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Time to resume data taking in ARCA

15 September 2021 – after the recovery of two old detection units, already left disconnected after previous sea campaigns – the so-called PPM-DU (Pre-Production Model of Detection Unit), a 3-digital optical module unit used for qualification of the project in the sea as early as in 2014, and one of the first prototype full-size detection units deployed in spring 2016, the sea campaign of ARCA has been completed today.

A lot of good work has been done in this intense week – and we are very grateful for that to the onshore and offshore teams. We also thank all the various institutes which contributed to the construction and preparation to deployment of the detection units – in next entries on this blog we will report on these demanding activities.

As a summary, during this sea campaign:

  • the positioning system has been maintained by installing two acoustic beacons and recovering an exhausted one (these are autonomous devices running on batteries which need to be refurbished in due time)
  • five interlink cables were installed on the sea bottom
  • three new detection units were installed, i.e.: deployed to the sea bottom, connected to the submarine infrastructure, unfurled to their nominal shape (standing for almost 700 m above the sea floor) and proved to work
  • the launcher vehicles of the three installed detection units and the cable trays used for deploying the cables were of course recovered, to be reused for next campaigns

After completing this set of operations, Handin Tide safely sailed back to the port of Malta.

Note that it was decided not to install the remaining two detection units which were onboard the ship, due to a mechanical issue that will be solved. These two detection units have been taken back to shore. After adequate refurbishment, they will be added to those already in preparation. Nothing is lost therefore: they will be included in the next sea campaign.

In the end… it’s time to resume detector operation of ARCA now!

The KM3NeT Collaboration is very grateful to the onshore (in the picture) and offshore teams for their hard work, instrumental for the success of this sea campaign – note that the full operation was performed respecting all applicable rules against COVID-19: our onshore team got so close together only for the time of a… “cheese”!

ARCA enlarged with 3 new detection units!

14 September 2021 – the ARCA telescope is now enlarged with 3 new detection units.

The procedure for installing a detection unit in ARCA is as follows: firstly the detection unit is lowered from the deck of the ship. When it reaches a low level above the sea floor, the ROV (the submarine vehicle operated from the ship) comes in play: it takes a bridle and helps to guide the detection unit to its target position on the sea bottom; it also rotates it so that the panel for connection of the submarine cable faces the direction of the submarine junction box. Only at that point, the detection unit is lowered on the sea floor. After a quick visual check, the ROV detaches the deployment line. The ROV then picks up the cable which had been previously routed on the sea bottom and which is connected to the junction box on the opposite end, and plugs it to the detection unit. Then the onshore team is asked to perform a first round of test to ensure that the detection unit meets its functional requirements. After that, the ROV opens a release mechanism that lets the deployment vehicle on which the detection unit is furled free to go. The vehicle is buoyant and starts coming up; while doing so, it rotates, leaving the detection unit, which is tied to the anchor on the sea floor, upright – a sort of giant, and reversed yo-yo!

After unfurling, the deployment vehicle is recovered from the ship, to be reused for next deployments.

A final test of the newly installed and unfurled detection unit is then performed to confirm that the detection unit works as expected.

This happened three times today!

An optical spectrum analyzer is used in the shore station for a check of the quality of the communications with the detection unit (almost 100 km away, 3,500 m deep). Each signal (in the form of a peak) in the plot corresponds to one of the optical modules of the detection unit. Believe it: when this plot appears on the screen of the instrument, it is a fantastic reward for all the hard work done in the sea campaign and before!











A very busy day, offshore and onshore

13 September 2021 – Still a day packed of activities today!

The status at the moment is that all interlink cables have been layed down on the sea floor and two detection units have been deployed and connected to the junction box. The detection units are still furled on their launcher vehicles; they will be allowed to unfurl tomorrow – since the launcher vehicle has to be recovered from the ship after it reaches the surface, it is better to perform this operation in the daylight.

Pre-unfurling functional tests performed from the onshore control station show that those first two detection units are in good order.

Deployments of the next detection units will continue during the night.

The onshore team in the control station at Portopalo di Capo Passero, Sicily, Italy.









Good progress, despite adverse sea condition

12 September 2021 – there has been good progress in the operation so far!

The two cable reels are also deployed. The cables for connecting four detection units are already layed on the sea bottom and connected to the junction box. There is only one cable left to install.

While proceeding with these activities, however, the weather conditions worsened. The sky was still sunny, but waves mounted high: “We have a lot of sun here, but we are dancing a lot” commented Daniele Vivolo, who is among the KM3NeT team onboard the ship.

In such situation the risks when putting the equipment in water increase significantly. It was therefore decided to put the operation on hold, waiting for an improvement of the sea state.

