So how will CERN's LHC detect a Higgs boson

In summary, the Large Hadron Collider (LHC) at CERN is able to produce a Higgs boson by colliding protons at high energies. This collision creates a lot of new quarks which then combine to form various particles of different masses. The energy from the collision is converted into mass, including the mass of a Higgs boson. However, this process is not a certainty and requires a lot of collisions and data analysis to identify the specific particle tracks and decays that could indicate the presence of a Higgs boson.
  • #1
calgarian
14
0
So how will CERN's LHC produce a Higgs boson

I saw a video where a professor said

"So you do it by ... using e=mc[itex]^{2}[/itex] ... you collide some protons at huge energies, so that's giving you energy, and that energy gets converted into the mass of all possible new particles that there can be"

I'm not a physicist and I thought what the LHC was doing was colliding protons in order to break them into their constituent parts, one of which is a Higgs boson. But the quote above says that the collision is intended to create energy which somehow converts to mass. How exactly does energy spontaneously convert into mass?
 
Last edited:
Physics news on Phys.org
  • #2
The kinetic energy of the colliding protons can be used to create new massive particles - they are not present in the protons before!*
The energy is not created in the collision, it is put into the protons before by accelerating them.

*at least not in a relevant way. Just ignore this comment.
 
  • #3
Energy has mass. So when colliding particles together at high energies you already have mass there to use.

Note: I wrote the following before realizing the question was just about the energy and mass thing. I'm keeping it up here for now since it relates to the OP's thread title unless its blatantly wrong.

Protons are made up of Quarks, and the force that holds these quarks together inside a proton is the color force. It turns out that when you try to pull two quarks apart the color force DOESN'T get weaker with distance. Because of this, the farther you pull them apart the more energy you need to do so. At a certain point it is more favorable for two other quarks to be created using the energy you are pulling with than for the two quarks to continue to get further away from each other. These newly created quarks are bound by the strong force to the original two quarks, so instead of pulling two quarks apart you end up creating two more quarks and you come away with two hadrons, which are a class of particle that is made up of quarks.

Now, because of this effect, smashing protons together at huge energies results in not just two new quarks, but a LOT of new quarks. These new quarks all bind together and form various particles of various masses, most of which decay extremely quickly. During the various decay processes, even more types of particles can be created, such as leptons, photons, and bosons.

Now, if the higgs boson has a mass that is within the energy range of the LHC, then sometimes these various particles and decay processes can lead to the creation of a Higgs boson. By looking at the various particle tracks in the detectors and by following all the decay processes we can piece together where a higgs might be created. The problem is that this isn't a black and white picture where we can go "Bingo! There it is!". The particle creation and decay processes are inherently random in certain ways which forces us to collide HUGE numbers of protons together and look at all of their tracks in hopes of sorting out where the Higgs might be from the rest of the bunch, which we can refer to as "noise".

The entire process takes years to bear fruit, if at all, and currently the LHC has done over 1 trillion collisions in search of the Higgs boson.
 
  • #4
Drakkith said:
Note: I wrote the following before realizing the question was just about the energy and mass thing. I'm keeping it up here for now since it relates to the OP's thread title unless its blatantly wrong.
Yeah I realized afterwards that my title sucks. I guess I am asking a more general question of how energy gets converted into specific types of mass like a Higgs boson.
Drakkith said:
Energy has mass. So when colliding particles together at high energies you already have mass there to use.

As I say above I am having difficulty of how you go from a "general" form of mass in energy to, from the CERN professor's quote, "all possible new particles that there can be." How do specific "types" of mass just decide to show up out of nowhere?
 
  • #5
Drakkith said:
Energy has mass. So when colliding particles together at high energies you already have mass there to use.

This statement is nonsense. It's about as meaningful as saying that color has greasiness. Energy and mass are both properties that an object can have. A correct statement of the relationship between them is that mass is a type of energy. Specifically, it is the energy that the object has in the frame of reference where its momentum is 0.

