# Largest particle accelerator in existence

1. Mar 9, 2009

### ONON

I know not far in the past that that largest particle accelerator yet created was set to be activated. Can anyone please give me any information concerning whether or not it was activated and/or the consequences, if any, of what was discovered? Even the name of this contraption and where it is located would be appreciated information.

2. Mar 9, 2009

### Nyme

You are propably looking for the Large Hadron Collider, or LHC. See the wikipedia article
http://en.wikipedia.org/wiki/LHC

They activated it on 10 September 2008, but only for testing. No particle collisions at full power took place. An accident, involving a magnet quench and loss of coolant, happened on 19 September, and thus the collider is now under repair. It will be started up again in late September 2009, if there are no additional delays.

Many scientists say that LHC will be able to find the Higgs boson, explaining the mass of particles of the standard model. The facility's startup was also controversial, because some believed the collider could cause major problems like the forming of micro black holes. However, these claims do not have a scientific base, and thus most of the particle physics community finds the collider safe to use.

The discovery of Higgs boson will be a major event, and if it is not detected, the standard model will face some serious problems.

3. Mar 9, 2009

### humanino

This is quite naive.

4. Mar 9, 2009

### hamster143

Note that the launch of LHC has already been delayed multiple times. The original launch target was 2005. Then 2007. Then it was "launched" in 2008 just to be shut down for repairs for another year, less than two weeks after launch. It is a very complex system and it has all sorts of kinks that haven't been worked out. Even if it launches, there's no guarantee that it will work smoothly and continuously.

At the same time, the second largest particle accelerator in existence (Tevatron) has been smashing protons and pumping data pretty much 24/7.

In other words, it is getting increasingly likely that existence of Higgs will be confirmed by Tevatron before LHC is even fully operational.

That's assuming that Tevatron is not shut down due to budget cuts.

5. Mar 9, 2009

### tiny-tim

shhh …

this is the Large Hamster Collider

it's basically a huge exercise wheel

it was closed down by animal welfare inspectors … but they don't want us to know that

6. Mar 10, 2009

### Bob S

LHC (CERN near Geneva), which will be about 8 TeV (trillion electron volts) with two counter-rotating beams of protons, broke on Sept. 19 after several days of commissioning. They are hoping to turn it on again next September. The Fermilab Tevatron (near Chicago) is running now with two counter-rotating beams, one protons, and the other antiprotons, both about 980 GeV (0.98 TeV).

7. Mar 11, 2009

Staff Emeritus
Doubtful. There are huge regions of parameter space that the Tevatron doesn't cover. If the Higgs is there, you could run the Tevatron for a century and it wouldn't help.

8. Mar 11, 2009

### hamster143

If the Higgs is not there at all, you could run both Tevatron and LHC for a century and you won't find it. If it's there and it's a SM Higgs, it's already been excluded by Tevatron around 170 GeV as of last summer. Fermilab's experts say that, even in the worst-case scenario, their chances to discover a SM Higgs are currently 50-50. That is assuming that LHC will go online and work as expected, which we all know it won't.

If it's something less conventional though, then LHC will have its chance.

9. Mar 11, 2009

### mgb_phys

Weren't the magnets that failed built by Fermilab ?

10. Mar 11, 2009

### hamster143

I'm not sure.

First of all, magnets themselves did not fail. What happened was that an electrical circuit between two magnets overloaded and triggered a chain of events that resulted in an explosion that damaged the magnets.

Some magnets were built by Fermilab, some were built by KEK. I don't know who built the offending circuitry. My guess is that it was built on site by CERN personnel.

11. Mar 11, 2009

### humanino

Why would that be relevant anyway ?

12. Mar 11, 2009

### mgb_phys

Only in the sense that Fermilab are the competition to find the Higgs - twirls moustache and laughs manically like a comic book villain.

13. Mar 11, 2009

### mgb_phys

Only in the sense that Fermilab are the competition to find the Higgs - twirls moustache and laughs manically like a comic book villain.

ps. Yes - the earlier failure when they turned them on and the field strength pulled them out of their mounts was a design problem with the Fermilab magnets, the quench was a bad wiring joint

14. Mar 11, 2009

### humanino

Although it is definitely funny, it also a bit simplistic. The HEP remembers who builds magnets. Oxford instrument, for instance, is no longer considered such a reliable provider.

