Friday, 10 April 2015

Friday wrap-up: LHC first beam, mono-Z'...

Wherein I list some (mostly) recent happenings, ramble a bit, and provide links, in an order roughly determined by importance and relevance to particle physics. Views are my own. Content very definitely skewed by my own leanings and by papers getting coverage, and it may not even be correct. It is a blog after all...

  • Protons circulated the LHC for the first time since long shutdown last Sunday! If you want to relive the day you can read backwards through the live blog. Beams circled both ways (first Beam 2 [anticlockwise] then Beam 1) at the injection energy of 450 GeV, after the collimators placed along the way were each opened up in turn. For ATLAS and CMS the collimators placed ~100m away created some spectacular beam splash events. Below are the first recorded splash events from CMS and from ATLAS.

    Images from the day can be found here, and you can check the current LHC status here (or a more detailed status here). Since then there have been a bunch of technical tests and splashes. There's also an article from CERN about the plan up until collisions. In the immediate future we wait for both beams to ramp-up to 6.5 TeV. The magnets are trained and ready as of Saturday, and first probe beam reached 6.5 TeV this morning...

  • An interesting observation which Strassler brought up, and I have noticed as well: there is much more talk about dark matter as a goal for LHC Run II, in lieu SUSY. The CERN press release wrote, "The Brout-Englert-Higgs mechanism, dark matter, antimatter and quark-gluon plasma are all on the menu for LHC season 2," and Nature wrote, "In 2012, more than two years after the machine first started up, LHC experiments found the long-awaited Higgs boson... The second run does not have such an obvious target. Instead, physicists will scour the data for signs of phenomena that do not fit with the standard model of particle physics in hopes of solving mysteries such as the origins of dark matter."
  • On that (dark matter at the LHC) front, the arXiv awoke on Wednesday to a new mono-X, i.e. these-three-preprints discussing the mono-Z'. The salient processes are the three depicted in the below diagram (where the leptons could be replaced by jets, or a thin jet if the Z' is light and boosted), plus dark Higgs-strahlung.

    It's a sensible thing to go and look for, and I'm surprised it's taken so long to be looked at in a general context... though obviously it was high time! Now inviting speculation on the next mono-X... mono-W'? mono-stoponium? neutrinoless mono-beta decay?
  • Lastly, as is the tradition, a space image... here is a gravitationally lensed galaxy nearly 12 billion light-years away, imaged by ALMA.

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