## Friday, 26 June 2015

### Friday wrap-up: first physics, CMS magnet, diboson excess...

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...

Long time no blog -- turns out to be hard to keep up with everything in the midst of travel. So here are some "links without thinks" from the last month...
• As of June 3 the LHC has physics data being taken at 13 TeV! The live blog from the day can be found here [1 of 4], and there are five highlights videos on the CERN YouTube channel. The media hype for this milestone was significantly larger than for the first 13 TeV collisions 21 May. I wonder if this was a calculated decision from CERN... it seems that's what would have been preferred after the 7 TeV restart in 2010 (see Particle Fever e.g. 1:00:20).

ATLAS made public a dijet animation and the below pp collision events with 17 vertices(!) from June 3...

• There was a rumour a couple of weeks back that the CMS magnet was in trouble. The earliest article I am aware of is this one (dated 8 June), which with the help of Google Translate suggests oil contamination of the liquid helium involved in cooling the 4T superconducting magnet. You can read the immediate response of CMS physicists here. Now CMS has released a statement (14 June), which is partly quoted below.

CMS has been taking collision data since the 13TeV startup of the LHC on 3 June. During this period, the CMS magnet has been kept off due to an issue with the cooling system... The issue with the magnet cooling system was identified in the final preparatory phase leading to collisions in the LHC. While preparing for beam in CMS, a problem was found in the system that feeds liquid helium to the CMS superconducting magnet. The problem was diagnosed to be due to oil, which is used in the initial compression stages, reaching the so-called 'cold-box’ of the cryogenic system. The cold-box is a complex system with several sets of filters protecting three turbines along the path of the helium towards the magnet. In order to clean the oil contamination essentially all components of the cold-box have been extracted and replaced... CMS is confident that, following the LHC technical stop and the beam conditioning run that will start at the end of this week, after the low-intensity and commissioning period, the full magnetic field will be available for the 13 TeV LHC run.
• Certainly a month couldn't go by without another excess to keep people busy! Now it is in an ATLAS search for diboson resonances.

The excess is of ~3σ local significance in WZ, WW and ZZ channels, and 2.5σ global. Jester has a write-up and some thoughts, and notes that there is a small excess at around the same mass scale in similar CMS searches. Along with the CMS WH resonance and right-handed W excesses at around 2 TeV, who knows, maybe there's life out there in the desert yet... and not too far away...

(image credit John Pritchett)

PS: I hear the ATLAS $h\to \mu\tau$ analysis is hopefully out within weeks (context)...
• The OPERA experiment has observed (i.e. at 5σ significance) tau neutrino appearance in a muon neutrino beam.
• The Perimeter Institute Convergence conference June 20-24 is archiving its very interesting talks here.
• The CMB@50 Conference held at Princeton from 10-12 June has been "storified" by Renée Hložek, links at her blog.
• In space news and pretty pictures:
• The Philae lander on Comet 67P/Churyumov-Gerasimenko is awake again, and ready to do science...

• ... Pluto and Charon in colour from New Horizons...

(Only a couple of weeks now until closest approach: “Color observations are going to get much, much better, eventually resolving the surfaces of Charon and Pluto at scales of just kilometers.”)