15. Mar 12, 2009

Staff Emeritus
Which experts? I am shocked that they would say this.

The Higgs can be anywhere between 114 GeV and about 1000 GeV. With 4 pb-1, the Tevatron has excluded (at 95% CL) just over 1% of this region. According to the http://www-d0.fnal.gov/Run2Physics/HSS_Sum_Aug03.jpg" [Broken], it takes about six times as much data for a discovery than a 95% CL exclusion.

If CDF and D0 are very, very lucky, they will double their data sets. An increase of 50% is a conservative expectation, and reality will probably lie somewhere in between. A factor of six isn't being proposed by anyone, and even that would only open up 1% of the possible search space.

To say that the odds are 50-50 that they will find the Higgs is simply not supported by the information we have now.

Last edited by a moderator: May 4, 2017
16. Mar 13, 2009

Staff Emeritus
Just to add one more point, the present Tevatron exclusion limits are better than expectations (i.e. there was a fortunate statistical fluctuation). So this factor of six is probably closer to seven or eight.

17. Mar 13, 2009

### hamster143

Dmitri Denisov of Fermilab was quoted as saying the following at the recent AAAS annual meeting in Chicago:

"...I think we have the next two years to find it, based on the start date Lyn Evans has told us. And by that time we expect to say something very strong. The probability of our discovering the Higgs is very good - 90% if it is in the high mass range. And the chances are even higher - 96% - if its mass is around 170GeV (giga-electron volts). In that case we would be talking about seeing hints of the Higgs by this summer."

By the way, fresh off the presses:

http://www.fnal.gov/pub/presspass/press_releases/Higgs-mass-constraints-20090313.html

They have excluded SM Higgs between 160 and 170 GeV at 95% CL. SM Higgs can't be much heavier than 185 GeV because of electroweak constraints.

Recall that we need 3 to 5 years of LHC full time at project luminosity to discover Higgs.

Last edited by a moderator: May 4, 2017
18. Mar 13, 2009

### Bob S

The failure at the LHC on September 19 was in a splice in the superconducting return cable, not associated with any magnet. They will try to accelerate protons next September. Up until then the Tevatron will still hold the energy record (about 980 GeV per beam).

19. Mar 15, 2009

Staff Emeritus
Of course it can. Those constraints - or rather, their numerical value - assume that there is a desert between the electroweak scale and the GUT scale. In particular, it assumes that nothing stabilizes the Higgs mass against radiative corrections and that the mass remains low purely by accident. That's a model. Maybe a correct model, but it's still a model.

But that is under the assumption that the Higgs could be anywhere. Ruling out (or making a discovery) in the region accessible to the Tevatron takes less.

As I pointed out, to discover the Higgs, assuming it is lying just past the excluded region (the most favorable place for the Tevatron) will take 6-8 times as much data as they have now: around 25 fb-1. The most optimistic projections are 40% of that.

20. Mar 15, 2009

### hamster143

By the end of 2010, Tevatron should have enough data to rule out the entire 114-185 GeV range at 95% CL (if Higgs is not there) or to show evidence of Higgs at 3 sigma if it's fairly heavy, say, 150 GeV. If it keeps going beyond the end of 2010, and with some upgrades, 5 sigma discovery is possible.

According to some papers I read, LHC requires 2 $$fb^{-1}$$ to exclude Higgs from 114 GeV to 1 TeV and 5-10 $$fb^{-1}$$ for a discovery. (Although the mass range at which a 5 $$fb^{-1}$$ discovery is possible will probably be excluded by the Tevatron before LHC is even operational.) I can't find any luminosity ramp-up projections on LHC web site, but I recall vaguely that they intend to run at low energies and/or luminosities for the first year or so. How long will it take for LHC to collect 10 $$fb^{-1}$$ of data, if it's activated as planned in September 2009 and there are no further delays?

How long