• Higgs Boson: Yes/No/Maybe?

    It is always good to see science covered in the mainstream media. It is equally disheartening to see misinterpretation of scientific results. I am sure you’ve been hearing a lot about the “discovery” of the Higgs Boson particle, also (unfortunately) coined as the “God particle”. If you are not a physicist, you might find difficulty in interpreting the results. So, here is a particle physics 101 so that you can make your own opinion about the results.

    In particle physics (as in some other fields), results are statistical and are always presented with a “sigma” or standard deviation(s) away from the expected result (given by models). A higher value of sigma indicates a higher certainty of a given measurement. So, a six sigma signal is very promising and a two sigma signal is of almost no significance. So, a 3-sigma result, which means it has one in 740 chance of being a false signal, 4-sigma has one is 32, 000 and 5-sigma has one in 3.5 million.

    With experience from past discoveries and false signals, some standards have been adopted in order to judge the value of a result. Here is the key:

    3-sigma: some evidence/promising hint

    4-sigma: likely discovery

    5-sigma and higher: confirmed discovery

    Yesterday, US based Tevatron, which has been unfortunately decommissioned, announced a 2.9 sigma Higgs signal based on their analysis of archival data. Tomorrow, we are going to hear from CMS and ATLAS groups at CERN about their findings. I will let you make your own opinion!

    • http://paleblueblog.org/ Shawn Domagal-Goldman

      Dimitra, do the results from the Tevatron, CMS, and ATLAS groups agree? Do they find the Higgs boson at the same mass? And “how many sigmas” are the detections for the two CERN groups?

    • http://www.tifr.res.in/~atri Dimitra Atri

      Yes, all experiments agree within experimental uncertainties. It is a 5 sigma result! I am writing a detailed post.