In late afternoon, the sea had calmed down significantly, and the operations were resumed.

As we write this post, the first detection unit of the set of five included in this campaign is already in water, travelling into the deep, dark sea, down to 3,500 meters depth. There it will meet the ROV (the submarine vehicle operated from the ship), which will take care of the next steps: to assist in carefully positioning the detection unit on the sea bottom and to connect it to the cable already in place. Have a safe trip!

In the movie: the first detection unit is prepared for deployment.

First day of deployments at the ARCA site

11 September 2021 – operations are proceeding smoothly on Handin Tide.

The two new optical beacons of the positioning system are already placed on the sea bottom – these are autonomous devices not requiring a connection to the sea-floor network.

The deployment of the two reels carrying the long interlink cables for the detection units is proceeding. Installation of these cables requires time, because once a reel has reached the sea bottom, each cable has to be spooled off and layed down on the sea floor. These cables will be later used for connecting each detection unit to the submarine junction box which is already at the site (and connected to the 6 detection units already installed).

Once installation of the cables is completed, the deployment of the detection units can start – tomorrow!

The deck of the Handin Tide at the start of the operations (note that the yellow vehicle on the left is the Remotely Operated Vehicle – ROV – to be used for underwater operations).











Liveblog about the ongoing sea operation for ARCA

10 September 2021 – In the evening of September 10, five new detection units of KM3NeT, onboard the Handin Tide, will sail from Malta headed to the KM3NeT/ARCA detection site. This site is located 80 km off the coast of Capo Passero, Sicily (Italy). During a 1-week operation, the detection units will be deployed and connected to the ARCA neutrino telescope at 3,500 m depth, adding up to the six already in operation.

The expectation is high for this new, important step in the construction of KM3NeT. Despite the pandemic, the Collaboration has worked hard to keep the high integration speed needed for such an ambitious project. The detection units include components prepared in various European laboratories, and also the integration, testing and installation of the units on their deployment vehicles was a joint effort of many different KM3NeT teams.

As we write this note, the detection units are safely restrained on the deck of Handin Tide, the ship crew and the KM3NeT offshore team are onboard and ready, and the ship is about to set sail. Onshore, everything is ready in the control station in Portopalo di Capo Passero. The motivation, everywhere, is very high.

We look forward to several days packed with hard work and documented with extraordinary images from the sea surface and the deep sea.

Follow the action while it takes place through our social media channels and our ARCA-blog!



The detection units awaiting deployment on the deck of Handin Tide. Note that the equipment has been already prepared in the order in which it will be moved off the ship: first, two tripods carrying an acoustic beacon each (partially visible in the picture) for the acoustic positioning system, then the reels carrying long cables for connection to the existing submarine network on the sea floor, then the detection units.

Handin Tide left the harbour of Malta

10 September 2021 – the Handin Tide left the port of Malta around 5 p.m. CEST.

The navigation to the KM3NeT site is estimated to take about 10 hours.

The weather forecast is good. The activity on site will start early morning tomorrow.

Keep following the  ARCA-blog.

KM3NeT at ICRC2021

29 July 2021 – The International Cosmic Ray Conference (ICRC) has come to an end after two intense weeks.

The biannual conference organised under auspices of IUPAP, the International Union of Pure and Applied Physics. This year, the 37th edition of the conference was organised as an online version by DESY Zeuthen in Germany. The KM3NeT Collaboration participated in the conference with many contributions accepted by the International Science Committee of the conference.

Paschal Coyle, Spokesperson of the KM3NeT Collaboration, was invited to present a review talk on underwater neutrino telescopes, including obviously KM3NeT, but also its older sister ANTARES, the GVD telescope in Lake Baikal in Siberia, Russia and the new initiative P-ONE offshore the coast of Canada in the Pacific Ocean:


Five more talks covered the very first results obtained with ORCA and ARCA, as well as the prospects for neutrino oscillation measurements and mass ordering determination. With only 6 detection units ARCA6 sees candidates for atmospheric neutrinos; with only 6 detection units ORCA6 sees the effect of oscillation:

In addition, more than 20 poster contributions were presented by the members of our Collaboration. Among them, Thijs van Eden and Jordan Seneca, two PhD students at Nikhef, Amsterdam, who were awarded the best poster prize for their contribution discussing reconstruction of single and double cascade in KM3NeT. Congratulations Thijs and Jordan!



Yet another virtual spring meeting

A few weeks ago, KM3NeT held its two-week long spring meeting, once again virtually, like almost all meetings nowadays.

