
Physicists in Europe Find Tantalizing Hints of a New Particle - dil8
http://mobile.nytimes.com/2015/12/16/science/physicists-in-europe-find-tantalizing-hints-of-a-mysterious-new-particle.html
======
peterwaller
Official ATLAS and CMS plots:

[https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/CONFNOTES/ATL...](https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/CONFNOTES/ATLAS-
CONF-2015-081/)

[http://cms-results.web.cern.ch/cms-results/public-results/pr...](http://cms-
results.web.cern.ch/cms-results/public-results/preliminary-
results/EXO-15-004/index.html)

This video shows how one of the plots evolves over time as you discover a
particle (in this case, the Higgs, discovered in 2012):

[https://www.youtube.com/watch?v=zLZZOrpQFo4#t=3m](https://www.youtube.com/watch?v=zLZZOrpQFo4#t=3m)

A nice blog post:

[http://resonaances.blogspot.co.uk/2015/12/a-new-boson-
at-750...](http://resonaances.blogspot.co.uk/2015/12/a-new-boson-
at-750-gev.html)

While exciting, there are countless examples in history of such discoveries
disappearing as more data is collected.

~~~
cshimmin
> While exciting, there are countless examples in history of such discoveries
> disappearing as more data is collected.

As someone who works on ATLAS and has been watching this result develop over
the last several weeks (without knowing what was going on at CMS), my
excitement has been very tempered by this fact. Especially given that the
global p-value is quite modest (see also: Look Elsewhere Effect [1]).

For sure it's too early to know anything. But I have to say, when I heard the
CMS announcement yesterday that they were also seeing it, in almost exactly
the same place, it's much more exciting!

[1] [https://en.wikipedia.org/wiki/Look-
elsewhere_effect](https://en.wikipedia.org/wiki/Look-elsewhere_effect)

~~~
jessriedel
On the optimistic side: has anyone done an estimate of the global significance
taking into account the fact that CMS and ATLAS both saw the excess at the
same place (~740 GeV)? (Clearly, if the situation was a simple as each bin
being "excess" or "no excess", then you would only correct for the look-
elsewhere effect for _one_ of the experiments. When you turned your attention
to the second experiment, that bin would already be special. This is muddied
by the fact that things are not so clean, and the small blip of CMS was just
the largest of several blips, etc.)

On the pessimistic side: has anyone done a "fully global" significance test,
taking into account all the other bump hunts of similar a-priori interest?

~~~
cshimmin
> has anyone done an estimate of the global significance taking into account
> the fact that CMS and ATLAS both saw the excess at the same place (~740
> GeV)?

Not yet, and it's actually a bit tricky to think about how this should be
interpreted. Since neither experiment alone provides a super strong motivation
to look at 750 GeV (since their global significance is low), it's hard to
argue that one experiment can remove the LEE from the other by fixing the
search mass to 750 GeV. But IMO it doesn't even make sense to do this thing
post-hoc; otherwise one could always avoid the LEE by "fixing your attention"
on a single hypothesis mass where you had previously observed a local excess.

Now, suppose you had a (probably contrived) theory which specifically predicts
a particle at this mass in a way that is totally non-negotiable, so that the
only meaningful question to ask about the theory is "is there a particle X at
750 GeV?". In this case you can do away with the LEE and use the stronger
local p0 at that mass. Theorists are already flooding the arXiv with such
articles (and even have been since a day before the announcement... oops!).

But in the general case, really the best way to understand the combined
significance is to combine the datasets from CMS and ATLAS in a fully
correlated way that handles systematics etc, and then make the diphoton mass
plot again with the bigger dataset and evaluate the global significance of the
resulting bump, still accounting for the LEE. But this is a really big effort,
since the two detectors are substantially similar/different in many ways and
it takes great care to handle correlations etc between their resulting data.
Something like this was done for the Higgs discovery [1], in a paper which you
might recall made news [2] for having more authors than any paper in history!

[1] [http://arxiv.org/abs/1503.07589](http://arxiv.org/abs/1503.07589)

[2] [http://www.nature.com/news/physics-paper-sets-record-with-
mo...](http://www.nature.com/news/physics-paper-sets-record-with-more-
than-5-000-authors-1.17567)

------
yk
The most interesting paragraph of the article is:

    
    
       A coincidence is the most probable explanation for the 
       surprising bumps in data from the collider, physicists
       from the experiments cautioned, saying that a lot more
       data was needed and would in fact soon be available.
    

So the data analysis is extremely complicated, in part because the number of
tries depends on the correlation of datapoints. So if you look at 2 sigma
signal in one hundred datapoints you expect to find 5 and even worse, if you
try one hundred different measures then you expect 5 two-sigma events, if the
measures are independent, which they are not in practice. So to calculate the
number of tries is a highly non trivial business, which depends on exact
knowledge what each desperate grad student did on his weekend.

So the nice thing about data from both CMS and ATLAS is, that we can fix this
by asking, what is the probability that CMS sees something at the same energy
and in the same channel as the most interesting ATLAS result. And as it turns
out, it is a 2-sigma event. So there is just a one in twenty chance that this
occurs by random chance. However one in twenty is not exactly a discovery,
just the probability that the Niners win on Sunday.

Edit: Two things, first that analysis is of course very conservative and
second even if it is a real effect, it may be just a presently badly
understood background effect.

------
jgord
Dumb question from non-physicist - if the 'Standard Model' is a good theory,
why don't we have a good idea of where to find particles [ ie. predict their
mass and other properties ]?

Is the problem that its just hard to compute these values ?

Or does the theory not predict particle masses ?

Or do we need a fully unified theory of all fundamental forces, before we can
predict particle properties from first principles ?

