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25 years of Large Hadron Collider experimental programme

Thu, 12/14/2017 - 16:14

This week CERN marks 25 years since the meeting at Evian, where the first ideas for the LHC experimental programme were debuted (Image: Maximilien Brice/CERN)

On Friday 15 December 2017, CERN is celebrating the 25th anniversary of the Large Hadron Collider (LHC) experimental programme. The occasion will be marked with a special scientific symposium looking at the LHC’s history, the physics landscape into which the LHC experiments were born, and the challenging path that led to the very successful LHC programme we know today.

The anniversary is linked to a meeting that took place in 1992, in Evian, entitled Towards the LHC Experimental Programme, marking a crucial milestone in the design and development of the LHC experiments.

The symposium, which will be live webcast, will also include a presentation of the latest results from the four large experiments, ATLAS, CMS, LHCb and ALICE.

Join the live webcast from 11:00-16:00 CET.

At the LHC, tomorrow is already here

Tue, 12/05/2017 - 11:24

The CERN Control Centre in 2017, from where all the Laboratory's accelerators and technical infrastructure are controlled. The accelerator complex and the LHC produced a record amount of data in 2017. (Image: Julien Ordan/CERN)

On Monday, 4 December at 4.00 a.m., the accelerator operators hit the stop button on the accelerator complex and the Large Hadron Collider for their usual winter break. But while the machines are hibernating, there’s no rest for the humans, as CERN teams will be busy with all the maintenance and upgrade work required before the machines are restarted in the spring. 

The LHC has ended the year with yet another luminosity record, having produced 50 inverse femtobarns of data, i.e. 5 million billion collisions, in 2017. But the accelerator hasn’t just produced lots of data for the physics programmes. 

Before the technical stop, a number of new techniques for increasing the luminosity of the machine were tested. These techniques are mostly being developed for the LHC’s successor, the High-Luminosity LHC. With a planned start-up date of 2026, the High-Luminosity LHC will produce five to ten times as many collisions as the current LHC. To do this, it will be kitted out with new equipment and will use a new optics scheme, based on ATS (Achromatic Telescopic Squeezing), a configuration that was tested this year at the LHC. 

Handling beams of particles is a bit like handling beams of light. In an accelerator, dipole magnets act like mirrors, guiding the beams around the bends. Quadrupole magnets act alternately like concave or convex lenses, keeping the beams in line transversally, but mainly focusing them as much as possible at the interaction points of the experiments. Corrector magnets (hexapoles) correct chromatic aberrations (a bit like corrective lenses for astigmatism). Configuring the optics of an accelerator is all about combining the strengths of these different magnets.

One particularly efficient approach to increasing luminosity, and therefore the number of collisions, is to reduce the size of the beam at the interaction points, or in other words to compress the bunches of particles as much as possible. In the High-Luminosity LHC, more powerful quadrupole magnets with larger apertures, installed either side of the experiments, will focus the bunches before collision. However, for these magnets to be as effective as possible, the beam must first be considerably expanded: a bit like a stretching a spring as much as possible so that it retracts as much as possible. And this is where the new configuration comes in. Instead of just using the quadrupole magnets either side of the collision points, the ATS system also makes use of magnets situated further away from the experiments in the machine, transforming seven kilometres of the accelerator into a giant focusing system. 

Graph showing the integrated luminosity over the various runs of the LHC. In 2017, the LHC produced 50 inverse femtobarns of data, the equivalent of 5 million billion collisions. (Image: CERN)

These techniques have been used in part this year at the LHC and will be used even more during future runs. “The heart of the High-Luminosity LHC is already beating in the LHC,” explains Stéphane Fartoukh, the physicist who came up with the new concept.  “The latest tests, carried out last week, have once again proved the reliability of the scheme and demonstrated other potential applications, sometimes beyond our initial expectations.

