Transverse single spin asymmetries for the production of neutral pions in proton collisions at √s = 200 GeV

doctoral thesis

• Title (croatian): Transverzalne jednostruke spinske asimetrije pri produkciji neutralnih piona u protonskim sudarima na Vs=200GeV
• Author: Nikola Poljak
• Mentor: Mirko Planinić (mentor)
• Mentor: Leslie Carlisle Bland (komentor); strani drzavljanin: Nije dostupno
• Committee member: Krešo Kadija (predsjednik povjerenstva)
• Committee member: Mirko Planinić (član povjerenstva)
• Committee member: Leslie Carlisle Bland (član povjerenstva); strani drzavljanin: Nije dostupno
• Committee member: Miroslav Furić (član povjerenstva)
• Committee member: Ivica Picek (član povjerenstva)
• Granter: University of Zagreb; Faculty of Science; (Department of Physics); Zagreb
• Defense date and country: 2010-11-29, Croatia
• Scientific / art field, discipline and subdiscipline: NATURAL SCIENCES; Physics
• Universal decimal classification (UDC): 53 - Physics

Abstract

The STAR collaboration has reported precision measurements on the transverse single spin asymmetries for the production of forward π0 mesons from polarized proton collisions at √s = 200 GeV. To disentangle the contributions to forward asymmetries, one has to look beyond inclusive π0 production to the production of forward jets or direct photons. Present forward detector capabilities are not well matched to the complete reconstruction of forward jets, but do have sufficient acceptance for "jet-like" events. "Jet-like" events are the clustered response of an electromagnetic calorimeter that is primarily sensitive to incident photons, electrons and positrons. During the RHIC running in the year 2006, STAR with the Forward Pion Detector (FPD++) in place collected 6.8 pb-1 of data with an average polarization of 60%. FPD++ was a modular detector prototype of the Forward Meson Spectrometer (FMS) that consisted of two detectors placed symmetrically with respect to the beam line at a distance of 7.4 m from the interaction point. Readout of the FPD++ was triggered when the sum of energies in the central module of the calorimeter used for π0 measurements was larger than a threshold. This trigger minimizes the bias for "jet-like" events, making it appropriate to disentangling contributions to the forward transverse spin asymmetries. This thesis reports on the analysis, giving in specific detail all the calibration and analysis steps, as well as the final results. It has been demonstrated that the calibration procedures used earlier to calibrate the previous versions of the detector can be extended to the current setup. Results from earlier analyses were successfully reproduced and extended as well. It has been shown that the parts of the detector that were not used earlier have no systematic influence on the results. After the extraction of the "jet-like" events, their properties were carefully explored. The final result shows that the neutral pion asymmetry shows no dependence on the angle with respect to the "jet-like" event axis, thus showing that there is no net Collins contribution to the neutral pion asymmetries.

Abstract (croatian)

STAR kolaboracija je objavila precizna mjerenja transverzalnih jednostrukih spinskih asimetrija za produkciju neutralnih piona pod malim kutovima na energiji od √s = 200 GeV. Da bi se razdvojili doprinosi asimetriji na malim kutovima, potrebno je gledati dalje od produkcije neutralnih piona u produkciju mlazova. Trenutan kalorimetarski postav ne dozvoljava potpunu rekonstrukciju mlazova, ali ima dobru prihvatnost za "mlazolike" događaje. Ti događaji odgovaraju odazivu elektromagnetskog kalorimetra, koji je prvenstveno osjetljiv na upadne fotone, elektrone i pozitrone. Tijekom RHIC Run-a u 2006. godini, STAR je sa Forward Pion Detector ++ (FPD++) detektorom sakupio 6.8 pb-1 podataka sa prosječnom polarizacijom od 60 %. FPD++ je modularni detektor koji se sastojao od dva modula postavljena simetrično u odnosu na snopove na udaljenosti 7.4 m od točke interkacije. Očitanje FPD++a je bilo okinuto kad god bi ukupna energija u jednom od središnjih modula premašila neku prethodno zadanu vrijednost. Ovakav način okidanja idealan je za mlazolike događaje, što detektor čini izvrsnim alatom za razdvajanje doprinosa asimetriji. Ova teza daje izvještaj o analizi, dajući detalje svih koraka uključujući kalibraciju, analizu i konačan rezultat. Pokazano je da se procedure koje su se koristile ranije za kalibraciju prethodnih detektora mogu uspješno proširiti na trenutni postav. Rezultati koji su dobiveni prethodnim analizama su potvrđeni i prošireni ovom analizom. Također je pokazano da djelovi detektora koji se nisu koristili za prethodno objavljene rezultate nemaju sistematskih utjecaja na konačan rezultat. Nakon separacije multifotonskih događaja, njihova svojstva su pomno proučena. Konačan rezultat pokazuje da asimetrija neutralnih piona ne pokazuje ovisnost o kutu koji pion zatvara sa osi događaja, čime je dokazano da nema Collinsovog doprinosa pionskoj asimetriji.

• Keywords: single spin asymmetry; STAR collaboration; proton collisions
• Keywords (croatian): jednostruka spinska asimetrija; STAR kolaboracija; protonski sudari
• Language: english
• URN:NBN: urn:nbn:hr:217:120599
• Study programme: Title: Physics; Study programme type: university; Study level: postgraduate; Academic / professional title: doktor/doktorica znanosti, područje prirodnih znanosti, polje fizika (doktor/doktorica znanosti, područje prirodnih znanosti, polje fizika)
• Type of resource: Text
• Extent: 179 str.
• File origin: Born digital
• Access conditions: Open access
• Created on: 2017-08-24 07:50:38