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A feast of physics at the winter conferences


Eckhard Elsen is Director for Research and Computing

A first glimpse at the winter conferences of what the LHC’s extraordinary performance in 2016 means for physics

This year’s winter conferences are giving us a first glimpse of what the LHC’s extraordinary performance in 2016 means for physics. We are now in the second week of the Moriond conference. Week one gave us a wealth of exciting new results in electroweak physics, and week two promises a feast of QCD.

For me, the key message from Moriond is that we are really beginning to see how the large quantities of new data are extending the reach of LHC searches, while also bringing precision to our analyses of known physics. The LHC experiments are achieving the kind of precision at a hadron collider that once was only possible with an electron machine. This is a great tribute to the machine, the experiments and the computing infrastructure.

Hadrons are composite; the hard collisions occur between constituents, which only rarely carry a large share of energy of the hadron. This is why a large luminosity is needed to reach out to the highest collision energies. Maximising the number of collisions maximises the number of high-energy collisions, and that extends the energy reach. With the rich harvest of 2016 the experiments at the LHC have reached out much further in energy than ever before.

Exciting though this is, if there’s new physics to be found in the 2016 data, it’s likely to take some time to surface. It will not be like the discovery of BEH mechanism and the Higgs boson, which – as a relatively low mass particle by LHC standards – rapidly became apparent as soon as the collisions reached the energy needed to produce Higgs particles. New physics will need a combination of more data, increasingly sophisticated analyses and sound theoretical understanding, and that takes time.

Nevertheless, Moriond is providing a very appetising entrée to run-two physics to follow the amuse-bouche of last summer’s conferences. Highlights already presented include an updated measurement of the W particle mass from ATLAS’s run one data, which now has similar precision to the world’s best measurement. This shows how well the LHC collaborations understand their detectors, and how good they are becoming at extracting precise physics results and thus narrowing the phase space for new physics to hide. As an example of how well we are coming to know the Higgs particle, the CMS experiment’s measurements of the Higgs coupling to top quarks is impressive, and both experiments are giving us a solid understanding of the quark content of protons, a key ingredient for all LHC analyses.

As an example of the elaborate experimental techniques now possible with the LHC experiments, I’d like to mention LHCb’s measurement of the extremely rare, few-per-billion-level, decay of the Bs meson to a pair of muons, for which now even the lifetime has been extracted. With more data, this continues to be a powerful probing ground for new physics.

Although not the main outlet for heavy-ion physics, the ALICE experiment is presenting results at Moriond QCD that underline the value of the end-of-year proton-proton and proton-lead runs. Comparison of the experimental signatures in all these constellations is contributing greatly to our understanding of the process of quark gluon deconfinement in the Quark Gluon Plasma, matter as it would have been just after the Big Bang.

This is just a snapshot of the plethora of new results being presented at Moriond, and you’ll be able to learn more about some of them as they appear here on the CERN website as the conference progresses. As an idea of how bright the LHC future is, I’d like to leave you with this: at last year’s summer conferences, run two analyses were based on the first glimpse from 15 inverse femtobarns of data. The Moriond analyses included 40 inverse femtobarns, with much more still to come. I for one can’t wait for the main dish to be served as we proceed to the summer conferences.