cern na62 experiment

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CERN Accelerating science

NA62 is a new Kaon experiment at the CERN SPS accelerator. The goal is to measure the very rare Kaon decay K+-> pi+ nu nubar to make a decisive test of the Standard Model by extracting a 10% measurement of the CKM parameter |Vtd| . The NA62 experiment is situated in the cavern (TCC8 + ECN3) of the SPS North Area High Intensity Facility (NAHIF] where it re-uses existing infrastructure of the former CERN Kaon experiment [NA48].

The involvement of EP- DT group into NA62 is twofold:

STRAW Tracker Project Leader: Hans Danielsson

CERN has engaged together with JINR/Dubna the development and construction of a new ultra light Straw Tracker. The CERN parts are done in cooperation between EP-DT and EP-ESE. This Straw Tracker forms the unique spectrometer for outgoing tracks and consists of four straw tube chambers which are situated downstream of the decay region (see Figure above). A novel technology, developed in collaboration between EP-DT and Dubna, allows using very thin wall straws inside the vacuum tank reducing the material budget to 0.5% radiation length per chamber.

Technical Coordination, Infrastructure and Services: Hans Danielsson/TC

EP-DT provides the Technical Coordinator and is in charge of the overall integration of the experiment. In this context the group provides extensive mechanical and electrical support and assists the Technical Coordinator in his function. Several infrastructure parts are made in EP-DT comprising, in particular, the huge RICH Radiator vessel. In the framework of the Gas and Cooling services EP-DT is involved in the GTK cooling system, and in all the NA62 gas systems.

CERN Accelerating science

New straw trackers for NA62

The NA62 straw tracker is using pioneering CERN technology to measure charged particles from rare kaon decays

11 June, 2012

A precision technique is being tested for the first time at the NA62 experiment. A straw tracker will be placed directly into the experiment’s vacuum tank, allowing physicists to measure precisely the direction and momentum of particles from rare kaon decays. This decay rate may be influenced by particles and processes beyond the Standard Model.

“Though straw detectors have been around since the 1980s, NA62 straw trackers are different - they can work under vacuum,” says project leader Hans Danielsson. Straw detectors are small drift chambers; particles passing through a thin tube ionize gas molecules inside, which send signals as they collide with a wire. After 3 years of research and development, NA62 straws can withstand the high pressure exerted by the gas inside the experiment’s vacuum tank - an impressive 100 metres long by 2.5 m diameter. This is no mean feat, as NA62 straws have to be leak-proof and mechanically stable for over 2 metres to preserve the vacuum. Straw trackers are usually made by winding two conductive tapes in a spiral like the centre of a paper towel roll. Though the technique worked well for the ATLAS TRT straw detectors, it does not make mechanically stable, leak-proof straws, says Hans.

To tackle the problem, the NA62 team developed a new construction technique in collaboration with the Joint Institute for Nuclear Research (JINR) in Russia. A 31 mm band is rolled into a straw shape and then welded shut, leaving a single, 0.6 mm seam along its length. “We used ultrasonic welding to close the straw,” says Hans. “This welding technique not only made the straws completely leak-proof but also gave them the strength to keep them straight and withstand the vacuum pressure without breaking.”

About 2000 straws are now being assembled into 8 modules at CERN. Each module has 8 rows of straws, and each row is rotated 90 degrees to ensure that at least two coordinates are measured for each particle. The modules will be installed in the vacuum tank at four locations.

“We’re testing every straw individually, fitting them into the modules and connecting the electronics,” says Hans. A team from JINR will spend a few weeks testing modules and learning the assembly process.

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CERN Accelerating science

Exotic searches with NA62 experiment

The NA62 experiment at CERN focuses in the study of kaon physics; a branch of physics that has been one of the major protagonists of the field in the second half of the twentieth century, as it played a key role in the development of the Standard Model and in exploring the reasons of the observed CP violation: a phenomenon that may be involved in the observed matter-antimatter asymmetry in the universe.

The NA62 facility at CERN (Image Credits: CERN). 

The experiment aims at the very challenging task of measuring with 10% relative error the branching ratio of the ultra-rare decay K + → π + v vbar which is expected to occur only in about 8 out of 10 11 kaon decays. This will be achieved by means of an intense hadron beam, an accurate kinematical reconstruction and a redundant veto system for identifying and suppressing all background events.

