From CERN: “LS2 Report: Proton Synchrotron prepared for higher injection energies”

From CERN

11 February, 2020
Achintya Rao

CERN’s oldest working accelerator has a new injection kicker magnet and will soon receive a new septum as well.

The new kicker for the PS being installed in the accelerator (Image: Julien Ordan/CERN)

CERN Proton Synchrotron

Proton beams entering the Proton Synchrotron (PS) from the PS Booster have to be deflected into a circulating orbit before they can be accelerated. This is done by two specialised beam-line elements: a strong magnetic septum and a fast injection-kicker magnet. The latter is a precisely synchronised electromagnet that can be switched on and off in about 100 ns, providing a stable and uniform kick that only affects the injected beam batches, while leaving the already circulating beam unperturbed.

After the ongoing second long shutdown of CERN’s accelerator complex (LS2), the PS Booster will accelerate particles to 2 GeV, almost 50% higher than the pre-LS2 value of 1.4 GeV. The PS therefore needed a new septum and a new kicker capable of coping with this increased injection energy. On 31 January, as part of the LHC Injectors Upgrade (LIU) project, the new kicker magnet was installed, replacing the kicker that had operated since 1979. The magnet will soon be aligned, connected to the vacuum system and then connected to the power and control cables.

Like the magnet it replaced, the PS’s new kicker is made of four identical modules sitting in a 1-metre-long vacuum tank. Each module receives power from a separate pulse generator that consists of two high-power electrical switches – a main switch and a dump switch to control the pulse length – and around 280 metres of a so-called “pulse-forming line”, wound and stored on gigantic drums. These lines are thick, coaxial cables filled with sulphur hexafluoride (SF6) at a pressure of 10 bars, to provide the necessary insulation for the charging voltage of 80 kV. Since SF6 is a strong greenhouse gas, special care has to be taken to ensure that it is safely manipulated and recuperated, and that the system has no leaks.

In order to reduce the dependence on the SF6-based cables, part of the transmission line between the pulse generator and the magnet was replaced with conventional cables. “Disconnecting the SF6 cables from the magnet to connect the reserves was a two-person job, and required time-consuming gas-handling procedures to be followed,” explains Thomas Kramer from the TE-ABT (Accelerator Beam Transfer) group. “On the other hand, the new conventional cables have quick-release connectors and can be operated by one person fairly quickly.”

Kramer and colleagues also replaced the old analogue control system for the kicker, parts of which had been in place since the system was constructed in the 1970s. “Things made back then still work reliably,” smiles Kramer, while noting that the new digital systems make it possible to monitor the situation remotely.

One element that remains to be installed is the new septum. This is a delicate device used in the injection system, composed of two cavities separated by a thin wall: one cavity allows the beams from the PS Booster to enter the PS while the second is meant for the circulating beams. The new septum, which required construction of a novel power converter, will be installed upstream of the magnet in the coming weeks.

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From Accelerating News: “Power converters specially designed for CERN can now be used by the wider accelerator community”

From Accelerating News

11 Dec 2019
by Daniela Antonio, Quentin King (CERN)

The SOLEIL synchrotron facilities in Paris, France. Jean-Christophe BENOIST

The Electrical Power Converters (EPC) Group at CERN has developed new software layers to allow the broader particle accelerator community to use the CERN-specific power converters controls.

Power converters are a fundamental part of CERN’s accelerator complex, allowing it to function properly. In particle accelerators, the particle beams are guided by powerful magnets and are accelerated in metallic chambers called radiofrequency cavities. More than five thousand power converters electrically power both these structures. Many different types are needed, ranging in power from a few watts to more than one hundred megawatts. Some produce a steady current or voltage, while others must ramp, or pulse synchronously with all the other equipment in the accelerator. Therefore, the effective operation of each power converter depends on high-performance digital controls that regulate the current in the circuit.

Since the creation of the LHC, CERN power converters use specialised control computers called Function Generator/Controllers (FGCs), integrated into the power converters. An associated FGC software framework was developed to integrate the FGC hardware into CERN’s accelerator controls environment, which is unique to CERN. With the new software stack, the FGC hardware can now be integrated in the TANGO and EPICS control environments, which are the most common control frameworks used at other accelerator infrastructures. This update will open the door for FGCs and CERN-designed power converters to be deployed to other accelerator facilities, such as synchrotrons.

