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Collider hopes for a 'super' restart
Topic Started: 16 Feb 2015, 12:02 AM (41 Views)
skibboy
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15 February 2015

Collider hopes for a 'super' restart

By Jonathan Amos
BBC Science Correspondent, San Jose

A senior researcher at the Large Hadron Collider says a new particle could be detected this year that is even more exciting than the Higgs boson.

The accelerator is due to come back online in March after an upgrade that has given it a big boost in energy.

This could force the first so-called supersymmetric particle to appear in the machine, with the most likely candidate being the gluino.

Its detection would give scientists direct pointers to "dark matter".

And that would be a big opening into some of the remaining mysteries of the universe.

"It could be as early as this year. Summer may be a bit hard but late summer maybe, if we're really lucky," said Prof Beate Heinemann, who is a spokeswoman for the Atlas experiment, one of the big particle detectors at the LHC.

"We hope that we're just now at this threshold that we're finding another world, like antimatter for instance. We found antimatter in the beginning of the last century. Maybe we'll find now supersymmetric matter."

The University of California at Berkeley researcher made her comments at the annual meeting of the American Association for the Advancement of Science.

In the debris

Supersymmetry is an addition to the Standard Model, which describes nature’s fundamental particles and their interactions.

Susy, as it is sometimes known, fills some gaps in the model and provides a basis to unify nature's forces.

It predicts each of the particles to have more massive partners.

So the particle that carries light – the photon – would have a partner called the photino.

The quark, the building block of an atom’s protons and neutrons, would have a partner called the squark.

But when the LHC was colliding matter at its pre-upgrade energies, no sign of these superparticles was seen in the debris, which led to some consternation among theorists.

Now, with the accelerator about to reopen in the coming weeks, there is high hope the first evidence of Susy can be found.

The machine is going to double the collision energy, taking it into a domain where those theorists say the gluino really ought to emerge in sufficient numbers to be noticed.

The gluino is the superpartner of the gluon, which "glues" the quarks together inside protons and neutrons.

The LHC’s detectors would not see it directly. What they would track is its decay, which scientists would then have to reconstruct.

But importantly, those decay products should include the lightest and most stable superparticle, known as the neutralino – the particle that researchers have proposed is what makes up dark matter, the missing mass in the cosmos that gravitationally binds galaxies together on the sky but which cannot be seen directly with telescopes.

"This would rock the world,” said Prof Heinemann. "For me, it’s more exciting than the Higgs."

'The other side'

So, not only would supersymmetry proponents be elated because they would have their first superparticle, but science in general would have a firm foot on the road to understanding dark matter.

Dr Michael Williams, from the Massachusetts Institute of Technology, said: "We sometimes talk about the dark matter particle, but it’s perfectly plausible that dark matter is just as interesting as [normal] matter, [which] has a lot of particles that we know about.

"There might be just as many dark matter particles, or even more.

"Finding any particle that could be a dark matter candidate is nice because we could start to understand how it affects the galaxy and the evolution of the universe, but it also opens the door to whatever is on the other side, which we have no idea what is there."

Particle physicists have three major conferences in August and September, one of which is the main gathering of the supersymmetry community.

All these meetings are bound to draw huge interest.

But Prof Jay Hauser, who works on the CMS detector at the LHC, added a little caution on timings.

"Even if we did see something, remember it might be complicated enough that it takes us a while to explain it," he told reporters.

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skibboy
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LHC restart: Short circuit slows preparations

By Jonathan Webb
Science reporter, BBC News

Posted Image
Teams on the collider's big experiments like Atlas (pictured) are using the time to make extra tweaks

The rebooted Large Hadron Collider is facing a delay of days or even weeks, after a short circuit was detected in one of its powerful electromagnets.

Following a two-year break, the LHC is getting ready to smash protons together once again - at new, higher energies.

Before the collisions begin, proton beams must travel safely around its 27km circumference in both directions.

Those full laps were expected to begin this week, but that plan will now be revised.

Cern, the European nuclear research organisation which runs the LHC, said the "intermittent short circuit" was discovered on Saturday.

It affected one of the magnets that will eventually send protons racing around the LHC - specifically a magnet in "sector 3-4".

Nearby, sector 4-5 of the machine - the area which triggered a more eventful false start when the LHC first commenced operations in 2008 - had already been lagging behind the other seven in the gradual "training" process that the magnets must go through.

But the short circuit is a more serious problem, in terms of the delay it could impose on the restart.

Cern said it was "a well understood issue", but because the magnets are supercooled to temperatures approaching absolute zero (-273C), the repair could be time-consuming.

If it requires the faulty magnet to be warmed up and re-cooled, the delay may stretch from a few days to "several weeks", the organisation announced on Tuesday.

"Any cryogenic machine is a time amplifier, so what would have taken hours in a warm machine could end up taking us weeks," said Cern's director for accelerators, Frederick Bordry.

'No time wasted'

Scientists at Cern emphasised that the restart timetable was always flexible and that Run Two of the world's largest machine is still on target.

Rolf Heuer, the organisation's director general, said: "All the signs are good for a great Run Two. In the grand scheme of things, a few weeks' delay in humankind's quest to understand our Universe is little more than the blink of an eye."

