# I Possible ways to increase particle detector resolution?

Tags:
1. Feb 13, 2017

### rageoveralostpenny

So I'm doing some research for a physics essay on particle accelerators and I don't want to go into too much mathematical detail (as I haven't studied statistics or higher level Physics at school yet), but I have googled a lot of things and nothing seems to come up for methods scientists are currently using to improve energy resolution.

Other things that I haven't managed to clarify are:

-How higher particle energy upon collision results in a need for higher energy resolution. I understand that energy resolution is equivalent to the FWHM divided by the mean particle energy. Is it the case that the FWHM can remain the same (same curve width) but under higher energies, you are dividing by a larger number so obtain a smaller % resolution?

-If it is so hard to measure small resolutions, why are we even trying to accelerate particles faster and faster; is it because at a higher resolution more detail can be seen about the particle or some other reason that I didn't catch?

Last edited by a moderator: Feb 13, 2017
2. Feb 14, 2017

### Staff: Mentor

An essay on accelerators (the machines) or particle physics (the science done using those machines)?
Why do you think so? We want the best possible resolution at every experiment, both for high-energy and the low-energy experiments.

A quick google search should show that resolution is not the point.

You might be interested in my Insights article series about the LHC.

3. Feb 14, 2017

### rageoveralostpenny

The detectors and the particle physics behind the detectors. But I am confused resolution and its use in particle physics analysis, despite doing some searches on websites explaining energy resolution (mostly in a medical context)
It's for answering the first question here :
http://sciencechallenge.org/questions

I may have worded that wrong. What I wanted to clarify was, why resolution is always getting smaller?

Thanks, these are clear and detailed.

4. Feb 14, 2017

### Staff: Mentor

That is a weird use of "resolution". In particle physics, resolution is always the precision of measurement values - e. g. the uncertainty on the measurement of a particle energy. What Jonathan Butterworth means is different - it is the question how well we can see smaller structures. At low energies, we just see atoms. The first accelerators allowed to see the nucleus (->Rutherford experiment). Higher energies than lead to fusion and fission reactors: protons and neutrons as components of the nucleus. Even higher energies made the components of those nucleons accessible.

5. Feb 14, 2017

### rageoveralostpenny

Oh okay, thanks. So rather than specifically in the context of particle accelerators, what the question concentrates on is imaging of the smallest parts of atoms in a broad spectrum of ways - different methods that allow us to 'see' the effects of things like quarks?
This sounds a lot more complex than I envisioned to answer...

6. Feb 14, 2017

### ZapperZ

Staff Emeritus
Please note that you missed mfb's earlier comment that you are confusing "particle accelerator" (the "machine") with "particle physics" experiment, which usually involves particle colliders. Not all particle accelerators are particle colliders. In fact, 95% of particle accelerators are not particle collider or particle physics machines.

So you may want to change terminology to "particle colliders" for your essay to be accurate.

Secondly, the issue of "resolution" is relevant in practically ALL experimental physics, not just in high energy physics. The higher the resolution, the finer the details that can be extracted. And this resolution can apply to spatial, temporal, energy, momentum, etc... ALL of these quantities are affected by the resolution of the instrument being used. Why do you think 4K TV has more pixel density than the old standard resolution TV?

Going to higher energy often has nothing to do with increasing resolution. In fact, in many cases, higher energies can often lower the resolution. This is definitely true in photoemission spectroscopy, where we tend to use lower energy photons to get the best energy and momentum resolution.

Zz.

7. Feb 14, 2017

### Staff: Mentor

I knew ZZ would comment on that ;). Not all particle accelerators used for particle physics are particle colliders. Some are fixed-target experiments. "Particle accelerators for particle physics" covers both, but that is a clumsy description. If the essay is about particle physics, make particle physics the title. Accelerators can be mentioned as they are necessary tools.

Well, "imaging"... it's not like we can take pictures. We collide particles, we study the particles that fly away from the collision, and based on that we study what has happened in the collision.

