BEXCO - Room F(201/202/203/204)
[NU121] Baikal-GVD: The time calibration in 2016
The previous neutrino telescopes located in the lake Baikal have been one of the key players in the field of detection of high-energy cosmic neutrinos for many decades. In April 2015, the first part of the newly constructed next-generation neutrino telescope, Gigatone Volume Detector (GVD), was put into operation in the lake Baikal and started to take data. Moreover, the substantial extension of this detector is planned in the next few years. In the beginning of 2017 the new cluster is going to be installed which doubles the amount of OMs and than another two clusters are going to be installed every consecutive year. In total 8 clusters of 2304 OMs with overall effective volume ~ 0.4km3 will be deployed by 2020. The time calibration is a crucial step of the whole pre-physical analysis. It is the first step which has to be done to be able to reconstruct tracks and directions of the studied particles whereby the precision of time calibration determines the precision of reconstruction. For this purpose the extension of the BARS (Baikal Analysis and Reconstruction Software, C++) was developed which enables to process various types of time calibration runs and its aim is to reach a ns time precision. For purposes of time calibrations, the detector GVD was designed and constructed with various calibration sources which can provide a cross-check of obtained results. Every OM is equipped with two built-in LEDs with adjustable intensity and time delay. In addition in cluster Dubna, there are three LED matrices with 12 LEDs, 6 directed horizontally and 6 vertically, which can be used for inter-string time calibrations. In 2017 winter expedition the laser source for inter-cluster calibrations is going to be installed as well. In this talk, the different procedures of time calibration used at GVD in past as well as the newly developed ones will be described and the results of the 2016 time calibration of the cluster Dubna will be presented, especially precision and variations in time. Moreover, the measurements of the Time Walk Effect (TWE), which influence the precision of time measurements, in situ will be discussed in detail.