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New ALICE results show novel phenomena in proton collisions

Mon, 04/24/2017 - 13:25

As the number of particles produced in proton collisions (the blue lines) increase, the more of these so-called strange hadrons are measured (as shown by the orange to red squares in the graph) (Image: ALICE/CERN)

In a paper published today in Nature Physics, the ALICE collaboration reports that proton collisions sometimes present similar patterns to those observed in the collisions of heavy nuclei. This behaviour was spotted through observation of so-called strange hadrons in certain proton collisions in which a large number of particles are created. Strange hadrons are well-known particles with names such as Kaon, Lambda, Xi and Omega, all containing at least one so-called strange quark. The observed ‘enhanced production of strange particles’ is a familiar feature of quark-gluon plasma, a very hot and dense state of matter that existed just a few millionths of a second after the Big Bang, and is commonly created in collisions of heavy nuclei. But it is the first time ever that such a phenomenon is unambiguously observed in the rare proton collisions in which many particles are created. This result is likely to challenge existing theoretical models that do not predict an increase of strange particles in these events.

“We are very excited about this discovery,” said Federico Antinori, Spokesperson of the ALICE collaboration. “We are again learning a lot about this primordial state of matter. Being able to isolate the quark-gluon-plasma-like phenomena in a smaller and simpler system, such as the collision between two protons, opens up an entirely new dimension for the study of the properties of the fundamental state that our universe emerged from.”

The study of the quark-gluon plasma provides a way to investigate the properties of strong interaction, one of the four known fundamental forces, while enhanced strangeness production is a manifestation of this state of matter. The quark-gluon plasma is produced at sufficiently high temperature and energy density, when ordinary matter undergoes a transition to a phase in which quarks and gluons become ‘free’ and are thus no longer confined within hadrons. These conditions can be obtained at the Large Hadron Collider by colliding heavy nuclei at high energy. Strange quarks are heavier than the quarks composing normal matter, and typically harder to produce. But this changes in presence of the high energy density of the quark-gluon plasma, which rebalances the creation of strange quarks relative to non-strange ones. This phenomenon may now have been observed within proton collisions as well.

In particular, the new results show that the production rate of these strange hadrons increases with the ‘multiplicity’ – the number of particles produced in a given collision – faster than that of other particles generated in the same collision. While the structure of the proton does not include strange quarks, data also show that the higher the number of strange quarks contained in the induced hadron, the stronger is the increase of its production rate. No dependence on the collision energy or the mass of the generated particles is observed, demonstrating that the observed phenomenon is related to the strange quark content of the particles produced. Strangeness production is in practice determined by counting the number of strange particles produced in a given collision, and calculating the ratio of strange to non-strange particles.

Enhanced strangeness production had been suggested as a possible consequence of quark-gluon plasma formation since the early eighties, and discovered in collisions of nuclei in the nineties by experiments at CERN[1]’s Super Proton Synchrotron. Another possible consequence of the quark gluon plasma formation is a spatial correlation of the final state particles, causing a distinct preferential alignment with the shape of a ridge. Following its detection in heavy-nuclei collisions, the ridge has also been seen in high-multiplicity proton collisions at the Large Hadron Collider, giving the first indication that proton collisions could present heavy-nuclei-like properties. Studying these processes more precisely will be key to better understand the microscopic mechanisms of the quark-gluon plasma and the collective behaviour of particles in small systems.

The ALICE experiment has been designed to study collisions of heavy nuclei. It also studies proton-proton collisions, which primarily provide reference data for the heavy-nuclei collisions. The reported measurements have been performed with 7 TeV proton collision data from LHC run 1.

 

SPS: the last injector now up and running

Mon, 04/24/2017 - 12:23

The Super Proton Synchrotron (SPS) is the second-largest machine in CERN’s accelerator complex. (Image: Piotr Traczyk/CERN)

The Large Hadron Collider (LHC) is due to resume operation in early May 2017 and preparations are even ahead of schedule, by three days. On 21 April beams circulated in the Super Proton Synchrotron (SPS) for the first time this year. All four elements of CERN’s accelerator chain – Linear Accelerator 2 (Linac2), the Proton Synchrotron Booster (PSB), the Proton Synchrotron (PS) and the Super Proton Synchrotron – are now in operation.

Measuring nearly seven kilometres in circumference, the SPS takes particles from the PS and accelerates them to provide high-energy beams to the LHC. It also feeds the SPS North experimental area where, among others, the Common Muon and Proton Apparatus for Structure and Spectroscopy (COMPASS), and the NA61/ShineNA62 and NA63 experiments are situated. Since June 2016 the SPS also supplies protons to a new proof-of-principle experiment – the Advanced Proton Driven Plasma Wakefield Acceleration Experiment (AWAKE).

There were quite a few interventions in the SPS during the extended year-end technical stop (EYETS), including a massive de-cabling campaign in the PS Booster and the SPS, which has paved the way for the installation of new equipment for the LHC Injector Upgrade (LIU) project. This project is crucial to the planned increase of luminosity – number of collisions – of the High-Luminosity LHC, the future upgrade of the LHC, operational as from 2025.

Last year issues with the SPS internal beam dump limited the number of particle bunches that could be injected into the Large Hadron Collider (LHC). In response to that, a new beam dump was re-designed, produced, and successfully installed in the second week of March. This will allow the SPS to reach its full performance again for this year’s run.

