Imaging of the three-dimensional quark-gluon structure of the proton via analysis of deeply virtual electron scattering

doctoral thesis

• Title (english): Oslikavanje trodimenzijske kvarkovsko-gluonske strukture protona analizom duboko virtualnih raspršenja elektrona
• Author: Marija Čuić
• Mentor: Krešimir Kumerički (mentor)
• Committee member: Goran Duplančić (predsjednik povjerenstva)
• Committee member: Krešimir Kumerički (član povjerenstva)
• Committee member: Damir Bosnar (član povjerenstva)
• Granter: University of Zagreb; Faculty of Science; (Department of Physics); Zagreb
• Defense date and country: 2024, Croatia
• Scientific / art field, discipline and subdiscipline: NATURAL SCIENCES; Physics
• Universal decimal classification (UDC): 53 - Physics

Abstract

The study of the structure of the proton has been an ongoing effort ever since its first experimental discovery in 1917 by Rutherford. As experimental methods progressed, and the properties of the proton, such as its mass, spin and charge, were uncovered, the question of its underlying structure arose. Experiments conducted in 1969 at SLAC undoubtedly confirmed the fact that the proton is not an elementary particle, but that it consists of smaller particles, which we now recognize as quarks and gluons. From that point on, physicists tried to understand how exactly the interplay of quarks and gluons inside the proton gives rise to its properties. One of the ways we can experimentally study the proton is through hard exclusive processes, such as deeply virtual Compton scattering (DVCS) and deeply virtual meson production (DVMP), which give access to a class of functions called generalized parton distributions (GPDs). GPDs describe the three dimensional structure of the proton, and they are a potential solution to the proton spin puzzle. It is currently not possible to extract GPDs from measurements directly, since they are convoluted with hard scattering amplitudes inside cross sections, and deconvolution is in itself an ill-posed problem. These functions are also not possible to calculate from first principles due to the non-perturbative nature of QCD, so we rely on modeling
and machine learning methods in order to extract them from measurements. In this work we present recent results on the extraction of GPDs and relevant form factors from DVCS and DVMP data. Using the more recent proton DVCS data, we extract the set of leading Compton form factors (CFFs) with uncertainties and, by adding neutron DVCS data, we separate the contributions of up and down quarks to the CFF H. We make simultaneous fits to high energy deep inelastic scattering, DVCS and DVMP data at low x and study the impact of next-to-leading order (NLO) corrections, as well as the possibility of a unique description of these processes with twist-2 GPDs. We demonstrate a sizeable impact of NLO corrections and that extraction of unique GPDs becomes possible at NLO.

Abstract (english)

Proučavanje strukture protona započelo je prije više od 100 godina. Od prvog Rutherfordovog otkrića 1917., kada se smatralo da je proton točkasta čestica, preko razumijevanja da ipak ima podstrukturu, pa do mjerenja dubokog neelastičnog raspršenja 1969. na SLAC-u, gdje se potvrdilo da je ta podstruktura netrivijalna, proučavanje protona, osnovne građevne jedinice svemira, predstavlja uzbudljivo i rastuće područje u fizici. U ovom radu bavit ćemo se strukturom protona kroz proučavanje generaliziranih partonskih distribucija (GPD-ova). GPD-ovi predstavljaju interesantno područje istraživanja utoliko što objašnjavaju trodimenzijsku raspodjelu kvarkova i gluona u protonu, daju rješenje zagonetke protonskog spina, kao i mnoga druga svojstva. Povijesni tijek eksperimentalnog ispitivanja svojstava protona krenuo je s elastičnim raspršenjem. Nabijena proba, tipično elektron, sudara se s protonom i raspršuje se na njemu. Elektromagnetska interakcija probe s protonom, koja se prenosi virtualnim fotonima, daje nam uvid u raspodjelu električnog naboja protona. Već se ovakvim eksperimentom može vidjeti da proton nije točkasta čestica, nego da posjeduje prostornu protežnost. Povećavanjem energije elektrona dolazimo u režim neelastičnog raspršenja, gdje struktura protona apsorbira dio energije elektrona. Elektromagnetska svojstva protona razotkrivena ovim eksperimentom ne mogu doći od elementarne čestice, čime se nazire netrivijalna podstruktura protona.

• Keywords: proton; generalized parton distributions; deeply virtual Compton scattering; Compton form factors
• Keywords (english): proton; generalizirane partonske distribucije; duboko virtualno komptonsko raspršenje; komptonski form faktori
• Language: croatian
• URN:NBN: urn:nbn:hr:217:414762
• Promotion: 2024
• Project: Number: 824093; Title: Jaka nuklearna sila na granici znanja: temeljna istraživanja i primjene; Acronym: STRONG-2020; Leader: Milorad Korolija, Damir Bosnar, Krešimir Kumerički, Kornelija Passek-Kumerički; Jurisdiction: eu; Funder: Europska komisija; Funding stream: Obzor 2020
• Study programme: Title: Doctoral study; Study programme type: university; Study level: postgraduate; Academic / professional title: doktor/doktorica znanosti u području prirodnih znanosti (doktor/doktorica znanosti u području prirodnih znanosti)
• Type of resource: Text
• File origin: Born digital
• Access conditions: Open access
• Created on: 2024-02-16 13:09:33