The project to integrate FGCs into the EPICS and TANGO frameworks was conceived in 2014 and resulted in the successful transfer of FGC converter controls to a European manufacturer, who supplied the new power converter to the main cyclotron magnet of the TRIUMF laboratory in 2018. In 2019, CERN provided power converter technology and the associated converter controls to the European Synchrotron Radiation Facility (ESRF). TRIUMF uses EPICS while ESRF uses TANGO.

Thanks to its potential for future technology transfer, the FGC update was one of the five projects selected to receive funding from the KT Fund in 2019. The objective is to continue the FGC framework integration with more commonly used control environments in the context of a collaboration agreement between CERN and SOLEIL.

During the first phase of this collaboration, CERN provided training and lent a standalone FGC and a small power converter controlled by an FGC to SOLEIL. “The SOLEIL upgrade builds on previous experience, gradually moving to a unified controls’ environment for which the FGC framework is particularly suitable,” explains Nick Ziogas, Knowledge Transfer Officer at CERN. In 2020, during phase 2 of the collaboration, eleven controllers of existing commercial power converters installed at the SOLEIL synchrotron (Paris, France) will be replaced by FGCs. SOLEIL intends to procure 1,700 power converters with digital controllers by 2025 for its major upgrade to higher brilliance and these could hopefully be CERN designs using FGC for controls.

At a time when the broader high-energy physics community debates the next-generation of accelerator machines, many laboratories have major upgrades in store for the next decades, aiming to achieve a performance that could lead to more complex science. This means higher luminosity in colliders and higher brilliance in light sources and, therefore, an upgrade of the accelerator infrastructure.

“The FGC framework comes with a powerful software stack that allows for monitoring and diagnosis of faults and the automatic configuration of the controllers following a change of hardware components,” explains Quentin King, head of the Converter Controls Software Section in the EPC Group. “Powerful management tools are vital when large numbers of converter controllers are used. This is a major requirement from all light sources: to have good insight and understanding of what is happening in their power converters.”

The integration of CERN’s FGC framework with the most common accelerator control frameworks, including TANGO, results in an important knowledge transfer opportunity, since it allows the power converters specifically developed for CERN to be used by both partner laboratories and industry, in fields from particle physics to medical and biomedical research.

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Accelerating News is a quarterly online publication for the accelerator community.
ISSN: 2296-6536

The publication showcases news and results from the biggest accelerator research and development projects such as ARIES, HL-LHC, TIARA, FCC study, EuroCirCol, EUPRAXIA, EASITrain as well as interesting stories on other accelerator applications. The newsletter also collects upcoming accelerator research conferences and events.

Accelerating News is published 4 times a year, in mid March, mid June, mid September and mid December.

You can read Accelerating News via the homepage http://www.acceleratingnews.eu (link is external) or by email.

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History

Accelerating News evolved from the EuCARD quarterly project newsletter (see past issues), which was first published in June 2009 to a subscription list of approximately 200. Initiated by EuCARD and in collaboration with additional FP7 co-funded projects, the first edition of Accelerating News was published in April 2012 to an initial distribution list of about 800 subscribers. Currently more than 1750 members receive the quarterly issues.

From CERN: “NA61/SHINE gives neutrino experiments a helping hand”

From CERN

How particle measurements made by the NA61/SHINE experiment at CERN are helping neutrino experiments in the US and Japan

Inside the NA61/SHINE experiment at CERN (Image: CERN)

Neutrinos are the lightest of all the known particles that have mass. Yet their behaviour as they travel could help answer one of the greatest puzzles in physics: why the present-day universe is made mostly of matter when the Big Bang should have produced equal amounts of matter and antimatter. In two recent papers, the NA61/SHINE collaboration reports particle measurements that are crucial for accelerator-based experiments studying such neutrino behaviour.

Neutrinos come in three types, or “flavours”, and neutrino experiments are measuring with ever increasing detail how they and their antimatter counterparts, antineutrinos, “oscillate” from one flavour to another while they travel. If it turns out that neutrinos and antineutrinos oscillate in a different way from one another, this may partially account for the present-day matter–antimatter imbalance.

Accelerator-based neutrino experiments look for neutrino oscillations by producing a beam of neutrinos of one flavour and measuring the beam after it has travelled a long distance. The neutrino beams are typically produced by firing a beam of high-energy protons into long, thin carbon or beryllium targets. These proton–target interactions produce hadrons, such as pions and kaons, which are focused using magnetic aluminium horns and directed into long tunnels, in which they transform into neutrinos and other particles.

