Guess the Plot 11
    By Tommaso Dorigo | January 21st 2013 10:12 AM | 3 comments | Print | E-mail | Track Comments
    About Tommaso

    I am an experimental particle physicist working with the CMS experiment at CERN. In my spare time I play chess, abuse the piano, and aim my dobson...

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    It has been a while since the last time I posted the last riddle of this series. It was fun though, so upon seeing the graph below I immediately decided I would use it here, to let you guess what it is about. Please use the comments thread to provide your input: what does the graph represent ? What are the different coloured lines ? Why the funny behaviour ? What is on the x axis ? And on the y axis ?

    Of course it is virtually impossible to answer all the above without being given some hint. I can tell you it has to do with LHC searches, and that is all the help I am going to give you!


    x-axis: mass of a Higgs in GeV
    y-axis: a certain branching ratio in % (obviiously with the drop at 2 mtop)
    Colors: variation of a parameter such as tan_beta

    Cheers, Sven

    I'd switch "Higgs" for some SUSY particle but have no idea which one.

    I'm a bit suspicious of the branching ratio interpretation. Would percent be used?

    Okay - this was not fair altogether: Sven is the one who got the closest to it, but Sven is probably Sven Heinemeyer, who turns out to be one of the authors of FeynHiggs, the program which computes cross sections and branching fraction of SUSY Higgs particles in the MSSM... And the plot is, in fact, the sum of several different outputs of FeynHiggs: it represents the cross section times branching fraction of the production of an A (the CP-odd neutral Higgs boson of two-doublet models) and its decay into Zh, where Z is the regular standard model Z boson, and h is the lightest of the two CP-even Higgs bosons. The various curves represent the effective cross section for different values of tan(beta), one of the crucial parameters of two-doublet MSSM models. From top to bottom you can see curves relative to different values from 1 to 10 of tan(beta).

    In any case I see that the riddle has not been too popular - only two answers! Maybe the figure was really too difficult to guess ? I doubt that is the case; rather, un-inspiring. To me it is the opposite though: the various features of the curve are absolutely non-trivial, and each has some physics motivation. For instance the "peaks" at 350 GeV, where the A production is enhanced, but then the branching fraction into things other than top-antitop pairs is dampened. Or the "turn-on" at masses above the sum of Z and h. Of course the h mass is not 125 GeV here: it is whatever it is, once you specify the A mass (on the x axis) and tan(beta).

    The graph has been produced by a Ph.D. student from my analysis group, Alberto Zucchetta (I refrained from calling him "my" student since he is working at several different things at the moment, and none of them directly with me! - but I hope we will put together a search for these A particles in Zh final states: it should be fun!