Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:


Gluons don’t explain the spin surprise

New scattering data suggests that gluons make only a small contribution to the spin of protons and neutrons

Scientists have acquired more clues in the mystery of how the spin, or intrinsic angular momentum of a nucleon (proton or neutron), results from its constituent parts, quarks and gluons. Marco Stratmann at RIKEN’s Nishina Center for Accelerator-Based Science in Wako and co-workers (1) have used new scattering data to determine that the contribution from gluons is likely to be small.

Until about 20 years ago, it was assumed that the nucleon spin came about mainly from the sum of spins of its component quarks and antiquarks. This theory was discredited when scientists in the European Muon Collaboration at CERN, Switzerland, performed experiments scattering muons off nucleons.

“The result was very much off the theoretical expectation and has, ever since, been dubbed the ‘spin surprise’ or even ‘spin crisis’,” says Stratmann. “Quarks were shown to contribute only very little to the spin of the proton. This triggered a flurry of theoretical activity and motivated further experimental studies.”

RIKEN scientists have recently been involved in experiments at the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory in the USA, with the aim of determining whether the ‘missing’ nucleon spin is provided by the gluon spin. If the gluon spin contribution is small, there must be a role for the orbital angular momenta of both quarks and gluons.

Now Stratmann and co-workers have presented the first theoretical analysis that includes data from the RHIC. Their work also considers data from past experiments in deep inelastic scattering (DIS), the most basic type of scattering that provided the first evidence that quarks exist, and semi-inclusive deep inelastic scattering (SIDIS), which provides separate information on quarks and antiquarks.

The researchers determined the probability density functions of quarks and gluons and used a complicated optimization procedure to fit the functions to the data as well as possible. Their results suggest that the gluons have relatively small spin polarization, and so do not account for the spin of the nucleon.

“The spin structure of polarized nucleons is still poorly known despite the recent advances in both theory and experiment,” says Stratmann, “but experiments will continue to provide data, in particular the two RHIC experiments STAR and PHENIX. Soon the RHIC will produce the first data with two identified particles in the detector which will allow us to map the gluon polarization as a function of the gluon's momentum very precisely, and uncertainties will hopefully shrink by a factor of two or more.”


1. De Florian, D., Sassot, R., Stratmann, M. & Vogelsang, W. Global analysis of helicity parton densities and their uncertainties. Physical Review Letters 101, 072001 (2008).

The corresponding author for this highlight is based at the RIKEN Radiation Laboratory

Saeko Okada | ResearchSEA
Further information:

Further reports about: Gluons Quarks RHIC Relativistic Heavy Ion Collider antiquarks neutrons nucleon spin protons

More articles from Physics and Astronomy:

nachricht A new kind of quantum bits in two dimensions
19.03.2018 | Vienna University of Technology

nachricht 'Frequency combs' ID chemicals within the mid-infrared spectral region
16.03.2018 | American Institute of Physics

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Tiny implants for cells are functional in vivo

For the first time, an interdisciplinary team from the University of Basel has succeeded in integrating artificial organelles into the cells of live zebrafish embryos. This innovative approach using artificial organelles as cellular implants offers new potential in treating a range of diseases, as the authors report in an article published in Nature Communications.

In the cells of higher organisms, organelles such as the nucleus or mitochondria perform a range of complex functions necessary for life. In the networks of...

Im Focus: Locomotion control with photopigments

Researchers from Göttingen University discover additional function of opsins

Animal photoreceptors capture light with photopigments. Researchers from the University of Göttingen have now discovered that these photopigments fulfill an...

Im Focus: Surveying the Arctic: Tracking down carbon particles

Researchers embark on aerial campaign over Northeast Greenland

On 15 March, the AWI research aeroplane Polar 5 will depart for Greenland. Concentrating on the furthest northeast region of the island, an international team...

Im Focus: Unique Insights into the Antarctic Ice Shelf System

Data collected on ocean-ice interactions in the little-researched regions of the far south

The world’s second-largest ice shelf was the destination for a Polarstern expedition that ended in Punta Arenas, Chile on 14th March 2018. Oceanographers from...

Im Focus: ILA 2018: Laser alternative to hexavalent chromium coating

At the 2018 ILA Berlin Air Show from April 25–29, the Fraunhofer Institute for Laser Technology ILT is showcasing extreme high-speed Laser Material Deposition (EHLA): A video documents how for metal components that are highly loaded, EHLA has already proved itself as an alternative to hard chrome plating, which is now allowed only under special conditions.

When the EU restricted the use of hexavalent chromium compounds to special applications requiring authorization, the move prompted a rethink in the surface...

All Focus news of the innovation-report >>>



Industry & Economy
Event News

Virtual reality conference comes to Reutlingen

19.03.2018 | Event News

Ultrafast Wireless and Chip Design at the DATE Conference in Dresden

16.03.2018 | Event News

International Tinnitus Conference of the Tinnitus Research Initiative in Regensburg

13.03.2018 | Event News

Latest News

A new kind of quantum bits in two dimensions

19.03.2018 | Physics and Astronomy

Scientists have a new way to gauge the growth of nanowires

19.03.2018 | Materials Sciences

Virtual reality conference comes to Reutlingen

19.03.2018 | Event News

Science & Research
Overview of more VideoLinks >>>