The NA62 Trigger and Data Acquisition (TDAQ) system with the electronic board and its active components, which have been tested for radiation induced effects with muons at ISIS (image copyright: CERN)
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Nobel prize winning physicist Leon Lederman once described his ambition “To see all of physics reduced to a formula so elegant and simple that it will fit easily on the front of a t-shirt.” With the discovery of the Higgs boson, the standard model of particle physics is a step closer to that goal, but there are still discoveries to be made. The NA62 experiment at CERN will help – studying ultra-rare decays in particles called kaons to try and determine the likelihood that top quarks decay into down quarks. The experiment is set to start collecting data in October 2014, and the team have been using ISIS to test their equipment.
In the experiment high energy protons from CERN’s Super Proton Synchrotron are fired into a beryllium target. This creates a beam of almost 1 billion particles every second, about 6% of which are kaons. A small fraction of these kaons will decay, and the decay particles will be identified by detectors. The decays the group are looking for are incredibly rare - in over two years of taking data they expect to see around 80 events. So it is vital to ensure that the detector electronics is robust.
One particular challenge is that the electronics will be exposed to streams of other particles while the experiment is running. There is a risk that exposure to these particles will disrupt the electronics, causing them to fail, or to respond incorrectly. Muons and neutrons are particular causes for concern.
Dr Angela Romano and Dr Antonino Sergi are researchers on NA62 at the University of Birmingham. Dr Romano says, “We are trying to measure a very rare decay, and the circuit boards are in an environment with a high muon flux. We want to be sure that this doesn’t affect the correct operations of the board! There is an insidious problem of single event upsets, where a muon could discharge on the chip and modify the data the board acquires.”
Dr Sergi says, “Our chips will be exposed to very high numbers of muons during the experiment and, because of the rarity of the events we are looking for, we need to be sure that the chance of a single event upset is less than one in 1010. It’s like being able to identify a single table light in the power consumption of the country!”
Using port 4 on the RIKEN-RAL side of ISIS, the team have been able to simulate the muon exposure that the chips will receive in 2 years of operation in less than 10 hours. Dr Romano says, “What we are looking for here is a null result! We are hoping not to see any evidence that muons affect the electronic circuitry, and that will give us confidence that when we run the experiment for real that any decays we see are genuine and not the result of single event upsets.”
On this occasion the NA62 team have been specifically looking at single event upsets caused by muons, but neutrons are also a risk. The NA62 team is currently waiting for the assignment of a 3-day test between July and August 2014 at the VESUVIO instrument at ISIS for testing the electronic board with neutrons.
Dr Romano says "We are very pleased to have established this collaboration with ISIS; the neutron and muon instruments are optimal facilities for rapid testing of radiation induced effects and the support of the ISIS staff, able to help and advise throughout the whole experiment, has been essential to the success of the operation. We are keen in pursuing further the collaboration with ISIS and look forward to the next step of our test with neutrons."
Research date: April 2014
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