LHC -- Why no success except for the Higgs?

[Scott Tyler]

Why aren’t we seeing anything. 99.99991% the speed of light. Nothing. Also why would we need and lhc the size of galaxy to see graviton? Help?

 

[YoungPhysicist]

Why aren’t we seeing anything. 99.99991% the speed of light. Nothing. Also why would we need and lhc the size of galaxy to see graviton? Help?

LHC has found plenty of other stuff,too. Not just Higgs boson.

 

[Drakkith]

Why aren’t we seeing anything. 99.99991% the speed of light. Nothing.

It appears that there's just no other fundamental particles to see beyond the Higgs boson (do note that we have discovered other particles, but they aren't fundamental). At least with the data currently gathered and analyzed. I don't how to answer your question other than that.

Also why would we need and lhc the size of galaxy to see graviton? Help?

Gravitation is extremely weak compared to the other three fundamental forces, which makes it much more difficult to detect gravitons. We we would need an immense machine to to even get a hint of individual gravitons. The details of why are beyond my level of expertise.

 

[bhobba]

Why aren’t we seeing anything. 99.99991% the speed of light. Nothing. Also why would we need and lhc the size of galaxy to see graviton? Help?

Maybe there is nothing exciting to see? We are seeing tons of stuff, just nothing fundamental like the Higgs. Nature is as nature is - that's science - we simply try and understand nature - not get upset if it doesn't do what we may like it to do - or not like it to do. Some may really like the current situation - simply affirming the standard model - its not a worry that current theories are simply confirmed - in fact that's the most likely outcome.

Thanks
Bill

 

[bobob]

All of the standard model particles have been found. There is no theory which predicts anything definite, so the possibilities are endless and one of those possibilities is that there are no new particles to find at any energy we can attain soon or maybe ever. It's actually a bummer that the higgs was found. Had it not been found, that would have indicated new physics could be on the horizon. As it stands, no one has any idea of what to look for apart from what may be learned from studying neutrino oscillations.

 

[Orodruin]

It's actually a bummer that the higgs was found. Had it not been found, that would have indicated new physics could be on the horizon.

To be honest, the Higgs - or something like the Higgs - had to be within reach of the LHC. Anything else would have been very (very!) surprising and likely required some serious revisions of how we do particle physics, not just a sign of new physics on the horizon. The "bummer", if you want to use that expression, is that what was found very much looks like a Standard Model Higgs.

 

[CWatters]

People elsewhere have done experiments and got results that apparently conflict with the standard model but they are banned topics here. Perhaps one day we will see their work published in a suitably respected journal but until then.

 

[nikkkom]

Also why would we need and lhc the size of galaxy to see graviton? Help?

Gravitons are very weakly coupled to other particles. IOW: the probability of two protons in LHC exchanging a graviton is astoundingly low. To increase it, you need to "reduce the distance between protons", IOW: you need to decrease the uncertainty of their location. IOW: you need to increase their energy. A LOT. Like, a billion billion times compared to LHC.

 

[Vanadium 50]

People elsewhere have done experiments and got results that apparently conflict with the standard model but they are banned topics here. Perhaps one day we will see their work published in a suitably respected journal but until then.

Let's not mix cause and effect her. It's the fact that they are unpublished that prohibits their discussion, not the fact that they are discrepant.

 

[CWatters]

Understood.

 

[mathman]

Super-symmetry seems to be the only near term possibility for LHC to find something. So far nothing has turned up.

 

[Orodruin]

Super-symmetry seems to be the only near term possibility for LHC to find something.

What do you base this statement on? I do not think it is correct.

Edit: If it were true, then someone should tell the ATLAS collaboration to stop producing papers like this https://arxiv.org/abs/1606.02265 (random example, first I could find).

 

[Alice Vuyuklaki]

or maybe there isn't such thing as graviton

 

[mfb]

Super-symmetry seems to be the only near term possibility for LHC to find something. So far nothing has turned up.

There are many options. How likely they are depends on who you ask, but there are many other models predicting things the LHC could discover in the near future (even with datasets on disk already).

or maybe there isn't such thing as graviton

That would be really strange, but the LHC cannot find the standard massless graviton anyway.

 

[Alice Vuyuklaki]

No it wouldn't be that strange..string theory is just a theory and not a proven one..finding the graviton would be a step closer on proving it.

 

[CWatters]

https://www.physicsforums.com/index.php?threads/956330/

 

[mfb]

No it wouldn't be that strange..string theory is just a theory and not a proven one..finding the graviton would be a step closer on proving it.

This has nothing to do with string theory. The graviton should exist simply because there is gravity and quantum mechanics.
Finding the graviton would be "proof" that it exists (as much as there are proofs in physics), but the massless graviton cannot be found by any existing experiment. The LHC could find heavier graviton-like particles if they exist.

Be careful with strong statements if you are not sure they are right.

 

[bhobba]

This has nothing to do with string theory. The graviton should exist simply because there is gravity and quantum mechanics.

Indeed. People sometimes get a bit confused about what the issue with quantum gravity is. We do not have a theory of quantum gravity - and this is one of the major issues facing physics. BUT since Ken Wilson and the effective field theory approach we look at the issue differently:
https://arxiv.org/abs/1209.3511

The modern view based on Wilson's work is all theories are really effective theories only valid up to some scale, which seems to be about the Plank scale where some other as yet unknown theory takes over. This means gravity is in the same boat as all the other forces/particles of the standard model. If the gravitation did not exist we would really be in deep do do because it would beg the question - why is gravity different? It may be of course - science is based on experiment - but if it did not exist it would be a momentous discovery - then again how does one prove a negative?

