Leonardo de Vinci spent many of his latter days in the Loire Valley and if you visit Ambrois you may still see his ghost parading for the tourists. While he was there he contributed a number of beautiful designs into the châteaux of the region including this spiral staircase at the Royal Chateau de Blois. There is an even more spectacular example in the nearby picturesque Chateau de Chambord where he used a double helix design so that people can pass from one floor to another without meeting, but it is at Blois where this week we find a conference to discuss some new findings in particle physics and cosmology.
Dark Matter in Cosmology
Yesterday included a talk by Joe Silk, prof of astronomy at Oxford, who summarised our understanding on the cold dark matter model including dark energy and dark matter. Simulations of galactic cluster and structure formation favour a model where dark matter is made of weakly interacting cold particles. The mass should be in the range 10GeV to 10TeV. The lighter end seems at odds with accelerator experiments which should have produced such particles unless they have a very low cross-section for production from interaction with standard model particles. However, some of the detectors build to directly detect passing WIMPs have found evidence for 7 GeV particles. They have even seen an annual variation in the signal consistent with a cosmological origin. Dark Matter particles may also annihilate to produce a cosmic halo of positrons and electrons that space observatories such as PAMELA may have detected. From the slides Silk seems to have neglected to mention the results from Xenon100, now in theory the most sensitive dark matter detector, which is at odds with other results because it sees nothing. Over all it is a very exciting time for dark matter with the hope that the LHC will resolve the matter by producing the expected particles in proton collision.
Silk also looked at dark energy results and provided this awe-inspiring plot of how different observations constrain the two parameter space of cosmological models.
The blue SNe area is from the supernova data that first indicated the acceleration of the universe. This was followed by the CMB cosmic microwave background analysis that produced an orthogonal constraint to pin down the cosmological parameters to a narrow region consistent with a flat universe. This year a third source of data came from measurements of galactic structures giving the BAO band in excellent agreement with earlier data. This is also sufficient to show that dark energy is well modeled by a cosmological constant rather than a variable that changes with time. The effect of the constant is to have less impact in the early universe, while now it accounts for 73% of the non-gravitational energy of the universe. As the universe ages the cosmological constant will continue to increase its domination. Despite this observational triumph its theoretical origin remains mysterious and should be tied up with theories of quantum gravity not yet understood.
Searches for the Higgs Boson
Later in the afternoon Giovanni Punzi delivered a talk that has already caused a stir around the blogosphere, see here, here, here, here. First take a look at some of his collected plots for Higgs searches.
All these plots show a small excess around the 110GeV – 120GeV region, but the size is not significant and the positions are not quite consistent. Will we look back on these graphics in a few months time as the first signals of the Higgs or as statistical flukes?
The real interest today is in observations from jets at CDF. Here is a plot from a few weeks back that appeared to show a mystery bump. This was widely poo-poo’ed by commentators including myself who said that it could be a statistical fluke or a background effect.
It shows exactly the same thing! This rules out a statistical fluke at about the 5 sigma level. CDF has also responded to suggestions that it could be due to incorrect scaling of the background, showing that this cannot account for the excess when modelled carefully. Finally they rule out a standard model effect from top quarks. We are left to conclude that it must be a real new effect due to a particle of 150 GeV that is not part of the standard model. the big question is whether it is also seen at D0 and will the LHC confirm it?