For further information:

Record luminosity: well done LHC

Mon, 11/13/2017 - 14:56

View of the LHC tunnel. (Image : Maximilien Brice/CERN)

It’s the end of the road for the protons this year after a magnificent performance from the Large Hadron Collider (LHC). On Friday, the final beams of the 2017 proton run circulated in the LHC. The run ended, as it does every year, with a round up of the luminosity performance, the indicator by which the effectiveness of a collider is measured and on which the operators keep a constant eye.

The LHC has far exceeded its target for 2017. It has provided its two major experiments, ATLAS and CMS, with 50 inverse femtobarns of data, i.e. 5 billion million collisions. The inverse femtobarn (fb-1) is the unit used to measure integrated luminosity, or the cumulative number of potential collisions over a given period.

This result is all the more remarkable because the machine experts had to overcome a serious setback. A vacuum problem in the beam pipe of a magnet cell limited the number of bunches that could circulate in the machine. Several teams were brought in to find a solution. Notably, the arrangement of the bunches in the beams was changed. After a few weeks, luminosity started to increase again.

At the same time, over the course of the year, the operators have optimised the operating parameters. Using a new system put in place this year, they have notably reduced the size of the beams when they meet at the centre of the experiments. The more squeezed the beams, the more collisions occur each time they meet. Last year, the operators managed to obtain 40 collisions at each bunch crossing, with each bunch containing 100 billion particles. In 2017, up to 60 collisions were produced at each crossing.

Thanks to these improvements, the instantaneous luminosity record was smashed, reaching 2.06 x 1034cm-2s-1, or twice the nominal value. Instantaneous luminosity corresponds to the potential number of collisions per second.

The LHC will continue to operate for another two weeks for two special runs including a week for operation studies. The first special run will consist of carrying out proton collisions at 5.02 TeV (as opposed to the usual 13 TeV), the same energy as that planned for next year’s lead-ion runs. This will enable physicists to collect data with protons, which they will then be able to compare with the lead-ion data.

The second special run, at very low luminosity, will provide data for the TOTEM and ATLAS/ALFA experiments. These two experiments use detectors located on either side of two large LHC detectors: CMS in the case of TOTEM and ATLAS in the case of ATLAS/ALFA. They study interactions called elastic scattering, where two protons merely change direction slightly when they interact, rather than colliding. For these studies, the LHC makes the beams as wide as possible. What’s more, the energy will be limited to 450 GeV, i.e. the energy at which beams are injected from the accelerator complex into the LHC.

Finally, the operators will carry out a “machine development” campaign. Over a week, they will perform operating tests to improve the accelerator’s performance still further (it can never be too good) and begin to prepare the High-Luminosity LHC, which will take over from the LHC after 2025.

When these tests are over, the operators will stop the machine for the year-end technical shutdown. 

Graphs showing the integrated luminosity of the LHC in 2017. The unit is the inverse femtobarn. The green squares represent the achieved luminosity, while the blue line shows the planned luminosity. (Image: CERN)

Record luminosity: well done LHC

Mon, 11/13/2017 - 14:56

View of the LHC tunnel. (Image : Maximilien Brice/CERN)

It’s the end of the road for the protons this year after a magnificent performance from the Large Hadron Collider (LHC). On Friday, the final beams of the 2017 proton run circulated in the LHC. The run ended, as it does every year, with a round up of the luminosity performance, the indicator by which the effectiveness of a collider is measured and on which the operators keep a constant eye.

The LHC has far exceeded its target for 2017. It has provided its two major experiments, ATLAS and CMS, with 50 inverse femtobarns of data, i.e. 5 billion million million collisions. The inverse femtobarn (fb-1) is the unit used to measure integrated luminosity, or the cumulative number of potential collisions over a given period.

This result is all the more remarkable because the machine experts had to overcome a serious setback. A vacuum problem in the beam pipe of a magnet cell limited the number of bunches that could circulate in the machine. Several teams were brought in to find a solution. Notably, the arrangement of the bunches in the beams was changed. After a few weeks, luminosity started to increase again.

