Experiments may reveal new state of matterfor the 'glue particles', the gluons17 September 2012

Collisions between protons and lead nuclei wereestablished for the first time in the ALICE detector. Suchcollisions will enable scientists to investigate newaspects of the structure of nuclear particles.

(Phys.org)At the LHC accelerator at CERN,collisions between protons and lead nuclei wereestablished last week, for the first time in theALICE detector.

"These first tests exceeded all expectations. Theperformance of the LHC and the ALICE detector isremarkable. Collisions were established in recordtime and we collected the first collision data duringthe night, says Professor Jens Jrgen Gaardhje,at the Niels Bohr Institute, University ofCopenhagen and adds that the data now will beanalyzed at full speed.

Collisions between protons and lead nuclei willenable scientists to investigate new aspects of thestructure of nuclear particles. "It is of verysignificant interest to study asymmetric collisionsbetween large nuclei and the much smallerprotons", says Jens Jrgen Gaardhje andexplains, that when the protons hit a lead nucleus

it 'drills' a hole through the lead nucleus and leavesit relatively unscathed. As the proton cuts throughthe lead nuclei, the gluons inside the proton and thelead nucleus will collide and produce particles thatcan be measured in the Alice detector. In this wayone can investigate the properties of nuclearmatter, without heating it too much, as is done inlead-lead collisions.

It is the gluons, which are the bearers of the strongnuclear force, that the researchers are interested instudying. Gluons have the special property thatthey can interact with each other. This means thatgluons may split into several gluons of lesserenergy. If this splitting were to continue indefinitely,the nuclear particles would be filled with an infinitenumber of gluons of infinitely low energy andmomentum, Jens Jrgen Gaardhje explains andsays that this is untenable. Fortunately, through thesame mechanism gluons may also recombine andfuse together. It is therefore reasonable to assumethat a status quo is established, resulting in auniversal saturation density of gluons. The resultingstate of matter has been dubbed the Color GlassCondensate (CGC).

The existence of CGC has not so far beenunambiguously demonstrated, but the researchgroup, HEHI at Niels Bohr Institute measuredalready in 2005 indications that the CGC might berealized. If the CGC exists, it may be an entirelynew manifestation of Bose-Einstein Condensates(a situation in which the particles collect in thelowest energy states), in this case governed by thestrong interaction.

"This nights successful test run at CERN with theALICE detector is a preparation for the fullexperimental program scheduled to take place inJanuary-February of 2013. This initial run was sosuccessful, however, that it may already be able to

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give indications on whether the CGC exists innature. This state will be very interesting to studyand give us new opportunities to understand theproperties of saturated gluon matter ", says JensJrgen Gaardhje.

The research group, HEHI group atthe Niels BohrInstitute has built a special detector, the ForwardMultiplicity Detector (FMD), covering a largekinematical range, that will prove crucial for theinvestigation of the Color Glass Condensate.

Provided by University of Copenhagen

APA citation: Experiments may reveal new state of matter for the 'glue particles', the gluons (2012,September 17) retrieved 19 March 2015 from http://phys.org/news/2012-09-reveal-state-particles-gluons.html

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