~~~
toth
Well, we have found all the particles predicted by the Standard Model, last
one missing was the Higgs boson.

However, no-one really believes that the Standard Model is the ultimate
theory. There must be other stuff out there that we have found yet. What
people are looking for now are deviations from the standard model.

~~~
Someone1234
Does the standard model explain quantum entanglement?

edit: Nevermind, read this article:
[https://en.wikipedia.org/wiki/Physics_beyond_the_Standard_Mo...](https://en.wikipedia.org/wiki/Physics_beyond_the_Standard_Model)

------
andrewflnr
I'm confused about why they think it could be a graviton. Since gravity is an
infinite-range force, wouldn't its carrier be massless like the photon?

~~~
hasenj
Isn't the fabric of spacetime itself the carrier for gravity?

~~~
XorNot
No that's a convenient metaphor for gravity at large scales.

~~~
hasenj
or maybe particles are a convenient metaphor for small scales

------
irascible
First I read "heavy boson" and thought that sounded kinda metal, so it would
be cool if they named it that, but then I misread "whale boy", which is even
better, so I'm calling it now. Next heavy higgs boson will be called Whale
Boy.

~~~
skykooler
I like it.

------
Jerry2
Lubos Motl has a really good post that cuts through a lot of journalistic hype
and explains possibilities:

[http://motls.blogspot.com/2015/12/first-batch-of-9-pheno-
pap...](http://motls.blogspot.com/2015/12/first-batch-of-9-pheno-papers-on-
new.html)

I'll just quote the summary:

> _You see that the diversity of the explanations is huge – it 's a landscape
> of possibilities. Whether you like it or not, whenever certain things are
> uncertain, the possible answers are diverse. String theory's landscape
> reflects the same principle in another, more consistent and more
> constrained, formalism. And the purpose of this new particle is simply
> mysterious at this moment._

> _It seems very likely that the new particle is a j=0 scalar particle. And it
> seems guaranteed that it can 't be the only new particle that has to be
> added relatively to the Standard Model. But who are the friends of SS and
> what is their relationship and purpose? Nobody knows. If this extra
> knowledge about the particle emerges, we may start to call it a heavy axion,
> a technicolor or composite scalar, a pseudo-Nambu-Goldstone boson, or –
> which I find more likely – a new Higgs boson analogous to the (three-year)
> old one._

~~~
termain
How is 1+1=1 easy to achieve?

------
jbattle
"Parked along the underground racetrack are a pair of mammoth six-story
conglomerations of computers, crystals, wires and magnets: Atlas and C.M.S.,
each operated by 3,000 physicists who aim to catch and classify everything
that comes out of those microscopic samples of primordial fire."

Is that a typo? Are there really 6,000 physicists actively doing work on the
large hadron collider?

~~~
philippnagel
According to
[https://jobs.web.cern.ch/faq/all](https://jobs.web.cern.ch/faq/all) there
"are over 2,250 staff members" "but there can be up to 13,000 people on site
at any one time".

~~~
cshimmin
Those are jobs for the CERN facility alone (which also probably includes
services like HR, translation, janitorial, etc). But thousands more work
essentially full time as "CERN users". These scientists and engineers are
typically paid by member organizations around the world, i.e. universities
(think professors, postdocs, grad students) and national labs
(LBNL/Brookhaven/Fermilab etc in the US, in2p3 in France, DESY in Germany).

The ATLAS and CMS author lists are about 3000 each (generally all physicists),
but all told there are over 10,000 scientists, technicians, and engineers who
basically work full time running the LHC and its associated detectors.

That's not to mention all the people working on any of CERN's many other
projects that have nothing to do with the LHC.

~~~
arethuza
"nothing to do with the LHC"

Or possibly nothing to do with physics - I went to a conference at CERN in '94
about one of their computing projects.

I believe that project became quite popular.

------
helly
So to explain the world we see, we combine quantum theory, theory of
relativity, dark matter, gravitation, electromagnetism, two types of nuclear
force and a zoo of now 62 elementary particles?

I often wish for some kind of "Physical Philosophy". That tries to make sense
of the world independent from those theories. For example: what if the
theories just keep growing indefinitely? If we keep "finding" more and more
complex theories that explain some aspects of what we see better then the old
ones and keep "finding" new particles? What would that tell us about reality?
What if we found a very simple formula that explains everything with just one
type of particle and one dimension? Would it matter?

