Multiple solutions in supersymmetry and the Higgs

susyB.C. Allanach
Weak-scale supersymmetry is a well motivated, if speculative, theory beyond the Standard Model of particle physics.
It solves the thorny issue of the Higgs mass, namely: how can it be stable to quantum corrections, when they are expected to be 1015 times bigger than its mass? The experimental signal of the theory is the production and measurement of supersymmetric particles in the Large Hadron Collider experiments.
No such particles have been seen to date, but hopes are high for the impending run in 2015. Searches for supersymmetric particles can be difficult to interpret.
Here, we shall discuss the fact that, even given a well defined model of supersymmetry breaking with few parameters, there can be multiple solutions.
These multiple solutions are physically different, and could potentially mean that points in parameter space have been ruled out by interpretations of LHC data when they shouldn’t have been.
We shall review the multiple solutions and illustrate their existence in a universal model of supersymmetry breaking.
Read more at http://arxiv.org/pdf/1401.8185v1.pdf

Higgs boson is too saintly and supersymmetry too shy


by Michael Slezak
HOPES of using the Higgs boson and the elegant theory of supersymmetry as shortcuts to discovering the mysteries of the universe are evaporating fast. That’s the verdict of a major update from the Large Hadron Collider in CERN, near Geneva, Switzerland – the first since a boson resembling the Higgs was spotted there earlier this year.

“If our understanding of nature is correct, then the details of what happens next are more complicated than we had hoped,” says Matthew Walker of CMS, one of the major LHC detectors.

In July, when CMS and its sister detector, ATLAS, announced the discovery of the boson, anomalies in the data hinted at physics beyond the standard model, the well-established description of the universe’s particles and forces.

Such new physics is urgently needed because the standard model contains no mention of dark matter, makes incorrect predictions about the universe’s antimatter and requires awkward “fine-tuning” to incorporate the Higgs mass reported in July.

The Higgs isn’t searched for directly, but spotted via a slew of particles that the standard model predicts it decays to. One anomaly in July’s particle debris was insufficient tau leptons, which could have implied the existence of non-standard particles (see “diagram”).

But on 14 November, armed with twice as much data, CMS and ATLAS researchers told the Hadron Collider Physics Symposium in Kyoto, Japan, that the number of taus has crept up, removing the hint of deviant physics. CMS also reported a signal suggesting that the boson behaves the same when viewed in a mirror, giving it the property of positive parity, which the standard model also predicts.

There’s still one anomaly left. In July, the newly discovered boson seemed to decay twice as often as predicted into pairs of photons, which could be the signature of an extra, non-standard particle, or of a non-standard Higgs. If that anomaly disappears too, the probable Higgs boson will look very standard indeed, which is strange because of all the known possible extensions to the standard model, none predicts a completely standard Higgs.

One explanation could lie in a theory called the Neutrino Minimal Standard Model (nuMSM), in which dark matter is actually a neutrino and the Higgs behaves so similarly to the standard model that the differences would be unobservable. Instead nuMSM might be discovered via space-based detectors that look for its proposed dark-matter particles, but it’s a long shot. Just because it seems to fit right now doesn’t mean nuMSM is the most plausible scenario, says Raymond Volkas of the University of Melbourne, Australia.

As if the boson’s good behaviour wasn’t frustrating enough, the LHC’s searches for particles predicted by supersymmetry (SUSY) have turned up nothing. As SUSY – which proposes a heavier superpartner for each known particle – extends the standard model to include dark matter and other omissions, this failure deals a further blow to possible sources of new physics at the LHC. It is also stoking exchanges between SUSY supporters and sceptics (see “SUSY no-show fuels debate”).

SUSY particles could show up at the higher LHC energies scheduled for 2014, after its year-long planned rest next year. But that is cold comfort to those hoping to have gleaned clues already. “I would, as a hunter of new physics, have liked to see it different to what we have now,” says Albert De Roeck of CMS. “But the data is the data.”
Read more: www.newscientist.com

New SUSY Limits From ATLAS


By Tommaso Dorigo
A new ATLAS search for supersymmetric signatures in 2011 LHC data has appeared last week in the arxiv. The result ? No hint of a signal, not even for ready money.

