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A second intriguing MSSM paper June 14, 2007

Posted by dorigo in astronomy, internet, news, physics, science.

Only today did I have a chance, with a week of delay, to give a close look at a fresh new paper by J.Ellis, S.Heinemeyer, K.A.Olive and G:Weiglein,  “Light Heavy MSSM Higgs Bosons at Large Tan(Beta)“.

The paper is a very interesting attempt at fitting our whole knowledge of those particle physics and astrophyisics observable quantities most connected to the choices of parameters within the Minimal SuperSymmetric extension of the Standard Model (MSSM) in a way that best marries the tentative Higgs signal which appeared last January in a beautiful analysis by CDF of MSSM higgs decays to tau lepton pairs.

The analysis, produced by CDF with the first available 1/fb worth of proton-antiproton collisions collected by the Tevatron, found a 2-sigma excess of reconstructed events in the tau-tau mass distribution, compatible with a 160 GeV MSSM higgs boson for a value of tan(beta) -a crucial parameter of the theory- close to 45. The find  made ripples in the web and on the media , but as exciting as it may be, the chances that it is a real new signal are zilch if compared to the odds that it is a mere fluctuation of the data.

Despite this cool-down remark, it is a perfectly legal thing to do to ask oneself how well does a “heavy” (in the sense that we are talking about the heavier of the neutral scalars – there are three in the MSSM) higgs and a value tan(beta)=45 go along with the other constraints on MSSM parameters coming from Bs decays to muon pairs, neutralino searches and bounds from dark matter searches, and g-2 measurements.

The new paper does exactly that, and it is a pleasant read. The authors use the model called NUHM, which they have shown in a previous paper to be a very interesting choice in the range of possible MSSM scenarios. From the abstract:

“…we find that a light heavy MSSM Higgs signal in the unexcluded part of the sensitive region could indeed be accommodated in this simple model, even after taking into account other constraints from cold dark matter, electroweak precision observables and B physics observables.”

It appears especially intriguing to note, as they are quick to do, that

“In this case the NUHM suggests that supersymmetric signatures should also be detectable in the near future in some other measurements such as BR(Bs->mu mu), BR(b->sgamma) and (g-2), and Mh would have to be very close to the LEP exclusion limit. In addition, the dark matter candidate associated with this model should be on the verge of detection in direct detection experiments.”

In their conclusions they specify things quite plainly in a few points:

“1) the predicted value of BR(Bs->mu mu) in the allowed region is generally > 2×10^(-8). Thus, this channel may offer good prospects within the near future for either supporting or contradicting the NUHM interpretation[…]

2) Mh must be very close to the LEP lower limit….This part of parameter space could be probed at the Tevatron with 8/fb of integrated luminosity.

3) The predicted value of BR(b->sgamma) in the allowed region is 4.6×10^(-4), which is about one standard deviation above the current experimental value […] Consequently, an improvement in the present theoretical uncertainty might enable a discrepancy to appear.

4) The discrepancy between experimental measurement of (g-2) and the SM calculation can easily be explained in this scenario […]”

And finally, quite interesting to note: 

“Performing a chi^2 fit for nine precision and B-physics observables along the lines of Ref.[19] yields a total value of chi^2=9-10 in the allowed part of the NUHM parameter space […]”

I must say I also appreciate a lot the realistic toning down which they put at the end of the paper:

“Very likely the weaker CDF tan(beta) bound from the search for heavy Higgs bosons compared to its expected sensitivity [i.e. the fact CDF saw a small excess at 160 GeV – TD] is due to a statistical fluctuation that will eventually evaporate. Nevertheless, it is interesting to know whether a signal at this level could be accommodated within the MSSM.”

Needless to say, the best thing about all the above is that it is a quite concrete view of the experimental panorama, and a meaningful stab in the darkness of Supersymmetric theories. At the very least, we will be able to exclude a very plausible scenario in the near future… It is good to have at least some power to falsify new physics theories nowadays!

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