8. Feb 14, 2017

### rageoveralostpenny

I did have a slight idea that they were separate, since a lot of the websites related accelerators to radiography and CRT. But I didn't know that the majority accelerators are not particle colliders - that's probably why my searches are not returning useful results.

I see so in my answer, would the best way to word things be to talk about resolution in particle physics itself, since there is no link between higher energy and resolution?

9. Feb 14, 2017

### Staff: Mentor

I would avoid using "resolution" for anything distance/size-related in particle physics.

10. Feb 15, 2017

### ChrisVer

The resolution is related neither to the particle physics (the science of studying elementary particles) nor accelerators (machines which accelerate the particles).... In particle physics, by studying the process of your interest, you have like fixed results (from experimentalists that's the truth information). Resolution comes into game when you have detectors.
Detectors tend to smear what they measure, mainly because they are electric machines which have flaws, are of finite size or because they have several dead-times to record some particle/signal.

11. Feb 19, 2017

### rageoveralostpenny

Then... what is the definition that I should formally identify it with?

So if you want to increase machine precision you can iron out the flaws? I think I read somewhere that in some cases using quantum circuitry can improve the precision?

For purposes of being succinct, I'd like to edit the focus of my question. After asking around, it appears that the main topic of the first question at http://sciencechallenge.org/questions is how to improve the standard model - which includes the idea of resolution of detectors. It also seems that this article http://rsta.royalsocietypublishing.org/content/374/2075/20150260#sec-1 by Butterworth may tie into the answer.

12. Feb 19, 2017

### Staff: Mentor

The definition of what, and what does "it" refer to?

Resolution of particle detectors is a measure how well they can measure the momenta and energies of particles. Consider the momentum measurement, for example: Particle detectors have a magnetic field that bends the flight path of particles. The faster the particles (more momentum), the less they get bent. How do we measure this? We add multiple layers of material that can detect where a particle went through. They work a bit like a camera each. They give a good idea where the particle was went it went through the material, but they do not have infinite precision. You combine the information from multiple layers to determine how much the particle trajectory was curved. The individual measurements are not exact, so the combined estimate won't be exact either: You have a finite resolution. As an example, your measurement might have the result "the momentum of the particle was 50 GeV/c with an uncertainty of 1 GeV/c". Ignore the units here, the point is just that your measurements are never perfect.
You can rarely fix individual components somewhere in a complex detector. You can replace them. Most of the time you have to live with smaller defects. Better analysis software can help a lot to work with those issues.
Without context, that statement looks very odd.

The Standard Model is a fixed theory. Every deviation from that is not called Standard Model any more. Those models are theories, not experimental results. Experimental results guide the development of theories. If we would find a deviation from Standard Model predictions, that would help a lot. Better detectors increase the chance to find something as the measurements become more precise. Better accelerators are important as well.

13. Feb 20, 2017

### ChrisVer

Some things are not even flaws but constant features throughout your measurement. For example, a Time Of Flight detector has some deadtime - this is something you cannot fix. That's because the electronic signal would have to somehow be recorded, and it takes time to do so (dead time). There are further imperfections which you can take into account and try to, at least, reach a point where you understand how they affect your measurement. In the end you'll use them to define your systematic uncertainties or throw the measurement away (eg in cases of dead material/badly functioning parts in your detector).
Afterall it all depends on to what precision you want to reach...

14. Feb 21, 2017

### rageoveralostpenny

Thank you for your help so far, the part describing detectors made a lot of sense to me (a rare thing).
I read about the standard model on the CERN website but the last paragraph seems a bit vague. Here it is:
"although the Standard Model accurately describes the phenomena within its domain, it is still incomplete. Perhaps it is only a part of a bigger picture that includes new physics hidden deep in the subatomic world or in the dark recesses of the universe. New information from experiments at the LHC will help us to find more of these missing pieces."

I understand that gravity is not able to be united with the standard model because it's a macroscopic force, and the maths describing the standard model is mathematically incompatible with the maths describing gravity... The sentence above which suggests 'deep in the subatomic world': what does that mean? Are quarks not the smallest divisible particles?
Finally, do we need to improve resolution at all to find an answer to the problem of uniting gravity to the standard model if we can get indirect evidence for quarks' interactions and existence?

