Wednesday, September 24, 2014

BICEP2 + Planck + Foreground = Good Physics

     The Planck CMB polarization paper came out this week and its results were not good news for the BICEP2 team as shown herehere, and here. I'd commented on the BICEP2 result earlier here, Basically saying that this is how science gets done.  Now we have the future to look forward to and more results coming in at other frequencies and maybe better energy resolution so hopefully in the future we will know about primordial gravitational waves.  Again may you live in interesting times!

     What only gets briefly mentioned is that what we do have is really good data on galactic dust and the galactic magnetic field.  So people who study that should be very happy.  Again what is one research groups hindrance is another groups prize.  This happened else where in physics.  At the LHC looking for the Higgs boson its signal sits on top of a large background.  Understanding this background is important so that you can be confident in your Higgs signal.  Understanding this background means understanding the physics that gives rise to this background and here understanding and computing QCD processes becomes important.  Hence you have large groups that look at all the QCD processes that can contribute to this background and then calculate their cross sections and then see how these match the background.  So here you get more understanding and conformation of the Standard Model in trying to understand the background underneath your Nobel prize winning discovery of the Higgs boson.

    In my own research years ago in looking at the excitation of giant resonances in nuclei excited with inelastic proton scattering, the resonances sat on top of a background.  One minimized this background as much as possible but it was still there and didn't go away.  That was because as we learned that background was there because there was real physics going on that caused this background.  The background was a real signal and not instumental problems.  The background as we determined was caused by quasifree scattering of the incident protons from nuclei in the targets.  The target nucleus being a collection of nucleons acted like a collection of nucleons sort of like a collection of pool balls racked up and we were hitting these pool balls and sometimes we were exciting the nucleons  in that manner instead of other nuclear processes.  This area of study led to other experiments studying this quasifree scattering.  So looking for one signal our background signal became interesting in itself.

     Funny how science moves ahead.

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