LIVE: Ask the scientists at ATLAS what the next year holds

Tue, 04/18/2017 - 15:01

ATLAS physicists will be live in the control room today at 17:00 speaking about what they hope to achieve in the coming months (Image: Sophia Bennett/CERN)

Join us on Facebook today, 19 April 2017, at 17:00, as we meet some of ATLAS’s scientists to learn exactly what’s been going on at CERN’s largest detector over the past few months.

Since December the Large Hadron Collider has been shut down for essential maintenance and repairs, but now the machines are all gearing up to start running again from May.

If you follow our Facebook page, you’ll get the chance to hear our scientists explaining live what they did during the shut down, what the plan is for this year and to answer any of your questions.

Watch the Facebook Live here.

A 360° panoramic view of one end of the ATLAS detector, in October 2016. We can see two of the large wheels that bear the muon chambers (a type of sub-detector). The blue cylinder in the centre houses the tube in which the particles are accelerated. The ATLAS detector is a huge cylinder, 25 metres in diameter and 46 metres high, brimming with millions of sensors. (Image: Maximillien Brice/ CERN)

LHCb finds new hints of possible Standard Model deviations

Tue, 04/18/2017 - 11:55

The LHCb cavern (Image: Maximilien Brice/CERN)

The LHCb experiment finds intriguing anomalies in the way some particles decay. If confirmed, these would be a sign of new physics phenomena not predicted by the Standard Model of particle physics. The observed signal is still of limited statistical significance, but strengthens similar indications from earlier studies. Forthcoming data and follow-up analyses will establish whether these hints are indeed cracks in the Standard Model or a statistical fluctuation.

Today, in a seminar at CERN, the LHCb collaboration presented new long-awaited results on a particular decay of B0 mesons produced in collisions at the Large Hadron Collider. The Standard Model of particle physics predicts the probability of the many possible decay modes of B0 mesons, and possible discrepancies with the data would signal new physics.

In this study, the LHCb collaboration looked at the decays of B0 mesons to an excited kaon and a pair of electrons or muons. The muon is 200 times heavier than the electron, but in the Standard Model its interactions are otherwise identical to those of the electron, a property known as lepton universality. Lepton universality predicts that, up to a small and calculable effect due to the mass difference, electron and muons should be produced with the same probability in this specific B0 decay. LHCb finds instead that the decays involving muons occur less often.

While potentially exciting, the discrepancy with the Standard Model occurs at the level of 2.2 to 2.5 sigma, which is not yet sufficient to draw a firm conclusion. However, the result is intriguing because a recent measurement by LHCb involving a related decay exhibited similar behaviour.  

While of great interest, these hints are not enough to come to a conclusive statement. Although of a different nature, there have been many previous measurements supporting the symmetry between electrons and muons. More data and more observations of similar decays are needed in order to clarify whether these hints are just a statistical fluctuation or the first signs for new particles that would extend and complete the Standard Model of particles physics. The measurements discussed were obtained using the entire data sample of the first period of exploitation of the Large Hadron Collider (Run 1). If the new measurements indeed point to physics beyond the Standard Model, the larger data sample collected in Run 2 will be sufficient to confirm these effects. 

 

Find out more:

LHCb website

The accelerators awaken

Thu, 04/13/2017 - 14:40

Just like a bear after its winter sleep, CERN’s big machines are gradually awakening after the extended year-end technical stop (EYETS). The first beams for 2017 are expected to circulate in the Large Hadron Collider (LHC) in early May, but before that the accelerator complex and all the experiments that it serves have to be put back into operation, one after the other.

In the first week of April, the Linear accelerator 2 (Linac 2), starting point of the protons used in experiments at CERN, successfully accelerated its first proton beam, and made it ready to be sent to the Proton Synchrotron Booster (PSB).

On 10 April, the PSB was also restarted. As the second element of the chain, the PSB increases the energy of the beam received from Linac 2 and sends alternatively it to the Proton Synchrotron (PS) and to the Isotope mass Separator On-Line facility (ISOLDE).

The ISOLDE facility has gathered unique expertise in research with radioactive beams. Over 700 isotopes of more than 70 elements have been used in a wide range of research domains, from cutting edge nuclear structure studies, through nuclear astrophysics, to solid state and life sciences. 

The next step is to put the Proton Synchrotron (PS) back in operation on 17 April. It is the oldest accelerator still in service and currently the third component in the accelerator complex. It pushes the beams to even higher energy and sends them alternatively to the Super Proton Synchrotron (SPS), last element of the accelerator chain before the LHC. It also feeds the East Area where the Cosmics Leaving Outdoor Droplets (CLOUD) experiment is situated, the Antiproton Decelerator, and the neutron time-of-flight facility (n_TOF). 

The purpose of n_TOF is to study neutron-nucleus interactions, which play a key role in neutron-related processes, important in a wide range of context, from astrophysics, to hadrontherapy (the treatment of tumors with beams of hadrons), and the development of retreatment of nuclear waste. 

What happened while the LHC slept over winter?

Mon, 04/10/2017 - 16:19

The winter shutdown of the LHC enabled upgrades and maintenance to take place (Image: Maximilien Brice/CERN)

Since the beginning of December, hundreds of people have been busy underground at CERN, working to make important repairs and to upgrade many facilities, across the whole of CERN’s accelerator chain and experiments.

This year the annual shutdown, called the Extended Year End Technical Stop (EYETS) is particularly long, lasting until May 2017, to allow more work to be carried out than in previous years.

At the beginning of the shutdown, the entire machine was drained of its liquid helium to avoid wasting any of the precious element, while important work was done to the LHC’s cryogenics system.

