New LHC results 2015: Tuesday Dec 15 - interesting diphoton excess

[mfb]

Even if you stop at 10 tosses, such a scenario of 10 heads is still possible why should it surprise anyone?

It is possible that a meteorite will hit your house tomorrow. Would you be surprised? I'm quite sure! Would you be surprised if a meteorite would hit some house somewhere in the world? While this is still a rare event: probably not.
Where is the difference? You have categories of different size: "my house", "some random other house".

We have the same with the coin: We expect it to be fair, but we also consider the options "the coin gives head all the time" and "the coin gives tails all the time". Getting 10 times head in 10 attempts strongly favors the (previously unlikely) "all head" hypothesis compared to the fair coin.
A result of HTTHTHHHTHTHTTTHHTTTH is not surprising normally. If I predict exactly this pattern in advance, on the other hand, it stands out, and if we get exactly this pattern it is surprising.

There is a massive number of options how the thousands of events in the analyses can be distributed, but only a few unlikely of them give some peak-like structure. It is surprising to find one of those.

 

[Orodruin]

Even if you stop at 10 tosses, such a scenario of 10 heads is still possible why should it surprise anyone?

Because it is a very extreme result which would happen only one out of 2^10 times. Managing to get this result with only 10 tosses is very unlikely to happen. Sure, it could happen, but it is not likely to. It is much much more likely to obtain 5 heads and 5 tails in any given set if 10 tosses.

Let me ask you this: Would you take an even money bet where you win if a coin lands face up 10 times in a row? If so I have a betting proposal for you. I will even give you twice as good odds!

 

[MathematicalPhysicist]

It is possible that a meteorite will hit your house tomorrow. Would you be surprised? I'm quite sure! Would you be surprised if a meteorite would hit some house somewhere in the world? While this is still a rare event: probably not.
Where is the difference? You have categories of different size: "my house", "some random other house".

We have the same with the coin: We expect it to be fair, but we also consider the options "the coin gives head all the time" and "the coin gives tails all the time". Getting 10 times head in 10 attempts strongly favors the (previously unlikely) "all head" hypothesis compared to the fair coin.
A result of HTTHTHHHTHTHTTTHHTTTH is not surprising normally. If I predict exactly this pattern in advance, on the other hand, it stands out, and if we get exactly this pattern it is surprising.

There is a massive number of options how the thousands of events in the analyses can be distributed, but only a few unlikely of them give some peak-like structure. It is surprising to find one of those.

I must say that I still don't see the reason to be surprised.
Do you say that in a fair coin after tossing 10 times, the outcome of always heads is less likely than any other outcome?
Show me how do you calculate your probabilities.
What I am trying to say that after tossing ten times a fair coin we have (0.5)^10 chance of getting any sequence of outcomes.
The liklihood of getting heads 1000 times in a row is less likely than 10 times in a row, but it doesn't mean it can never happen.

As for the metorite, I wouldn't be suprised if it should hit something on Earth then it can happen to hit my house, it depends on its trajectory though.

 

[Orodruin]

Do you say that in a fair coin after tossing 10 times, the outcome of always heads is less likely than any other outcome?

This depends on your definition of "any other outcome". Of course, taking "any other outcome" as the complement of that one outcome, it is obvious that it is less likely. Taken as any other fixed series, of course not.

In physics you will often be dealing with macroscopic states where the observables are composed of several of the microstates. Even if each microstate is equally likely, the macrostate containing more microstates will be more likely and a macrostate containing only one microstate will be very unlikely. This is the situation here, as it was when you rolled 3-3 - the macro states are "you win" and "you lose". The "you lose" state has a 1/36 probability and you should therefore be more surprised if you win than if you lose based on the previous knowledge.

 

[nikkkom]

Please stop this bickering about how much exactly are you (not) surprised by the slight diphoton excess. It's not productive.

 

[MathematicalPhysicist]

This depends on your definition of "any other outcome". Of course, taking "any other outcome" as the complement of that one outcome, it is obvious that it is less likely. Taken as any other fixed series, of course not.