To get a reliable measurement of the neutrino oscillations, the researchers working on these experiments need to estimate the number of neutrinos in the beam before oscillation and how this number varies with the energy of the particles. Estimating this “neutrino flux” is hard, because neutrinos interact very weakly with other particles and cannot be measured easily. To get around this, researchers estimate instead the number of hadrons. But measuring the number of hadrons is also challenging, because there are too many of them to measure precisely.

This is where experiments such as NA61/SHINE at CERN’s Super Proton Synchrotron come in. NA61/SHINE can reproduce the proton–target interactions that generate the hadrons that transform into neutrinos. It can also reproduce subsequent interactions that protons and hadrons undergo in the targets and focusing horns. These subsequent interactions can produce additional neutrino-yielding hadrons.

The NA61/SHINE collaboration has previously measured hadrons generated in experiments at 31 GeV/c proton energy (where c is the speed of light) to help predict the neutrino flux in the Tokai-to-Kamioka (T2K) neutrino-oscillation experiment in Japan. The collaboration has also been gathering data at 60 and 120 GeV/c energies to benefit the MINERνA, NOνA and DUNE experiments at Fermilab in the US. The analysis of these datasets is progressing well and has most recently led to two papers: one describing measurements of interactions of protons with carbon, beryllium and aluminium, and another reporting measurements of interactions of pions with carbon and beryllium.

“These results are crucial for Fermilab’s neutrino experiments,” says Laura Fields, an NA61/SHINE collaboration member and co-spokesperson for MINERνA. “To predict the neutrino fluxes for these experiments, researchers need an extremely detailed simulation of the entire beamline and all of the interactions that happen within it. For that simulation we need to know the probability that each type of interaction will happen, the particles that will be produced, and their properties. So interaction measurements such as the latest ones will be vital to make these simulations much more accurate,” she explains.

“Looking into the future, NA61/SHINE will focus on measurements for the next generation of neutrino-oscillation experiments, including DUNE and T2HK in Japan, to enable these experiments to produce high-precision results in neutrino physics,” Fields concludes.

See also this Experimental Physics newsletter article.

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From CERN: “The plot thickens for a hypothetical “X17” particle”

From CERN

27 November, 2019
Ana Lopes

Additional evidence of an unknown particle from a Hungarian lab gives a new impetus to NA64 searches.

CERN NA64

The NA64 experiment at CERN (Image: CERN)

Fresh evidence of an unknown particle that could carry a fifth force of nature gives the NA64 collaboration at CERN a new incentive to continue searches.

In 2015, a team of scientists spotted [Physical Review Letters] an unexpected glitch, or “anomaly”, in a nuclear transition that could be explained by the production of an unknown particle. About a year later, theorists suggested [Physical Review Letters] that the new particle could be evidence of a new fundamental force of nature, in addition to electromagnetism, gravity and the strong and weak forces. The findings caught worldwide attention and prompted, among other studies, a direct search [Physical Review Letters] for the particle by the NA64 collaboration at CERN.

A new paper from the same team, led by Attila Krasznahorkay at the Atomki institute in Hungary, now reports another anomaly, in a similar nuclear transition, that could also be explained by the same hypothetical particle.

The first anomaly spotted by Krasznahorkay’s team was seen in a transition of beryllium-8 nuclei. This transition emits a high-energy virtual photon that transforms into an electron and its antimatter counterpart, a positron. Examining the number of electron–positron pairs at different angles of separation, the researchers found an unexpected surplus of pairs at a separation angle of about 140º. In contrast, theory predicts that the number of pairs decreases with increasing separation angle, with no excess at a particular angle. Krasznahorkay and colleagues reasoned that the excess could be interpreted by the production of a new particle with a mass of about 17 million electronvolts (MeV), the “X17” particle, which would transform into an electron–positron pair.

The latest anomaly reported by Krasznahorkay’s team, in a paper [.pdf above] that has yet to be peer-reviewed, is also in the form of an excess of electron–positron pairs, but this time the excess is from a transition of helium-4 nuclei. “In this case, the excess occurs at an angle 115º but it can also be interpreted by the production of a particle with a mass of about 17 MeV,” explained Krasznahorkay. “The result lends support to our previous result and the possible existence of a new elementary particle,” he adds.