With twelve detection units operating in the ARCA and ORCA detectors, it was a joy to discuss the progress of the data analysis groups and prepare for the reports at the summer conferences. With our smooth network of almost twenty production sites new detection units are being prepared at the maximum speed that the COVID-19 restrictions allow. New deployment campaigns are in preparation.

Although at a distance, we felt close to each other thanks to the virtual coffee breaks in the gather town set up by our colleagues of Laboratoire de Physique Corpusculaire de Caen (many thanks!). We concluded the meeting with an exciting quest to fix the unexpected problems found in a virtual shift room: this was a run against the clock to find out the password to get free from the locked room and reconvene for a final party at the bottom of the sea – real shifts won’t ever be so hilarious!

As usual, the meeting was also the occasion to welcome the many newcomers and to remind the accomplishments of those that are leaving the collaboration for a next step in their professional career. Thanks a lot for your work for KM3NeT. We wish you all the best and success in your  new working environment!

We sincerely congratulate Diego Real whose PhD thesis was recently awarded an important prize of the Spanish Society of Astronomy!

We were pleased to welcome new teams from the University of Toulon and Institut de Ciències del Mar in Barcelona – both aim at new investigations in the deep-sea environment and have already collaborated with the ANTARES telescope and the NEMO pilot project in the Mediterranean.

Among the new activities announced at the meeting: an Open Science Committee has been established, while the representatives of our early-career-scientists put forward a plan for making the life of our youngest collaborators easier even in these difficult times.

It was a fruitful and pleasant meeting!

The call for an institute to organise the next Collaboration meeting in the fall has been opened – hopefully the next meeting will be in person?

New publication: Neutrino Mass Ordering and Oscillation Parameters

05 May 2021 – The potential of KM3NeT to measure key properties of neutrinos – in March 2021, the KM3NeT Collaboration released a publication showing that  KM3NeT with its ORCA detector will be in an excellent position to study the phenomenon of neutrino oscillations!

Three neutrino flavours and oscillation

Neutrinos come in three species called flavours: the electron neutrino, the muon neutrino, and the tau neutrino. In the 1960’s, the first experiment was started to study the sun by measuring the flux of electron neutrinos that the solar nuclear processes copiously produce. The experiment revealed that the flux was inconsistent with the expectations! Many solutions were put forward to explain the discrepancy until a measurement of the flux of neutrinos of all three flavours was made and found compatible with the expectation. This key measurement meant that the expectations for the neutrino flux produced by the sun were correct and that the electron neutrinos were converted into other flavours while traveling to Earth. This phenomenon is called neutrino oscillation, subsequently detected also in other contexts. This phenomenon is only explained by quantum mechanics and requires that the neutrinos, initially thought massless, are actually massive!

Neutrino admixture

The neutrinos with definite masses happen to be different from the neutrinos with definite flavours. In other words, a neutrino of a given flavour is an admixture of the neutrinos of definite mass as shown in the top part of fig:1. Because of the mass difference between the neutrino mass states, these states do not propagate at the same velocity. As a result, the neutrino admixture evolves during the propagation, as shown in the bottom part of fig:1. In other words, while propagating, the neutrino flavour changes.


Figure 1: Top:the mass state admixtures corresponding to the flavour (so-called weak) states for 2 neutrinos. Middle: a muon neutrino is produced at t=0. As time goes, the neutrino mixture varies reaching periodically a pure muon neutrino state. The probability for the neutrino to be detected in each flavour is represented at the bottom. Reproduced from Slansky et al. Los Alamos Sci. 25 (1997) pp. 28-63.

Using atmospheric neutrinos

The KM3NeT Collaboration aims to study this oscillation phenomenon using neutrinos produced in the collisions of cosmic rays onto the atmosphere. Using these neutrinos, the KM3NeT Collaboration will be able to measure one of the key parameters ruling the neutrino admixture: the so-called θ23 mixing angle. We will also be able to measure the squared mass difference between two of the neutrino mass states – δm232 – and to tell which of the three mass states is the heaviest, i.e. determining the neutrino mass ordering as shown in fig:2. Finally, we will check if the standard three neutrino oscillation paradigm is valid by measuring the fraction of cosmic-ray induced neutrinos that have oscillated to the tau neutrino.

Figure 2: Sensitivity to neutrino mass ordering as a function of data taking time for both normal (red upward pointing triangles) and inverted ordering (blue downward pointing triangles). See the paper for more details and the values of the oscillation parameters considered to obtain the result.

Unique potential

The publication relies on precise simulations to determine the sensitivity of the KM3NeT/ORCA detector to these parameters. The prospects show that the experiment has a unique ability to make these measurements and that world best results can be obtained in few years of data taking with the full detector.

The publication has been submitted to EPJ-C and is available as a pre-print as arXiv:2103.09885.