~~~
Udo
The world is complex, but we haven't gotten to the stage yet where you should
feel lost, even as a layman. It is absolutely possible to know enough
classical physics, QM, and theory of relativity to have a decent understanding
of our current models. You absolutely don't have to be able to recite a table
of elementary particles in order to understand this.

> _I often wish for some kind of "Physical Philosophy". That tries to make
> sense of the world independent from those theories._

If your sense-making framework can (or must?) be independent from the facts,
there is an enormous multitude from all cultures available for you to choose
from. But if facts are important to you, and you don't know where to start,
watch some popular science documentaries. If you prefer a touch of philosophy,
I can suggest the original Cosmos series by Carl Sagan. But on the whole,
sense and meaning is not something that can be prescribed by scientific
knowledge - it can, however, help inform your own decisions about sense and
meaning.

> _For example: what if the theories just keep growing indefinitely?_

This does not describe the current state of physics research. In fact, we are
almost _struggling_ to discover new physics, and so far most particle physics
experiments line up so well with theory it's almost frustrating. What we can
see right now is not the bottomless fractal recursion into nothingness which
you describe.

~~~
fjdjjddj
Look, its just that it's all so complex. These must be emergent phenomena of
something deeper - otherwise you have a universe which pops into existence
fully formed with these particular properties, this particular family of
particles and forces. These experiments are a bit like 3d scanning a tree in
millimeter detail and then declaring that you have a perfect knowledge of
trees. Don't get me wrong this is very important stuff, we need this knowledge
to find the underlying systems. But it creates a degree of philosophical
unease in the sensitive individual. For me it seems necessary to say that if
this universe is all that exists, it must necessarily exist from first
principles. My hunch is that what we are seeing is the population dynamics of
all possible systems of interacting elements - or atleast a tiny little piece
of it.

~~~
Udo
> _These must be emergent phenomena of something deeper_

Deeper might be the wrong word in this context, but I don't think many
physicists would disagree that there is probably a small set of rules and
variables that makes up the substrate of reality. For all we know, the
universe could be a really basic cellular automaton.

> _These experiments are a bit like 3d scanning a tree in millimeter detail
> and then declaring that you have a perfect knowledge of trees._

That does not describe our current scientific process at all, which is to find
underlying abstractions and models instead of just cataloguing concrete
findings.

I also think there is a problem with the understanding of higher-order
(emergent, as you say) phenomena: they often do not follow from the basic
underlying rules in an immediately obvious manner. What they do is they become
systems in their own right, with their own mechanics worth studying.

To use an analogy, just because you know everything about sugar and flour
doesn't mean you know everything that's going on in a bakery.

> _But it creates a degree of philosophical unease in the sensitive
> individual._

It's not the universe's job to make us feel comfortable, nor is it science's
job to discard findings on the grounds that we personally don't like their
implications. The universe does not care about our comfort, and philosophical
considerations are not part of the fabric of nature outside of your personal
mental frameworks.

There are many things about nature or the universe at large that make me
uncomfortable, but that doesn't mean these facts should somehow be discarded.

> _My hunch is that what we are seeing is the population dynamics of all
> possible systems of interacting elements - or atleast a tiny little piece of
> it._

I read this several times, and I have no idea what that means.

------
SteveWatson
Paywall

~~~
briggsly
Simple workaround. Copy the article title and paste it into a Google search.
When Google is the referrer, they drop the paywall [1]. For NYTimes and WSJ
articles, this works almost every time.

[1] [http://www.techtimes.com/articles/38718/20150310/7-ways-
to-g...](http://www.techtimes.com/articles/38718/20150310/7-ways-to-get-
around-the-paywalls-of-wall-street-journal-new-york-times-and-more.htm)

~~~
euyyn
Thanks!

------
eli_gottlieb
So they haven't rejected the null hypothesis yet, and they're still getting
themselves written-up in the New York Times?

~~~
jsprogrammer
The null hypothesis is unrejectable.

Heh. Downmod.

~~~
cshimmin
Null hypothesis: There is so such thing as toast.

Experiment: I had toast for breakfast.

Null hypothesis rejected.

~~~
jsprogrammer
I believe "There is no such thing as toast." is only a theorem.

Theorems may be rejected all day long.

Edit: A null hypothesis in this schema would be something like (a bit
ridiculous, but not my example): If toast exists and I eat it for breakfast, I
should be able to detect that I ate it for breakfast at a higher rate than the
false positive rate of my ability to determine whether what I eat for
breakfast is or is not toast.

Keep downmodding. Or, you know, refute what I have said.

~~~
krick
You could just open the Wikipedia, you know:
[https://en.wikipedia.org/wiki/Null_hypothesis](https://en.wikipedia.org/wiki/Null_hypothesis)

 _the term "null hypothesis" usually refers to a general statement or default
position that there is no relationship between two measured phenomena, or no
difference among groups_

 _Rejecting or disproving the null hypothesis — and thus concluding that there
are grounds for believing that there is a relationship between two phenomena —
is a central task in the modern practice of science, and gives a precise
criterion for rejecting a hypothesis._

~~~
jsprogrammer
What is the relevance of this wikipedia quote to my comment?

