Particle Physics: Higgs Hunt etc. - Page 4

On December 13 2011 21:00 radiatoren wrote:
Sorry for necroing, but today should be an important day in getting closer to an answer of if the Higgs-boson exist or doesn't.



source

it was released yesterday. There is about 1 hour till the public seminar!

Watch it live here!

On December 13 2011 21:00 radiatoren wrote:
Sorry for necroing, but today should be an important day in getting closer to an answer of if the Higgs-boson exist or doesn't.



source

it was released yesterday. There is about 1 hour till the public seminar!

Watch it live here!

On December 13 2011 22:36 opisska wrote:
OMG they are so desperate. 1.5 sigma excess? WHAT? Wasn't that CERN who pressed that anything under 5 sigma should be neglected? (and even then, it does not have to mean anything, pentaquarks were once observed with a qutote 7 sigma confidence. Does anyone today believe in pentaquarks? No.) So far this seminar looks more overhyped than Stephano!

edit: OK, the combined result is slightly better but still. This really should not be hyped liked this.

On December 13 2011 22:49 Cascade wrote:
Pretty strong signal for a SM Higgs at 126 GeV.
Like a bit above 95% certaintly depending on how you look at it as I understand. Global 2.4 sigma significance.

*Cautiously optimistic*
edit: got wrong percentage, so many numbers in the presentation..

On December 13 2011 22:59 opisska wrote:


This is anything but a "pretty strong signal". In any other enviroment, the speaker would be laughed at after the kind of presentation we have just seen from the ATLAS spokesperson. If I came to my boss with an intention to show somethink like this on a public seminar, I would probalby be fired

On December 13 2011 22:36 opisska wrote:
OMG they are so desperate. 1.5 sigma excess? WHAT? Wasn't that CERN who pressed that anything under 5 sigma should be neglected? (and even then, it does not have to mean anything, pentaquarks were once observed with a qutote 7 sigma confidence. Does anyone today believe in pentaquarks? No.) So far this seminar looks more overhyped than Stephano!

edit: OK, the combined result is slightly better but still. This really should not be hyped liked this.

On December 13 2011 23:08 Rannasha wrote:


They're not that hyped. It's mostly the media that's hyping it up. CERN is just doing an end-of-year seminar with an update on the results. Yeah, there are good indications of a Higgs boson at 126 GeV, but it's hardly conclusive. This is the first year where there's a real body of data from LHC to actually analyze. At the end of last year, the amount of data available was many times less as the engineers were still working on improving the collision rate in the detectors. So in that sense it's the first glimpse into the results. That's what makes it an interesting seminar.

On December 14 2011 01:24 Mortal wrote:
And CERN dodges again. ._.

Scientists from the US Tevatron accelerator say they have spotted possible hints of the Higgs boson at a mass similar to that seen at the LHC.

The findings add weight to the idea that the Higgs - purported to give all other particles their mass - exists near a mass of 125 gigaelectronvolts.

However, the new data are not themselves sufficiently statistically assured to rate the find a "discovery".

The results were presented at the Moriond physics conference in Italy.

The Tevatron, based at the US national laboratory Fermilab, was for two decades the world's premier particle accelerator, but was shut down in 2011 after negotiations to extend funding failed.
Continue reading the main story
Statistics of a 'discovery'
Quarter

Particle physics has an accepted definition for a "discovery": a five-sigma level of certainty
The number of standard deviations, or sigmas, is a measure of how unlikely it is that an experimental result is simply down to chance rather than a real effect
Similarly, tossing a coin and getting a number of heads in a row may just be chance, rather than a sign of a "loaded" coin
The "three sigma" level represents about the same likelihood as tossing more than eight heads in a row
Five sigma, on the other hand, would correspond to tossing more than 20 in a row
With independent confirmation by other experiments, five-sigma findings become accepted discoveries

However, like all particle-smashers, the Tevatron created a tremendous amount of data that remained to be analysed.

The latest data hint at the existence of a particle between 115 and 135 gigaelectronvolts (GeV; this is between about 120 and 140 times as heavy as the protons found in every atom) with a certainty of about 2.2 sigma.

That means that there is about a one in 36 chance that the anomaly they see is the result of happenstance - far less assured than the "five sigma" threshold that physicists use to demarcate a formal discovery.

However, what makes the find more compelling is that the Large Hadron Collider has found a suggestive "bump" in its data at about the same mass, despite being a radically different experiment.

The LHC collides protons together, while the Tevatron used protons and their antimatter counterpart, antiprotons.

Both experiments hunt for the Higgs by looking at what those high-energy particles decay into.

At the Tevatron, the data are from the production of bottom quarks and their counterparts bottom antiquarks, whereas at the LHC the primary search is for the production of the light particles known as photons.

"It's a different accelerator, different detectors and a different decay channel," said Rob Roser, spokesman for CDF, one of the two main Tevatron detectors.
Continue reading the main story
What is an electronvolt?
Particle interaction simulation (SPL)

Charged particles tend to speed up in an electric field, defined as an electric potential - or voltage - spread over a distance
One electronvolt (eV) is the energy gained by a single electron as it accelerates through a potential of one volt
It is a convenient unit of measure for particle accelerators, which speed particles up through much higher electric potentials
But because of the equivalence of mass and energy laid out in E=MC2, physicists also speak of the mass of particles in electronvolts

"It adds to the picture, and it's starting to make a compelling case," he told BBC News. "But we can't make quite as bold a statement as we would like.

"I just wish either one of us just had more data right now. It's frustrating."

The two main detectors at the LHC, CMS and Atlas, also presented results at the meeting on Wednesday, but the experiments have precious little further data relative to those presented late last year.

That will radically change later this year as the facility will produce three times the amount of data this year as in 2011.

However, recent analysis of Atlas data has "excluded" the mass range up to 122.5 GeV. The Tevatron data, meanwhile, exclude its presence at the heavier masses of 147-179 GeV, also completely consistent with what the LHC has found.

As has been said before, if it indeed exists, there are few places left for the Higgs boson to hide.

Tony Weidberg, a University of Oxford physicist who works at the LHC's Atlas detector, said that the Tevatron results were consistent with the idea of a comparatively "light" Higgs boson.

"It's interesting because it's another little hint," Dr Weidberg told BBC News. "It makes it a little bit more likely that we're going to end the year with a discovery rather than an exclusion.

"The proof of the pudding will be in the LHC data that we'll get this year; by the end of the year we'll have moved away from hints to either discovery or exclusion - and either of those results is exciting to me."