A short film on the ups, but mainly downs, of a difficult search.
A couple of weeks ago we hosted a small-ish meeting at UCL, the sixth “Boost” workshop. I’ve written about these before and I enjoy them a lot. It was great to welcome lots of friends and colleagues to my own university this time (and nice not to have to fly much this summer!). Apart from the physics, dinner at Lord’s cricket ground, and showing bemused foreigners the tiny urn containing the Ashes, was a highlight.
The “Boost” in the title of the meeting refers to the fact that there is enough energy in the particle collisions Large Hadron Collider to not only produce massive particles (such as the W and Z bosons, the top quark, and the Higgs boson), but to give them a lot of kinetic energy too. That is, they are travelling at high speeds, or boosts. Reconstructing such particles requires some special techniques, and the meeting is devoted to developing and exploiting these techniques.
The Higgs appears in the list above, and studying it is one important application of these techniques.
Higgs bosons decay quickly, and can do so in many different ways. During the hunt for the Higgs, each of these decay modes was being chased by a different team, and each should in principle have contributed to the discovery. Two of the most challenging decay modes are those when the Higgs decays to b-quarks (where boosted Higgs bosons are especially imortant), and when it decays to tau leptons. Neither of these modes has been unequivocally seen (at the “five sigma’ confidence we tend to require) but there is good evidence for them already, and we expect clear measurements when the LHC restarts next year.
One of the attendees at the Boost meeting was Phil Harris, who was part of the team on the CMS experiment looking for the tau decay mode. When CMS and ATLAS announced the Higgs discovery on 4 July 2012, the CMS tau result was “preliminary” and had some … problems. Not only was nothing seen, but it actually reduced the significance of the overall signal. The film below is a really nice account of what it felt like to be part of that; and Phil’s reaction at the end, when the final result from LHC run 1 data was produced, might be a bit of a surprise. Enjoy.
Also at the Guardian.