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Michael Schmitt | USLHC | USA

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How should we check the CDF Anomaly?

There has been lots of buzz about the CDF anomaly, and many blog entries and discussion.   For example, there is Flip’s excellent discussion here, as well as entries at many other physics blogs.

Everyone understands, of course, that the next step is for CMS and ATLAS to check their data and see whether they might also observe a hint of a signal.   While the LHC luminosity is about 100 times smaller than what CDF used, the detectors are better and the cross sections are larger, so maybe they can see something.  It’s worth looking, right?

So, if you are are physicist with LHC data on your hard drive, how do you begin?  Instinct says: just implement the CDF cuts and run on the data.  If those cuts produce a signal at CDF, they should produce one at CMS or ATLAS, too, right?

Well, maybe.  But that attitude might be too simplistic.   If you look at the CDF plot below, you’ll see two peaks.   The point is not:  CDF looked at the di-jet mass (MJJ) spectrum and saw a bump.  The point is:  CDF established a signal for a predictable standard model (SM) process, namely, ppbar→W+V, where  V is W and Z together, and next to this SM signal, saw an extra bump.  The fact that they see W+V at the expected rate provides some strong proof that their analysis is valid. If they could not manage to see W+V, then I would be reluctant to take their analysis seriously.  And although they did not couch their discussion this way, for me an important fact is that the anomalous bump is roughly half the size of the SM W+V one.

So, in my opinion, any experiment that wants to check whether the CDF anomaly is present in their data must show that they at least see the W+V signal, first.  This is more important than blindly implementing the CDF cuts.   Show the benchmark, and then we will see whether there is an additional peak, roughly half the size, about 60 GeV higher in mass.

CDF anomaly

CDF MJJ distribution


4 Responses to “How should we check the CDF Anomaly?”

  1. Flip Tanedo says:

    Hi Michael! Welcome to the blog! I’m especially excited to have you join us, I’ve been a big fan of “Collider Blog.” :-)

  2. Michael Schmitt says:

    Hi Flip – thanks! I do feel welcome here. :) I hope I can keep up with the high quality of posts at US LHC Blog. There will certainly be lots to discuss in the coming year. -Michael

  3. Matthias says:

    hi there

    I’m a Researcher in Science Education in Switzerland and check various CERN webpages regularly. As it is my everyday work to eplain (more or less) complicated things from the realm of nature to kids, teens or teachers, let me say that you (Flip, Michael,…) do a very good (and important) job!
    One question from my side: How much data will CMS and/or ATLAS need to get in the same sensitivity range as CDF? Will something like 0.2 fm-1 be enough? I can easily imagine, that this is not that easy to answer, but maybe you can give me an educatet guess? Thanks


  4. Michael says:

    Hi Matthias,

    its nice to hear that these blog entries are helpful for education – that’s great!

    It is not easy to estimate how much luminosity would be needed to make a definitive statement about the CDF anomaly. CMS and ATLAS each have about 36 pb-1 from 2010, and are accumulating a few more tens of pb-1 now. My guess is that a couple hundred pb-1 would be needed to see W+V clearly, but this is really only a guess – I have not done any quantitative study, which would require more time than I have available. Stay tuned in the coming months, as the LHC delivers more collision data…


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