The most immediate possibility to search for new physics is through the core NA62 goal namely the precise measurement of K-> π v vbar which puts a very precise prediction of the Standard Model under scrutiny. Presently, theories of physics beyond the Standard Model have been proposed that would give sizable differences in both K + → π +  v vbar  and K L  → π 0  ν νbar branching ratios. The tiny branching ratios present an experimental challenge as these decays are extremely difficult to measure. NA62 aims at measuring a number of about 100 events in about two years of data taking. For this purpose at least 10 13  K +  decays are required assuming an acceptance of O (∼ 10%). To obtain a contribution of the background below 10%, a rejection factor of 10 12  in rejecting the other kaon decay modes is needed and this is what drives to a large extent the design of the NA62 experiment.

Apart from high-precision measurement of rare processes, the NA62 collaboration is also looking into the possibility of the existence of exotic particles. One key insight is the fact that NA62 is actually dumping a large number of protons in the effort to produce the K + beam. The interactions of these protons can be further studied as they may provide a hint for new physics. Out of the dumped protons, new weakly interacting particles with very long lifetimes could be produced. Another possibility is that such particles could be produced from upstream meson decays.

Babette Dobrich, a CERN fellow working in the NA62 experiment, explains: “Due to their very weak coupling, such particles would be able to traverse the material in front of the decay volume without interacting and reveal themselves by decaying in the sensitive volume of the experiment. Depending on the final states we are expecting, data can be taken in "dump mode" or in parallel with the data taking for kaons by applying appropriate triggers. In this way we look for scalar- and pseudo-scalar bosons, like axions, dark photons and heavy neutral leptons.”

Following, her PhD in particle phenomenology, specifically on new physics searches and QED tests with laser-based experiments, Babette applied to DESY for her first post-doc. Babette’s research activities are focused - but not limited - to axions and axion-like particles. Her interest stems from the fact that particularly QCD axions themselves are an excellent dark matter candidate. She explains: “in general pseudo-scalars have received lately much interest for example in the context of dark matter model-building, because they can be a mediator for the interactions between dark matter and SM particles” and adds: “More generally, until we have a very clear picture of where new physics is hiding, I am a fan of the idea of putting the search instruments that we have at hand to a broad use and NA62 provides an excellent opportunity in this respect.”.

The search for new physics in NA62 presents certain experimental challenges. Perhaps one of the main difficulties is to better understand the halo particle background; mainly muons from upstream meson decays that enter the decay volume in data taking with beam or in "dump mode".

View of the "TAXes" of NA62 (during installation without side- and roof-shielding) downstream of the target in which  NA62's Kaon beam is produced. The "TAXes" act as a dump for all SPS protons that pass the target without interaction. New, weakly interacting particles might be produced from the dumped protons and can be detected in the downstream decay volume. (Image Credit: Sylvain Girod/CERN).  

Searches with NA62 for long-lived new particles complement well LHC as well as lab-size new physics searches. Sticking to the example of axion-like particles, one will find a growing literature arguing for the existence of these particles over a wide mass range. Some regions of their parameter space can be excluded purely by astrophysical arguments. However, in the experimentally unexplored parameter space, LHC experiments could find axions roughly above the GeV scale while there is a number of running and proposed experiments to cover the mass region below keV.

“In the case of NA62, we expect to be mainly sensitive in the MeV up to GeV region, thus helping to fill a gap. Albeit NA62 was not built for this purpose I think we can do a good job in this area. After all, unless we have a very clear picture of where the new physics is, we should make a broad use of the opportunities we have.”

For Babette starting to work with NA62 involved a personal challenge since her previous experimental experience was limited to a lab-based laser experiment in DESY. She recalls: “there were many things I had to learn from the start like certain software tools and some high-energy detector concepts. Once someone told me that I should ‘think less like a theorist’.” and continues “However it turned out I was lucky to join a very welcoming collaboration. Since we are a comparably small experiment, it was easy to identify the right people who could help with a particular question. I am very much indebted to several people who took time to discuss and answer my questions”.

