Title Measurement of the p(e, e' π+)n reaction with the short-orbit spectrometer at Q2 = 0.078 (GeV/c)2 Title (croatian) Mjerenje reakcije p(e, e' π+)n spektrometrom kratke orbite na Q2 = 0.078(GeV/c)2 Author Ivica Friščić Mentor Damir Bosnar (mentor)Committee member Matko Milin (predsjednik povjerenstva)Committee member Tamara Nikšić (član povjerenstva)Committee member Neven Soić (član povjerenstva)Committee member Ulrich Müller (član povjerenstva) Committee member Damir Bosnar (član povjerenstva)Granter University of Zagreb Defense date and country 2015-03-24, Croatia Scientific / art field, NATURAL SCIENCES Universal decimal classificationUDC ) 53 - Physics Abstract The precise measurement of the cross section for the p(e, e' π+)n reaction at certain kinematics, allows one to separate the cross section into quantities at a given four-momentum transfer Q2, which carry the information about the nucleon structure. Since the data at low Q2 are not known with an intended precision, a new measurement of the p(e, e' π+)n reaction was performed at Q2 = 0.078 (GeV/c)2 and at an invariant mass of W = 1094 MeV - approximately 15 MeV above the reaction threshold. The experimental work was accomplished by the A1 collaboration at the Institute for Nuclear Physics at the Johannes Gutenberg University of Mainz, Germany. The high quality electron beam was provided by the MAMI B accelerator with the energy range from 180 to 855 MeV. The produced charged pion was detected in the short-orbit spectrometer (SOS), which was constructed for a detection of the low-energy pions. The scattered electron was detected in the standard spectrometer A. For the first time, the complete analysis of the p(e, e' π+)n reaction data measured with the SOS was performed. New SOS-specific correction methods were developed to ensure a consistent data analysis. Some of the most important methods are the procedure of pion decay correction, the simulation for the determination of the muon contamination in the SOS data. The measurement was done and the analysis was carried out for five different kinematical settings. The relative total errors of the obtained p(e, e' p+)n cross sections were between 3.1% and 3.7%. Three cross sections were measured in a parallel kinematics at the virtual photon polarizations ε = 0.897, 0.591 and 0.306. In case of the parallel kinematics only the transverse and the longitudinal terms appear in the measured cross section. These terms were separated using the Rosenbluth method. For the highest ε = 0.897 value two measurements were performed with the SOS offsets at +18.7 and -18.7 (in the centre-of-mass frame), or in other words to the left and to the right from the parallel kinematics direction of the pion. In this way it was possible to determine the transversal-longitudinal interference term of the cross section. The relative total errors of the transverse, the longitudinal and the interference term were 6.7%, 14.7% and 10.5%, respectively. The results for the cross section terms, which contain the information about the nucleon structure, were compared with predictions of the selected theoretical models.
Abstract (croatian) Precizno mjerenje udarnog presjeka reakcije p(e, e' π+)n na pažljivo biranim kinematikama, omogućava nam, da na danom prijenosu četveroimpulsa Q2, udarni presjek možemo separirati na veličine, koje u sebi nose informacije o strukturi nukleona. Kako na niskim vrijednostima Q2 nema podataka zadovoljavajuće preciznosti, napravljeno je novo mjerenje p(e, e' π+)n reakcije na Q2 = 0.078 (GeV/c)2 i na invarijantnoj masi W = 1094 MeV – otprilike 15 MeV iznad praga reakcije. Eksperiment je proveden u okviru A1 kolaboracije na Institutu za nuklearnu fiziku Johannes Gutenberg Sveučilišta u Mainzu, Njemačka. Visoko kvalitetni snop elektrona davao je MAMI B akcelerator koji omogućava energije u rasponu od 180 do 855 MeV. Producirani nabijeni pion detektiran je u spektrometru kratke orbite (SOS), koji je specijaliziran za detekciju niskoenergijskih piona. Raspršeni elektron detektiran je u standardnom spektrometru A. Po prvi puta napravljena je kompletna analiza podataka mjerenja p(e, e' π+)n reakcije koji su dobiveni koristeći SOS. Kako bi analiza bila valjana, razvijene su nove korekcijske metode specifične za SOS. Neke od najvažnijih metoda su postupak za određivanje korekcije zbog raspada piona, simulacija za određivanje mionske kontaminacije u SOS-ovim podacima itd. Analiza je provedena za pet različitih kinematika. Relativne ukupne greške dobivenih udarnih presjeka p(e, e' π+)n reakcije bile su između 3.1% i 3.7%. Tri udarna presjeka mjerena su u paralelnoj kinematici za iznose polarizacije virtualnog fotona ε = 0.897, 0.591 i 0.306. U slučaju paralelne kinematike u mjerenom udarnom presjeku pojavljuju se samo transverzalni i longitudinalni članovi. Njih smo izdvojili pomoću Rosenbluth-ove metode. Za najveću ε = 0.897 vrijednost napravljena su dva mjerenja za pomake SOS-a od +18.7 i -18.7 (u sustav centra mase), ili drugim riječima lijevo i desno u odnosu na smjer piona u paralelnoj kinematici. Na taj je način bilo moguće odrediti transverzalno-longitudinalni interferencijski član udarnog presjeka. Relativne ukupne greške transverzalnog, longitudinalnog i interferencijskog člana iznosile su redom 6.7%, 14.7% i 10.5%. Sami članovi udarnog presjeka sadrže informaciju o strukturi nukleona, stoga su dobiveni rezultati uspoređeni sa predviđanjima odabranih teorijskih modela.
Keywords
charged pion electroproduction
magnetic spectrometer
SOS
pion decay
muon contamination
cross section
Keywords (croatian)
elektroprodukcija nabijenih piona
magnetski spektrometar
SOS
raspad piona
mionska kontaminacija
udarni presjek
Language english URN:NBN urn:nbn:hr:217:476141 Study programme Title: Physics Type of resource Text Extent 134 str. File origin Born digital Access conditions Open access Terms of use Created on 2017-08-21 12:23:46