Sergei Gninenko, spokesperson for the NA64 collaboration at CERN, which has not found signs of X17 in its direct search, says: “The Atomki anomalies could be due to an experimental effect, a nuclear physics effect or something completely new such as a new particle. To test the hypothesis that they are caused by a new particle, both a detailed theoretical analysis of the compatibility between the beryllium-8 and the helium-4 results as well as independent experimental confirmation is crucial.”

The NA64 collaboration searches for X17 by firing a beam of tens of billions of electrons from the Super Proton Synchrotron accelerator onto a fixed target.

The Super Proton Synchrotron (SPS), CERN’s second-largest accelerator

If X17 did exist, the interactions between the electrons and nuclei in the target would sometimes produce this particle, which would then transform into an electron–positron pair. The collaboration has so far found no indication that such events took place, but its datasets allowed them to exclude part of the possible values for the strength of the interaction between X17 and an electron. The team is now upgrading their detector for the next round of searches, which are expected to be more challenging but at the same time more exciting, says Gninenko.

Among other experiments that could also hunt for X17 in direct searches are the LHCb experiment and the recently approved FASER experiment, both at CERN.

CERN/LHCb detector

CERN FASER experiment schematic

Jesse Thaler, a theoretical physicist from the Massachusetts Institute of Technology, says: “By 2023, the LHCb experiment should be able to make a definitive measurement to confirm or refute the interpretation of the Atomki anomalies as arising from a new fundamental force. In the meantime, experiments such as NA64 can continue to chip away at the possible values for the hypothetical particle’s properties, and every new analysis brings with it the possibility (however remote) of discovery.”

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From CERN: “LHCf gears up to probe birth of cosmic-ray showers”

From CERN

11 November, 2019
Ana Lopes

CERN LHCf

One of the LHCf experiment’s two detectors, LHCf Arm2, seen here during installation into a particle absorber that surrounds the LHC’s beam pipe. (Image: Lorenzo Bonechi)

Cosmic rays are particles from outer space, typically protons, travelling at almost the speed of light. When the most energetic of these particles strike the atmosphere of our planet, they interact with atomic nuclei in the atmosphere and produce cascades of secondary particles that shower down to the Earth’s surface. These extensive air showers, as they are known, are similar to the cascades of particles that are created in collisions inside particle colliders such as CERN’s Large Hadron Collider (LHC). In the next LHC, run starting in 2021, the smallest of the LHC experiments – the LHCf experiment – is set to probe the first interaction that triggers these cosmic showers.

Observations of extensive air showers are generally interpreted using computer simulations that involve a model of how cosmic rays interact with atomic nuclei in the atmosphere. But different models exist and it’s unclear which one is the most appropriate. The LHCf experiment is in an ideal position to test these models and help shed light on cosmic-ray interactions.

In contrast to the main LHC experiments, which measure particles emitted at large angles from the collision line, the LHCf experiment measures particles that fly out in the “forward” direction, that is, at small angles from the collision line. These particles, which carry a large portion of the collision energy, can be used to probe the small angles and high energies at which the predictions from the different models don’t match.

Using data from proton–proton LHC collisions at an energy of 13 TeV, LHCf has recently measured how the number of forward photons and neutrons varies with particle energy at previously unexplored high energies. These measurements agree better with some models than others, and they are being factored in by modellers of extensive air showers.

In the next LHC run, LHCf should extend the range of particle energies probed, due to the planned higher collision energy. In addition, and thanks to ongoing upgrade work, the experiment should also increase the number and type of particles that are detected and studied.

What’s more, the experiment plans to measure forward particles emitted from collisions of protons with light ions, most likely oxygen ions. The first interactions that trigger extensive air showers in the atmosphere involve mainly light atomic nuclei such as oxygen and nitrogen. LHCf could therefore probe such an interaction in the next run, casting new light on cosmic-ray interaction models at high energies.

Find out more in the Experimental Physics newsletter article.

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From CERN: “CERN Council appoints Fabiola Gianotti for second term of office as CERN Director General”

From CERN

6 November, 2019

At its 195th Session today, the CERN Council selected Fabiola Gianotti, as the Organization’s next Director-General, for her second term of office.

President of the CERN Council, Ursula Bassler and Director-General of CERN, Fabiola Gianotti (Image: CERN)

At its 195th Session today, the CERN Council selected Fabiola Gianotti, as the Organization’s next Director-General, for her second term of office. The appointment will be formalised at the December Session of the Council, and Gianotti’s new five-year term of office will begin on 1 January 2021. This is the first time in CERN’s history that a Director-General has been appointed for a full second term.