The new dipole magnet ready to be installed in sector 1-2. The magnet was finally replaced on Monday, 16 January. (Image: CERN)

After removing the helium, scientists and engineers were also able to check the cooling and ventilation, vacuum, electrical and other systems, to make sure they were running properly.

Next, the technical team have had to replace one of the 1232 magnets in the LHC’s ring. Once the magnet was replaced, the team had to carry out many tests at room temperature, triple-checking the magnet was connected properly with no leaks, or deformation.

Also, the Super Proton Synchrotron (SPS) beam dump needed replacing. Beam dumps are radiation-shielded blocks, deep underground, where scientists can choose to send beams that have become degraded so that they can be safely absorbed. 

Researchers re-designed and produced a new beam dump that would allow the SPS to reach its full performance for the 2017 run (Image: Maximilien Brice/ CERN)

Issues with the SPS dump last year had limited the number of particle bunches that could be injected into the Large Hadron Collider (LHC), so it needed to be replaced. A heroic effort was made to re-design and produce a new beam dump, which was finally installed in March and will allow the SPS to reach its full performance again for the 2017 run.

A large part of the shutdown had been identifying and labelling individual cables and removing unnecessary ones in preparation for the many new cables that will be needed for future upgrades.

Over the past few weeks the helium has been re-injected into the system and is being slowly cooled so that the machine can be handed back to the operations teams. From now, the injectors in the accelerator chain are being reawakened.

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A timelapse video showing the CMS detector closing, as the experiments are now getting ready for the LHC restart in early May (Image: CMS/ CERN)

The experiments also used this time to maintain and improve their machines, including the replacement of the detector’s pixel tracker, at the heart of the experiment. All the experiments are now doing final checks before the caverns close, in time for the LHC to be able to inject the first beam in early May.

 

Arts at CERN announces four new artists in residency

Thu, 04/06/2017 - 16:05

Haroon Mirza, The National Apavilion of Then and Now, 2011. Courtesy hrm199 and Lisson Gallery. (Image: Kiki Triantafyllou)

Arts at CERN is delighted to announce the winners of the four artist residency awards for 2017: the studio hrm199 led by artist Haroon Mirza, Laura Couto Rosado, Cheolwon Chang and Tomo Savić-Gecan.

Arts at CERN is CERN’s arts and science programme, fostering dialogue between prominent scientists and visionary artists at the world’s leading centre for particle physics.

“Since 2011, Arts at CERN has developed a wide network of partnerships with eminent cultural institutions around the globe. The programme’s success now means four artistic residencies can take place every year here at CERN, bringing together the worlds of science and art to inspire each other in new creative expressions,” says Charlotte Warakaulle, Director for International Relations at CERN.

“I am thrilled to invite studio hrm199, Laura Couto, Cheolwon Chang and Tomo Savić-Gecan to this unusual and highly scientific environment, where I am certain the artists’ research and ideas will be expanded with many different cultural and creative angles, thanks to the interactions with CERN scientists,” affirms Mónica Bello, head of Arts at CERN.

The winner of “Collide Pro Helvetia”, in partnership with the Swiss Arts Council, Pro Helvetia, is the artist and designer Laura Couto. She will spend three months at CERN exploring design principles inspired by fundamental particles and the way these are described by physicists.

“Collide is a unique opportunity for a creator to confront his ideas to the actual practices and knowledge of renowned scientists. It is a life-and-career-changing experience. We are pleased to offer this chance to Laura Couto Rosado, who unanimously convinced the jury with her work at the crossroads between physics, interaction design and poetry” says Michel Vust, Project Leader Pro Helvetia.

As part of the ongoing collaboration with FACT - Foundation for Art and Creative Technology in Liverpool - in “Collide International”, the artists Haroon Mirza and Jack Jelfs, forming studio hrm199, will reside at CERN for two months, where they will work in close collaboration with a research scientist. Afterwards, the artists will spend one month at the Liverpool institution to later engage in production. The jury chose the studio platform hrm199 for its ability to consistently extend the ambitious standards of creativity and to build on an ongoing fascination with media, time and transmission.

FACT's Director Prof. Mike Stubbs says: "The jury is very excited for the applicants for this second year of FACT and Arts at CERN's COLLIDE International Residency Award. In our first year, we have hosted Yunchul Kim and have, together with our partners LJMU, Liverpool University and Liverpool City Council, been stunned by the magic of his initial research. We were also very impressed by artists Julieta Aranda and James Bridle, who were runners up for the award in 2016. FACT intends Kim's new work and the work of Haroon (winner of 2017's award) to be displayed as part of a very exciting new exhibition in 2018."

Moreover, the two country-specific awards named “Accelerate” have been presented to South Korean and Croatian artists. Seoul-based artist Cheolwon Chang plans to investigate the geometric properties of nature and how mathematics influences further understanding of our universe. His award has been made possible thanks to collaboration between CERN and ARKO, the Korean Arts Council, and he plans to pursue his research in connection with particle physics.

The Croatian artist Tomo Savić-Gecan will come to CERN for one month thanks to CERN’s partnership with the Ministry of Culture of Croatia and Kontjener Bureau of Contemporary Art Praxis in Zagreb. He will gather inspiration through dialogue with theoretical and experimental physicists to develop a specific project for CERN, understanding the implications of time-space research.

Retired MRI scanner gets new life studying the stars

Tue, 04/04/2017 - 11:18

The ex-MRI scanner magnet has travelled all the way from Australia to be used in an experiment at CERN’s ISOLDE facility (Image: Karl Johnston/CERN)

A team of researchers has successfully taken a magnet from a decommissioned MRI scanner used by a Brisbane, Australia, hospital for scanning patients, and recycled it for use in an experiment at CERN’s ISOLDE facility.

