
The secret lives of long-lived particles - rch
http://www.symmetrymagazine.org/article/the-secret-lives-of-long-lived-particles
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jimmytidey
I'm really fascinated by the idea that physics might be completed in my
lifetime. I know it's a naive point of view - people thought the same around
1900, just before quantum mechanics and special relativity were discovered.

I also realise that CERN hasn't made the breakthrough researchers hoped for.

But what if the idea of long-lived particles, or another theory, comes good?
It reconciles the standard model with relativity and explains dark matter, and
then... it's all over. The rest is tidying up details.

Wouldn't that be the strangest time to be alive? I think some people would be
disappointed, but I'd be thrilled.

~~~
ISL
It's questions all the way down.

Even if we knew the complete theory of everything, the immediate question
would become, "Why is the theory of everything the exact theory of
everything?"

~~~
hleszek
Because of the Anthropic principle !

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jimmytidey
Conceivably, you could have empirical evidence for multiple universes, at
which point the anthropic principle becomes a normal explanation. Until then,
obvious it remains a bit of a non-explanation.

~~~
platz
I hate the Anthropic principle.. it appears to be able to justify anything

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M_Grey
You should hate anything that isn't testable and falsifiable, that's good
hatred.

~~~
snowwrestler
Science can't tell us whether something will ever be testable or falsifiable;
we just know what we know now.

So there's no scientific reason to hate any particular idea. Rather, the
concepts direct the priority of effort--let's not spend time on things that
are not currently testable or falsifiable.

The "hatred" aspect comes from somewhere else besides science, and honestly I
think it's harmful more often than it is helpful.

~~~
M_Grey
_Science can 't tell us whether something will ever be testable or
falsifiable; we just know what we know now._

That's... almost literally the opposite of reality.

~~~
snowwrestler
I phrased it poorly.

What I meant is that, given a hypothesis that is not currently testable or
falsifiable, we cannot use current scientific knowledge to prove that it will
never be testable or falsifiable.

To your point, the way I wrote it above, it sounds like I believe nothing can
ever be tested or falsified. Obviously we have tested and falsified many
hypotheses.

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M_Grey
I'm glad you clarified, because I was getting distressed at the idea of
someone so eloquent thinking something so crazy.

To clarify a bit myself though, remember that we're talking about something
for which the standards of "testable" and "falsifiable" often just mean, "even
in some thought experiment." For example people predicting collisions with
another universe have a pretty wild hypothesis, but they proposed some ways to
explore that idea involving studying the CMB background.

When we're talking about the anthropic principle as a hypothetical foundation
for a complete understanding of physics though... there's really no room even
in theory for testing or falsifying that notion. That's what was being hated,
and the hate of which I'm in support.

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snowwrestler
I can think of two hypotheses that can't currently be ruled out:

1) We're living in a computer simulation of a universe, which was built and
operated for our benefit by some unknown intelligence(s).

2) Our universe is just one of an infinitely many universes, each of which has
slightly different values for the physical constants. Our universe seems well-
suited to our life because of selection bias--in the universes not suited to
life, there is no life to observe that fact.

These both relate to various formulations of the anthropic principle. The
principle itself can't be used to prove the correctness of one or the other.
But it's possible that we will find some experiment in the future that will
allow us to test one or the other.

~~~
M_Grey
I think that's why those concepts are entertained by a large number of people
in the scientific community, over drinks at least. Of course, if someone tried
to get serious funding to study it, right now, there might be a different
reaction.

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cdumler
This seems wrong to me. I know the LHC records total energy in and compares
total energy out. Wouldn't any long lived particles would "appear" as areas of
missing energy?

~~~
ISL
Yes, unless they appear as something you think you understand.

In the specific case of this article, they're interested in particles that
look a lot like a muon. The signature of a muon in a particle detector is that
it leaves a charged track in the inner tracker, passes through the substantial
mass of the electromagnetic calorimeter without saying much, and then goes
_pow_ in the muon detector (usually alternating plates of steel and detector).

A long-lived particle could be quite similar; a charged track, a lot of
nothing, and a decay in the muon tracker.

Any particle that might roughly replicate the muon's signature might have
hidden from existing searches for new physics. The proposal in the article is
to cover the muon detector with higher-resolution trackers. If the "muon"'s
decay doesn't conform to the standard plan, higher resolution would make it
apparent.

I'm not enough of an expert to know how sensitive this method is in comparison
to other ways of hunting long-lived particles, but I have taken a class or two
from one of the authors. If Lubatti's pitching the idea, it's worth thinking
about.

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cshimmin
Well said but a few details are a bit off. The alternating plates of metal and
detector is actually the hadronic calorimeter, which the muons also go
straight through (but which stop almost everything else). The muon detectors
are outside of that, and are just various types of spark chambers that get
zapped as the muon passes through them. Generally the muons neither stop nor
decay in the detector.

~~~
ISL
Ah, true story. That makes more sense. Thanks!

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grabcocque
Supersymmetry and String Theories.

Two theories that are not even not even wrong.

Their proponents dance and shift in the prevailing intellectual currents such
that there's no possibility they could EVER be proven wrong.

There's no null result, no complete experimental failure, that could ever
possibly convince them they might, just might, have made an error.

~~~
shepardrtc
I think you're trivializing the process through which these theories are
created. This is incredibly difficult stuff. There is very, very difficult
math involved and there are very difficult tests that have to be done with
very expensive machines. These things aren't just made on a lark while have a
pint or two one afternoon. And even while creating them, there is no guarantee
that even if the math is correct that the theory is correct. Theorists know
this. But they do it anyway because we need them to. Its hard work and they
don't get enough recognition for it (aside from the few that make it on TV).

~~~
effie
> But they do it anyway because we need them to. Its hard work and they don't
> get enough recognition for it (aside from the few that make it on TV).

They certainly don't do it because "we need them to". That's not how
theoretical physicists and mathematicians think. It's more of a quest for the
holy grail for some and more of an interesting puzzle to solve for the others.
That's why some of them just can't stop, even if it's overwhelmingly clear
that we have no way to create and probe the extreme conditions where something
new and unexpected that would guide the theory could happen. Just because the
math is hard does not mean they should get more recognition for it - one
should look at the fruits of the work for that. It's not wrong to get occupied
with solving famous puzzles, but everything in proportion.

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werkinprogress
> In the past, physicists assumed that new particles produced in particle
> collisions would decay immediately, almost precisely at their points of
> origin.

But wouldn't missing energy be evident?

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krastanov
The missing energy is evident indeed, but this is not the point. You usually
use the missing energy as a proof of a neutral particle, not a fast decaying
particle. And you can not say what that neutral particle was because you did
not measure anything about it.

More importantly, the particle we are considering, the one that decays really
fast, near the origin, will decay into other particles, and those can be
detected.

~~~
werkinprogress
If the new resultant particle(s) don't decay immediately near the collision
why wouldn't their missing energy be evident?

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werkinprogress
Install a 10 foot thick lead shield at the end of the detector and glue a $10
motion detector light to it. Problem solved. You're welcome, CERN.

