Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Gluons don’t explain the spin surprise

17.11.2008
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.”

Reference

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:
http://www.rikenresearch.riken.jp/research/583/
http://www.researchsea.com

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

More articles from Physics and Astronomy:

nachricht Engineering team images tiny quasicrystals as they form
18.08.2017 | Cornell University

nachricht Astrophysicists explain the mysterious behavior of cosmic rays
18.08.2017 | Moscow Institute of Physics and Technology

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: Fizzy soda water could be key to clean manufacture of flat wonder material: Graphene

Whether you call it effervescent, fizzy, or sparkling, carbonated water is making a comeback as a beverage. Aside from quenching thirst, researchers at the University of Illinois at Urbana-Champaign have discovered a new use for these "bubbly" concoctions that will have major impact on the manufacturer of the world's thinnest, flattest, and one most useful materials -- graphene.

As graphene's popularity grows as an advanced "wonder" material, the speed and quality at which it can be manufactured will be paramount. With that in mind,...

Im Focus: Exotic quantum states made from light: Physicists create optical “wells” for a super-photon

Physicists at the University of Bonn have managed to create optical hollows and more complex patterns into which the light of a Bose-Einstein condensate flows. The creation of such highly low-loss structures for light is a prerequisite for complex light circuits, such as for quantum information processing for a new generation of computers. The researchers are now presenting their results in the journal Nature Photonics.

Light particles (photons) occur as tiny, indivisible portions. Many thousands of these light portions can be merged to form a single super-photon if they are...

Im Focus: Circular RNA linked to brain function

For the first time, scientists have shown that circular RNA is linked to brain function. When a RNA molecule called Cdr1as was deleted from the genome of mice, the animals had problems filtering out unnecessary information – like patients suffering from neuropsychiatric disorders.

While hundreds of circular RNAs (circRNAs) are abundant in mammalian brains, one big question has remained unanswered: What are they actually good for? In the...

Im Focus: RAVAN CubeSat measures Earth's outgoing energy

An experimental small satellite has successfully collected and delivered data on a key measurement for predicting changes in Earth's climate.

The Radiometer Assessment using Vertically Aligned Nanotubes (RAVAN) CubeSat was launched into low-Earth orbit on Nov. 11, 2016, in order to test new...

Im Focus: Scientists shine new light on the “other high temperature superconductor”

A study led by scientists of the Max Planck Institute for the Structure and Dynamics of Matter (MPSD) at the Center for Free-Electron Laser Science in Hamburg presents evidence of the coexistence of superconductivity and “charge-density-waves” in compounds of the poorly-studied family of bismuthates. This observation opens up new perspectives for a deeper understanding of the phenomenon of high-temperature superconductivity, a topic which is at the core of condensed matter research since more than 30 years. The paper by Nicoletti et al has been published in the PNAS.

Since the beginning of the 20th century, superconductivity had been observed in some metals at temperatures only a few degrees above the absolute zero (minus...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Call for Papers – ICNFT 2018, 5th International Conference on New Forming Technology

16.08.2017 | Event News

Sustainability is the business model of tomorrow

04.08.2017 | Event News

Clash of Realities 2017: Registration now open. International Conference at TH Köln

26.07.2017 | Event News

 
Latest News

A Map of the Cell’s Power Station

18.08.2017 | Life Sciences

Engineering team images tiny quasicrystals as they form

18.08.2017 | Physics and Astronomy

Researchers printed graphene-like materials with inkjet

18.08.2017 | Materials Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>