A first involvement of Vilnius University researchers started in 1994, when prof. Juozas Vaitkus researchers‘ team joined prof. Kenway Smith (spokesperson of RD8) team at the Glasgow university (Scotland) to investigate radiation induced defects in GaAs. In 1995 Vilnius University team joined CERN RD8 collaboration, and the research was supported by Lithuanian branch of International Center of Culture „World Laboratory“ (project leader prof. Juras Pozela) and by the Royal Society (London) long term program (project leaders K.Smith and J.Vaitkus).

In 2004 a Cooperation Agreement was signed between CERN and the Government of Lithuania concerning further development of scientific and technical co-operation in particle physics. A Protocol to this agreement was signed in 2005 covering the participation of universities and scientific institutions from Lithuania in particle physics experiments at CERN. Lithuania has actively participated in the CMS experiment, and the RD39 and RD50 collaborations as a result.

CMS: Efforts to involve Lithuania in the CMS Collaboration were intensified after the signing of the Cooperation Agreement with an important stimulus provided by Lithuanian physicists, some from academic institutions outside of Lithuania (especially by prof. Guenakh Mitselmacher, the University of Florida Physics Department).   As a result of this, a number of Lithuanian scientists and students started active participation in CERN and CMS research activities.

During this period closer contacts were established between the Vilnius Institute of Theoretical Physics and Astronomy (ITPA) and CMS.

Lithuania joined CMS on 22 June 2007 with two institutes, Vilnius University and the Lithuanian Academy of Sciences. Since then they are contributing to the annual maintenance and operation as well as construction and upgrade costs of the experiment.

Two Lithuanian physicists from the University of Vilnius (A.Juodagalvis and J.Vaitkus) are currently authors of CMS physics publications and several more, employed by institutes outside of Lithuania, are participating in CMS physics analysis in various areas.

Some of the specific topics of involvement are Standard model physics (Drell-Yan process) and the Higgs decay to taus or muons. The CMS subsystems where Lithuanian participation is gradually progressing are the Gas Electron Multiplier (GEM; team leader dr. Andrius Juodagalvis), and the Beam Radiation Instrumentation and Luminosity (BRIL) projects. Lithuanian engineers have also played a significant role in the calibration of the Hadron Calorimeter (HCAL).

The area in which Lithuania is delivering the most significant support to CMS is in IT-related services, mainly by providing qualified computing engineers and students, principally from the Vilnius University Faculty of Mathematics and Informatics (team of prof. A.Juozapavičius).

Since 2007 on average ten Lithuanian computing engineers from Vilnius University continuously collaborated with CMS in the areas of Core Computing, Offline and Physics Performance, and Dataset operation tasks. More recently, Lithuanian computing engineers have also been involved in Data Acquisition work. The support as well as the tools and procedures elaborated by these engineers are recognized as being of very high quality and greatly appreciated for data collection efficiency and certification support for the operation of the experiment. The Baltic Grid (I and II) was a European Union project in which both CERN and Vilnius University were participating partners from 2005 to 2010. It was designed to increase the impact, adoption and reach, and to further improve the support of services and users of the grid infrastructure addressing the needs of HEP communities including CMS. In this framework, the Vilnius University Faculty of Mathematics and Informatics established a Tier-3 computing facility on its premises with the objective of familiarizing students and employees with CERN/CMS computing. Over the past decade, CMS has hosted a number of Lithuanian students for varying periods of time with some hundred in total having contributed to the data processing, efficient collection and certification of high quality data for the CMS experiment.

RD39: The main focus of the collaboration is on development of radiation hard cryogenic silicon detectors for applications of LHC experiments and their future upgrades. Notable activities include the Charge Injected Detector (CID) development, and Beam Loss Monitor (BLM) detectors. For over 10 years a group from the University of Vilnius (team leader prof. Eugenijus Gaubas) specialising in radiation defects in detectors has been actively participating in RD39 research, aiming to develop cryogenic detectors for particle physics experiments and the LHC accelerator. Research fields include creation and development of measurement technologies, instruments for investigations of the impact of high energy radiations, simulations of functional characteristics of radiation induced defects, and detectors. The main results have been presented at RD39 workshops between 2006 and 2016 and published in many scientific articles, RD39 publications, and status reports. An RD39 Workshop was organised in Lithuania in June, 2007.

RD50: The RD50 collaboration is developing radiation tolerant semiconductor devices for very high luminosity colliders and Vilnius University team (leader prof. J.Vaitkus) contributes since its beginning in 2002 . The current focus of the research program is on development of silicon detectors for the High-Luminosity LHC programme. As one of the founding members, the Department of Semiconductor Physics from Vilnius University has been participating for 14 years in the research activities of the collaboration. Their main scientific contribution lies in the defect characterization of radiation damaged semiconductor materials with potential use as base material for radiation tolerant semiconductor vertex and tracking detectors. The Vilnius team performed substantial work on the characterization of GaN based sensors, evaluating their potential use as tracking detectors in high radiation environments. In addition they were key players in the RD50 WODEAN (Workshop on Defect Analysis in irradiated silicon detectors) project. Their expertise and experimental equipment for photoconductivity and carrier lifetime measurements is unique within the collaboration and has delivered valuable input for the understanding of radiation damage in silicon sensors. More recently, the focus of their experimental work changed towards characterization of different silicon materials such as high resistivity epitaxial, Floating Zone and Czochralski silicon of different conductivity types. The carrier lifetime measurements of the Vilnius Group as a function of radiation fluence for a wide variety of different particles showed a remarkable linearity over several orders of magnitude in radiation fluence. This work led to the design of a new fluence monitoring device, further developed within the AIDA and AIDA-2020 EU projects.

The latest contributions of the Vilnius team are in the area of radiation induced defect simulations, and in particular on the simulation of defect cluster related damage and the development of a new defect characterization method based on pulsed photo-ionization spectroscopy. Vilnius University hosted the 10th RD50 Workshop, has delivered scientific contributions to almost all of the 21 Workshops, and published more than 20 papers in the framework of RD50. Prof. J.Vaitkus has held management responsibilities within the collaboration; convening the “New materials” research line for 5 years (2002-2007) and since 2011 acting as Deputy Collaboration Board Chair. In 2016 team of prof. Gintautas Tamulaitis joined AIDA-2020 project and CERN RD18 „Crystal Clear Collaboration“.

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