The ISOLDE Solenoidal Spectrometer (ISS) project will design and construct instruments to explore the nuclear reactions that occur when stars explode in supernovae.

The decision was made to re-commission the 15-year-old magnet when it was discovered that building a new one could cost almost 1,250,000 CHF. Instead, the entire process of shipping and re-commissioning the retired MRI magnet was around 160 000 CHF (€149,500).

“Finding a suitable MRI magnet that can go up to a strength of 4 Tesla is not easy, but we found out about this Australian magnet from our collaborators at Argonne National Laboratory and it was exactly what we needed,” explains Professor Robert Page,  of the University of Liverpool, who leads the international collaboration using the magnet.

ISOLDE is CERN’s radioactive ion beam facility, where they study the different properties of hundreds of atomic isotopes.

Once the superconducting magnet arrived at CERN, the cryogenics team got to work cooling it with liquid helium, to see if it was still capable of producing the strong fields required by the ISS project.

The project, will take beams of radioactive ions, produced by bombarding heavy nuclei with protons from the Proton Synchrotron Booster (PSB) at CERN, and fire them at a heavy hydrogen (deuterium) target inside the magnet itself. As the particles are fired at the target, neutrons are transferred to some particles to create ions with unusual numbers of protons and neutrons – these are the exotic ions studied at ISOLDE.

But this process leaves protons without their neutron partner. The strong magnetic field from the MRI magnet causes these protons to spiral backwards and land, just nanoseconds later, on a silicon detector.

From the position of the proton on the detector and its energy, the energy levels of the exotic ions can be determined. In this way the team hopes to understand how the forces in atomic nuclei with differing numbers of protons and neutrons give rise to their very different properties, and how elements are created by supernovae.

The ISS project includes researchers from the University of Liverpool, STFC Daresbury Laboratory, the University of Manchester and the Katholieke Universiteit Leuven.

Ancient particle accelerator discovered on Mars

Sat, 04/01/2017 - 08:35

New images of the surface of Mars taken by NASA’s Mars Reconnaissance Orbiter probe have revealed the presence of the largest particle accelerator (Image: Daniel Dominguez/ CERN)

The search for water, or even signs of life, on the planet Mars has been ongoing for some time. But with today’s announcement by CERN and NASA scientists, the exploration of the red planet has revealed a major new discovery. New images of the surface of Mars taken by NASA’s Mars Reconnaissance Orbiter probe, analysed by an interdisciplinary team of experts from the fields of geology, archaeology and particle physics, have revealed the presence of the largest particle accelerator ever built. The team has shown that Olympus Mons, previously thought to be the largest volcanic formation in the solar system, is in fact the remains of an ancient particle accelerator thought to have operated several million years ago. 

A landslide stretching over several kilometres spotted by the probe’s high-resolution camera, sparked the scientists’ attention. This apparently recent event revealed a number of structures, which intrigued the scientists, as their shapes clearly resembled those of superconducting accelerating cavities such as those used in the Large Hadron Collider (LHC). With a circumference of almost 2000 kilometres, this particle accelerator would have been around 75 times bigger than the LHC, and millions of times more powerful. However, it is not yet known which type of particles might have been accelerated in such a machine.

Ancient Egyptian hieroglyphs, the meaning of which was previously a mystery, seem to corroborate these observations, leading scientists to believe that the pyramids might have served as giant antennae (Image: Daniel Dominguez/ CERN)

This major discovery could also help to explain the Egyptian pyramids, one of archaeology’s oldest mysteries. Heavily eroded structures resembling pyramids also appear on the images in the immediate vicinity of Olympus Mons. In addition, ancient Egyptian hieroglyphs, the meaning of which was previously a mystery, seem to corroborate these observations, leading scientists to believe that the pyramids might have served as giant antennae. The pyramids on Earth might therefore have allowed the accelerator to be controlled remotely. “The accelerator control room was probably under the pyramids,” said Friedrich Spader, CERN’s Head of Technical Design.

This particle accelerator – a veritable “stargate” – is thought to have served as a portal into the solar system for a highly technologically advanced civilisation with the aim of colonisation. “The papyrus that was recently deciphered indicates that the powerful magnetic field and the movement of the particles in the accelerator were such that they would create a portal through spacetime,” said Fadela Emmerich, the leader of the team of scientists. “It’s a phenomenon that is completely new to CERN and we can’t wait to study it!” Such a technology could revolutionise space travel and open the way for intergalactic exploration.

Olympus Mons was until now considered to be the biggest volcano in the solar system, with its most recent lava flows estimated to be about 2 million years old. Scientists believe that this dating is quite accurate, on the basis of the latest measurements carried out by NASA’s Mars Odyssey probe. “This would mean that the particle accelerator was last used around 2 million years ago,” suggested Eilert O’Neil, the geologist who led this aspect of the research.

The powerful synchrotron radiation emitted by the particle accelerator generated an intense heat, which explains the volcanic structure and the presence of lava flows. “We have also suspected for a long time that a large quantity of water must have existed on the surface of Mars. We can only assume that this water was used at the time to cool the machines,” revealed Friedrich Spader.

“We’re probably talking about forgotten technologies and a highly advanced ancient civilisation,” said Eilert O’Neil. “Maybe even our own distant ancestors.”

 

 

Webcast: How does CERN inform UNOSAT's humanitarian efforts

Fri, 03/31/2017 - 08:31

A UNOSAT officer works on satellite imagery of Haiti (Image: Maximilien Brice/ CERN)

On Friday 31 March 2017 at 11:00, Einar Bjorgo, manager of UNOSAT, will give an overview of the variety of activities carried out by UNOSAT since 2001.

