Mjerenje reakcije p(e, e' π+)n spektrometrom kratke orbite na Q2 = 0.078(GeV/c)2

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.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

Rational Synthesis of Mixed-Metal Microporous Metal–Organic Frameworks with Controlled Composition Using Mechanochemistry

Mechanochemistry enables targeted, rapid synthesis of bimetallic metal−organic frameworks (MOFs) with a controlled 1:1 stoichiometric composition of metal nodes. In particular, ball milling enabled the use of specifically synthesized solid coordination complexes of Zn(II), Mg(II), Ni(II), and Co(II) for the assembly of a range of microporous mixed-metal MOF-74 materials composed of pairs of d-block or main group metals in a predetermined 1:1 stoichiometric ratio, including ZnMg-, ZnCo-, ZnCu-, MgZn-, MgCo-, NiZn-, NiMg-, NiCo-, CoZn-, CoMg-, CoCu-, and MgCa-MOF-74. By using specifically prepared precursors in the ynthesis of diverse mixed-metal MOF-74 targets, this rational synthesis represents the first entry of mechanochemistry into the target-oriented synthesis of mixed- metal MOFs

Quasi-elastic polarization-transfer measurements on the deuteron in anti-parallel kinematics

We present measurements of the polarization-transfer components in the $^2$H$(\vec e,e'\vec p)$ reaction, covering a previously unexplored kinematic region with large positive (anti-parallel) missing momentum, $p_{\rm miss}$, up to 220 MeV$/c$, and $Q^2=0.65$ $({\rm GeV}/c)^2$. These measurements, performed at the Mainz Microtron (MAMI), were motivated by theoretical calculations which predict small final-state interaction (FSI) effects in these kinematics, making them favorable for searching for medium modifications of bound nucleons in nuclei. We find in this kinematic region that the measured polarization-transfer components $P_x$ and $P_z$ and their ratio agree with the theoretical calculations, which use free-proton form factors. Using this, we establish upper limits on possible medium effects that modify the bound proton's form factor ratio $G_E/G_M$ at the level of a few percent. We also compare the measured polarization-transfer components and their ratio for $^2$H to those of a free (moving) proton. We find that the universal behavior of $^2$H, $^4$He and $^{12}$C in the double ratio $\frac{(P_x/P_z)^A}{(P_x/P_z)^{^1\rm H}}$ is maintained in the positive missing-momentum region

Precizna digitalizirana spektroskopija u fundamentalnim istraživanjima u subatomskoj fizici i primjenama

U fokusu ovog projekta su vrlo precizna spektroskopska mjerenja u subatomskoj fizici i primjene specifičnih nuklearnih metoda u medicinskom oslikavanju. Dio prijedloga uvodi nove teme u istraživanja nedavno započeta na Fizičkom odsjeku u Zagrebu, a dio prijedloga je nastavak prijašnjih istraživanja, započetih u okviru sadašnjeg projekta Hrvatske zaklade za znanost (HRZZ), na sudaraču DAPΦNE u Labortori Nazionali di Frascati (LNF) i na neutron time-of-flight postrojenju (n_TOF) na CERN-u. Zajedničko svojstvo svih predloženih istraživačkih tema je uporaba moderne digitalne elektronike (digitalizatora), koja ili sprema kompletan signal iz detektora za off-line analizu ili/i ima raznovrsne sposobnosti procesiranja signala. U posljednjem desetljeću takva elektronika je doživjela vrlo dinamičan razvoj i danas pruža mogućnosti za složena mjerenja koja bi inače bila vrlo teška ili čak neizvediva s konvencionalnom analognom elektronikom. Ta elektronika znatno smanjuje broj potrebnih elektroničkih jedinica i praćena naprednim tehnikama analize podataka omogućava izvođenje sofisticiranih, vrlo preciznih mjerenja na samoj fronti istraživanja u subatomskoj fizici i na manjim sveučilišnim odjelima