The LEP Collider Will Be Closed Down

mukund writes "The Large Electron-Positron (LEP) collider will be dismantled soon, as this article on BBC News reports. The LEP is the world's largest particle collider and is built inside a 27km long tunnel. The collider has been used to confirm the existence of the Higgs particle unsuccessfully. A new project to build another larger collider is on the way. The article says, "According to commentators, whoever finds the Higgs first will probably win a Nobel Prize.""

Comments

Say that again

[billybob2001]

The collider has been used to confirm the existence of the Higgs particle unsuccessfully.

Is that like the Presidential election was used to confirm the new President unsuccessfully?

Higgs info

[mackga]

There was a great story on All Things Considered yesterday, I think, about this. The guy they interviewed explained what was going on and why very clearly. I'm not into this much, but understood the basic concepts pretty well. For those in the audience asking "What's a Higgs?", here's a link to a Scientific American Article about the Higgs Boson. I tried to get to NPR's site to see if they have a link to the story, but the site is pretty hosed right now. I wonder why :)

This is a 'good thing'! really!

[GoNINzo]

The shutdown of LEP is actually a good thing... With the shutdown of the LEP, the construction of the LHC be started on. This collider will allow energies in the TeV range, with is 10 times the LEP or Fermilab Tevatron. If they had delayed in the building of this, the Relativisitic Heavy Ion Collider (RHIC) might beat them to the higher energy ranges. Plus, you never know when funding might be cut, etc.

Let a lower powered accelerator attempt to find the Higgs, I STILL don't believe it will be discovered, because it's been stated over and over 'we just need a little more power to find the Higgs boson!'. The problem is that all of these vast teams are lead by one or two scientists, who desperately want the Nobel Prize. Hence, good science is sometimes ignored in favor of the limelight... I'm just glad 'good physics' prevailed this time around.

I had hoped to talk about this on BottomQuark but lost all my research midway through the discussion. whoops. `8r) I wonder if there is such a thing as an amateur partical physics person....

--
Gonzo Granzeau

Why the LEP shutdown.

[The Iconoclast]

The Large Electron Positron (LEP) Collider is being shutdown to make room for the LHC (Large Hadron Collider). The LEP smashed electrons and positrons together (hence the name). The LHC will smach protons and anti-protons together. Protons and anti-protons are a thousand times more massive than electrons and positrons. Therefore, since mass and energy are equivalent (E=mc**2), the LHC will be able to reach energies many orders of magnitude higher than the LEP. The LEP is being shutdown because the LHC will use the same tunnel at CERN in the Alps that the LEP used (as a cost saving measure).

Fermi's Tevatron, Higgs particle, sci note, data

[arete]

I'm working at Fermi in production of the RunII CDF detector (as an engineer, not a physicist) and from what I hear, taking LEP down means we are nearly assured of the Higgs before LHC comes up - unless it is truely impossible at Tevatron's size, which seems unlikely, currently. Things here seem to be going quite well, imo.

To give a (very) rough explanation of the Higgs: when you smash things together with very high energies, you get a huge explosion (huge, considering it was started by one proton and one antiproton) and all sorts of fragments are produced.

However, we have to measure these fragments using very odd means, because it is mostly impossible to directly measure most of these things... you can only measure the effects they have on the relatively normal stuff we can build a detector out of. (if you build it out of these things, the detector would vanish in much less than a second...) So the more "normal" fragments are relatively easier to measure, because they interact more with the more normal detector.

In recent high energy physics history there has been a string of these things, Higgs is the next.

Someone said they first saw sci notation in 93, and I'm amazed. I'd heard in Junior High earlier than that... or did you mean something else.

Btw, Fermi has a significant linux community. Also, (from a bad memory and this isn't my department but) they have to filter the incoming data in realtime, keeping only the most interesting 1/millionth of it - and that data alone is a couple CDs/second worth of data. Lots o' bandwidth there...

The Scoop from inside LEP

[tbo]

Here's an email that's been circulating through the physics department at my university. It does a pretty good job of explaining what's up with LEP, and why it would be nice to keep it going for just a little while longer. The short of it is that they think they've found Higgs, but need a bit more data to be sure.

Anyway, here's the email:
-------------------

Hi,

Since we've been getting a lot of enquiries about the reports of a Higgs
Boson 'discovered' at LEP, I thought I'd give you more info.

There are 4 experimental groups taking data at the LEP electron-positron
collider. On Friday Nov.3, the each of the 4 experimental groups
presented our analyses to the LEPC (LEP Experimental Committee) i.e. the
Research Board, at CERN. And one analysis combining the results of all 4
expts was also presented.

The LEP experiments were all scheduled to stop data taking on Nov.1, after
over 11 years of experimental data taking -- probing & testing of the
Standard Model to unprecedented precision. Stopping and dismantling LEP is
necessary before the installation of the LHC accelerator and detectors may
begin, as LHC uses the LEP tunnels. (LHC is the Large Hadron proton-proton
Collider, which has discovering the Higgs Boson as a centerpiece of its
physics program)

LEP reached the highest energies ever this year, with 208.2 GeV as the
highest energy reach possible, (limited by the number of RF cavities) but
the accelerator is so unstable at this energy that less than 4% of this
year's data was taken up there. The bulk of this year's data was in the
205-207 GeV range.