At the same time, over the course of the year, the operators have optimised the operating parameters. Using a new system put in place this year, they have notably reduced the size of the beams when they meet at the centre of the experiments. The more squeezed the beams, the more collisions occur each time they meet. Last year, the operators managed to obtain 40 collisions at each bunch crossing, with each bunch containing 100 billion particles. In 2017, up to 60 collisions were produced at each crossing.

Thanks to these improvements, the instantaneous luminosity record was smashed, reaching 2.06 x 1034cm-2s-1, or twice the nominal value. Instantaneous luminosity corresponds to the potential number of collisions per second.

The LHC will continue to operate for another two weeks for two special runs including a week for operation studies. The first special run will consist of carrying out proton collisions at 5.02 TeV (as opposed to the usual 13 TeV), the same energy as that planned for next year’s lead-ion runs. This will enable physicists to collect data with protons, which they will then be able to compare with the lead-ion data.

The second special run, at very low luminosity, will provide data for the TOTEM and ATLAS/ALFA experiments. These two experiments use detectors located on either side of two large LHC detectors: CMS in the case of TOTEM and ATLAS in the case of ATLAS/ALFA. They study interactions called elastic scattering, where two protons merely change direction slightly when they interact, rather than colliding. For these studies, the LHC makes the beams as wide as possible. What’s more, the energy will be limited to 450 GeV, i.e. the energy at which beams are injected from the accelerator complex into the LHC.

Finally, the operators will carry out a “machine development” campaign. Over a week, they will perform operating tests to improve the accelerator’s performance still further (it can never be too good) and begin to prepare the High-Luminosity LHC, which will take over from the LHC after 2025.

When these tests are over, the operators will stop the machine for the year-end technical shutdown. 

Graphs showing the integrated luminosity of the LHC in 2017. The unit is the inverse femtobarn. The green squares represent the achieved luminosity, while the blue line shows the planned luminosity. (Image: CERN)

LHC reaches 2017 targets ahead of schedule

Mon, 10/30/2017 - 16:59

Trillions of protons race around the LHC’s 27-km ring in opposite directions more than 11 000 times a second, travelling at 99.9999991% the speed of light. (Image: Max Brice and Julien Ordan/CERN)

Today, CERN Control Centre operators announced good news: the Large Hadron Collider (LHC) has successfully met its production target for 2017, delivering more than 45 inverse femtobarns* to the experiments.

This achievement was all the more impressive as it was ahead of schedule. The LHC still has 19 more days of proton collisions, continuing to provide physics data to the experiments. Yet, earlier this year, it seemed unlikely that this target would be achieved. An issue had developed with a small group of magnets, collectively known as 16L2, which was affecting machine performance. Then, in early September, thanks to effective and creative collaboration between various teams at CERN, several ways to deal with the technical issue were developed, enabling the LHC and its injector chain to reach top performances again. In addition, by the end of September, the 2017 production run had been shortened by bringing special runs planned for 2018 forward to 2017, putting yet more pressure on the operators to deliver in a shorter time frame. 

The LHC has outperformed its target for 2017, delivering more collisions than expected to LHC experiments.

Nonetheless, with the target met, as well as another recent milestone achieved when twice the design luminosity was reached, the LHC has once again shown its excellence. That being said, physicists are already looking ahead to upgrades decades in the future and considering the physics potential that they will bring. Today, scientists are gathering at CERN to begin a three-day workshop to review, extend and further refine our understanding of the physics potential of the High-Luminosity LHC – the planned upgrade of the LHC – and even beyond.

In the more immediate future, once the main proton physics run end this year, the LHC will have 15 days of special runs plus machine development before its winter shutdown begins on 11 December. At that point, the “year-end technical stop” (YETS) will be used to help consolidate and improve the machine, ahead of its restart in spring 2018.

 

* The inverse femtobarn (fb-1) is the unit of measurement for integrated luminosity, indicating the cumulative number of potential collisions. One inverse femtobarn corresponds to around 100 million million collisions.

