Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Sifting out the sources of spin

02.11.2009
High-energy proton collisions help solve the puzzle of what determines the proton’s spin

Along with the neutron, the proton is the basic building block of the atomic nucleus. But, the source of the proton’s spin—a fundamental property, along with charge—has been a long standing puzzle to scientists.

By analyzing data from the BNL Relativistic Heavy Ion Collider (RHIC), the PHENIX collaboration at Brookhaven National Laboratory in Upton, USA, including scientists from the RIKEN BNL Research Center and the RIKEN Nishina Center for Accelerator-Based Science, has now ruled out gluons—the particles that exchange the so-called strong force between the quarks that make up the proton—as the dominant contributor to proton spin.

There are three quarks—two ‘up’ quarks and one ‘down’ quark— in the proton. Each quark has a spin of ½ and they configure with respect to each other—two up and one down—so the sum of their spins is ½. For this reason, scientists thought the spin of the proton, which is also ½, came entirely from quarks.

Experiments in the 1980s, however, showed that quarks only contribute about 25% of the total spin of the proton. “This result was so surprising that it was called the ‘spin-crisis’,” says Yasuyuki Akiba, a member of the PHENIX team. Particle physicists were therefore confronted with a fundamental question: What else contributes to the spin of the proton?

Some models predict that the missing spin comes mainly from gluons, while others suggest that the contribution from the orbital angular momentum of quarks within the proton may also be significant. To determine the contribution from gluons, the PHENIX team analyzed data from a year-long experiment performed at RHIC in 2006.

In this experiment, protons were collided at very high energies approximating 200 GeV, where 1 GeV is equal to one billion electron volts, to produce particles called pions. The researchers derived the gluon contribution to the proton spin from the difference between the number of pions produced by colliding protons with their spins lined up in the same direction to one another versus those lined up in opposite directions.

The important result from the PHENIX team’s work is that the gluon contribution to the proton spin is actually small. “The best estimate is that it is about 40%, but the data don’t rule out that it is zero,” explains Akiba. “Although there is still a significant uncertainty in this result, our data show that models predicting large gluon spin can now be firmly excluded.”

The corresponding author for this highlight is based at the Experimental Group, RIKEN BNL Research Center

Journal information

Adare, A., Afanasiev, S., Aidala, C., Ajitanand, N.N., Akiba, Y., Al-Bataineh, H., Alexander, J., Aoki, K., Aphecetche, L., Asai, J. et al. (PHENIX Collaboration) Gluon-spin contribution to the proton spin from the double-helicity asymmetry in inclusive π0 production in polarized p + p collisions at √s = 200 GeV. Physical Review Letters 103, 012003 (2009)

Saeko Okada | Research asia research news
Further information:
http://www.rikenresearch.riken.jp/eng/research/6054
http://www.researchsea.com

More articles from Physics and Astronomy:

nachricht First Juno science results supported by University of Leicester's Jupiter 'forecast'
26.05.2017 | University of Leicester

nachricht Measured for the first time: Direction of light waves changed by quantum effect
24.05.2017 | Vienna University of 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: Can the immune system be boosted against Staphylococcus aureus by delivery of messenger RNA?

Staphylococcus aureus is a feared pathogen (MRSA, multi-resistant S. aureus) due to frequent resistances against many antibiotics, especially in hospital infections. Researchers at the Paul-Ehrlich-Institut have identified immunological processes that prevent a successful immune response directed against the pathogenic agent. The delivery of bacterial proteins with RNA adjuvant or messenger RNA (mRNA) into immune cells allows the re-direction of the immune response towards an active defense against S. aureus. This could be of significant importance for the development of an effective vaccine. PLOS Pathogens has published these research results online on 25 May 2017.

Staphylococcus aureus (S. aureus) is a bacterium that colonizes by far more than half of the skin and the mucosa of adults, usually without causing infections....

Im Focus: A quantum walk of photons

Physicists from the University of Würzburg are capable of generating identical looking single light particles at the push of a button. Two new studies now demonstrate the potential this method holds.

The quantum computer has fuelled the imagination of scientists for decades: It is based on fundamentally different phenomena than a conventional computer....

Im Focus: Turmoil in sluggish electrons’ existence

An international team of physicists has monitored the scattering behaviour of electrons in a non-conducting material in real-time. Their insights could be beneficial for radiotherapy.

We can refer to electrons in non-conducting materials as ‘sluggish’. Typically, they remain fixed in a location, deep inside an atomic composite. It is hence...

Im Focus: Wafer-thin Magnetic Materials Developed for Future Quantum Technologies

Two-dimensional magnetic structures are regarded as a promising material for new types of data storage, since the magnetic properties of individual molecular building blocks can be investigated and modified. For the first time, researchers have now produced a wafer-thin ferrimagnet, in which molecules with different magnetic centers arrange themselves on a gold surface to form a checkerboard pattern. Scientists at the Swiss Nanoscience Institute at the University of Basel and the Paul Scherrer Institute published their findings in the journal Nature Communications.

Ferrimagnets are composed of two centers which are magnetized at different strengths and point in opposing directions. Two-dimensional, quasi-flat ferrimagnets...

Im Focus: World's thinnest hologram paves path to new 3-D world

Nano-hologram paves way for integration of 3-D holography into everyday electronics

An Australian-Chinese research team has created the world's thinnest hologram, paving the way towards the integration of 3D holography into everyday...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Marine Conservation: IASS Contributes to UN Ocean Conference in New York on 5-9 June

24.05.2017 | Event News

AWK Aachen Machine Tool Colloquium 2017: Internet of Production for Agile Enterprises

23.05.2017 | Event News

Dortmund MST Conference presents Individualized Healthcare Solutions with micro and nanotechnology

22.05.2017 | Event News

 
Latest News

How herpesviruses win the footrace against the immune system

26.05.2017 | Life Sciences

Water forms 'spine of hydration' around DNA, group finds

26.05.2017 | Life Sciences

First Juno science results supported by University of Leicester's Jupiter 'forecast'

26.05.2017 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>