Measuring muon tracks in Baikal-GVD using a fast reconstruction algorithm

The Baikal Gigaton Volume Detector (Baikal-GVD) is a km$^3$-scale neutrino detector currently under construction in Lake Baikal, Russia. The detector consists of several thousand optical sensors arranged on vertical strings, with 36 sensors per string. The strings are grouped into clusters of 8 strings each. Each cluster can operate as a stand-alone neutrino detector. The detector layout is optimized for the measurement of astrophysical neutrinos with energies of $\sim$ 100 TeV and above. Events resulting from charged current interactions of muon (anti-)neutrinos will have a track-like topology in Baikal-GVD. A fast $\chi^2$-based reconstruction algorithm has been developed to reconstruct such track-like events. The algorithm has been applied to data collected in 2019 from the first five operational clusters of Baikal-GVD, resulting in observations of both downgoing atmospheric muons and upgoing atmospheric neutrinos. This serves as an important milestone towards experimental validation of the Baikal-GVD design. The analysis is limited to single-cluster data, favoring nearly-vertical tracks.Comment: 15 pages, 6 figures, 1 table, to be published in Eur. Phys. J.

Laser abrading of carbon fibre reinforced composite for improving paint adhesion

Surface contaminations (originating from manufacturing processes), smooth surface, and poor wettability of carbon fiber reinforced polymer (CFRP) composite impair its successful paint adhesion. Surface pretreatment of composite materials is often required. Previous approaches of using manual sand-papering result in non-uniform surface conditions and occasional damages to the fibres. Furthermore, the process is labour intensive, slow and can be hazardous to the workers if protections are not appropriate. This paper reports an investigation into a new surface treatment method based on laser multi-tasking surface abrading and surface cleaning/texturing for the improvement of paint adhesion. A KrF Excimer laser with a wavelength of 248 nm is used as the laser source. Significant improvement in paint adhesion has been demonstrated compared with as-received and sand-papered samples. This improvement is achieved by eliminating surface contaminants, minimizing chain scission and increasing in surface active functional groups as well as increasing in surface roughness. The former two play dominant roles