LHC reaches 2017 targets ahead of schedule

Mon, 10/30/2017 - 16:59

Trillions of protons race around the LHC’s 27km ring in opposite directions more than 11,000 times a second, travelling at 99.9999991 per cent the speed of light. (Image: Max Brice and Julien Ordan/CERN)

Today, CERN Control Centre operators announced good news, the Large Hadron Collider (LHC) has successfully met its production target for 2017, delivering more than 45 inverse femtobarns* to the experiments.

This achievement was all the more impressive as it was ahead of schedule. The LHC still has 19 more days of proton collisions, continuing to provide physics data to the experiments. Yet earlier this year it looked unlikely that this target would be achieved. An issue had developed with a small group of magnets known as 16L2 that was affecting machine performance. Then, early September, thanks to effective and creative collaboration between different teams around CERN, alternative ways to deal with the technical issue were developed that made the LHC and its injector chain reach top performances again. In addition, by the end of September, the 2017 production run was shortened by advancing special runs planned for 2018 to 2017, putting yet more pressure on the operators to deliver in a smaller timeframe. 

The LHC has outperformed its target for 2017, delivering more collisions than expected to LHC experiments.

None-the-less with the target met, as well as another recent milestone of reaching twice the design luminosity, the LHC has once again shown its excellence. That being said, physicists are already looking to upgrades tens of years in the future and the physics potential that they bring. Today at CERN, scientists are gathering to begin a three-day workshop to review, extend and further refine understanding of the physics potential of the High Luminosity LHC – the planned upgrade of the LHC – and even beyond.

In the more immediate future, once the main proton physics run end this year, the LHC will have 15 days of special runs plus machine development before its winter shutdown begins on 11 December. At that point, the “Year-end technical stop” (YETS) will be used to help consolidate and improve the machine, ahead of its restart in spring 2018.

 

* The inverse femtobarn (fb-1) is the unit of measurement for integrated luminosity, indicating the cumulative number of potential collisions. One inverse femtobarn corresponds to around 80 million million collisions.

For one day only LHC collides xenon beams

Thu, 10/12/2017 - 22:35

One of the xenon ion collisions recorded by the ALICE detector. (Image: ALICE/CERN)

Today, the LHC is getting a taste of something unusual. For eight hours, the Large Hadron Collider is accelerating and colliding xenon nuclei, allowing the large LHC experiments, ATLAS, ALICE, CMS and LHCb, to record xenon collisions for the first time.

Xenon is a noble gas, present in miniscule quantities in the atmosphere. Its atoms consist of 54 protons and between 70 and 80 neutrons, depending on the isotope. The xenon collisions in the LHC (of atoms with 54 protons and 75 neutrons) are therefore similar to the heavy-ion collisions that are regularly carried out at the LHC. Normally, lead nuclei, which have a much greater mass, are used. “But a run with xenon nuclei was planned for the NA61/SHINE fixed-target experiment at the SPS (Super Proton Synchrotron),” explains Reyes Alemany Fernandez, who is in charge of heavy-ion runs. “We are therefore taking the opportunity for a short run with xenon at the LHC.

It’s a unique opportunity both to explore the LHC’s capabilities with a new type of beam and to obtain new physics results,” says John Jowett, the physicist in charge of heavy-ion beams at the LHC.

And who knows? Maybe this unprecedented run will lead to some surprising discoveries. “The experiments will conduct the same kind of analyses with xenon ions as they do with lead ions, but, because the xenon nuclei have less mass, the geometry of the collision is different,” explains Jamie Boyd, LHC programme coordinator, who is responsible for liaison between the LHC machine and experiment teams. Heavy-ion collisions allow physicists to study quark-gluon plasma, a state of matter that is thought to have briefly existed just after the Big Bang. In this extremely dense and hot primordial soup, quarks and gluons moved around freely, without being confined by the strong force of protons and neutrons, as they are in our Universe today.

