Volume 548 Issue 7665



News Features

News & Views

The fastest-rotating fluid p.34

A state of matter called a quark–gluon plasma is produced in energetic collisions of heavy ions. The rotation of this plasma has been measured for the first time, providing insights into the physics of the strong nuclear force. See Letter p.62

doi: 10.1038/548034a

Neurons couple up to make decisions p.35

The use of state-of-the-art techniques to study neuronal activity during a navigational task involving sound stimuli broadens our understanding of how neuronal populations produce complex behaviours. See Letter p.92

doi: 10.1038/nature23100

Energy sensing through a sugar diphosphate p.36

The molecule fructose-1,6-bisphosphate, which is produced during glucose metabolism, has been shown to mediate cellular sensing of glucose deprivation through an unexpected mechanism. See Letter p.112

doi: 10.1038/nature23099

Ozone-like layer in an exoplanet atmosphere p.38

The nature of exoplanetary atmospheres is hotly debated. The thermal spectrum of an exoplanet called a hot Jupiter reveals the presence of an analogue of Earth's ozone layer, although its composition is unknown. See Letter p.58

doi: 10.1038/548038b

A precision approach to tumour treatment p.40

Progress is being made in the use of personalized approaches to create both in vitro and in vivo tumour models that could be used to aid cancer drug-treatment decisions and increase our understanding of how tumours respond to therapy.

doi: 10.1038/nature23101




An ultrahot gas-giant exoplanet with a stratosphere p.58

Observations of the gas-giant exoplanet WASP-121b reveal near-infrared emission lines of water, suggesting that the planet has a stratosphere—a layer in the upper atmosphere where temperature increases with altitude.

doi: 10.1038/nature23266

Global Λ hyperon polarization in nuclear collisions p.62

The extreme energy densities generated by ultra-relativistic collisions between heavy atomic nuclei produce a state of matter that behaves surprisingly like a fluid, with exceptionally high temperature and low viscosity. Non-central collisions have angular momenta of the order of 1,000ћ, and the resulting fluid may have a strong vortical structure that must be understood to describe the fluid properly. The vortical structure is also of particular interest because the restoration of fundamental symmetries of quantum chromodynamics is expected to produce novel physical effects in the presence of strong vorticity. However, no experimental indications of fluid vorticity in heavy ion collisions have yet been found. Since vorticity represents a local rotational structure of the fluid, spin–orbit coupling can lead to preferential orientation of particle spins along the direction of rotation. Here we present measurements of an alignment between the global angular momentum of a non-central collision and the spin of emitted particles (in this case the collision occurs between gold nuclei and produces Λ baryons), revealing that the fluid produced in heavy ion collisions is the most vortical system so far observed. (At high energies, this fluid is a quark–gluon plasma.) We find that Λ and hyperons show a positive polarization of the order of a few per cent, consistent with some hydrodynamic predictions. (A hyperon is a particle composed of three quarks, at least one of which is a strange quark; the remainder are up and down quarks, found in protons and neutrons.) A previous measurement that reported a null result, that is, zero polarization, at higher collision energies is seen to be consistent with the trend of our observations, though with larger statistical uncertainties. These data provide experimental access to the vortical structure of the nearly ideal liquid created in a heavy ion collision and should prove valuable in the development of hydrodynamic models that quantitatively connect observations to the theory of the strong force.

doi: 10.1038/nature23004