Over the last 15 years, UNOSAT has helped guide emergency teams through various locations and supported to humanitarian assistance efforts and programmes to protect cultural heritage.

Hosted at CERN, UNOSAT benefits from the Organization's IT infrastructure whenever a situation requires, helping the UN to stay at the forefront of satellite-analysis. Specialists in both geographic information systems (GIS) and analysis of satellite data, supported by IT engineers and policy experts, use this knowledge to produce extremely precise maps of regions of the world affected, or threatened, by natural disaster or conflict.

 

Where to watch the webcast:

Webcast: http://cern.ch/go/D8GC

Indico page:https://indico.cern.ch/event/622865/

Silicon sandwiches feed LHC’s upgraded collision appetite

Wed, 03/29/2017 - 12:30

The scientist carefully places the sensors in the probe station and tests them by applying a high voltage using a needle. The team must wear protective equipment to keep the sensor safe from dust and scratches (Image: Ulysse Fichet/CERN)

In a special, dust-free, clean laboratory, straddling the Swiss-French border, a group of physicists spend their time probing hand-sized hexagons of silicon. These hexagons are a fraction of a millimetre thick and are made up of over a hundred smaller hexagons, individual sensors each roughly one centimeter across. Together with layers of metal, the sensors will form a new subdetector to replace part of the end-cap calorimeters in CERN’s CMS experiment.

A calorimeter measures the energy a particle loses as it passes through. It is usually designed to stop entirely or “absorb” most of the particles coming from a collision. The new calorimeter sensors will be used to measure the energy and arrival time and to trace the path of individual particles that fly out in the form of debris from the collision point in the centre of the experiment. Once in place, this will be the first time that this type of silicon sensor has ever been used in the calorimeter of a particle detector on such a large scale. 

Eva Sicking works on the probe station. She explains: “Currently we use individual probe needles to contact the cell we want to test and all of its direct neighbours, but we’re also developing a probe card with many pins below it so we can lower the card and connect all the pins and test all the sensors cells in one go, so we won’t need to place each of the eight needles individually.” (Image: Ulysse Fichet/CERN)

The sensors are part of a wider upgrade project to make sure that the experiments are able to cope with a larger number of particle collisions as a result of the High-Luminosity LHC (HL-LHC) upgrade in 2025, and the increased potential for discovery that comes with it. The current technology is based on long, clear lead-tungstate crystals designed to cope with the radiation in the detectors Although they will operate fine for the LHC era, until 2025, the amount of radiation expected during HL-LHC will darken the crystals until they become blind to particles passing through them.

The sensors constitute the core part of the new subdetector, which will replace the current end-cap at CMS, pictured (Image: David Barney/CERN)

“The lead-tungstate crystals we use now are designed to operate at comparably low collision rates and in a low-radiation environment.  With the HL-LHC, we’ll have hundreds of collisions at one time, so we needed something that could withstand the increased radiation and resolve showers from particles very close to each other in space and time,” explains Eva Sicking, the applied physicist leading this silicon sensor project. “We want to be able to distinguish the different particles that we see, and also know which ones came from which collisions.”

“These sensors not only provide a system that’s more radiation-hard; at the same time they also provide more information on where exactly the particles passed through. They also give us very good timing information, so we can determine exactly when this particle arrived, and thanks to the small cells it can do that for many collisions at the same time,” continues Andreas Maier, who is also working on the project. 

Metal Sandwiches

To make sure the sensors are able to do this, instead of long crystals, the team are moving away from long crystals and instead building sandwiches – layers of the sensor alternating with layers of a heavy metal, such as lead. 

A team of CMS researchers have already tested the first sandwich calorimeter prototype with single particles, but in the upgraded HL-LHC multiple particle collisions will occur at once and hundreds of debris particles will pass through the sensors at the same time. The prototype is based on silicon and dense metals – the image shows the alternating layers of metal and the silicon sensor. The particle beam will run from the left of the image through to the right. (Image: David Barney/CERN)

To test each sensor in the sandwich, the team is using a special probe station, with eight needles sitting above a vacuum plate. The plate holds the delicate, and expensive, silicon sensors firmly in place so that the needles can be manoeuvred and lowered to connect with contact pads marked on each sensor. They then apply a high voltage to the sensor to record the data that will be used to assess the sensor’s quality.

Using the probe station, the physicists test how much voltage can be applied to each sensor – the more voltage the sensors can withstand, the better any radiation damage can be mitigated. Impurities in the crystal or damages can cause high leakage current in the sensor. Such a cell will draw a large current which would make the full sensor difficult or even impossible to operate (Image: Ulysse Fichet/CERN)

Sensitive instruments tell the team what the electrical current generated in the sensor is, as well as a measure called capacitance. If either of these run above a set level, the sensor cannot be used, as it will create noise that interferes with the data from any particle tracks. If the noise is too high, the researchers can assess if there is a problem at production level. If a problem is found, they go back to the manufacturers to make sure it’s ironed out before the real sensors go into production. All the sensors eventually used will go through this process, either at CERN or at other institutes.

 

Optimising power

Measuring current is particularly important because it can have an impact on how much power and energy is required when the machine is running. 

The software shows the current running through each sensor, and the tile made of multiple smaller sensors is shown on the bottom right (Image: Andreas Maier/CERN)

“In an ideal world, the sensor would not show any leakage current, but in reality, impurities are introduced during the production of these sensors. Therefore, the current we measure is an indicator of the production quality,” Florian Pitters, another member of the group, explains.