Colliding objects allow the conversion of some or all of their kinetic energy into mass specifically because the two objects together have less momentum than either one individually.

Protons are made up of Quarks, and the force that holds these quarks together inside a proton is the color force. It turns out that when you try to pull two quarks apart the color force DOESN'T get weaker with distance. Because of this, the farther you pull them apart the more energy you need to do so. At a certain point it is more favorable for two other quarks to be created using the energy you are pulling with than for the two quarks to continue to get further away from each other. These newly created quarks are bound by the strong force to the original two quarks, so instead of pulling two quarks apart you end up creating two more quarks and you come away with two hadrons, which are a class of particle that is made up of quarks.

Now, because of this effect, smashing protons together at huge energies results in not just two new quarks, but a LOT of new quarks. These new quarks all bind together and form various particles of various masses, most of which decay extremely quickly. During the various decay processes, even more types of particles can be created, such as leptons, photons, and bosons.

Now, if the higgs boson has a mass that is within the energy range of the LHC, then sometimes these various particles and decay processes can lead to the creation of a Higgs boson. By looking at the various particle tracks in the detectors and by following all the decay processes we can piece together where a higgs might be created. The problem is that this isn't a black and white picture where we can go "Bingo! There it is!". The particle creation and decay processes are inherently random in certain ways which forces us to collide HUGE numbers of protons together and look at all of their tracks in hopes of sorting out where the Higgs might be from the rest of the bunch, which we can refer to as "noise".

The entire process takes years to bear fruit, if at all, and currently the LHC has done over 1 trillion collisions in search of the Higgs boson.

Most of the interesting processes at high energy colliders aren't at all related to the fragmentation and hadronization processes you're describing here. The high energy (partonic) collisions that lead to the production of heavy particles not present in the initial state actually happen on a much shorter time scale than the processes you're discussing. The Higgs (and other interesting heavy particles) are directly produced in the collisions of the quarks and gluons that are already present in the two protons. The remaining quarks and gluons which don't participate in the direct collision undergo the processes you've described.
 
  • #6
calgarian said:
As I say above I am having difficulty of how you go from a "general" form of mass in energy to, from the CERN professor's quote, "all possible new particles that there can be." How do specific "types" of mass just decide to show up out of nowhere?
It is random which particles are produced in a specific collision. Actually it depends on your favorite interpretation of QM, but for practical purposes it is just a random event. A higgs (if it exists with ~125GeV mass) is produced about once every 10 billion collisions.
In general, lighter particles are much more frequent - a charm anticharm quark pair (~1.5 GeV per quark) is produced about every 10 collisions, and single collisions can easily produce something like 30 light quarks (<0,1 GeV).
 
  • #7
Parlyne said:
This statement is nonsense. It's about as meaningful as saying that color has greasiness. Energy and mass are both properties that an object can have. A correct statement of the relationship between them is that mass is a type of energy. Specifically, it is the energy that the object has in the frame of reference where its momentum is 0.

I disagree with mass being a "form" of energy. But given the lack of a concrete definition of the term "mass" let's agree to disagree for now.

Most of the interesting processes at high energy colliders aren't at all related to the fragmentation and hadronization processes you're describing here. The high energy (partonic) collisions that lead to the production of heavy particles not present in the initial state actually happen on a much shorter time scale than the processes you're discussing. The Higgs (and other interesting heavy particles) are directly produced in the collisions of the quarks and gluons that are already present in the two protons. The remaining quarks and gluons which don't participate in the direct collision undergo the processes you've described.

Ok, that makes sense.
 
  • #8
I came across this quote in an article about CERN's search for the Higgs boson:
It fires streams of protons in opposite, but parallel, directions in the tunnel. The beams are then bent by powerful magnets so that some of the protons collide in four giant labs, which are lined with detectors to record the sub-atomic debris that results.

Based on the responses ITT, am I correct in concluding that the bolded part is misleading or poorly worded at best? My new understanding is that they will not be looking at debris, as that term is normally used, but rather at particles generated from the energy of the collision. Is my new understanding correct?
 