Thanks
Bill

 

[mfb]

then again how does one prove a negative?

By producing a situation where you expect to see something, and then failing to see it. That's how all the exclusion limits work. We can make pretty clear predictions how gravitons should behave. We just cannot build detectors where we would expect to see them.

 

[Alice Vuyuklaki]

Hmm okay then..but can i ask something..we know that there are 4 dimensions...at least.. and one of them is time...we also know that gravity is the curvature of space and time..and then we also know that time is quantized and space also(Planck length and Planck time)...couldn't that associate with graviton somehow?or that gravity is quantized.. Or am i too confused..

P.S. Excuse me for any faults..english isn't my native language.

 

[Drakkith]

.and then we also know that time is quantized and space also(Planck length and Planck time)

As far as I am aware neither space nor time is quantized in either GR or the standard model of particle physics. Planck length and Planck time have nothing to do with quantization unless I've missed something important.

 

[Alice Vuyuklaki]

As far as I am aware neither space nor time is quantized in either GR or the standard model of particle physics. Planck length and Planck time have nothing to do with quantization unless I've missed something important.

okay..thank you

 

[bhobba]

Remember we really do not know what's going on at about or below the Plank scale. We have some possibilities like String Theory so let's look at what it says. I am no expert in it so I can't point you to any literature, just some general information I have read. String theory was developed in flat space-time, but really we should consider the more general case if it had some kind of curvature. In string theory this evidently leads to a striking result - for the string theory equations to be consistent that curvature must be exactly as specified by Einstein. This is quite a remarkable result I wish I knew the detail of, but string theory is not an easy subject so I probably will not get around to delving into the detail,

The point here though is there is no reason at all to suppose space-time has some kind of 'granular' nature at its fundamental level. Note that at present String Theory has not delivered on its promise as much as people hoped and has morphed somewhat:
https://www.ias.edu/news/cole-stringtheory-quanta

What the future may bring of course we have no way of knowing, but certainly it could easily be space-time is just as continuous as we currently suppose it is.

Thanks
Bill

 

[bobob]

To be honest, the Higgs - or something like the Higgs - had to be within reach of the LHC. Anything else would have been very (very!) surprising and likely required some serious revisions of how we do particle physics, not just a sign of new physics on the horizon. The "bummer", if you want to use that expression, is that what was found very much looks like a Standard Model Higgs.

Exactly. That was my point. Had the higgs not been found, nuclear and particle physics would have become much more interesting.

 

[vanhees71]

Also, I think the too common idea of the LHC being "not successful" is flawed, and it's flawed because of a flawed conception what science is all about, i.e., to investigate quantitatively and precisely what's going on in Nature, and indeed that the Higgs has been found and verified in very many decay channels to behave as predicted from the Standard Model and the given masses of the elementary particles etc. after 50 years being predicted by various theorists, is a success, but not the only one. Another success is that, despite great expectations by many physicists to find "physics beyond the Standard Model" nothing was found or claimed to have been found. It shows that science if performed very well at CERN, and it's also a (somewhat unexpected )finding how well the Standard Model works after all. Despite this, there's not only HEP but also relativistic heavy-ion-collision physics going on at the LHC, and there also many interesting things have been found, like the amazing fact that light (anti-)nuclei follow the general chemical-freeze-out line as the hadrons (with a temperature of around 150 MeV) and many more details. With the current detector updates (e.g., of ALICE) I think there'll be more to come in the next few months/years.

 

[gleem]

The LHC is producing huge amounts of data. I have read that only about 1% has been analyzed and that the 1% is chosen on the basis that it is believed to have interesting physics on the basis of current knowledge. But who know what is in the other 99% of the proverbial haystack.

 

[mfb]

That number depends on how you count.

The big LHC experiments had about 6% of the collisions expected over the lifetime of the LHC: Roughly 1% in Run 1 at lower energy, 1.5% in 2015/2016 and 3.5% in 2017 and 2018 at the current record energy. Many publications are based on Run 1 and/or 2016 data. We'll see another round of new results in a few months, based on 2015-2018 ("Run 2"). Some analyses will take more time, however, we can expect results based on Run 2 well into 2020-2021.

Does that mean we get to 100% of the collisions analyzed in detail at some point? No. Only 0.001% of all collisions are stored in ATLAS and CMS (more in LHCb and ALICE), 99.999% have to be thrown away while data-taking to keep data rates manageable. The trigger system looks for the most interesting events and discards everything else. There is a lot of work going into the selection criteria but you can always find some exotic model that won't be found simply because no one wrote a trigger to record suitable events. The experiments do store smaller sets of more inclusive selections for background studies, data quality checks and so on but then usually the datasets are too small to find something new.

 

[gleem]

This sounds like my experience in low energy nuclear physics many many years ago. I did my doctorate using a magnetic spectrograph. For any given bombarding particle a reaction could release protons, neutrons, deuterons, tritons, helium 3 and 4 or more. The spectrograph would be set to detect and momentum analyze a particular particle in a particular momentum range. You would loose a lot on information and some of the recorded information would be uninteresting or irrelevant and discarded ( actually using nuclear emulsions we had a semi permanent record of those events). Sometime old runs were used to survey this discarded data for future studies.