What technology can result from such expensive experiment as undertaken in CERN?
The truth is we don't know. But when you think about it, how can we know? If we knew what technology would eventually come out of experiments like this, why would we not build that technology now?
Large expensive machines like the CERN supercollider help us to further understand the laws of nature. And through understanding these laws, new technologies arise. But we, the physicists, have absolutely no idea what wonderful technologies might result tomorrow because we invested so heavily in science today.
It's purported in 1850 after Faraday developed the electric generator, the British minister of finance asked him what practical value there was to electricity. Faraday could not have known that electricity would one day form the backbone of all modern society (but that didn't stop him from making a snarky remark). It's hard to predict the future; we labour in science in the hopes that what we do will prove useful for some new and amazing technologies. But we don't know what technologies will result from our expensive laboratories any more than Faraday knew that electricity would allow you to make a computer.
Places like CERN are a huge forcing function for computer science - think high performance computing, networking, data storage, etc. If my memory is correct, Tim Berners-Lee was at CERN when he started developing the WWW...
In practice very little new technology results from experiments like those at CERN. While they are pushing the envelope on some things like the design of resonators, power klystrons and particle detector technology, the immediate technological return on those things is relatively small, even though one can argue that modern x-ray imaging (tomography) has profited highly from folks who did high energy and nuclear physics as students.
More importantly, though, facilities like CERN and the hundreds of associated institutions are teaching tens of thousands of students to think far outside the box. Very few of these students will stick with high energy physics in the long run (there are not that many paid jobs there). Most of them will go on to do other things, and they will use what they have learned about technology and management under difficult conditions at an extreme science/engineering project like LHC to push the envelope in whatever they will be doing in their lives. That is of enormous economic value to participating nations. If all of us would be happy with plain vanilla jobs, then all of us would still be stuck on the farm.
Apart from that, having been part of something like that is a constant source of pride in anybody's life who has been there. It's not something you forget the day you walk out the door. It gives you an idea of what humans can do, if they set their minds to something!