“I congratulate Fabiola Gianotti very warmly for her reappointment as Director-General for another five-year term of office. With her at the helm, CERN will continue to benefit from her strong leadership and experience, especially for important upcoming projects such as the High-Luminosity LHC, implementation of the European Strategy for Particle Physics, and the construction of the Science Gateway,” said President of the CERN Council, Ursula Bassler. “During her first term, she excelled in leading our diverse and international scientific organisation, becoming a role model, especially for women in science”.

“I am deeply grateful to the CERN Council for their renewed trust. It is a great privilege and a huge responsibility,” said CERN Director-General, Fabiola Gianotti. “The following years will be crucial for laying the foundations of CERN’s future projects and I am honoured to have the opportunity to work with the CERN Member States, Associate Member States, other international partners and the worldwide particle physics community.”

Gianotti has been CERN’s Director-General since 1 January 2016. She received her Ph.D. in experimental particle physics from the University of Milano in 1989 and has been a research physicist at CERN since 1994. She was the leader of the ATLAS experiment’s collaboration from March 2009 to February 2013, including the period in which the LHC experiments ATLAS and CMS announced the discovery of the Higgs boson. The discovery was recognised in 2013 with the Nobel Prize in Physics being awarded to theorists François Englert and Peter Higgs. Gianotti is a member of many international committees, and has received numerous prestigious awards. She was the first woman to become the Director-General of CERN.

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From CERN: “Medipix: Two decades of turning technology into applications”

From CERN

18 October, 2019

The story of how detector components ended up in medical imaging, in art restoration and even in space.

The Timepix3 chip developed by the Medipix3 collaboration (Image: CERN)

How could microchips developed for detectors at the Large Hadron Collider (LHC) be used beyond high-energy physics? This was a question that led to the Medipix and Timepix families of pixel-sensor chips. Researchers saw many possible applications for this technology, and for the last 20 years these chips have been used in medical imaging, in spotting forgeries in the art world, in detecting radioactive material and more. A recent CERN symposium commemorated the two decades since the Medipix2 collaboration was established, in 1999.

Pixel-sensor chips are used in detectors at the LHC to trace the paths of electrically charged particles. When a particle hits the sensor, it deposits a charge that is processed by the electronics. This is similar to light hitting pixels in a digital camera, but instead they register particles up to 40 million times a second.

In the late 1990s, engineers and physicists at CERN were developing integrated circuits for pixel technologies. They realised that adding a counter to each pixel and counting the number of particles hitting the sensors could allow the chips to be used for medical imaging. The Medipix2 chip was born. Later, the Timepix chip added the ability to record either the arrival time of the particles or the energy deposited within a pixel.

As the chips evolved from Medipix2 to Medipix3, their growing use in medical imaging led to the first colour X-ray of parts of the human body in 2018, with the first clinical trials now beginning in New Zealand. In addition, the versatile chips have gone beyond medicine, for example, a start-up called InsightART allows researchers to use Medipix3 chips to peer through the layers of works of art and study the composition of materials to determine the authenticity of pieces attributed to renowned artists.

The team behind InsightART, based in Prague, recently scanned an alleged Van Gogh, concluding that the work was most likely to have been produced by the Dutch master, having observed an underlying sketch very similar to other figures Van Gogh painted at the time. The work will be sent to the Van Gogh Museum to be vetted with this evidence, and it might be that not one but two Van Goghs have been found in the same piece.

Timepix-based detectors have been aboard the International Space Station since 2012 to measure the radiation dose to which astronauts and equipment are exposed, and in 2015, high-school students from the UK sent their own Timepix-based detector to the ISS with astronaut Tim Peake. The ability of the chips to detect gamma rays has been exploited to help with the decommissioning of nuclear reactors and is being evaluated for the detection of thyroid cancer with greater resolution than before and with a lower radiation dose to the patient.

The Medipix and Timepix chips, developed by three collaborations involving around 32 institutes in total, have been remarkable examples of knowledge transfer from CERN to wider society.

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From CERN: “LS2 Report: renovation of the electrical infrastructure”

From CERN

15 October, 2019
Anaïs Schaeffer

The BE1 input station in Prévessin is currently undergoing maintenance and consolidation work (Image: CERN)

You arrive at your office, switch on the lights and pick up the phone, while your computer hums into life. Without electricity, the scenario is slightly different… CERN’s electrical network is so reliable that we forget what’s going on behind the scenes.

