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    The Plot Of The Week - MSSM Higgs Limits
    By Tommaso Dorigo | June 28th 2011 12:50 AM | 22 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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    I feel quite grateful to the DZERO collaboration for publishing today in the Cornell arxiv the preprint of their search for neutral MSSM Higgs bosons in the tau-pair decay mode. Not more than 12 hours ago in fact I had been looking for a suitable figure which could summarize the status of searches for those particles, to help a student who is about to graduate; but had not found anything satisfactory.

    Now DZERO throws no less than 7.3 inverse femtobarns of collisions at this important search. I guess this is the swan song for this particular analysis at the Tevatron, because the LHC experiments have already surpassed the sensitivity of their American competitors, with one two-hundredth (!) of the available statistics.

    But let me not get ahead of myself. Before I show the result, let me first discuss one meaningful figure from the article, showing the output of a global likelihood discriminant capable of nicely distinguish the decays of Higgs bosons to tau lepton pairs from all the concurring backgrounds. The figure on the right considers the case of a Higgs mass of 180 GeV, where the discrimination from Z decays (in red) is easy but the one from top decays (in purple) is harder. As you can see, a MSSM signal (for higgs mass of 180 GeV, shown in hatched light blue) would appear as a significant enhancement at high values of the discriminant D_f. This particular value of parameter space points is in fact excluded by the DZERO analysis; it refers to a value close to the boundary of the DZERO sensitivity curve (tan(beta)=40).

    And now let us look at the results, shown in the graph below. The figure describes the relevant region of the MSSM parameter space (in a particular choice of some of the additional parameters, a configuration called "m_h max" which grants the maximum possible value to the lowest-mass neutral scalar) as a function of two crucial parameters: the value of tan(beta) and the mass of the CP-odd A boson.

    In the graph you can see the region excluded by the new DZERO search in blue: the region which the DZERO data disfavors is the one at high tan(beta), where the coupling of the Higgs to down-type fermions would have allowed large production rates and decays to tau pairs. As you notice, the limit resulting from the search performed by CMS with just 36 inverse femtobarns (duly reported in the figure with a dashed red line) is more stringent, except in a small region for intermediate Higgs masses.

    If one wished to argue more in detail about the sensitivity of the two experiments, one should in truth take the dashed curves, which show the expected limits (i.e., the median range of the exclusion limit that the experiments would expect to set with  the available data and the analyses used). In this case one could still argue that at low mass the DZERO search is still superior to the CMS one; but of course, given that the CERN experiments are already sitting on thirty times more data than that reported in the graph, there is no question that this is now exclusively a LHC business. I look forward to the next ATLAS and CMS results for summer conferences, where the breathing space for the MSSM in the Higgs sector is going to become really uncomfortable. Of course: the MSSM is a beautiful, wrong construct, if you ask me.

    Comments

    The allowed "head" on the left side of the figure is intriguing. The limits are weaker than expected; the data seem to repel us from the center of the head, like if something were there. ;-) Is there something else than can rule out e.g. m_A = 100 GeV and tan(beta)=28 or so?

    dorigo
    Well Lubos, but you see that there CMS has a better limit than expected... As normally happens (if backgrounds are correctly evaluated, and predictions are non correlated), when one experiment fluctuates up, the other fluctuates down ;-)

    I am unaware of anything excluding your pet point, but be patient and it will get ruled out too!

    Cheers,
    T.
    Rick Ryals
    Where's the "Like" button at?... ;)
    dorigo
    On the top right, just below the title Rick!

    Cheers,
    T.
    Rick Ryals
    HaHa... I was referring to your comment, but thanks.
    Except that even CMS has a fingerprint going in the right direction around that point. ;-) CMS generally has stronger limits then expected, but around this head, they're the same, so the relative shape of the real-expected limit is similar around that point.

    It is not my pet point. I have other pet points haha.

    Hi Tommaso,

    can you explain the difference between "expected" and "exclusion"?

    In particular, what's the difference in their computation.

    Thanks,

    Stefano

    Stefano, a difference is that the "expected exclusion" doesn't depend on the new data you took while "exclusion" does. "Expected exclusion" is calculated from the assumption that the Standard Model - with an ad hoc subtraction of all Higgs boson contributions etc. because they haven't been seen - is the right description. So the expected exclusion is the calculated average what you would expect to be the exclusion limit after the same amount of data. The real exclusion is a real exclusion extracted from the data.

    It's like when you're testing a theory that Greece has responsible people in it. So you may have an "expected moment when Greece runs out of money". Last year, when the country swallowed 110 billion euro, the expected point was around 2013 or so. However, the observed point is July 2011, earlier than expected, by two years. So it is about a 60-sigma evidence that Greece doesn't have any responsible people and the money has been thrown - and is still being thrown - into a trash bin.

    dorigo
    Hi Lubos,

    all right, except that one should substitute "median" for "average" in your first paragraph.

    Cheers,
    T.
    There is nothing uncomfortable for the MSSM about this particular search, because just about every MSSM model has M_A >> 300 GeV.

    The future searches for MSSM Higgs may make breathing uncomfortable for the MSSM, but mostly only to the extent that they make it even more uncomfortable for the Standard Model Higgs.

    And, of course "36 inverse femtobarns" should be "36 inverse picobarns" in the last sentence of the next-to-last paragraph.

    dorigo
    Hi Anna,

    ah! Ok, thinking in femtobarns units by now... Will correct!

    In general I agree... SUSY is much more harmed by the direct Missing Et searches than by these ones... But I like to remark every time I can that as space points get wiped out, one's belief in the theory should decrease, lest one declares that one rejects Bayesian thinking.

