good or bad sign when the audience just starts arguing amongst itself?

now we get to how to hide supersymmetry, to save it, not of course that is needed, yet.
“Stealth supersymmetry” – cute idea, just add an X and stuff
the stuff becomes problematic, starts requiring tuning to avoid conflict with already known constraints, but then doesn’t it all now

Remind me: do we actually know for sure that the universe must be consistent?
Or must I now vanish in a puff of logic?

I think I need to go back and think about adaptive load balancing block solving of sparse, nasty almost diagonal matrices; that and whether kinetic energy turbulence really affects sound wave propagation (duh, of course it does, but how much…)?

Ok, punchline: making some general assumptions, basically that one lightest supersymmetric partner particle is coupling to normal matter and that some other random spartners are available to balance things as needed, but don’t come in at comparable interaction cross-sections, then mass constraints are currently in the 600-800 GeV range, ie the supersymmetric particle must be more massive than that.
But not too much more massive.
Not if we want to keep things simple.


  1. #1 Collin
    August 16, 2011

    Or just drop the supersymmetry thing altogether, and look for other ways bosons and fermions can coexist?

    (Nah, that would be pandering to those hicks that still believe in quaint notions like reality and time.)

  2. #2 make
    August 27, 2011

    What does supersymmetry do to violate notions of reality and time?

    Why would they drop hypotheses that haven’t been excluded by empirical evidence, and that provide natural solutions to fine-tuning problems etc.?

    Do you not realise theorists are, and always have been, looking for other possible solutions?

    Finally, it’s not a “coexistence” problem. Your whole post is naive and unresearched.

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