Some of the teams who contributed to the xenon run, in the CERN control centre. (Image: Jules Ordan/CERN)

Switching from protons to xenon isn’t a piece of cake, however. A team has been preparing the accelerator complex for the xenon run since the start of the year. Atoms of the gas are accelerated and stripped of their 54 electrons in four successive accelerators before being launched into the LHC. “The number of bunches and the revolution frequency varies a lot between protons and xenon nuclei,” explains Reyes Alemany Fernandez. “One of the difficulties is adjusting and synchronising the accelerators’ radiofrequency systems.”

After the xenon run in the LHC lasting a few hours, xenon nuclei will continue to circulate in the accelerator complex, but only as far as the SPS. For eight weeks, the SPS will supply xenon ions to the NA61/SHINE experiment, which is also studying quark-gluon plasma, but whose analyses will complement those carried out by the LHC experiments. More specifically, NA61/SHINE is interested in the deconfinement point, a collision-energy threshold above which the creation of quark-gluon plasma would be possible. NA61/SHINE is thus systematically testing many collision energies using ions of different masses. After lead, beryllium and argon, it’s now xenon’s turn to take the stage.

A chart showing different types of stable nuclei, with their atomic number, i.e. the number of protons, Z, shown on the horizontal axis and the number of neutrons, N, shown on the vertical axis. The three types already accelerated in the LHC, i.e. protons (hydrogen), lead nuclei and xenon nuclei, are shown in red with their mass number, A (N + Z).

 

For one day only LHC collides xenon beams

Thu, 10/12/2017 - 22:35

One of the xenon ion collisions recorded by the ALICE detector. (Image: ALICE/CERN)

Today, the LHC is getting a taste of something unusual. For eight hours, the Large Hadron Collider is accelerating and colliding xenon nuclei, allowing the large LHC experiments, ATLAS, ALICE, CMS and LHCb, to record xenon collisions for the first time.

Xenon is a noble gas, present in miniscule quantities in the atmosphere. Its atoms consist of 54 protons and between 70 and 80 neutrons, depending on the isotope. The xenon collisions in the LHC (of atoms with 54 protons and 75 neutrons) are therefore similar to the heavy-ion collisions that are regularly carried out at the LHC. Normally, lead nuclei, which have a much greater mass, are used. “But a run with xenon nuclei was planned for the NA61/SHINE fixed-target experiment at the SPS (Super Proton Synchrotron),” explains Reyes Alemany Fernandez, who is in charge of heavy-ion runs. “We are therefore taking the opportunity for a short run with xenon at the LHC.

It’s a unique opportunity both to explore the LHC’s capabilities with a new type of beam and to obtain new physics results,” says John Jowett, the physicist in charge of heavy-ion beams at the LHC.

And who knows? Maybe this unprecedented run will lead to some surprising discoveries. “The experiments will conduct the same kind of analyses with xenon ions as they do with lead ions, but, because the xenon nuclei have less mass, the geometry of the collision is different,” explains Jamie Boyd, LHC programme coordinator, who is responsible for liaison between the LHC machine and experiment teams. Heavy-ion collisions allow physicists to study quark-gluon plasma, a state of matter that is thought to have briefly existed just after the Big Bang. In this extremely dense and hot primordial soup, quarks and gluons moved around freely, without being confined by the strong force of protons and neutrons, as they are in our Universe today.

Some of the teams who contributed to the xenon run, in the CERN control centre. (Image: Jules Ordan/CERN)

Switching from protons to xenon isn’t a piece of cake, however. A team has been preparing the accelerator complex for the xenon run since the start of the year. Atoms of the gas are accelerated and stripped of their 54 electrons in four successive accelerators before being launched into the LHC. “The number of bunches and the revolution frequency varies a lot between protons and xenon nuclei,” explains Reyes Alemany Fernandez. “One of the difficulties is adjusting and synchronising the accelerators’ radiofrequency systems.”

