APS Physics Tip Sheet – Jun 3, 2014
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New Four-Quark State Confirmed
The LHCb experiment provides conclusive evidence for the existence of a new four-quark particle called Z(4430).
In 2013, two collaborations (BESIII in Chine and Belle in Japan) reported the experimental signatures of a new particle called ZC(3900) that contained four quarks, defying the conventional wisdom that quarks only combine in pairs or triplets. LHCb—one of seven particle physics detector experiments collecting data at the Large Hadron Collider accelerator at CERN— has now reported a definitive observation of another four quark particle called Z(4430), for which some experimental hints were first collected by Belle in 2008. The analysis of the decay of B mesons generated by LHC’s collisions has revealed that Z(4330) is a bound state of four quarks and characterized its spin, charge and symmetry.
* LHCb Collaboration (contact author: Tomasz Skwarnicki), “Observation of the resonant character of the Z(4430) state,” Physical Review Letters (expected publication date: Jun 4)
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Understanding Marine Biodiversity
Biodiversity on land has been expanding exponentially, from few species at the beginning of the Phanerozoic to some million species today. But the growth dynamics of marine life has been very different: According to fossil records, about 500 million years ago the number of marine species began growing exponentially and then leveled off for 200 million years, before exploding again. A team of researchers from Germany and Switzerland has now constructed a model of species dependence that could explain this observation. The authors’ analysis, based on network dynamics, shows that a biodiversity stagnation can occur when species at the top of the ecological pyramid are dependent on only a few species at the bottom, whose extinctions can thus wipe out the whole ecosystem. Applying their model in combination with paleontological datasets, the authors argue this situation explains the observed slow-down of marine biodiversity.
* F. Stollmeier, T. Geisel, and Jan Nagler (contact author), “Possible origin of stagnation and variability of Earth’s biodiversity,” Physical Review Letter (expected publication date: June 5)
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The Physics of Adhesives
From Scotch™ tape and cling wrap to the footpads that allow spiders and geckos to climb vertical walls, dry adhesives serve as removable joints between dissimilar materials. Adhesion is often determined by weak bonds (of van der Waals type) and detachment is governed by the collective failure of such bonds. Researchers in Sweden have modeled the microscopic process of peeling off a thin film adhering to a surface with small bumps. The results show that tiny, random fluctuations in the bonds between the film and the surface can cause the film to peel off in a series of discrete steps, rather than in one continuous motion. Compared to previous work, the new model could provide better estimates of the forces needed to detach thin films from surfaces. This would be particularly important for nanotechnology applications, helping scientists find optimal ways to peel away sheets of graphene and other substances in the lab.
* Stefan B. Lindström (contact author), L. Johansson, and N.R. Karlsson, “Metastable states and activated dynamics in thin-film adhesion to patterned surfaces,” Physical Review E (expected publication date: Jun 6)
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Journal articles and preprints are available to journalists on request.
Matteo Rini, PhD
Deputy Editor, Physics