Leakage current is acceptable below a certain level, but it is amplified as you add more sensors together and the power supply and cooling system has to deal with a larger amount of power and dissipated heat.

“Approximately 25% of the final electricity bill will be due only to leakage current. So if we can suppress it, that’s good.” Andreas

If there’s any problem in the final sensors, it could cause the entire tile to short, rendering it useless. So these tests are vital to ensuring that the whole detector system runs at its best and that these components don’t create barriers to future discovery.

“There have been mistakes with things that people just couldn’t have known, until we tested them. We’ve discovered a few times that ways we intended to go just had to be abandoned, so we chose a new path. That’s how research goes,” says Andreas.

 

Cosmic collisions at the LHCb experiment

Mon, 03/27/2017 - 14:12

An example of a fully reconstructed proton-helium collision event in the LHCb detector. The particle identified as an antiproton is shown in pink. (Image: LHCb collaboration)

Last week at the 52nd Rencontres de Moriond EW in La Thuile, Italy, the LHCb experiment presented the results of an unprecedented and unusual study. Instead of the usual proton-proton collisions, this time the LHCb detector registered collisions between protons and helium nuclei, which were injected near the interaction point of the experiment. This type of collision can usually only be seen far above the Earth’s atmosphere, where cosmic-ray particles – highly energetic particles from outside the Solar System – hit interstellar “dust” primarily made up of hydrogen and helium, and are detected by satellite-based experiments. Scientists want to better understand this process and, in particular, are trying to understand how many antiprotons are created when the highly-energetic cosmic-ray protons hit the helium nuclei of the interstellar medium.

The ultimate reason for this relates to the search for dark matter signals. Dark matter is an invisible type of matter – i.e. it doesn’t emit any type of electromagnetic radiation – which makes up one quarter of the matter-energy content of our universe, but its origin is as yet unknown. If dark matter is made of some kind of (as yet undiscovered) stable particles, whose existence is foreseen in many extensions of the Standard Model of particle physics, these dark matter particles might collide and produce ordinary particles and antiparticles, notably including antiprotons. 

However, antiprotons can also be created via the collision of cosmic-ray protons with hydrogen and helium nuclei in the interstellar medium. Therefore, a potential sign of the presence of dark matter could be the observation of a number of antiprotons exceeding that expected from “standard” processes. And indeed, the PAMELA and AMS-02 space-based experiments found exactly such an intriguing excess of antiprotons compared to protons in cosmic-ray measurements, with an impressive level of precision.

Eureka? Unfortunately not yet, as our theoretical understanding of antiproton production from cosmic-ray collisions is still affected by large uncertainties, especially regarding the probability of antiproton production in proton-helium collisions (the so-called “cross-section”). A precise determination of the expected number of antiprotons from cosmic rays has been impossible so far, thus preventing a straightforward interpretation of the satellite experiments’ results.

Here is where the LHCb experiment came in. The idea of injecting noble gasses – such as neon, helium and argon – into the beam pipe near the interaction region was proposed for various reasons related to proton-beam luminosity measurements. But its potential was quickly recognised by the LHCb physicists and their colleagues working in astroparticle physics: the gas-injection technique could also be used to simulate the cosmic environment and measure, for the first time, the production cross-section of antiprotons in proton-helium collisions.

The proton-helium collision data used in this analysis were recorded in early May 2016. Thanks to its specialised capabilities in identifying various particles, in particular antiprotons, the LHCb experiment was also able to measure the antiproton production cross-section in a large range of relevant energies, achieving an overall precision of around 10%. This measurement significantly shrinks the uncertainty on the values of the antimatter production cross-section in proton-helium collisions that have been used so far in theoretical cosmic-ray models (see the image below).

The LHCb result will have a considerable impact on the predictions for the number of antiprotons expected from cosmic-ray collisions with the interstellar medium, and the astrophysics community is now busy incorporating it into their calculations. This work will enable the interpretation of PAMELA and AMS-02 data on the antiproton flux from space to become more constrained, shedding light on its possible dark-matter origin.

More information on this result can be found on the LHCb website.

Antiproton production cross-section in the collisions of LHC protons with helium nuclei as a function of the antiproton energy in different energy ranges. Some of the most popular models used in cosmic-ray physics are represented by the coloured solid lines, and the LHCb results are the data points superimposed. The spread amongst model predictions indicate the large uncertainty on the value of the antimatter production cross-section in proton-helium collisions prior to the LHCb measurement. It must be noted that the the vertical scale is logarithmic, hence a small vertical displacement (of the data points) corresponds to an actual large difference with respect to the theoretical models, represented by the couloured lines. (Image: LHCb collaboration)

Raising the (G)bar for antimatter exploration

Fri, 03/17/2017 - 17:01

Installation of the GBAR linac in its shielding bunker. The electrons accelerated to 10 MeV toward a target will produce the positrons that are necessary to form antihydrogen with the antiprotons coming from the ELENA decelerator. (Image: Max Brice/CERN)

The absence of antimatter in the universe is a long-standing jigsaw puzzle in physics. Many experiments have been exploring this question by finding asymmetries between particles and their antimatter counterparts.

GBAR (Gravitational Behaviour of Antihydrogen at Rest), a new experiment at CERN, is preparing to explore one aspect of this puzzle – what is the effect of gravity on antimatter? While theories exist as to whether antimatter will behave like matter or not, a definitive experimental result is still missing.