So if you are on a hurry, you can just have a glance at the graph below, which summarizes the measurement in terms of excluded regions of a slice of the complicated parameter space of SUSY theories…..

Read more: www.science20.com

Recent Results Of CMS

Two days ago I discussed at ICFP 2012 the most recent results of the CMS experiment at the CERN Large Hadron Collider. In the allotted time of my talk I could only cover few analyses, and I obviously chose some of the most interesting ones, so that was already a summary. Here I am bringing the information collapse one step further, by giving a itemized summary of some of the points I made, just in case you are interested. If you want to, you can also download the original slides of my talk from here (but be careful, it’s a 8Mb file).

– The LHC has yielded over 5 inverse femtobarns of proton-proton collisions to CMS to analyze in 2011, and these data have been used for dozens of new results. Now we have on tape another 5/fb of data from the 2012 run, but these have not been looked at yet (results will be ready in a few days).

– We can broadly divide 2011 results into three areas: searches for Higgs bosons, Standard Model measurements, and new physics searches.

– CMS searched for the Higgs boson in eight independent final states, further divided in over forty categories. The combined results of these searches say that the particle must be lighter than 127 GeV (and heavier than 115 according to LEP II), or heavier than 600 GeV. We know the latter is not an option as far as the Standard Model is concerned, because it would now be utterly inconsistent with other electroweak measurements. So we might argue that if the SM Higgs exists, we already know its mass to better than 10% accuracy.

– CMS finds a signal with a local significance of 3.1 standard deviations at 124 GeV. If this excess is due to the Higgs boson, it is likely that the new data, once analyzed, will produce additional evidence which can be considered conclusive proof for the particle’s existence.

– A new baryon, the Ξb*, has been observed in its fully exclusive cascade decay into J/ψ, proton, and pions (with intermediate Ξb and Λ states). Its mass is just short of 6 GeV (see picture on the right, showing the peak in the distribution of Q-value of the two-body decay Ξb*–>Ξb π).

– Rare decays of the Bs meson have been searched, and a tight limit on the Bs->μμ decay has been obtained by combining CMS results with LHCb and ATLAS ones. New physics models are strongly constrained by this limit because many realizations of NP would yield enhancements in the branching ratio for the dimuon decay mode.

– CMS now measures the top quark mass and cross section in a number of different techniques. The precision on the top mass is reaching the Tevatron average (1.25 GeV total error now). A new era of precision top physics measurements has started, with e.g. limits on Flavour-changing neutral current top decays constrained at the 0.34% level, and top-antitop mass difference measured to within 0.5 GeV (of course it is zero!).

– A large number of interesting searches for new physics returned null results. Supersymmetry has been investigates in dozens of possible signatures, with no positive result.

Below is my conclusions slide:

Read more: www.science20.com

New CERN Results On Rare B Decays

A Tombstone To SUSY ?

 The CERN average of searches for rare B decays to muon pairs has been shown yesterday in a talk given by Mitesh Patel at the “Physics at the LHC” conference, which is being held in Vancouver (BC) this week. And the results are not very encouraging for supporters of Supersymmetry: the data is compatible with a Standard Model signal, but there is almost no space left for additional contributions due to the exchange of virtual SUSY particles in the loops producing the decays……
Read more:www.science20.com

No SUSY In New CMS Search


By Tommaso Dorigo
This week’s graph comes from a recent publication by the CMS experiment, the one I am a proud member of together with about 3000 colleagues from all over the world.
CMS (see a 3-D sketch below) is one of the two huge detectors collecting the faint signals of particles produced in the powerful 8-TeV proton-proton collisions delivered by the CERN Large Hadron Collider. The CMS experiment has recently been publishing one by one the results of many largely independent searches for Supersymmetric particles in the data collected during 2011; not surprising to sceptics like me, these results are all “negative” ones: they describe the absence of a signal, which is however a very informative datum, since it can be turned into a bound on possible models of new physics…..
Read more: www.science20.com