Last edited:
  • #9
calgarian said:
I came across this quote in an article about CERN's search for the Higgs boson:


Based on the responses ITT, am I correct in concluding that the bolded part is misleading or poorly worded at best? My new understanding is that they will not be looking at debris, as that term is normally used, but rather at particles generated from the energy of the collision. Is my new understanding correct?

Pretty much.
 
  • #10
But it is also a fact that a lot of the collision products are uninteresting for the process searched for and actually an obstacle in the experiment, hence the use of the term "debris".
 
  • #11
... so that some of the protons collide in four giant labs, which are lined with detectors to record the sub-atomic debris that results

kloptok said:
But it is also a fact that a lot of the collision products are uninteresting for the process searched for and actually an obstacle in the experiment, hence the use of the term "debris".

The author of the article used the term "debris" to describe something that the experiment is designed to record, as opposed to being uninteresting and obstacles as you describe them.
 
  • #12
Really, this is about how one would define the word "debris". I came across the following:

debris
1.
a. The scattered remains of something broken or destroyed; rubble or wreckage.
b. Carelessly discarded refuse; litter.

Looking at the second definition (b), I see your point. Not everything is "litter" in the collision, in that case it would be of no point doing the experiment. However, the first definition (a) certainly applies, at least the first part. The protons are "broken" or "destroyed" and the scattered remains are then the "sub-atomic debris". And it was not my intention to say that the experiment is only designed to record that which is not labeled as "debris" (and thus ignore the "debris"). You want to detect as much as possible to get a full understanding of each event.

But this is all just semantics. What I meant with "uninteresting" and "obstacle" is that when colliding two hadrons there are a lot of things happening which do not belong to the hard process. In the forward and backward direction a large number of particles are created from what is left of the hadron after partons have collided in the hard process. This is what I alluded to when I wrote "uninteresting". Of course, you should not discard this entirely as you need as much information as possible on the event to be able to sum up momenta etc.

The point is that in a hadron collision, there are lots of things happening which do not directly belong to the hard process and it is a lot of work to isolate what you are looking for. Hence an "obstacle to the experiment".
 
  • #13
I'm really not sure what point you are arguing, kloptok. The point I am making is that as a non-physicist I had been confused as to what the LHC is doing because of articles like the one I quoted. The author makes it sound as if we will find the Higgs boson in "the scattered remains" of the collided protons, which implies that when a proton is broken into pieces one of those pieces is a Higgs. I recently learned the correct understanding of the process, which is that the Higgs will arise from the energy released in the collision of the two protons.
 
  • #14
Alright, I didn't note that you were a non-physicist, sorry about that. And you are right in your understanding, I didn't mean to make it sound like you had misunderstood it. Rather I wanted to supplement your understanding.

Anyway, let's take it from the beginning: At the LHC protons are collided. The large kinetic energy of the colliding protons creates a multitude of particles, among which can be the Higgs. But in every collision there will in the end also be hundreds, maybe thousands, of other particles also produced, and a lot of them coming from the particles inside the proton which didn't collide. These particles make it difficult to see if the Higgs was there in the first place, as you have to isolate the few particles that actually come from the decay of the Higgs from all the other particles. This is I would say the reason why you will often encounter terms such as "debris" in articles about collisions with protons (or other composite particles), such as at the LHC. As a physicist looking for the Higgs, there is a huge amount of work to work through all this other information from each collision. An electron-positron collider for example will provide much "cleaner" collision with a lot less particles to keep track of, since the electron/positron is point-like. Hence these collisions are in this sense easier to analyse. Again, my point was not to confuse, just to try to clarify the use of the word "debris" and why one would use it in the context of proton collisions, which are very complicated to analyse due to the proton's compositeness. The important thing is obviously to understand what the author's mean when writing "sub-atomic debris" and why they would write such a thing, and not exactly how the word debris is defined.