GBAR will measure the effect of gravity on antihydrogen atoms. Located in the Antiproton Decelerator (AD) hall, GBAR is the first of five experiments that will be connected to the new ELENA deceleration ring. On 1 March, the first component of the experiment was installed – a linear accelerator (linac). In sharp contrast to the LHC’s chain of big accelerators and fast particles, the AD world of antimatter is small and its particles are as slow as they come. The GBAR linac is only 1.2 metres long and it will be used to create positrons, the antimatter equivalent of electrons.

The experiment will use antiprotons supplied by ELENA and positrons created by the linac to produce antihydrogen ions. They consist of one antiproton and two positrons, and their positive charge makes them significantly easier to manipulate. With the help of lasers, their velocity will be reduced to half a metre per second. This will allow them to be directed to a fixed point. Then, trapped by an electric field, one of their positrons will be removed with a laser, which will make them neutral again. The only force acting on them at this point will be gravity and they will be free to make a 20-centimetre fall, during which researchers will observe their behaviour.

The results might turn out to be very exciting. As the spokesperson of GBAR, Patrice Pérez, explains: “Einstein’s Equivalence Principle states that the trajectory of a particle is independent of its composition and internal structure when it is only submitted to gravitational forces. If we find out that gravity has a different effect on antimatter, this would mean that we still have a lot to learn about the universe.”

Five other experiments are based at the Antiproton Decelerator, two of which – AEGIS and ALPHA – are also studying the effect of gravity on antimatter.

CERN: ideal for entrepreneurship, for those who take a leap

Fri, 03/17/2017 - 10:09

Entrepreneurship students brainstorming potential applications for CERN technologies during the NTNU Screening Week in 2016. (Image: Sophia Elizabeth Bennet/CERN)

It is well-known that CERN is a hub for top-notch scientists, engineers and professionals from all corners of the world, committed to advance their fields, to explore the unknown and to learn. But this combination is also stimulating for the entrepreneurial spirit and therefore makes CERN an ideal place to explore and get started new business ideas, to discover exciting technologies and to build a skilled, diverse start-up team.

Creating platforms where people can meet is an important part of facilitating entrepreneurship at CERN, and through initiatives such as THE Port, Challenge Based Innovation (CBI), the Entrepreneurship Meet-ups and the Knowledge Transfer seminars, future change-makers meet and opportunities are created.

Creativity, commitment & diversity

Creativity, commitment and diversity are cornerstones of both science and entrepreneurship and core values of the Organization. Being at the forefront of multiple fields requires continuous innovation, and much like entrepreneurial companies, CERN tackles the inherent fuzziness of the unknown.

Tapping into the knowledge of the heterogeneous crowd at CERN can create magic. One example is the Better Body Bags. What started as a weekend hack at THE Port hackathon, turned into an R&D contract with the International Committee of the Red Cross and being selected among the TOP25 start-ups in Switzerland in 2014. Also from THE Port 2014, the topic of building a low cost, inflatable fridge for field operations led to a brand-new start-up, Ideabatic, which was recently awarded a €25 000 prize by ViiV Healthcare.

Cutting-edge technology, skills & knowledge

The people working at CERN possess unique knowledge and skills, and cutting-edge technologies are continuously developed at the laboratory. These may have applications across markets, and innovations developed might have potential to disrupt whole industries.

Originating from the NTNU Screening Week in 2012, the CERN spin-off TIND is providing solutions for library management and data preservation based on the open source software Invenio. 2017 marks their third year in business, and they have now permanently expanded their operations to the United States. Terabee is another example, originally providing aerial inspections and imaging services by deploying drones. After a fruitful collaboration with CERN, where sensors were made to ensure the safety of operations in the complex environments of the LHC, its business was expanded to include sensor development.

A jump in the dark

Sometimes, it is not easy leaving a safe environment such as that of CERN. Indeed, while CERN can keep you safely hooked for life, the decision of branching out implies taking on new risks in a whole new environment. Piero Zucchelli, founder and CEO of Andrew Alliance, went through this journey – what he describes as a “jump in the dark” – from the CERN Experimental Physics department to the start-up business. Now, a decade after initially deciding to leave CERN to be an entrepreneur, Piero Zucchelli is returning to share his honest story. “We know exactly what we leave behind, but we don’t know what we don’t know”, Zucchelli says.

Find out more at the next Knowledge Transfer seminar: “From CERN to Entrepreneurship: we don’t know what we don’t know”, 24 March 2017, by Piero Zucchelli, CEO of Andrew Alliance, here.

Here’s what open-heart surgery at the LHC looks like

Tue, 03/14/2017 - 14:05

Preparations being made in the underground experimental cavern of CMS prior to the installation of the second-generation Pixel Tracker of CMS

Scientists at CERN have now completed “open-heart surgery” on one of the detectors at the Large Hadron Collider (LHC). In a complex operation that ran from 27 February to 9 March, the giant Compact Muon Solenoid (CMS) detector received a new “heart” – it’s Pixel Tracker.

Detectors at the LHC, such as CMS, record the signatures of particles produced when beams of protons (or, occasionally, lead nuclei) are smashed together. The detectors are built around the LHC’s beam pipe, within which the collisions take place. As the particles fly through the detectors, they traverse several layers of equipment that are tasked with making specific measurements about their properties. But, when these collisions occur, it isn’t a single proton hitting another proton: several dozen simultaneous collisions take place within CMS. This phenomenon is known as “pile-up” and can be thought of as exposing a film camera to multiple images and recording all the multiple exposures in a single photograph.

