05 February 2020 – The ORCA6 detector of KM3NeT is taking data since 27 January 2020 on a 24/7 scheme. Physicists are ‘on-shift’ to remotely or on-site operate the detector in the deep sea. The recorded data is stored in the computer centres of the KM3NeT Collaboration for further analysis.
The first step is to reconstruct from the recorded light flashes the path of charged particles through the ORCA6 detector. Most of them are muon particles generated in the Earth’s atmosphere and travelling through the detector from above. We showed already an example in the news item of 27 January.
In the video below we show a series of five charged particles entering the detector from below or from the side. This is an indication that they have been created in an interaction of a neutrino with the matter surrounding the detector.
In the picture below, you see the plots that KM3NeT physicists like: six plots showing for each of the six detection units in ORCA6 the optical sensors that – in the pitch dark deep sea – are ‘hit’ by faint light. Each time a sensor is hit, the position of that sensor in the sea and the time it was hit is recorded. The plots show on the y-axis the height of the sensors in the detector and on the x-axis the time. The red circles and the red line show how the light cone generated by a charged particle from below has crossed the detector. As function of time (in nanoseconds), the position of the next hit sensor is higher in the detector, indicating that the particle is travelling upwards. The blue circles are background hits.
With the installation of two more detection units at the French site of KM3NeT, the first phase of building the ORCA detector is completed! Since 27 January 2020, the detector is taking data with six detection units.
During a sea operation the 24-26 January 2020, the two new detection units have been connected to the KM3NeT/ORCA seafloor network at the KM3NeT/ORCA deep sea site, 40 km offshore from Toulon, France. The detection units were successfully positioned twenty metres apart.to within a metre of their target position 2.5 km below the sea surface. This highlights the skills of the staff on board the deployment ship, the precision of the custom acoustic positioning system and the maturity of the deployment method based on an innovative launching vehicle.
Immediate data taking
Using a robot, remotely operated from a second ship, the deployed units were connected to the seafloor network of the ORCA site. After a visual inspection of the detection units by the robot, the power was switched on and data taking with ORCA6 started immediately.
The ORCA detector has now six detection units – hence ORCA6. These are six vertical lines each with 18 sensor modules. A module houses 31 light sensors (photo-multiplier tubes) to record the faint Cherenkov light generated by charged particles in the sea water. That makes now 6x18x31= 3348 photo-multipliers in total in ORCA6. Each photo-multiplier records the intensity of the light flash and when it arrives. A compass, tilt meter and acoustic receiver record the position of the module in the sea water. With these measurements the path the charged particle took through the detector is precisely reconstructed.
The video below shows a selection of down-going cosmic rays (muons) passing through the ORCA6 detector soon after power up.
Operating six detection units is an important milestone for KM3NeT as it marks the completion of the so-called ‘Phase 1’ of the project. In the next phase of KM3NeT/ORCA, the detector will be extended to 115 detection units.
08 November 2019 – We are happy to welcome the Sun Yat-sen University (SYSU), China, in our collaboration!
The HEP group at the School of Physics in SYSU is involved in various aspects of the intensity frontier, cosmic frontier and energy frontier, being involved in the Daya Bay reactor neutrino experiment, the Jiangmen Underground Neutrino Observatory, and the Large High Altitude Air Shower Observatory experiment among others.
The high-energy astrophysics group at the School of Physics and Astronomy focuses on theoretical study and data analysis of extreme high-energy phenomena, such as GRB, SNR and AGN. Together with the Tianqin Research Center at SPA, which is devoted to Tianqin project – a LISA-like space gravitational wave project, the group is focusing on the multi-messenger study, combining information from various messengers from space, such as electromagnetic radiation, neutrinos and gravitational waves.
“In short, the team at SYSU has a broad endeavor in neutrino physics and multi-messenger studies. With the help of KM3NeT, we will be able to further reach the neutrino spectrum in the cosmic frontier, crossing-over with other interesting sciences.” says Lily Yang, PI of the new KM3NeT group.
19 August 2019 – Since this spring, the KM3NeT telescopes are routinely operating with five detection units: four at the ORCA site, one at the ARCA site. First data results have been reported on the international conferences and workshops.
For the ORCA detector, off shore the French Provencal coast, four units were installed and connected to the seabed network. An earlier deployed unit was damaged during inspection and had to be recovered for repair in the labs of the Collaboration. It will be re-deployed in a next sea campaign. Also during the Spring-campaigns, three autonomous acoustic beacons were deployed at the seabed in the vicinity of the ORCA array. They are used for acoustic positioning of the optical modules in the detection units that move with the slowly varying deep sea currents. Sea campaigns for further expansion of the ORCA detector are scheduled after the summer break.
Offshore Sicily at the site of ARCA, after a fix of the seabed network, a detection unit that was deployed three years ago, could be revived and is again taking data since. Currently, the seabed network is being re-designed to allow for the extension of the ARCA detector to more than 200 detector units. The successful though temporary fix of the existing network makes connection of more detection units possible, while waiting for the implementation of the upgraded network.
Differences between ARCA and ORCA
The technology used for the ARCA and ORCA detectors is almost identical, but the difference in volume and height of the detectors and the density of optical modules in the detectors are strikingly different. When finished, the volume of ARCA will be more than 100 times larger then that of ORCA. ARCA will have a volume of about 1 Gton and ORCA ‘only’ about 8 Mton, while the number of optical modules in ARCA will only be twice that of ORCA: about 4000 vs about 2000. Consequently, module density in ORCA will be about five times larger than that in ARCA. How is that achieved? In both detectors, eighteen optical modules are attached to each vertical detection unit. In ARCA, the distance between the lowest and the highest module is about 600. In ORCA this is about 150 m. Also the horizontal spacing between detection units is different: about 90 m in ARCA vs about 20 m in ORCA. Although, ARCA will have only twice the number of detection units, its foot print on the sea bed is much larger that that of ORCA.
The geometrical differences reflect the main scientific purpose for which the detectors will be used. These are also visible in the first character of their names: ARCA stands for ‘Astroparticle Research with Cosmics in the Abyss’. The sparsely instrumented detector is optimised for the detection of high-energy cosmic neutrinos from distant sources in the Universe. ORCA is the acronym for ‘Oscillation Research with Cosmics in the Abyss’. The more densily instrumented detector is optimised to measure lower energy neutrinos, thus providing data for the study of neutrinos oscillating between the three known neutrino flavours. The words ‘in the Abyss’ refer to the locations of the detectors several kilometres deep in the Mediterranean Sea.