Every experiment sees "Higgs candidates". These are events which look like
e+ e- --> Higgs ZBoson, with each the Higgs and ZBoson subsequently
decaying. For 3 of the 4 of the expts, the "candidates" seen are
absolutely and entirely consistent with what's expected from known
Standard Model processes i.e. background. ( 2 Z's, 2 W's, and other
processes which can look very similar to ZH)

3 of the 4 LEP groups have completed analyses which result in upper limits
on Standard Model Higgs masses. 1 (ALEPH) reports a 115 GeV Higgs with a
significance equivalent to a 3.4 sigma excess over background
expectations. When all 4 expts combine our data, this diminishes to a 2.9
sigma effect for a 115 GeV SM Higgs boson.

Our UBC group is a part of the OPAL experiment, one of the four expts.
OPAL rules out a Standard Model Higgs boson at masses under 208GeV at 95%
confidence level. Our OPAL bottom line can be seen in a talk by Arnulf
Quadt of OPAL, at the LEPC presentations:
http://www.physics.ubc.ca/~janis/arnulf.ps If we are to interpret our
results in terms of a Higgs Boson at 115 GeV, we have a 1.3 sigma excess
over background processes at this mass. We have a 2.6 sigma effect at 107
GeV. You give us a mass, we can tell you if we see an excess above, or
depletion below the background expectations. (the 2.6sigma at 207 GeV is
the largest deviation from expected background at high energies)

The combined 4 experiments talk at LEPC by Peter Igo-Kemenes, incidently
also an OPAL collaborator, (emailed to you by Douglas) may be seen at
http://lephiggs.web.cern.ch/LEPHIGGS/talks/pik_l epc_nov3_2000.ps

You can see the ALEPH LEPC talk at:
http://alephwww.cern.ch/ALPUB/seminar/lepc_nov00 .pdf

Judge it for yourself. I'd say we are in an interesting situation and it
woudl be shame to stop the LEP program now with these interesting hints
from ALEPH. With another year of data taking at LEP (and hence a year
delay in the LHC) we would be able to confirm or refute the existence of a
115 GeV Higgs at a honking 5 sigma level... what we usually refere to as
the "discovery level" It would be very exciting if we could indisputably
discover the Higgs Boson. But I would say we do not have a Higgs Boson at
this time.

CERN has not issued any press releases on this matter (as of Saturday
evening). Only the LA Times has. Even NY Times has not.

Real Lowdown

[Anonymous Coward]

Hiya,

Not a usual poster on slashdot, but it seems that few/none of the other Higgs searchers at LEP are sticking their necks up. For the benefit of non-Higgs searchers in particle physics, and for those willing to wade through some details, here's a Higgs searcher's perspective on the story.

Unfortunately, the majority of the information presented on this has been to the public session of what is essentially an internal meeting of LEP. What the experiments (and the LEP Higgs group) have shown in their brief presentations are summaries of much more detailed work which is of course still ongoing (data taking only finished a few days ago).

The comments that I've seen in this forum from physicists are coming from what could be termed either the general community, or the competition. They reasonably point out that brief status reports of ongoing analyses have not convinced *them* that the Higgs is there, but unfortunately this was the structure of the forum in which the results were presented. Another interpretation is that we didn't properly anticipate confusion about issues that seemed obvious to the experts.

One common misinterpretation seems to be that LEP observes only 3-4 Higgs candidates, which is actually very false. This is just the number of events collected that really 'stood up' as extremely signal-like. In fact, hundreds of possible Higgs candidates were collected, and they are each given a rating on a "signal-like" scale. If you skim off the top few, you get four events, three from Aleph and one from L3. Up until very recently, Delphi also had one, but it dropped down on the signal scale after reanalysis.

As you drop down on the scale, to the point where you'd expect half of your events to be background and half to be signal, you expect 7 from background, and observe 14. The weight distribution agrees across the board with the signal distribution. These are divided among all four experiments and all search topologies. In fact, the sample was divided in several different ways for consistency checking purposes, and they all came out looking exactly like a Higgs signal. It gave us goosebumps to see the results of these tests.

If there's no signal, we've had a one in a thousand blip. There is a standard for discovery which requires that to be a bit less than one in a million. We are confident that, if it's real, we'd be able to reach that one in a million, and if it's not, that the effect would dry up. The whole point is that this is an exciting observation which we'd like to verify that is at the edge of our sensitivity. To do that properly would take six months of extra running, which all of the LEP experiments requested. The whole point is that it's not yet conclusive. The CERN management has been weighing questions of cost of running (in dollars and delay of future projects) vs chance that we did just get a freaky blip in the background, and has unfortunately decided not to take the risk. People will have the next 6-7 years to wonder if what we saw was real or not before it can be tested again.

At the moment, the most complete information is at the Physics Co-ordinator's Page.

A collection of all of the presentations at the public sessions of the LEPC meetings can be found here.

Cheers,
Pete McNamara