You can for example look at this picture, which shows a collision where four muons are produced (the blue lines, the rest in form of white lines is the "debris"): http://www.atlas.ch/photos/atlas_photos/selected-photos/events/FourMuon.jpgphotos/events/1112301_01.jpg [Broken]
 
Last edited by a moderator:
  • #15
kloptok said:
You can for example look at this picture, which shows a collision where four muons are produced (the blue lines, the rest in form of white lines is the "debris"): http://www.atlas.ch/photos/atlas_photos/selected-photos/events/FourMuon.jpgphotos/events/1112301_01.jpg [Broken]

Hmm. 404 Not Found error on the link.
 
Last edited by a moderator:
  • #16
That's odd. It's from www.atlas.ch-->Multimedia-->Images-->Events-->Proton Collision Events ( http://www.atlas.ch/photos/events-collision-proton.html [Broken] ). The fourth one from the left, entitled "Event with 4 muons" (but not the first one called this though).
 
Last edited by a moderator:
  • #17
Wikipedia has an entry. Look at the two Feynman diagrams in the figure on the right of this paragraph.
 
  • #18
http://www.atlas.ch/photos/atlas_photos/selected-photos/events/FourMuon.jpg [Broken] is the image, I think the link has some copy&paste-error.

But in every collision there will in the end also be hundreds, maybe thousands, of other particles also produced, and a lot of them coming from the particles inside the proton which didn't collide.
Thousands is a bit much (that corresponds to heavy ion collisions), but ~100 are not uncommon together with high-energetic processes. However, keep in mind that most collisions to not produce higgs/top/W/Z, and tend to produce less particles.
 
Last edited by a moderator:
  • #19
mfb said:
http://www.atlas.ch/photos/atlas_photos/selected-photos/events/FourMuon.jpg [Broken] is the image ...

Can someone give a brief primer on what information is conveyed by an image like that? I've seen similar images but I have no clue what the images are saying. I imagine the length and direction of the lines means something?
 
Last edited by a moderator:
  • #20
Dickfore said:
Wikipedia has an entry. Look at the two Feynman diagrams in the figure on the right of this paragraph.

Hmm ... so does this mean that the Higgs will be produced from a combination of the energy released in the collision and stuff that makes up the protons? I was getting the understanding that that they would just pop up "magically" out of pure energy (again, I am not a physicist :tongue:)
 
  • #21
calgarian said:
Hmm ... so does this mean that the Higgs will be produced from a combination of the energy released in the collision and stuff that makes up the protons? I was getting the understanding that that they would just show up "magically" out of pure energy (again, I am not a physicist :tongue:)

There is no such thing as "pure energy". Energy is contained in the form of excitations of quantum fields of matter, which can be single-particle excitations, when the energy is contained in the the temporal component of its 4-momentum whose square is equal to the squared mass of the particle, or bound states of several particles, and then the energy is distributed between the kinetic energies of the constituting particles and the "potential energy" of their bonds (still carried by the quantum field whose particles are the force carrier bosons).
 
  • #22
calgarian said:
Can someone give a brief primer on what information is conveyed by an image like that? I've seen similar images but I have no clue what the images are saying. I imagine the length and direction of the lines means something?

The picture shows the cylindrically formed detector which is placed around the collision point. In this case the view is from the side, the beam goes along the horizontal axis in the center. The lines represent particles and their paths in the detector, colours specify type of particle. In the picture I linked to the blue lines are particles called muons (a heavier sibling to the electron). That the lines are long mean that these particles have traveled all the way through the detector to the outermost part. In this case the white lines represent "the rest", which are mostly different types of hadrons (particles composed of quarks, such as protons, neutrons and pions and other mesons). There is no real consensus for depicting a certain type of particle in a specific colour, this will in general be different in different pictures.

All the yellow and green bars (the green bars are small and look more like dots) represent energy deposited in different parts of the detector, higher bar naturally means more energy deposited and hence a more energetic particle.

mfb said:
Thousands is a bit much (that corresponds to heavy ion collisions), but ~100 are not uncommon together with high-energetic processes. However, keep in mind that most collisions to not produce higgs/top/W/Z, and tend to produce less particles.
Thanks for your input!
 