The tracking system determines the trajectories of charged particles flying through it, and identifies the charge and momenta of the particles, helping to determine the origins of the various particles seen by CMS. Physicists can thus separate the overlapping collisions into individual interactions.

The CMS tracking system is made of silicon sensors and has two components that perform a complementary roles: the inner of the two is called the Pixel Tracker and the outer one is the Strip Tracker. The Pixel Tracker sees the greatest onslaught of particles flying through CMS and, unavoidably, it will lose its ability to measure the particles’ properties accurately. In addition, the LHC continues to improve its performance and is expected to provide CMS with an even greater number of simultaneous interactions: even more exposures on each photograph. It had therefore been planned around five years ago to replace the original Pixel Tracker of CMS, removed earlier this year, with an entirely new one.

The new Pixel Tracker has four layers instead of the previous three in the central region (called BPIX for Barrel PIXel) and has three disks instead of the previous two capping each end (called FPIX for Forward PIXel). These additional layers raise the number of silicon pixels in CMS from 66 million to 124 million, increasing the “resolution” of the “photographs” CMS takes, so to speak.


The FPIX disks were manufactured by 19 institutes in the US. They can be seen here at the CMS Tracker Integration Facility at Meyrin, Switzerland before being taken to the CMS experimental site outside Cessy, France for installation. The Pixel Tracker’s various components were stored and tested carefully on the surface in a clean room prior to installation. (Image: Maximilien Brice/CERN)

To be installed within CMS, the various components of the Pixel Tracker had to be lowered by crane down the 100-metre-deep shaft into the underground experimental cavern of CMS. They were then raised by a second crane onto the installation platform for insertion. This image shows the first half of the BPIX located inside its “cassette” being placed on this platform before being inserted into the CMS detector. The BPIX, manufactured by 23 institutes from eight European countries, is only the size of a shoebox, but has a large number of electronics and cooling components that go with it. (Image: Maximilien Brice/CERN)

Once lowered onto the installation platform, the protective coverings of the device was removed and it was slowly and carefully slid into place around the LHC beam pipe. Here, the second half of BPIX is being prepared for insertion. (Image: Maximilien Brice/CERN)

The LHC beam pipe can be seen prominently in this picture with the two halves of BPIX fitting snugly around it. The particle beams of the LHC fly within this beam pipe before colliding with each other inside CMS. 6. (Image: Maximilien Brice/CERN)

Surgery in action! Appropriate protection during installation of the FPIX prevents contamination of the device. (Image: Maximilien Brice/CERN)

The many wires and electronics connected to the Pixel Tracker’s active components had to be thoroughly checked during the installation procedure and had to be moved into place delicately. (Image: Maximilien Brice/CERN)

The installation of the final FPIX component brings the long operation of replacing the CMS Pixel Tracker to a successful end. CMS will soon be moved into its data-taking configuration to prepare for the first proton-proton collisions of 2017, expected in early June. (Image: Maximilien Brice/CERN)

Immerse yourself into the CMS detector and observe the installation of the new Pixel Tracker from within the underground experimental cavern with this interactive 360º photograph. (Image: Max Brice/CERN)

LHCb observes an exceptionally large group of particles

Tue, 03/14/2017 - 13:52

A typical LHCb event fully reconstructed. Particles identified as pions, kaon, etc. are shown in different colours. (Image: LHCb collaboration)

The LHCb experiment at CERN is a hotbed of new and outstanding physics results. In just the last few months, the collaboration has announced the measurement of a very rare particle decay and evidence of a new manifestation of matter-antimatter asymmetry, to name just two examples.

In a paper released today, the LHCb collaboration announced the discovery of a new system of five particles all in a single analysis. The exceptionality of this discovery is that observing five new states all at once is a rather unique event.

The particles were found to be excited states – a particle state that has a higher energy than the absolute minimum configuration (or ground state) – of a particle called "Omega-c-zero", Ωc0. This Ωc0 is a baryon, a particle with three quarks, containing two “strange” and one “charm” quark. Ωc0 decays via the strong force into another baryon, called "Xi-c-plus", Ξc+ (containing a “charm”, a “strange” and an “up” quark) and a kaon K-. Then the Ξc+ particle decays in turn into a proton p, a kaon K- and a pion π+.

From the analysis of the trajectories and the energy left in the detector by all the particles in this final configuration, the LHCb collaboration could trace back the initial event – the decay of the Ωc0 – and its excited states. These particle states are named, according to the standard convention, Ωc(3000)0, Ωc(3050)0, Ωc(3066)0, Ωc(3090)0 and Ωc(3119)0. The numbers indicate their masses in megaelectronvolts (MeV), as measured by LHCb.

This discovery was made possible thanks to the specialised capabilities of the LHCb detector in the precise recognition of different types of particles and also thanks to the large dataset accumulated during the first and second runs of the Large Hadron Collider. These two ingredients allowed the five excited states to be identified with an overwhelming level of statistical significance – meaning that the discovery cannot be just a statistical fluke of data.

The next step will be the determination of the quantum numbers of these new particles – characteristic numbers used to identify the properties of a specific particle – and the determination of their theoretical significance. This discovery will contribute to understanding how the three constituent quarks are bound inside a baryon and also to probing the correlation between quarks, which plays a key role in describing multi-quark states, such as tetraquarks and pentaquarks.

More information on this result can be found on the LHCb website and in the scientific paper.  

The image above shows the data (black dots) of the reconstructed mass distribution resulting from the combination of the Ξc+ and K- particles. The five particle states are the five narrow peaks standing out from the distribution of data. (Image: LHCb collaboration)

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