15. Feb 21, 2017

### Staff: Mentor

Maybe (there are searches if quarks could be composite particles), but that is not the point. There could be other undiscovered particles, "hidden in the subatomic world" (well ...). We would have to find them via their interaction with known particles (because we can only collide particles and build detectors out of things we know).

An improved precision in energy/momentum measurements always helps to search for new things. Other key points are the collision energy (you have to have enough energy to produce the potential undiscovered particles) and the total number of collisions (the particles could be very rare - if a particle just gets produced once every trillion collisions, you won't see it with just a billion collisions).

16. Feb 21, 2017

### ChrisVer

The standard model is not incomplete only because it does not contain gravity. Afterall quantum gravity, if things work as we see them doing until today, is not going to be detectable in LHC or in any near-to-come future; since it's predicted to become important at energies as high as 10^19 GeV. When LHC looks for something connected to gravity, this is relevant with extra dimensions (which can decrease that energy threshold significantly by compactification). There are more realistic problems the SM can't provide reasonable answers (like Dark Matter candidates, CP Violation of the early universe etc).

Deep in the subatomic world is not to be taken literally. It means higher energies. Searching for new particles or phenomena will prove the standard model incomplete.

Improving the resolution of your observed quantities affects your systematics and can give more precise results. Of course how far you wanna go with it [depending on how much you gain] depends on your study. Sometimes hadron colliders are not even the best place to conduct precision measurements. A measurement of let's say the polarization of Z bosons conducted at LHC won't compete with the results obtained from LEP at precision, although it adds up to it. On the other hand, for example, looking at an excess of events in some distribution doesn't have to be terribly precise to give an answer of "yes, I saw something" or "no, I didn't". Of course both need some decent amount of precision [otherwise you can't make any comment if what you're looking at is a pile of cr*p].

17. Feb 22, 2017

### rageoveralostpenny

In other words, by having better precision in measurements, fewer collisions are needed to obtain trends, because there is less uncertainty - so the chance of finding rarer particles is higher? You mentioned earlier that detectors worked in layers; is there any way to improve the precision i.e. more/ thinner layers?

18. Feb 22, 2017

### Staff: Mentor

In general: Yes.
More layers, thinner layers, more and smaller sensitive elements in them, faster detectors, more bandwidth to get the data out of the detector, larger detectors, ...
Unfortunately all those things tend to increase the price (and development effort), and funding is limited.

19. Feb 26, 2017

### rageoveralostpenny

What does compactification actually do? I googled it but Wikipedia is very bad at explaining things simply. I gather it's something to do with ignoring higher dimension? And what energies would this reduce the collision energy needed to study quantum gravity?

And referring to the last part of your answer, why does it sometimes not matter if you can't conclusively decide if you saw a particle from several events?

20. Feb 26, 2017

### Staff: Mentor

Consider a straw: From far away, it looks like a one-dimensional object. If you look closer, you see that it is actually a two-dimensional surface, but one dimension is very small (just the circumference of the straw). Extra dimensions could be like that.

With 3 dimensions (without extra dimensions), the gravitational force scales with 1/r2. Reduce the distance by a factor 10 and the force increases by a factor 100. That is what we observe for stars, planets and in the lab. But that is only the "large" view. The smallest gravity experiments work at distances of about 100 micrometers. What happens if there are extra dimensions that are just 1 micrometer large (the "circumference of the straw")? It would mean that at small scales (<< 1 micrometer), we don't have three dimensions. We might have 4, 5, or even more space dimensions. With 4 dimensions, gravity scales with 1/r3: Reduce the distance by a factor 10 and the force increases by a factor 1000. With 8 dimensions, gravity scales with 1/r7: Reduce the distance by a factor 10 and the force increases by a factor 10,000,000. As you can see, with extra dimensions gravity at small scales can become much stronger than without. It might become strong enough to study it at colliders.
You can never identify everything correctly. The necessary quality depends on the analysis and the precision you want to reach.