The Laboratory’s electrical infrastructure – which plays an essential role in the excellent performance of our experiments and accelerators, and of all CERN facilities – is anything but trivial. In its nominal configuration, it comprises two substations (BE1 and BE2) with an input voltage of 400 kilovolts (kV), supplied by the French electrical grid. Downstream, these are connected to another substation that lowers the voltage to 66 kV. Part of this network supplies facilities several kilometres away (notably in the LHC), while the other undergoes a further conversion to 18 kV in order to supply the nearby Meyrin and Prévessin sites, as well as the SPS. To provide redundancy, CERN’s electrical infrastructure is also connected to the Swiss grid, ensuring that a reduced power supply continues in the event of a problem with the French grid or CERN’s internal network. The switchover to the Swiss grid happens automatically thanks to an “auto-transfer” system.

During LS2, due to the major renovation and maintenance work under way, CERN’s electrical network is working somewhat differently. “At the beginning of July, the BE1 input station was disconnected. We are now consolidating its protection system because, since this station dates from the 1970s, some of its equipment had reached the end of its life,” says Davide Bozzini, technical coordinator in the Electrical Engineering (EN-EL) group. During the course of the work, which should finish some time in November, the BE2 substation is therefore supplying the entire Laboratory alone.

CERN’s newest and biggest power transformer, for the new BE2 electrical substation, was installed in September 2018 to reinforce CERN’s electrical network (Image: CERN)

In mid-September, Meyrin’s main substation, ME9, which has supplied the site with 18 kV since the 1960s, was “unplugged”. It is being completely renovated and should come back into operation at the end of April 2020. In parallel, the auto-transfer system will also be entirely renovated. While these two renovations are taking place, the connection to the Swiss grid has also had to be suspended. This enables the EN-EL group to carry out important work on the ME9 substation, but also deprives CERN’s general network of one of its sources, which could, in rare cases, lead to temporary power cuts*.

Major work is also under way on the SPS, where five of the seven 18 kV substations located at the seven SPS surface points are being renovated. Work on four of them required new buildings to be constructed, which meant that the EN-EL group could start work before LS2 began, while the accelerator was still running.

The EN-EL group is also working on the LHC Injectors Upgrade (LIU) project. “Our LIU activities are very varied, just like the needs of our clients,” says Davide Bozzini. “In the PS Booster and the PS, for example, we have replaced several electrical boards and low-voltage switch boxes dating from the 1970s, as well as the lighting systems, which were antiquated and have now been replaced with new radiation-resistant lights. The latter were developed by the EN-EL group in collaboration with manufacturers.”

Many other activities, notably maintenance, are also under way in preparation for future runs: maintenance of several hundred transformers and circuit breakers, replacement of the batteries of critical supply systems in the LHC, updating of network status control systems, etc. Currently, more than 200 people (personnel from CERN and from external companies) are working on the consolidation, maintenance and operation of CERN’s electrical infrastructure, on which depend all the activities carried out at the Laboratory.

See the full article here.

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From CERN: “From cosmic rays to clouds”

From CERN

10 October, 2019
Ana Lopes

A new run of the CLOUD experiment examines the direct effect of cosmic rays on clouds.

The CLOUD experiment in the CERN East Hall at the start of the CLOUDy run, on 23 September 2019. The chamber is enclosed inside a thermal housing that precisely controls the temperature between -65 °C and +40 °C. Instruments surrounding the chamber continuously sample and analyse its contents. (Image: CERN)

CERN’s colossal complex of accelerators is in the midst of a two-year shutdown for upgrade work. But that doesn’t mean all experiments at the Laboratory have ceased to operate. The CLOUD experiment, for example, has just started a data run that will last until the end of November.

The CLOUD experiment studies how ions produced by high-energy particles called cosmic rays affect aerosol particles, clouds and the climate. It uses a special cloud chamber and a beam of particles from the Proton Synchrotron to provide an artificial source of cosmic rays. For this run, however, the cosmic rays are instead natural high-energy particles from cosmic objects such as exploding stars.

