IMHO, your field of study (Theoretical particle physics) + Java or any other programming knowledge gives you a huge advantage. How about learning (basic or even advanced) Linux, distributed computing, algorithms, etc? You certainly need Unix/Linux skills for most scientific research projects. Many of my friends from other disciplines (Polymer, Mechanical, Industrial, Electrical engineers) are also good computer programmers (C, C++, Java, Python, etc) . Few guys are now studying in Uppsala, Sweden :)
How about looking for all science related computer jobs in universities, scientific/research labs, government/private science labs, electronic product companies, pharmaceuticals, defense, etc? AFAIK, EU has a lot of particle physics labs. Are you interested in expanding your search to those countries/labs? I guess you might have done that already. May be, one more try?! Physics or Science or research oriented IT jobs are your best bet.
If you want to jump into the IT programmers pool, you have many options, based on the job market in Sweden. I don't know the details of Sweden IT market. Big corporate jobs look for Java/J2EE experience; please look at the skillset they want. You need strong Java & J2EE skills, Spring, Hibernate (ORM), Application servers (JBoss, Websphere, Tomcat) and other related topics. For mobile companies, you could learn Android. Your knowledge of particle physics may be helpful in few conversations, I would hope.
You could also try consulting jobs by joining one of the IT consulting/recruiting companies instead of full time employment. Send them your resume and see what they can offer you.