When it eventually comes to the science, there are many big items on the LHC team's wish list for Run Two - including detecting dark matter, making further observations of the Higgs boson, and ultimately, the search for a "new physics" outside of the Standard Model.

Posted Image
Two parallel pipes carry the beams in a 27km circle at fractionally less than the speed of light

Particle physicist Jonathan Butterworth, from University College London, works on Atlas - one of four major experiments spaced around the LHC's huge circle.

He told BBC News that the experiment teams were ready to go, and waiting to hear more from the scientists and engineers who manage the beams.

"It's a very separate organisation, basically," Prof Butterworth said. "The accelerator guys are all within Cern - and we're sort of ready and waiting. We do what they tell us at this stage."

But he added that the time will not be wasted.

The experiment teams can make extra improvements to their own systems while they wait - particularly to the computer code used to control the detectors and analyse data.

"Every day, we have people frantically coding stuff up to be even more ready," he said.

Muon practice

Dr Andre David, who works for Cern on the CMS experiment, also said the additional time would be valuable.

He and his colleagues are "enjoying" the chance to make sub-millimetre adjustments to some of the detectors inside CMS.

"We are profiting from this time to collect more cosmic ray data, which is crucial to align the very tiny inner detectors," Dr David told the BBC.

Cosmic rays are particles from outer space that bombard the Earth, but few of them penetrate the atmosphere.

High-energy muons, however, interact so infrequently with matter that some of them make it right into the LHC tunnels, 30 storeys underground.

Posted Image
The proton beams are steered by magnets which must be "trained" with gradually increasing current

"As they go through the experiment, we can detect them, just like any other muon produced in a collision," Dr David said. "These muons are extremely valuable, because we can figure out where the signals are that they leave behind - without any beams."

By making miniscule adjustments to the alignment of their detectors, the researchers can "smooth out" the way they will identify and measure these particles when they fall out as debris from proton collisions.

Those collisions were originally - tentatively - timetabled to kick off in May, but the short circuit now makes that estimate seem even less certain.

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skibboy
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LHC restart sees first collisions

By Jonathan Webb
Science reporter, BBC News
5 May 2015

Posted Image
Experiments like CMS, pictured during the shutdown, are now sealed up and colliding protons

The Large Hadron Collider has smashed protons together for the first time since early 2013.

The low-energy collisions, part of preparations for the next round of experiments, began on Tuesday morning.

Proton beams circled the LHC and collided at an energy of 450 gigaelectronvolts (GeV) per beam.

The aim for this second run of the LHC, following its planned two-year shutdown for repairs and improvements, is to stage collisions at 7,000 GeV per beam.

A key milestone was reached on Easter Sunday when proton beams once again did full circuits of the LHC's 27km subterranean circle.

Now the two beams have been steered into each other - another important step in the gradual restart of the world's biggest particle accelerator.

'Shopping list' of checks

According to the current schedule, collisions will first take place at those new, historic energies in the week commencing June 1st.

Even those will only be used for calibration; "physics collisions" with usable results will start some time after that.

Posted Image
The Atlas experiment released this snapshot of tracks produced by fallout from one of the first collisions

Posted Image
A similar plot was released by the CMS experiment

Excitement is building for physicists working at Cern - the European nuclear research campus near Geneva, Switzerland, which houses the LHC.

______________________________________________________________________________________________________________________________________________________________________


What is an electronvolt?

Posted Image
The LHC's experiments create showers of particles

-Particle accelerators use strong electric fields to speed up tiny pieces of matter

-An electronvolt (eV) is the energy gained by one electron as it accelerates through a potential of one volt

-The LHC reaches particle energies measured in trillions of eV: teraelectronvolts (TeV)

-This is only the energy in the motion of a flying mosquito - per particle

-All together, the hundreds of trillions of particles in each LHC beam have the energy of a TGV high-speed train travelling at 150 km/h

______________________________________________________________________________________________________________________________________________________________________


"These are the first colliding beams in the machine for over two years, and it brings home that physics collisions are close," said Prof Tara Shears from the University of Liverpool, who works on LHCb - one of four big experiments, spaced around the LHC's ring, where the collisions occur.

She said these early collisions are very valuable, even though they are only happening at injection energy, which means the LHC itself isn't adding any acceleration to the protons.

They simply circulate and collide with the energy already delivered by the accelerators that feed protons into the main ring.

Instead of getting physics results, Prof Shears and her team use this early data to fine-tune their experiments.

"This time, we used the data to make sure subdetectors are time-aligned with each other," she told BBC News.

"We have a shopping list of checks to do; checking the trigger, our luminosity calculation, the performance of each part of our experiment, and we'll work through this with these collision runs."

Some of the experiment teams released images illustrating Tuesday's first collisions.

They show the various paths taken by debris from smashed-together protons, pieced together using data from some of the layers of detectors inside the experiments.

The LHC was the scene for the famous discovery of the Higgs boson in 2012, towards the end of its first run.

In its second tilt, researchers hope that the almost doubled energy levels will yield new insights beyond the Standard Model of particle physics.

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