“Cosmic rays, whether natural or artificial, leave a trail of ions in the chamber,” explains CLOUD spokesperson Jasper Kirkby, “but the Proton Synchrotron provides cosmic rays that can be adjusted over the full range of ionisation rates occurring in the troposphere, which comprises the lowest ten kilometres of the atmosphere. That said, we can also make progress with the steady flux of natural cosmic rays that make it into our chamber, and this is what we’re doing now.”

In its 10 years of operation, CLOUD has made several important discoveries on the vapours that form aerosol particles in the atmosphere and can seed clouds. Although most aerosol particle formation requires sulphuric acid, CLOUD has shown that aerosols can form purely from biogenic vapours emitted by trees, and that their formation rate is enhanced by cosmic rays by up to a factor 100.

Most of CLOUD’s data runs are aerosol runs, in which aerosols form and grow inside the chamber under simulated conditions of sunlight and cosmic-ray ionisation. The run that has just started is of the “CLOUDy” type, which studies the ice- and liquid-cloud-seeding properties of various aerosol species grown in the chamber, and direct effects of cosmic-ray ionisation on clouds.

The present run uses the most comprehensive array of instruments ever assembled for CLOUDy experiments, including several instruments dedicated to measuring the ice- and liquid-cloud-seeding properties of aerosols over the full range of tropospheric temperatures. In addition, the CERN CLOUD team has built a novel generator of electrically charged cloud seeds to investigate the effects of charged aerosols on cloud formation and dynamics.

“Direct effects of cosmic-ray ionisation on the formation of fair-weather clouds are highly speculative and almost completely unexplored experimentally,” says Kirkby. “So this run could be the most boring we’ve ever done – or the most exciting! We won’t know until we try, but by the end of the CLOUD experiment, we want to be able to answer definitively whether cosmic rays affect clouds and the climate, and not leave any stone unturned.”

See the full article here.

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From CERN : “NA62 spots two potential instances of rare particle decay”

From CERN

23 September, 2019
Ana Lopes

The NA62 experiment has detected two candidate events for the decay of a positively charged kaon into a pion and a neutrino–antineutrino pair.

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Are there new, unknown particles that can explain dark matter and other mysteries of the universe? To try to answer this question, particle physicists typically sift through the myriad of particles that are produced in particle collisions. But they also have an indirect but powerful way of looking for new particles, which is to measure processes that are both rare and precisely predicted by the Standard Model of particle physics. A slight discrepancy between the Standard Model prediction and a high-precision measurement would be a sign of new particles or phenomena never before observed.

One such process is the transformation, or “decay”, of a positively charged variant of a particle known as kaon into a positively charged pion and a neutrino–antineutrino pair. In a seminar that took place today at CERN, the NA62 collaboration reported two potential instances of this ultra-rare kaon decay. The result, first presented at the International Conference on Kaon Physics, shows the experiment’s potential to make a precise test of the Standard Model.

The Standard Model predicts that the odds of a positively charged kaon decaying into a positively charged pion and a neutrino–antineutrino pair (K+ → π+ ν ν) are only about one in ten billion, with an uncertainty of less than ten percent. Finding a deviation, even if small, from this prediction would indicate new physics beyond the Standard Model.

The NA62 experiment produces positively charged kaons (K+) and other particles by hitting a beryllium target with protons from the Super Proton Synchrotron accelerator. It then uses several types of detector to identify and measure the K+ kaons and the particles into which they decay.

In 2018, the NA62 team reported finding one candidate event for the K+ → π+ ν ν decay in a dataset recorded in 2016 that comprised about 100 billion K+ decays. In its new study, the collaboration analysed an approximately 10-fold larger dataset recorded in 2017 and spotted two candidate events. By combining this result with the previous result, the team finds that the relative frequency (known as “branching ratio”) of the K+ → π+ ν ν decay would be at most 24.4 in 100 billion K+ decays. This combined result is compatible with the Standard Model prediction and allowed the team to put limits on beyond-Standard-Model theories that predict frequencies larger than this upper bound.

“This is a great achievement and one we will build upon. Having clearly established our experimental technique, we’ll now explore ways to perfect it using a dataset that we took in 2018,” says spokesperson Cristina Lazzeroni. “The 2018 dataset is twice as large as the 2017 dataset, so it should allow us to find more events and make a more precise test of the Standard Model.”

For a detailed account of the results, see the recording of the CERN seminar and the EP newsletter article.

See the full article here.

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Please help promote STEM in your local schools.

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Meet CERN in a variety of places:

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THE FOUR MAJOR PROJECT COLLABORATIONS

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