What's Next for the LHC After the Discovery of the Higgs Boson?

[RJ Emery]

Now that the Higgs boson has been discovered, I am certain more runs will be made to confirm its existence and to increase the reliability of its ev measurement. When that is done, what will the LHC be used for next? Having done its job, will it be decommissioned?

 

[Bill_K]

Not hardly! The Higgs still needs to be confirmed, and thoroughly investigated. And it was more or less expected. What we all want to find is something unexpected. For this we will need a very large amount of data, maybe ten times as much as we have so far.

For the rest of 2012 the LHC will continue the present run, hoping to get another 5/fb of data. All of 2013 and maybe the first half of 2014 will be the "long shutdown" in which repairs are done to enable a boost in energy from the present 4 TeV per beam to 6.5 TeV per beam.

Further down the road (2017 - 2020?) modifications to increase the luminosity, hopefully by as much as a factor of 10.

 

[Lord Crc]

Also there's LHCb and ALICE, which weren't looking for the Higgs in the first place AFAIK. LHCb may find some interesting results by the end of this year, hinting at non-SM physics from what I understand.

 

[ZapperZ]

Now that the Higgs boson has been discovered, I am certain more runs will be made to confirm its existence and to increase the reliability of its ev measurement. When that is done, what will the LHC be used for next? Having done its job, will it be decommissioned?

This is a bit silly. Even without being aware of all the physics that the LHC can do/discover, one only has to look back at the history of the Tevatron since its first discovery of the Top quark, which was many, MANY, years ago.

Please note that no country, no agency, and NO ONE will fund a $10 billion scientific facility that has only ONE major function and purpose! That would be utterly insane even for someone like me who advocates science funding!

Zz.

 

[mfb]

Also there's LHCb and ALICE, which weren't looking for the Higgs in the first place AFAIK.

There is a small Higgs subgroup at LHCb, but it does not contribute to the "mainstream" Higgs search done by ATLAS and CMS.
Anyway, all experiments have a broad range of analyses. Higgs is just the most popular one.

In addition to your link, I would like to add delta ACP, which is still puzzling, too.

 

[lpetrich]

Searches for supersymmetry-related particles.

In addition to the supersymmetry partners of Standard-Model particles, one gets more Higgs particles than are in the Standard Model. In the Minimal Supersymmetric Standard Model (MSSM), one gets both signs of a charged Higgs and three neutral Higgses, with one of them being approximately the Standard-Model Higgs. If the others are much more massive, then their masses will be very close to each other, and it may be difficult to distinguish them.

The LHC detector teams will likely present their latest results on SUSY-related particles at ICHEP, unless they've had to spend all their time on the Higgs particle.

 

[RJ Emery]

... For the rest of 2012 the LHC will continue the present run, hoping to get another 5/fb of data. All of 2013 and maybe the first half of 2014 will be the "long shutdown" in which repairs are done to enable a boost in energy from the present 4 TeV per beam to 6.5 TeV per beam. ...

That's very interesting. Thanks for sharing the grand plan. When the data runs begin at 6.5 TeV, we may get to see a whole new menagerie of particles. That would be most exciting.

Announcing the discovery of the Higgs boson was something of a let down. It was more or less expected. What would have been a surprise was no detection at all.

 

[lpetrich]

I didn't find it a letdown. I was happy to see that question get resolved.

 

[mikeph]

that means 13 TeV collisions? Can someone explain why the energy must be in the tera- range to observe a particle with mass ~100 GeV? Is it just a question of higher probabilities if you give more energy?

 

[mfb]

Yes, it is a question of probability. While it can happen that most of the energy of a proton is contained in a single quark or gluon ("parton"), it is very unlikely. You need a certain fraction of the whole energy to produce a Higgs boson. At the Tevatron (~2.3 TeV), this was something like ~5%, at the LHC it is a bit more than 1%. The production rate depends crucially on this fraction.

 

[lpetrich]

The LHC gives a top-quark mass value as good as the Tevatron's: ICHEP2012 (04-11 July 2012) - Tevatron and LHC top mass combinations The combined relative precision is 0.54%.

So let's see how the LHC might do on the Higgs particle's decay width. I've found CrossSections < LHCPhysics < TWiki, and I estimate a decay width of 0.003 GeV from the third graph in Figure 2.

To see how well one might be able to do, I consulted the Particle Data Group. For particles with masses close to the putative Higgs particle's mass, I find

Z mass: 91.1876(21) GeV, Z width: 2.4852(23) GeV
W mass: 80.385(15) GeV, W width: 2.085(42) GeV
Top-quark mass: 173.5 +- 0.6 +- 0.8 GeV, top-quark width: 2.0 +0.7-0.6 GeV

So I doubt that the Higgs particle's decay width will ever be measured at the LHC.

 

[mfb]

I agree that it is probably impossible to observe the decay width - it is possible to give upper limits (observed width) and lower limits (no observed decay length), but I would expect that the lower limit stays some orders of magnitude below the expected width.

Edit 2015: The experiments found an indirect way. The Higgs boson can be produced "off-shell" (with a mass significantly above 125 GeV). While this is a rare process, it can be studied, and the amount of events depends on the Higgs width. CMS and ATLAS were able to set upper limits lower than 10 times the predicted width, with more data they are probably able to get an actual width estimate. This is not completely model-independent, however.

 

[tom.stoer]

How will LHC identify SUSY particles? Missing invariant mass due to lightest and stable SUSY particle? I guess it's even harder than for the Higgs due to background. Is it possible to identify specific SUSY particles and to narrow down the possibilities for a specific SUSY model? Or will it be only something like "there is something new?" What are the allowed mass ranges for (e.g.) MSSM theoretically and experimentally - I mean, which energy range has already been excluded by the LHC?

 

[mfb]

Some SUSY particles should produce a whole decay chain of particles, until the lightest SUSY particle leaves the detector undetected. These decay chains could be observed. If they find something SUSY-related, they should be able to determine masses and other properties of the particles, this would allow to determine which SUSY model is realized, and to measure its parameters.

The excluded range depends on the model, as far as I know many exclusion limits are in the range of 1-3 TeV.