There is a lot of discussion about what particle physicists should focus on next. So first, let me point out a SLAC seminar by UC Irvine professor Tim Tait on what the Higgs boson actually is and why we've been looking for it for such a long time.
In brief, the Higgs mechanism is the simplest way that we could come up with to complete the Standard Model of physics. If the newly found boson really is the Standard Model Higgs boson, then we guessed correctly, and the Standard Model of Particle Physics is complete.
But here's the catch: We don't want to have complete Standard Model. Not only would that be extremely boring, but the Standard Model falls short in addressing some fundamental questions: What is dark matter? What is dark energy? Why is there apparently so much more matter than anti-matter in the universe? We know the Standard Model cannot give a complete picture. Instead, we're looking for extensions or other theoretical frameworks altogether, for example supersymmetry. With these theories, we could maybe address some of these questions, but we lack conclusive evidence why the theory should be true. So far, the precision tests that were carried out at LEP, SLD, and other experiments since then have provided spectacular confirmation of the Standard Model, but have failed to put the finger on the cracks that we know exist.
The discovery of the Higgs boson now gives us a new handle on understanding nature. All the time that we've been looking for the boson, we've spent on understanding this last piece to the Standard Model in great detail. We know exactly what it has to look like in order to fit perfectly. (We just didn't know where it was until now.) Now we need to measure its properties with the highest possible precision to find deviations from these predictions. The LHC was not really built for this task. It will be able to identify large deviations from the predictions, but precision measurements will be extremely difficult. So what's next?
There have been ideas about a Higgs factory in form of a muon collider. Unfortunately, nobody knows how to build such a machine, and it could well be a decade or more before we can start thinking about building such a machine.
Instead, I have been working on detector research for linear colliders for the past decade. The LHC took over 20 years from inception to first collisions. It is unlikely that the next machine will be built faster. People have been working on the ILC and on CLIC for over a decade already. That means we will start to take data in ten years at the earliest. The easy questions have been answered. Answers to the next questions requires a continuous effort. These big expensive machines are not toys, but scientific instruments. They drive progress in science, technology, education, and, by virtue of being international collaborations, even politics. They are without a doubt worthwhile the money we want to spend to build them. The upcoming Symposium on the European Strategy for Particle Physics will be an important step towards the realization of the next big machine.