Today there is a growing number of people in the NA62 collaboration interested in this sort of physics. They are brought together under the “long-lived exotica” working group. It turns out that some of the analyses for exotics have many synergies with the core analysis, like the optimization of veto conditions. Regarding the “dump runs" Babette explains: “we realized that even very small samples of just a day  in some instances may have physics impact, whilst being, e.g., a useful tool to asses backgrounds that are also present in regular data taking”.

The NA62 collaboration has put forward a proposal to have some dedicated run-time for the physics searches explained above after the second long shut-down. This is one of the proposals submitted to the Physics Beyond Collider working group. Babette notes: “an easy improvement to get better parameter reach "on paper" would be, for example, to have a "dump" closer to the decay volume. This would make us sensitive to a sizeable un-probed parameter space of particles that -if they exist - now decay before reaching our decay volume. The feasibility of such beam-line modifications has yet to be assessed. But it is already exciting to study our impact on models that we might be able to test in the near future.”

CERN - European Organization for Nuclear Research - Physics Department - NA62

The na62 detector.

The ultra-rare kaon decay experiment relies on the following factors to achieve the required level of background rejection with respect to the signal channel:

• high-resolution timing - to support a high-rate environment;
• kinematic rejection – involving cutting on the square of the missing mass of the observed particles in the decay with respect to the incident kaon vector;
• particle identification of kaons, pions, muons, electrons and photons;
• hermetic vetoing of photons out to large angles and of muons within the acceptance;
• redundancy of information.

• An intense, momentum-selected hadron beam of secondary particles. The K+ component in the beam is positively identified with respect to the other beam particles by an upgraded differential Čerenkov ( CEDAR ) counter;
• The coordinates and momentum of individual beam particles are registered before entering the decay region by 3 silicon pixel tracking detectors ( GTK ) tracking detectors.
• A large-acceptance, magnetic spectrometer with tracking detectors ( STRAW Tracker ) in vacuum are required to detect and measure the coordinates and momentum of charged particles originating from the decay region.
• These are backed-up by a ring-imaging Čerenkov ( RICH ) counter to identify pions with respect to muons.
• A set of photon-veto detectors provides hermetic coverage from zero out to large (~50mr) angles from the decay region. This is assured by the existing, high-resolution, e.m. ( LKR ) calorimeter, supplemented, at small and forward angles, by intermediate ring ( IRC ) and small-angle ( SAC ) calorimeters and, at large angles, by a series of annular photon-veto ( LAV ) detectors.
• The LKr calorimeter is backed up by muon-veto detectors ( MUV ), composed of a two-part hadron calorimeter followed by additional iron and a transversally-segmented hodoscope. This system supplements and provides redundancy with respect to the RICH in the detection and rejection of muons.
• These detectors are complemented by ‘guard-ring’ counters ( CHANTI ) surrounding the last GTK station, to veto charged particles upstream of the decay region and a transversally-segmented, charged-particle hodoscope ( CHOD ), covering the acceptance and located between the RICH and the LKr calorimeter.
• All these components of the detector are inter-connected with a high-performance trigger and data-acquisition (TDAQ) system.      

CERN Accelerating science

Students from Estonia, Japan and the USA win the 11th edition of Beamline for Schools

Three teams of secondary school pupils from Estonia, Japan and the United States have been selected to carry out their own experiments using accelerator beams at CERN and DESY

25 June, 2024

Winners of the 2024 CERN Beamline for Schools competition: Sakura Particles” from Japan (left), “Mavericks” from Estonia (top right) and “SPEEDers” from the USA (bottom right) “(Images: Sakura Particles, Mavericks, SPEEDers)

Geneva and Hamburg, 25 June 2024.  Beamline for Schools (BL4S)  is a physics competition run by CERN , the European laboratory for particle physics, open to secondary school pupils from all around the world. Participants are invited to prepare a proposal for a physics experiment that can be undertaken at the beamline of a particle accelerator, either at CERN or at DESY (Deutsches Elektronen-Synchrotron in Hamburg, Germany). In 2024, three winning teams have been chosen, based on the scientific merit of their proposal and the communication merit of their video.

