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Nucleon parton distributions from hadronic quantum fluctuations
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, High Energy Physics.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Nuclear Physics.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, High Energy Physics. Swedish Collegium for Advanced Study, Uppsala, Sweden.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Nuclear Physics.
2019 (English)In: Physical Review D, ISSN 2470-0010, Vol. 100, no 3, article id 034003Article in journal (Refereed) Published
Abstract [en]

A physical model is presented for the nonperturbative parton distributions in the nucleon. This is based on quantum fluctuations of the nucleon into baryon-meson pairs convoluted with Gaussian momentum distributions of partons in hadrons. The hadronic fluctuations, here developed in terms of hadronic chiral perturbation theory, occur with high probability and generate sea quarks as well as dynamical effects also for valence quarks and gluons. The resulting parton momentum distributions f(x,Q20) at low momentum transfers are evolved with conventional Dokshitzer-Gribov-Lipatov-Altarelli-Parisi equations from perturbative QCD to larger scales. This provides parton density functions f(x,Q2) for the gluon and all quark flavors with only five physics-motivated parameters. By tuning these parameters, experimental data on deep-inelastic structure functions can be reproduced and interpreted. The contribution to sea quarks from hadronic fluctuations explains the observed asymmetry between ¯u and ¯d in the proton. The strange-quark sea is strongly suppressed at low Q2, as observed.

Place, publisher, year, edition, pages
2019. Vol. 100, no 3, article id 034003
National Category
Other Physics Topics Subatomic Physics
Research subject
Physics with specialization in Elementary Particle Physics
Identifiers
URN: urn:nbn:se:uu:diva-383265DOI: 10.1103/PhysRevD.100.034003ISI: 000478997000004OAI: oai:DiVA.org:uu-383265DiVA, id: diva2:1315142
Funder
Swedish Research Council, 621-2011-5107Available from: 2019-05-12 Created: 2019-05-12 Last updated: 2019-09-27Bibliographically approved
In thesis
1. The interplay between quark and hadronic degrees of freedom and the structure of the proton
Open this publication in new window or tab >>The interplay between quark and hadronic degrees of freedom and the structure of the proton
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

We study the low-energy sector of the strong interaction which is the least understood part of the Standard Model, the theory that describes the interactions of all known particles. The ideal particles for this study are the proton and the neutron, collectively called the nucleon. They make up the nucleus of all the atoms of our world and understanding them has been of high priority ever since their discovery. We show that one cannot neglect the effects of other hadrons, such as neutrons and pions when studying the proton. A large part of the proton's hadronic wavefunction is shown to consist of the wavefunctions of other hadrons. In other words, when probing the proton there is a sizeable probability that one is probing some other hadron surrounding the proton as a quantum fluctuation.

The nucleon itself consists of elementary particles known as quarks and gluons, collectively called partons. Exactly how the properties of these partons make up the properties of the nucleon has been the subject of active research ever since their discovery. Two main issues are the flavor asymmetry of the proton sea and the spin structure of the nucleon. To address these questions we study the interplay between the partonic and hadronic degrees of freedom. We introduce a model based on a convolution between hadronic quantum fluctuations as described by chiral perturbation theory, and partonic degrees of freedom motivated by a physical model of the nucleon having only few physically constrained parameters.

We present the hadronic distribution functions and the parton distribution functions. The results are in agreement with a large set of experimental data. These include the structure functions of the proton and the neutron. Agreement with the sum rules of the spin structure functions offers new insight into the spin structure of the nucleon.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2018. p. 99
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1711
National Category
Subatomic Physics
Identifiers
urn:nbn:se:uu:diva-357911 (URN)978-91-513-0420-5 (ISBN)
Public defence
2018-10-10, 80101, 09:00 (English)
Opponent
Supervisors
Available from: 2018-09-17 Created: 2018-08-21 Last updated: 2019-09-27

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