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Particle identification (PID) based on Cherenkov-imaging techniques is an essential ingredient of the experimental apparata of several running and future experiments dedicated to hadron physics. The progress of fundamental research in this field requires a continuous and innovative update of this family of particle detectors.

Forthcoming experiments will be even more demanding in terms of performance, and the role of detectors based on Cherenkov-imaging technique in these experimental setups is crucial in various domains of hadron physics: heavy and light quark spectroscopy (superBelle at KEK, PANDA at FAIR, COMPASS at CERN-SPS), rare kaon decays (NA62 at CERN-SPS), nucleon Generalized Parton Distributions and transverse spin structure (COMPASS2 at CERN-SPS, PANDA at FAIR), hadron fragmentation functions in hot nuclear matter (upgrade of ALICE at CERN-LHC), super-dense baryonic matter (CBM at FAIR), hypernuclei (PANDA at FAIR) and precision measurements of CP violation in B decays (experiments at superB factories).

This JRA aims at opening the way to new, revolutionary photon detectors based on carbon nanotubes. Once developed, these can be used in a variety of detectors based on Cherenkov-imaging technique.

A carbon nanotube (CNT) is a layer of graphite rolled into a cylinder. The cylindrical material is a one-dimensional structure with diameter that ranges from 0.5 nm to 10 nm, and length of hundreds μm. Nanotubes can be grown by chemical vapor deposition in complex structures in which tens of single nanotubes are grouped one inside another (multi-wall carbon nanotubes) creating a stronger and denser layer. The excellent chemical stability and mechanical strength of arrays of nanotubes oriented perpendicular to an electrode make this nanomaterial an ideal field emitter.

CNTs act as metallic conductors or as semiconductors according their chiral indexes. Recent studies demonstrated that their semi-conducting properties strongly depend on the temperature of the growing process and that multi-wall nanotubes show a good sensitivity in a large wavelength range, from UV to IR. CNTs grown on a silicon substrate have already been proposed as cheap devices sensitive to light. So far however, their photoelectric properties have been poorly investigated.

The first goal of this project is to study the response of arrays of densely packed nanotubes to single UV photons, both in vacuum and in various gases, as a function of their orientation relative to the substrate. A second step will explore the feasibility to build hybrid photocathodes by depositing thin films of cesium, alkali antimony or zinc oxide compounds on a carbon nanotube substrate to produce coupled semiconducting nanowires with energy gap tuned towards the UV energies. The single-photon sensitivity of these nano-structures will be likely enhanced by their geometry characterized by a large surface-volume ratio and by a higher capability to trap holes because of unsaturated bonds on the larger surface.

In parallel, the overall architecture of a photon detector that can effectively operated with this photocathode will be studied, designed, prototyped and validated with laboratory and test-beam results. This development includes the design and construction of dedicated digital read-out. The validation of the detector principle will be performed making use of standard photocathodes.

The final goal of these studies, to be obtained in a following R&D programme, is represented by checking the hybrid nanotube-based photocathode with the photon detector developed, to prove the feasibility of this innovative photon detector with CNT-based photocathodes for Cherenkov-imaging counters.

1.      Photon detector prototype (delivery month from start date: 18)

2.      Prototype of a digital read-out system for the photon detector (delivery month from start date: 30)

The future experimental programs in hadron physics requiring high-performance PID based on Cherenkov-imaging detectors have been listed above together with the laboratories where the experiments will run. The majority of the involved infrastructures either in operation, or under construction, or recently proposed are in Europe: FAIR at Darmstadt, SPS and LHC at CERN, the proposed superFlavour facility at LNF. The research programs at these infrastructures will largely profit of the outcomes of this JRA, whose aim is to open the way to innovative photon detectors for the Cherenkov-imaging detector family.

The innovative design needed for several detector components requires corresponding R&D efforts to find solutions in some cases at the limit of the presently available technologies. As always in the past for all the relevant ring-imaging Cherenkov projects, non negligible technical and technological aspects, often quite challenging, are present. They span different fields: ionizing particle detectors, software tools, optics, electronics, mechanics, material technologies, nanotechnologies. The participants’ expertise and field of excellence cover all these fields. Nevertheless, satisfactory answers to technical and technological questions or requirements often come only from the cooperation with selected industries. Part of the work within this JRA activity will necessitate the identification of industrial partners to provide adequate answers to the activity requirements. Thus, this activity is likely to have some impact in industry as well.