6.9.2019 A doctoral dissertation improves our description of nuclei at the level of fundamental particles (Paakkinen)

High-energy collision experiments can probe the structure of nuclei even down to the level of fundamental particles. In his doctoral dissertation Petja Paakkinen gives new information about the quark and gluon structure of nuclei. The research shows that the gluon distributions in protons and neutrons of heavy nuclei are similarly modified as has been previously observed for the quarks.
Published
6.9.2019

Atomic nuclei are composed of protons and neutrons. These, in turn, are composed of even smaller quarks and gluons, whose mutual strong interaction holds also the nuclei together. This very same interaction alters the internal structure of protons and neutrons when they are in close proximity inside the atomic nuclei. The dissertation aims at improving our understanding of these modifications.

The research uses data from the gargantuan particle collider at CERN. With this Large Hadron Collider (LHC), a beam of protons is made to collide with a beam of lead ions, the results of which can be used to investigate the fine structure of the lead nucleus.

”Whereas earlier experiments have given us information predominantly about the quark structure of nuclei, hadron colliders like the LHC are able to probe also the nuclear gluon structure more directly. The results show that gluon distributions in heavy nuclei are similarly modified as have previously been observed with quarks”, tells M.Sc Petja Paakkinen from the Ģֱ.

Distributions of different quarks are subject to similar nuclear modifications

Also, whether different quark distributions have different nuclear modifications has been poorly known.

”There are six different quarks, out of which ''up'' and ''down'' -quarks form protons and neutrons. A proton comprises of two up-quarks and one down-quark, and a neutron the other way around. Since a nucleus has typically almost equal amount of both, it has been difficult to compare the distributions of different quarks”, Petja Paakkinen explains.

This is now investigated by analysing results from a variety of different collision processes. These give evidence that different quarks feel the nuclear modifications in a similar way, but further studies are needed to confirm this.

The results of the dissertation can also be used in analysing the outcomes of similar collider experiments.

”For example, the improved understanding of nuclear quark and gluon structure gives substantial aid in studying the properties of the quark-gluon-plasma – a nuclear matter of very high temperature – produced in lead-lead collisions at CERN”, Paakkinen describes.

The research is published in JYU Dissertations -series, number 115, 2019, Ģֱ. ISBN 978-951-39-7828-0 (PDF) URN:ISBN:978-951-39-7828-0 ISSN 2489-9003.
Link to publication:

M.Sc. Petja Paakkinen defends his doctoral dissertation in Theoretical Physics ”New constraints for nuclear parton distribution functions from hadron–nucleus collision processes” on Friday 6th of September 2019 at 12 o’olock at Department of Physics in lecture hall FYS1 (Survontie 9, Ylistönrinne). Opponent is Professor Juan Rojo (Vrije Universiteit Amsterdam, Netherlands) and custos Docent Hannu Paukkunen (Ģֱ). The doctoral dissertation is held in English.

For further information:
Petja Paakkinen, petja.k.m.paakkinen@student.jyu.fi
Communications officer Tanja Heikkinen, tanja.s.heikkinen@jyu.fi, tel. +358 50 581 8351
The Faculty of Mathematics and Science 
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