All new for NA62

This week sees the start of the first run of the new NA62 experiment. This will be a unique opportunity for the collaboration to test its new beam, new detectors and new data acquisition system before the physics run in 2014. Speaking to the Bulletin, the NA62 technical coordinator Ferdinand Hahn shares the many challenges that the various teams faced to be on time for beam. Ready, steady, start!


A Large Angle Veto detector (white) in place in the NA62 decay volume (blue).

With components from almost all the detectors in place downstream of the decay point of the mother particles – the kaons – and of the KTAG detector that tags the kaons before they decay, NA62 is ready for its first technical run. This unique run will test all the equipment as well as the trigger and the data acquisition systems. “This year, we will have about five weeks of beam from the SPS before the long shutdown of all the CERN machines,” says Ferdinand Hahn, NA62 Technical Co-ordinator. “During that long shutdown, and before the restart of the injector chain, we plan to complete the installation of all the remaining detectors.”

Once completed, the NA62 experiment will be CERN’s flagship for the study of rare kaon decays, in particular that where the mother particle decays into a pion and two neutrinos. “Studying rare processes like those involving kaons allows us to make precise tests of the Standard Model as their theoretical predictions are very good," says Augusto Ceccucci, NA62 Spokesperson. "By measuring the rate of some of these decays, we will be able to determine a combination of Cabibbo-Kobayashi-Maskawa matrix elements independently. Discrepancies compared to expectations might be a signature of new physics.”

The technical run will provide the NA62 collaboration with useful information about how the various detectors work together. Including a new beam dump, the experimental set-up extends over a total length of 270 metres, of which 85 metres are in vacuum. “Closing the huge vacuum tank turned out to be a great challenge and we owe much of the credit to our technician Tonio Goncalves Martins De Oliveira,” says Ferdinand Hahn. “Because of some delays during the installation phase, the commissioning time for the new vacuum system was extremely short. However, colleagues from EN-MEF, TE-VSC and other technical units did an outstanding job to allow us to start up the whole system in time.”

Although this run is by no means a test of the physics performance of the experiment, the collaboration expects to be able to reconstruct the tracks of the first kaons during these initial tests. “The KTAG detector will allow us to tag kaons and correlate them with the decay products that leave signals in the downstream detectors,” anticipates Augusto Ceccucci, NA62 Spokesperson. “With a bit of luck, we will be able to reconstruct whole kaon decays.”


The history of kaons at CERN

Kaons are particles made of quarks, one of which is the strange quark. There are charged (K+ and K-) and neutral kaons. The neutral kaons come in two types: a short-lived one (K0S) and a long-lived one (K0L).

CP-violation was first observed in kaon decays at the US Brookhaven laboratory by Christenson, Cronin, Fitch and Turlay in 1964 with their Nobel prize-winning experiment. They showed that long-lived neutral kaons occasionally decay into two pions, a CP-violating process. Sakharov outlined his three conditions soon after, and in 1973, Japanese physicists Kobayashi and Maskawa showed how to incorporate CP-violation into the theoretical framework of electromagnetic and weak forces. Their work pointed the way to CERN’s NA31 and Fermilab's E731 experiments and their successors, NA48 and KTeV.

NA48, the predecessor of NA62, is best known for establishing direct CP-violation in the two pion decays of the neutral kaons about a decade ago. A first extension (NA48/1) studied K0S rare decays while a second extension (NA48/2) focused on the search for CP-violation and the study of ππ scattering in charged kaon decays.



by Antonella Del Rosso