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Title	Monitoring of absolute mirror alignment at COMPASS RICH-1 detector
Author(s)	Alexeev, M (INFN, Turin ; Piemonte Orientale U., Alessandria ; Bari U. ; INFN, Trieste) ; Birsa, R (INFN, Trieste) ; Bradamante, F (INFN, Trieste ; Trieste U.) ; Bressan, A (INFN, Trieste ; Trieste U.) ; Chiosso, M (INFN, Turin ; Turin U.) ; Ciliberti, P (INFN, Trieste ; Trieste U.) ; Dalla Torre, S (INFN, Trieste) ; Denisov, O (INFN, Turin) ; Duic, V (INFN, Trieste ; Trieste U.) ; Ferrero, A (INFN, Turin ; Turin U.) ; Finger, M (Charles U. ; Dubna, JINR) ; Gayde, J Ch (CERN) ; Giorgi, M (INFN, Trieste ; Trieste U.) ; Gobbo, B (INFN, Trieste) ; Levorato, S (INFN, Trieste) ; Maggiora, A (INFN, Turin) ; Martin, A (INFN, Trieste ; Trieste U.) ; Menon, G (INFN, Trieste) ; Panzieri, D (INFN, Turin ; Piemonte Orientale U., Alessandria) ; Pesaro, G (INFN, Trieste ; Trieste U.) ; Polak, J (Liberec Tech. U. ; COMPAS, Turnov) ; Rocco, E (INFN, Turin ; Turin U.) ; Sbrizzai, G (INFN, Trieste ; Trieste U.) ; Schiavon, P (INFN, Trieste ; Trieste U.) ; Slunecka, M (Charles U. ; Dubna, JINR) ; Sozzi, F (INFN, Trieste ; Trieste U.) ; Steiger, L (Liberec Tech. U. ; COMPAS, Turnov) ; Sulc, M (Liberec Tech. U. ; COMPAS, Turnov) ; Takekawa, S (INFN, Trieste ; Trieste U.) ; Tessarotto, F (INFN, Trieste)
Publication	2014
Number of pages	4
In:	Nucl. Instrum. Methods Phys. Res., A 766 (2014) 208-211
In:	8th International Workshop on Ring Imaging Cherenkov Detectors, Hayama, Kanagawa, Japan, 2 - 6 Dec 2013, pp.208-211
DOI	10.1016/j.nima.2014.06.066
Subject category	Detectors and Experimental Techniques
Abstract	The gaseous COMPASS RICH-1 detector uses two spherical mirror surfaces, segmented into 116 individual mirrors, to focus the Cherenkov photons onto the detector plane. Any mirror misalignment directly affects the detector resolution. The on-line Continuous Line Alignment and Monitoring (CLAM) photogrammetry-based method has been implemented to measure the alignment of individual mirrors which can be characterized by the center of curvature. The mirror wall reflects a regular grid of retroreflective strips placed inside the detector vessel. Then, the position of each mirror is determined from the image of the grid reflection. The images are collected by four cameras. Any small mirror misalignment results in changes of the grid lines’ positions in the image. The accuracy limits of the CLAM method were checked by laser interferometry and are below 0.1 mrad.
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