“Mavericks”, a team from the Secondary School of Sciences in Tallinn and the Hugo Treffner Gymnasium in Tartu, Estonia, and the team “Sakura Particles”, which brings together pupils from Kawawa Senior High School in Kanagawa, Joshigakuin Senior High School and Junten High School in Tokyo, Kawagoe Girls High School in Saitama and Kitano High School in Osaka, Japan, will travel to CERN in September 2024 to perform the experiments that they proposed. The team “SPEEDers” from Andover High School in Andover, USA, will carry out their experiment at a DESY beamline.

A beamline is a facility that provides high-energy fluxes of subatomic particles that can be used to conduct experiments in different fields, including fundamental physics, material science and medicine. 

BL4S started in 2014 in the context of CERN’s 60th anniversary. Over the past 10 years, more than 20 000 pupils from all over the world have taken part in the competition, and 25 teams have been selected as winners. The participation rate has been rising consistently over the years, with a record 461 teams from 78 countries submitting an experiment proposal in 2024. 

“Preparing a proposal for a particle physics experiment is a very challenging task. The success of Beamline for Schools shows that, when provided with the right support, high-school students can design feasible, interesting and imaginative experiments,” says Charlotte Warakaulle, CERN Director for International Relations. “We are continuously impressed by the quality of the proposals, and this year is no exception. The candidates demonstrated impressive creativity and great rigour, two essential qualities for students who might decide to take up scientific careers.”

The fruitful collaboration between CERN and DESY  started in 2019 during a long shutdown period of the CERN accelerators. This is the sixth year that the German laboratory has hosted competition winners. 

“Every year I am very impressed by the creativity and determination of the team members,” says Beate Heinemann, Director in charge of Particle Physics at DESY. “I am already looking forward to hosting the team from the USA this year. This programme is so important to me as it advances not only science but also the cultural exchange between young people from different nations.”

“Our experiment will focus on detector development for high-altitude ballooning applications,” says Saskia Põldmaa, one of the “Mavericks” members, from Estonia. “This is by far the biggest opportunity we have had so far in our lifetime so we will hold onto it dearly. We can’t wait to calibrate our homemade muon detector!”

“Our team focuses on detector development for muon tomography applications. We will test and optimise our homemade two-dimensional position-sensitive detector,” says Chiori Matsushita from the Japanese “Sakura Particles” team. “CERN has always been a dream for us. Finally getting to go there, not as a tourist but to do experiments, is amazing!”

“We focus on beam diagnostics: our aim is to measure and analyse the Smith-Purcell (SP) radiation emitted by different diffraction gratings when DESY’s electron or positron beams pass by,” says Niranjan Nair from the US “SPEEDers” team. “We are thrilled to have the opportunity to not just watch scientific advancement passively, but actively contribute to it at DESY: the ultimate goal of our experiment is to research SP radiation as a tool for beam diagnostics.”

The winning proposals were selected by a committee of CERN and DESY scientists from a shortlist of 49 particularly promising experiments. In addition, three teams will be recognised for the most creative video proposals and another 13 teams for the quality of physics outreach activities they are organising in their local communities, taking advantage of the knowledge gained by participating in BL4S.

Beamline for Schools is an education and outreach project funded by the  CERN & Society Foundation ’s donors.   This 11th edition is supported notably by ROLEX through its Perpetual Planet Initiative and by the Wilhelm and Else Heraeus Foundation.

Further information:

• BL4S website:  https://beamlineforschools.cern/
• 2024 edition:  https://beamline-for-schools.web.cern.ch/2024-edition
• Shortlisted teams and special prizes in 2024:  https://beamline-for-schools.web.cern.ch/sites/default/files/BL4S_all-winners_2024_final.pdf  
• Previous winners:  https://beamlineforschools.cern/resources/winners
• Countries represented among the shortlisted teams: Bahrain, Bangladesh, Belgium, Brazil, Canada, Chile, Czechia, Denmark, Estonia, France, Germany, Greece, Hong Kong SAR China, India, Indonesia, Italy, Japan, Kazakhstan, Pakistan, Poland, Romania, Singapore, Spain, Thailand, Türkiye, United Arab Emirates, United Kingdom, United States. 
• The prizes awarded for the best outreach project have been kindly provided by the Belgian project  “Stars Shine for Everyone” .

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