After the xenon run in the LHC lasting a few hours, xenon nuclei will continue to circulate in the accelerator complex, but only as far as the SPS. For eight weeks, the SPS will supply xenon ions to the NA61/SHINE experiment, which is also studying quark-gluon plasma, but whose analyses will complement those carried out by the LHC experiments. More specifically, NA61/SHINE is interested in the deconfinement point, a collision-energy threshold above which the creation of quark-gluon plasma would be possible. NA61/SHINE is thus systematically testing many collision energies using ions of different masses. After lead, beryllium and argon, it’s now xenon’s turn to take the stage.

A chart showing different types of stable nuclei, with their atomic number, i.e. the number of protons, Z, shown on the horizontal axis and the number of neutrons, N, shown on the vertical axis. The three types already accelerated in the LHC, i.e. protons (hydrogen), lead nuclei and xenon nuclei, are shown in red with their mass number, A (N + Z).

 

For one day only LHC collides xenon beams

Thu, 10/12/2017 - 22:35

The team working on the ion run in the CERN control centre as the xenon run begins. (Image: Jules Ordan/CERN)

Today, the LHC is getting a taste of something unusual. For eight hours, the Large Hadron Collider is accelerating and colliding xenon nuclei, allowing the large LHC experiments, ATLAS, ALICE, CMS and LHCb, to record xenon collisions for the first time.

Xenon is a noble gas, present in miniscule quantities in the atmosphere. Its atoms consist of 54 protons and between 70 and 80 neutrons, depending on the isotope. The xenon collisions in the LHC (of atoms with 54 protons and 75 neutrons) are therefore similar to the heavy-ion collisions that are regularly carried out at the LHC. Normally, lead nuclei, which have a much greater mass, are used. “But a run with xenon nuclei was planned for the NA61/SHINE fixed-target experiment at the SPS (Super Proton Synchrotron),” explains Reyes Alemany Fernandez, who is in charge of heavy-ion runs. “We are therefore taking the opportunity for a short run with xenon at the LHC.

It’s a unique opportunity both to explore the LHC’s capabilities with a new type of beam and to obtain new physics results,” says John Jowett, the physicist in charge of heavy-ion beams at the LHC.

And who knows? Maybe this unprecedented run will lead to some surprising discoveries. “The experiments will conduct the same kind of analyses with xenon ions as they do with lead ions, but, because the xenon nuclei have less mass, the geometry of the collision is different,” explains Jamie Boyd, LHC programme coordinator, who is responsible for liaison between the LHC machine and experiment teams. Heavy-ion collisions allow physicists to study quark-gluon plasma, a state of matter that is thought to have briefly existed just after the Big Bang. In this extremely dense and hot primordial soup, quarks and gluons moved around freely, without being confined by the strong force of protons and neutrons, as they are in our Universe today.

 

The LHC screen during the xenon-ion run. (Image: CERN)

Switching from protons to xenon isn’t a piece of cake, however. A team has been preparing the accelerator complex for the xenon run since the start of the year. Atoms of the gas are accelerated and stripped of their 54 electrons in four successive accelerators before being launched into the LHC. “The number of bunches and the revolution frequency varies a lot between protons and xenon nuclei,” explains Reyes Alemany Fernandez. “One of the difficulties is adjusting and synchronising the accelerators’ radiofrequency systems.”

After the xenon run in the LHC lasting a few hours, xenon nuclei will continue to circulate in the accelerator complex, but only as far as the SPS. For eight weeks, the SPS will supply xenon ions to the NA61/SHINE experiment, which is also studying quark-gluon plasma, but whose analyses will complement those carried out by the LHC experiments. More specifically, NA61/SHINE is interested in the deconfinement point, a collision-energy threshold above which the creation of quark-gluon plasma would be possible. NA61/SHINE is thus systematically testing many collision energies using ions of different masses. After lead, beryllium and argon, it’s now xenon’s turn to take the stage.

A chart showing different types of stable nuclei, with their atomic number, i.e. the number of protons, Z, shown on the horizontal axis and the number of neutrons, N, shown on the vertical axis. The three types already accelerated in the LHC, i.e. protons (hydrogen), lead nuclei and xenon nuclei, are shown in red with their mass number, A (N + Z).