    Cheers,
    T.
    Hi, I was wondering if you could write an article on how the lack of SUSY/MSSM, lack of extra dimensions, and lack of missing energy harms or does not harm string theory. I am confused, how is it that none of the lectures at the QG 11 is a mixed conference in Zurich involve the failures of SUSY and how to compensate for that. Am I over emphysizing the importance of SUSY to string theory? My professor at college had briefly stated that although SUSY is not required for ST, the most promising models suggest it. Therefore EDM uniformity and the lack of detection of SUSY removes the most promising models of ST.

    In fact in Blau's paper "String Theory as a Theory of Quantum Gravity: A Status Report" he states:

    Originally Posted by Blau
    Supersymmetry: Required for stability of string theory / allows controlled calculations - significance for quantum gravity in general beyond that? (but strongly coupled gauge theories without supersymmetry have regretful tendency to exhibit instabilities; and who knows what happens when one includes full set of standard model fields in other approaches to quantum gravity)

    and

    Originally Posted by Blau
    "Space is Emergent! When Xa diagonal ) interpretation as ordinary space-time coordinates of N D0-branes. For these “flat directions” of the potential to be preserved by quantum corrections, supersymmetry is essential!"

    Yet he does not mention SUSY any further in the article. I have not read all the articles for ST, but so far it seems String theorists are brushing aside the problem of SUSY and ST. Do any of the papers cited talk about the 2011 indiction of SUSY and how it effects ST?

    Is this the biggest elephant in the closet for string theorists or is it not as big a deal as I believe?

    Hi,
    "as space points get wiped out, one's belief in the theory should decrease"
    lets say one's belief in the most constrained versions of the MSSM should decrease.

    Actually, the preferred mass for a SM Higgs boson has been already excluded long ago! This does not restrain me from believing in the electroweak symmetry breaking mechanism. To beautiful not to be true.
    In that sense, that's Gods particle for me.

    We should let belief to the church, as one of my undergrad advisors told me after I said that I believed my calculation was right.
    F.

    I always enjoy your articles, Tommaso. Would you please explain this statement.

    >> "the MSSM is a beautiful, wrong construct, if you ask me"

    Thanks

    dorigo
    Hi Frank,

    nothing much... Only that I do not believe it is a correct theory of nature. It is just an interesting attempt, but I can't reconcile it with Occam's razor!

    Cheers,
    T.
    Rick Ryals
    Words of a truly scientific mind, T.  Too bad that the theoretical branch of your discipline no longer abides by this constraint.  I am confident that you will be vindicated.
    Hi,

    Thanks for this nice review. However, I think I have found a small glitch. You wrote:

    "the limit resulting from the search performed by CMS with just 36 inverse femtobarns (duly reported in the figure with a dashed red line) is more stringent, except in a small region for intermediate Higgs masses."

    But, if I look at the figure, it seems to me that the observed limit is the full line, then the CMS limit would be more stringent than the D0 limit for all Higgs masses. Is that Ok?

    Regards,

    J

    dorigo
    Hi J,

    indeed, that sentence has two separate mistakes. One is the one you mention, the other is that it is 36 picobarns, not femtobarns.

    I will fix it as I find some time....

    Cheers,
    T.
    Sorry I meant to post this at the bottom
    Hi, I was wondering if you could write an article on how the lack of SUSY/MSSM, lack of extra dimensions, and lack of missing energy harms or does not harm string theory. I am confused, how is it that none of the lectures at the QG 11 mixed conference in Zurich involve the failures of SUSY and how to compensate for that. Am I over emphysizing the importance of SUSY to string theory? My professor at college had briefly stated that although SUSY is not required for ST, the most promising models suggest it. Therefore EDM uniformity and the lack of detection of SUSY removes the most promising models of ST.

    In fact in Blau's paper "String Theory as a Theory of Quantum Gravity: A Status Report" he states:

    Originally Posted by Blau
    Supersymmetry: Required for stability of string theory / allows controlled calculations - significance for quantum gravity in general beyond that? (but strongly coupled gauge theories without supersymmetry have regretful tendency to exhibit instabilities; and who knows what happens when one includes full set of standard model fields in other approaches to quantum gravity)

    and

    Originally Posted by Blau
    "Space is Emergent! When Xa diagonal ) interpretation as ordinary space-time coordinates of N D0-branes. For these “flat directions” of the potential to be preserved by quantum corrections, supersymmetry is essential!"

    Yet he does not mention SUSY any further in the article. I have not read all the articles for ST, but so far it seems String theorists are brushing aside the problem of SUSY and ST. Do any of the papers cited talk about the 2011 indiction of SUSY and how it effects ST?

    Is this the biggest elephant in the closet for string theorists or is it not as big a deal as I believe?

    dorigo
    Dear TI,

    I am afraid I am not an expert on string theory and its manifestations in particle physics. I can only say that no observation at the LHC can disprove (or prove) the correctness of String Theory. So I basically am not very interested in whether something hints at it. Yes, some sort of SUSY appears called for, but there is no proof that I know of (and I would not understand it anyway).

    In general, a String theorist can always go hide in the landscape if all his or her "predictions" get refuted... I would like to hear what Lubos has to say about this though: I sort of remember he claims that some sort of SUSY is indeed required - at least for himself to remain a believer. But remember, there's always split SUSY, where LHC would be unable to disprove anything at all... These theorists are clever, their theories come with a back-door built in.

    I suggest you turn this question to the Reference Frame, and to Not Even Wrong, for two diametrically opposed views on the matter. The latter appears to deal exactly with the theme of your question (with comments by David Gross) in the latest posting.

    Cheers,
    T.
    Thanks for the insight! Sorry for the delay response, but I had trouble finding this link. Wouldn't the lack of EDM distortion also make split supersymmetry very unlikely as some kind of distortion must be seen for SUSY to exist?

    If Planck's length is 10^-35 how are we able to see 10^-48? I am confused!