DUNE will measure the products of neutrino interactions with argon nuclei at the far detector. But what is the probability for a muon neutrino to oscillate to an electron neutrino, as a function of energy? To obtain this probability from our far detector data, we must know the flux of neutrinos produced at Fermilab, the cross section for neutrino scattering on argon, and the relationship between what the detector sees and the neutrino energy. A near detector can provide this crucial information.
The Near Detector Task Force, led by Steve Brice and expected to produce a final report and disband by this coming April, is evaluating three possible near detector designs: a liquid argon TPC (LArTPC), a high-pressure gaseous argon TPC (GArTPC), and a low-mass, fine-grained tracking detector (FGT).
MINOS and NOvA designed their near detectors to be as similar as possible to their far detectors. This strategy has several advantages. In particular, neutrinos interact with the same mix of nuclei at both near and far detectors, and many of the same algorithms can be used to determine the flavor and energy of the neutrinos. A LArTPC near detector would provide some advantages for DUNE, as well, however the decision is not so simple in our case. Given the high intensity expected from the LBNF beam and the long drift time of a TPC, a near LArTPC detector would see many neutrino interactions in a single beam spill, but with ambiguities between position and timing that may be challenging to resolve.
The intense LBNF beam permits DUNE to also consider pursuing a relatively low-mass near detector and still achieve a sufficient interaction rate. This option leads to a potentially higher-resolution detector that can make even finer-grained measurements of neutrino interactions than a LArTPC can.
DUNE is pursuing a strategy to agree on a Near Detector concept by the end of the 2017, which will then be taken forward to a full conceptual design. To this end DUNE has set up a new Near Detector Concept Study.
Starting with the work from the the task force, this new effort will develop the DUNE collaboration Near Detector concept. In the end, the concept may combine two or more of the above detector technologies into a hybrid near detector system.
The Near Detector Concept Study will host a three-day workshop at Fermilab March 27-29, 2017 open to anyone interested in this effort. The group expects to narrow the scope to two or three concepts by the May collaboration meeting, hold a second workshop this summer, and present the options to the collaboration at the August meeting. The goal is to settle on design concept for the near detector by the end of this year.