In physics you will often be dealing with macroscopic states where the observables are composed of several of the microstates. Even if each microstate is equally likely, the macrostate containing more microstates will be more likely and a macrostate containing only one microstate will be very unlikely. This is the situation here, as it was when you rolled 3-3 - the macro states are "you win" and "you lose". The "you lose" state has a 1/36 probability and you should therefore be more surprised if you win than if you lose based on the previous knowledge.

The last paragraph is more clarifying.

 

[ChrisVer]

However I was wondering, how are they calculating the global and the local significance?
from @mfb 's post:

Therefore, experiments usually give two significance numbers: a local significance ("what is the probability that we see so many events at this specific point?”) and a global one ("what is the probability that we see such an excess at some place in the tested range?”).

I think the plots with the p-values ( Figure 2 ) were giving the local significance, because they were giving the significance at specific points in the mass disribution.
for the global one : What is the "tested range"?

 

[Orodruin]

However I was wondering, how are they calculating the global and the local significance?

Usually by Monte Carlo simulation. You simulate a large number of experiments given the null hypothesis and compare with your actual result.

 

[mfb]

The local one: from the p-value. You can calculate the likelihood of the fit with and without signal and compare them.
The global one: CMS didn't specify it, but probably similar to ATLAS: make toys without signal, look how frequent excesses above 2 sigma local significance are, extrapolate to whatever got observed. They cite this paper.

 

[ChrisVer]

Should spend some time into sitting and understanding the Looking Elsewhere Effect...

 

[Haelfix]

Its worth pointing out that the lee is a bit of a dark art in particle physics, unlike the coin toss example. It introduces some model dependence and subtle issues with how you calculate backgrounds. Its definitely something you want to take into account, but it is not completely standardized and has been known to differ in detail between different collaborations (and can cause some epic debates)

 

[Ovolo]

How do we know that it would be a new particle, and not a kind of moiré or superposition effect induced in the Higgs Field due to the high luminosity?

 

[Vanadium 50]

not a kind of moiré or superposition effect induced in the Higgs Field due to the high luminosity?

Because that's nonsense.

Sorry, but we only discuss conventional science here.

 

[Vanadium 50]

ts worth pointing out that the lee is a bit of a dark art in particle physics

I would argue that a lot of the problem stems from people trying to use trial factors to get them out of the hole of a posteriori statistics. You look for a narrow peak and find one with a width of 6%, and the try and go back, and figure out what the p-value would have been had that been your a priori search. That's not a well designed statistical question, and trying to shoehorn it into that formalism is not seamless.

 

[Ovolo]

Because that's nonsense.

Sorry, but we only discuss conventional science here.

I admit, it might have been slightly nonsensical, but in conventional science we have tools like a compass to learn and understand the magnetic field.

My question related more to how do we get to know something more about the Higgs Field by colliding particles?

It is therefor that I mentioned superposition in relation to the particle collisions. If you drop an apple into a pond you get certain amplitude, and when you drop it from a higher distance you get higher amplitude, all with the same particle (apple). Now if you start dropping a whole collections of apples (same particles) into the pond (higher luminosity), in that case waves can start to add up … wouldn’t there be a threshold where this becomes noticeable in relation to the distance between each unique collision in distance and time.

For instance the force of gravity of a particle stretches out infinity, how far does ‘it’ stretches out for particle collisions in relation to the Higgs Field? In super conventional science, you can collide cars and hear a bang and measure how fast waves travel, the same thing for finding out that Electromagnetic waves travel also at the speed of light.

Anyway, since we are doing something unconventional science to begin with, looking for new unknown physics, I was curious how you can rule out what makes sense and what not? How do we pinpoint that what we see is due to the particle or due to the properties of the field?

 

[nikkkom]

If you drop an apple into a pond you get certain amplitude, and when you drop it from a higher distance you get higher amplitude, all with the same particle (apple). Now if you start dropping a whole collections of apples (same particles) into the pond (higher luminosity), in that case waves can start to add up … wouldn’t there be a threshold where this becomes noticeable in relation to the distance between each unique collision in distance and time.

Even LHC luminosity is far, far below the value where this would have any effect.

For instance the force of gravity of a particle stretches out infinity, how far does ‘it’ stretches out for particle collisions in relation to the Higgs Field?

Gravity does not affect interactions on LHC energy scale.