  • #23
kloptok said:
The picture shows ...

Thanks!

kloptok said:
All the yellow and green bars (the green bars are small and look more like dots) represent energy deposited in different parts of the detector, higher bar naturally means more energy deposited and hence a more energetic particle.

Why are the yellow and green bars not lines like the muons and the hadrons? What types of particles are these? Also, I'm assuming the longer lines means more energy just like the higher bars?
 
  • #24
Not quite, the lines rather show the paths of the particles as they travel through the detector. Longer lines means that the particle has gotten further from the collision point. The bars are associated with the lines. It is a bit difficult to see in this picture, but if a particle gets to a certain, let's say "green", part of the detector it will be accompanied by a green bar depicting the energy deposited. If a particle gets to both the "green" and the "yellow" part of the detector there will be both a yellow and a green bar associated with that line. These particular parts ("green" and "yellow") will slow down the particle so it might be that a particle is fully stopped in the "green" part before it reaches the "yellow" part. Then there would only be a green bar and no yellow one.

The muon is so penetrating that is goes through both the "green" part and the "yellow" without being stopped.

You can take a look at this link to learn more about modern detectors: http://www.particleadventure.org/modern_detect.html The "green"/"yellow" detector parts I have been talking about are the two types of calorimeters, the electromagnetic and hadron calorimeters (which are red and green respectively in this link).
 
  • #25
kloptok said:
[...] which are mostly different types of hadrons (particles composed of quarks, such as protons, neutrons and pions and other mesons)
"other mesons" are nearly 100% kaons. All other hadrons do not live long enough to reach the calorimeters with significant probability.
Add electrons and photons, and you have all types of particles in proton-proton collisions which can be detected.


@calgarian: The image is something you could call "artist's impression" - not really useful if you want to see something, but very colorful.
 
  • #26
Thanks for the explanations! Interesting stuff.
 
  • #27
Fascinating topic. How about the original thread title is rearranged to:

So will CERN's LHC detect a Higgs boson?

I wonder what the consensus is among people in this forum? Have they found enough evidence to announce the discovery of the Higgs or has some other particle been found? Or will it be announced the Higgs does not exist at all and it's back to the drawing board?

I am interested to know the predictions from people with greater knowledge than I have about these things...

Many thanks!
 
  • #28
esmeralda4 said:
Fascinating topic. How about the original thread title is rearranged to:

So will CERN's LHC detect a Higgs boson?

I wonder what the consensus is among people in this forum? Have they found enough evidence to announce the discovery of the Higgs or has some other particle been found? Or will it be announced the Higgs does not exist at all and it's back to the drawing board?

I am interested to know the predictions from people with greater knowledge than I have about these things...

Many thanks!

They previously announced a 3 sigma confidence level that the higgs was between a certain mass range, but that isn't enough to say for certain. I believe there will be a press release or something here in a few days with more news. We'll see!
 
  • #29
I thought an announcement was going to be made on the 4th July?

Now, I want to get this straight, I'm not a Daily Mail reader - but it seems to me that this article is incredibly premature?

http://www.dailymail.co.uk/sciencet...e-discovered-Wednesday.html?ito=feeds-newsxml

Maybe I shouldn't feel like this but there is a part of me that hopes the announcement will be that it hasn't been found. I think that would be a really exciting 'negative result' for Physics.

But as I declared previously, I can not claim to be greatly knowledgeable in this area so I am fascinated to hear what others think...
 
  • #30
It's a news article and they say in there "it is believed" and other things that tell me that they are guessing that it is found but are not sure.
 
