Observing "weather" (stratospheric temp.) with cosmic rays

An article in New Scientist reports on an analysis of cosmic ray muon data from the MINOS underground detector, which correlates with "sudden" (24-hour timescale) temperature changes in the stratosphere. The original article in Geophysical Research Letters gives you a good flavor for how this kind of analysis is actually done, and written up for publication. The figure below (Figure 3 of the article) shows the beautiful correlation between the temperature (5-day running average in blue) as measured by sounding balloons, and the muon rate in MINOS (also 5-day running average, red band with uncertainties). The alignment of the two curves is obviously not known a priori. The exact numerical calibration between muon counts (red, right scale) and temperature (blue, left scale) is a fitted output of the analysis, not an input.To me, it's just kind of neat that particle physics can relate so sharply to some "real world" large-scale properties.

Topic by kelseymh 10 years ago  |  last reply 10 years ago

Two "hot topics" from particle physics -- read the actual papers!

I've noticed that two recent particle physics "discoveries" (what I'd call analysis results) are beginning to get some media coverage, at least in the science press. Below, I provide links to the actual papers (the preprints in arXiv), and a bit of my own opinion. I encourage the curious to read, or at least skim, the papers --- there will probably be a lot you don't understand (these are technical research papers, after all!), so don't hesitate to ask questions.Dark matter "observation" by PAMELA satellite -- excess of high energy positrons in cosmic rayshttp://arxiv.org/abs/0810.4995The PAMELA data are high-statistics, and they've done an excellent job with their systematics anddetector calibration. Their low energy data are entirely consistent with previous results, which makes the excess and plateau seen above 10 GeV rather compelling. I don't think we know enough about conventional astrophysical sources of positrons to have any confidence ascribing this result to "new physics.""Ghost particles" in Fermilab p-antip collisions -- excess of high impact parameters muonshttp://arxiv.org/abs/0810.5357Charged particles (like muons) are identified in big detectors such as CDF (and BaBar) by picking up signals from their occasional interactions with low density material, and fitting a trajectory in space to those "hits." You can't put active detector material all the way down to where the beams collide, so an extrapolation from the detector region to the "interaction point" is required. There can be many complicated and non-obvious systematic uncertainties affecting those fits. The fact that only about 1/3 of CDF was willing to sign this paper suggests to me that the systematics in this analysis are not really under control yet, and any interpretation of the result should be taken with a grain of salt.

Topic by kelseymh 10 years ago  |  last reply 10 years ago

The Large Hadron Collider: is it worth it?

The Large Hadron Collider(LHC) is to be unveiled this year. It is designed to solve the much talked about energy crisis, and hopes to do so, but can it be worth all of it? From Wikipedia- (On October 25, 2005, a technician, José Pereira Lages, was killed in the LHC tunnel when a crane load was accidentally dropped. The construction of LHC was approved in 1995 with a budget of 2.6 billion Swiss francs, with another 210 millionfrancs (€140 M) towards the cost of the experiments. However, cost over-runs, estimated in a major review in 2001 at around 480 million francs (€300 M) for the accelerator, and 50 million francs (€30 M) for the experiments, along with a reduction in CERN's budget, pushed the completion date from 2005 to April 2007.[14] 180 million francs (€120 M) of the cost increase have been due to the superconducting magnets. There were also engineering difficulties encountered while building the underground cavern for the Compact Muon Solenoid. In part this was due to faulty parts lent to CERN by fellow laboratories Argonne National Laboratory or Fermilab (home to the Tevatron, the world's largest particle accelerator until CERN finishes the Large Hadron Collider). [15] The total cost of the project is anticipated to be between US$5 and US$10 billion.[2] On March 27, 2007, there was an incident during a pressure test involving one of the LHC's inner triplet magnet assemblies provided by Fermilab and KEK. No people were injured, but a cryogenic magnet support broke. Fermilab director Pier Oddone stated 'In this case we are dumbfounded that we missed some very simple balance of forces.' This fault had been present in the original design, and remained during four engineering reviews over the following years.[41] Analysis revealed that its design, made as thin as possible for better insulation, was not strong enough to withstand the forces generated during pressure testing. Details are available in a statement from Fermilab, with which CERN is in agreement.[42][43])

Topic by BkrevWlevqe 10 years ago  |  last reply 10 years ago