From CMS at CERN: “Colliding different particle species: the LHC’s proton-lead run”

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Achintya Rao

“The new year brings a new type of collision at the LHC: the accelerator will smash protons and lead nuclei together, allowing CMS and the other LHC experiments to study the cold nuclear matter we expect these collisions to produce. Although we caught a glimpse of these asymmetric proton-lead (pPb) collisions during a pilot run last September, the next four weeks will bring the first sustained pPb run and provide valuable data. Indeed the small data sample from 2012 already revealed interesting phenomena, and raised interest in this study.

A proton-lead collision at a centre-of-mass energy of 5 TeV per nucleon. In this side-on view, the proton beam enters from the right side of the image and leaves on the left; the lead beam travels in the opposite direction. The event was selected requiring a muon trigger, and the muon (red line) was reconstructed in the CSC detectors.

For this run, CMS will combine forces with TOTEM so as to cover a greater range of collision data. The two are essentially separate entities — independent experiments that use different analysis software — and they are fully complementary. CMS measures in the central region and TOTEM exclusively measures in the very forward region.

One arm of a TOTEM T2 detector during the installation in the interaction point

Julia Velkovska, … a co-convener of the HI [Heavy Ions] group , explains the motivations behind colliding these different particle species together: ‘Not only does it act as a straight reference for lead collisions, but it is an interesting physics system in its own right. In addition, there are a lot of things that we think we can address now that weren’t on the cards a few months ago: the ridge we observed in the pilot run raised a lot of new questions and new approaches on how to analyse the data have been proposed.’”

See the full article here.

And, now “And we have Stable Beams for the pPb run!” says CMS.


Provided by Symmetry Magazine

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