  • #31
My personal feeling is that CERN will on Wednesday announce a higher sigma level than earlier, but still not the required 5 sigma. If, as is speculated in the Daily Mail article, there will be an announcement of a 4 sigma significance this is not enough to conclude a discovery of the particle. In the Daily Mail article it sounds as if this is a sure discovery, this is not true. Statistical flukes can still happen at this confidence level. We will just have to wait until Wednesday I guess. I think the seminar can be followed live here:
http://webcast.web.cern.ch/webcast/

It would indeed be intriguing if there was no discovery, but at the same time I personally feel that particle physics needs a positive result in order to justify the experiment with the general public. Even though a no-show is interesting theoretically it doesn't sound very good that loads of tax money was spent to discover nothing and it will be difficult to motivate future experiments.
 
  • #32
The Tevatron used proton/antiproton annihilation; for those collisions, essentially all the energy in the collision became free energy, and the gamut of possible products was limited only by energy.
The LHC collides hadrons (of which protons are one example) and as such, there are strong force effects which will prefer certain particles. The have a large ion collision experiment (using Pb ions), besides just proton collisions; with their energies, they should see a quark-gluon plasma without differentiation into hadrons for a measurable time.
 
  • #33
If the SM higgs is there, the expected signal significance in 2012 data should be somewhere around 3-4 sigma (for each experiment), and the combination could give something like 4-5 sigma. However, statistical fluctuations might change this, so more than 5 sigma or just 3 sigma in the combination are possible, too.

I would expect a possible 5-sigma-measurement form the combination of ATLAS+CMS, if no individual experiment already reaches this. But taking more data is the better way to increase the significance*.

*assuming the Higgs is there, which I expect with >90% probability
The Tevatron used proton/antiproton annihilation; for those collisions, essentially all the energy in the collision became free energy, and the gamut of possible products was limited only by energy.
While the Tevatron could use more high-energetic quark/antiquark-annihilations, more than ~50% of the beam energy was very unlikely. Remember that the proton momentum is distributed over 3 quarks and some virtual particles. Hard (quark) collisions use the momentum of one quark (per proton) only for heavy particles.
 

1. What is the Higgs boson and why is it important?

The Higgs boson is a subatomic particle that is theorized to give other particles their mass. It is important because it helps explain why particles have mass and is a crucial piece in the Standard Model of particle physics.

2. How will the LHC detect the Higgs boson?

The LHC will use high-energy particle collisions to recreate the conditions of the early universe. These collisions will produce a variety of particles, including the Higgs boson, which can be detected and studied by the LHC's detectors.

3. How does the LHC's detector work?

The LHC has four main detectors - ATLAS, CMS, ALICE, and LHCb - that are designed to detect different types of particles and their properties. These detectors use a variety of technologies, such as tracking devices and calorimeters, to measure the energy and trajectory of particles produced in collisions.

4. What are the challenges of detecting the Higgs boson?

The Higgs boson is a very rare and short-lived particle, making it difficult to detect. Additionally, it can decay into a variety of other particles, making it challenging to distinguish from background noise. The LHC's detectors are designed to overcome these challenges and have been continuously upgraded to improve their sensitivity.

5. What will the discovery of the Higgs boson mean for science?

The discovery of the Higgs boson would confirm the existence of the Higgs field, which is responsible for giving particles their mass. This would provide a deeper understanding of the fundamental forces and particles in the universe and could potentially lead to new discoveries and technologies in the future.

Similar threads

  • High Energy, Nuclear, Particle Physics
Replies
13
Views
2K
  • High Energy, Nuclear, Particle Physics
Replies
11
Views
1K
  • High Energy, Nuclear, Particle Physics
Replies
8
Views
1K
  • Advanced Physics Homework Help
Replies
2
Views
818
  • High Energy, Nuclear, Particle Physics
Replies
7
Views
2K
  • High Energy, Nuclear, Particle Physics
Replies
1
Views
1K
  • High Energy, Nuclear, Particle Physics
Replies
1
Views
970
  • High Energy, Nuclear, Particle Physics
Replies
2
Views
1K
  • High Energy, Nuclear, Particle Physics
Replies
2
Views
1K
  • High Energy, Nuclear, Particle Physics
Replies
1
Views
6K
Back
Top